**8. Conclusion**

Sugarcane and woody biomass, which are abundant and readily available, are frontrunner materials as lignocellulosic feedstock for the production of biomass ethanol despite its dif‐ ferences in regard to structure and chemical composition, which relates to different respons‐ es for the same type of pretreatment.

In general, the biomass lignin content, which is an important parameter for enzymatic sac‐ charification, is higher in woody biomass than in agricultural residues, such as sugarcane bi‐ omass. This is particularly true for softwood, which responds poorly to several pretreatment techniques, as shown throughout this chapter. This fact corroborates the need for the devel‐ opment of tailor-made pretreatments based on the biomass type, so that a suitable choice can benefit the subsequent bio-based conversion steps for enzymatic hydrolysis and ethanol fermentation.

The choice of pretreatment should also take into account the foreseen utilization of the main biomass molecular components (cellulose, hemicelluloses and lignin) for the ethanol pro‐ duction process or within the framework of the biorefinery concept. Considering the use of an ethanologenic microorganism able to ferment C6 and C5 sugars, it would be desirable to apply pretreatments such as milling or extrusion, avoiding the formation of a separated hemicelluloses stream, as observed for acidic pretreatment. However, even for the case of hydrothermal or steam pretreatments, the operational conditions can be fitted to minimize the removal of hemicellulose. Considering now a biorrefinery concept which broadens the biomass derived products, the C6 sugars could still be fermented into ethanol, while the C5 stream could be used for the production, via biotechnological routes, of a wide range of chemicals with higher added value. In that cause, the best suited pretreatments would be the acid pretreatment, which releases mostly C5 sugars, steam-based and LHW processes, which separates an oligosaccharides-rich stream. In both cases, lignin can be used as a val‐ uable solid fuel or as a source of aromatic structures for the chemical industry.

Regarding innovative and promising biomass pretreatment technologies, the use of ILs stands out. These versatile class of chemicals can be tailored to suit the selective extraction and recovery of the biomass components, such as the recovery of a cellulose-hemicellulose rich material in an amorphous form which is prone to enzymatic hydrolysis with high yields and rates. Additionally, the possibility of recovering the extracted lignin broadens and in‐ creases the efficiency for the use of biomass.

Table 4 lists the pretreatment options presented in this chapter and its general effects in the bio‐ mass composition and structure. All pretreatments cause an increase in the surface area, which responds for the increased enzymatic digestibility of the treated materials. However, the sub‐ stantial decrease in cellulose crystallinity is only observed for the treatments using ball milling and IL. This effect is of paramount importance for the increased rates and yields of cellulose en‐ zymatic hydrolysis. The acid, LHW and steam explosion pretreatments are more effective on hemicelluloses and on the modification of the lignin structure, which also cause a higher for‐ mation of inhibitors in comparison to milling, extrusion and IL pretreatments.


+++ expressive effect; ++ moderate effect; + low effect; - no effect; nd: not determined

SSA: Specific surface area

CrI: Crystallinity index

nutrient for its growth during the pretreatment, which affects negatively the sugar yield at the end of the process [3]. In addition, the consumption of lignin also reduces the biomass energy utilization. At present, the use of biological pretreatments may represent a competi‐ tive option only if associated with other pretreatment techniques, in order to reduce the en‐ ergy requirement of the total pretreatment process [167]. In future, if less recalcitrant genetically modified plant materials are available, biological pretreatments may represent

72 Sustainable Degradation of Lignocellulosic Biomass - Techniques, Applications and Commercialization

Sugarcane and woody biomass, which are abundant and readily available, are frontrunner materials as lignocellulosic feedstock for the production of biomass ethanol despite its dif‐ ferences in regard to structure and chemical composition, which relates to different respons‐

In general, the biomass lignin content, which is an important parameter for enzymatic sac‐ charification, is higher in woody biomass than in agricultural residues, such as sugarcane bi‐ omass. This is particularly true for softwood, which responds poorly to several pretreatment techniques, as shown throughout this chapter. This fact corroborates the need for the devel‐ opment of tailor-made pretreatments based on the biomass type, so that a suitable choice can benefit the subsequent bio-based conversion steps for enzymatic hydrolysis and ethanol

The choice of pretreatment should also take into account the foreseen utilization of the main biomass molecular components (cellulose, hemicelluloses and lignin) for the ethanol pro‐ duction process or within the framework of the biorefinery concept. Considering the use of an ethanologenic microorganism able to ferment C6 and C5 sugars, it would be desirable to apply pretreatments such as milling or extrusion, avoiding the formation of a separated hemicelluloses stream, as observed for acidic pretreatment. However, even for the case of hydrothermal or steam pretreatments, the operational conditions can be fitted to minimize the removal of hemicellulose. Considering now a biorrefinery concept which broadens the biomass derived products, the C6 sugars could still be fermented into ethanol, while the C5 stream could be used for the production, via biotechnological routes, of a wide range of chemicals with higher added value. In that cause, the best suited pretreatments would be the acid pretreatment, which releases mostly C5 sugars, steam-based and LHW processes, which separates an oligosaccharides-rich stream. In both cases, lignin can be used as a val‐

uable solid fuel or as a source of aromatic structures for the chemical industry.

creases the efficiency for the use of biomass.

