Preface

This book presents important information about the structure of cellulose as well as its uses and applications.

In Chapter 1, "Insights from over 10 Years of Cellulosic Biofuel Modeling", Daniel Inman et al. present insights gained from more than ten years of system dynamic modeling of cellulose to the biofuel industry in the United States. They use a publicly available Biomass Scenario Model to explore the impact of logistics, economies of scale, and shared industrial learning on the developing cellulose-to-biofuels industry in the United States. One theme from this study as well as from the work performed over the last decade is the importance of the movement of the system toward maturation, both in terms of the supply system and the conversion processes. Mature processes imply lower investment risk, better yields, and better process economics.

In Chapter 2, "Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic Biorefinery", María E. Eugenio Martín et al. study the use of non-wood raw materials to obtain cellulosic fibers. There exists a renewed interest in the use of non-woody raw materials due to them being an abundant source of low-cost fibers. In addition, they are sometimes the only exploitable source of fibers in certain geographical areas, mainly in developing countries. Moreover, the great variety of characteristics, fiber dimensions, and chemical composition of these alternative raw materials give them great potential to produce different types of papers. The pulp and paper industry is an excellent starting point for the development of lignocellulosic biorefineries, possessing the necessary technology and infrastructure as well as extensive experience in lignocellulosic biomass transformation.

In Chapter 3, "Influence of Size Classifications on the Structural and Solid-State Characterization of Cellulose Materials", Sunday Samuel Oluyamo and Mathew Adefusika Adekoya show the influence of size classification on the properties of cellulose materials. Their study focuses on the influence of size classifications on the structural and solid-state characterization of cellulose obtained from wood dust. The isolated cellulose exhibits good mechanical and solid-state properties with promising applications in device utilization.

In Chapter 4, "An Update on Overview of Cellulose, Its Structure and Applications", Praveen Kumar Gupta et al. review the chemistry of cellulose, its extraction, and the properties that help various industries to make the most of it. Cellulose is one of the most ubiquitous organic polymers on the planet. It is a significant structural component of the primary cell wall of green plants, various forms of algae, and oomycetes. It is a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. There are various extraction procedures for cellulose developed by using different processes like oxidation, etherification, and esterification that convert the prepared celluloses into cellulose derivatives. Since it is a non-toxic, bio-degradable polymer with high tensile and compressive strength, cellulose has widespread use in various fields such as

nanotechnology, pharmaceuticals, the food industry, cosmetics, the textile and paper industry, and drug-delivery systems.

In Chapter 5, "Microbial Cellulases: An Overview and Applications", S. K. Jayasekara and R. R. Ratnayake present a review on cellulases, which are a complex group of enzymes secreted by a broad range of microorganisms including fungi, bacteria, and actinomycetes. They discuss the structure, function, possible applications, and novel biotechnological trends of cellulase enzymes. Furthermore, they examine the possibility of using low-cost, enzymatic pretreatment methods of lignocellulosic material in order to use it as an efficient raw material for biofuel production.

In the final sixth chapter, "Multi-Finishing of Polyester and Polyester Cotton Blend Fabrics Activated by Enzymatic Treatment and Loaded with Zinc Oxide Nanoparticles", Al-Balakocy N.G. et al. discuss the possibility of applying enzymatic treatments for fabric surface activation that can facilitate the loading of zinc oxide nanoparticles (ZnO NPs) onto polyester (PET) and polyester cotton blend (PET/C) fabrics prepared by sol-gel method.

We would like to thank the management at IntechOpen for their support while editing this book.

> **Alejandro Rodríguez Pascual** Professor, Chemical Engineering Department, Universidad de Córdoba, Spain

#### **María E. Eugenio Martín**

**1**

Section 1

Reviews

Tenured scientist, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Madrid, Spain

Section 1 Reviews

**3**

**Chapter 1**

**Abstract**

cellulosic biofuel

**1. Introduction**

(https://github.com/NREL/bsm-public).

results from the publicly-available version1

1 https://github.com/NREL/bsm-public; git commit # e62598a.

**1.1 Biofuels in the United States**

*and Steve Peterson*

Insights from over 10 Years of

imply lower investment risk, better yields, and better process economics.

**Keywords:** system dynamics, biofuels, biomass, modeling, renewable energy,

The Biomass Scenario Model (BSM), developed by the U.S. Department of Energy (DOE), is used to explore the emerging biofuels industry in the United States. Over the course of the last decade, the model has evolved along with the biofuels industry. This evolution includes numerous upgrades to the model and associated software, updates to the underlying data, and public release of the model

The BSM has supported multiple analysis studies focused on various components of the feedstocks-to-biofuels supply chain; links to publications and reports associated with these studies can be found on NREL's OpenEI BSM wiki pages (https://openei. org/wiki/Biomass\_Scenario\_Model). Two important themes, which serve as focal points for this chapter, have emerged from our analyses: (a) the importance of feedstock logistics and (b) the impact of shared industrial learning. We present illustrative

Biofuels—specifically soy-based biodiesel and corn-starch-based ethanol (**Figure 1**)—have benefited from government support within the United States. Both the ethanol and biodiesel markets have grown following the Energy Tax Act [1], a law passed by the federal government in 1978 to promote fuel efficiency with

of the BSM that explore both themes.

*Daniel Inman, Emily Newes, Brian Bush, Laura Vimmerstedt*

We present insights gained from over 10 years of system dynamic modeling of the cellulose to biofuel industry in the United States. We use a publicly-available Biomass Scenario Model to explore the impact of logistics system, economies of scale, and shared industrial learning on the developing cellulose-to-biofuels industry in the United States. One theme from this study as well as from the work performed over the last decade is the importance of the movement of the system toward maturation, both in terms of the supply system and the conversion processes. Mature processes

Cellulosic Biofuel Modeling

#### **Chapter 1**

## Insights from over 10 Years of Cellulosic Biofuel Modeling

*Daniel Inman, Emily Newes, Brian Bush, Laura Vimmerstedt and Steve Peterson*

#### **Abstract**

We present insights gained from over 10 years of system dynamic modeling of the cellulose to biofuel industry in the United States. We use a publicly-available Biomass Scenario Model to explore the impact of logistics system, economies of scale, and shared industrial learning on the developing cellulose-to-biofuels industry in the United States. One theme from this study as well as from the work performed over the last decade is the importance of the movement of the system toward maturation, both in terms of the supply system and the conversion processes. Mature processes imply lower investment risk, better yields, and better process economics.

**Keywords:** system dynamics, biofuels, biomass, modeling, renewable energy, cellulosic biofuel

#### **1. Introduction**

The Biomass Scenario Model (BSM), developed by the U.S. Department of Energy (DOE), is used to explore the emerging biofuels industry in the United States. Over the course of the last decade, the model has evolved along with the biofuels industry. This evolution includes numerous upgrades to the model and associated software, updates to the underlying data, and public release of the model (https://github.com/NREL/bsm-public).

The BSM has supported multiple analysis studies focused on various components of the feedstocks-to-biofuels supply chain; links to publications and reports associated with these studies can be found on NREL's OpenEI BSM wiki pages (https://openei. org/wiki/Biomass\_Scenario\_Model). Two important themes, which serve as focal points for this chapter, have emerged from our analyses: (a) the importance of feedstock logistics and (b) the impact of shared industrial learning. We present illustrative results from the publicly-available version1 of the BSM that explore both themes.

#### **1.1 Biofuels in the United States**

Biofuels—specifically soy-based biodiesel and corn-starch-based ethanol (**Figure 1**)—have benefited from government support within the United States. Both the ethanol and biodiesel markets have grown following the Energy Tax Act [1], a law passed by the federal government in 1978 to promote fuel efficiency with

1 https://github.com/NREL/bsm-public; git commit # e62598a.

**Figure 1.**

*Growth of the ethanol industry and a timeline of major biofuel legislation.*

favorable tax incentives. Other government measures, such as guaranteed loans and research funds, helped de-risk the markets further [2].

Ethanol received another boost when methyl tertiary butyl ether (MTBE) was banned [3], which opened new markets for ethanol as an oxygenate in gasoline. Ethanol use in gasoline was reinforced a year later with the 2015 passing of the Energy Policy Act [4], which removed oxygenation requirements and mandated that refiners blend up to 10% ethanol by volume [5], adhering to the new Renewable Fuels Standard.

From 1978 to 2005, energy policies continued to favor the domestic ethanol industry through production tax credits and capitol grants, among other industry incentives. The passing of the Energy Independence and Security Act of 2007 slanted in favor of lignocellulosic ethanol—increasing biofuel volume requirements while incentivizing lignocellulosic feedstocks over corn starch through Renewable Identification Numbers (RINs) [5].

Ethanol continues to be the primary biofuel in the US. However, because of limits on blending, incompatible distribution and dispensing equipment, and limited market penetration of vehicles capable of using high ethanol blends (~ E-85), the overall biofuel market has been limited and less than anticipated volumetric goals reported in early legislation [6]. Additionally, much of the ethanol blended in the US is derived from cornstarch, which is classified as a "renewable fuel" by the EPA, meaning the fuel achieves a 20% reduction in CO2 as compared to conventional gasoline. To develop a more environmentally sustainable biofuels industry in the US, corn -starch-based ethanol is limited to 15 billion gallons annually, whereas lignocellulosic biofuels are incentive through their eligibility for D5 and D3 RINs. Despite legislation that provides incentives for advanced and cellulosic biofuels, the market for such fuels has been slow to take off.

One factor that has limited the market for advanced and cellulosic biofuels is the development of integrated biorefineries. The technologies for converting lignocellulosic feedstocks into ethanol and hydrocarbons are underdeveloped.Technologies for

**5**

**Figure 2.**

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

markets for biomass feedstocks may not exist altogether.

feedstock species, and programs that incentivize producers [10].

sion making of various agents along the supply chain.

*A basic stock-flow structure and corresponding mathematical representation.*

**1.3 System dynamics modeling**

explanation of these concepts.

**1.2 The Biomass Scenario Model**

feedstock processing and handling have, at best, recently become commercial, and the

Many of the physical processes, decision processes, feedbacks and constraints found in the biomass-to-biofuels supply chain are represented in the BSM [11]. The BSM is a system dynamics model developed under the auspices of the DOE as part of a multi-year project at the National Renewable Energy Laboratory. It is a tool designed to better understand biofuels policy as it impacts the development of the supply chain for biofuels in the United States and the economic agents influencing development through their decisions. The model is intended to generate and explore plausible scenarios for the evolution of a biofuel transportation fuel industry in the United States, representing multiple pathways leading to the production of fuel ethanol as well as advanced biofuels such as biomass-based hydrocarbons such as biomass-based gasoline, diesel, jet fuel, and butanol. The BSM, which is implemented using the STELLA [12] system dynamics simulation platform, integrates representations of resource availability, physical/technological/economic constraints, behavior, and policy to model dynamic interactions across the supply chain. It simulates the deployment of biofuels given technological development and the reaction of the investment community to those technologies in the context of land availability, the competing oil market, consumer demand for biofuels, and government policies over time. It has a strong emphasis on the behavior and deci-

System dynamics is used in a wide range of modeling applications to represent and simulate complex non-linear systems driven by multiple interacting physical and social components. As a modeling philosophy, system dynamics relies on three key concepts: stocks, flows, and system feedback [13]. **Figure 2** shows a basic stockflow structure and corresponding mathematical representation. Below is a brief

These biorefineries are gaining support from both public and private channels [7]. Among the former, both the DOE and the U.S. Department of Agriculture (USDA) have helped commercialize renewable, non-starch biofuels and development of feedstock supplies. Their R&D leadership in the sector has helped develop lignocellulosic feedstocks and has gone beyond biofuels to include growth in bioproducts and biopower [8]. The USDA is also empowering the sector through its Biorefinery Assistance Program, which guarantees loans for biorefineries [9], and through research into alternative

*Cellulose*

**Figure 1.**

favorable tax incentives. Other government measures, such as guaranteed loans and

Ethanol received another boost when methyl tertiary butyl ether (MTBE) was banned [3], which opened new markets for ethanol as an oxygenate in gasoline. Ethanol use in gasoline was reinforced a year later with the 2015 passing of the Energy Policy Act [4], which removed oxygenation requirements and mandated that refiners blend up to

From 1978 to 2005, energy policies continued to favor the domestic ethanol industry through production tax credits and capitol grants, among other industry incentives. The passing of the Energy Independence and Security Act of 2007 slanted in favor of lignocellulosic ethanol—increasing biofuel volume requirements while incentivizing lignocellulosic feedstocks over corn starch through Renewable

Ethanol continues to be the primary biofuel in the US. However, because of limits on blending, incompatible distribution and dispensing equipment, and limited market penetration of vehicles capable of using high ethanol blends (~ E-85), the overall biofuel market has been limited and less than anticipated volumetric goals reported in early legislation [6]. Additionally, much of the ethanol blended in the US is derived from cornstarch, which is classified as a "renewable fuel" by the EPA, meaning the fuel achieves a 20% reduction in CO2 as compared to conventional gasoline. To develop a more environmentally sustainable biofuels industry in the US, corn -starch-based ethanol is limited to 15 billion gallons annually, whereas lignocellulosic biofuels are incentive through their eligibility for D5 and D3 RINs. Despite legislation that provides incentives for advanced

One factor that has limited the market for advanced and cellulosic biofuels is the development of integrated biorefineries. The technologies for converting lignocellulosic feedstocks into ethanol and hydrocarbons are underdeveloped.Technologies for

10% ethanol by volume [5], adhering to the new Renewable Fuels Standard.

and cellulosic biofuels, the market for such fuels has been slow to take off.

research funds, helped de-risk the markets further [2].

