Application of Anaerobic Digestion

Gordon and Breach Science

Nioolsou MC. Thermophysical Properties of Matter. Vol. 10. New York-Washington: IFI/PLENUM; 1973

M, Moriarty NW, Eiteneer B,

[32] Touloukian YS, Powell RW, Ho CY,

[33] Smith GP, Golden DM, Frenklach

Goldenberg M, et al. Available from: h ttp://www.me.berkeley.edu/gri\_mech

[34] Kee RJ, Rupley FM, Miller JA. Report No. SAND89–8009B UC-706; Sandia National Laboratories; 1989

[35] Kee RJ, Grcar JF, Smooke MD, Miller JA. Report No. SAND85-8240 UC-401; Sandia National Laboratories;

[36] Abdul Aziz NIH, Hanafiah MM, Mohamed Ali MY. Sustainable biogas production from agrowaste and effluents—A promising step for smallscale industry income. Renewable Energy. 2019;132:363-369. DOI: 10.1016/j.renene.2018.07.149

1985

182

Publications; 1982

Anaerobic Digestion

Chapter 9

Abstract

1. Introduction

185

renewable eco-friendly fuel carriers.

Friendly Fuel

Adeola Suhud Shote

Biofuel: An Environmental

energy balances are positive for both fuel substitutes.

Keywords: biofuel, biodiesel, bioethanol, emission, combustion

Various types of biofuels and feedstocks are considered and discussed in terms of their environmental and economic feasibilities. Biofuel is gaining the centre stage as human activities keep rising and the consequent increase in the discharge of lethal emissions is also a subject of concern. The need to cut down greenhouse gas emissions (i.e. CO2, N2O, CO, NO, SO2) is imperative to preserve our natural biodiversity. Biodiesel and bioethanol are the most common, viable alternatives and infinite green fuels that can be used in internal combustion engine. Biodiesel (commonly from waste cooking oil, nonedible vegetable oil, animal fat and tallow) and bioethanol (usually from forestry waste, Lignocellulosic biomass, starchy and sugary vegetable sources, and agricultural residues) are synthesized from straight vegetable feedstocks to bring their characters close to that of the fossil diesel and gasoline. The candidates as green fuels have the potential to significantly reduce the greenhouse gas emissions by as much as 30% from their combustion in internal combustion engine. The various possible methods used for their productions determine the fuel sensitivity to the environment and the energy balance. In general, the

The serious concerns of the global climate change, the rising trend of environmental pollution among others have necessitated researchers and industries to develop renewable alternative and cleaner energies across the world. The need for alternative and sustainable energy sources also arises from the global rise in population and the consequent increase in energy demand even as industrialization keeps on expanding. Therefore, the need to drive the world with efficient and ecofriendly energy carriers is paramount. Biofuels are one of the renewable, sustainable sources of energy carriers that can drive the modern day world with the high prospect and potential of reducing greenhouse gas emissions [1–5]. This reduction in this greenhouse gas emission will certainly be in line with Kyoto Protocol. Yet, no fuel system is completely free of environmental concerns [6]. The high dependency and pressure on finite fossil fuels will be shifted due to the global call to look into

The key sectors that need to be driven by efficient and cleaner fuel substitutes are the aviation, transportation and the manufacturing industries. Over the last two decades, a number of biofuels have been developed. These include bioethanol,

### Chapter 9

## Biofuel: An Environmental Friendly Fuel

Adeola Suhud Shote

### Abstract

Various types of biofuels and feedstocks are considered and discussed in terms of their environmental and economic feasibilities. Biofuel is gaining the centre stage as human activities keep rising and the consequent increase in the discharge of lethal emissions is also a subject of concern. The need to cut down greenhouse gas emissions (i.e. CO2, N2O, CO, NO, SO2) is imperative to preserve our natural biodiversity. Biodiesel and bioethanol are the most common, viable alternatives and infinite green fuels that can be used in internal combustion engine. Biodiesel (commonly from waste cooking oil, nonedible vegetable oil, animal fat and tallow) and bioethanol (usually from forestry waste, Lignocellulosic biomass, starchy and sugary vegetable sources, and agricultural residues) are synthesized from straight vegetable feedstocks to bring their characters close to that of the fossil diesel and gasoline. The candidates as green fuels have the potential to significantly reduce the greenhouse gas emissions by as much as 30% from their combustion in internal combustion engine. The various possible methods used for their productions determine the fuel sensitivity to the environment and the energy balance. In general, the energy balances are positive for both fuel substitutes.

Keywords: biofuel, biodiesel, bioethanol, emission, combustion

### 1. Introduction

The serious concerns of the global climate change, the rising trend of environmental pollution among others have necessitated researchers and industries to develop renewable alternative and cleaner energies across the world. The need for alternative and sustainable energy sources also arises from the global rise in population and the consequent increase in energy demand even as industrialization keeps on expanding. Therefore, the need to drive the world with efficient and ecofriendly energy carriers is paramount. Biofuels are one of the renewable, sustainable sources of energy carriers that can drive the modern day world with the high prospect and potential of reducing greenhouse gas emissions [1–5]. This reduction in this greenhouse gas emission will certainly be in line with Kyoto Protocol. Yet, no fuel system is completely free of environmental concerns [6]. The high dependency and pressure on finite fossil fuels will be shifted due to the global call to look into renewable eco-friendly fuel carriers.

The key sectors that need to be driven by efficient and cleaner fuel substitutes are the aviation, transportation and the manufacturing industries. Over the last two decades, a number of biofuels have been developed. These include bioethanol,

biodiesel, biogas, synthetic fuel, hydrogen and so on. Most of these fuels can be blended or used directly in internal combustion engine (ICE) [7, 8]. The cost of production of some these fuels is still relatively on the high side even despite the fact that they have lower environmental consequences when compared with fossil fuel. The various production methodologies could be responsible for the high cost of these biofuels [9]. Syntheses like fermentation, alcoholysis, Saccharification, acidolysis, hydrolysis, esterification, gasification, liquefaction and extraction have been used to produce biofuels.

(PMS) in spark ignition engine (SIE). Engine modification is not necessary for blends between 5 and 20%. The blend is often represented as E(percentage)G, that is E15G. The middle term '15' represent the percentage of the blend. However, higher blends may require engine modification. This adds to the final cost of the use of bioethanol in SIE. Besides, many advantages are associated with the candidate's use in SIE. The blends help in engine lubrication, thereby reducing the wear rate and reducing the engine temperature. It also has the advantage of cutting down the

The production and quality of bioethanol produced is significantly boosted by the pretreatment procedures. Various pretreatment methods are presented in [14, 15] for lignocellulosic substrates and the merits of employing a pretreatment procedure. Pretreatment is necessary for the substrate feedstock because it gives direct yield of fermentable sugar ready for hydrolysis and heating. It also inhibits degradation and retards the activities of inhibitors for the final conversion to ethanol [15]. It gives a positive energy balance at the long run as the pretreatment process reduces the production cost, wastage of materials and time before the final fermentation process [15, 16]. The pretreatment processes involve the reduction of the size of the feedstock matrix-fraction (some time through the use of enzyme called amylase or through the mechanical means like milling). Hydrolysis and heating can then follow so that the

Microorganisms like fungi can also be employed for the pretreatment of feedstocks particularly lignocellulosic materials. This involves breaking of the lignin structure. This pretreatment method is usually used on a laboratory scale because the process is slow and does not require much energy input as chemical processes

The chemical pretreatment (alkaline/acid) is desirable for large scale industrial

production due to the availability and affordability of chemical which are not affected by ambient changes unlike biological pretreatment agents [14]. Diluted acid pretreatment is usually preferred due to the draw backs of the use of concentrated acid pretreatment like corrosion of production line components. Within a short period of time and at about 160°C, sugar monomers are formed. The common agents used for acid pretreatment include nitric acid (HNO3), hydrochloric acid (HCl), sulfuric acid (H2SO4), organic acid (lactic/acetic acids) and that of the alkaline are sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2) ammonium hydroxide (NH4OH) [14]. The various pretreatment methods and effects are sum-

The traditional method involves liquefaction and saccharification of starch. Saccharification involves the hydrolysis of cellulose or starch (polysaccharides) to simple monosaccharides. Carbohydrates (such as sucrose, maltose) are broken

The process is usually catalyzed using biological method (an enzyme) or chemical method (acid/base) [15, 18]. The saccharification procedure is very important because it determines the time, quality and quantity of the final product which is the bioethanol. Crystalline nature of cellulose fiber, lignin and hemicellulose content, porosity of lignocellulosic substrate affect the hydrolysis process [19]. Some drawbacks like increase in process cost from the chemical obtained, acid recovery, corrosion of production line components are associated with the use of chemical

down to give simple sugar (like glucose, fructose, galactose).

greenhouse gas emissions [13].

are not involved [17].

marized in Table 1.

187

2.2 Synthesis of bioethanol

2.1 Pre-treatment for bioethanol

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

enzyme can easily acts on the pretreated substrate [15].

The combustion of hydrocarbon fuel with O2 from the atmosphere gives equivalent amount of CO2 and H2O. The other discharges are carbon monoxide (CO), nitrogen oxides (NO, N2O) and nitrogen compounds (NH3 and HCN), sulfur gases (SO2, CS2, OCS), compounds of halogens and carbons (CH3Br and CHCl). Combustion of these finite fossil fuels and other biomass led to the global alteration in the atmosphere with respect to huge emissions discharges from these two main contributors [10]. Combustion from automobile, stationary sources are largely responsible for most of the greenhouse gas emissions to date (through CO2, stratospheric O3, and soot) and also some opposing effects (through SO2). It has had minimal effect on stratospheric O3 (through CH3Cl, CH3Br, CH4) but has likely influenced the stratospheric oxidant levels (through CO, NOx, NMHC), specifically the Northern Hemisphere [10]. Even though energy is key to drive the daily and economic activities but it should not be to the detriment of humanity.

Bioethanol, biogas and biodiesel are the most widely used biofuels. Bioethanol production is very high in Brazil and USA due to large volume of production of sugar cane and corn respectively. Research is also directed to the use of cellulose to produce ethanol [11]. Cellulose is converted to sugar and thereafter to ethanol. However, biodiesel is common in the Scandinavian countries and Germany in Europe. Biodiesel is usually blended using about 5–20% in these countries [12]. Germany is one of the top countries known for the production of biodiesel. Biogas on the other hand is usually produced from animal waste. The leading countries in the production of biogas in Europe are Germany and Great Britain. As the production of biofuel is gaining interest, bio-refineries are being cited in advanced countries like the USA, Germany to produce biofuels and other associated products.

Gasification of biomass to produce methanol, ethanol, dimethylether, syn-diesel could also result in the production of hydrogen and methane which may be used in vehicles. Largely, all these conversion processes are still relatively high in cost.

### 1.1 Biofuel as an alternative fuel

Researches are going on in the use of sustainable alternative fuels for automobile and stationery machines. The most prominent of those technologies being under investigation are the use of electric and hybrid automobiles, compressed natural gas (CNG), dimethylether, hydrogen, liquid biofuel, liquefied petroleum gas (LPG) and liquefied natural gas (LNG) among others. The centre of discussion here will focus on two prominent liquid fuels which are biodiesel and bioethanol. Their environmental impact and their sensitivity analysis will be looked into in detail.

These fuels are sourced mainly from vegetable feedstock chain supplies. These may include edible and nonedible vegetable sources that are sustainable [1].

### 2. Bioethanol

The feedstocks include sorghum, sugar beet, wheat, cassava and so on. Bioethanol can be used in straight or even blended form with premium motor spirit

### Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

biodiesel, biogas, synthetic fuel, hydrogen and so on. Most of these fuels can be blended or used directly in internal combustion engine (ICE) [7, 8]. The cost of production of some these fuels is still relatively on the high side even despite the fact that they have lower environmental consequences when compared with fossil fuel. The various production methodologies could be responsible for the high cost of these biofuels [9]. Syntheses like fermentation, alcoholysis, Saccharification, acidolysis, hydrolysis, esterification, gasification, liquefaction and extraction have

The combustion of hydrocarbon fuel with O2 from the atmosphere gives equivalent amount of CO2 and H2O. The other discharges are carbon monoxide (CO), nitrogen oxides (NO, N2O) and nitrogen compounds (NH3 and HCN), sulfur gases (SO2, CS2, OCS), compounds of halogens and carbons (CH3Br and CHCl). Combustion of these finite fossil fuels and other biomass led to the global alteration in the atmosphere with respect to huge emissions discharges from these two main contributors [10]. Combustion from automobile, stationary sources are largely responsible for most of the greenhouse gas emissions to date (through CO2, stratospheric O3, and soot) and also some opposing effects (through SO2). It has had minimal effect on stratospheric O3 (through CH3Cl, CH3Br, CH4) but has likely influenced the stratospheric oxidant levels (through CO, NOx, NMHC), specifically the Northern Hemisphere [10]. Even though energy is key to drive the daily and

economic activities but it should not be to the detriment of humanity.

Bioethanol, biogas and biodiesel are the most widely used biofuels. Bioethanol production is very high in Brazil and USA due to large volume of production of sugar cane and corn respectively. Research is also directed to the use of cellulose to produce ethanol [11]. Cellulose is converted to sugar and thereafter to ethanol. However, biodiesel is common in the Scandinavian countries and Germany in Europe. Biodiesel is usually blended using about 5–20% in these countries [12]. Germany is one of the top countries known for the production of biodiesel. Biogas on the other hand is usually produced from animal waste. The leading countries in the production of biogas in Europe are Germany and Great Britain. As the production of biofuel is gaining interest, bio-refineries are being cited in advanced countries like the USA, Germany to produce biofuels and other associated products.

Gasification of biomass to produce methanol, ethanol, dimethylether, syn-diesel could also result in the production of hydrogen and methane which may be used in vehicles. Largely, all these conversion processes are still relatively high in cost.

