and to a major acidic stability, but also showed that only short MnPs have the capacity of oxidizing ABTS independently (in the absence of Mn2+) [78]. Fernández-Fueyo *et al.* using PELE [56] and electronic couplings calculations by the fragment charge difference (FCD) approach [80], provided computational information for the ABTS oxidation at the heme-propionate channel and the relation between the C-tail length and the MnPs catalytic properties. Since only small differences exist between long and extralong MnPs, there was no representative for the long MnP subfamily. Calculations were performed using the crystal structure of the extralong isoenzyme MnP6 [78] and its *in silico* shortened-tail form. Local exploration of the ABTS diffusion at the entrance of the heme-propionate channel using PELE showed that for the shortened-tail form of MnP6 the most favorable structures had ABTS closer to the active site. In contrast, for the extralong isoenzyme, the tool failed to provide a structure with good interaction energy, and ABTS was located at a longer distance from the active site. It was observed that the C-tail interferes with the entrance of the ligand into the heme-propionate channel and that longer Gluh35-Asph179 distances enable the approach of ABTS in the shortened-tail form. The C-tail in the extralong MnP seems to limit the mobility of the residues at the entrance of the channel, and also Asph179 and Gluh35 block the access of ABTS even in the most energetically favourable position. Moreover, QM/MM calculations (B3LYP/ OPLS2005) using the FCD approach were performed in the best positions predicted for both systems, showing electronic coupling values of one order of magnitude higher for the shortened-tail MnP (4.315E−5 eV) than for the extralong MnP (4.65E-6 eV), demonstrating the higher capacity of the shortened-tail MnP to oxidize ABTS. Rational enzyme engineering of MnP6 from *C. subvermispora* has also been carried out with the help of computational methods [81]. Here, this highly stable peroxidase at low pH was rationally mutated and activated for the oxidation of ABTS based on the analysis of MnP4, a less stable but ABTS-oxidizing MnP from *Pleurotus ostreatus* [82]. Acebes *et al*. started the engineering research using PELE for the active site inspection on both systems, ABTS-MnP6 and ABTS-MnP4. Results of these explorations showed that in the energetically minimum structure of MnP4 located at the main heme channel, two histidines, H220 and H142, interacted forming hydrogen bonds with ABTS's negatively charged sulfonates. These two histidines were not found in MnP6, but instead G139 and N218 were found in their respective positions. Thus, *in silico* G139H and N218H mutations were built in MnP6. Further PELE exploration of the ligand diffusion of ABTS on MnP4 and MnP6 double mutant showed similar energy values, distance and binding modes between these two systems. These results were also supported by electronic coupling calculations using the FCD method, where this double mutant presented an increase of the electronic coupling value of almost three orders of magnitude compared to wild type MnP6 and about ~four times lower than in MnP4. Experimental results confirmed

the activation of MnP6 toward the oxidation of ABTS.

DyP-type peroxidases were described 10 years ago like a new family of the heme-peroxidases [83]. The structural difference of them with the other class of fungal, plant and animal peroxidases is that they do not have well conserved amino acids around the heme moiety. Initial studies in DyPs exhaustively characterized this region and after being reported the

**2.5. Dye-decoloring peroxidase**

132 Lignin - Trends and Applications

as a protein engineering strategy, the enlargement of the heme pocket by the single mutations F359G and L357G, and the evaluation of the sulfoxidizing reactivity of mutants toward methyl-phenyl sulfide (MPS) and methyl-*p*-tolyl sulfide (MTS). It is worth mentioning that the tuning of the stereoselectivity in sulfoxidation reactions has many applications in organic synthesis and in enzymatic reactions. The mutant F359G was observed to be highly stereoselective and reactive producing the *S* sulfoxide of MPS and MTS, while native DyP had no sulfoxidation activity, and the L357G variant produced racemic mixtures of sulfoxides *R* and *S* enantiomers but with lower catalytic efficiencies. PELE simulations showed that the sulfoxidation ability present in the mutants was due to a better access of the substrates to the reactive heme cofactor. In addition to this, QM/MM calculations performed at the DFT M06-L(lacvp\*)/ OPLS level with QSite [88] elucidated that the high stereoselectivity and reactivity observed in the mutant F359G could be explained by the substantial difference between the spin density populations on the substrate molecules for the two enantiomers, (0.8% pro R-enantiomer, 21.8% pro S-enantiomer) in MPS and (12.5% pro R-enantiomer, 25.8% pro S-enantiomer) in MTS [89]. Other study including computational methodologies was reported by Strittmatter *et al.* [24]. Docking experiments were performed in A*au*DyPI using N-heterocyclic derivatives like substrates to explore its binding interaction in the heme pocket. The observation of competitive inhibition by imidazole with regard to H2 O2 conversion and changes in the Soret band of A*au*DyPI in the presence of imidazole derivatives was correlated with the computational data and permitted to predict which compound was a good candidate for coordination or not with the heme iron [24].

boosting electron transfer to the Cu T1 site. Moreover, the new mutant was tested at working conditions for the enzymatic synthesis of PANI from ANL, which showed an increment of absorbance of 36% compared to the parent when production of PANI was followed at 800 nm. Finally, an *in silico* cross validation was performed for aniline derivative DMPD. After applying the same computational protocol and measuring the kinetic parameters for biological oxidation of this substrate, by mutant and parent laccases, the authors found that substrate spin density increased from 39 to 68% by the presence of N207S/N263D mutations in the engineered laccase which also was consistent with the observed increase in *kcat* (from 459 ± 18 to 741 ± 48 s−1). The authors concluded that applied computational approach provided a reliable *in silico* screening, reducing experimental validation to precisely design laccase mutants. In a second case of rational protein engineering, the substrate binding pocket of a chimeric laccase (3A4) was redesigned in order to improve the oxidation of synapic acid (SA), a ligninrelated phenol of industrial interest [91]. This time the authors started using an experimentally protocol, iterative saturation mutagenesis [92], for screening more than 15,000 clones, from which two variants (C14F12 and CA32F1) and parent 3A4 were purified and characterized. Then, they rationalized the effect of mutations using computational methods. To do so, the 3D structures for 3A4 (mutation V162A), C14F12 (mutations V162A and F392N) and CA32F1 (mutations V162R, T164E and F392N) were built from coordinates of PM1L (PDB code: 5ANH), which shares 98% sequence identity with the chimeric variant 3A4. The 3D models were energy minimized with a force field and, in case of triple mutant variant, a 20 ns MD simulation was necessary to assure the structural stability of the model. With respect to

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SA, it was modeled in its protonated and deprotonated form, SAH and SA−

means that 3A4 laccase oxidized, preferentially, SAH instead of SA−

was about 88%. On the other hand, SA−

The SA−

to its p*K*a = 4.9 and MD simulations and experiments were performed at pH = 5.0 and 3.0. Then the binding modes of SA, and other substrates, on the T1 site of chimeric proteins were sampled with PELE [56]. Finally, and after filtering structures based on their energy from PELE simulations, the atomic Mulliken spin density of the substrate was computed on randomly selected structures that were minimized with QM/MM methodology including in the QM part the substrate, the T1 copper atom, and residues H394, C450, H455, I452 and F460; meanwhile the rest of structure was modeled classically with OPLS force field. The main results from computational simulation, and their relation with experimental findings, in this research work can be resumed as follow: (1) In 3A4, SAH binds with high affinity inside T1 site interacting with residues P393 and N207 through its carboxylic acid moiety and with residues A162, P163 and the side chain of S264 through its phenolic group. Its average spin density

instead a second site was explored. In that site substrate bound in a different orientation and further away from the metal center due to the favorable interaction between the negatively charged carboxylate group, the backbone of G391 and F392 and the hydroxyl group of S387.

with more affinity to T1 site than SAH showing the same interactions of its carboxylic group with residues G391, N392 and S387's side chain. Notably, the mutation F392N created a favorable binding site for the negatively charged substrate with the N392 side chain; therefore substrate's phenolic group showed two main orientations (one inside T1 site and other pointing

averaged spin densities in those sites were 87 and 61%, respectively. That roughly

, respectively, due

showed fewer structures populating the T1 site and

. (2) In C14F12, SA−

binds

### **3. Rational protein design successful cases**

In this section, we aim to briefly present two relevant and successful cases of rational protein design, where computational tools played a key role in improvement of catalytic activity of laccase as a key representative of oxidoreductase family. The first case was reported in 2016 by Santiago *et al.* [90]. That research work described the computer-aided engineering of a double mutant laccase that showed improved kinetic parameters (*kcat* and *kM*), when compared to parent enzyme, for oxidation of several arylamines. The authors studied the biological oxidation of four substrates (aniline (ANL), *p*-phenylenediamine (PPD), ABTS and *N*,*N*-dimethylp-phenylenediamine (DMPD)) that are of industrial interest for synthesis of conductive polyaniline (PANI), in case of ANL, or precursors of high-value reagents like methylene blue as potential antimalarial agent, in case of DMPD. The computational protocol used to design the double mutant of laccase was as follows: (1) determining of the binding event of substrates nearby T1 site by means of Monte Carlo-based molecular simulations using software PELE [56]; (2) estimating the spin density fraction localized on the substrate by means of QM/MM calculations on randomly selected structures; and (3) designing the laccase-binding site in order to improve substrate oxidation rate. This computational protocol was validated experimentally by estimating the kinetic parameters of substrates and comparing them with parent laccase. Notably, in case of ANL a 2-fold *kcat* increase was achieved by introducing two mutations at T1 site namely N207S/N263D that stabilized the oxidized form of ANL thereby boosting electron transfer to the Cu T1 site. Moreover, the new mutant was tested at working conditions for the enzymatic synthesis of PANI from ANL, which showed an increment of absorbance of 36% compared to the parent when production of PANI was followed at 800 nm. Finally, an *in silico* cross validation was performed for aniline derivative DMPD. After applying the same computational protocol and measuring the kinetic parameters for biological oxidation of this substrate, by mutant and parent laccases, the authors found that substrate spin density increased from 39 to 68% by the presence of N207S/N263D mutations in the engineered laccase which also was consistent with the observed increase in *kcat* (from 459 ± 18 to 741 ± 48 s−1). The authors concluded that applied computational approach provided a reliable *in silico* screening, reducing experimental validation to precisely design laccase mutants.

as a protein engineering strategy, the enlargement of the heme pocket by the single mutations F359G and L357G, and the evaluation of the sulfoxidizing reactivity of mutants toward methyl-phenyl sulfide (MPS) and methyl-*p*-tolyl sulfide (MTS). It is worth mentioning that the tuning of the stereoselectivity in sulfoxidation reactions has many applications in organic synthesis and in enzymatic reactions. The mutant F359G was observed to be highly stereoselective and reactive producing the *S* sulfoxide of MPS and MTS, while native DyP had no sulfoxidation activity, and the L357G variant produced racemic mixtures of sulfoxides *R* and *S* enantiomers but with lower catalytic efficiencies. PELE simulations showed that the sulfoxidation ability present in the mutants was due to a better access of the substrates to the reactive heme cofactor. In addition to this, QM/MM calculations performed at the DFT M06-L(lacvp\*)/ OPLS level with QSite [88] elucidated that the high stereoselectivity and reactivity observed in the mutant F359G could be explained by the substantial difference between the spin density populations on the substrate molecules for the two enantiomers, (0.8% pro R-enantiomer, 21.8% pro S-enantiomer) in MPS and (12.5% pro R-enantiomer, 25.8% pro S-enantiomer) in MTS [89]. Other study including computational methodologies was reported by Strittmatter *et al.* [24]. Docking experiments were performed in A*au*DyPI using N-heterocyclic derivatives like substrates to explore its binding interaction in the heme pocket. The observation of com-