*Growth of the ethanol industry and a timeline of major biofuel legislation.*

Identification Numbers (RINs) [5].

**4**

feedstock processing and handling have, at best, recently become commercial, and the markets for biomass feedstocks may not exist altogether.

These biorefineries are gaining support from both public and private channels [7]. Among the former, both the DOE and the U.S. Department of Agriculture (USDA) have helped commercialize renewable, non-starch biofuels and development of feedstock supplies. Their R&D leadership in the sector has helped develop lignocellulosic feedstocks and has gone beyond biofuels to include growth in bioproducts and biopower [8]. The USDA is also empowering the sector through its Biorefinery Assistance Program, which guarantees loans for biorefineries [9], and through research into alternative feedstock species, and programs that incentivize producers [10].

#### **1.2 The Biomass Scenario Model**

Many of the physical processes, decision processes, feedbacks and constraints found in the biomass-to-biofuels supply chain are represented in the BSM [11]. The BSM is a system dynamics model developed under the auspices of the DOE as part of a multi-year project at the National Renewable Energy Laboratory. It is a tool designed to better understand biofuels policy as it impacts the development of the supply chain for biofuels in the United States and the economic agents influencing development through their decisions. The model is intended to generate and explore plausible scenarios for the evolution of a biofuel transportation fuel industry in the United States, representing multiple pathways leading to the production of fuel ethanol as well as advanced biofuels such as biomass-based hydrocarbons such as biomass-based gasoline, diesel, jet fuel, and butanol. The BSM, which is implemented using the STELLA [12] system dynamics simulation platform, integrates representations of resource availability, physical/technological/economic constraints, behavior, and policy to model dynamic interactions across the supply chain. It simulates the deployment of biofuels given technological development and the reaction of the investment community to those technologies in the context of land availability, the competing oil market, consumer demand for biofuels, and government policies over time. It has a strong emphasis on the behavior and decision making of various agents along the supply chain.

#### **1.3 System dynamics modeling**

System dynamics is used in a wide range of modeling applications to represent and simulate complex non-linear systems driven by multiple interacting physical and social components. As a modeling philosophy, system dynamics relies on three key concepts: stocks, flows, and system feedback [13]. **Figure 2** shows a basic stockflow structure and corresponding mathematical representation. Below is a brief explanation of these concepts.

**Figure 2.**

*A basic stock-flow structure and corresponding mathematical representation.*

#### *1.3.1 Stocks and flows*

Accumulations, and the activities that cause accumulations to rise and fall over time, are fundamental to the generation of dynamics. System dynamics models are built up from stock and flow primitives. In the BSM, we use stocks to represent concepts such as prices, inventories, conversion facilities, and station owners who are contemplating investment in E85 tankage and dispensing equipment. Corresponding flows would include price changes; production, consumption, and shrinkage of inventories; investment or obsolescence of facilities; and deciding not to invest in tankage and equipment.

#### *1.3.2 Feedback*

Dynamic social systems can contain rich webs of feedback processes. Positive feedbacks tend to drive reinforcing growth in key quantities, while negative feedbacks support self-correcting behavior. In the BSM, we have sought to capture key feedbacks within and across each stage of the supply chain.

The BSM is built and designed using a top-down, modular approach representing the flow of feedstocks to flow down the supply chain to be converted into biofuels, with feedback mechanisms among and between the various modules. Our modeling approach respects the need for transparency, modularity, and extensibility. This enables standalone analysis of individual modules as well as testing of different module combinations. As shown in **Figure 3**, the model is framed as a set of interconnected sectors and modules. Each supply-chain element is modeled as a standalone module but is linked to the others to receive and provide feedback. The feedstock production module simulates the production of biomass as well as five major commodity crops (corn, wheat, soybeans, cotton, and other grains) through farmer decision logic, land allocation dynamics, new agricultural practices, markets, and prices. The feedstock logistics module models the harvesting, collection,

**7**

**Table 1.**

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

ferences in key variables.

**2. Modeling approach**

storage, preprocessing, and transportation of biomass feedstocks from the field (or forest) to the biorefinery. The conversion module represents more than a dozen biofuel conversion technologies at pre-commercial and commercial scales. In the model, the biofuel produced in the conversion stage is then distributed to dispensing locations and end users. The model is solved numerically at a sub-monthly level and typically reports annual output for the 30–40-year timeframe. Modules receive and react to information in a response to, among other factors, industrial learning, project economics, installed infrastructure, consumer choices, and investment dynamics. The model is geographically stratified using the 10 USDA farm production regions [14] as a basis, which facilitates analysis of regional dif-

We used the BSM to examine the impacts of (1) feedstock format and logistics, (2) biorefinery economies of scale, and (3) the impacts of shared industrial learning between fuel production technologies. In order to understand potential synergies between logistics, scale, and shared learning we modeled 10 combinations of feedstock logistics and economies of scale (**Table 1**). The feedstock formats and logistics considered include bale-based and advanced densified formats. At present, in the United States, the advanced densified logistics system is under development and we do not yet know the mechanism(s) for how these innovations may infuse into the broader market. Because of this, we model the transition from the current bale-based system to the advanced densified system based on the extent to which a commercial-scale industry has taken hold within a given region. In other words, the market demand has to be sufficiently large before large-scale investment in advanced logistics systems is warranted. Therefore, the transition to an advanced densified feedstock system is based on the number of commercial-scale biorefineries that are constructed within a given region during a model simulation. It should be noted that this study is not intended to assess the mechanism by which the biofuels industry transitions to more advanced feedstock logistics systems, but instead is focused on the system-level impact of the different feedstock logistics systems. The feedstock logistics systems modeled in this study are: Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional

**Combination Format Economies of scale Shared learning** 1 Bale 1 0 Densified A 1 0 Densified B 1 0 Densified A ≤2.5 0 Densified B ≤2.5 0 6 Bale 1 1 Densified A 1 1 Densified B 1 1 Densified A ≤2.5 1 Densified B ≤2.5 1

*Feedstock format and economies of scale combinations explored in this study.*

**Figure 3.**

*The modules in the BSM represent elements of the biomass-to-biofuels supply chain.*

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

storage, preprocessing, and transportation of biomass feedstocks from the field (or forest) to the biorefinery. The conversion module represents more than a dozen biofuel conversion technologies at pre-commercial and commercial scales. In the model, the biofuel produced in the conversion stage is then distributed to dispensing locations and end users. The model is solved numerically at a sub-monthly level and typically reports annual output for the 30–40-year timeframe. Modules receive and react to information in a response to, among other factors, industrial learning, project economics, installed infrastructure, consumer choices, and investment dynamics. The model is geographically stratified using the 10 USDA farm production regions [14] as a basis, which facilitates analysis of regional differences in key variables.

#### **2. Modeling approach**

*Cellulose*

*1.3.1 Stocks and flows*

*1.3.2 Feedback*

Accumulations, and the activities that cause accumulations to rise and fall over time, are fundamental to the generation of dynamics. System dynamics models are built up from stock and flow primitives. In the BSM, we use stocks to represent concepts such as prices, inventories, conversion facilities, and station owners who are contemplating investment in E85 tankage and dispensing equipment. Corresponding flows would include price changes; production, consumption, and shrinkage of inventories; investment or obsolescence of facilities; and deciding not to invest in tankage and equipment.

Dynamic social systems can contain rich webs of feedback processes. Positive feedbacks tend to drive reinforcing growth in key quantities, while negative feedbacks support self-correcting behavior. In the BSM, we have sought to capture key

The BSM is built and designed using a top-down, modular approach represent-

ing the flow of feedstocks to flow down the supply chain to be converted into biofuels, with feedback mechanisms among and between the various modules. Our modeling approach respects the need for transparency, modularity, and extensibility. This enables standalone analysis of individual modules as well as testing of different module combinations. As shown in **Figure 3**, the model is framed as a set of interconnected sectors and modules. Each supply-chain element is modeled as a standalone module but is linked to the others to receive and provide feedback. The feedstock production module simulates the production of biomass as well as five major commodity crops (corn, wheat, soybeans, cotton, and other grains) through farmer decision logic, land allocation dynamics, new agricultural practices, markets, and prices. The feedstock logistics module models the harvesting, collection,

feedbacks within and across each stage of the supply chain.

*The modules in the BSM represent elements of the biomass-to-biofuels supply chain.*

**6**

**Figure 3.**

We used the BSM to examine the impacts of (1) feedstock format and logistics, (2) biorefinery economies of scale, and (3) the impacts of shared industrial learning between fuel production technologies. In order to understand potential synergies between logistics, scale, and shared learning we modeled 10 combinations of feedstock logistics and economies of scale (**Table 1**). The feedstock formats and logistics considered include bale-based and advanced densified formats. At present, in the United States, the advanced densified logistics system is under development and we do not yet know the mechanism(s) for how these innovations may infuse into the broader market. Because of this, we model the transition from the current bale-based system to the advanced densified system based on the extent to which a commercial-scale industry has taken hold within a given region. In other words, the market demand has to be sufficiently large before large-scale investment in advanced logistics systems is warranted. Therefore, the transition to an advanced densified feedstock system is based on the number of commercial-scale biorefineries that are constructed within a given region during a model simulation. It should be noted that this study is not intended to assess the mechanism by which the biofuels industry transitions to more advanced feedstock logistics systems, but instead is focused on the system-level impact of the different feedstock logistics systems. The feedstock logistics systems modeled in this study are: Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional

**Table 1.** *Feedstock format and economies of scale combinations explored in this study.* agricultural equipment and transported via truck in large round bales; Densified *A*—feedstock is harvested and collected using advanced equipment and is densified and delivered to a centralized depot from which the refinery receives feedstock, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e. capable of processing 2,000 dry Mg per day) is constructed in the region; and Densified *B*—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once five commercial-scale biorefineries (i.e. capable of processing 2,000 dry Mg per day) are constructed within a given region. We explored the impact of economies of scale by (1) holding the biorefinery scale constant at 2,000 dry Mg per day and (2) allowing the biorefineries to be constructed up to 2.5 times the base design case throughput of 2,000 dry Mg per day.

Shared learning (also known as spillover learning) is the process by which proximate industries have mutually beneficial conditions from accrued industrial learning (learning by doing). The process of industrial learning and shared learning has been documented in the literature [15, 16]. Examples of shared learning include knowledgeable employees working for different companies or different processes that use a technology purchased from a third party, movement of employees between firms, government-sponsored research being published in the open literature, informal sharing and/or trading of information through professional societies/conferences, and patents. In this study we explore two scenarios—(1) no shared learning between similar processes, (2) shared learning between similar processes (e.g., thermochemical processes learn from one another, biochemical processes learn from each other).

For this study, background model conditions include modeling incentives that are currently in-place and allowing them to end according to their legislative schedules. Specifically, we include the Low Carbon Fuel Standard of California, RIN credits, and the Biomass Crop Assistance Program [6, 17, 18]. For each of these we use historical data and allow them each to expire according to their respective schedules. The results and implications presented in this study should be viewed in the context of this minimal incentive environment.