Researches are going on in the use of sustainable alternative fuels for automobile and stationery machines. The most prominent of those technologies being under investigation are the use of electric and hybrid automobiles, compressed natural gas (CNG), dimethylether, hydrogen, liquid biofuel, liquefied petroleum gas (LPG) and liquefied natural gas (LNG) among others. The centre of discussion here will focus on two prominent liquid fuels which are biodiesel and bioethanol. Their environmental impact and their sensitivity analysis will be looked into in detail. These fuels are sourced mainly from vegetable feedstock chain supplies. These

may include edible and nonedible vegetable sources that are sustainable [1].

The feedstocks include sorghum, sugar beet, wheat, cassava and so on. Bioethanol can be used in straight or even blended form with premium motor spirit

been used to produce biofuels.

Anaerobic Digestion

1.1 Biofuel as an alternative fuel

2. Bioethanol

186

(PMS) in spark ignition engine (SIE). Engine modification is not necessary for blends between 5 and 20%. The blend is often represented as E(percentage)G, that is E15G. The middle term '15' represent the percentage of the blend. However, higher blends may require engine modification. This adds to the final cost of the use of bioethanol in SIE. Besides, many advantages are associated with the candidate's use in SIE. The blends help in engine lubrication, thereby reducing the wear rate and reducing the engine temperature. It also has the advantage of cutting down the greenhouse gas emissions [13].

### 2.1 Pre-treatment for bioethanol

The production and quality of bioethanol produced is significantly boosted by the pretreatment procedures. Various pretreatment methods are presented in [14, 15] for lignocellulosic substrates and the merits of employing a pretreatment procedure. Pretreatment is necessary for the substrate feedstock because it gives direct yield of fermentable sugar ready for hydrolysis and heating. It also inhibits degradation and retards the activities of inhibitors for the final conversion to ethanol [15]. It gives a positive energy balance at the long run as the pretreatment process reduces the production cost, wastage of materials and time before the final fermentation process [15, 16]. The pretreatment processes involve the reduction of the size of the feedstock matrix-fraction (some time through the use of enzyme called amylase or through the mechanical means like milling). Hydrolysis and heating can then follow so that the enzyme can easily acts on the pretreated substrate [15].

Microorganisms like fungi can also be employed for the pretreatment of feedstocks particularly lignocellulosic materials. This involves breaking of the lignin structure. This pretreatment method is usually used on a laboratory scale because the process is slow and does not require much energy input as chemical processes are not involved [17].

The chemical pretreatment (alkaline/acid) is desirable for large scale industrial production due to the availability and affordability of chemical which are not affected by ambient changes unlike biological pretreatment agents [14]. Diluted acid pretreatment is usually preferred due to the draw backs of the use of concentrated acid pretreatment like corrosion of production line components. Within a short period of time and at about 160°C, sugar monomers are formed. The common agents used for acid pretreatment include nitric acid (HNO3), hydrochloric acid (HCl), sulfuric acid (H2SO4), organic acid (lactic/acetic acids) and that of the alkaline are sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2) ammonium hydroxide (NH4OH) [14]. The various pretreatment methods and effects are summarized in Table 1.

### 2.2 Synthesis of bioethanol

The traditional method involves liquefaction and saccharification of starch. Saccharification involves the hydrolysis of cellulose or starch (polysaccharides) to simple monosaccharides. Carbohydrates (such as sucrose, maltose) are broken down to give simple sugar (like glucose, fructose, galactose).

The process is usually catalyzed using biological method (an enzyme) or chemical method (acid/base) [15, 18]. The saccharification procedure is very important because it determines the time, quality and quantity of the final product which is the bioethanol. Crystalline nature of cellulose fiber, lignin and hemicellulose content, porosity of lignocellulosic substrate affect the hydrolysis process [19]. Some drawbacks like increase in process cost from the chemical obtained, acid recovery, corrosion of production line components are associated with the use of chemical

catalysis [20]. However, the use of dilute acid is often preferred as it contributes to less impact on the environment. The enzymatic approach is mostly carried out in an orbital shaker (120–150 rpm) at about 40–50°C for 120 h [21]. β-Glucosidase, Cellulase are commonly used for the hydrolysis of complex starch [22]. Thereafter, the fermentation of sugar extracted from starch plant, followed by distillation. Enzyme, bacteria or yeast are used during the fermentation process to accelerate the

Ethyl tertiary butyl ether (ETBE) is also worthy of mentioning here since it can also be obtained from some of the agricultural produce like barley, wheat which can be blended with PMS. They are usually produced in the refinery. Lignocellulose residue is gaining more research interest due to the reduction in the cost of production [14]. The lignocellulose contains cellulose, hemicelluloses and lignin. Hydrolysis are used to fractionalize some agricultural produce like maize so that complete conversion to ethanol and carbon dioxide can be obtained easily and efficiently with

The schematic process of production chain of bioethanol is depicted in Figure 1. The process starts with milling of the feedstock for easy extraction of the starch. Yeast is added to make the extraction easy. The next stage is hydrolysis. Enzyme is added to obtain single sugar (glucose) and starch before fermentation by bacteria or microorganisms. Thereafter, distillation is followed to remove large volume of water in the product and then dehydration to further remove the water content so that the outcome concentration will increase. There are various pretreatment methods that can be used to obtain high quality ethanol [14, 23]. Figure 2 presents the summary of the pretreatment and conversion methods while Table 1 presents the pretreatment methods and the various merits and drawbacks from the use of

formation of the product in an anaerobic environment. The simple sugar is converted to ethanol and carbon dioxide. Some time, saccharification and fermentation are considered simultaneously due to low cost, reduced process time, prevention of cellulose inhibition, high yield of ethanol [22]. Most of the world's ethanol is produced in Brazil and USA. Corn is used to synthesize bioethanol in the USA while sugar cane is used substantially in Brazil [13]. However, in Spain, bioethanol is produced from barley and in France it is obtained from beet. Agricultural biomass or residue from waste paper or corn stalks can also be used to obtain bioethanol [13]. Other agricultural produce that can be used to generate ethanol are

wheat, potato, maize cassava etc.

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

2.3 The ethanol conversion process

reduced wastage.

Figure 1.

189

Bioethanol conversion scheme [29].

### Table 1.

Pretreatment methods for lignocellulosic feedstocks in bioethanol synthesis [14].

### Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

Pretreatment method

Anaerobic Digestion

Concentrated acid

Ammonia fiber explosion

Ammonia recycled percolation

Steam explosion

Supercritical fluid technology

Table 1.

188

Diluted acid Hydrolyses hemicelluloses;

Hydrolyses both

hemicelluloses

hemicelluloses

crystallinity

Alkali Removes lignin and

area

Biological Degrades lignin and

Mechanical Reduces cellulose

area

Ionic liquids Reduces cellulose

Ozonolysis Reduces lignin

crystallinity Removes lignin

transformation

solubility

area

Organosolv Hydrolyses linin and hemicelluloses

Causes lignin transformation Causes hemicellulose

Increase accessible surface

Pretreatment methods for lignocellulosic feedstocks in bioethanol synthesis [14].

Alters the structure of lignin Reduces cellulose more amenable for additional enzymatic treatment

hemicelluloses and cellulose

Increases accessible surface

Increases accessible surface

Slightly removes lignin and hemicelluloses to an extent

Removes lignin Highly selective

Effects Pros Cons

the conc acid

High glucose yield Operational cost reduction due to moderate operating

High lignin removal High digestibility

delignification

High digestibility Green solvent

Cost effective

hemicellulose

Cost effective

Wet oxidation Removes lignin Low formation of inhibitors High cost of oxygen and

No formation of inhibitors Mild operational conditions

High yield of glucose and

No formation of inhibitor

Pure lignin recovery High digestibility

temperature Low formation of degradable products No enzyme are required

Less corrosion effect than

Generation of degradation products due to high temperature Low sugar concentration

exit stream

compounds

consumption

High energy consumption

with high lignin content High cost due to large amount of ammonia

Large-scale application still under investigation

High cost due large amount of ozone required

compounds Partial hemicellulose degradation

matrix

Generation of inhibitory

Incomplete disruption of the lignin carbohydrate

Does not affect lignin and hemicelluloses Very high pressure requirements

alkaline catalyst

High cost

Solvents need to be drained and recycled

Low energy consumption Low hydrolysis rate

No formation of inhibitors High power and energy

Low formation of inhibitors Not efficient for biomass

Long residence time Irrecoverable salt formation

Acid recovery is mandatory Equipment corrosion Generation of inhibitory

Low formation of inhibitors

catalysis [20]. However, the use of dilute acid is often preferred as it contributes to less impact on the environment. The enzymatic approach is mostly carried out in an orbital shaker (120–150 rpm) at about 40–50°C for 120 h [21]. β-Glucosidase, Cellulase are commonly used for the hydrolysis of complex starch [22]. Thereafter, the fermentation of sugar extracted from starch plant, followed by distillation. Enzyme, bacteria or yeast are used during the fermentation process to accelerate the formation of the product in an anaerobic environment. The simple sugar is converted to ethanol and carbon dioxide. Some time, saccharification and fermentation are considered simultaneously due to low cost, reduced process time, prevention of cellulose inhibition, high yield of ethanol [22]. Most of the world's ethanol is produced in Brazil and USA. Corn is used to synthesize bioethanol in the USA while sugar cane is used substantially in Brazil [13]. However, in Spain, bioethanol is produced from barley and in France it is obtained from beet. Agricultural biomass or residue from waste paper or corn stalks can also be used to obtain bioethanol [13]. Other agricultural produce that can be used to generate ethanol are wheat, potato, maize cassava etc.

Ethyl tertiary butyl ether (ETBE) is also worthy of mentioning here since it can also be obtained from some of the agricultural produce like barley, wheat which can be blended with PMS. They are usually produced in the refinery. Lignocellulose residue is gaining more research interest due to the reduction in the cost of production [14]. The lignocellulose contains cellulose, hemicelluloses and lignin. Hydrolysis are used to fractionalize some agricultural produce like maize so that complete conversion to ethanol and carbon dioxide can be obtained easily and efficiently with reduced wastage.

### 2.3 The ethanol conversion process

The schematic process of production chain of bioethanol is depicted in Figure 1. The process starts with milling of the feedstock for easy extraction of the starch. Yeast is added to make the extraction easy. The next stage is hydrolysis. Enzyme is added to obtain single sugar (glucose) and starch before fermentation by bacteria or microorganisms. Thereafter, distillation is followed to remove large volume of water in the product and then dehydration to further remove the water content so that the outcome concentration will increase. There are various pretreatment methods that can be used to obtain high quality ethanol [14, 23]. Figure 2 presents the summary of the pretreatment and conversion methods while Table 1 presents the pretreatment methods and the various merits and drawbacks from the use of

Figure 1. Bioethanol conversion scheme [29].

3. Biodiesel

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

acid chain.

and Zhu [32].

Table 2.

191

Fatty acid in vegetable oil [30].

Biodiesel is currently gaining more and more interest as the desire to use ecofriendly fuel substitute keeps increasing because of the increase in the fluctuations in the crude-fuel prices internationally and the environmental consequences of fossil fuel. There are numerous ways of producing biodiesel from different feedstocks and different catalysts. Some of the feedstock include but not limited to grapeseed, camelina, lupin, linseed, rapeseed, sunflower, peanut, palm oil, palm kernel oil, poppyseed, olive, chestnut, karanja, pongamia, soybeans, canola, corn, crambe, jatropha, cottonseed and so on. Animal fat can also be used to synthesize biodiesel. The common methods of production are transesterification (alkaline catalyzed), the use of enzyme (e.g. lipase) catalyst, supercritical method of production (under high temperature and relatively high pressure) and the use of acid catalyst [30]. However, the commonly used method for the production of biodiesel is the

transesterification method because of its simplicity and ease of handling.

whole chain of production more costly.

are produced as the principal products [31].

of the vegetable oil is shown in Figure 3.

Vegetable oils normally contain fatty acids which makes the properties (like viscosity, density, flash point, pour point cloud point, cetane number) to be high in value and mostly unsuitable to be used in internal combustion engine (ICE) without engine modification. So, the essence of the conversion to biodiesel is to remove or lower the effect of the fatty acid composition in Table 2 [30]. The chemical structures of common fatty acids are also presented in Table 3. Some oils that are having lower fatty acid content can be used directly or in blended form as biodiesel fuel in compression ignition engine (CIE) which may require modification. This makes the

'xx' indicates number of carbons, and 'y' number of double bonds in the fatty

The production of biodiesel starts with oil extraction (usually with hexane). The high fatty acid oil containing triglycerides reacts with alcohol (usually methanol or ethanol) to produce esters and glycerol in the presence of a catalyst (KOH or NaOH). The whole processes are reversible processes and are in three steps as shown in Eqs. (1)–(3) [16]. Excess alcohol is desirable to accelerate the reaction towards the products side. The kinetics parameter kx are in Noureddini

Transesterification of rapeseed oil in the supercritical methanol method shows that at temperature of 239°C and a pressure of 8.09 MPa, glycerin and methyl esters

The main product is biodiesel and the by product is glycerol which are mainly used in the cosmetics and pharmaceutical industries.

Pretreatment and bioethanol conversion processes [27].

respective pretreatment method. In more recent time, response surface methodology (RSM) and artificial neural network (ANN) have been used to optimize the production of bioethanol [24]. ANN is used to perform complex cognitive procedurals which mimic the biological function of human brain. ANN genetic algorithm is used to simulate the biological processes in the ethanol production so that the major parameters can be varied to obtain a much desired output.

### 2.4 Impact of bioethanol and its sensitivity on the environment

This is related to the emission pattern compared with the fossil premium motor spirit (FPMS) and the energy balance for the synthesis of the ethanol. The energy balance involves the input feedstock and the by-product. Bioethanol has a huge potential to reduce the hazardous gas emissions due to its vegetable source. It helps in the complete combustion process because it is oxygenated thereby reducing the emissions by as much as 30%. Bioethanol from lignocellulosic biomass resource has huge strategic potential in cutting down of greenhouse gas emissions into the environment and reducing the consumption of crude fuel [21]. It can be blended with PMS due to its characteristics such as low cetane number, high octane number, high heat of vaporization that are close to that of the fossil gasoline [25]. The use of this large lignocellulosic biomass has the potential to reduce transportation cost which will contribute tremendously to positive energy balance [26]. Ethanol production from lignocellulose also has advantages over first generation biofuel in that it makes use of low cost biomass and employs a production process that is environmentally friendly [27].