O2

of A*au*DyPI in the presence of imidazole derivatives was correlated with the computational data and permitted to predict which compound was a good candidate for coordination or not

In this section, we aim to briefly present two relevant and successful cases of rational protein design, where computational tools played a key role in improvement of catalytic activity of laccase as a key representative of oxidoreductase family. The first case was reported in 2016 by Santiago *et al.* [90]. That research work described the computer-aided engineering of a double mutant laccase that showed improved kinetic parameters (*kcat* and *kM*), when compared to parent enzyme, for oxidation of several arylamines. The authors studied the biological oxidation of four substrates (aniline (ANL), *p*-phenylenediamine (PPD), ABTS and *N*,*N*-dimethylp-phenylenediamine (DMPD)) that are of industrial interest for synthesis of conductive polyaniline (PANI), in case of ANL, or precursors of high-value reagents like methylene blue as potential antimalarial agent, in case of DMPD. The computational protocol used to design the double mutant of laccase was as follows: (1) determining of the binding event of substrates nearby T1 site by means of Monte Carlo-based molecular simulations using software PELE [56]; (2) estimating the spin density fraction localized on the substrate by means of QM/MM calculations on randomly selected structures; and (3) designing the laccase-binding site in order to improve substrate oxidation rate. This computational protocol was validated experimentally by estimating the kinetic parameters of substrates and comparing them with parent laccase. Notably, in case of ANL a 2-fold *kcat* increase was achieved by introducing two mutations at T1 site namely N207S/N263D that stabilized the oxidized form of ANL thereby

conversion and changes in the Soret band

petitive inhibition by imidazole with regard to H2

**3. Rational protein design successful cases**

with the heme iron [24].

134 Lignin - Trends and Applications

In a second case of rational protein engineering, the substrate binding pocket of a chimeric laccase (3A4) was redesigned in order to improve the oxidation of synapic acid (SA), a ligninrelated phenol of industrial interest [91]. This time the authors started using an experimentally protocol, iterative saturation mutagenesis [92], for screening more than 15,000 clones, from which two variants (C14F12 and CA32F1) and parent 3A4 were purified and characterized. Then, they rationalized the effect of mutations using computational methods. To do so, the 3D structures for 3A4 (mutation V162A), C14F12 (mutations V162A and F392N) and CA32F1 (mutations V162R, T164E and F392N) were built from coordinates of PM1L (PDB code: 5ANH), which shares 98% sequence identity with the chimeric variant 3A4. The 3D models were energy minimized with a force field and, in case of triple mutant variant, a 20 ns MD simulation was necessary to assure the structural stability of the model. With respect to SA, it was modeled in its protonated and deprotonated form, SAH and SA− , respectively, due to its p*K*a = 4.9 and MD simulations and experiments were performed at pH = 5.0 and 3.0. Then the binding modes of SA, and other substrates, on the T1 site of chimeric proteins were sampled with PELE [56]. Finally, and after filtering structures based on their energy from PELE simulations, the atomic Mulliken spin density of the substrate was computed on randomly selected structures that were minimized with QM/MM methodology including in the QM part the substrate, the T1 copper atom, and residues H394, C450, H455, I452 and F460; meanwhile the rest of structure was modeled classically with OPLS force field. The main results from computational simulation, and their relation with experimental findings, in this research work can be resumed as follow: (1) In 3A4, SAH binds with high affinity inside T1 site interacting with residues P393 and N207 through its carboxylic acid moiety and with residues A162, P163 and the side chain of S264 through its phenolic group. Its average spin density was about 88%. On the other hand, SA− showed fewer structures populating the T1 site and instead a second site was explored. In that site substrate bound in a different orientation and further away from the metal center due to the favorable interaction between the negatively charged carboxylate group, the backbone of G391 and F392 and the hydroxyl group of S387. The SA− averaged spin densities in those sites were 87 and 61%, respectively. That roughly means that 3A4 laccase oxidized, preferentially, SAH instead of SA− . (2) In C14F12, SA− binds with more affinity to T1 site than SAH showing the same interactions of its carboxylic group with residues G391, N392 and S387's side chain. Notably, the mutation F392N created a favorable binding site for the negatively charged substrate with the N392 side chain; therefore substrate's phenolic group showed two main orientations (one inside T1 site and other pointing to the solvent) with improved spin densities of 93 and 48%, respectively. This, in turn, was in agreement with improvement of catalytic constants for C14F12 (*kcat* = 251 s−1) relative to 3A4 (*kcat* = 156 s−1) that could be due to improved oxidation of SA− (that is abundant at this pH than at pH = 3). (3) In CA32F1, the SAH and SA− species were also bound with high affinity to T1 site, showing spin densities of 99 and 86%, respectively. However the relative orientation of the side chains from R162, E164 and D205, and specially the new acid–basic pair formed by R162 and E164, affected the substrate oxidation. Overall, the authors concluded that QM and MD calculations were performed to rationalize the effect of the selected mutations, revealing the critical role of the residues of the enzyme pocket in order to provide the precise binding of the substrate that enabled an efficient electron transfer to the T1 Cu. Additionally, they stressed the usefulness of atomic simulations for unveiling the molecular determinants for the efficient oxidation of a target molecule by these kind of enzymes.

presented here with the aim to improve catalytic processes that are urgently demanded in

J. A-M. and I. F-V. thank financial support from project FONDECYT No. 1140618. J.R. and R.R. acknowledge support from CONICYT to perform their doctoral studies through scholarships

, Isabel Fuenzalida-Valdivia1

Computational Modeling Methods for Understanding the Interaction of Lignin...

http://dx.doi.org/10.5772/intechopen.70554

137

, Jefferson Romero1

environmental, food, chemical, pharmaceutical and energy industries.

\*, Rodrigo Recabarren1

1 Centro de Bioinformática y Simulación Molecular (CBSM), University of Talca,

[1] Ralph J, Lundquist K, Brunow G, Lu F, Kim H, Schatz PF, et al. Lignins: Natural polymers from oxidative coupling of 4-hydroxyphenyl-propanoids. Phytochemistry Reviews.

[2] Ragauskas AJ, Beckham GT, Biddy MJ, Chandra R, Chen F, Davis MF, et al. Lignin valorization: Improving lignin processing in the biorefinery. Science. 16 May 2014;**344**(6185):1246843

[3] Pandey MP, Kim CS. Lignin depolymerization and conversion: A review of thermochemical methods. Chemical Engineering and Technology. 2011 Jan 1;**34**(1):29-41

[4] Zhou C-H, Xia X, Lin C-X, Tong D-S, Beltramini J. Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels. Chemical Society Reviews. 2011 Oct 17;**40**(11):

[5] Nanayakkara S, Patti AF, Saito K. Chemical depolymerization of lignin involving the redistribution mechanism with phenols and repolymerization of depolymerized prod-

[6] Dashtban M, Schraft H, Syed TA, Qin W. Fungal biodegradation and enzymatic modification of lignin. International Journal of Biochemistry and Molecular Biology. 23 May

**Acknowledgements**

**Author details**

Jans Alzate-Morales1

Talca, Chile

**References**

5588-5617

2010;**1**(1):36-50

2004 Jan 1;**3**(1-2):29-60

and Angel T. Martinez2

No. 21160905 and No. 21130949, respectively.

\*Address all correspondence to<EMAIL_ADDRESS>
2 Biological Research Centre (CIB), CSIC, Madrid, Spain

ucts. Green Chemistry. 2014 Mar 24;**16**(4):1897-1903

### **4. Perspectives and conclusions**

This chapter aimed to collect and highlight the increasing evidence of computational modeling methods as supporting and validation tools in the study of oxidoreductases as biocatalysts and the characterization of their biotransformation products. We decided to focus on five enzymes that have been investigated intensively during last years due to their broad application as biocatalysts in chemical, agriculture, environmental and biotechnological applications. Those enzymes are LiP, MnP and VP, which are heme peroxidases in the peroxidase-catalase superfamily, DyP as a recently discovered heme peroxidase in the CDE superfamily (including chlorite dismutases, DyPs and the EfeB proteins of *E. coli*), and laccase as the most studied member of copper-containing oxidoreductases. The relevant literature was intensively searched for reports were computational methods—mainly MD simulations, QM and QM/MM—were presented as auxiliary tools to explain the experimental evidence in aspects like substrate binding and oxidation of lignin or derivatives against different binding sites reported for these enzymes, improvement of catalytic activity of a given oxidoreductase for a specific substrate, rational protein design and more recently computed-aided protein engineering. However, we believe that, despite the recent advances in hardware, software and algorithms, the use of computational modeling methods in the understanding of substrate binding and enzymatic catalytic processes between oxidoreductases and their substrates is yet scarce. Nevertheless, the two recently successful and relevant applications, that were discussed in last section, about the interplay between experimental and computational protocols applied to directed evolution of improved laccases as biocatalysts are very encouraging. This accumulated knowledge in rational protein design from presented case studies on laccase paves the way to other studies of the same kind in enzymes from oxidoreductases.

Undoubtedly, during next years the research in this area will be benefited from advance in computational software and hardware as well as from more accurate and predictive computational tools. Additionally, it is expected that more efficient biocatalysts are successfully and quickly generated from conjunction between these experimental/computational techniques presented here with the aim to improve catalytic processes that are urgently demanded in environmental, food, chemical, pharmaceutical and energy industries.

### **Acknowledgements**

to the solvent) with improved spin densities of 93 and 48%, respectively. This, in turn, was in agreement with improvement of catalytic constants for C14F12 (*kcat* = 251 s−1) relative to 3A4

site, showing spin densities of 99 and 86%, respectively. However the relative orientation of the side chains from R162, E164 and D205, and specially the new acid–basic pair formed by R162 and E164, affected the substrate oxidation. Overall, the authors concluded that QM and MD calculations were performed to rationalize the effect of the selected mutations, revealing the critical role of the residues of the enzyme pocket in order to provide the precise binding of the substrate that enabled an efficient electron transfer to the T1 Cu. Additionally, they stressed the usefulness of atomic simulations for unveiling the molecular determinants for the

This chapter aimed to collect and highlight the increasing evidence of computational modeling methods as supporting and validation tools in the study of oxidoreductases as biocatalysts and the characterization of their biotransformation products. We decided to focus on five enzymes that have been investigated intensively during last years due to their broad application as biocatalysts in chemical, agriculture, environmental and biotechnological applications. Those enzymes are LiP, MnP and VP, which are heme peroxidases in the peroxidase-catalase superfamily, DyP as a recently discovered heme peroxidase in the CDE superfamily (including chlorite dismutases, DyPs and the EfeB proteins of *E. coli*), and laccase as the most studied member of copper-containing oxidoreductases. The relevant literature was intensively searched for reports were computational methods—mainly MD simulations, QM and QM/MM—were presented as auxiliary tools to explain the experimental evidence in aspects like substrate binding and oxidation of lignin or derivatives against different binding sites reported for these enzymes, improvement of catalytic activity of a given oxidoreductase for a specific substrate, rational protein design and more recently computed-aided protein engineering. However, we believe that, despite the recent advances in hardware, software and algorithms, the use of computational modeling methods in the understanding of substrate binding and enzymatic catalytic processes between oxidoreductases and their substrates is yet scarce. Nevertheless, the two recently successful and relevant applications, that were discussed in last section, about the interplay between experimental and computational protocols applied to directed evolution of improved laccases as biocatalysts are very encouraging. This accumulated knowledge in rational protein design from presented case studies on laccase paves the way to other studies of the same kind in

Undoubtedly, during next years the research in this area will be benefited from advance in computational software and hardware as well as from more accurate and predictive computational tools. Additionally, it is expected that more efficient biocatalysts are successfully and quickly generated from conjunction between these experimental/computational techniques

(that is abundant at this pH than

species were also bound with high affinity to T1

(*kcat* = 156 s−1) that could be due to improved oxidation of SA−

efficient oxidation of a target molecule by these kind of enzymes.

at pH = 3). (3) In CA32F1, the SAH and SA−

136 Lignin - Trends and Applications

**4. Perspectives and conclusions**

enzymes from oxidoreductases.