#### **3. Insights**

#### **3.1 Feedstock logistics and economies of scale**

Insights reported herein should be considered in the context of the US Energy Information Administration's Reference oil price scenario. Overall, the impact of economies of scale is modest (**Figure 4**). However, the impact of feedstock format and logistics system is salient. The impact of feedstock format and logistics, without spillover learning, are shown in **Figures 5** and **6**. Moving from the status quo bale-based feedstock system to a densified advanced logistics system (Densified A and B) can facilitate higher volumes of feedstock production in response to higher demand for biofuels. Densified feedstock formats can be transported over longer distances, at lower costs, than bale-based systems, thus opening up larger areas of collection, enabling higher-throughput refineries, helping to insulate the system against risks associated with feedstock procurement (e.g., regional supply shocks such as those caused by drought, flooding, pests, etc.). Comparing simulations from the Densified A to those from Densified B, there is a clear advantage to moving to a densified feedstock supply system earlier in the simulation (Densified A transitions after construction of one commercial-scale facility whereas Densified B transitions after five commercial-scale facilities are constructed). Comparing feedstock and biofuel production levels, the system under the Densified A scenario begins growth earlier and reaches a sustained

**9**

*constructed in the model.*

**Figure 5.**

**Figure 4.**

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

*Simulated cellulosic feedstock production for a 35-year period, in the United States, with and without economies of scale. Feedstock production volumes for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a centralized depot from which the refinery receives feedstock, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries*

*Simulated cellulosic biofuel (ethanol and hydrocarbons) production for a 35-year period, in the United States. Fuel production volumes are shown for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a refinery, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is*

*(i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

#### **Figure 4.**

*Cellulose*

agricultural equipment and transported via truck in large round bales; Densified *A*—feedstock is harvested and collected using advanced equipment and is densified and delivered to a centralized depot from which the refinery receives feedstock, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e. capable of processing 2,000 dry Mg per day) is constructed in the region; and Densified *B*—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once five commercial-scale biorefineries (i.e. capable of processing 2,000 dry Mg per day) are constructed within a given region. We explored the impact of economies of scale by (1) holding the biorefinery scale constant at 2,000 dry Mg per day and (2) allowing the biorefineries to be constructed up to 2.5 times the base design case throughput of 2,000 dry Mg per day. Shared learning (also known as spillover learning) is the process by which proximate industries have mutually beneficial conditions from accrued industrial learning (learning by doing). The process of industrial learning and shared learning has been documented in the literature [15, 16]. Examples of shared learning include knowledgeable employees working for different companies or different processes that use a technology purchased from a third party, movement of employees between firms, government-sponsored research being published in the open literature, informal sharing and/or trading of information through professional societies/conferences, and patents. In this study we explore two scenarios—(1) no shared learning between similar processes, (2) shared learning between similar processes (e.g., thermochemical processes learn from one another,

For this study, background model conditions include modeling incentives that are currently in-place and allowing them to end according to their legislative schedules. Specifically, we include the Low Carbon Fuel Standard of California, RIN credits, and the Biomass Crop Assistance Program [6, 17, 18]. For each of these we use historical data and allow them each to expire according to their respective schedules. The results and implications presented in this study should be viewed in

Insights reported herein should be considered in the context of the US Energy Information Administration's Reference oil price scenario. Overall, the impact of economies of scale is modest (**Figure 4**). However, the impact of feedstock format and logistics system is salient. The impact of feedstock format and logistics, without spillover learning, are shown in **Figures 5** and **6**. Moving from the status quo bale-based feedstock system to a densified advanced logistics system (Densified A and B) can facilitate higher volumes of feedstock production in response to higher demand for biofuels. Densified feedstock formats can be transported over longer distances, at lower costs, than bale-based systems, thus opening up larger areas of collection, enabling higher-throughput refineries, helping to insulate the system against risks associated with feedstock procurement (e.g., regional supply shocks such as those caused by drought, flooding, pests, etc.). Comparing simulations from the Densified A to those from Densified B, there is a clear advantage to moving to a densified feedstock supply system earlier in the simulation (Densified A transitions after construction of one commercial-scale facility whereas Densified B transitions after five commercial-scale facilities are constructed). Comparing feedstock and biofuel production levels, the system under the Densified A scenario begins growth earlier and reaches a sustained

biochemical processes learn from each other).

the context of this minimal incentive environment.

**3.1 Feedstock logistics and economies of scale**

**8**

**3. Insights**

*Simulated cellulosic feedstock production for a 35-year period, in the United States, with and without economies of scale. Feedstock production volumes for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a centralized depot from which the refinery receives feedstock, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

#### **Figure 5.**

*Simulated cellulosic biofuel (ethanol and hydrocarbons) production for a 35-year period, in the United States. Fuel production volumes are shown for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a refinery, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

#### *Cellulose*

#### **Figure 6.**

*Simulated cellulosic feedstock production for a 35-year period, in the United States. Feedstock production volumes for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a refinery, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

#### **Figure 7.**

*Simulated cellulosic ethanol and hydrocarbon production for a 35-year period in the United States, showing impact of spillover (or shared) learning across technology pathways and for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a centralized depot from which the refinery receives feedstock, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

**11**

**3.2 Shared learning**

**Figure 8.**

ment (**Figure 8**).

**4. Summary**

economics.

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

*output varies in output varies in opposite direction from input.*

higher level of output. Industrial learning is a high-leverage nonlinear system parameter

*Causal loop diagram illustrating the reinforcing (positive) feedback loop among learning, maturity, investment attractiveness, and production, for two generic fuel production pathways (A and B). Note: (+) sign at arrowheads means that input and output tend to vary in the same direction; (−) sign at arrowhead means that*

Simulated lignocellulosic biofuel production with and without shared learning, in the United States, is shown in **Figure 7**. Shared learning has been shown to exert [15, 16]. Shared learning has a marked impact on both cellulosic ethanol and hydrocarbon production. In the latter case, without shared learning, cellulosic hydrocarbons do not experience any appreciable production. Industrial learning is a key system lever and acts on the system through a positive feedback loop, whereby higher learning rates result in stronger relationship between production and growth in maturity, which increases the investment attractiveness. A technology that attracts more initial investment will then have more fuel production, with associated learning advances. This increase in maturity, and the associated improvements in cost and performance, raises the attractiveness of future invest-

A key theme from this study as well as from the work performed over the last decade is the importance of the movement of the system toward maturation, both in terms of the supply system and the conversion processes. On the feedstock supply side, advanced supply systems have advantages relative to bale in terms of transport, handling, storage, and losses. From the conversion process perspective, mature processes imply lower investment risk, better yields, and better process

in which small changes early on result in large differences later in the simulation.

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

#### **Figure 8.**

*Cellulose*

**Figure 6.**

**10**

**Figure 7.**

*Simulated cellulosic ethanol and hydrocarbon production for a 35-year period in the United States, showing impact of spillover (or shared) learning across technology pathways and for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a centralized depot from which the refinery receives feedstock, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

*Simulated cellulosic feedstock production for a 35-year period, in the United States. Feedstock production volumes for three feedstock format and logistics systems. Bale—feedstock is delivered to the biorefinery from within a 50-mile radius and is harvested using conventional agricultural equipment and transported via truck in large round bales; Densified A—feedstock is harvested and collected using advanced equipment and is densified and delivered to a refinery, transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the of one commercial-scale biorefinery (i.e., capable of processing 2000 dry mg per day) is constructed in the model; and Densified B—transition to an advanced system in which feedstock is harvested and collected using advanced equipment begins once the construction of five commercial-scale biorefineries (i.e., capable of processing 2000 dry mg per day) is constructed in the model.*

*Causal loop diagram illustrating the reinforcing (positive) feedback loop among learning, maturity, investment attractiveness, and production, for two generic fuel production pathways (A and B). Note: (+) sign at arrowheads means that input and output tend to vary in the same direction; (−) sign at arrowhead means that output varies in output varies in opposite direction from input.*

higher level of output. Industrial learning is a high-leverage nonlinear system parameter in which small changes early on result in large differences later in the simulation.

#### **3.2 Shared learning**

Simulated lignocellulosic biofuel production with and without shared learning, in the United States, is shown in **Figure 7**. Shared learning has been shown to exert [15, 16]. Shared learning has a marked impact on both cellulosic ethanol and hydrocarbon production. In the latter case, without shared learning, cellulosic hydrocarbons do not experience any appreciable production. Industrial learning is a key system lever and acts on the system through a positive feedback loop, whereby higher learning rates result in stronger relationship between production and growth in maturity, which increases the investment attractiveness. A technology that attracts more initial investment will then have more fuel production, with associated learning advances. This increase in maturity, and the associated improvements in cost and performance, raises the attractiveness of future investment (**Figure 8**).

#### **4. Summary**

A key theme from this study as well as from the work performed over the last decade is the importance of the movement of the system toward maturation, both in terms of the supply system and the conversion processes. On the feedstock supply side, advanced supply systems have advantages relative to bale in terms of transport, handling, storage, and losses. From the conversion process perspective, mature processes imply lower investment risk, better yields, and better process economics.

Our simulations suggest that it is beneficial for the feedstock supply system to transition away from short-distance (i.e., <50 miles) transport of bales and/or any other low-density formats, to a densified system modeled after the modern commodity grain system, using larger collection radii and centralized depots. Our simulations also suggest that the temporal component is substantial—earlier transition to a high density, commodity logistics system leads to the largest gains in cellulosic feedstock production and utilization—in our model, densified A scenario accelerates maturation of the feedstock supply 21. By the end of our simulation, the Densified A scenario results in ~15% greater feedstock production.

Industrial learning (learning by doing) is a key system lever in developing industries such as the biofuel/bioproducts industry. Because the industrial learning process follows a positive feedback loop, small perturbations have large system impacts. Shared learning amplifies the industrial learning process. Advances across similar industries are shared among the industries, resulting in a substantial positive impact on the industry. A potential extension would be to look at what percent of learning needs to be shared across similar technologies for a substantial increase in overall biofuel production.

### **Author details**

Daniel Inman1 \*, Emily Newes1 , Brian Bush1 , Laura Vimmerstedt1 and Steve Peterson2

1 The Strategic Energy Analysis Center, National Renewable Energy Laboratory, Golden, Colorado, USA

2 Thayer School of Engineering at Dartmouth College, Hanover, New Hampshire, USA

\*Address all correspondence to<EMAIL_ADDRESS>
© 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.

**13**

PLAW-110publ140

[7] Bacovsky D, Ludwiczek N, Ognissanto M, Worgetter M. Status

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

> of Advanced Biofuels Demonstration Facilities in 2012: A Report to IEA Bioenergy Task 39 (No. T39-P1b). International Energy Agency; 2013. http://task39.sites.olt.ubc.ca/ files/2013/12/2013\_Bacovsky\_Statusof-Advanced-Biofuels-Demonstration-

Facilities-in-2012.pdf

may\_2013.pdf

113publ79.pdf

[8] U.S. Department of Energy. Bioenergy Technologies Office Multi-Year Program Plan. 2013. http:// bioenergy.energy.gov/pdfs/mypp\_

[9] U.S. Department of Agriculture. Biorefinery Assistance Program [WWW document]. 2015. Available from: http://www. rd.usda.gov/programs-services/ biorefinery-assistance-program

[10] Agricultural Act of 2014. Pub L No. 113-79, 128 Stat 649. February 4, 2014. https://www.govinfo.gov/content/ pkg/PLAW-113publ79/pdf/PLAW-

[11] Peterson S, Peck C, Stright D, Newes E, Inman D, Vimmerstedt L, et al. Overview of the Biomass Scenario Model. NREL/CP\_6A20- 60172. 2015. https://www.nrel.gov/

docs/fy15osti/60172.pdf

iseesystems.com

[12] Isee Systems. Lebanon, NH. Available from: https://www.