Various methods of biofuel feedstocks, production loading methodologies and the environmental and economic viability of biofuel production are issues that are attracting and promoting the use of biofuels. However, biofuels combustion in ICE were found to have the prospect of reducing the greenhouse gas emissions [28] thereby lowering the average mean temperature of the atmosphere in the long run. This is in line with Kyoto protocol. The global pressure on the finite premium motor spirit (PMS) and automotive gas oil (AGO) will reduce significantly by using biofuel in straight or blended forms. Biofuels also have the merits of renewability and sustainability. The energy balance of most biofuels is positive as production is maximized.

### 3. Biodiesel

respective pretreatment method. In more recent time, response surface methodology (RSM) and artificial neural network (ANN) have been used to optimize the production of bioethanol [24]. ANN is used to perform complex cognitive procedurals which mimic the biological function of human brain. ANN genetic algorithm is used to simulate the biological processes in the ethanol production so

This is related to the emission pattern compared with the fossil premium motor spirit (FPMS) and the energy balance for the synthesis of the ethanol. The energy balance involves the input feedstock and the by-product. Bioethanol has a huge potential to reduce the hazardous gas emissions due to its vegetable source. It helps in the complete combustion process because it is oxygenated thereby reducing the emissions by as much as 30%. Bioethanol from lignocellulosic biomass resource has huge strategic potential in cutting down of greenhouse gas emissions into the environment and reducing the consumption of crude fuel [21]. It can be blended with PMS due to its characteristics such as low cetane number, high octane number, high heat of vaporization that are close to that of the fossil gasoline [25]. The use of this large lignocellulosic biomass has the potential to reduce transportation cost which will contribute tremendously to positive energy balance [26]. Ethanol production from lignocellulose also has advantages over first generation biofuel in that it makes use of low cost biomass and employs a production process that is environ-

Various methods of biofuel feedstocks, production loading methodologies and the

environmental and economic viability of biofuel production are issues that are attracting and promoting the use of biofuels. However, biofuels combustion in ICE were found to have the prospect of reducing the greenhouse gas emissions [28] thereby lowering the average mean temperature of the atmosphere in the long run. This is in line with Kyoto protocol. The global pressure on the finite premium motor spirit (PMS) and automotive gas oil (AGO) will reduce significantly by using biofuel in straight or blended forms. Biofuels also have the merits of renewability and sustainability. The energy balance of most biofuels is positive as production is maximized.

that the major parameters can be varied to obtain a much desired output.

2.4 Impact of bioethanol and its sensitivity on the environment

mentally friendly [27].

190

Figure 2.

Anaerobic Digestion

Pretreatment and bioethanol conversion processes [27].

Biodiesel is currently gaining more and more interest as the desire to use ecofriendly fuel substitute keeps increasing because of the increase in the fluctuations in the crude-fuel prices internationally and the environmental consequences of fossil fuel. There are numerous ways of producing biodiesel from different feedstocks and different catalysts. Some of the feedstock include but not limited to grapeseed, camelina, lupin, linseed, rapeseed, sunflower, peanut, palm oil, palm kernel oil, poppyseed, olive, chestnut, karanja, pongamia, soybeans, canola, corn, crambe, jatropha, cottonseed and so on. Animal fat can also be used to synthesize biodiesel. The common methods of production are transesterification (alkaline catalyzed), the use of enzyme (e.g. lipase) catalyst, supercritical method of production (under high temperature and relatively high pressure) and the use of acid catalyst [30]. However, the commonly used method for the production of biodiesel is the transesterification method because of its simplicity and ease of handling.

Vegetable oils normally contain fatty acids which makes the properties (like viscosity, density, flash point, pour point cloud point, cetane number) to be high in value and mostly unsuitable to be used in internal combustion engine (ICE) without engine modification. So, the essence of the conversion to biodiesel is to remove or lower the effect of the fatty acid composition in Table 2 [30]. The chemical structures of common fatty acids are also presented in Table 3. Some oils that are having lower fatty acid content can be used directly or in blended form as biodiesel fuel in compression ignition engine (CIE) which may require modification. This makes the whole chain of production more costly.

'xx' indicates number of carbons, and 'y' number of double bonds in the fatty acid chain.

The production of biodiesel starts with oil extraction (usually with hexane). The high fatty acid oil containing triglycerides reacts with alcohol (usually methanol or ethanol) to produce esters and glycerol in the presence of a catalyst (KOH or NaOH). The whole processes are reversible processes and are in three steps as shown in Eqs. (1)–(3) [16]. Excess alcohol is desirable to accelerate the reaction towards the products side. The kinetics parameter kx are in Noureddini and Zhu [32].

Transesterification of rapeseed oil in the supercritical methanol method shows that at temperature of 239°C and a pressure of 8.09 MPa, glycerin and methyl esters are produced as the principal products [31].

The main product is biodiesel and the by product is glycerol which are mainly used in the cosmetics and pharmaceutical industries. The basic conversion scheme of the vegetable oil is shown in Figure 3.

Table 2. Fatty acid in vegetable oil [30].

$$\text{Triglyceride}\ (\text{TG}) + \text{R'OH} \overset{\text{k\_1}}{\underset{\text{k\_4}}{\rightleftharpoons}} \text{Diglyceride}\ (\text{DG}) + \text{R'COOR1} \tag{1}$$

In general, the energy balance of most biodiesels is positive depending on the source of the vegetable oil, production, extraction and esterification. Zhang et al. [9] found out that the plant capacity, feedstock of oil and the method used to synthesize biodiesel are the most significant factors determining the final cost of biodiesel. The use of glycerol in the cosmetics and pharmaceutical industries will boost the energy balance of the biodiesel significantly. Since biodiesel is gaining more ground in terms of the usage, then the energy balance tends to be more positive. Biodiesel are found to reduce greenhouse gas emissions [5, 7]. Biodiesels also have the advantage of lubricating and bringing down the temperature of ICE. The generic NOx emissions are not significantly affected as the concentration of the blends increase in the fuel mixture [5]. NOx formation is governed by Zeldovich

Acid catalyst (tetraoxosulphate VI acid) is also used instead of alkali catalyst (NaOH or KOH) to lower the activation energy for quick formation of esters and glycerin. However, the reaction takes longer time (about 2 days) to complete. The molar ratio is kept at 30:1 and the temperature range is between 60 and 80°C. The triglyceride is usually used with one mole of sulfuric acid to give 90% conversion to

Other methods involve the use of enzyme to fast track the rate of chemical reaction and the formation of esters. This method is very expensive because of the cost of enzyme which invariably affects the energy balance of the entire chain of

The summary of the common methods used for the production of biodiesel are

3.2 The summary of technologies at developmental stage dealing with biofuel

and the end results will be economically reliable [33].

Saponified products

reaction

Variable Alkali catalyst Lipase

Water in vegetable oil Interference with

Different techniques for ester production [16].

a. Pyrolysis of oil: lignocellulosic biomass is usually used to synthesize bioethanol. The process normally starts with pretreatment procedures. However, any of the biomass substrates can be used to produce biodiesel. Research is till on going in the development of reactor for accelerated pyrolysis processes. A lot of investment and researches are still needed in this area so that the process

catalysis

Yield of methyl esters Normal Higher Good Normal Recovery of glycerol Difficult Easy — Difficult

Cheap Relatively

expensive

60–70 30–40 239–385 55–80

Repeated washing None — Repeated washing

Supercritical alcohol

Methyl esters Esters Esters

No influence — Interference with

Medium Cheap

Acid catalysis

reaction

mechanism.

production processes.

presented in Table 4.

production

Reaction temperature

Purification of methyl

Production cost of

esters

catalyst

Table 4.

193

Free fatty acid in vegetable oil

( o C)

ester and glycerin in about 2 days [16].

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

$$\text{Diglyceride} \left( \text{DG} \right) + \text{R'OH} \overset{\text{k}\_1}{\underset{\text{k}\_2}{\rightleftharpoons}} \text{Monologyeride} \left( \text{MG} \right) + \text{R'COOR2} \tag{2}$$

$$\text{Monoglyceride} \left(\text{MG}\right) + \text{R'OH} \underset{\text{k\_6}}{\overset{\text{k\_3}}{\rightleftharpoons}} \text{Glycerol} \left(\text{GL}\right) + \text{R'COOR3} \tag{3}$$

### 3.1 Impact of biodiesel and its sensitivity on the environment

This centers on the emissions comparison of the finite fossil diesel with biodiesel. Shote et al. [5] conducted a research on the emission patterns of the biodiesel blends compared with petroleum diesel. One hundred percent biodiesel was found to have lowest impact on the environment in terms of the hazardous emissions (CO, NO, NO2, NOx). Besides, the result also shows gradual reduction of the emissions pattern as the concentration of PKO-based biodiesel increases in the blend.

### Table 3.

Chemical structure of common fatty acids [31].

Figure 3. Biodiesel conversion scheme [16].

### Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

Triglyceride TG ð Þþ R<sup>0</sup>

Monoglyceride MG ð Þþ R<sup>0</sup>

Diglyceride DG ð Þþ R<sup>0</sup>

Anaerobic Digestion

the blend.

Table 3.

Figure 3.

192

Biodiesel conversion scheme [16].

Chemical structure of common fatty acids [31].

OH \$ k1 k4

> OH \$ k3 k6

This centers on the emissions comparison of the finite fossil diesel with biodiesel. Shote et al. [5] conducted a research on the emission patterns of the biodiesel blends compared with petroleum diesel. One hundred percent biodiesel was found to have lowest impact on the environment in terms of the hazardous emissions (CO, NO, NO2, NOx). Besides, the result also shows gradual reduction of the emissions pattern as the concentration of PKO-based biodiesel increases in

Fatty acid Chemical name of fatty acids Structure (xx:y) Formula Lauric Dodecanoic 12:1 C12H24O2 Myristic Tetradecanoic 14:1 C14H28O2 Palmitic Hexadecanoic 16:0 C16H32O2 Stearic Octadecanoic 18:0 C18H36O2 Arachidic Eicosanoic 20:0 C20H40O2 Behenic Docosanoic 22:0 C22H44O2 Lignoceric Tetracosanoic 24:0 C24H48O2 Oleic cis-9-Octadecenoic 18:1 C18H34O2 Linoleic cis-9,cis-12-Octadecadienoic 18:2 C18H32O2 Linolenic cis-9,cis-l2,cis-15-Octadecatrienoic 18:3 C18H30O2 Erucle cis-13-Docosenoic 22:1 C32H42O2

OH \$ k2 k5

3.1 Impact of biodiesel and its sensitivity on the environment

Diglyceride DG ð Þþ <sup>R</sup>'

Glycerol GL ð Þþ <sup>R</sup>'

Monoglyceride MG ð Þþ <sup>R</sup>'

COOR1 (1)

COOR2 (2)

COOR3 (3)

In general, the energy balance of most biodiesels is positive depending on the source of the vegetable oil, production, extraction and esterification. Zhang et al. [9] found out that the plant capacity, feedstock of oil and the method used to synthesize biodiesel are the most significant factors determining the final cost of biodiesel. The use of glycerol in the cosmetics and pharmaceutical industries will boost the energy balance of the biodiesel significantly. Since biodiesel is gaining more ground in terms of the usage, then the energy balance tends to be more positive. Biodiesel are found to reduce greenhouse gas emissions [5, 7]. Biodiesels also have the advantage of lubricating and bringing down the temperature of ICE. The generic NOx emissions are not significantly affected as the concentration of the blends increase in the fuel mixture [5].

Acid catalyst (tetraoxosulphate VI acid) is also used instead of alkali catalyst (NaOH or KOH) to lower the activation energy for quick formation of esters and glycerin. However, the reaction takes longer time (about 2 days) to complete. The molar ratio is kept at 30:1 and the temperature range is between 60 and 80°C. The triglyceride is usually used with one mole of sulfuric acid to give 90% conversion to ester and glycerin in about 2 days [16].

Other methods involve the use of enzyme to fast track the rate of chemical reaction and the formation of esters. This method is very expensive because of the cost of enzyme which invariably affects the energy balance of the entire chain of production processes.

The summary of the common methods used for the production of biodiesel are presented in Table 4.

### 3.2 The summary of technologies at developmental stage dealing with biofuel production

a. Pyrolysis of oil: lignocellulosic biomass is usually used to synthesize bioethanol. The process normally starts with pretreatment procedures. However, any of the biomass substrates can be used to produce biodiesel. Research is till on going in the development of reactor for accelerated pyrolysis processes. A lot of investment and researches are still needed in this area so that the process and the end results will be economically reliable [33].

### Table 4.

Different techniques for ester production [16].

b.Hydrothermal upgrading process: this process involves hydrolysis of biomass at high pressure and moderate temperature to produce bio-crude. It is also at the development sage just like pyrolysis process.

References

[1] Balat M, Balat H. Progress in biodiesel processing. Applied Energy. 2010;87:1815-1835. DOI: 10.1016/j.

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

[2] Fergione J, Hill J, Tilman D, Polasky S, Hawthorne P. Land clearing and the biofuel carbon debt. Science. 2008;319: 1235-1238. DOI: 10.1126/science. 1152747. Epub 2008 Feb 7

internal combustion engine with ethanol-gasoline blended fuels varying compression ratios and ignition timing. Energy & Fuels. 2009;23(5):2319-2324.