Regarding innovative and promising biomass pretreatment technologies, the use of ILs stands out. These versatile class of chemicals can be tailored to suit the selective extraction and recovery of the biomass components, such as the recovery of a cellulose-hemicellulose rich material in an amorphous form which is prone to enzymatic hydrolysis with high yields and rates. Additionally, the possibility of recovering the extracted lignin broadens and in‐

an important alternative.

es for the same type of pretreatment.

**8. Conclusion**

fermentation.

LHW: Liquid hot water

WDM: Wet-disk milling

**Table 4.** General effects of different pretreatments on the composition and structure of the biomass.

Table 5 presents sixteen biomass ethanol plants (pilot, demonstration and commercial scale) which are operating or under construction. It is also presented, for each case, the feedstock and the biomass pretreatment that is used in these facilities. At the current scenario the ma‐ jority of the units have implemented processes that generate a hemicelluloses rich stream: three units use diluted acid, three units use LHW and three units use steam-explosion pre‐ treatment. Two units describe its process as a thermal-mechanical pretreatment which could also generate of a hemicelluloses rich stream. One unit applies a mild alkaline pretreatment that precludes lignin separation and the remaining four units have not disclosed the choice of pretreatment. A variety of feedstocks, such as pine wood chips, wood wastes, forest resi‐ dues, garden waste, wheat, barley and oat straw, corn cob, corn stover, corn straw as well as perennial energy grasses, are used with different pretreatment types.

As the pretreatment step accounts for a substantial part of the biomass ethanol production cost, it is expected that the research in this field will continue to seek for improvements of existing methods or for the development of new and more advanced options.


**Author details**

RJ, Brazil

de Janeiro, Brazil

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Ayla Sant'Ana da Silva1

Maria Antonieta Ferrara3

, Ricardo Sposina Sobral Teixeira1

and Elba Pinto da Silva Bon1

1 Departamento de Bioquímica, Instituto de Química, Universidade Federal do Rio de Ja‐ neiro, Centro de Tecnologia, Av. Athos da Silveira Ramos, Ilha do Fundão, Rio de Janeiro,

2 Instituto Nacional de Tecnologia (INT), Ministério da Ciência, Tecnologia e Inovação, Rio

3 Instituto de Tecnologia em Fármacos FarManguinhos/ FIOCRUZ, Rua Sizenando Nabuco,

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[2] Kumar P, Barrett DM, Delwiche MJ, Stroeve P. Methods for pretreatment of lignocel‐ lulosic biomass for efficient hydrolysis and biofuel production. Industrial & Engi‐

[3] Sousa LC, Chundawat SPS, Balan V, Dale BE. Cradle-to-crave assessment of existing lignocellulose pretreatment technologies. Current Opinion in Biotechnology

[4] Sousa ELL, Macedo IC. Ethanol and bioelectricity: sugarcane in the future of the en‐

[5] Freitas LC, Kaneko S. Ethanol demand under the flex-fuel technology regime in Bra‐

[6] Soccol CR, Vandenberghe LPS, Medeiros ABP, Karp SG, Buckeridge M, Ramos LP, Pitarelo AP, Ferreira-Leitão V, Gottschalk LMF, Ferrara MA, Bon EPS, Moraes LMP, Araújo JA, Torres FAG. Boethanol from lignocelluloses: status and perspectives in

[7] Zhu JY, Pan XJ. Woody biomass pretreatment for cellulosic ethanol production: tech‐ nology and energy consumption evaluation. Bioresource Technology 2010;101

Viridiana Santana Ferreira-Leitão1,2, Rodrigo da Rocha Olivieri de Barros1

, Rondinele de Oliveira Moutta1

http://dx.doi.org/10.5772/53378

Sugarcane and Woody Biomass Pretreatments for Ethanol Production

,

,

75

All pretreatments were followed by separated enzymatic hydrolysis and fermentation (SHF) or simultaneous sacchari‐ fication and fermentation (SSF).

The data presented in this table was based on the official information provided in each company website.

Scale was defined as follow: Pilot – P; D – Demonstration; Commercial – C.

Operational status was defined as follow: Under construction – UC; Operational - O

<sup>1</sup> Two reactors in series, the hemicellulose is hydrolyzed in the first reactor and the cellulose is decomposed in the sec‐ ond reactor at >200 °C.

2 Combination of steam-explosion and wet oxidation, applying both the addition of oxygen and a pressure release at high temperature (170-200° C)

**Table 5.** Pilot, demonstration and commercial scale biomass ethanol plants.