2014. Availabe from: http://

[13] Sterman J. Learning from evidence in a complex world. American Journal of Public Health. 2006;**96**(3):505-514

[14] U.S. Department of Agriculture, Economic Research Service. U.S. Farm Resource Regions. Retrieved from Agricultural Resource Management Survey (ARMS): Resource Regions.

webarchives.cdlib.org/wayback.public/ UERS\_ag\_1/20111128195215, http://

[1] Energy Tax Act of 1978 Public Law 95-618, 92 Stat. 3174. https://www. govinfo.gov/app/details/STATUTE-92/

Administration. Fuel Ethanol Overview, 1981-2012. 2014. https://www.eia.gov/

[3] U.S. Environmental Protection Agency. State Actions Banning MTBE (Statewide) (No. EPA420-B-04-009). 2004. https://nepis.epa.gov/Exe/ZyNET. exe/P1004KHN.TXT?ZyActionD=ZyDo cument&Client=EPA&Index=2000+Th ru+2005&Docs=&Query=&Time=&En dTime=&SearchMethod=1&TocRestric t=n&Toc=&TocEntry=&QField=&QFi eldYear=&QFieldMonth=&QFieldDay= &IntQFieldOp=0&ExtQFieldOp=0&X mlQuery=&File=D%3A%5Czyfiles%5C Index%20Data%5C00thru05%5CTxt% 5C00000021%5CP1004KHN.txt&User= ANONYMOUS&Password=anonymous &SortMethod=h%7C-&MaximumDocu ments=1&FuzzyDegree=0&ImageQuali ty=r75g8/r75g8/x150y150g16/i425&Disp lay=hpfr&DefSeekPage=x&SearchBack =ZyActionL&Back=ZyActionS&BackD esc=Results%20page&MaximumPages= 1&ZyEntry=1&SeekPage=x&ZyPURL

[4] Energy Policy Act of 2005. Public Law 109-58. https://www.govinfo.gov/

app/details/PLAW-109publ58

[5] U.S. Environmental Protection Agency. Gasoline|Methyl Tertiary Butyl Ether (MTBE)|US EPA [WWW Document]. 2013. Available from: http://www.epa.gov/mtbe/gas.htm

[6] H.R. 6 (110th). Energy Independence and Security Act of 2007. Pub L No. 110-140, 121 Stat 1492. 2007. https:// www.govinfo.gov/app/details/

STATUTE-92-Pg3174

**References**

petroleum/data.php

[2] U.S. Energy Information

*Insights from over 10 Years of Cellulosic Biofuel Modeling DOI: http://dx.doi.org/10.5772/intechopen.84874*

#### **References**

*Cellulose*

production.

in overall biofuel production.

**Author details**

and Steve Peterson2

Golden, Colorado, USA

Daniel Inman1

**12**

USA

provided the original work is properly cited.

\*, Emily Newes1

\*Address all correspondence to<EMAIL_ADDRESS>
© 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,

, Brian Bush1

1 The Strategic Energy Analysis Center, National Renewable Energy Laboratory,

2 Thayer School of Engineering at Dartmouth College, Hanover, New Hampshire,

, Laura Vimmerstedt1

Our simulations suggest that it is beneficial for the feedstock supply system to transition away from short-distance (i.e., <50 miles) transport of bales and/or any other low-density formats, to a densified system modeled after the modern commodity grain system, using larger collection radii and centralized depots. Our simulations also suggest that the temporal component is substantial—earlier transition to a high density, commodity logistics system leads to the largest gains in cellulosic feedstock production and utilization—in our model, densified A scenario accelerates maturation of the feedstock supply 21. By the end of our simulation, the Densified A scenario results in ~15% greater feedstock

Industrial learning (learning by doing) is a key system lever in developing industries such as the biofuel/bioproducts industry. Because the industrial learning process follows a positive feedback loop, small perturbations have large system impacts. Shared learning amplifies the industrial learning process. Advances across similar industries are shared among the industries, resulting in a substantial positive impact on the industry. A potential extension would be to look at what percent of learning needs to be shared across similar technologies for a substantial increase

[1] Energy Tax Act of 1978 Public Law 95-618, 92 Stat. 3174. https://www. govinfo.gov/app/details/STATUTE-92/ STATUTE-92-Pg3174

[2] U.S. Energy Information Administration. Fuel Ethanol Overview, 1981-2012. 2014. https://www.eia.gov/ petroleum/data.php

[3] U.S. Environmental Protection Agency. State Actions Banning MTBE (Statewide) (No. EPA420-B-04-009). 2004. https://nepis.epa.gov/Exe/ZyNET. exe/P1004KHN.TXT?ZyActionD=ZyDo cument&Client=EPA&Index=2000+Th ru+2005&Docs=&Query=&Time=&En dTime=&SearchMethod=1&TocRestric t=n&Toc=&TocEntry=&QField=&QFi eldYear=&QFieldMonth=&QFieldDay= &IntQFieldOp=0&ExtQFieldOp=0&X mlQuery=&File=D%3A%5Czyfiles%5C Index%20Data%5C00thru05%5CTxt% 5C00000021%5CP1004KHN.txt&User= ANONYMOUS&Password=anonymous &SortMethod=h%7C-&MaximumDocu ments=1&FuzzyDegree=0&ImageQuali ty=r75g8/r75g8/x150y150g16/i425&Disp lay=hpfr&DefSeekPage=x&SearchBack =ZyActionL&Back=ZyActionS&BackD esc=Results%20page&MaximumPages= 1&ZyEntry=1&SeekPage=x&ZyPURL

[4] Energy Policy Act of 2005. Public Law 109-58. https://www.govinfo.gov/ app/details/PLAW-109publ58

[5] U.S. Environmental Protection Agency. Gasoline|Methyl Tertiary Butyl Ether (MTBE)|US EPA [WWW Document]. 2013. Available from: http://www.epa.gov/mtbe/gas.htm

[6] H.R. 6 (110th). Energy Independence and Security Act of 2007. Pub L No. 110-140, 121 Stat 1492. 2007. https:// www.govinfo.gov/app/details/ PLAW-110publ140

[7] Bacovsky D, Ludwiczek N, Ognissanto M, Worgetter M. Status of Advanced Biofuels Demonstration Facilities in 2012: A Report to IEA Bioenergy Task 39 (No. T39-P1b). International Energy Agency; 2013. http://task39.sites.olt.ubc.ca/ files/2013/12/2013\_Bacovsky\_Statusof-Advanced-Biofuels-Demonstration-Facilities-in-2012.pdf

[8] U.S. Department of Energy. Bioenergy Technologies Office Multi-Year Program Plan. 2013. http:// bioenergy.energy.gov/pdfs/mypp\_ may\_2013.pdf

[9] U.S. Department of Agriculture. Biorefinery Assistance Program [WWW document]. 2015. Available from: http://www. rd.usda.gov/programs-services/ biorefinery-assistance-program

[10] Agricultural Act of 2014. Pub L No. 113-79, 128 Stat 649. February 4, 2014. https://www.govinfo.gov/content/ pkg/PLAW-113publ79/pdf/PLAW-113publ79.pdf

[11] Peterson S, Peck C, Stright D, Newes E, Inman D, Vimmerstedt L, et al. Overview of the Biomass Scenario Model. NREL/CP\_6A20- 60172. 2015. https://www.nrel.gov/ docs/fy15osti/60172.pdf

[12] Isee Systems. Lebanon, NH. Available from: https://www. iseesystems.com

[13] Sterman J. Learning from evidence in a complex world. American Journal of Public Health. 2006;**96**(3):505-514

[14] U.S. Department of Agriculture, Economic Research Service. U.S. Farm Resource Regions. Retrieved from Agricultural Resource Management Survey (ARMS): Resource Regions. 2014. Availabe from: http:// webarchives.cdlib.org/wayback.public/ UERS\_ag\_1/20111128195215, http://

#### *Cellulose*

www.ers.usda.gov/Briefing/ARMS/ resourceregions/resourceregions. htm#new

[15] McDowell R. Learning by doing and spillovers in renewable energy [Ph.D. thesis]. Massachusetts Institute of Technology, Department of Economics; 2016

[16] Irwin DA, Klenow PJ. Learning-bydoing spillovers in the semiconductor industry. Journal of Political Economy. 1994;**105**(6):1200-1227

[17] Executive Order S-01-07. State of California, Office of the Governor. 2007. Available from: https://www.arb.ca.gov/ fuels/lcfs/eos0107.pdf

[18] Public Law 110-246-June 18, 2008. The Food, Conservation, and Energy Act of 2008. Available from: https:// www.agriculture.senate.gov/imo/ media/doc/pl110-246.pdf

**15**

**Chapter 2**

**Abstract**

Biorefinery

Alternative Raw Materials for

Pulp and Paper Production in

*María Eugenia Eugenio, David Ibarra,*

*Isabel Bascón and Alejandro Rodríguez*

available alongside traditional products.

pulp, paper, biorefinery

**1. Introduction**

*Raquel Martín-Sampedro, Eduardo Espinosa,*

the Concept of a Lignocellulosic

The main source of cellulosic fibre used for pulp and paper production comes from wood, while non-wood fibres are used to a lesser extent. However, a renewed interest exists in the use of non-woody raw materials due to their abundance as source of low-cost fibres and because they are sometimes the only exploitable source of fibres in certain geographical areas, mainly in developing countries. Moreover, the great variety of characteristics, fibre dimensions and chemical composition of these alternative raw materials give them a great potential to produce different types of papers. On the other hand, the pulp and paper industry is an excellent starting point for the development of lignocellulosic biorefineries, possessing the necessary technology and infrastructure as well as extensive experience in lignocellulosic biomass transformation. Since its beginnings, the pulp and paper industry has been practicing certain aspects of the biorefinery concept, generating the energy necessary for the production of cellulosic pulp from the combustion of lignocellulosic waste and black liquors, recovering the chemical reagents used and generating high value-added products (e.g. tall oil) together with cellulosic pulp. However, the evolution of the pulp and paper industry to a lignocellulosic biorefinery requires technological innovations to make bioenergy and new bioproducts

**Keywords:** alternative raw material, agricultural residues, annual plant (vegetables),

Several successful industrial factories based on alternative raw materials for pulp and paper production already exist nowadays [1, 2]. Lignocellulose is the major structural component of plants and is by far the most abundant type of earthly biomass [1, 3]. It mainly consists of cellulose (40–60%), hemicellulose (10–40%) and lignin (15–30%), with minor amounts of extractives, proteins and inorganic compounds [1, 3]. Lignocellulose components can be found in both woody (e.g.

#### **Chapter 2**

*Cellulose*

htm#new

2016

www.ers.usda.gov/Briefing/ARMS/ resourceregions/resourceregions.

[15] McDowell R. Learning by doing and spillovers in renewable energy [Ph.D. thesis]. Massachusetts Institute of Technology, Department of Economics;

[16] Irwin DA, Klenow PJ. Learning-bydoing spillovers in the semiconductor industry. Journal of Political Economy.

[17] Executive Order S-01-07. State of California, Office of the Governor. 2007. Available from: https://www.arb.ca.gov/

[18] Public Law 110-246-June 18, 2008. The Food, Conservation, and Energy Act of 2008. Available from: https:// www.agriculture.senate.gov/imo/

1994;**105**(6):1200-1227

fuels/lcfs/eos0107.pdf

media/doc/pl110-246.pdf

**14**

## Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic Biorefinery

*María Eugenia Eugenio, David Ibarra, Raquel Martín-Sampedro, Eduardo Espinosa, Isabel Bascón and Alejandro Rodríguez*

#### **Abstract**

The main source of cellulosic fibre used for pulp and paper production comes from wood, while non-wood fibres are used to a lesser extent. However, a renewed interest exists in the use of non-woody raw materials due to their abundance as source of low-cost fibres and because they are sometimes the only exploitable source of fibres in certain geographical areas, mainly in developing countries. Moreover, the great variety of characteristics, fibre dimensions and chemical composition of these alternative raw materials give them a great potential to produce different types of papers. On the other hand, the pulp and paper industry is an excellent starting point for the development of lignocellulosic biorefineries, possessing the necessary technology and infrastructure as well as extensive experience in lignocellulosic biomass transformation. Since its beginnings, the pulp and paper industry has been practicing certain aspects of the biorefinery concept, generating the energy necessary for the production of cellulosic pulp from the combustion of lignocellulosic waste and black liquors, recovering the chemical reagents used and generating high value-added products (e.g. tall oil) together with cellulosic pulp. However, the evolution of the pulp and paper industry to a lignocellulosic biorefinery requires technological innovations to make bioenergy and new bioproducts available alongside traditional products.

**Keywords:** alternative raw material, agricultural residues, annual plant (vegetables), pulp, paper, biorefinery

#### **1. Introduction**

Several successful industrial factories based on alternative raw materials for pulp and paper production already exist nowadays [1, 2]. Lignocellulose is the major structural component of plants and is by far the most abundant type of earthly biomass [1, 3]. It mainly consists of cellulose (40–60%), hemicellulose (10–40%) and lignin (15–30%), with minor amounts of extractives, proteins and inorganic compounds [1, 3]. Lignocellulose components can be found in both woody (e.g.

spruce, pine, eucalypt, poplar, etc.) and non-woody biomass, the latter including vegetables (e.g. bamboo, tagasaste, kenaf, abaca, etc.) and agriculture residues from harvesting and pruning operations (e.g. barley straw, wheat straw, orange tree pruning, olive tree pruning, etc.) and from agro-food industry [e.g. bagasse, empty fruit bunches from oil palm (EFB), etc.]. Cellulose is a linear and highly ordered polymer of cellobiose (D-glucopyranosyl β-1,4-D-glucopyranose), whereas hemicellulose represents a family of branched carbohydrate polymers containing both pentoses (e.g. xylose, arabinose) and hexoses (e.g. galactose, mannose, glucose) and showing often uronic acids (e.g. glucuronic acid) and acetyl moieties as sidechain groups [1, 3]. By contrast, lignin is a three-dimensional network buildup of dimethoxylated (syringyl, S), monomethoxylated (guaiacyl, G) and non-methoxylated (p-hydroxyphenyl, H) phenylpropanoid units, derived from the corresponding p-hydroxycinnamyl alcohols, which give rise to a variety of subunits including different ether and carbon–carbon bonds [4].