J. A-M. and I. F-V. thank financial support from project FONDECYT No. 1140618. J.R. and R.R. acknowledge support from CONICYT to perform their doctoral studies through scholarships No. 21160905 and No. 21130949, respectively.

### **Author details**

Jans Alzate-Morales1 \*, Rodrigo Recabarren1 , Isabel Fuenzalida-Valdivia1 , Jefferson Romero1 and Angel T. Martinez2

\*Address all correspondence to<EMAIL_ADDRESS>
1 Centro de Bioinformática y Simulación Molecular (CBSM), University of Talca, Talca, Chile

2 Biological Research Centre (CIB), CSIC, Madrid, Spain

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**Chapter 6**

**Provisional chapter**

**Conversion of Lignin to Heat and Power, Chemicals or**

Energy transition toward low carbon, high sustainable and efficient generation and distribution systems will change the supply matrix of the world and create new opportunities but challenges still remain. Energy generation from biomass, or bioenergy, is one of such renewable sources and its use might be generalized in the following years. Bioenergy is a very promising strategy to provide energy not only for mobility but also for onsite places for heat and power generation. Besides, bioenergy differentiates from other renewable energies that biomass may be the source of a myriad of molecules enabling the bio-based economy and allowing the replacement in an extent of solvents, petrochemicals, and polymers produced by the petroleum industry. Biomass is generally composed of some large polymers found in nature such as cellulose, hemicellulose, proteins, starch, chitin, and lignin. The latter is a complex phenylpropanoid biopolymer conferring mechanical strength to plant cell walls and one of major spread in nature along with cellulose and chitin. Lignin has a plenty of potential uses in modern bio-based economy, from conventional paper industry uses to more challenging conversion to useful chemicals, materials, and clean biofuels. This chapter undertakes a rapid overview on lignin applications in order to describe the basis of a lignin-based

**Conversion of Lignin to Heat and Power, Chemicals or**

DOI: 10.5772/intechopen.71211

© 2016 The Author(s). Licensee InTech. 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,

© 2018 The Author(s). Licensee InTech. 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.

and reproduction in any medium, provided the original work is properly cited.

Although the world energy balance is dominated by fossil fuels, one major issue raised is how to change the future energy matrix toward more sustainable and renewable sources of energy.

**Keywords:** lignocellulosic materials, lignin, biorefinery, bioeconomy, heat and

**Fuels into the Transition Energy Strategy**

**Fuels into the Transition Energy Strategy**

Myriam Adela Amezcua-Allieri and Jorge Aburto

Additional information is available at the end of the chapter

thermal power, bio-based chemicals, biofuels

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71211

Myriam Adela Amezcua-Allieri and

Jorge Aburto

**Abstract**

economy.

**1. Introduction**

**Provisional chapter**

### **Conversion of Lignin to Heat and Power, Chemicals or Fuels into the Transition Energy Strategy Fuels into the Transition Energy Strategy**

**Conversion of Lignin to Heat and Power, Chemicals or**

DOI: 10.5772/intechopen.71211

Myriam Adela Amezcua-Allieri and Jorge Aburto

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71211

Myriam Adela Amezcua-Allieri and

#### **Abstract**

Jorge Aburto

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[87] Bauß A, Langenmaier M, Strittmatter E, Plattner DA, Koslowski T. Thermodynamic integration networks and their application to charge transfer reactions within the AauDyPI fungal peroxidase. The Journal of Physical Chemistry. B. 2016 Jun 9;**120**(22):4937-4944

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[92] Reetz MT, Carballeira JD. Iterative saturation mutagenesis (ISM) for rapid directed evo-

2015 Oct 29;**119**(43):13583-13592

144 Lignin - Trends and Applications

2016 Aug 5;**6**(8):5415-5423

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Science & Technology. 31 May 2016;**6**(11):3900-3910

lution of functional enzymes. Nature Protocols. 2007;**2**(4):891-903

Catalysis Science & Technology. 2016 Aug 8;**6**(16):6277-6285

Energy transition toward low carbon, high sustainable and efficient generation and distribution systems will change the supply matrix of the world and create new opportunities but challenges still remain. Energy generation from biomass, or bioenergy, is one of such renewable sources and its use might be generalized in the following years. Bioenergy is a very promising strategy to provide energy not only for mobility but also for onsite places for heat and power generation. Besides, bioenergy differentiates from other renewable energies that biomass may be the source of a myriad of molecules enabling the bio-based economy and allowing the replacement in an extent of solvents, petrochemicals, and polymers produced by the petroleum industry. Biomass is generally composed of some large polymers found in nature such as cellulose, hemicellulose, proteins, starch, chitin, and lignin. The latter is a complex phenylpropanoid biopolymer conferring mechanical strength to plant cell walls and one of major spread in nature along with cellulose and chitin. Lignin has a plenty of potential uses in modern bio-based economy, from conventional paper industry uses to more challenging conversion to useful chemicals, materials, and clean biofuels. This chapter undertakes a rapid overview on lignin applications in order to describe the basis of a lignin-based economy.

**Keywords:** lignocellulosic materials, lignin, biorefinery, bioeconomy, heat and thermal power, bio-based chemicals, biofuels

### **1. Introduction**

Although the world energy balance is dominated by fossil fuels, one major issue raised is how to change the future energy matrix toward more sustainable and renewable sources of energy.

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. © 2018 The Author(s). Licensee InTech. 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.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

The inclusion of renewables—wind, solar, geothermal, water and biomass—in the energy matrix has been marginal because of high costs and underdeveloped technologies. However, recognition of the damaging environmental impact from excessive dependence on fossil fuels, along with the growing concerns about the supply of some fossil fuels to meet rising global demand for energy, has brought into focus, the need for a cleaner and more diversified energy mix. Considering the challenges of the twenty-first century, including energy transition toward low carbon, bioenergy plays a key role in the diversification of sources of energy supply. In addition, the use of alternative fuels and bio-based chemicals will be increased to complete the energy matrix.

Biomass can be used directly (e.g., fuel wood for heating and cooking) or indirectly by converting it into a liquid or gaseous fuel (e.g., alcohol from sugar crops or biogas from animal waste). The main biomass processes utilized in the future are expected to be direct combustion of residues and wastes for electricity and heat generation, bioethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. The future of biomass electricity generation lies in biomass-integrated gasification/gas turbine technology, which offers high-energy conversion efficiencies. Biomass will compete favorably with fossil mass for niches in the chemical feedstock industry [9]. Hence, bioenergy is recognized as the energy derived from the conversion of biomass and where the biomass may be used directly as fuel, or processed into solids, liquids, and gases [16].

Biomass is mainly composed of three macromolecular biopolymers known as cellulose, hemicellulose, and lignin. Cellulose is composed of β-D-glucopyranose units linked by (1-4) glucosidic bonds and different polymorphs has been described from high to amorphous crystallinities [22]. On the other hand, hemicellulose is mostly amorphous and generally classified into four groups: (1) xyloglycans (xylans), (2) mannoglycans (mannans), (3) xyloglucans and (4) mixed-linked β-glucans [12]. They are considered the most abundant biopolymers on superior plants on earth just followed by lignin.

In this chapter, we present the actual and potential contribution of lignin as a source of solid, gas or liquid biofuels but also as a platform for bio-based chemicals and materials.

The main classification of wood includes softwood (gymnosperm as pine or spruce) and hardwood (angiosperm as oak and walnut); the former is usually cheaper than the latter because about 80% of all timber comes from softwood. Softwoods have a wide range of applications and are found in building components (e.g., windows, doors), furniture, medium-density fiberboard (MDF), paper, Christmas trees and so on. Hardwood is usually used in high-quality furniture, decks, flooring and construction that need to have a long life. Lignin present in softwood usually has more coniferyl alcohol (75%) and less p-coumaryl (5%) and sinapyl alcohol

Lignin in biomass may be valued through the generation of thermal and electric power as well as the production of materials and chemicals (**Figure 2**). Here, we focus on industrial uses of biomass-containing lignin and processed or extracted lignin. Therefore, we focus on sawmill, agroindustrial and agricultural activities. Concerning forestry activities in sawmills, we refer to FAO definitions. Please keep in mind that there is not sufficient data and mass balance may be not complete. Hence, roundwood refers to all quantities of woods removed from trees inside the forests and from trees outside the forests. It includes all woods removed with or without bark, including woods removed in its round form or split form and considered fuel wood, sawlogs and veneer

content (20%) than that present in hardwood (50, 10 and 40%, respectively; [24]).

**Biomass Cellulose**

Agave bagasse (*Agave*

Sugarcane bagasse (*Saccharum officinarum*)

*atrovirens*)

**(%)**

**Hemicellulose**

**Lignin (%)**

Conversion of Lignin to Heat and Power, Chemicals or Fuels into the Transition Energy Strategy

45.9 26.6 8.7 15.5 868

32.3 35.2 22.4 19.1 721.7

**Calorific value (GJ/ton)**

**Density of compressed material (kg/m3**

http://dx.doi.org/10.5772/intechopen.71211

**)**

147

**(%)**

Wood (*Pinus* spp.) 43.3 25.9 29.6 18.3 906.8

Corn stubble (*Zea mays*) 39.1 30.9 18.6 15.6 928.2 Wheat Straw (*Triticum* spp.) 42.9 28.9 21.6 17.9 899

**Table 1.** Biomass composition, calorific values and densities of compressed materials [18].

**Figure 1.** Lignin precursors from left to right: p-coumaryl, coniferyl and sinapyl alcohols.

### **2. Lignin**

Lignin is an amorphous and highly branched polyphenolic polymer with phenylpropane units, which may be present in varying amounts in biomass, comprising around 8–30% of biomass weight (**Table 1**). The complex structure of lignin contains numerous ether linkages, hydroxyl and methoxy groups and, therefore, a high-oxygen content. This cross-linked macromolecule is composed of three types of monolignols or lignin precursors, also known as phenolic monomers, including p-coumaryl, coniferyl and sinapyl alcohol (**Figure 1**). These precursors correspond to the p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units in lignin, respectively [7]. Lignin is considered the clue agent that gives robustness and strength to the cellulose microfibril systems surrounded by hemicellulose [10, 11].