[9] Zhang Y, Dube MA, McLean DD, Kates M. Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis. Bioresource Technology. 2003;90: 229-240. DOI: 10.1016/so960-8524(03)

[10] Prather MJ, Logan JA. Twenty-Fifth

Symposium (International) on Combustion. Pittsburgh: The Combustion Institute; 1994. p. 1513. DOI: /10.1016/S0082-0784(06)80796-4

[11] Schifter I, Diaz L, Rodriguez R, Gomez JP, Gonzalez U. Combustion and emissions behaviour for ethernol— Gasoline blends in a single cylinder engine. Fuel. 2011;90(12):3586-3592. DOI: /10.1016/j.fuel.2011.01.034

[12] Shote AS, Betiku E, Asere AA.

transmethylation of Nigerian palm kernel oil. Ife Journal of Technology. 2009;18(2):1-4. DOI: http://ijt.oauife.

[13] Hanif M, Mahlia TIM, Aditiya HB,

bioehtanol production from Sir Kanji 1 cassava in Malaysia. Biofuel Research Journal. 2017;13:537-544. DOI: 10.18331/

[14] Refaat AA. 5.13—Biofuels from waste materials. In: Sayigh A, editor. Comprehensive Renewable Energy. 1st ed. Oxford: Elsevier; 2012. p. 217–261 DOI: /Letcher/978-0-08-087872-0. Ch5

[15] Aditiya HB, Mahlia TMI, Chong WT, Hadi N, Sebayang AH. Second

Biodiesel production by

Abu Bakar MS. Energy and environmental assessments of

edu.ng

BRJ2<IP_ADDRESS>

DOI: 10.1021/ef800899r

00150-0

[3] Scharlemann JPW, Laurance WF. How green are biofuels? Science. 2008;

319:43-44. DOI: 10.1126/

[4] Searchinger T, Heimlich R, Houghton RA, Dong F, Elobeid A, Fabiosa J. Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land use change. Science. 2008;319:1238-1240. DOI: 10.1126/science.1151861. Epub

[5] Shote AS, Betiku E, Asere AA. Characteristics of CO and NOx emissions from combustion of

2018;1-6. DOI: 10.1016/ j.jksues.2018.02.005. In Press

fuel.2014.05.053

195

transmethylated palm kernel oil-based biodiesel blends in a compression ignition engine. Journal of King Saud University—Engineering Sciences.

[6] Hoekman SK. Biofuels in the U.S.— Challenges and opportunities. Renewable Energy Journal. 2009;34:14-22. DOI: 10.1016/j.renene.2008.04.030

[7] Rahman MM, Pourkhesalian AM, Jahirul MI, Stevanovic S, Pham PX, Wang H, et al. Particle emissions from biodiesels with different physical properties and chemical composition. Fuel. 2014;134:201-208. DOI: /10.1016/j.

[8] Cooney CP, Worm JJ, Naber JD. Combustion characterisation in an

science.1153103

2008 Feb 7

apenergy.2010.01.012

### Acknowledgements

The author gratefully acknowledged Obafemi Awolowo University, Ile-Ife for her support.

### Author details

Adeola Suhud Shote University of Pretoria, Hatfield, South Africa

\*Address all correspondence to: adeolashoteyahoo.ca

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

### References

b.Hydrothermal upgrading process: this process involves hydrolysis of biomass at high pressure and moderate temperature to produce bio-crude. It is also at the

c. Dimethylether: this is produced from gasification of biomass. It could also be obtained from natural gas. It is one of the conventional diesel fuel substitutes that is capable of cutting down NOx emissions from its combustion in CIE. It is

d.Fischer-Tropsch: synthetic gas is produced from fossil fuels. Research is still on going to produce synthetic gas from biomass feedstock. In the past, the primary feedstock for its production is fossil fuel. The origin of this synthetic fuel can be traced to Germany. Production of synthetic fuel through pyrolysis

e. Synthetic fuel: this fuel is synthesized by recycling organic waste. A lot of work is going on in this area to optimize the processes. It can be blended with

The author gratefully acknowledged Obafemi Awolowo University, Ile-Ife for

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

development sage just like pyrolysis process.

commonly synthesized from methanol.

of biomass is still under investigation.

conventional fuel.

Acknowledgements

Anaerobic Digestion

her support.

Author details

194

Adeola Suhud Shote

University of Pretoria, Hatfield, South Africa

provided the original work is properly cited.

\*Address all correspondence to: adeolashoteyahoo.ca

[1] Balat M, Balat H. Progress in biodiesel processing. Applied Energy. 2010;87:1815-1835. DOI: 10.1016/j. apenergy.2010.01.012

[2] Fergione J, Hill J, Tilman D, Polasky S, Hawthorne P. Land clearing and the biofuel carbon debt. Science. 2008;319: 1235-1238. DOI: 10.1126/science. 1152747. Epub 2008 Feb 7

[3] Scharlemann JPW, Laurance WF. How green are biofuels? Science. 2008; 319:43-44. DOI: 10.1126/ science.1153103

[4] Searchinger T, Heimlich R, Houghton RA, Dong F, Elobeid A, Fabiosa J. Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land use change. Science. 2008;319:1238-1240. DOI: 10.1126/science.1151861. Epub 2008 Feb 7

[5] Shote AS, Betiku E, Asere AA. Characteristics of CO and NOx emissions from combustion of transmethylated palm kernel oil-based biodiesel blends in a compression ignition engine. Journal of King Saud University—Engineering Sciences. 2018;1-6. DOI: 10.1016/ j.jksues.2018.02.005. In Press

[6] Hoekman SK. Biofuels in the U.S.— Challenges and opportunities. Renewable Energy Journal. 2009;34:14-22. DOI: 10.1016/j.renene.2008.04.030

[7] Rahman MM, Pourkhesalian AM, Jahirul MI, Stevanovic S, Pham PX, Wang H, et al. Particle emissions from biodiesels with different physical properties and chemical composition. Fuel. 2014;134:201-208. DOI: /10.1016/j. fuel.2014.05.053

[8] Cooney CP, Worm JJ, Naber JD. Combustion characterisation in an

internal combustion engine with ethanol-gasoline blended fuels varying compression ratios and ignition timing. Energy & Fuels. 2009;23(5):2319-2324. DOI: 10.1021/ef800899r

[9] Zhang Y, Dube MA, McLean DD, Kates M. Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis. Bioresource Technology. 2003;90: 229-240. DOI: 10.1016/so960-8524(03) 00150-0

[10] Prather MJ, Logan JA. Twenty-Fifth Symposium (International) on Combustion. Pittsburgh: The Combustion Institute; 1994. p. 1513. DOI: /10.1016/S0082-0784(06)80796-4

[11] Schifter I, Diaz L, Rodriguez R, Gomez JP, Gonzalez U. Combustion and emissions behaviour for ethernol— Gasoline blends in a single cylinder engine. Fuel. 2011;90(12):3586-3592. DOI: /10.1016/j.fuel.2011.01.034

[12] Shote AS, Betiku E, Asere AA. Biodiesel production by transmethylation of Nigerian palm kernel oil. Ife Journal of Technology. 2009;18(2):1-4. DOI: http://ijt.oauife. edu.ng

[13] Hanif M, Mahlia TIM, Aditiya HB, Abu Bakar MS. Energy and environmental assessments of bioehtanol production from Sir Kanji 1 cassava in Malaysia. Biofuel Research Journal. 2017;13:537-544. DOI: 10.18331/ BRJ2<IP_ADDRESS>

[14] Refaat AA. 5.13—Biofuels from waste materials. In: Sayigh A, editor. Comprehensive Renewable Energy. 1st ed. Oxford: Elsevier; 2012. p. 217–261 DOI: /Letcher/978-0-08-087872-0. Ch5

[15] Aditiya HB, Mahlia TMI, Chong WT, Hadi N, Sebayang AH. Second

generation bioethanol production: A critical review. Renewable and Sustainable Energy Reviews. 2016;66: 631-653. DOI: 10.1016/j.rser.2016.07.015

[16] Gupta A, Verma JP. Sustainable bioethanol production from agro-residues: A review. Renewable and Sustainable Energy Reviews. 2014;2015:550-567. DOI: 10.1016/j.rser.2014.08.032

[17] Sun Y, Cheng J. Hydrolysis of lignocellulosic material for ethanol production: A review. Bioresource Technology. 2002;98:673-686. DOI: 10.1016/s0960-8524(01)00212-7

[18] Prado JM, Lachos-perez D, Forstercarneiro T, Rostagno MA. Food and bioproducts processing sub- and supercritical water hydrolysis of agricultural and food industry residues for the production of fermentable sugars: A review. Food and Bioproducts Processing. 2015;98:95-123. DOI: 10.1016/j.fbp.2015.11.004

[19] Karimi K, Emtiazi G, Taherzadeh MJ. Ethanol production from dilute acid pretreated rice straw by simultaneous saccharification and fermentation with Mucor indicus, Rhizopus oryzae, and Saccharomyces cerevisiae. Enzyme and Microbial Technology. 2006;40: 138-144. DOI: 10.1016/j.enzmictec. 2005.10.046

[20] Noomtim P, Cheirsilp B. Production of butanol from palm empty fruit bunches hydrolyzate by Clostridium acetobutylicum. Energy Procedia. 2011;9: 140-146. DOI: 10.1016/j. egypro.2011.09.015

[21] Derman E, Abdulla R, Marbawi H, Sabullah MK. Oil palm empty fruit bunches as a promising feedstock for bioethanol production in Malaysia. Renewable Energy. 2018;129:285-298. DOI: 10.1016/j.renene.2018.06.003

[22] Raman JK, Gnansounou E. Ethanol and lignin production from Brazilian

empty fruit bunch biomass. Bioresource Technology. 2014;172:241-248. DOI: 10.1016/j.biortech.2014.09.043

Current state and prospects. Applied Microbiology Biotechnology. 2006;69: 627-642. DOI: 10.1007/s00253-005-

Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

[30] Marchetti JM, Miguel VU, Errazu AF. Possible methods for biodiesel production. Renewable and Sustainable Energy Reviews. 2007;11:1300-1311. DOI: 10.1016/j.rser.2005.08.006

[31] Barnwal BK, Sharma MP. Prospects of biodiesel production from vegetable oils in India. Renewable and Sustainable Energy Reviews. 2005;9:363-378. DOI:

[32] Noureddini H, Zhu D. Kinetics of transesterification of soybean oil. Journal of American Oil Chemist's Society. 1997;74:1457-1463. DOI: 10.1007/s11746-997-0254-2

[33] Chacon FAT. Techno-economic assessment of biofuel production in the European Union (thesis). Germany: Faculty of Business Admin, Technische University Freiberg; 2004. DOI: http://

10.1016/j.rser.2004.05.007

www.globalbioenergy.org

197

0229-x

[23] Sathendraa ER, Baskarb G, Praveenkumara R, Gnansounou E. Bioethanol production from palm wood using Trichoderma reesei and Kluveromyces marxianus. Bioresource Technology. 2019;271:345-352. DOI: 10.1016/j.biortech.2018.09.134

[24] Baskar G, Selvakumari AE, Aiswarya R. Biodiesel production from castor oil using heterogeneous Ni doped ZnO nanocatalyst. Bioresource Technology. 2018;250:793-798. DOI: 10.1016/j.biotech.2017.12.010

[25] Tan KT, Lee KT, Mohamed AR. Role of energy policy in renewable energy accomplishment: The case of secondgeneration bioethanol. Energy Policy. 2008;36:3360-3365. DOI: 10.1016/j. enpol.2008.05.016

[26] Silva JOV, Almeida MF, Alvim-Ferraz MC, Dias JM. Integrated production of biodiesel and bioethanol from sweet potato. Renewable Energy. 2018;124:114-120. DOI: 10.1016/j. renene.2017.07.052

[27] Boonchuaya P, Techapunb C, Leksawasdib N, Seesuriyachanb P, Hanmoungjaib P, Watanabec M, et al. An integrated process for xylooligosaccharide and bioethanol production from corncob. Bioresource Technology. 2018;256:399-407. DOI: 10.1016/j.biortech.2018.02.004

[28] Lee S, Teramoto Y, Endo T. Enzymatic saccharification of woody biomass micro/nanofibrillated by continuous extrusion process I—Effect of additives with cellulose affinity. Bioresource Technology. 2009;100: 275-279. DOI: 10.1016/j.biotech. 2008.05.051

[29] Lin Y, Tanaka S. Ethanol fermentation from biomass resources: Biofuel: An Environmental Friendly Fuel DOI: http://dx.doi.org/10.5772/intechopen.82856

Current state and prospects. Applied Microbiology Biotechnology. 2006;69: 627-642. DOI: 10.1007/s00253-005- 0229-x

generation bioethanol production: A critical review. Renewable and Sustainable Energy Reviews. 2016;66: 631-653. DOI: 10.1016/j.rser.2016.07.015

Anaerobic Digestion

empty fruit bunch biomass. Bioresource Technology. 2014;172:241-248. DOI: 10.1016/j.biortech.2014.09.043

[23] Sathendraa ER, Baskarb G, Praveenkumara R, Gnansounou E. Bioethanol production from palm wood

using Trichoderma reesei and

[24] Baskar G, Selvakumari AE,

ZnO nanocatalyst. Bioresource Technology. 2018;250:793-798. DOI: 10.1016/j.biotech.2017.12.010

enpol.2008.05.016

renene.2017.07.052

2008.05.051

Kluveromyces marxianus. Bioresource Technology. 2019;271:345-352. DOI: 10.1016/j.biortech.2018.09.134

Aiswarya R. Biodiesel production from castor oil using heterogeneous Ni doped

[25] Tan KT, Lee KT, Mohamed AR. Role of energy policy in renewable energy accomplishment: The case of secondgeneration bioethanol. Energy Policy. 2008;36:3360-3365. DOI: 10.1016/j.

[26] Silva JOV, Almeida MF, Alvim-Ferraz MC, Dias JM. Integrated production of biodiesel and bioethanol from sweet potato. Renewable Energy. 2018;124:114-120. DOI: 10.1016/j.