The main non-food use of lignocellulosic biomass is the production of cellulosic pulp from which a wide range of products can be obtained, highlighting the production of paper. At the beginning of the 1990s, there was the conviction that the arrival of new information technologies would reduce the consumption of paper; however the data of world consumption of paper and cardboard revoke this idea as it went from 240 million tonnes in 1990 to 413 million tonnes in 2016, of which 77.3 million tonnes are consumed in Europe [5]. In the past, the raw materials used in the manufacture of paper were herbaceous biomass such as flax, cotton, bamboo and cereal straw. It was not until the middle of the nineteenth century when woody materials began to be used, mainly due to the increased demand for paper because of the emergence and increased use of printing. Today, most of the cellulosic fibers used come from wood species, mainly hardwoods and softwoods [1, 2, 6]. Nevertheless, in recent years there has been an increase in consumer awareness of the need to preserve the environment, which is why they demand a more ecological production of paper, both in the use of raw materials and in manufacturing processes. With the same purpose, government bodies devote economic and human resources to research into alternative raw materials to conventional ones. For these reasons, a large number of studies on the use of non-woody materials, including agriculture residues and vegetables as alternative source for cellulosic pulp production, have emerged in recent years [1, 7–14].

Some of the advantages of using non-woody raw materials can be mentioned: (i) in developing countries with scarce forest resources, non-woody biomass provides an effective alternative to importing wood, paper, or cellulosic pulp. In these countries, there may be a large area devoted to food crops, which would provide considerable amounts of agricultural residues and agro-food industries [1, 15]; (ii) non-woody biomass increases the added value of agri-food crops by taking advantage of their residues (traditionally used for burning or agricultural amendments) to obtain a product in great demand such as paper [1, 15]; (iii) production of special papers, whose most suitable raw materials are certain vegetable alternatives to conventional woods [1, 16]; and (iv) since the morphological characteristics of the fibers and the chemical composition of the non-woody species are very varied, a wide range of papers can be obtained by properly selecting and/or mixing these raw materials [1, 14].

#### **2. Availability of raw materials**

The availability of raw materials is very important when approaching the industrial facility for the production of cellulosic pulp. Availability is related to

**17**

lignocellulosic materials.

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic…*

the production and location of the various lignocellulosic materials that can be used for the intended purpose. In the case of agricultural residues from harvesting and pruning operations, it can be said that they are very abundant in Spain. Specifically, it is estimated that the production of the most important agricultural residues, due to their abundance, such as cereal straw, sunflower stalks, vine shoots, cotton stems, olive, orange and peach tree pruning and vegetable and other similar crop wastes, represents about 50 million tonnes per year, with Andalusia

Due to its abundance, it seems that the most recommended agricultural residue for the manufacture of paper pulp is cereal straw since it represents almost 20% of the agricultural residues considered in 2007, and the technology used in its collection is fully developed [1, 17–19]. Regarding the waste from the agri-food industry used for the production of cellulosic pulp, the bagasse from the extraction of sugar cane and waste from the palm oil industry (EFB) should be highlighted [20].

With regard to alternative vegetables for cellulosic pulp production, they can be classified in three groups: (i) plants of wild nature such as bamboo, different types of cane, esparto grass, etc. [21]; (ii) plants from plantations with industrial uses, such as sorghum, abaca, sisal, jute, hemp, kenaf, flax, etc. [7, 22]; and (iii) other plants, mainly herbaceous species, grasses and legumes, which produce high biomass yields when grown in intensive plantations (tagasaste, *Leucaena* spp.,

The prolonged storage of lignocellulosic raw materials is always necessary in the pulp and paper industry. In the case of raw materials that are harvested only at a specific period of the year, the storage is even more important. Therefore, these raw materials must be collected in order to meet the annual needs of a factory, so that it operates all year round, with the consequent better use of installed capacity. On the other hand, many alternative lignocellulosic materials are more easily deteriorated due to their non-woody special properties, such as straws, herbaceous vegetables, etc., mainly if they contain high percentages of humidity. In fact, of all the factors that influence the storage of this type of sources, the most relevant is the residual humidity. Given that these materials do not require too rigorous conservation, as they are not intended for food, the rule of allowing slightly higher humidity than the "Caurie safety" humidity obtained by adjusting the experimental data on equilibrium humidity and relative humidity of the environment of the adsorption isotherms to the Caurie equation can generally be adapted. Applying this standard and observing the experimental adsorption isotherms, it appears that wheat straw, vine shoots and cotton stems can be well conserved in environments with relative humidity below 60–70%, while other agricultural residues such as olive tree pruning or sunflower stems require lower values [26]. On the other hand, it has been verified that the recommended maximum relative humidity values, according to the standard followed in this work, coincide with those obtained experimentally when storing the different agricultural residues considered in environments with different relative humidity for 10 or 12 months. As the chemical composition of these agricultural residues is considered as well as their fibrous structure does not differ so much from other agricultural residues such as wastes from agro-food industries, forestry residues and vegetable materials in general, the above conclusions can be extended to all these alternative

*DOI: http://dx.doi.org/10.5772/intechopen.90041*

contributing with more than 20% [1, 17].

**3. Storage of lignocellulosic materials**

etc.) [23–25].

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic… DOI: http://dx.doi.org/10.5772/intechopen.90041*

the production and location of the various lignocellulosic materials that can be used for the intended purpose. In the case of agricultural residues from harvesting and pruning operations, it can be said that they are very abundant in Spain. Specifically, it is estimated that the production of the most important agricultural residues, due to their abundance, such as cereal straw, sunflower stalks, vine shoots, cotton stems, olive, orange and peach tree pruning and vegetable and other similar crop wastes, represents about 50 million tonnes per year, with Andalusia contributing with more than 20% [1, 17].

Due to its abundance, it seems that the most recommended agricultural residue for the manufacture of paper pulp is cereal straw since it represents almost 20% of the agricultural residues considered in 2007, and the technology used in its collection is fully developed [1, 17–19]. Regarding the waste from the agri-food industry used for the production of cellulosic pulp, the bagasse from the extraction of sugar cane and waste from the palm oil industry (EFB) should be highlighted [20].

With regard to alternative vegetables for cellulosic pulp production, they can be classified in three groups: (i) plants of wild nature such as bamboo, different types of cane, esparto grass, etc. [21]; (ii) plants from plantations with industrial uses, such as sorghum, abaca, sisal, jute, hemp, kenaf, flax, etc. [7, 22]; and (iii) other plants, mainly herbaceous species, grasses and legumes, which produce high biomass yields when grown in intensive plantations (tagasaste, *Leucaena* spp., etc.) [23–25].

#### **3. Storage of lignocellulosic materials**

The prolonged storage of lignocellulosic raw materials is always necessary in the pulp and paper industry. In the case of raw materials that are harvested only at a specific period of the year, the storage is even more important. Therefore, these raw materials must be collected in order to meet the annual needs of a factory, so that it operates all year round, with the consequent better use of installed capacity. On the other hand, many alternative lignocellulosic materials are more easily deteriorated due to their non-woody special properties, such as straws, herbaceous vegetables, etc., mainly if they contain high percentages of humidity. In fact, of all the factors that influence the storage of this type of sources, the most relevant is the residual humidity. Given that these materials do not require too rigorous conservation, as they are not intended for food, the rule of allowing slightly higher humidity than the "Caurie safety" humidity obtained by adjusting the experimental data on equilibrium humidity and relative humidity of the environment of the adsorption isotherms to the Caurie equation can generally be adapted. Applying this standard and observing the experimental adsorption isotherms, it appears that wheat straw, vine shoots and cotton stems can be well conserved in environments with relative humidity below 60–70%, while other agricultural residues such as olive tree pruning or sunflower stems require lower values [26]. On the other hand, it has been verified that the recommended maximum relative humidity values, according to the standard followed in this work, coincide with those obtained experimentally when storing the different agricultural residues considered in environments with different relative humidity for 10 or 12 months. As the chemical composition of these agricultural residues is considered as well as their fibrous structure does not differ so much from other agricultural residues such as wastes from agro-food industries, forestry residues and vegetable materials in general, the above conclusions can be extended to all these alternative lignocellulosic materials.

*Cellulose*

spruce, pine, eucalypt, poplar, etc.) and non-woody biomass, the latter including vegetables (e.g. bamboo, tagasaste, kenaf, abaca, etc.) and agriculture residues from harvesting and pruning operations (e.g. barley straw, wheat straw, orange tree pruning, olive tree pruning, etc.) and from agro-food industry [e.g. bagasse, empty fruit bunches from oil palm (EFB), etc.]. Cellulose is a linear and highly ordered polymer of cellobiose (D-glucopyranosyl β-1,4-D-glucopyranose), whereas hemicellulose represents a family of branched carbohydrate polymers containing both pentoses (e.g. xylose, arabinose) and hexoses (e.g. galactose, mannose, glucose) and showing often uronic acids (e.g. glucuronic acid) and acetyl moieties as sidechain groups [1, 3]. By contrast, lignin is a three-dimensional network buildup of dimethoxylated (syringyl, S), monomethoxylated (guaiacyl, G) and non-methoxylated (p-hydroxyphenyl, H) phenylpropanoid units, derived from the corresponding p-hydroxycinnamyl alcohols, which give rise to a variety of subunits

The main non-food use of lignocellulosic biomass is the production of cellulosic pulp from which a wide range of products can be obtained, highlighting the production of paper. At the beginning of the 1990s, there was the conviction that the arrival of new information technologies would reduce the consumption of paper; however the data of world consumption of paper and cardboard revoke this idea as it went from 240 million tonnes in 1990 to 413 million tonnes in 2016, of which 77.3 million tonnes are consumed in Europe [5]. In the past, the raw materials used in the manufacture of paper were herbaceous biomass such as flax, cotton, bamboo and cereal straw. It was not until the middle of the nineteenth century when woody materials began to be used, mainly due to the increased demand for paper because of the emergence and increased use of printing. Today, most of the cellulosic fibers used come from wood species, mainly hardwoods and softwoods [1, 2, 6]. Nevertheless, in recent years there has been an increase in consumer awareness of the need to preserve the environment, which is why they demand a more ecological production of paper, both in the use of raw materials and in manufacturing processes. With the same purpose, government bodies devote economic and human resources to research into alternative raw materials to conventional ones. For these reasons, a large number of studies on the use of non-woody materials, including agriculture residues and vegetables as alternative source for cellulosic pulp produc-

Some of the advantages of using non-woody raw materials can be mentioned: (i) in developing countries with scarce forest resources, non-woody biomass provides an effective alternative to importing wood, paper, or cellulosic pulp. In these countries, there may be a large area devoted to food crops, which would provide considerable amounts of agricultural residues and agro-food industries [1, 15]; (ii) non-woody biomass increases the added value of agri-food crops by taking advantage of their residues (traditionally used for burning or agricultural amendments) to obtain a product in great demand such as paper [1, 15]; (iii) production of special papers, whose most suitable raw materials are certain vegetable alternatives to conventional woods [1, 16]; and (iv) since the morphological characteristics of the fibers and the chemical composition of the non-woody species are very varied, a wide range of papers can be obtained by

The availability of raw materials is very important when approaching the industrial facility for the production of cellulosic pulp. Availability is related to

including different ether and carbon–carbon bonds [4].

tion, have emerged in recent years [1, 7–14].

**2. Availability of raw materials**

properly selecting and/or mixing these raw materials [1, 14].

**16**

#### **4. Characterization of lignocellulosic materials**

Theoretically speaking any plant containing a reasonable amount of fibres can be used as a raw material for pulp and paper production. In practice, this is not the case. Besides the abundance of the plant, a steady supply and many other requirements are necessary. The fibre content of the plant is important. The plant contains in addition to fibres many non-fibrous cells, e.g. parenchyma cells. Fibres themselves vary much in different plants regarding their length, width, fine structures or microstructures, as well as their chemical composition. In one and the same plant, there are different types of fibres. The same fibre type is not equal in dimension but contains a spectrum of different dimensions. For this reason, one speaks of "average fibre length". The length of the fibre is one of the most important parameters affecting paper strength [1].