Conversion of Lignin to Heat and Power, Chemicals or Fuels into the Transition Energy Strategy http://dx.doi.org/10.5772/intechopen.71211 147

**Table 1.** Biomass composition, calorific values and densities of compressed materials [18].

The inclusion of renewables—wind, solar, geothermal, water and biomass—in the energy matrix has been marginal because of high costs and underdeveloped technologies. However, recognition of the damaging environmental impact from excessive dependence on fossil fuels, along with the growing concerns about the supply of some fossil fuels to meet rising global demand for energy, has brought into focus, the need for a cleaner and more diversified energy mix. Considering the challenges of the twenty-first century, including energy transition toward low carbon, bioenergy plays a key role in the diversification of sources of energy supply. In addition, the use of alternative fuels and bio-based chemicals will be increased to

Biomass can be used directly (e.g., fuel wood for heating and cooking) or indirectly by converting it into a liquid or gaseous fuel (e.g., alcohol from sugar crops or biogas from animal waste). The main biomass processes utilized in the future are expected to be direct combustion of residues and wastes for electricity and heat generation, bioethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. The future of biomass electricity generation lies in biomass-integrated gasification/gas turbine technology, which offers high-energy conversion efficiencies. Biomass will compete favorably with fossil mass for niches in the chemical feedstock industry [9]. Hence, bioenergy is recognized as the energy derived from the conversion of biomass and where the biomass may be used directly as fuel,

Biomass is mainly composed of three macromolecular biopolymers known as cellulose, hemicellulose, and lignin. Cellulose is composed of β-D-glucopyranose units linked by (1-4) glucosidic bonds and different polymorphs has been described from high to amorphous crystallinities [22]. On the other hand, hemicellulose is mostly amorphous and generally classified into four groups: (1) xyloglycans (xylans), (2) mannoglycans (mannans), (3) xyloglucans and (4) mixed-linked β-glucans [12]. They are considered the most abundant biopolymers on

In this chapter, we present the actual and potential contribution of lignin as a source of solid,

Lignin is an amorphous and highly branched polyphenolic polymer with phenylpropane units, which may be present in varying amounts in biomass, comprising around 8–30% of biomass weight (**Table 1**). The complex structure of lignin contains numerous ether linkages, hydroxyl and methoxy groups and, therefore, a high-oxygen content. This cross-linked macromolecule is composed of three types of monolignols or lignin precursors, also known as phenolic monomers, including p-coumaryl, coniferyl and sinapyl alcohol (**Figure 1**). These precursors correspond to the p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units in lignin, respectively [7]. Lignin is considered the clue agent that gives robustness and strength

gas or liquid biofuels but also as a platform for bio-based chemicals and materials.

to the cellulose microfibril systems surrounded by hemicellulose [10, 11].

complete the energy matrix.

146 Lignin - Trends and Applications

or processed into solids, liquids, and gases [16].

superior plants on earth just followed by lignin.

**2. Lignin**

**Figure 1.** Lignin precursors from left to right: p-coumaryl, coniferyl and sinapyl alcohols.

The main classification of wood includes softwood (gymnosperm as pine or spruce) and hardwood (angiosperm as oak and walnut); the former is usually cheaper than the latter because about 80% of all timber comes from softwood. Softwoods have a wide range of applications and are found in building components (e.g., windows, doors), furniture, medium-density fiberboard (MDF), paper, Christmas trees and so on. Hardwood is usually used in high-quality furniture, decks, flooring and construction that need to have a long life. Lignin present in softwood usually has more coniferyl alcohol (75%) and less p-coumaryl (5%) and sinapyl alcohol content (20%) than that present in hardwood (50, 10 and 40%, respectively; [24]).

Lignin in biomass may be valued through the generation of thermal and electric power as well as the production of materials and chemicals (**Figure 2**). Here, we focus on industrial uses of biomass-containing lignin and processed or extracted lignin. Therefore, we focus on sawmill, agroindustrial and agricultural activities. Concerning forestry activities in sawmills, we refer to FAO definitions. Please keep in mind that there is not sufficient data and mass balance may be not complete. Hence, roundwood refers to all quantities of woods removed from trees inside the forests and from trees outside the forests. It includes all woods removed with or without bark, including woods removed in its round form or split form and considered fuel wood, sawlogs and veneer

**Figure 2.** Scheme of lignin uses.

logs, wood pulp, round and split and other industrial roundwood. All fuel wood is roundwood that will be used for cooking, heating or power production, while wood pulp is the fibrous material prepared from pulpwood, wood chips, particles, residues or recovered paper by mechanical and/or chemical processes for the manufacturing of paper and other cellulose products [13].

According to FAO, the world production of industrial roundwood, wood fuel and wood pulp is shown in **Table 2**. This forestry biomass might be considered as the available raw material for processing into power, materials, chemicals and fuels. If we look at specific countries, USA and China lead the potential production of roundwood in coming years (**Figure 3**). Nevertheless, European countries such as France and UK as well as Latin American countries such as Chile and Mexico together represent the potential production of China but with a smaller population.

**Figure 3.** Industrial roundwood potential production in selected countries between 2020 and 2050.

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**Figure 4.** Lignin potential production from roundwood products in selected countries (1000 cubic meters; [13]).

Regarding regional plant production, *Agave* is a succulent genus belongs to the monocot family Agavaceae [29] and the most important plants in Mexico are *A. tequilana*, *A. angustifolia*, and *A. atrovirens,* which are used for the production of spirit and fermented non-distilled beverages such as Tequila, Mezcal and Pulque, respectively. Agave plants have a lower content of lignin ranging from 7 to 16% [18, 29], and are considered easier to process when compared to wood species (lignin content around 30%) and Gramineae such as cane sugar, corn, wheat (lignin content around 18–22%).

As we mentioned earlier, lignin is the third most abundant biopolymer on earth, when we assess the occurrence on superior plants and it plays an important role in the transition energy global agenda (**Figure 4**). OECD countries, in **Figure 4**, possess an interesting potential of roundwood-derived lignin production that can help to achieve the Paris 21st COP's agreement.

**Table 2.** World production of roundwood, fuel wood and wood pulp [13].

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**Figure 3.** Industrial roundwood potential production in selected countries between 2020 and 2050.

logs, wood pulp, round and split and other industrial roundwood. All fuel wood is roundwood that will be used for cooking, heating or power production, while wood pulp is the fibrous material prepared from pulpwood, wood chips, particles, residues or recovered paper by mechanical and/or chemical processes for the manufacturing of paper and other cellulose products [13].

According to FAO, the world production of industrial roundwood, wood fuel and wood pulp is shown in **Table 2**. This forestry biomass might be considered as the available raw material for processing into power, materials, chemicals and fuels. If we look at specific countries, USA and China lead the potential production of roundwood in coming years (**Figure 3**). Nevertheless, European countries such as France and UK as well as Latin American countries such as Chile and Mexico together represent the potential production of China but with a smaller population. Regarding regional plant production, *Agave* is a succulent genus belongs to the monocot family Agavaceae [29] and the most important plants in Mexico are *A. tequilana*, *A. angustifolia*, and *A. atrovirens,* which are used for the production of spirit and fermented non-distilled beverages such as Tequila, Mezcal and Pulque, respectively. Agave plants have a lower content of lignin ranging from 7 to 16% [18, 29], and are considered easier to process when compared to wood species (lignin content around 30%) and Gramineae such as cane sugar, corn, wheat

As we mentioned earlier, lignin is the third most abundant biopolymer on earth, when we assess the occurrence on superior plants and it plays an important role in the transition energy global agenda (**Figure 4**). OECD countries, in **Figure 4**, possess an interesting potential of roundwood-derived lignin production that can help to achieve the Paris 21st COP's agreement.

**) World production (metric tons)**

(lignin content around 18–22%).

**Figure 2.** Scheme of lignin uses.

148 Lignin - Trends and Applications

**Wood product World production (thousand m3**

Roundwood 1.836,541 1,240,906 Wood fuel 1.863.828 1,259,343 Wood pulp 255,930 172,926

**Table 2.** World production of roundwood, fuel wood and wood pulp [13].

**Figure 4.** Lignin potential production from roundwood products in selected countries (1000 cubic meters; [13]).

**Figure 5.** Sugarcane production in selected countries in 2013 and estimation of lignin content based on own data [30].

Sugarcane is another interesting crop since its industrial processing is already done in an integrated biorefinery, where all plant is valued into sugar, molasses, heat and electric power, and in some cases, into ethanol as oxygenated agent in gasoline (**Figure 5**). Indeed, since the earlier 1970s, countries like Brazil has undergone an intensive program of sugarcane production because there is an enormous need of alternative fuel for gasoline, considering Brazil's dependency of oil and gas importations during that time. Other countries like India, Mexico and, in a lesser extent, the USA produce sugarcane and sugarcanerelated products but they also have an important potential of value-added lignin from the bagasse.

**3. Generation of heat and power**

**Figure 6.** Maize and wheat production in selected countries in 2014 [13].

Mexican Network in Spanish; [15].

According to the Chemical Sciences Roundtable of the National Research Council [21], burning biomass to produce energy and heat is nothing new, but doing so at a large scale still cannot economically compete with coal and natural gas. Local, small-scale biomass-to-power systems may prove to be the most efficient way of generating energy from biomass. Already, small-scale production of biogas from biomass and on-site co-generation of electricity and heat is widespread in Europe. Farm-sized units are in operation in the United States as well. One interesting example is sugarcane-producing mills which find its residue, sugarcane bagasse, a reliable and affordable source of thermal and power generation for auto-consumption needs with an installed capacity between 10 and 50 MW. Sugarcane has 16% of fiber or bagasse (dry basis) with almost 9% of lignin ([1, 6, 18]; see **Figure 5**). Then, we estimated the potential energy supply considering a caloric value of 19.1 GJ/ton for sugarcane bagasse (see **Table 1** and **Figure 7**). We obtained for Mexico, a 188 PJ/year potential energy from sugarcane bagasse, which is lower but within the range reported by IRENA and REMBIO (Bioenergy

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Traditional crops such as maize and wheat may be considered as a source of biomass and lignin for energy and chemical production (**Figure 6**). Their production is spread all around the world but some countries like Mexico has forbidden the use of cereal grains, rich in starch and considered as a cultural value, for energy uses. Nevertheless, we must consider that such biomass already has conventional and important value-added uses in land fertility, erosion mitigation and livestock breeding. The partial use of such biomass may be accompanied with integral policies that protect and assure the quality of renewable soil as well as the mitigation of disturbance on conventional value chains and stakeholders.

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**Figure 6.** Maize and wheat production in selected countries in 2014 [13].

#### **3. Generation of heat and power**

**Figure 5.** Sugarcane production in selected countries in 2013 and estimation of lignin content based on own data [30].