[27] Boonchuaya P, Techapunb C, Leksawasdib N, Seesuriyachanb P, Hanmoungjaib P, Watanabec M, et al.

xylooligosaccharide and bioethanol production from corncob. Bioresource Technology. 2018;256:399-407. DOI: 10.1016/j.biortech.2018.02.004

[28] Lee S, Teramoto Y, Endo T. Enzymatic saccharification of woody biomass micro/nanofibrillated by continuous extrusion process I—Effect of additives with cellulose affinity. Bioresource Technology. 2009;100: 275-279. DOI: 10.1016/j.biotech.

[29] Lin Y, Tanaka S. Ethanol

fermentation from biomass resources:

An integrated process for

[16] Gupta A, Verma JP. Sustainable bioethanol production from agro-residues: A review. Renewable and Sustainable Energy Reviews. 2014;2015:550-567. DOI: 10.1016/j.rser.2014.08.032

[17] Sun Y, Cheng J. Hydrolysis of lignocellulosic material for ethanol production: A review. Bioresource Technology. 2002;98:673-686. DOI: 10.1016/s0960-8524(01)00212-7

[18] Prado JM, Lachos-perez D, Forstercarneiro T, Rostagno MA. Food and bioproducts processing sub- and supercritical water hydrolysis of agricultural and food industry residues for the production of fermentable sugars: A review. Food and Bioproducts Processing. 2015;98:95-123. DOI: 10.1016/j.fbp.2015.11.004

[19] Karimi K, Emtiazi G, Taherzadeh MJ. Ethanol production from dilute acid pretreated rice straw by simultaneous saccharification and fermentation with Mucor indicus, Rhizopus oryzae, and Saccharomyces cerevisiae. Enzyme and Microbial Technology. 2006;40: 138-144. DOI: 10.1016/j.enzmictec.

[20] Noomtim P, Cheirsilp B. Production of butanol from palm empty fruit bunches hydrolyzate by Clostridium acetobutylicum. Energy Procedia. 2011;9:

[21] Derman E, Abdulla R, Marbawi H, Sabullah MK. Oil palm empty fruit bunches as a promising feedstock for bioethanol production in Malaysia. Renewable Energy. 2018;129:285-298. DOI: 10.1016/j.renene.2018.06.003

[22] Raman JK, Gnansounou E. Ethanol and lignin production from Brazilian

2005.10.046

196

140-146. DOI: 10.1016/j. egypro.2011.09.015

[30] Marchetti JM, Miguel VU, Errazu AF. Possible methods for biodiesel production. Renewable and Sustainable Energy Reviews. 2007;11:1300-1311. DOI: 10.1016/j.rser.2005.08.006

[31] Barnwal BK, Sharma MP. Prospects of biodiesel production from vegetable oils in India. Renewable and Sustainable Energy Reviews. 2005;9:363-378. DOI: 10.1016/j.rser.2004.05.007

[32] Noureddini H, Zhu D. Kinetics of transesterification of soybean oil. Journal of American Oil Chemist's Society. 1997;74:1457-1463. DOI: 10.1007/s11746-997-0254-2

[33] Chacon FAT. Techno-economic assessment of biofuel production in the European Union (thesis). Germany: Faculty of Business Admin, Technische University Freiberg; 2004. DOI: http:// www.globalbioenergy.org

Chapter 10

Abstract

1. Introduction

50% [1].

199

Experimental Study of CO2

Plasticization in Polysulfone

Yin Fong Yeong and Norwahyu Jusoh

Membrane for Biogas Processing

Serene Sow Mun Lock, Kok Keong Lau, Azmi Mohd Shariff,

Polymeric membranes have emerged for biogas processing to remove CO2 from

CH4. Nonetheless, it is also acknowledged that polymeric membranes have the tendency to sorb highly condensable CO2, which consequently swells the polymeric matrix, typically at operating condition higher than the plasticization pressure. The swelling increases void spaces for transport of gas penetrants, which results in an increment in permeability of all gas components at the cost of substantial decrease in membrane selectivity. Despite observations of the end results of plasticization, it is found that many transport property studies include only permeability measurements near ambient conditions. Complementary information on the individual contributions of the sorption and diffusion coefficients to the overall performance typically at non-ambient operating conditions is rarely reported. Therefore, in present study, experimental study has been conducted to fabricate polysulfone (PSF) film. Validity of the developed polysulfone membrane has been verified through characterization and validated with gas transport behavior of published results. Subsequently, transport properties of CO2 though the PSF membrane at varying operating temperatures has been elucidated. The dual mode sorption and partial immobilization models have been employed to quantify the gas transport properties

of noncondensable CH4 and condensable CO2 through PSF membrane.

Keywords: membrane, plasticization, solubility, diffusivity, permeability

The ever-growing worldwide energy demand has directed the attention of government agencies and energy companies towards uncovering renewable energy over recent years as an alternative to achieve sustainable global energy policy [1]. The effort is done to circumvent the volatility of fuel price in the petrochemical market while meeting expanding user demand [2]. Biogas produced from microbial digestion of waste is found to contain high concentration of methane (CH4), which can be utilized for combustion process to circumvent usage of fossil fuels while meeting energy demand. Nonetheless, biogas also contains a huge amount of side products, typically carbon dioxide (CO2), whereby the amount can reach as high as

### Chapter 10

## Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

Serene Sow Mun Lock, Kok Keong Lau, Azmi Mohd Shariff, Yin Fong Yeong and Norwahyu Jusoh

### Abstract

Polymeric membranes have emerged for biogas processing to remove CO2 from CH4. Nonetheless, it is also acknowledged that polymeric membranes have the tendency to sorb highly condensable CO2, which consequently swells the polymeric matrix, typically at operating condition higher than the plasticization pressure. The swelling increases void spaces for transport of gas penetrants, which results in an increment in permeability of all gas components at the cost of substantial decrease in membrane selectivity. Despite observations of the end results of plasticization, it is found that many transport property studies include only permeability measurements near ambient conditions. Complementary information on the individual contributions of the sorption and diffusion coefficients to the overall performance typically at non-ambient operating conditions is rarely reported. Therefore, in present study, experimental study has been conducted to fabricate polysulfone (PSF) film. Validity of the developed polysulfone membrane has been verified through characterization and validated with gas transport behavior of published results. Subsequently, transport properties of CO2 though the PSF membrane at varying operating temperatures has been elucidated. The dual mode sorption and partial immobilization models have been employed to quantify the gas transport properties of noncondensable CH4 and condensable CO2 through PSF membrane.

Keywords: membrane, plasticization, solubility, diffusivity, permeability

### 1. Introduction

The ever-growing worldwide energy demand has directed the attention of government agencies and energy companies towards uncovering renewable energy over recent years as an alternative to achieve sustainable global energy policy [1]. The effort is done to circumvent the volatility of fuel price in the petrochemical market while meeting expanding user demand [2]. Biogas produced from microbial digestion of waste is found to contain high concentration of methane (CH4), which can be utilized for combustion process to circumvent usage of fossil fuels while meeting energy demand. Nonetheless, biogas also contains a huge amount of side products, typically carbon dioxide (CO2), whereby the amount can reach as high as 50% [1].

It is highly desirable to remove the CO2 contaminants from CH4 since the unequivocal symptoms of climate change have urged continuous pressure on oil and gas companies to adopt practices that reduce carbon footprint to mitigate the effect of greenhouse gases global warming [3]. In addition to minimization of the environment pollution, the undesired CO2 must be removed in order to increase the heating value of biogas since the abundant impurities constitute to no heating value [4]. The removal of CO2 in the biogas also prevents corrosion of pipelines and process equipments that are of great importance to curb gas leakage along the transportation process since the leakage can contribute to public hazards [5]. It has been proposed that the produced biogas requires processing to contain a minimal of 95% CH4 in order to be economically viable [1].

that of plasticization pressure and amount of CO2 that invoke plasticization, in different glassy polymer classes through measurement of gas permeation and sorption [10]. Kapantaidakis et al. demonstrated accelerated CO2 plasticization effect in ultrathin polymer structures by measuring gas permeance at increasing operating pressures [13]. Horn and Paul [14] studied the CO2 plasticization (reversible) and conditioning (non-reversible) effects in thin and thick glassy polymeric membranes to reaffirm conclusion by Kapantaidakis et al. [14]. Tiwari et al. extended the study by Horn and Paul [14] to high free volume glassy perfluoropolymers through evaluation of CO2 permeability and ellipsometry measurement [15]. Reviews of study related to CO2 plasticization in different membranes have been provided in

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

From previous works, it is found that many transport property studies devoted to plasticization include only study of membrane morphology and permeability measurements near ambient conditions. Complementary information on the individual contributions of the sorption and diffusion coefficients to the overall performance at non-ambient and elevated temperatures is rarely reported. Most of the laboratory data have been limited to study of gas transport characteristic within polymeric membrane at ambient operating temperatures (25–35°C). This is because it appears to be not convenient and time consuming to control the operating condi-

Hence, the objective of present study is to study the effect of CO2 to plasticization of Polysulfone membrane at varying operating conditions. PSF have the most advantages among all polymeric membranes since it easily forms thin film on membrane support surfaces, while demonstrating behaviors such as chemical inertness, good mechanical strength and stable property, which have encouraged their usage in biogas processing. Bos et al. reported a plasticization pressure of 34 bar at 23°C [10] for polysulfone. Nonetheless, the collected data is limited and not extended to elevated pressure, as well as other operating temperatures. In typical biogas processing, the entering gas are in the range of 35–55°C in order to suit the temperature for membrane separation [17]. In our recent work, we studied the interaction of CO2 with polysulfone membranes at varying operating temperatures and CO2 concentrations through employment of atomistic simulation technique and concluded that lower operating temperature constituted to more apparent plasticization effect to membrane morphology [18]. Nonetheless, the

Therefore, this work aims to assemble a sequence of experimental procedure to study gas transport property, which includes solubility, diffusivity and permeability, during plasticization at varying operating temperatures. In an overall, firstly PSF membrane has been fabricated through in-house experimental procedure. Then, the PSF membrane has been analyzed through characterization in order to evaluate applicability of developed membrane. Subsequently, the solubility and permeability of noncondensable methane at varying operating temperatures have been measured and validated with published experimental data to determine applicability of the experimental setup. Then, the gas transport property of condensable CO2 at different operating temperatures has been elucidated to study CO2 plasticization effect in membrane. Finally, empirical models have been used to quantify gas

This section discusses the methodology that has been adapted in current work.

study has not been extended to study of gas transport property.

works by Suleman et al. [16].

DOI: http://dx.doi.org/10.5772/intechopen.80957

tions at different ranges.

transport behavior of the gases.

The overall workflow is presented in Figure 2.

2. Methodology

201

Polymeric membrane applied in gas separation is an alternative that has gained attention in industrial scale application in comparison to conventional technologies (e.g. distillation and absorption) over recent years. The advantages associated to polymeric membrane include taking up a considerably confined space, merely involves physical separation that is free from chemical reaction for consideration of process safety, lower energy consumption and smaller operating cost requirement [6, 7]. Polymeric membrane has been utilized exceptionally in application of CO2 removal from CH4 for processing of biogas. However, a problem that hinders further expansion of the usage of polymeric membranes in such application has emerged due to CO2 induced plasticization.

During CO2 plasticization, sorption of condensable gas penetrants in the membrane matrix interacts with functional group of the pristine polymeric chain. The interaction contributes to ease of mobility of polymeric chains, which consequently increases the void channels in the membrane [8]. Schematic representation of the plasticization phenomena that increases free volume of the polymeric glassy membrane is provided in Figure 1 [9].

As a result, plasticization increases void channels that form passage for gas permeation of all gas species [10]. Nonetheless, when empty spaces increase, the sieving capability of the polymeric membrane also reduces simultaneously. This causes reduction in the membrane selectivity ∝A=<sup>B</sup> ¼ PA=PB as an ultimate result. Therefore, it is vital to understand CO2 plasticization in polymeric membranes since it is highly possible to cause undesirable product lost that decreases profitability of the biogas processing plant.

The observation of CO2 plasticization in glassy polymeric membranes has been well addressed with a long history. Wessling et al. conducted experiments comparing the kinetics of mass uptake (sorption) and the volume increase (dilation) due to sorption to give a deeper understanding of the plasticizing effect of CO2 in commercial 6FDA membrane [11]. Houde et al. employed the wide angle X-ray diffraction (WAXD) to investigate the mechanism of plasticization in various glassy polymers [12]. Bos et al. reported CO2 plasticization phenomena, which includes

Figure 1.

Plasticization phenomena resulting in facilitated polymer mobility and increased free volume in the polymer, adapted from Kikic et al. [9].

### Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing DOI: http://dx.doi.org/10.5772/intechopen.80957

that of plasticization pressure and amount of CO2 that invoke plasticization, in different glassy polymer classes through measurement of gas permeation and sorption [10]. Kapantaidakis et al. demonstrated accelerated CO2 plasticization effect in ultrathin polymer structures by measuring gas permeance at increasing operating pressures [13]. Horn and Paul [14] studied the CO2 plasticization (reversible) and conditioning (non-reversible) effects in thin and thick glassy polymeric membranes to reaffirm conclusion by Kapantaidakis et al. [14]. Tiwari et al. extended the study by Horn and Paul [14] to high free volume glassy perfluoropolymers through evaluation of CO2 permeability and ellipsometry measurement [15]. Reviews of study related to CO2 plasticization in different membranes have been provided in works by Suleman et al. [16].

From previous works, it is found that many transport property studies devoted to plasticization include only study of membrane morphology and permeability measurements near ambient conditions. Complementary information on the individual contributions of the sorption and diffusion coefficients to the overall performance at non-ambient and elevated temperatures is rarely reported. Most of the laboratory data have been limited to study of gas transport characteristic within polymeric membrane at ambient operating temperatures (25–35°C). This is because it appears to be not convenient and time consuming to control the operating conditions at different ranges.