Chemical characterization, which gives rise to the percentages of the main chemical constituents of lignocellulosic materials (generally cellulose, hemicellulose, lignin, as well as extractives and ash), is of great interest since it can indicate their possible applications for obtaining cellulosic pulps, in terms of the most suitable process to follow and the type of pulp that can be obtained. In this characterization, the contents of holocellulose, lignin, α-cellulose, hemicellulose, and extractives in water, 1% soda and ethanol-benzene and ash are determined as the most important. For this chemical characterization, TAPPI test methods, including TAPPI T 204 om-88, TAPPI T 211 om-93, TAPPI T 222 om-88 [27], and NREL analytical methods (National Renewable Energy Laboratory NREL/TP-510-42168) are usually employed [28].

When comparing the results obtained by different authors, a good concordance is generally observed for each specific material. Sometimes discrepancies appear that can be attributed to the different procedures used as well as to the different origins and varieties of the raw materials considered. For example, the chemical characterization results obtained for rice straw were analysed and compared with (i) some agriculture residues from harvesting and pruning operations and from agro-food industry (e.g. olive tree pruning, wheat straw, sunflower stems, sorghum stems, bagasse, vine shoots, and cotton stems); (ii) some vegetables (e.g. *Leucaena colinsi*, *Leucaena leucocephala, Chamaecytisus proliferus*, *Retama monosperma*, *Phragmites* spp*.*, *Arundo donax, Prosopis juliflora*, and *Paulownia fortunei*); and (iii) softwoods (pine) and hardwoods (eucalyptus) [23, 29]. From this comparison it could be deduced that:

**19**

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic…*

• The holocellulose content of rice straw (60.7%) is similar to the value found for olive tree pruning and lower than the values found for the rest of the agricultural residues considered, as well as those of the alternative vegetables

• The content of α-cellulose of rice straw (41.2%) is lower than the values

presented by the cotton stems, *L. colinsi*, *L. leucocephala*, *C. proliferus*, *R. monosperma*, pine and eucalyptus; higher than the values corresponding to olive tree pruning, wheat straw, *Phragmites*, *P. fortunei*, *Prosopis juliflora*; and similar to

• The lignin content of rice straw (21.9%) is similar to the values corresponding to the cotton stems, *L. leucocephala* and *R. monosperma*; lower than the values found for *Phragmites* spp*.*, *A. donax*, *P. fortunei* and pine; and higher than those

In the same way, following the same example of rice straw, the experimental data on its physical characterization, which determines the size of its fibers, are compared with those of other lignocellulosic materials such as wheat straw, sunflower stalks, vine shoots, cotton tree stalks, olive tree pruning, sorghum stalks and pine and eucalyptus woods. After a biometric analysis with the rice straw studied, it is concluded that the length of its fibers (1.29 mm) is similar to that corresponding to the stems of sorghum, superior to those of the other agricultural residues consid-

In summary, it can be stated that the alternative non-woody materials under consideration have acceptable chemical and physical characteristics for the produc-

The manufacture of cellulosic pulp consists of the separation of cellulose fibers, which are cemented by the middle wall, composed mainly of lignin using physical or chemical methods [1, 2, 6]. In order to obtain cellulosic pulps from alternative non-woody materials, different chemical classical processes have been used (using chemical reagents such as soda, sodium sulphate and sodium sulfite) and organosolv (using organic solvents). In general, non-woody raw materials have a less density and more porous structure and, also in most of the cases, less lignin content, which means less energy and chemical requirements for fibre separation during pulp production. In addition, they have shorter growth cycles, reaching maturity faster than wood species, and in many cases the pulp yields

Soda pulping is the oldest pulping processes known and consists of subjecting raw materials, cut and conditioned, to a cooking process with a given concentration of sodium hydroxide, at a specific temperature and cooking time, depending on the quality of the pulp to be obtained (chemical or semi-chemical) and the characteristics of the raw materials used [1, 2, 6]. A recovery of reagents and purification of black liquors is finally carried out. Each of these sections of the process can group

*DOI: http://dx.doi.org/10.5772/intechopen.90041*

considered and those of pine and eucalyptus.

the values of the other species considered.

ered and to that of eucalyptus but inferior to that of pine.

of the other species considered.

tion of pulp and paper [30].

obtained are higher [30].

*5.1.1 Soda pulping*

**5.1 Classical pulping processes**

**5. Cellulosic pulp production**

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic… DOI: http://dx.doi.org/10.5772/intechopen.90041*

In the same way, following the same example of rice straw, the experimental data on its physical characterization, which determines the size of its fibers, are compared with those of other lignocellulosic materials such as wheat straw, sunflower stalks, vine shoots, cotton tree stalks, olive tree pruning, sorghum stalks and pine and eucalyptus woods. After a biometric analysis with the rice straw studied, it is concluded that the length of its fibers (1.29 mm) is similar to that corresponding to the stems of sorghum, superior to those of the other agricultural residues considered and to that of eucalyptus but inferior to that of pine.

In summary, it can be stated that the alternative non-woody materials under consideration have acceptable chemical and physical characteristics for the production of pulp and paper [30].

#### **5. Cellulosic pulp production**

The manufacture of cellulosic pulp consists of the separation of cellulose fibers, which are cemented by the middle wall, composed mainly of lignin using physical or chemical methods [1, 2, 6]. In order to obtain cellulosic pulps from alternative non-woody materials, different chemical classical processes have been used (using chemical reagents such as soda, sodium sulphate and sodium sulfite) and organosolv (using organic solvents). In general, non-woody raw materials have a less density and more porous structure and, also in most of the cases, less lignin content, which means less energy and chemical requirements for fibre separation during pulp production. In addition, they have shorter growth cycles, reaching maturity faster than wood species, and in many cases the pulp yields obtained are higher [30].

#### **5.1 Classical pulping processes**

#### *5.1.1 Soda pulping*

Soda pulping is the oldest pulping processes known and consists of subjecting raw materials, cut and conditioned, to a cooking process with a given concentration of sodium hydroxide, at a specific temperature and cooking time, depending on the quality of the pulp to be obtained (chemical or semi-chemical) and the characteristics of the raw materials used [1, 2, 6]. A recovery of reagents and purification of black liquors is finally carried out. Each of these sections of the process can group

*Cellulose*

affecting paper strength [1].

are usually employed [28].

could be deduced that:

eucalyptus.

**4. Characterization of lignocellulosic materials**

Theoretically speaking any plant containing a reasonable amount of fibres can be used as a raw material for pulp and paper production. In practice, this is not the case. Besides the abundance of the plant, a steady supply and many other requirements are necessary. The fibre content of the plant is important. The plant contains in addition to fibres many non-fibrous cells, e.g. parenchyma cells. Fibres themselves vary much in different plants regarding their length, width, fine structures or microstructures, as well as their chemical composition. In one and the same plant, there are different types of fibres. The same fibre type is not equal in dimension but contains a spectrum of different dimensions. For this reason, one speaks of "average fibre length". The length of the fibre is one of the most important parameters

Chemical characterization, which gives rise to the percentages of the main chemical constituents of lignocellulosic materials (generally cellulose, hemicellulose, lignin, as well as extractives and ash), is of great interest since it can indicate their possible applications for obtaining cellulosic pulps, in terms of the most suitable process to follow and the type of pulp that can be obtained. In this characterization, the contents of holocellulose, lignin, α-cellulose, hemicellulose, and extractives in water, 1% soda and ethanol-benzene and ash are determined as the most important. For this chemical characterization, TAPPI test methods, including TAPPI T 204 om-88, TAPPI T 211 om-93, TAPPI T 222 om-88 [27], and NREL analytical methods (National Renewable Energy Laboratory NREL/TP-510-42168)

When comparing the results obtained by different authors, a good concordance is generally observed for each specific material. Sometimes discrepancies appear that can be attributed to the different procedures used as well as to the different origins and varieties of the raw materials considered. For example, the chemical characterization results obtained for rice straw were analysed and compared with (i) some agriculture residues from harvesting and pruning operations and from agro-food industry (e.g. olive tree pruning, wheat straw, sunflower stems, sorghum stems, bagasse, vine shoots, and cotton stems); (ii) some vegetables (e.g. *Leucaena colinsi*, *Leucaena leucocephala, Chamaecytisus proliferus*, *Retama monosperma*, *Phragmites* spp*.*, *Arundo donax, Prosopis juliflora*, and *Paulownia fortunei*); and (iii) softwoods (pine) and hardwoods (eucalyptus) [23, 29]. From this comparison it

• The value of the hot water soluble content of rice straw (7.3%) is lower than that of the rest of agricultural residues, except for bagasse and cotton stems; it is higher than the values found for the vegetables considered, except for *P.*

• The value of soda extractives at 1% of rice straw (57.7%) is higher than the values corresponding to the rest of agricultural residues and vegetable consid-

• The content of ethanol-benzene extractives in rice straw (0.56%) is lower than that of the materials considered: agricultural and agro-food residues, veg-

• The ash content of rice straw (9.2%) is higher than the values presented by the rest of agricultural residues and much higher than the values of pine and

*fortunei*, and higher than the values for pine and eucalyptus.

ered, as well as those of pine and eucalyptus.

etables, pine and eucalyptus.

**18**

together different operations. Thus, for example, in the preparation of the raw material, a debarking is carried out in the case of woody plants or pith is removed in the case of some vegetables (e.g. sunflower stalks), a cutting or reduction in size to produce chips or flakes, a cleaning to remove impurities, and so on. In the pulping section, the operations of impregnation of the raw material, cooking or delignification to separate lignin, washing of the solid fraction resulting from cooking and draining of the same to eliminate the fluid used in the washing can be integrated. In the same way, the sections of reagents recovery and purification of residual black liquors are made up of different operations.

Soda pulps have been obtained from different alternative raw materials, specially agriculture residues such as wheat straw [31], sunflower stalks [32, 33], vine shoots [34], olive tree pruning [35], sorghum stalks [36, 37], tagasaste [24], EFB [20, 38], *H. funifera* [39] and rice straw [29, 38, 40], obtaining different yields depending on the conditions of soda concentration, temperature and cooking time used. Soda pulping has also been carried out using additives such as anthraquinone and parabenzoquinone, which accelerate the delignification process and stabilize carbohydrates, improving the yield of the process with respect to the conventional "soda" process when operated under the same working conditions. Assays have been carried out using wheat straw, olive tree pruning, rice straw and EFB. For rice straw and EFB, pulps have also been obtained using KOH in aqueous solutions [20, 40].

Miao et al. [22] also analysed the composition of the hemp root bast (HRT) to further subject it to a process of soda pulping and bleach it with an elemental chlorine free (ECF) bleaching sequence. These authors conclude that HRT is a suitable raw material to make paper obtaining a pulp with high viscosity and brightness (893 mL/g and 85.52% ISO, respectively). González et al. and Marrakchi et al. [41, 42] also applied soda pulping to orange tree wood and *Stipa tenacissima* stems, respectively. The first ones studied the influence of operational variables in both pulping and pulp beating (temperature, 155–185°C; time, 40–90 min; soda concentration, 10–16%; and number of PFI beating revolutions, 0 to 3000) on the yield and on the pulp refining degree as well as the physical properties of resulting paper sheets. These authors found an optimum compromise as regards operating conditions (170°C, 40 min, 13% soda concentration and 2700 number of PFI beating revolutions), obtaining a pulp with tensile index, burst index and tear index of around 59.11 Nm/g, 4.10 kN/g and 2.79 mNm2 /g, respectively; these values deviate from their maximum values in 5.8, 2.2, and 1.4%, respectively. The pulp yield under these operating conditions is 43.9%; the refining degree is of 39.5°SR with the advantage of an increased drainability in paper production. These conditions involve a lower temperature, time, soda concentration and refining than those required to maximize the studied paper properties; so it is possible to save energy, chemicals and capital for industrial facilities. On the other hand, Marrakchi et al. [42] analysed the composition and fibre characteristics of the *S. tenacissima* steams and of its corresponding soda unbleached and bleached pulps. They conclude that the properties of *S. tenacissima* fibers are intermediate between those of non-wood and wood plants and are most often close to those of eucalyptus fibers. After studying a refining process and characterizing paper sheets obtained, these authors demonstrate the high potentiality of this non-wood species for papermaking applications.

