Bioenergy systems for the future 1 biomass an overview

Bioenergy systems for the future 1 biomass an overview Bioenergy systems for the future 1 biomass an overview Bioenergy systems for the future 1 biomass an overview Bioenergy systems for the future 1 biomass an overview Bioenergy systems for the future 1 biomass an overview

or cultivated by humans, terrestrial and marine, produced directly or indirectlythrough the process of photosynthesis involving chlorophyll In general, biomasscan be defined as anything having an organic matrix Thus, the term biomass identifies

a great variety of heterogeneous materials and matrices In order to limit the range ofthe present analysis, we consider only biomass of plant origin and specifically agri-cultural and agro-industrial residues and wastes, energy crops, and forestry residuesand wastes We do not consider the problems related to land use and how energy cropproduction competes for land with food production Indeed, the concept of energyfrom biomass regards biomass as a renewable energy product obtained as a side prod-uct of a primary product, for example, fruit tree prunings or straw as a by-product ofcereal production The potential global availability of unexploited biomass alonecould provide 10%–20% of the primary energy demand of the planet

What are the main reasons biomass should be exploited as a source of energy? mass is universally available and is therefore a strategic resource in case of a shortage oftraditional energy resources This energy could also help reduce the overall cost ofenergy and the demand for fossil-sourced energy Another positive contribution could

Bio-be the reduction of atmospheric emissions of greenhouse gases, since the complete duction cycle, processing, and use of this material theoretically have a zero carbon diox-ide balance However, although biomass is the first fuel of humans and has been burnedfor thousands of years, no method to define guidelines for its use by correct moderntechnologies has yet been developed This is because biomass is the residual part of dif-ferent crops and these residues vary widely, macroscopically, and at molecular level

pro-We also have to consider that, besides structural components, crop and food industryresidues often contain bioactive substances such as antioxidants, flavonoids, lignans,and carotenoids that could be extracted This possibility would depend on the economicand environmental sustainability of purifying and reutilizing these resources.Bioenergy Systems for the Future http://dx.doi.org/10.1016/B978-0-08-101031-0.00001-6

© 2017 Elsevier Ltd All rights reserved.

The production of energy from biomass is therefore complex, requiring agriculturalproduction to be considered as part of a process based on global sustainability prin-ciples: environmental, economic, and social This means that for all types of agricul-tural production, we consider not only the primary product (usually food) but also theresidues, which if correctly processed could lead to products with biological activityuseful in the food, pharmaceutical, and cosmetic industries At the end of these pro-cesses, the fibrous structural part of plant matter can be recovered and used for energyproduction In this way, energy production from biomass is not divorced from agri-cultural production but becomes an element in a circular process that at least partlyresembles a natural cycle, placing inputs and outputs of the system in a framework

of global sustainability Practices typical of production lines are replaced by an connected system The land where different crops are grown is regarded as a systemthat provides different types of farm and food industry residues, processing of whichshould occur in a plant (biorefinery) that combines different technologies in order tomaximize recovery of components with high biological and chemical value (eco-nomic importance) and maximize the energy obtained from the material remaining

inter-at the end of the process (Fig 1.1)

The biorefinery is therefore a plant designed in relation to an area of reference (onaverage a 10–15 km radius) in which processes using crop residues to obtain productsfor the pharmaceutical, cosmetic, food, and other industries are combined with energyproduction from the plant structural components, which are the final residue aftercomplete exploitation In specific cases, the biomass for energy production may alsocontain starches, sugars, and oily substances that cannot be used for food

Agricultural products

In this chapter, we analyze the chemical characteristics of plant biomass and line the processes necessary to recover its energy content.

out-1.2 Chemical characterisation of biomass

Residual biomass can generally be classified as consisting largely of polysaccharides

or lignin The processes by which its energy content is extracted are shown ically inFig 1.2, which also includes oil-rich biomass High-molecular-weight poly-saccharides are the main constituents of biomass: cellulose and hemicellulosesaccount for 60%–80% of woody material and together with lignin constitute the struc-tural component of plants

schemat-1.2.1 Cellulose

Cellulose is a high-molecular-weight linear polymer ofD-glucose, with up to 10,000monomer units, that only occurs in plants It is the most abundant polysaccharide pre-sent in nature It consists of glucose units linked byβ-1,4-glucoside bonds About40%–50% of all the carbon on the planet is estimated to occur in this polymer Other