Hence, the objective of present study is to study the effect of CO2 to plasticization of Polysulfone membrane at varying operating conditions. PSF have the most advantages among all polymeric membranes since it easily forms thin film on membrane support surfaces, while demonstrating behaviors such as chemical inertness, good mechanical strength and stable property, which have encouraged their usage in biogas processing. Bos et al. reported a plasticization pressure of 34 bar at 23°C [10] for polysulfone. Nonetheless, the collected data is limited and not extended to elevated pressure, as well as other operating temperatures. In typical biogas processing, the entering gas are in the range of 35–55°C in order to suit the temperature for membrane separation [17]. In our recent work, we studied the interaction of CO2 with polysulfone membranes at varying operating temperatures and CO2 concentrations through employment of atomistic simulation technique and concluded that lower operating temperature constituted to more apparent plasticization effect to membrane morphology [18]. Nonetheless, the study has not been extended to study of gas transport property.

Therefore, this work aims to assemble a sequence of experimental procedure to study gas transport property, which includes solubility, diffusivity and permeability, during plasticization at varying operating temperatures. In an overall, firstly PSF membrane has been fabricated through in-house experimental procedure. Then, the PSF membrane has been analyzed through characterization in order to evaluate applicability of developed membrane. Subsequently, the solubility and permeability of noncondensable methane at varying operating temperatures have been measured and validated with published experimental data to determine applicability of the experimental setup. Then, the gas transport property of condensable CO2 at different operating temperatures has been elucidated to study CO2 plasticization effect in membrane. Finally, empirical models have been used to quantify gas transport behavior of the gases.

### 2. Methodology

This section discusses the methodology that has been adapted in current work. The overall workflow is presented in Figure 2.

It is highly desirable to remove the CO2 contaminants from CH4 since the unequivocal symptoms of climate change have urged continuous pressure on oil and gas companies to adopt practices that reduce carbon footprint to mitigate the effect of greenhouse gases global warming [3]. In addition to minimization of the environment pollution, the undesired CO2 must be removed in order to increase the heating value of biogas since the abundant impurities constitute to no heating value [4]. The removal of CO2 in the biogas also prevents corrosion of pipelines and process equipments that are of great importance to curb gas leakage along the transportation process since the leakage can contribute to public hazards [5]. It has been proposed that the produced biogas requires processing to contain a minimal of

Polymeric membrane applied in gas separation is an alternative that has gained attention in industrial scale application in comparison to conventional technologies (e.g. distillation and absorption) over recent years. The advantages associated to polymeric membrane include taking up a considerably confined space, merely involves physical separation that is free from chemical reaction for consideration of process safety, lower energy consumption and smaller operating cost requirement [6, 7]. Polymeric membrane has been utilized exceptionally in application of CO2 removal from CH4 for processing of biogas. However, a problem that hinders further expansion of the usage of polymeric membranes in such application has

During CO2 plasticization, sorption of condensable gas penetrants in the membrane matrix interacts with functional group of the pristine polymeric chain. The interaction contributes to ease of mobility of polymeric chains, which consequently increases the void channels in the membrane [8]. Schematic representation of the plasticization phenomena that increases free volume of the polymeric glassy mem-

As a result, plasticization increases void channels that form passage for gas permeation of all gas species [10]. Nonetheless, when empty spaces increase, the sieving capability of the polymeric membrane also reduces simultaneously. This

Therefore, it is vital to understand CO2 plasticization in polymeric membranes since it is highly possible to cause undesirable product lost that decreases profitability of

The observation of CO2 plasticization in glassy polymeric membranes has been well addressed with a long history. Wessling et al. conducted experiments comparing the kinetics of mass uptake (sorption) and the volume increase (dilation) due to sorption to give a deeper understanding of the plasticizing effect of CO2 in commercial 6FDA membrane [11]. Houde et al. employed the wide angle X-ray diffraction (WAXD) to investigate the mechanism of plasticization in various glassy polymers [12]. Bos et al. reported CO2 plasticization phenomena, which includes

Plasticization phenomena resulting in facilitated polymer mobility and increased free volume in the polymer,

as an ultimate result.

causes reduction in the membrane selectivity ∝A=<sup>B</sup> ¼ PA=PB

95% CH4 in order to be economically viable [1].

Anaerobic Digestion

emerged due to CO2 induced plasticization.

brane is provided in Figure 1 [9].

the biogas processing plant.

Figure 1.

200

adapted from Kikic et al. [9].

Subsequently, the membranes were subjected to vacuum drying at a heating rate of 20°C/h from 40 to 180°C followed by annealing at 180°C for 24 h. This is to prevent formation of defects in the membrane due to fast evaporation of the solvent. Finally, the PSF membrane film was carefully peeled off from the Petri dish once

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

In this section, the characterization analysis that has been used to investigate morphology of the prepared membrane has been discussed. The analysis is crucial to evaluate that the fabricated PSF membrane is dense and defect free. At the same time, it is aimed to ensure that all undesirable solvents that can potentially affect membrane characteristic have been removed accordingly. This is to confirm its applicability prior to measurement of gas solubility and permeability behavior in

The variable pressure field emission scanning electron microscope (VP-FESEM, Zeiss Supra 55 VP) was employed to evaluate membrane morphology of the fabricated PSF membrane. Cross sectional side of the membranes were prepared for VP-FESEM analysis via immersion in liquid nitrogen before fracturing the film in order to prevent morphology distortion. All the membrane samples were subsequently sputter coated with platinum using Quorum Q150R S coater prior to imaging. Membrane samples were observed using VP-FESEM with magnification at 500.

Fourier transform infrared spectrometer (FTIR, Perkin Elmer Spectrum One) was operated under transmission with 50 scans in the wavelength range of 450–

4000 cm<sup>1</sup> to determine IR spectra of the fabricated PSF membrane.

2.2.1 Variable pressure field emission scanning Electron microscope

the cast solution was completely dried.

Flow diagram of procedure for preparation of PSF membrane.

DOI: http://dx.doi.org/10.5772/intechopen.80957

2.2.2 Fourier transform infrared spectrometer

2.2 Sample characterization

Figure 3.

subsequent sections.

203

Figure 2. Process diagram of overall workflow.

This section describes the materials and fabrication methodology to prepare the PSF membrane as well as analysis methodology to validate the developed membrane. In addition, the pressure decay and constant-pressure variable volume methodology for measurement of gas penetrants solubility and permeability have been elaborated.

### 2.1 Materials and membrane fabrication

The polysulfone (PSF) dense film was prepared via solution casting method using N-Methyl-2-pyyrolidone (NMP) as solvent [19, 20] with a composition of 25 wt% PSF. The PSF was manufactured and supplied in pellet form by Aldrich (MW 35,000 by light scattering) while NMP from Merck (analytical grade) was used as received. Flow diagram characterizing the chronological procedure for fabrication of PSF dense membrane is depicted in Figure 3.

In the beginning, the PSF pellets were dehydrated overnight to get rid of unwanted water content by heating it in a vacuum oven. Subsequently, the amount of dried PSF pellets and filtered NMP solvent was measured prior to mixing them together for 24 hours. When approaching the end of the mixing process, a clear homogenous solution was observed.

Then, an ultrasonication water bath has been employed to desonicate the mixture with a total duration of 4 h before leaving it for 24 h free standing degas. This is aimed to remove any bubbles formed during the mixing protocol while enhancing its homogeneity. The casting solution was then poured into a leveled and clean glass Petri dish, which was covered with aluminum foil to reduce its evaporation rate.

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing DOI: http://dx.doi.org/10.5772/intechopen.80957

### Figure 3.

This section describes the materials and fabrication methodology to prepare the PSF membrane as well as analysis methodology to validate the developed membrane. In addition, the pressure decay and constant-pressure variable volume methodology for measurement of gas penetrants solubility and permeability have

The polysulfone (PSF) dense film was prepared via solution casting method using N-Methyl-2-pyyrolidone (NMP) as solvent [19, 20] with a composition of 25 wt% PSF. The PSF was manufactured and supplied in pellet form by Aldrich (MW 35,000 by light scattering) while NMP from Merck (analytical grade) was used as received. Flow diagram characterizing the chronological procedure for

In the beginning, the PSF pellets were dehydrated overnight to get rid of unwanted water content by heating it in a vacuum oven. Subsequently, the amount of dried PSF pellets and filtered NMP solvent was measured prior to mixing them together for 24 hours. When approaching the end of the mixing process, a clear

Then, an ultrasonication water bath has been employed to desonicate the mixture with a total duration of 4 h before leaving it for 24 h free standing degas. This is aimed to remove any bubbles formed during the mixing protocol while enhancing its homogeneity. The casting solution was then poured into a leveled and clean glass Petri dish, which was covered with aluminum foil to reduce its evaporation rate.

been elaborated.

Anaerobic Digestion

Process diagram of overall workflow.

Figure 2.

202

2.1 Materials and membrane fabrication

homogenous solution was observed.

fabrication of PSF dense membrane is depicted in Figure 3.

Flow diagram of procedure for preparation of PSF membrane.

Subsequently, the membranes were subjected to vacuum drying at a heating rate of 20°C/h from 40 to 180°C followed by annealing at 180°C for 24 h. This is to prevent formation of defects in the membrane due to fast evaporation of the solvent. Finally, the PSF membrane film was carefully peeled off from the Petri dish once the cast solution was completely dried.

### 2.2 Sample characterization

In this section, the characterization analysis that has been used to investigate morphology of the prepared membrane has been discussed. The analysis is crucial to evaluate that the fabricated PSF membrane is dense and defect free. At the same time, it is aimed to ensure that all undesirable solvents that can potentially affect membrane characteristic have been removed accordingly. This is to confirm its applicability prior to measurement of gas solubility and permeability behavior in subsequent sections.

### 2.2.1 Variable pressure field emission scanning Electron microscope

The variable pressure field emission scanning electron microscope (VP-FESEM, Zeiss Supra 55 VP) was employed to evaluate membrane morphology of the fabricated PSF membrane. Cross sectional side of the membranes were prepared for VP-FESEM analysis via immersion in liquid nitrogen before fracturing the film in order to prevent morphology distortion. All the membrane samples were subsequently sputter coated with platinum using Quorum Q150R S coater prior to imaging. Membrane samples were observed using VP-FESEM with magnification at 500.

### 2.2.2 Fourier transform infrared spectrometer

Fourier transform infrared spectrometer (FTIR, Perkin Elmer Spectrum One) was operated under transmission with 50 scans in the wavelength range of 450– 4000 cm<sup>1</sup> to determine IR spectra of the fabricated PSF membrane.

### 2.3 Solubility measurement (pressure decay methodology)

The principle is based on a dual-chamber pressure decay setup, which has been demonstrated in detailed elsewhere [21]. In this approach, the quantity of gas originally introduced to a sorption system and equilibrated quantity of gas left behind after sorption into a polymer located within the sorption system are determined. This requires measurement in the decline of pressure after sorption of gas into a polymer under study, the temperature of gas, and volume of the system in which the experiment takes place. By measuring the aforementioned variables, the initial and final number of gases existing in the sorption system can be determined directly.

The concentration of gas molecule, x, sorbed within the polymer membrane at any operating temperature has been obtained through Eq. (1), where 22,414 cm3 /mol corresponds to a simple numerical conversion factor and Vp (cm3 ) is volume of the polymer sample in the membrane chamber, which has been determined through the conventional fluid displacement method.

$$\boldsymbol{\omega} = \boldsymbol{n}\_p \left( \frac{22414}{V\_p} \right) \tag{1}$$

Huang et al. work [22]. The procedure has been conducted in the vacuum oven for 30 min to prevent any oxidation since equilibration at the rubbery state should be tentatively achieved over this time span based on Struik's report [23]. After heating, the polymer membrane has been immediately removed from the vacuum oven and has been quenched to ambient temperature, while preparing the membrane for

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

For the separation process, the membrane sample of 3.14 cm<sup>2</sup> effective area has been mounted in a membrane test cell to study the separation efficiency at various operating conditions. The membrane area has been constituted by cautiously locating the membrane films on aluminum tape over a circle hole with a diameter of 1 cm while avoiding any folding that destroys the membrane surface. Finally, a second piece of aluminum tape and Whatman® Anodisc filter has been adhered to the underside of the membrane for mechanical support to withstand a wide range of

The process of mounting the membrane within the test cell has been conducted

At least three measurements were performed to evaluate the flowrate and composition during membrane separation process. Since the current study addresses high pressure conditions, non-ideal gas conditions should be considered. The driving force for this case is described as the distinction in fugacity from the high to low end across the membrane. A nonideal equation of state has been employed to compute fugacity of CO2 and CH4 on the feed side. On the other hand, since the permeate pressure is remained at atmospheric condition, the nonideality associated to real gas behavior can be disregarded. The permeability of gas component i

within 15 min before bringing the polymer membrane to the desired operating temperature, which are 35, 45 and 55°C respectively. The pressure has been increased gradually from atmospheric condition to a maximum of 50 bars with an increment step of 5 bars. Upstream gas at required operating pressure, temperature and flow rate has been introduced into the membrane for permeation test. Volumetric permeation rates in the permeate stream has been determined with a soap bubble flow meter. Lastly, the entire system should be evacuated to fully degas the

permeation test.

Figure 4.

operating pressure.

205

system before proceeding to other experiment.

Parallel membrane cell for reproducibility of gas permeation.

DOI: http://dx.doi.org/10.5772/intechopen.80957

(barrer), Pi, is calculated based on Eq. (2).

In this study, in order to invoke sorption of polymeric membranes at varying operating temperatures, a constant temperature water bath has been employed. In this context, temperature of the system is consistently controlled at the designated value by submerging the sorption cell within the temperature regulated water bath. Operating temperature is increased gradually from 35 to 55°C with an interval of 10°C for each incremental step. As for pressure increment, it has been continually increased from 5 to 50 bars with an interval of 5 bars to determine sorption isotherm of gases. CH4 gas has been introduced to the sorption cell first prior to CO2 since condensable gases can potentially cause irreversible plasticization and swelling effect to the membrane morphology that affects its sorption capability as an end result.