#### *5.1.2 Kraft pulping*

The pulp obtained by this procedure is usually called Kraft (strong) if used for raw papers or "sulphate" if they are going to receive a further bleaching, although

**21**

*5.1.3 Sulfite pulping*

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic…*

both denominations are used indistinctly. The name "sulphate" is due to the fact that it is the sodium sulphate, and not the sodium sulphide, the reagent that is replaced, although the real agent that acts during the reaction is the sulphide that is generated in the recovery treatment of residual black liquors [1, 2, 6]. The process can be divided into two parts: the first is the obtaining of the pulp, and the second is

According to different authors [1, 2, 6], Kraft pulping process consists of the

i.The chips are taken to the reactor where they are cooked with white liquor (dissolution of sodium hydroxide and sodium sulphide), controlling the

ii.Pulping takes place during the established time, under appropriate pressure

iii.The black or residual liquor and the pulp are separated by filtration. The pulp is washed, and the black liquor is sent to the reagent recovery phase.

iv.Once washed, the pulp goes to the bleaching stage or to the raw paper

In the reagent recovery phase, organic compounds dissolved in black liquor are used to produce energy, thus reducing the rate of polluting effluents. The stages of recovery are as follows: (i) concentration of the black liquor in the evaporators; (ii) spraying of the concentrated black liquor in the oven, where the carbon reduces the sodium sulphate to sodium sulphide; (iii) the melted solids are discharged and dissolved in water, resulting in the green liquors; and (iv) the green liquor is sent to the causticizing stage, where the sodium carbonate reacts with the calcium oxide to

Some studies have been carried out to obtain Kraft pulps using alternative materials to traditional wood, including olive tree wood [43], *Cynara cardunculuns* L. [44], vine shoots [34], wheat straw [45] and kenaf [46]. Nevertheless, due to the more accessible structure of these materials compared to conventional wood materials, a soda process is usually applied to them, as this process is less pollutant. Thus, as an example, a factorial design of central composition experiments to find equations that relate the characteristics of the pulp and paper sheets with the operation variables have been realized using olive tree pruning [47, 48]. From these studies, it can be concluded that, in order to obtain pulp with suitable characteristics to be bleached to obtain paper and with good mechanical properties in the paper sheets, it is necessary to operate with an active alkali concentration of 25%, at 175°C during 90 min. The paper sheets obtained from olive tree pruning pulps were produced in different degrees of refining and were characterized attending their stretch index, burst index, and tear index. All paper sheets reach between 33 and 39 kN m/kg in the stretch index, between 1.5 and 2 kN/g in the burst index and 0.7–2.5 N m2

Sulfite pulps are obtained by cooking the lignocellulosic material with a solution of bisulfite and sulfur dioxide [1, 2, 6]. The cooking liquor is obtained by burning sulfur to obtain sulfur dioxide which is absorbed in a base of calcium, magnesium, sodium or ammonium. The most important variables of the "sulfite" process

tear index and not using a high refining degree (<45°SR) [47, 48].

/g in

the recovery of the chemical reagents used from black liquors.

*DOI: http://dx.doi.org/10.5772/intechopen.90041*

following stages:

"liquid/solid" ratio.

manufacturing plant.

form sodium hydroxide [1, 2, 6].

conditions.

#### *Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic… DOI: http://dx.doi.org/10.5772/intechopen.90041*

both denominations are used indistinctly. The name "sulphate" is due to the fact that it is the sodium sulphate, and not the sodium sulphide, the reagent that is replaced, although the real agent that acts during the reaction is the sulphide that is generated in the recovery treatment of residual black liquors [1, 2, 6]. The process can be divided into two parts: the first is the obtaining of the pulp, and the second is the recovery of the chemical reagents used from black liquors.

According to different authors [1, 2, 6], Kraft pulping process consists of the following stages:

In the reagent recovery phase, organic compounds dissolved in black liquor are used to produce energy, thus reducing the rate of polluting effluents. The stages of recovery are as follows: (i) concentration of the black liquor in the evaporators; (ii) spraying of the concentrated black liquor in the oven, where the carbon reduces the sodium sulphate to sodium sulphide; (iii) the melted solids are discharged and dissolved in water, resulting in the green liquors; and (iv) the green liquor is sent to the causticizing stage, where the sodium carbonate reacts with the calcium oxide to form sodium hydroxide [1, 2, 6].

Some studies have been carried out to obtain Kraft pulps using alternative materials to traditional wood, including olive tree wood [43], *Cynara cardunculuns* L. [44], vine shoots [34], wheat straw [45] and kenaf [46]. Nevertheless, due to the more accessible structure of these materials compared to conventional wood materials, a soda process is usually applied to them, as this process is less pollutant. Thus, as an example, a factorial design of central composition experiments to find equations that relate the characteristics of the pulp and paper sheets with the operation variables have been realized using olive tree pruning [47, 48]. From these studies, it can be concluded that, in order to obtain pulp with suitable characteristics to be bleached to obtain paper and with good mechanical properties in the paper sheets, it is necessary to operate with an active alkali concentration of 25%, at 175°C during 90 min. The paper sheets obtained from olive tree pruning pulps were produced in different degrees of refining and were characterized attending their stretch index, burst index, and tear index. All paper sheets reach between 33 and 39 kN m/kg in the stretch index, between 1.5 and 2 kN/g in the burst index and 0.7–2.5 N m2 /g in tear index and not using a high refining degree (<45°SR) [47, 48].

#### *5.1.3 Sulfite pulping*

Sulfite pulps are obtained by cooking the lignocellulosic material with a solution of bisulfite and sulfur dioxide [1, 2, 6]. The cooking liquor is obtained by burning sulfur to obtain sulfur dioxide which is absorbed in a base of calcium, magnesium, sodium or ammonium. The most important variables of the "sulfite" process

*Cellulose*

solutions [20, 40].

together different operations. Thus, for example, in the preparation of the raw material, a debarking is carried out in the case of woody plants or pith is removed in the case of some vegetables (e.g. sunflower stalks), a cutting or reduction in size to produce chips or flakes, a cleaning to remove impurities, and so on. In the pulping section, the operations of impregnation of the raw material, cooking or delignification to separate lignin, washing of the solid fraction resulting from cooking and draining of the same to eliminate the fluid used in the washing can be integrated. In the same way, the sections of reagents recovery and purification of residual black

Soda pulps have been obtained from different alternative raw materials, specially agriculture residues such as wheat straw [31], sunflower stalks [32, 33], vine shoots [34], olive tree pruning [35], sorghum stalks [36, 37], tagasaste [24], EFB [20, 38], *H. funifera* [39] and rice straw [29, 38, 40], obtaining different yields depending on the conditions of soda concentration, temperature and cooking time used. Soda pulping has also been carried out using additives such as anthraquinone and parabenzoquinone, which accelerate the delignification process and stabilize carbohydrates, improving the yield of the process with respect to the conventional "soda" process when operated under the same working conditions. Assays have been carried out using wheat straw, olive tree pruning, rice straw and EFB. For rice straw and EFB, pulps have also been obtained using KOH in aqueous

Miao et al. [22] also analysed the composition of the hemp root bast (HRT) to further subject it to a process of soda pulping and bleach it with an elemental chlorine free (ECF) bleaching sequence. These authors conclude that HRT is a suitable raw material to make paper obtaining a pulp with high viscosity and brightness (893 mL/g and 85.52% ISO, respectively). González et al. and Marrakchi et al. [41, 42] also applied soda pulping to orange tree wood and *Stipa tenacissima* stems, respectively. The first ones studied the influence of operational variables in both pulping and pulp beating (temperature, 155–185°C; time, 40–90 min; soda concentration, 10–16%; and number of PFI beating revolutions, 0 to 3000) on the yield and on the pulp refining degree as well as the physical properties of resulting paper sheets. These authors found an optimum compromise as regards operating conditions (170°C, 40 min, 13% soda concentration and 2700 number of PFI beating revolutions), obtaining a pulp with tensile index, burst index and

values deviate from their maximum values in 5.8, 2.2, and 1.4%, respectively. The pulp yield under these operating conditions is 43.9%; the refining degree is of 39.5°SR with the advantage of an increased drainability in paper production. These conditions involve a lower temperature, time, soda concentration and refining than those required to maximize the studied paper properties; so it is possible to save energy, chemicals and capital for industrial facilities. On the other hand, Marrakchi et al. [42] analysed the composition and fibre characteristics of the *S. tenacissima* steams and of its corresponding soda unbleached and bleached pulps. They conclude that the properties of *S. tenacissima* fibers are intermediate between those of non-wood and wood plants and are most often close to those of eucalyptus fibers. After studying a refining process and characterizing paper sheets obtained, these authors demonstrate the high potentiality of this non-wood species for papermak-

The pulp obtained by this procedure is usually called Kraft (strong) if used for raw papers or "sulphate" if they are going to receive a further bleaching, although

/g, respectively; these

tear index of around 59.11 Nm/g, 4.10 kN/g and 2.79 mNm2

liquors are made up of different operations.

**20**

ing applications.

*5.1.2 Kraft pulping*

includes impregnation of the chips with the cooking reagents, dimensions and quality of the chips, temperature, time, pressure, pH of the white liquor, concentrations of sulfur dioxide combined (total and free), "liquid/solid" ratio and raw material used. Several "sulfite" processes have been proposed, including acid sulphite, bisulphite, alkaline sulphite, multistage sulphite, high-yield sulphite, etc., to obtain dissolving pulp [1, 2, 6]. In addition to these variables, it has been proposed to use molybdate or anthraquinone as catalysts, achieving a stabilization of the polysaccharides and an acceleration in delignification.

The sulfite process has been studied for several alternative raw materials but not as much as the soda and Kraft processes. Then, different studies of sulfite process with olive tree [35, 49], sunflower stalk [50], bagasse [51] and wheat straw [52] have been reported.

#### *5.1.4 Organosolv pulping*

These processes are characterized by the fact that the separation of lignin from lignocellulosic materials is achieved by solubilization with organic solvents, which are subsequently recovered for a new pulping cycle, resulting in a concentrate rich in lignin, from which different by-products can be obtained [53]. Among organic solvents used, alcohols (ethanol, methanol, butanol, etc.) and organic acids (acetic and formic acids) are commonly employed for non-woody materials [1, 2, 18, 24, 34, 54–66]. Nevertheless, acetone and other solvents such as phenol, formaldehyde, ethanolamine, ethylene glycol and ethanol-water have also been used for these alternative raw materials [1, 2, 19, 23, 34, 38, 60, 67–71], demonstrating that these materials can be used for the manufacture of pulp and paper through different processes with acceptable characteristics.

#### *<IP_ADDRESS> Pulping using alcohols*

These are the most widely used processes due to the selectivity that these solvents contribute to the separation of the lignin and their easy recovery by distillation. In the case of the ethanol process, the influence of the operating variables (ethanol concentration, temperature, time and liquid/solid ratio) on the characteristics of the pulp and paper sheets obtained from different alternative raw materials, including olive tree [62], wheat straw [1, 2, 18], tagasaste [24, 57], sunflower stalk and *P. fortunei* [54, 55] and vine shoots [34], has been studied. As an example, in the case of wheat straw, when pulping is carried out at 200°C, with an ethanol concentration of 75% for 60 min, acceptable good values are obtained for yield (37.6%), holocellulose (88.8%), α-cellulose (46.9%) and lignin (7.2%) [1, 2, 18]. Methanol and butanol have also been used on wheat straw [37, 61].

#### *<IP_ADDRESS> Pulping using organics acids*

Along with the processes that use alcohols, the processes that use organic acids are the following most used. The most common are those that use acetic acid and formic acid, and different studies have been reported with EFB [58], rice straw [63], jute [66], rapeseed straw [56], cardoon stalk [64], and wheat straw [65].