Fatty acids Glycerol

Triglycerides

Glucose

Amylose amilopectins

Reserve polysaccharides

Chitins peptidoglycans

polymers ofD-glucose exist in nature, for example, starch, which consists of two mers, amylose (about 20%) and amylopectin (about 80%), that differ from cellulose

poly-by virtue of alpha-1,4-glucoside bonds in the case of amylose and alpha-1,4-glucosideand alpha-1,6-glucoside bonds in the case of amylopectin

The structural basis of cellulose is cellobiose, 4-o-β-D-glucopyranosyl-Dglucopyranose, shown inFig 1.3

-As shown inFig 1.3, all hydroxide groups are in equatorial position Rotation ofglucose molecules at the 1,4 bond is limited due to residual repulsive van der Waalsforces The cellobiose conformation is the most favorable from the steric point ofview: it is stabilized by the formation of a hydrogen bond between the hydroxide

in position 3 and the oxygen atom of the next pyranose ring unit, as shown inFig 1.4 The fact that the cellulose molecule is linear and the presence of hydrogenbonds between units (OHdH⋯O) prevents any rotational mobility in the direction ofthe principal axis determines a linear ribbon-like structure

The hydrophilic groups are arranged laterally, and all hydrophobic hydrogen atomsare on the surface This makes the polymer cluster in long chains (microfibrils) Cel-lulose fibers are arranged in a very specific way and have fractal-like features(Ummartyotin and Manuspiya, 2015; Lavoine et al., 2012)

O

1

4 5

HO HO

OH

6

O

2 3

Fig 1.4 Linear conformation of polymer chains in crystal structures of cellulose II, vieweddown thec-axis in P21

Reproduced with permission from Kaduk, J.A., Blanton, T.N., 2013 An improved structuralmodel for cellulose II Powder Diffr 28, 194–199

Cellulose microfibrils are also stabilized by specific and aspecific interactions(hydrogen bonds and van der Waals forces) between chains, which prevent any trans-lational dynamics of the molecules but impart great flexibility and elasticity to thestructure for torsional movements The association of microfibrils into macrofibrilaggregates gives them great mechanical resistance, similar to that of steel (seeFig 1.5) In plants, a rigid wall with high mechanical resistance enables these cell sys-tems to take up large volumes of water without stressing cell structure Similar behav-ior in animal cells having only a cell membrane would cause an increase inintracellular pressure and damage/lysis of the membrane.

The cellulose present in plant cells has a structure in which crystalline and phous regions alternate (Fig 1.6) X-ray diffraction shows regions with monoclinicand triclinic crystalline phases (Fig 1.7) These regions are very stable and resistant

amor-to attack by cellulase enzymes

The most vulnerable part of the molecule is the amorphous region, which isattacked by cellulase (an enzyme complex consisting of exo- and endoglucanaseand β-glucosidase), causing hydrolysis of the glucose in the cellulose molecule(Fig 1.8) Hydrolysis of cellulose at glucose units is the focus of the process of bio-ethanol production, where glucose is exploited for industrial production of bioethanol

by classical fermentation (e.g., bySaccharomyces cerevisiae)

There are two possible approaches: acid hydrolysis of cellulose or enzyme lysis Current industrial processes tend to favor enzyme hydrolysis Various methods

hydro-of industrial production hydro-of very effective high-yield cellulase have been developed,

(a) Cellulose fibers

(b) Macrofibril

(c) Microfibril

(d) Chains of

cellulose molecules

Fig 1.5 Organization of linear chains of cellulose into microfibrils, macrofibrils, and cellulosefibers

Reproduced with permission from Nutrition Resources, 2006 Chemistry review:

carbohydrates Jones and Bartlett Publishers.http://nutrition.jbpub.com/resources/

chemistryreview9.cfmAccessed 2016

nanomaterials: a review Nanoscale 4, 3274–3294.

c

c

b b

a a

Cellulose phase I α triclinic P1

Cellulose phase I α

triclinic P1

Cellulose phase I β monoclinic P21

Cellulose phase I β monoclinic P21

a(A) = 6.717 (7) b(A) = 5.962 (2) c(A) = 10.400 (6) a(°) = 118.08 (5)

b(°) = 114.80 (5)

g(°) = 80.37 (5)

a(A) = 7.784 (8) b(A) = 8.201 (8) c(A) = 10.338 (10) g(°) = 96.5 (5)

Fig 1.7 Crystalline structure of cellulose, characterized by phase I alpha triclinic P1 and phase