Sugarcane is another interesting crop since its industrial processing is already done in an integrated biorefinery, where all plant is valued into sugar, molasses, heat and electric power, and in some cases, into ethanol as oxygenated agent in gasoline (**Figure 5**). Indeed, since the earlier 1970s, countries like Brazil has undergone an intensive program of sugarcane production because there is an enormous need of alternative fuel for gasoline, considering Brazil's dependency of oil and gas importations during that time. Other countries like India, Mexico and, in a lesser extent, the USA produce sugarcane and sugarcanerelated products but they also have an important potential of value-added lignin from the

Traditional crops such as maize and wheat may be considered as a source of biomass and lignin for energy and chemical production (**Figure 6**). Their production is spread all around the world but some countries like Mexico has forbidden the use of cereal grains, rich in starch and considered as a cultural value, for energy uses. Nevertheless, we must consider that such biomass already has conventional and important value-added uses in land fertility, erosion mitigation and livestock breeding. The partial use of such biomass may be accompanied with integral policies that protect and assure the quality of renewable soil as well as the mitigation of disturbance on conventional value chains and

bagasse.

150 Lignin - Trends and Applications

stakeholders.

According to the Chemical Sciences Roundtable of the National Research Council [21], burning biomass to produce energy and heat is nothing new, but doing so at a large scale still cannot economically compete with coal and natural gas. Local, small-scale biomass-to-power systems may prove to be the most efficient way of generating energy from biomass. Already, small-scale production of biogas from biomass and on-site co-generation of electricity and heat is widespread in Europe. Farm-sized units are in operation in the United States as well. One interesting example is sugarcane-producing mills which find its residue, sugarcane bagasse, a reliable and affordable source of thermal and power generation for auto-consumption needs with an installed capacity between 10 and 50 MW. Sugarcane has 16% of fiber or bagasse (dry basis) with almost 9% of lignin ([1, 6, 18]; see **Figure 5**). Then, we estimated the potential energy supply considering a caloric value of 19.1 GJ/ton for sugarcane bagasse (see **Table 1** and **Figure 7**). We obtained for Mexico, a 188 PJ/year potential energy from sugarcane bagasse, which is lower but within the range reported by IRENA and REMBIO (Bioenergy Mexican Network in Spanish; [15].

**Figure 7.** Potential energy from sugarcane bagasse and its isolated lignin in main producing countries.

In developing countries such as Mexico, Chile and even China, the predominant fuel in rural areas is still wood fuel from forest clearing and recollection (**Figure 8**), but traditional generation of heat for cooking through open fires or stoves generates a lot of smoke, carbon black, has low conversion efficiencies with 10–20%, and biomass is often sourced unsustainably. On the other hand, industrialized countries have developed more sophisticated forms as pellets and bricks produced from wood processing industries [20].

Nowadays, the biomass feedstock can be quiet different depending on regional or international distribution for specific needs and consumptions like residential (<0.5 MW) to medium (0.5–10 MW) and large plant power capacities (>10 MW; **Table 3**). According to International Energy Agency (IEA) [16], residential thermal generation as well as medium and large power generation with biomass is already economic and environmental competitive with other fuels such as coal and natural gas.

Indeed, renewable energies for heat and power generation are increasingly competing with fossil fuels since the reduction of capex and opex costs altogether with their better performance, even without government subsidies but carbon tax implementation might accelerate their adoption. Many factors affect the capital cost for renewable project including market, government policy, technology availability and maturity and capacity factors such as scale size. Solar photovoltaic and wind are considered as raw feedstock, free in contrast with the heat and power generation from biomass where its availability, logistics, conditioning, quality/volume, regulatory issues

among others affect its cost as energy source. These costs may hugely vary depending also on scale and country, but some weighted costs show that all three technologies may compete on the field but government policy must assure equal conditions based on competitiveness (**Figure 9**). We observed that biomass is one of the more competitive alternatives for power generation in all world regions in contrast with fossil fuels and other renewable energies, but usually the lack of

**Figure 8.** Wood fuel potential production in selected countries between 2020 and 2050.

**husk**

Plant capacity 0.5–50 0.5–50 10–50 50

**Table 3.** Some biomass feedstocks to produce power and heat, and related costs [16].

Capex (USD/kW) 6000–9800 6000–9800 3900–5800 2400–4200

**Wastes Processing residues Locally collected**

**Timber residues, black liquor, bagasse, rice**

<0 0–4 4–8 8–12

14–18 14–18 18–33 28–40

**feedstocks**

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**crops**

**Agricultural residues, roundwood, energy**

**Internationally traded**

**Roundwood, wood chips, biomass pellets,**

**feedstocks**

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**biomethane**

**Biomass**

Feedstock costs (USD/

Typical power generation efficiency

GJ)

(%)

**Organic waste, sewage sludge, manure**

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**Figure 8.** Wood fuel potential production in selected countries between 2020 and 2050.

In developing countries such as Mexico, Chile and even China, the predominant fuel in rural areas is still wood fuel from forest clearing and recollection (**Figure 8**), but traditional generation of heat for cooking through open fires or stoves generates a lot of smoke, carbon black, has low conversion efficiencies with 10–20%, and biomass is often sourced unsustainably. On the other hand, industrialized countries have developed more sophisticated forms as pellets

**Figure 7.** Potential energy from sugarcane bagasse and its isolated lignin in main producing countries.

Nowadays, the biomass feedstock can be quiet different depending on regional or international distribution for specific needs and consumptions like residential (<0.5 MW) to medium (0.5–10 MW) and large plant power capacities (>10 MW; **Table 3**). According to International Energy Agency (IEA) [16], residential thermal generation as well as medium and large power generation with biomass is already economic and environmental competitive with other fuels

Indeed, renewable energies for heat and power generation are increasingly competing with fossil fuels since the reduction of capex and opex costs altogether with their better performance, even without government subsidies but carbon tax implementation might accelerate their adoption. Many factors affect the capital cost for renewable project including market, government policy, technology availability and maturity and capacity factors such as scale size. Solar photovoltaic and wind are considered as raw feedstock, free in contrast with the heat and power generation from biomass where its availability, logistics, conditioning, quality/volume, regulatory issues

and bricks produced from wood processing industries [20].

such as coal and natural gas.

152 Lignin - Trends and Applications

**Table 3.** Some biomass feedstocks to produce power and heat, and related costs [16].

among others affect its cost as energy source. These costs may hugely vary depending also on scale and country, but some weighted costs show that all three technologies may compete on the field but government policy must assure equal conditions based on competitiveness (**Figure 9**). We observed that biomass is one of the more competitive alternatives for power generation in all world regions in contrast with fossil fuels and other renewable energies, but usually the lack of

Krfat lignin is used in oil refineries as carbon crackers, cement additive and production of biofuels, BTX and other specialty chemicals such as vanillin and phenols. Lignosulfonate chemical is used in textile industries, thanks to its water solubility and functional properties as binders, dispersants, emulsifying and complexing agents. Nevertheless, the need for a sulfur-free agent is reconsidering lignosulfonate market hegemony for cleaner and sustainable sources of lignin [5]. Lignin may also be recovered by solubilizing the recalcitrant crystalline cellulose and amorphous hemicellulose using chemical, thermochemical, biological and/or enzymatic approaches [3, 7, 19, 23, 25]. We have recently developed a mixed chemical-enzymatic pretreatment of lignocellulosics to solubilize almost all cellulose and hemicellulose, except a lignin-rich polymer as seen by FTIR analysis (**Figure 11**). Indeed, we can see the empty cells where cellulose used to be leaving an interesting hole material with infrared characteristic signals at 4000–2500 cm−1 νO─H,1700–1740 cm−1 νC═O carbonyl and carboxylic groups, 1590–1610 cm−1 νC═C aromatic

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**Figure 10.** Scheme of conventional production of lignin derivatives in paper industry.

Here, lignin might be the source of materials, energy, biofuels or bio-based chemicals but we may consider two routes to achieve this: (1) its conditioning to obtain materials or bioenergy and (2) its depolymerization followed by conversion to polymers, fuels or bulk or fine chemicals (**Figure 12**). The simplest approach considers a biorefinery where lignin may serve as an energy source through direct combustion, gasification or pyrolysis, as discussed later in the section, but also for the production of materials such as activated carbon and/or biochar [8, 14]. Indeed, biochar production during pyrolysis of biomass or the fraction of lignin must be considered in an integrated biorefinery, where it helps for the economy and environmental impact of the whole process. Additional studies are needed in order to quantify the carbon capture by soil and

The present and future transition into a less depending fossil fuels economy needs not only renewable energy but also renewable raw materials like biomass and lignin to satisfy the need for materials and chemicals used in our everyday life. Biomass is the only renewable source known today that may support not only the generation of heat and electric power but also the processing and manufacturing of fuels and goods. Solar energy also has indeed the potential to achieve this; it does every day in leaves, algae and microorganisms such as microalgae and cyanobacteria [2]. Nevertheless, its development is still incipient but full of encouraging challenges.

emissions due to bio-oil displacement of fossil fuels and decreased

emission from soils by better soil aeration [5, 17].

skeletal and 1126 cm−1 νC─O─C ether groups.

microbes, reduction of CO2

use of fertilizers, as well as reduction of NOx

**Figure 9.** Weighted average cost of electricity (USD/kWh) by world regions and compared with fossil fuel power generation costs [15, 16].

an affordable and reliable source of biomass, related with social issues, may increase considerable associated risk, which makes the credits and the biomass costs more expensive. Wood- and lignin-based biomass might play an important role in the generation of sustainable heat and power, but they are needed policies that help to transit on this sinuous road.

### **4. Chemicals and fuels**

Lignin as a polymeric material and pulping wood derivative has followed the development of paper industry all around the world since the end of nineteenth century. In such industry, lignin must be separated in order to get access to the more valuable cellulose. Hence, the alkali and acidic procedures are the more expanded method in industry and they allow obtaining of lignin derivatives such as alkali, kraft, lignosulfonate and organosolv lignin, respectively (**Figure 10**). An effective method to separate lignin is the organosolv process, which uses alcohol mixtures with water at high temperature near 200°C, sometimes with the aid of an alkali or acid in order to improve the lignin removal and wood pulp quality. Today, by far Kraft lignin dominates the market over lignosulfonate and organosolv lignin with a 90% share.

**Figure 10.** Scheme of conventional production of lignin derivatives in paper industry.

an affordable and reliable source of biomass, related with social issues, may increase considerable associated risk, which makes the credits and the biomass costs more expensive. Wood- and lignin-based biomass might play an important role in the generation of sustainable heat and

**Figure 9.** Weighted average cost of electricity (USD/kWh) by world regions and compared with fossil fuel power

Lignin as a polymeric material and pulping wood derivative has followed the development of paper industry all around the world since the end of nineteenth century. In such industry, lignin must be separated in order to get access to the more valuable cellulose. Hence, the alkali and acidic procedures are the more expanded method in industry and they allow obtaining of lignin derivatives such as alkali, kraft, lignosulfonate and organosolv lignin, respectively (**Figure 10**). An effective method to separate lignin is the organosolv process, which uses alcohol mixtures with water at high temperature near 200°C, sometimes with the aid of an alkali or acid in order to improve the lignin removal and wood pulp quality. Today, by far Kraft lignin dominates the market over lignosulfonate and organosolv lignin

power, but they are needed policies that help to transit on this sinuous road.

**4. Chemicals and fuels**

generation costs [15, 16].

154 Lignin - Trends and Applications

with a 90% share.

Krfat lignin is used in oil refineries as carbon crackers, cement additive and production of biofuels, BTX and other specialty chemicals such as vanillin and phenols. Lignosulfonate chemical is used in textile industries, thanks to its water solubility and functional properties as binders, dispersants, emulsifying and complexing agents. Nevertheless, the need for a sulfur-free agent is reconsidering lignosulfonate market hegemony for cleaner and sustainable sources of lignin [5].