The pulping of wheat straw with acetic acid and formic acid has been carried out, studying the influence of operation variables on the properties of the resulting pulps. Comparing the results obtained when operating for times ranging between 0.5 and 2 h, at temperatures of 75–125°C and 150–200°C, and with concentrations of 50–100% and 50–80% of the formic and acetic acids, respectively, it is concluded

**23**

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic…*

that to obtain pulp with acceptable holocellulose (88.2%), α-cellulose (40.2%) and lignin (6.4%) contents are more effective than formic acid, operating at 50% concentration, 100°C and 2 h. This fact is mainly due to it requiring less acid and lower working temperature, with the consequent savings in chemical reagents and

Several studies have been studied with acetone solvent mainly on wheat straw [1, 2, 19, 60, 67]. From these studies it is concluded that it must be operated at 200°C, for 95–100 min and with 55–60% of acetone to obtain high holocellulose and α-cellulose values and low lignin and extractives, although the yield of the pulp is low [60]. To obtain good values of breaking length (3456 m), elongation

sheets formed, a temperature of 200°C has to be used. On the other hand, if the brightness has to be high, it has to be operated at 140°C for 1 h with a concentra-

The refining of pulp is an operation that modifies, through the action of mechanical work and in the presence of an aqueous medium, the morphology of the fibres and their physicochemical structure, decisively changing the properties of the paper sheets obtained from the refined pulp [1, 2, 6]. Using a Sprout-Bauer refiner, the influence of refining pulp from different agricultural residues (wheat straw, sunflower stems, vine shoots, olive tree pruning, cotton stems and sorghum stems) on the corresponding pulp and paper sheets was studied [1, 2, 19, 32, 69]. In view of the results, it can be concluded that olive tree pruning pulp must be severely refined to obtain good quality paper, although the maximum values of the ring crush test (RCT) and the tear index are reached for refining grades of 45 and 55°SR, respectively. In the case of EFB soda-anthraquinone pulp, a study has been carried out in a PFI refiner, studying the influence of the cooking variables (soda concentration, temperature and time) and the number of turns in the PFI on the properties of the resulting paper sheets [20]. From this study it is deduced that under some operation conditions, 15% of soda, 170°C, 70 min and 2,400 turns in the PFI, the properties of paper sheets obtained deviate less than 12% from their optimum values (59.6 Nm/g for the traction index, 4.48% for elongation, 4.17 kN/g

of 47.5°SR, acceptable for the formation of paper sheets. Under these conditions, reagents, energy and immobilized capital are saved with respect to the maximum

The bleaching of cellulosic pulps is carried out for the elimination and/or modification of some constituents that add color to the raw pulp, generally using chemical reagents in one or more stages and trying to degrade the cellulose fibers as little as possible [1, 2, 6]. The main light-absorbing substances in the pulps are lignin and resins, so in order to bleach a pulp, these substances must be chemically transformed into a solid state in order to reduce their light absorption characteristics or

/g) of the paper

/g for the tear index), for a degree of refining

(1.42%), burst index (1.36 KN/g) and tear index (3.86 mNm2

*DOI: http://dx.doi.org/10.5772/intechopen.90041*

energy for heating [65].

*<IP_ADDRESS> Acetone process*

tion of 60% acetone [65].

**6. Refining of cellulosic pulps**

for the burst index and 7.20 mNm2

**7. Bleaching of cellulosic pulps**

values of the operating variables used [20].

#### *Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic… DOI: http://dx.doi.org/10.5772/intechopen.90041*

that to obtain pulp with acceptable holocellulose (88.2%), α-cellulose (40.2%) and lignin (6.4%) contents are more effective than formic acid, operating at 50% concentration, 100°C and 2 h. This fact is mainly due to it requiring less acid and lower working temperature, with the consequent savings in chemical reagents and energy for heating [65].

#### *<IP_ADDRESS> Acetone process*

*Cellulose*

been reported.

*5.1.4 Organosolv pulping*

includes impregnation of the chips with the cooking reagents, dimensions and quality of the chips, temperature, time, pressure, pH of the white liquor, concentrations of sulfur dioxide combined (total and free), "liquid/solid" ratio and raw material used. Several "sulfite" processes have been proposed, including acid sulphite, bisulphite, alkaline sulphite, multistage sulphite, high-yield sulphite, etc., to obtain dissolving pulp [1, 2, 6]. In addition to these variables, it has been proposed to use molybdate or anthraquinone as catalysts, achieving a stabilization of the polysac-

The sulfite process has been studied for several alternative raw materials but not as much as the soda and Kraft processes. Then, different studies of sulfite process with olive tree [35, 49], sunflower stalk [50], bagasse [51] and wheat straw [52] have

These processes are characterized by the fact that the separation of lignin from lignocellulosic materials is achieved by solubilization with organic solvents, which are subsequently recovered for a new pulping cycle, resulting in a concentrate rich in lignin, from which different by-products can be obtained [53]. Among organic solvents used, alcohols (ethanol, methanol, butanol, etc.) and organic acids (acetic and formic acids) are commonly employed for non-woody materials [1, 2, 18, 24, 34, 54–66]. Nevertheless, acetone and other solvents such as phenol, formaldehyde, ethanolamine, ethylene glycol and ethanol-water have also been used for these alternative raw materials [1, 2, 19, 23, 34, 38, 60, 67–71], demonstrating that these materials can be used for the manufacture of pulp and paper through different

These are the most widely used processes due to the selectivity that these solvents contribute to the separation of the lignin and their easy recovery by distillation. In the case of the ethanol process, the influence of the operating variables (ethanol concentration, temperature, time and liquid/solid ratio) on the characteristics of the pulp and paper sheets obtained from different alternative raw materials, including olive tree [62], wheat straw [1, 2, 18], tagasaste [24, 57], sunflower stalk and *P. fortunei* [54, 55] and vine shoots [34], has been studied. As an example, in the case of wheat straw, when pulping is carried out at 200°C, with an ethanol concentration of 75% for 60 min, acceptable good values are obtained for yield (37.6%), holocellulose (88.8%), α-cellulose (46.9%) and lignin (7.2%) [1, 2, 18]. Methanol

Along with the processes that use alcohols, the processes that use organic acids are the following most used. The most common are those that use acetic acid and formic acid, and different studies have been reported with EFB [58], rice straw [63],

The pulping of wheat straw with acetic acid and formic acid has been carried out, studying the influence of operation variables on the properties of the resulting pulps. Comparing the results obtained when operating for times ranging between 0.5 and 2 h, at temperatures of 75–125°C and 150–200°C, and with concentrations of 50–100% and 50–80% of the formic and acetic acids, respectively, it is concluded

jute [66], rapeseed straw [56], cardoon stalk [64], and wheat straw [65].

charides and an acceleration in delignification.

processes with acceptable characteristics.

and butanol have also been used on wheat straw [37, 61].

*<IP_ADDRESS> Pulping using alcohols*

*<IP_ADDRESS> Pulping using organics acids*

**22**

Several studies have been studied with acetone solvent mainly on wheat straw [1, 2, 19, 60, 67]. From these studies it is concluded that it must be operated at 200°C, for 95–100 min and with 55–60% of acetone to obtain high holocellulose and α-cellulose values and low lignin and extractives, although the yield of the pulp is low [60]. To obtain good values of breaking length (3456 m), elongation (1.42%), burst index (1.36 KN/g) and tear index (3.86 mNm2 /g) of the paper sheets formed, a temperature of 200°C has to be used. On the other hand, if the brightness has to be high, it has to be operated at 140°C for 1 h with a concentration of 60% acetone [65].

#### **6. Refining of cellulosic pulps**

The refining of pulp is an operation that modifies, through the action of mechanical work and in the presence of an aqueous medium, the morphology of the fibres and their physicochemical structure, decisively changing the properties of the paper sheets obtained from the refined pulp [1, 2, 6]. Using a Sprout-Bauer refiner, the influence of refining pulp from different agricultural residues (wheat straw, sunflower stems, vine shoots, olive tree pruning, cotton stems and sorghum stems) on the corresponding pulp and paper sheets was studied [1, 2, 19, 32, 69]. In view of the results, it can be concluded that olive tree pruning pulp must be severely refined to obtain good quality paper, although the maximum values of the ring crush test (RCT) and the tear index are reached for refining grades of 45 and 55°SR, respectively. In the case of EFB soda-anthraquinone pulp, a study has been carried out in a PFI refiner, studying the influence of the cooking variables (soda concentration, temperature and time) and the number of turns in the PFI on the properties of the resulting paper sheets [20]. From this study it is deduced that under some operation conditions, 15% of soda, 170°C, 70 min and 2,400 turns in the PFI, the properties of paper sheets obtained deviate less than 12% from their optimum values (59.6 Nm/g for the traction index, 4.48% for elongation, 4.17 kN/g for the burst index and 7.20 mNm2 /g for the tear index), for a degree of refining of 47.5°SR, acceptable for the formation of paper sheets. Under these conditions, reagents, energy and immobilized capital are saved with respect to the maximum values of the operating variables used [20].

#### **7. Bleaching of cellulosic pulps**

The bleaching of cellulosic pulps is carried out for the elimination and/or modification of some constituents that add color to the raw pulp, generally using chemical reagents in one or more stages and trying to degrade the cellulose fibers as little as possible [1, 2, 6]. The main light-absorbing substances in the pulps are lignin and resins, so in order to bleach a pulp, these substances must be chemically transformed into a solid state in order to reduce their light absorption characteristics or

be oxidized, reduced or hydrolysed, to make them soluble in aqueous solutions and thus be able to be removed from the pulps.

The need to reduce pollution from bleached pulp mills has led to the study of new bleaching sequences [1, 2, 6], with research focusing in three main directions: (i) bleaching processes with reagents without elemental chlorine (ECF), which consist of the total substitution of chlorinated stages by compounds such as chlorine dioxide (without elemental chlorine), regardless of whether other bleaching agents totally free of chlorine, such as oxygen, hydrogen peroxide, etc., are also used; (ii) bleaching processes with totally chlorine free reagents (TCF), using reagents such as oxygen, hydrogen peroxide and ozone, mainly [72]; and (iii) biological bleaching processes involving microorganisms or enzymes produced by them.

ECF and TCF bleaching processes including enzymatic stages have been studied for different alternative raw materials. It is worth highlighting the TCF processes which have been studied using different chemical reagents individually (hydrogen peroxide, oxygen, ozone, sodium perborate and peracetic acid) or with OZP bleaching sequences (where Z is an ozone stage) [1, 2, 6].

Hydrogen peroxide has been used for the bleaching of Kraft olive tree pruning pulp with a Kappa index of 21, operating at a temperature of 70°C and a consistency of 10%, and following a factorial design of experiments in which the peroxide concentration varies from 1 to 5% and the time from 30 to 210 min, finding that it is recommended to use a low-medium concentration of peroxide (1–3%) and a long time (210 min) [73]. Comparing the results with those of bleached pulps with other reagents, it is concluded that the viscosity of the pulps is higher in the case of peroxide bleached pulps than those bleached with oxygen, ozone or chlorine dioxide. To improve the Kappa index and brightness values of peroxide bleached pulp, it is desirable to combine hydrogen peroxide with oxygen or to use the combination oxygen and ozone [74].

For the bleaching of abaca soda pulp with peracetic acid [75], the influence of the operating conditions on the Kappa index, viscosity and brightness of the pulp and on the breaking length and burst index of the paper sheets was studied. Following a factorial design of experiments, it is concluded that operating at 55°C, with 4.5% peracetic acid for 150 min, a brightness of 79.9% is obtained (only 6.5% lower than the maximum possible) and the maximum possible values for the breaking length (6547 m), burst index (5.0 kN/g) and viscosity (1519 mL/g).

Peracetic acid has also been considered in the bleaching of olive tree pruning, finding that it has to be operated at 55°C for 90 min, a consistency of 10% and an acid concentration of 2.5%, providing good values for brightness and Kappa index and improving the viscosity of the bleached pulp with respect to crude pulp [76].

In the bleaching of abaca soda pulp with sodium perborate [77], the influence of the concentration of reagent (1–5%), temperature (60–80°C) and time (1–2 h) on the characteristics of the bleached pulp and the resulting paper sheets has been studied. It is concluded that in order to obtain pulp with the highest possible values of viscosity (1601 mL/g) and breaking length (5943 m), it is necessary to operate at 60°C, 1% perborate and 60 min, achieving a brightness of 62.7%, only 11.9% below the maximum possible.

For abaca soda pulp, the bleaching processes using hydrogen peroxide, peracetic acid, sodium perborate and the OZP sequence were compared from the point of view of pulp yield and brightness, breaking length and burst and tear indexes of the paper sheets. Overall, the best results are achieved for peracetic bleached pulp (4.5%, at 55°C for 0.5 h), providing little loss of yield (<1%) and some values for breaking length (6.555 m), burst index (4.97 kN/g) and tear index (15.77 mNm2 /g), which only decrease, with respect to those of the raw starting pulps, by 7.0, 8.8 and 20.9%, respectively, while brightness (77.4%) increases by 56.7%; with the

**25**

*Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic…*

additional advantage that by operating at a lower temperature and for less time than in the other bleaching processes considered, energy savings are produced for heating and immobilized capital for industrial installations. The pulp bleached with the OZP sequence has more brightness but loses more yield. Moreover, the characteristics of the paper sheets are worse, and the process requires higher costs of reagent,

The OZP sequence has been applied to EFB soda-anthraquinone and diethanolamine pulps [79]. For similar Kappa index values for the two pulps (14.2 and 17.3), the paper sheets of the raw soda-anthraquinone pulp exhibit higher values for tensile (25.8 Nm/g), elongation (2.35%), burst index (1.69 kN/g) and tear index (0.50

/g) and brightness (60.6%) than the diethanolamine pulp, but the latter has