### 2.4 Permeation measurement

This section describes the experimental setup for gas permeation testing across the PSF membrane. The apparatus adopted a constant-pressure variable volume system to measure gas permeability by measuring the permeate flow rate at atmospheric downstream pressure using a bubble flow meter. Schematic diagram for gas permeation measurement has been provided in Figure 4.

The system consists of a feed inlet point, a pressure regulation system and a mass flow controller. The amount of gas from feed inlet point was controlled using a mass flow controller. The permeation apparatus is developed for high pressure testing devoted to CO2 and CH4. For high pressure applications, all fittings and valves were supplied by Swagelok with pressure-rating > 70 bar while all sensors are capable to read a maximum pressure of 100 bars. In addition, operating temperature of the membrane has been controlled at constant and designated value by regulating oven temperature. Before conducting experiment, the system has been evacuated with a vacuum pump overnight to eliminate any gas or vapors in the system. Leak tests have been performed after degassing process to ensure that the equipment is safe before experiment proceeded.

For polymer structure, it is important to heat it �10°C above its glass transition temperature, Tg, in the absence of any mechanical stress to erase all previous thermal history as well as to relax any molecular orientation captured during film formation [22]. The thermal history removal protocol has been adapted from

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing DOI: http://dx.doi.org/10.5772/intechopen.80957

### Figure 4. Parallel membrane cell for reproducibility of gas permeation.

Huang et al. work [22]. The procedure has been conducted in the vacuum oven for 30 min to prevent any oxidation since equilibration at the rubbery state should be tentatively achieved over this time span based on Struik's report [23]. After heating, the polymer membrane has been immediately removed from the vacuum oven and has been quenched to ambient temperature, while preparing the membrane for permeation test.

For the separation process, the membrane sample of 3.14 cm<sup>2</sup> effective area has been mounted in a membrane test cell to study the separation efficiency at various operating conditions. The membrane area has been constituted by cautiously locating the membrane films on aluminum tape over a circle hole with a diameter of 1 cm while avoiding any folding that destroys the membrane surface. Finally, a second piece of aluminum tape and Whatman® Anodisc filter has been adhered to the underside of the membrane for mechanical support to withstand a wide range of operating pressure.

The process of mounting the membrane within the test cell has been conducted within 15 min before bringing the polymer membrane to the desired operating temperature, which are 35, 45 and 55°C respectively. The pressure has been increased gradually from atmospheric condition to a maximum of 50 bars with an increment step of 5 bars. Upstream gas at required operating pressure, temperature and flow rate has been introduced into the membrane for permeation test. Volumetric permeation rates in the permeate stream has been determined with a soap bubble flow meter. Lastly, the entire system should be evacuated to fully degas the system before proceeding to other experiment.

At least three measurements were performed to evaluate the flowrate and composition during membrane separation process. Since the current study addresses high pressure conditions, non-ideal gas conditions should be considered. The driving force for this case is described as the distinction in fugacity from the high to low end across the membrane. A nonideal equation of state has been employed to compute fugacity of CO2 and CH4 on the feed side. On the other hand, since the permeate pressure is remained at atmospheric condition, the nonideality associated to real gas behavior can be disregarded. The permeability of gas component i (barrer), Pi, is calculated based on Eq. (2).

2.3 Solubility measurement (pressure decay methodology)

The principle is based on a dual-chamber pressure decay setup, which has been demonstrated in detailed elsewhere [21]. In this approach, the quantity of gas originally introduced to a sorption system and equilibrated quantity of gas left behind after sorption into a polymer located within the sorption system are determined. This requires measurement in the decline of pressure after sorption of gas into a polymer under study, the temperature of gas, and volume of the system in which the experiment takes place. By measuring the aforementioned variables, the initial and final number of gases existing in the sorption system can be determined directly.

The concentration of gas molecule, x, sorbed within the polymer membrane at

is volume of the polymer sample in the membrane chamber, which has been deter-

In this study, in order to invoke sorption of polymeric membranes at varying operating temperatures, a constant temperature water bath has been employed. In this context, temperature of the system is consistently controlled at the designated value by submerging the sorption cell within the temperature regulated water bath. Operating temperature is increased gradually from 35 to 55°C with an interval of 10°C

increased from 5 to 50 bars with an interval of 5 bars to determine sorption isotherm of gases. CH4 gas has been introduced to the sorption cell first prior to CO2 since condensable gases can potentially cause irreversible plasticization and swelling effect to the membrane morphology that affects its sorption capability as an end result.

This section describes the experimental setup for gas permeation testing across the PSF membrane. The apparatus adopted a constant-pressure variable volume system to measure gas permeability by measuring the permeate flow rate at atmospheric downstream pressure using a bubble flow meter. Schematic diagram for gas

The system consists of a feed inlet point, a pressure regulation system and a mass flow controller. The amount of gas from feed inlet point was controlled using a mass flow controller. The permeation apparatus is developed for high pressure testing devoted to CO2 and CH4. For high pressure applications, all fittings and valves were supplied by Swagelok with pressure-rating > 70 bar while all sensors are capable to read a maximum pressure of 100 bars. In addition, operating temperature of the membrane has been controlled at constant and designated value by regulating oven temperature. Before conducting experiment, the system has been evacuated with a vacuum pump overnight to eliminate any gas or vapors in the system. Leak tests have been performed after degassing process to ensure that the equipment is safe

For polymer structure, it is important to heat it �10°C above its glass transition

temperature, Tg, in the absence of any mechanical stress to erase all previous thermal history as well as to relax any molecular orientation captured during film formation [22]. The thermal history removal protocol has been adapted from

/mol corresponds to a simple numerical conversion factor and Vp (cm3

22414 Vp  )

(1)

any operating temperature has been obtained through Eq. (1), where

x ¼ np

for each incremental step. As for pressure increment, it has been continually

mined through the conventional fluid displacement method.

permeation measurement has been provided in Figure 4.

22,414 cm3

Anaerobic Digestion

2.4 Permeation measurement

before experiment proceeded.

204

$$P\_i = \frac{tV\_P}{A\_m \left(f\_h - f\_l\right)}\tag{2}$$

3.1.2 FTIR

Figure 6.

in present work.

FTIR spectrum of synthesized PSF membrane.

DOI: http://dx.doi.org/10.5772/intechopen.80957

at 1101.12 cm<sup>1</sup>

207

714.33 and 687.73 cm<sup>1</sup>

FTIR is the most effective alternative to elucidate the functional group of membrane. Figure 6 depicts the IR spectrum of the PSF polymeric membrane obtained

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

For PSF membrane, the peak at 2965.58 cm<sup>1</sup> correspond to stretching vibration of asymmetric and symmetric C-H bond. On the other hand, the peaks at 1581.54 and 1484.61 cm<sup>1</sup> represent the C=C bond in the PSF repeat chain. The IR spectra peak observed at 1407.65 and 1363.70 cm<sup>1</sup> correspond to the asymmetric and symmetric C-H bending deformation of methyl group. Amine stretching is depicted

presence of asymmetric C-O-C stretching by aryl ether group. The peaks at 1167.53 and 1101.12 cm<sup>1</sup> are assigned to asymmetric and symmetric O=S=O stretching of sulfonate group. In addition, the peak at 1407.65 cm<sup>1</sup> has been attributed to stretching vibration of aromatics in PSF. All the functional groups are consistent to those observed in the repeat unit of Polysulfone [18]. The good accordance demonstrates the validity of the synthesized PSF membrane and elimination of any impurities/solvent that can potentially affect the membrane separation performance.

To validate applicability of the sorption laboratory setup, gas methane has been introduced to the PSF membrane with operating pressure at an incremental step, to acquire the sorption behavior of CH4 in PSF membrane, as shown in Figure 7. Experimental data by Sada et al. that studied the effect of operating temperature to the solubility of CH4 within PSF has also been provided as Ref. [24]. The sorption experimental data obtained from current work exhibits close agreement with published results by Sada et al. [24]. The good compliance suggests that the fabricated PSF polymeric membrane and experimental setup are of adequate soundness

From Figure 7, it is shown that the concentration of CH4 being sorbed into the polymeric membrane is enhanced when operating pressure increases at all operating temperature. The increment in CH4 concentration can be explained through greater driving force that advances the sorption of gas molecules within the free

3.2 Validation with transport properties of methane

to produce defects and error free experimental results.

, while phenyl ring substitution band is noticed at 851.57, 830.00,

. IR spectrum noticeable at 1231.85 cm<sup>1</sup> represents the

In Eq. (2), VP is the permeate flow rate (cm3 (STP)/s), t is the thickness of membrane (cm), Am is the membrane area (cm2 ), f <sup>h</sup> and fl are the fugacities in feed side and permeate side respectively (cmHg), subscript i denotes CO2 or CH4. The permeability of the membrane is expressed in the unit of Barrer (1 Barrer = <sup>1</sup> � <sup>10</sup>�<sup>10</sup> cm<sup>3</sup> (STP) cm/s cm2 cmHg).

### 3. Results and discussion

In this part, the results pertaining to experimental section from the fabricated PSF polymeric membrane, gas transport properties of incondensable CH4 and condensable CO2 within the PSF membrane and empirical model to quantify the permeation behavior have been discussed.

### 3.1 Membrane morphology

To understand the membrane morphology, several characterization methodologies have been conducted to analyze the fabricated membrane, which comprised those of VP-FESEM and FITR, as discussed in the subsections.

### 3.1.1 VP-FESEM

The structure of dense PSF membrane at a magnification of 500 is depicted in Figure 5.

The PSF membrane is consisted of a dense, nonporous and single polymer layer that is homogenous in all directions. The thickness of the membrane is �78 μm. The smooth membrane configuration without defects ensures its applicability for solubility and gas permeation measurement in subsequent section.

### Figure 5. Cross sectional of PSF dense membrane.

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing DOI: http://dx.doi.org/10.5772/intechopen.80957

Figure 6. FTIR spectrum of synthesized PSF membrane.

### 3.1.2 FTIR

Pi <sup>¼</sup> tVP

In Eq. (2), VP is the permeate flow rate (cm3 (STP)/s), t is the thickness of

In this part, the results pertaining to experimental section from the fabricated PSF polymeric membrane, gas transport properties of incondensable CH4 and condensable CO2 within the PSF membrane and empirical model to quantify the per-

To understand the membrane morphology, several characterization methodologies have been conducted to analyze the fabricated membrane, which comprised

The structure of dense PSF membrane at a magnification of 500 is depicted in

The PSF membrane is consisted of a dense, nonporous and single polymer layer that is homogenous in all directions. The thickness of the membrane is �78 μm. The smooth membrane configuration without defects ensures its applicability for

those of VP-FESEM and FITR, as discussed in the subsections.

solubility and gas permeation measurement in subsequent section.

side and permeate side respectively (cmHg), subscript i denotes CO2 or CH4. The permeability of the membrane is expressed in the unit of Barrer (1 Barrer =

membrane (cm), Am is the membrane area (cm2

<sup>1</sup> � <sup>10</sup>�<sup>10</sup> cm<sup>3</sup> (STP) cm/s cm2 cmHg).

meation behavior have been discussed.

3. Results and discussion

Anaerobic Digestion

3.1 Membrane morphology

3.1.1 VP-FESEM

Figure 5.

Figure 5.

206

Cross sectional of PSF dense membrane.

Am f <sup>h</sup> � fl

(2)

), f <sup>h</sup> and fl are the fugacities in feed

FTIR is the most effective alternative to elucidate the functional group of membrane. Figure 6 depicts the IR spectrum of the PSF polymeric membrane obtained in present work.

For PSF membrane, the peak at 2965.58 cm<sup>1</sup> correspond to stretching vibration of asymmetric and symmetric C-H bond. On the other hand, the peaks at 1581.54 and 1484.61 cm<sup>1</sup> represent the C=C bond in the PSF repeat chain. The IR spectra peak observed at 1407.65 and 1363.70 cm<sup>1</sup> correspond to the asymmetric and symmetric C-H bending deformation of methyl group. Amine stretching is depicted at 1101.12 cm<sup>1</sup> , while phenyl ring substitution band is noticed at 851.57, 830.00, 714.33 and 687.73 cm<sup>1</sup> . IR spectrum noticeable at 1231.85 cm<sup>1</sup> represents the presence of asymmetric C-O-C stretching by aryl ether group. The peaks at 1167.53 and 1101.12 cm<sup>1</sup> are assigned to asymmetric and symmetric O=S=O stretching of sulfonate group. In addition, the peak at 1407.65 cm<sup>1</sup> has been attributed to stretching vibration of aromatics in PSF. All the functional groups are consistent to those observed in the repeat unit of Polysulfone [18]. The good accordance demonstrates the validity of the synthesized PSF membrane and elimination of any impurities/solvent that can potentially affect the membrane separation performance.

### 3.2 Validation with transport properties of methane

To validate applicability of the sorption laboratory setup, gas methane has been introduced to the PSF membrane with operating pressure at an incremental step, to acquire the sorption behavior of CH4 in PSF membrane, as shown in Figure 7. Experimental data by Sada et al. that studied the effect of operating temperature to the solubility of CH4 within PSF has also been provided as Ref. [24]. The sorption experimental data obtained from current work exhibits close agreement with published results by Sada et al. [24]. The good compliance suggests that the fabricated PSF polymeric membrane and experimental setup are of adequate soundness to produce defects and error free experimental results.