Lignin may also be recovered by solubilizing the recalcitrant crystalline cellulose and amorphous hemicellulose using chemical, thermochemical, biological and/or enzymatic approaches [3, 7, 19, 23, 25]. We have recently developed a mixed chemical-enzymatic pretreatment of lignocellulosics to solubilize almost all cellulose and hemicellulose, except a lignin-rich polymer as seen by FTIR analysis (**Figure 11**). Indeed, we can see the empty cells where cellulose used to be leaving an interesting hole material with infrared characteristic signals at 4000–2500 cm−1 νO─H,1700–1740 cm−1 νC═O carbonyl and carboxylic groups, 1590–1610 cm−1 νC═C aromatic skeletal and 1126 cm−1 νC─O─C ether groups.

Here, lignin might be the source of materials, energy, biofuels or bio-based chemicals but we may consider two routes to achieve this: (1) its conditioning to obtain materials or bioenergy and (2) its depolymerization followed by conversion to polymers, fuels or bulk or fine chemicals (**Figure 12**). The simplest approach considers a biorefinery where lignin may serve as an energy source through direct combustion, gasification or pyrolysis, as discussed later in the section, but also for the production of materials such as activated carbon and/or biochar [8, 14].

Indeed, biochar production during pyrolysis of biomass or the fraction of lignin must be considered in an integrated biorefinery, where it helps for the economy and environmental impact of the whole process. Additional studies are needed in order to quantify the carbon capture by soil and microbes, reduction of CO2 emissions due to bio-oil displacement of fossil fuels and decreased use of fertilizers, as well as reduction of NOx emission from soils by better soil aeration [5, 17].

The present and future transition into a less depending fossil fuels economy needs not only renewable energy but also renewable raw materials like biomass and lignin to satisfy the need for materials and chemicals used in our everyday life. Biomass is the only renewable source known today that may support not only the generation of heat and electric power but also the processing and manufacturing of fuels and goods. Solar energy also has indeed the potential to achieve this; it does every day in leaves, algae and microorganisms such as microalgae and cyanobacteria [2]. Nevertheless, its development is still incipient but full of encouraging challenges.

**Figure 11.** Scanning electronic micrographs of sugarcane bagasse before (top left) and after (top right) chemical and enzymatic pretreatment. FTIR spectra of pretreated (a) sugarcane bagasse, (b) lignosulfonate lignin and (c) alkali lignin.

**Figure 12.** Scheme of conventional and potential products from lignin. BTX: benzene, toluene and xylene isomers and

**Market niches Lignin derivative Market volume (Mtons/year) Price (USD/ton)**

Specialized chemicals Lignin-based vanillin 3200 1200

Commodity chemicals BTX 102 1200

**Table 4.** Market volumes (Mtons) and price (USD/tons) of some conventional and emerging chemicals and fuels [26].

Biofuels and fuels Bio-jet fuel-based on lignin/

biomass

Lignosulfonates 1,000,000 350 Kraft lignin 100,000 364 Organosolv lignin 1000 919

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Crude oil-based vanillin 12,800 1200 Natural vanillin 60 600,000

Phenol 8 1500

Fossil oil-based jet fuel 252,456 400

1–50% in mix with fossil jet fuel 1300–6400

DMSO: dimethyl sulfoxide.

Conventional paper related

derivatives

A modern and integrated biorefinery will process low-value biomass into energy for selfconsumption and export excess to the grid. More valuable biomass may be used for the production of edible or nonedible oils, protein-rich flour for fish/shrimp farms and used to convert the lignocellulosics into fuels and chemicals [4]. We have identified four additional market niches for lignin derivatives: (1) conventional paper-related derivatives; (2) specialized chemicals; (3) commodity chemicals; and (4) biofuels (**Table 4**).The first two have already established markets since low value-added generic industrials to high value-added flavor and fragrance additives. The latter use has a high demanding worldwide market for aromatic and phenolbased compounds that may be obtained from lignin. This approach must be considered in a biorefinery scheme since their high price may account for the financial sustainability and competiveness of the business. Indeed, the flavor and fragrance industry may reconsider inverting the balance between the use of aromatic compounds from fossil source against biomass or lignin raw materials, that is, compounds like phenylacetic acid, benzoates, phenylacetates, cinnamates, phenols, phenyl esters, alcohols and ethers, among many others [27].

In present and near future terms, biorefineries must be additionally considered to balance the production of biofuels and chemicals that can be used without any or less change in current Conversion of Lignin to Heat and Power, Chemicals or Fuels into the Transition Energy Strategy http://dx.doi.org/10.5772/intechopen.71211 157

**Figure 12.** Scheme of conventional and potential products from lignin. BTX: benzene, toluene and xylene isomers and DMSO: dimethyl sulfoxide.

A modern and integrated biorefinery will process low-value biomass into energy for selfconsumption and export excess to the grid. More valuable biomass may be used for the production of edible or nonedible oils, protein-rich flour for fish/shrimp farms and used to convert the lignocellulosics into fuels and chemicals [4]. We have identified four additional market niches for lignin derivatives: (1) conventional paper-related derivatives; (2) specialized chemicals; (3) commodity chemicals; and (4) biofuels (**Table 4**).The first two have already established markets since low value-added generic industrials to high value-added flavor and fragrance additives. The latter use has a high demanding worldwide market for aromatic and phenolbased compounds that may be obtained from lignin. This approach must be considered in a biorefinery scheme since their high price may account for the financial sustainability and competiveness of the business. Indeed, the flavor and fragrance industry may reconsider inverting the balance between the use of aromatic compounds from fossil source against biomass or lignin raw materials, that is, compounds like phenylacetic acid, benzoates, phenylacetates, cin-

**Figure 11.** Scanning electronic micrographs of sugarcane bagasse before (top left) and after (top right) chemical and enzymatic pretreatment. FTIR spectra of pretreated (a) sugarcane bagasse, (b) lignosulfonate lignin and (c) alkali lignin.

156 Lignin - Trends and Applications

namates, phenols, phenyl esters, alcohols and ethers, among many others [27].

In present and near future terms, biorefineries must be additionally considered to balance the production of biofuels and chemicals that can be used without any or less change in current

**Table 4.** Market volumes (Mtons) and price (USD/tons) of some conventional and emerging chemicals and fuels [26].

established technologies, known as drop-in fuels and chemicals. In this sense, lignin as a source of chemical compounds such as benzene, toluene, and xylenes might be relevant today to some petrochemical platforms but the demand is insignificant related to other higher volume markets as biofuels or specialized chemicals. Additionally, environmental and health issues will certainly become more stringent in near future, limiting the use of such compounds. Nevertheless, the society will need more advanced chemicals, building units, and materials, and lignin may be a reliable and sustainable source of new upcoming technology platforms.

[2] Alstrum-Acevedo JH, Brennaman MK, Meyer TJ. Chemical approaches to artificial pho-

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[3] Amezcua-Allieri M, Gutiérrez-Villegas JC, Aburto J. Combustibles avanzados de aviación. Instituto Mexicano del Petróleo, Copyrights 03-2017-022410275400-01; 2017. Available online on: http://rtbioenergia.org.mx/wp-content/uploads/2016/12/Divulgacion\_Biojetfuel-

[4] Amezcua-Allieri M, Sánchez-Durán T, Aburto J. Study of chemical and enzymatic hydrolysis of cellulosic material to obtain fermentable sugars. Journal of Chemistry. 2017;**9**.

[5] Azadi P, Inderwildi OR, Farnood R, King DA. Liquid fuels, hydrogen and chemicals from lignin: A critical review. Renewable and Sustainable Energy Reviews. 2013;**21**:506-523 [6] Barrera I, Amezcua-Allieri MA, Estupiñan L, Martínez T, Aburto J. Technical and economical evaluation of bioethanol production from lignocellulosic residues in Mexico: Case of sugar cane and blue agave bagasses. Chemical Engineering Research and

[7] Barrera I, Guzmán N, Peña E, Vázquez T, Cerón-Camacho R, Folch J, Honorato J, Aburto J. Ozonolysis of alkaline lignin and sugarcane bagasse: Structural changes and their effect

[8] Carrot SPJM, Ribeiro-Carrott MML. Lignin—From natural adsorbent to activated car-

[9] Demirbas A. Energy Sources Part A: Recovery Utilization and Environmental Effects.

[10] Chen Z, Wan C. Biological valorization for converting lignin into fuels and chemicals.

[11] Bilal M, Asgher M, Iqbal HMN, Hu H, Zhang H. Biotransformation of lignocellulosic materials into value-added products: A review. International Journal of Biological

[12] Ebringerová A. Structural diversity and application potential of hemicelluloses. Macro-

[13] Food and Agriculture Organization of the United Nations (FAO). Forest products. In:

[14] Holladay JE, Bozell JJ, White JF, Johnson D. Top value-added chemicals from biomass. In: Volume II. Results of screenings for potential candidates from biorefinery lignin. Pacific Northwest National Laboratory. United States of America: PNNL-16983; 2007

[15] International Energy Agency (IEA). Renewable power generation costs in 2014. 2015

[16] International Energy Agency (IEA). Technology roadmap. Bioenergy for heat and power;

on saccharification. Biomass and Bioenergy. 2017;**94**:167-172

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tosynthesis. 2. Inorg. Chem. 2005;**44**(20):6802-6827

booklet-vf.pdf [consulted on May 2017]

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2017;**39**(8):754-760

2012

Macromolecules. 2017;**98**:447-458

molecular Symposia. 2006;**232**:1-12

FAO Statistics Series Co. 205. 2014. Rome, 2016

Article ID 5680105. DOI: 10.1155/2017/5680105

Lignin-based biofuels may be obtained basically from three routes: (1) hydrothermal depolymerization and excess oxygen elimination; (2) slow or fast pyrolysis to depolymerize the lignin into a bio-oil that must be processed to eliminate excess of oxygen, and (3) gasification followed by biomass to liquids (BTL) process or Fischer-Tropsch process for the obtention of different fuel fractions or even alcohols [3, 28]. Even if these technologies represent the today and near future options to satisfy the need for clean, sustainable and neutral carbon fuels; the real issue is the deployment of such technologies and their spread adoption in order to comply with the world weather change commitments.

### **5. Final remarks**

Lignin is a versatile polyphenol raw material comporting a significant presence in biomass. Due to its chemical nature, it is difficult to isolate and process into chemical commodities, specialized chemicals, thermal and/or electric power and also advanced biofuels. The actual energy transition requires a significant change of paradigm between the past unsustainable fossil energy source to more advanced environmental, health and socially committed sources of reliable, renewable and sustainable forms of energy; among those, bioenergy from biomass and lignin will play an important role. As a part of biomass, lignin has plenty of potential uses in a modern bio-based economy, from conventional paper products to more challenging processes such as its conversion to useful chemicals, materials, and clean biofuels in a biorefinery scheme.

### **Author details**

Myriam Adela Amezcua-Allieri and Jorge Aburto\*

\*Address all correspondence to<EMAIL_ADDRESS>
Division of Biomass Conversion, Instituto Mexicano del Petróleo, Mexico City, Mexico

### **References**

[1] Aburto J, Martínez T, Murrieta F. Technical and economical evaluation of bioethanol production from lignocellulosic residues. Tecnología, Ciencia, Educación. 2008;**23**(1):23-30

[2] Alstrum-Acevedo JH, Brennaman MK, Meyer TJ. Chemical approaches to artificial photosynthesis. 2. Inorg. Chem. 2005;**44**(20):6802-6827

established technologies, known as drop-in fuels and chemicals. In this sense, lignin as a source of chemical compounds such as benzene, toluene, and xylenes might be relevant today to some petrochemical platforms but the demand is insignificant related to other higher volume markets as biofuels or specialized chemicals. Additionally, environmental and health issues will certainly become more stringent in near future, limiting the use of such compounds. Nevertheless, the society will need more advanced chemicals, building units, and materials, and lignin may

Lignin-based biofuels may be obtained basically from three routes: (1) hydrothermal depolymerization and excess oxygen elimination; (2) slow or fast pyrolysis to depolymerize the lignin into a bio-oil that must be processed to eliminate excess of oxygen, and (3) gasification followed by biomass to liquids (BTL) process or Fischer-Tropsch process for the obtention of different fuel fractions or even alcohols [3, 28]. Even if these technologies represent the today and near future options to satisfy the need for clean, sustainable and neutral carbon fuels; the real issue is the deployment of such technologies and their spread adoption in order to com-

Lignin is a versatile polyphenol raw material comporting a significant presence in biomass. Due to its chemical nature, it is difficult to isolate and process into chemical commodities, specialized chemicals, thermal and/or electric power and also advanced biofuels. The actual energy transition requires a significant change of paradigm between the past unsustainable fossil energy source to more advanced environmental, health and socially committed sources of reliable, renewable and sustainable forms of energy; among those, bioenergy from biomass and lignin will play an important role. As a part of biomass, lignin has plenty of potential uses in a modern bio-based economy, from conventional paper products to more challenging processes such as its conversion to useful chemicals, materials, and clean biofuels in a biorefinery scheme.

Division of Biomass Conversion, Instituto Mexicano del Petróleo, Mexico City, Mexico

[1] Aburto J, Martínez T, Murrieta F. Technical and economical evaluation of bioethanol production from lignocellulosic residues. Tecnología, Ciencia, Educación. 2008;**23**(1):23-30

be a reliable and sustainable source of new upcoming technology platforms.

ply with the world weather change commitments.

Myriam Adela Amezcua-Allieri and Jorge Aburto\* \*Address all correspondence to<EMAIL_ADDRESS>
**5. Final remarks**

158 Lignin - Trends and Applications

**Author details**

**References**

[17] Laird DA, Brown RC, Amonette JE, Lehmann J. Review of the pyrolysis platform for coproducing bio-oil and biochar. Biofuels, Bioproducts and Biorefining. 2009;**3**(5):547-562

**Chapter 7**

**Provisional chapter**

**Biomass Gasification: A Review of Its Technology, Gas**

Gasification technology presents one option for energy-conversion technique from woody biomass contaminated by radionuclides released in March 2011 during the Fukushima Dai-ichi Nuclear Power Plant accident. The gasification process converts carbonaceous materials into combustible gases, carbon dioxide, and residues. Owing to their smallscale distributed configuration, woody biomass gasification plants are suitable for gasifying Japan's biomass and have been installed increasingly in Japan recently. This chapter reviews current trends of gasification and life cycle assessment (LCA) of total systems,

**Keywords:** biomass gasification, gas cleaning, desulphurisation, radioactive materials,

Lignin is a crosslinked macromolecular material based on a phenylpropanoid monomer structure. Vascular plant species such as fern-related plants, gymnosperms, and angiosperms have lignin structures. Woody plants such as softwoods and hardwoods are composed, respectively, of 25–35% and 20–25%. Recently, small-scale woody biomass power generation plants have been installed increasingly in Japan. Such plants are suitable for gasifying Japan's

To utilise small-scale biomass more effectively, biomass plants must be installed near energy source and demand sites in order to shorten transport distances. This is especially effective for small-scale woody biomass plants. Here small scale is defined as a plant scale of at most

biomass because of their small-scale, distributed characteristics.

**Biomass Gasification: A Review of Its Technology, Gas**

DOI: 10.5772/intechopen.70727

© 2016 The Author(s). Licensee InTech. 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,

© 2018 The Author(s). Licensee InTech. 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.

and reproduction in any medium, provided the original work is properly cited.

**Cleaning Applications, and Total System Life Cycle**

**Cleaning Applications, and Total System Life Cycle**

**Analysis**

**Analysis**

Kenji Koido and Takahiro Iwasaki

Kenji Koido and Takahiro Iwasaki

http://dx.doi.org/10.5772/intechopen.70727

including gas cleaning.

life cycle assessment

**1. Introduction**

**Abstract**

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

**Provisional chapter**

### **Biomass Gasification: A Review of Its Technology, Gas Cleaning Applications, and Total System Life Cycle Analysis Cleaning Applications, and Total System Life Cycle Analysis**

**Biomass Gasification: A Review of Its Technology, Gas**

DOI: 10.5772/intechopen.70727

Kenji Koido and Takahiro Iwasaki Kenji Koido and Takahiro Iwasaki Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.70727

#### **Abstract**

[17] Laird DA, Brown RC, Amonette JE, Lehmann J. Review of the pyrolysis platform for coproducing bio-oil and biochar. Biofuels, Bioproducts and Biorefining. 2009;**3**(5):547-562

[18] Honorato A, Trejo S, Aburto J. Base de datos de materiales lignocelulósicos. Project

[19] Merino Pérez O, Almazán V, Martínez-Palou R, Aburto J. Screening of ionic liquids for pretreatment of Taiwan grass in Q-Tube minireactors for improving bioethanol produc-

[20] Mustafa B, Kahraman B. Wood as an Energy Source: Potential Trends, Usage of Wood, and Energy Politics. Energy Sources, Part A: Recovery, Utilization, and Environmental

[21] National Research Council (US). Chemical Sciences Roundtable. Opportunities and Obstacles in Large-Scale Biomass Utilization. The Role of the Chemical Sciences and Engineering Communities A Workshop Summary. Washington, DC: National

Academies Press (US). ISBN-13: 978-0-309-27864-5 ISBN-10: 0-309-27864-3; 2012

[23] Rabemanolontsoa H, Saka S. Various pretreatments of lignocellulosics. Bioresource

[24] Saka S. Chapter 2. Chemical composition and distribution. In: NSH D, Nobuoi S, editors. Wood and Cellulosic Chemistry. 2nd ed. New York: Marcel Dekker, Inc.; 2000

[25] Sindhu R, Binod P, Pandey A. Biological pretreatment of lignocellulosic biomass – An

[26] Smolarski N. High-Value Opportunities for Lignin: Unlocking its Potential. Frost & Sullivan; 2012. Available online on: https://www.greenmaterials.fr/wp-content/ uploads/2013/01/high-value-opportunities-for-lignin-unlocking-its-potential-market-

[27] Surburg H, Panten J. Common Fragrance and Flavor Materials. 5th ed. Weinheim:

[28] Wang W-C, Tao L, Markham J, Zhang Y, Tan E, Batan L, Warner E, Biddy M. Review of biojett fuel conversion technologies. In: Technical Report NREL/TP-5100-66291. National Renewable Energy Laboratory (NREL), United States of America; 2016. Available online

[29] Escamilla-Treviño LL. Potential of plants from the Genus Agave as bioenergy crops.

[30] Unión Nacional de Cañeros. http://caneros.org.mx/ Consuted online on July 2017

on: www.nrel.gov/publications Consulted online on June 2017

Bioenergy Research. United States of America. 2012;**5**(1):1-9

[22] O'Sullivan AC. Cellulose: The structure slowly unravels. Cellulose. 1997;**4**:173-207

151370. Mexico: CONACyT; 2017

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Effects. 2006;**28**(9):837-844

Technology. 2016;**199**:83-91

Wiley-VCH Verlag; 2006

tion. Waste and Biomass Valorization. 2016;**8**(3):733-742

overview. Bioresource Technology. 2016;**199**:76-82

insights.pdf Consulted online May 2017

Gasification technology presents one option for energy-conversion technique from woody biomass contaminated by radionuclides released in March 2011 during the Fukushima Dai-ichi Nuclear Power Plant accident. The gasification process converts carbonaceous materials into combustible gases, carbon dioxide, and residues. Owing to their smallscale distributed configuration, woody biomass gasification plants are suitable for gasifying Japan's biomass and have been installed increasingly in Japan recently. This chapter reviews current trends of gasification and life cycle assessment (LCA) of total systems, including gas cleaning.

**Keywords:** biomass gasification, gas cleaning, desulphurisation, radioactive materials, life cycle assessment

### **1. Introduction**

Lignin is a crosslinked macromolecular material based on a phenylpropanoid monomer structure. Vascular plant species such as fern-related plants, gymnosperms, and angiosperms have lignin structures. Woody plants such as softwoods and hardwoods are composed, respectively, of 25–35% and 20–25%. Recently, small-scale woody biomass power generation plants have been installed increasingly in Japan. Such plants are suitable for gasifying Japan's biomass because of their small-scale, distributed characteristics.

To utilise small-scale biomass more effectively, biomass plants must be installed near energy source and demand sites in order to shorten transport distances. This is especially effective for small-scale woody biomass plants. Here small scale is defined as a plant scale of at most

2 MWe. Power generation in such small-scale plants requires biomass gasification technology in order to obtain higher thermal efficiency. Gasification is a process that converts carbonaceous materials into carbon monoxide, hydrogen, carbon dioxide, and gaseous hydrocarbons (producer gas). Producer gas can be supplied as fuel to internal combustion engines and power generators. To maximise the efficiency of woody biomass conversion, producer gas should be utilised not only for power generation but also for thermal production from the producer gas' sensible heat. Cogeneration system for heat and power production is called combined heat and power (CHP).

Recently, many kinds of biomass gasification combined heat and power (BGCHP) systems have been developed (mainly in Europe). These micro/small-scale CHP systems can be connected and integrated to achieve an appropriate plant scale according to the biomass supply and heat and power demands. Further description of BGCHP is presented in section 2.4.

Woody biomass in Fukushima was contaminated by radionuclides released between 12 and 31 March 2011 due to the Fukushima Dai-ichi Nuclear Power Plant accident. To safely utilise the contaminated woody biomass in Fukushima as biomass gasification (BG) fuel, the radioactivity of products and by-products such as offgas and ashes in ash bins and on filters must be investigated.

Among these, dry woody/herbaceous biomasses are used as feedstocks for BG plants in Japan. For instance, woody biomasses contain waste woods (construction wastes and timber offcuts) and unutilised woods (forest thinnings, remaining timbers, and damaged trees) composed of cedar, cypress, pine, etc. Short-rotation woody crops (eucalyptus, willow, etc.) are categorised as produced woods. Energy crops such as willow are expected to be cultivated in land fallow and used as biomass because non-food-producing farmlands have been recently

**Moisture Classification Wastes Unutilised Produced**

Herbaceous Crop residues (rice

Livestock excreta

food oil

wastes, Kitchen wastes

Forest thinnings, Remaining forest timbers, Damaged

Biomass Gasification: A Review of Its Technology, Gas Cleaning Applications, and Total System…

/ wheat straw, rice

Short-rotation woody crops (eucalyptus, willow, etc.)