From Figure 7, it is shown that the concentration of CH4 being sorbed into the polymeric membrane is enhanced when operating pressure increases at all operating temperature. The increment in CH4 concentration can be explained through greater driving force that advances the sorption of gas molecules within the free

### Figure 7.

CH4 sorption isotherm for polysulfone. [♦ In-house collected sorption data ⋄ Sorption data by Sada et al. [24]. Close line - Prediction of dual mode sorption model by Eq. (3) with parameters in Table 1 for in-house collected sorption data Open line - Prediction of dual mode sorption model by Eq. (3) with parameters in Table 1 for sorption data by Sada et al. [24]. ( 30/35°C, 40/45°C, 50/55°C)].

spaces of polymeric membrane matrix. The sorption of CH4 gas molecules is found to be decreasing when operating temperature is increased [18]. The decrement is intuitively reasonable since gas molecules have higher affinity to remain in the gaseous state than rather being sorbed into the membrane at higher operating temperature. In addition, the sorption isotherm of CH4 is found to exhibit good correlation to the dual mode sorption model as depicted in Eq. (3).

$$\mathbf{C}\_{\mathbf{i}} = \mathbf{C}\_{\text{Di}} + \mathbf{C}\_{\text{Hi}} = \mathbf{k}\_{\text{Di}} \mathbf{f}\_{\text{i}} + \frac{\mathbf{C}\_{\text{Hi}}' \mathbf{b}\_{\text{i}} \mathbf{f}\_{\text{i}}}{\mathbf{1} + \mathbf{b}\_{\text{i}} \mathbf{f}\_{\text{i}}} \tag{3}$$

characteristics as a whole. The reported values are found to be consistently higher for lower operating temperature attained through higher sorption capacity as explained earlier. The good compliance with previous published literatures and fit to the commonly employed dual mode sorption model demonstrates that the dual mode sorption cell is of high accuracy for plasticization study in subsequent section. Similarly, validity of the gas permeation cell has been investigated by comparing measured methane permeability data with published experimental results by Sada et al. [24], such as that shown in Figure 8 whereby a close agreement has been obtained in between the two. Measured permeabilities for methane in polysulfone films are illustrated as a function of upstream gas pressure in Figure 8. At every temperature, the mean permeability coefficients were found to decrease with an increase in upstream pressure. Such pressure dependence seems to be characteristic of glassy polymers. The gas permeability is found to be consistently higher at greater operating temperature. The contributing factor is free volume within the structure of the polymer has increased as the temperature is further increased,

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

DOI: http://dx.doi.org/10.5772/intechopen.80957

The permeability of gas through a glassy polymeric membrane is frequently characterized through the partial immobilization model [29], which has evolved from the dual mode sorption model in Eq. (3), such as that presented in Eq. (4).

D0,<sup>i</sup> and Fi represent the diffusion coefficient in the limit when concentration of the mobile gas CM,i!0 and the ratio of the diffusivity through the microvoids to that through the polymeric matrix. The additional parameters in the model have been

For these results, D0,<sup>i</sup> and Fi appear to be a function of temperature. It is found that D0,<sup>i</sup> increases with increment in temperature, which has been rationalized through the enhancement in diffusion energy. A small Fi value corresponds to a relatively low diffusivity through the Langmuir regions. At lower operating

CH4 gas permeability data for polysulfone. [♦ In-house permeability data ⋄ Permeability data by Sada et al. [24]. Line - Prediction of partial immobilization model by Eq. (4) with parameters in Table 2 for in-house

collected permeability ( 35°C, 45°C, 55°C)].

FiC<sup>0</sup> Hibi 1 þ bifi

Hi and bi are parameters from dual mode sorption model, while

(4)

Pi ¼ kD,iD0,<sup>i</sup> 1 þ

while gaining additional energy to execute diffusional jump.

In Eq. (4), kD,i, C<sup>0</sup>

summarized in Table 2.

Figure 8.

209

The dual mode sorption model suggests that the total concentration of gas i in a polymer matrix is composed of two idealized molecular scale environment, in which Ci is the total concentration of gas in the polymer; CDi is equilibrium population existing in the polymer matrix under the dissolved mode and is governed by Henry's Law equation, while CHi is the non-equilibrium population existing in excess within the hole-filling environment governed by Langmuir parameters [25–27]. Moreover, kDi is the Henry's law coefficient that characterizes dissolution of a pure gas, i, in the polymer, bi and C<sup>0</sup> Hi is the Langmuir hole affinity parameter and the capacity parameter respectively, while fi is fugacity of the gas system [26, 28]. The fitted dual mode sorption parameters are provided in Table 1, which has been summarized alongside the reported values by Sada et al. [24].

In has been demonstrated from Table 1 that the parameters are in satisfactory agreement with one another, attributed to the small distinction of the solubility

### Table 1.

Dual-mode sorption parameters for methane in polysulfone film as a function of operating temperature.

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing DOI: http://dx.doi.org/10.5772/intechopen.80957

characteristics as a whole. The reported values are found to be consistently higher for lower operating temperature attained through higher sorption capacity as explained earlier. The good compliance with previous published literatures and fit to the commonly employed dual mode sorption model demonstrates that the dual mode sorption cell is of high accuracy for plasticization study in subsequent section.

Similarly, validity of the gas permeation cell has been investigated by comparing measured methane permeability data with published experimental results by Sada et al. [24], such as that shown in Figure 8 whereby a close agreement has been obtained in between the two. Measured permeabilities for methane in polysulfone films are illustrated as a function of upstream gas pressure in Figure 8. At every temperature, the mean permeability coefficients were found to decrease with an increase in upstream pressure. Such pressure dependence seems to be characteristic of glassy polymers. The gas permeability is found to be consistently higher at greater operating temperature. The contributing factor is free volume within the structure of the polymer has increased as the temperature is further increased, while gaining additional energy to execute diffusional jump.

The permeability of gas through a glassy polymeric membrane is frequently characterized through the partial immobilization model [29], which has evolved from the dual mode sorption model in Eq. (3), such as that presented in Eq. (4).

$$P\_i = k\_{D,i} \mathbf{D}\_{0,i} \left[ \mathbf{1} + \frac{\mathbf{F}\_i \mathbf{C}\_{\text{Hi}}' \mathbf{b}\_i}{\mathbf{1} + \mathbf{b}\_i \mathbf{f}\_i} \right] \tag{4}$$

In Eq. (4), kD,i, C<sup>0</sup> Hi and bi are parameters from dual mode sorption model, while D0,<sup>i</sup> and Fi represent the diffusion coefficient in the limit when concentration of the mobile gas CM,i!0 and the ratio of the diffusivity through the microvoids to that through the polymeric matrix. The additional parameters in the model have been summarized in Table 2.

For these results, D0,<sup>i</sup> and Fi appear to be a function of temperature. It is found that D0,<sup>i</sup> increases with increment in temperature, which has been rationalized through the enhancement in diffusion energy. A small Fi value corresponds to a relatively low diffusivity through the Langmuir regions. At lower operating

Figure 8.

spaces of polymeric membrane matrix. The sorption of CH4 gas molecules is found to be decreasing when operating temperature is increased [18]. The decrement is intuitively reasonable since gas molecules have higher affinity to remain in the gaseous state than rather being sorbed into the membrane at higher operating temperature. In addition, the sorption isotherm of CH4 is found to exhibit good

CH4 sorption isotherm for polysulfone. [♦ In-house collected sorption data ⋄ Sorption data by Sada et al. [24]. Close line - Prediction of dual mode sorption model by Eq. (3) with parameters in Table 1 for in-house collected sorption data Open line - Prediction of dual mode sorption model by Eq. (3) with parameters in Table 1 for sorption data by Sada et al. [24]. ( 30/35°C, 40/45°C, 50/55°C)].

> C0 Hibifi 1 þ bifi

Hi is the Langmuir hole affinity parameter and the capacity param-

(3)

correlation to the dual mode sorption model as depicted in Eq. (3).

(STP) cm3–<sup>1</sup> bar<sup>1</sup>

The number in bracket is the experimental value by Sada et al. [24].

polymer, bi and C<sup>0</sup>

a

208

Table 1.

Figure 7.

Anaerobic Digestion

the reported values by Sada et al. [24].

Temperature (°C) kDi (cm<sup>3</sup>

Ci ¼ CDi þ CHi ¼ kDifi þ

The dual mode sorption model suggests that the total concentration of gas i in a polymer matrix is composed of two idealized molecular scale environment, in which Ci is the total concentration of gas in the polymer; CDi is equilibrium population existing in the polymer matrix under the dissolved mode and is governed by Henry's Law equation, while CHi is the non-equilibrium population existing in excess within the hole-filling environment governed by Langmuir parameters [25–27]. Moreover, kDi is the Henry's law coefficient that characterizes dissolution of a pure gas, i, in the

eter respectively, while fi is fugacity of the gas system [26, 28]. The fitted dual mode sorption parameters are provided in Table 1, which has been summarized alongside

In has been demonstrated from Table 1 that the parameters are in satisfactory agreement with one another, attributed to the small distinction of the solubility

35 0.4123 (0.4352 @ 30°C)<sup>a</sup> 0.1055 (0.1145 @ 30°C)<sup>a</sup> 8.45 (9.26 @ 30°C)a 45 0.3859 (0.4076 @ 40°C)<sup>a</sup> 0.0812 (0.0874 @ 40°C)<sup>a</sup> 7.21 (7.63 @ 40°C)<sup>a</sup> 55 0.3589 (0.3711 @ 50°C)a 0.0678 (0.0738 @ 50°C)<sup>a</sup> 5.34 (6.03 @ 50°C)a

Dual-mode sorption parameters for methane in polysulfone film as a function of operating temperature.

) bi (bar�<sup>1</sup>

) C<sup>0</sup>

Hi (cm3 (STP) cm3–<sup>1</sup>

)

CH4 gas permeability data for polysulfone. [♦ In-house permeability data ⋄ Permeability data by Sada et al. [24]. Line - Prediction of partial immobilization model by Eq. (4) with parameters in Table 2 for in-house collected permeability ( 35°C, 45°C, 55°C)].

Table 2.

Partial immobilization parameters for methane in polysulfone film, model adapted from Scholes et al. [29].

temperature, the Langmuir microvoids exist in a large number with greater sizes [29]. Therefore, gas molecules have a higher tendency to be transported through the Langmuir regions with lower resistance. When operating temperature is further increased, there is a reduction in the number and size of Langmuir microvoids, which consequently restraints the transport in such region. Therefore, there is a shift from dominancy of Langmuir to Henry's region with increment in operating temperature, which contributes to a smaller Fi value. In a similar manner, the satisfactory compliance with Sada et al. published literatures and fit to the commonly employed partial immobilization model demonstrates that the permeation cell rig is of high accuracy for measurement of CO2 plasticization study in next section.

As for gas permeability of CO2 through PSF membrane at varying pressures, it has been tabulated in Figure 10. Similarly, applicability of the data has been demonstrated through good compliance with published experimental data by

Dual-mode sorption parameters for carbon dioxide in polysulfone film as a function of operating temperature.

) bi (bar�<sup>1</sup>

) C<sup>0</sup>

Hi (cm3 (STP) cm3–<sup>1</sup>

)

(STP) cm3–<sup>1</sup> bar<sup>1</sup>

The number in bracket is the experimental value by Sada et al. [24].

35 0.6748 (0.5872)<sup>b</sup> 0.3678 (0.1757)b 18.20 (19.40)<sup>b</sup> 45 0.5840 (0.5014)<sup>b</sup> 0.3415 (0.1530)<sup>b</sup> 15.93 (17.1)<sup>b</sup> 55 0.4932 0.3152 13.67

Experimental Study of CO2 Plasticization in Polysulfone Membrane for Biogas Processing

It is found that gas permeability experiences a decrement before reaching the plasticization pressure at 34.9, 36.1 and 38.0 bars respectively for operating temperature of 35, 45 and 55°C. This has been attributed to rapid decrement in gas solubility when the sorption level off at high pressure due to saturation of favorable sites. Nevertheless, beyond the plasticization pressure, an increase in permeability has been observed because the diffusion coefficient increases with pressure much more rapidly than the solubility coefficient that decreases with pressure, which has been elucidated through plasticization effect that enhances the diffusivity of gas molecules to a large extend when the polymeric membrane is swelled. Viewing from the impact of plasticization pressure, it is shifted to higher value at greater operating temperature. This has been attributed to lower sorption of condensable CO2 when the gas has the tendency to maintain at its gas state with increment in

The parameters for partial immobilization model of CO2 have been summarized in Table 4 with a similar trend observed to that for methane. Nonetheless, the parameters are only applicable to condition before the plasticization pressure is met. After that, the plasticization behavior has been characterized through Eq. (5) that describes permeability of gas within the glassy membrane undergoing

Variables describing the modified partial immobilization model for plasticized

Regardless of demonstrating a similar trend of increment in value with increasing temperature, the D0,<sup>i</sup> values after plasticization are found to be relatively smaller as compared to its counterpart with pristine unaltered PSF structure. This has been attributed to a smaller amount of mobile gas when the favorable sites become concentrated and occupied. With respect to temperature dependency, β<sup>i</sup> is found to decrease with increment in temperature, which implies that the plasticization potential reduces with temperature. It has been proposed that polymeric membrane experiences a decrement in Langmuir microvoids with increment in operating temperature [29]. Therefore, there are fewer pathways for CO2 to interact with functional group of the polymeric chains, which consequently reduces the plasticization potential at higher temperature. In addition, the condensable CO2 also has a higher tendency to exist in the gaseous state, which reduces its plasticization power when operating tem-

FiC<sup>0</sup> Hibi kDið Þ 1 þ bifi

(5)

� 1

exp βikDifi 1 þ

Sada et al. [24].

b

Table 3.

Temperature (°C) kDi (cm3

DOI: http://dx.doi.org/10.5772/intechopen.80957

temperature.

plasticization [29].

perature is increased.

211

Pi <sup>¼</sup> <sup>D</sup>0,i βifi

membrane are provided in Table 4 as well.

### 3.3. CO2 plasticization in PSF membranes

CO2 sorption in PSF membrane has been measured with increment in operating pressure at varying operating temperatures, such as that provided in Figure 9.

Published literature data by Sada et al. for solubility of CO2 within PSF has also been provided [24]. In an overall, it is depicted that the collected sorption data of present study is not substantially different from the reported values by Sada et al. [24]. The sorption data of present work is consistently higher than that reported by Sada et al. at different operating temperatures, which can be deduced via the difference in source of polysulfone to prepare the membrane samples. The sorption data also demonstrates a good agreement with the dual mode sorption model, with close compliance with that reported by Sada et al. [24], such as that summarized in Table 3.

### Figure 9.