163

http://dx.doi.org/10.5772/intechopen.70727

Grasses (Napier grass, sorghum, Miscanthus etc.)

Landfill gas Cultivated maize, Cultivated sugar cane

trees

husk)

Timber offcuts

Dry Woody Construction wastes,

Wet Sludge /Excreta Sewage sludge,

Other Other Molasses, Waste

**Table 1.** Classification of biomass feedstocks.

Common food Food-processing

For unutilised herbaceous biomass, crop residues such as rice/wheat straw and rice husks [2] are available, while for produced herbaceous biomass, grasses such as Napier grass, sorghum, and Miscanthus are usable. Above all, rice husks contain abundant silica. The ash by-

There are various kinds of gasifiers (e.g., fixed-bed, fluidised, pressurised, etc.). This chapter describes the simplest fixed-bed gasifiers. Fixed-bed gasifiers have a long history and have established confidence through experience with small-scale biomass gasification reactors [4]. **Figure 1** schematically illustrates fixed-bed updraft and downdraft gasifiers. The flows of biomass and producer gases are counter-current for updraft and co-current for downdraft. The gasification reaction is comprised of four main reaction zones. Heat released during the combustion process is used for drying, pyrolysis, and reduction processes in the gasifier.

For both gasifier types, biomass fuels are supplied into each gasifier followed by a drying process. The dried biomass is then pyrolysed to release volatiles and gases. These products are combusted partially or completely using air fed with heat released from the combustion process. The gases, tars, and chars resulting after combustion are reduced in the reduction zone. The positional relationship of these processes is shown schematically in **Figure 2**.

product from gasifiers has potential use in nanomaterials [3].

abandoned in Japan [1].

**2.2. Gasifier**

This chapter reviews current trends of gasification and life cycle assessment (LCA) of total systems, including gas cleaning. Previously, there have been no reviews of small-scale gasification process for hydrogen production and CHP and no critical review of LCA of BG processes. Gas cleaning is one of the most important processes in BG systems for controlling contaminants in producer gases and preserving the catalysts of fuel cells and gas engines.

### **2. Gasification technology**

A biomass gasifier is comprised of four reaction zones, i.e. drying, pyrolysis, combustion, and reduction. The produced gas (syngas) contains impurities to be cleaned utilising a bag filter, activated carbon, scrubber, etc. This chapter describes the fates of two contaminants, radionuclides and sulphur, during the gasification process. The radioactivity of caesium-137 (137Cs) and caesium-134 (134Cs) in fly ash over a bag filter was observed using a germanium semiconductor detector. The fate of sulphur was also reviewed because sulphur often triggers fuel cell catalyst poisoning and gas engine erosion. The LCA of a total system based on the energy profit ratio and environmental impact is then reviewed.

### **2.1. Biomass feedstock**

Biomass feedstocks are classified based on several factors: moisture content, material, and form, as presented in **Table** 1. Biomass is broadly divided into three groups: dry, wet, and other. Dry biomass is classified as woody or herbaceous and wet biomass as sludge/excreta, common food, or other. Each classification has three sub-categories: waste, unutilised, and produced.

**Table 1.** Classification of biomass feedstocks.

Among these, dry woody/herbaceous biomasses are used as feedstocks for BG plants in Japan. For instance, woody biomasses contain waste woods (construction wastes and timber offcuts) and unutilised woods (forest thinnings, remaining timbers, and damaged trees) composed of cedar, cypress, pine, etc. Short-rotation woody crops (eucalyptus, willow, etc.) are categorised as produced woods. Energy crops such as willow are expected to be cultivated in land fallow and used as biomass because non-food-producing farmlands have been recently abandoned in Japan [1].

For unutilised herbaceous biomass, crop residues such as rice/wheat straw and rice husks [2] are available, while for produced herbaceous biomass, grasses such as Napier grass, sorghum, and Miscanthus are usable. Above all, rice husks contain abundant silica. The ash byproduct from gasifiers has potential use in nanomaterials [3].

#### **2.2. Gasifier**

2 MWe. Power generation in such small-scale plants requires biomass gasification technology in order to obtain higher thermal efficiency. Gasification is a process that converts carbonaceous materials into carbon monoxide, hydrogen, carbon dioxide, and gaseous hydrocarbons (producer gas). Producer gas can be supplied as fuel to internal combustion engines and power generators. To maximise the efficiency of woody biomass conversion, producer gas should be utilised not only for power generation but also for thermal production from the producer gas' sensible heat. Cogeneration system for heat and power produc-

Recently, many kinds of biomass gasification combined heat and power (BGCHP) systems have been developed (mainly in Europe). These micro/small-scale CHP systems can be connected and integrated to achieve an appropriate plant scale according to the biomass supply and heat and power demands. Further description of BGCHP is presented in section 2.4.

Woody biomass in Fukushima was contaminated by radionuclides released between 12 and 31 March 2011 due to the Fukushima Dai-ichi Nuclear Power Plant accident. To safely utilise the contaminated woody biomass in Fukushima as biomass gasification (BG) fuel, the radioactivity of products and by-products such as offgas and ashes in ash bins and on filters must

This chapter reviews current trends of gasification and life cycle assessment (LCA) of total systems, including gas cleaning. Previously, there have been no reviews of small-scale gasification process for hydrogen production and CHP and no critical review of LCA of BG processes. Gas cleaning is one of the most important processes in BG systems for controlling contaminants in producer gases and preserving the catalysts of fuel cells and gas engines.

A biomass gasifier is comprised of four reaction zones, i.e. drying, pyrolysis, combustion, and reduction. The produced gas (syngas) contains impurities to be cleaned utilising a bag filter, activated carbon, scrubber, etc. This chapter describes the fates of two contaminants, radionuclides and sulphur, during the gasification process. The radioactivity of caesium-137 (137Cs) and caesium-134 (134Cs) in fly ash over a bag filter was observed using a germanium semiconductor detector. The fate of sulphur was also reviewed because sulphur often triggers fuel cell catalyst poisoning and gas engine erosion. The LCA of a total system based on the

Biomass feedstocks are classified based on several factors: moisture content, material, and form, as presented in **Table** 1. Biomass is broadly divided into three groups: dry, wet, and other. Dry biomass is classified as woody or herbaceous and wet biomass as sludge/excreta, common food, or other. Each classification has three sub-categories: waste, unutilised, and produced.

energy profit ratio and environmental impact is then reviewed.

tion is called combined heat and power (CHP).

be investigated.

162 Lignin - Trends and Applications

**2. Gasification technology**

**2.1. Biomass feedstock**

There are various kinds of gasifiers (e.g., fixed-bed, fluidised, pressurised, etc.). This chapter describes the simplest fixed-bed gasifiers. Fixed-bed gasifiers have a long history and have established confidence through experience with small-scale biomass gasification reactors [4]. **Figure 1** schematically illustrates fixed-bed updraft and downdraft gasifiers. The flows of biomass and producer gases are counter-current for updraft and co-current for downdraft. The gasification reaction is comprised of four main reaction zones. Heat released during the combustion process is used for drying, pyrolysis, and reduction processes in the gasifier.

For both gasifier types, biomass fuels are supplied into each gasifier followed by a drying process. The dried biomass is then pyrolysed to release volatiles and gases. These products are combusted partially or completely using air fed with heat released from the combustion process. The gases, tars, and chars resulting after combustion are reduced in the reduction zone. The positional relationship of these processes is shown schematically in **Figure 2**.

**Figure 1.** Schematic of updraft and downdraft fixed-bed gasifiers [5].

#### **2.3. Gasification mechanisms**

Gasification proceeds through many kinds of simultaneous or consecutive complex reactions. Reactions corresponding to each reaction zone are shown in this section. **Figure 3** represents several main reaction pathways in biomass gasification reactions. The reactions for each pathway (or reaction zone) are presented in **Table 2** based on the literature [7, 8].

*2.3.2. Pyrolysis*

Pyrolysis C*x*

Steam-tar reforming C*n*

Water-gas shift (WGS) CO + H2

Heterogeneous WGS C + H2

Steam reforming of methane CH4

Dry reforming of methane CH4

H2

H2

Ethylene 2CO + 4H2 ↔ C2

Ethane 2CO + 5H2 ↔ C2

Propane 3CO + 7H2 ↔ C3

Butane 4CO + 9H2 ↔ C4

S formation S + H2 ⇄ H2

S-COS equilibrium H2

In the absence of oxygen, volatiles with weaker molecular bonds begin to be thermally decomposed at 200–240 °C; this continues up to 400 °C. The volatiles are vaporised to produce gases, tars, and chars. The chars are also pyrolysed with gas production and weight loss of about 30% [9]. Pyrolysis takes place owing to heat transfer from radiation, convection, and conduction to the biomass as shown in **Figure 3a**. The pyrolysis reactions are represented as Reaction (R1) in **Table 2**.

 Biomass gasification pathway proposed based on Ref. [10, 11].

**Name of reaction Chemical reaction ∆** *Hr(298)*

O*z* → *a*CO2

 + *b*H2

 + *f*C2+ + char  + tar

O → (2*n* + *m*/2) H2

O + *c*CH4

Partial oxidation C + 0.5 O2 → CO −111 (R2) Complete oxidation C + O2 → CO2 −394 (R3)

Hydrogenating gasification C + 2H2 ↔ CH4 123.7 168.6 (R5) Boudouard equilibrium C + CO2 ↔ 2CO 205.3 140.1 (R6)

H*y*

+ *d*CO + *e*H2

H*m* + 2*n*H2

 + H2

O ↔ CO2

H4  + 2H2

H6  + 2H2

H8  + 3H2

**Table 2.** Chemical reactions occurring in biomass gasification (gasifying agent: steam).

H10 + 4H2

#### *2.3.1. Drying*

Biomass moisture at ordinary temperatures becomes water vapour during the drying process at about 100–250 °C. The conversion occurs owing to heat transfer between hot gases from the oxidation and biomass in the drying zone [4]. First, the moisture on the biomass surface evaporates followed by inherent moisture evaporation. The vapour produced is used for reduction reactions in the reduction zone, including the water-gas reaction.

**Figure 2.** Conceptual diagram of multiple steps in fixed-bed (a) updraft and (b) downdraft gasifiers [6].

Biomass Gasification: A Review of Its Technology, Gas Cleaning Applications, and Total System… http://dx.doi.org/10.5772/intechopen.70727 165

**Figure 3.** Biomass gasification pathway proposed based on Ref. [10, 11].

#### *2.3.2. Pyrolysis*

**2.3. Gasification mechanisms**

164 Lignin - Trends and Applications

**Figure 1.** Schematic of updraft and downdraft fixed-bed gasifiers [5].

*2.3.1. Drying*

Gasification proceeds through many kinds of simultaneous or consecutive complex reactions. Reactions corresponding to each reaction zone are shown in this section. **Figure 3** represents several main reaction pathways in biomass gasification reactions. The reactions for each path-

Biomass moisture at ordinary temperatures becomes water vapour during the drying process at about 100–250 °C. The conversion occurs owing to heat transfer between hot gases from the oxidation and biomass in the drying zone [4]. First, the moisture on the biomass surface evaporates followed by inherent moisture evaporation. The vapour produced is used for reduction

way (or reaction zone) are presented in **Table 2** based on the literature [7, 8].