I beta monoclinic P21

Reproduced with permission from Sarkar, A., Perez, S., 2012 A Database of Polysaccharide3D structures http://polysac3db.cermav.cnrs.fr/discover_cellulose.html last updated:

24 April 2012

making these enzymes particularly economical At present, this solution seems theonly sustainable process for the production of bioethanol from cellulose- andhemicellulose-rich materials (second-generation bioethanol) The main advantagesare that this process is not applied to food crops and that secondary products can

be recovered, increasing economic value and making even primary agricultural duction sustainable The only negative note is that for conversion plants to achieveeconomic sustainability of process, they must produce of the order of 50 milliontons/year of bioethanol

pro-1.2.2 Hemicellulose

Hemicelluloses make up about 20%–30% of lignocellulose biomass These polymersconsist of the same monomeric units as cellulose, but their structure is different Theyare branched polymers, whereas cellulose is linear; they have a shorter chain length of

500–3000 glucose units compared with the 10,000–15,000 glucose units of cellulose.While cellulose consists solely of glucose units linked with β-1,4-glycoside bonds,hemicellulose is a mix of polysaccharides consisting mainly of sugars with five carbonatoms (xylose and arabinose) and six carbon atoms (glucose, galactose, mannose, andrhamnose) In hemicellulose, glycoside links involving positions 2, 3, 4, and 6 are

Cellulases

Exo

Cellobiohydrolase

Acting from nonreducing end

e.g Piromyces sp E2 Cel6A

Cellobiohydrolase

Acting from reducing end

e.g Phanerochaete Cel17s

Pc_Cel7D Pc_Cel7A

Endoglucanase

Acting from the middle

e.g Piromyces E2 Cel9A

Product—cellobiose Product—cellobiose Product—oligosaccharides of

HO

HO

HO OH

OH

OH

HO OH

OH OH OH

OH OH

OH

OH

OH OH O

O

O

O O

O OO O

O O O O O

O

n n

HO

HO HO

HO

HO OH

OH

OH OH OH

OH

O O

Fig 1.8 Hydrolysis of cellulose by cellulase, a complex consisting of a pool of enzymes, such

as exocellulase, endocellulase, andβ-glucosidase

Reproduced with permission from Emerald Biology, 2014 Fuels for biofuels part 5: freecellulases and cellulose hydrolysis http://www.emeraldbiology.com/2014/03/fuels-for-biofuels-part-5-free.html Accessed 11 March 2014

possible, resulting in very disorderly and essentially amorphous polymers This erty makes them more soluble in water and more reactive and renders their basic sugarconstituents very readily hydrolyzed Hemicelluloses play an important function inwood, creating a network of connections between cellulose microfibrils, as shown

prop-inFig 1.9

Based on the prevalence of glucose units, hemicelluloses can be distinguished asxylan, glucuronoxylan, arabinoxylan, mannan, and glucomannan The most frequentsugar units are indicated inFig 1.10

1.2.3 Xylans

Xylans are polysaccharides containing xylose as basic monomeric unit The mainchain of xylans consists ofD-β-xylopyranose, the units of which are linked by 1,4bonds The linear chain has branches made up of xylose or arabinose (as L-ara-binofuranoside), 4-o-methylglucuronic acid, mannose, galactose, and rhamnose(Motta et al., 2013; Hao and Mohnen, 2014)

Xylans have very low water solubility, which can however increase with reduction

in the degree of polymerization of the molecule In nature, xylans are bound to

Microfibril structure Layered mesh of

microfibrils in

plant cell wall

Single microfibril

Hemicellulose Paracrystalline cellulose Crystalline cellulose

Fig 1.9 Hemicellulose creates a network of connections between microfibrils of cellulose.Reproduced with permission from US DOE, 2005 Genomics: GTL Roadmap, DOE/SC-0090.U.S Department of Energy Office of Science

O H

OH

O OH

H

OH H

H

H2OH OH

O H

HO

OH H

OH

H2H OH

O H

HO

H HO

H

H OH H

H

OH

O H

HO

H HO

OH

H H

OH

O OH

H

H HO

H

OH

H OH H

COOH

O H

HO

H HO

H

H OH

H

H HO

H

OH H

CHOH

O OH

H

H HO

H

COOH H

β- D -Glucopyranose β- L -Rhamnopyranose α- L -Fucopyranose

α- L -Arabinofuranose β- D -Xylopiranose β- D -Mannopyranose

β- L -Apiofuranose

β- L -Aceric acid

2-Keto3-deoxy- D 2octulosonic acid

-manno-3-Deoxy- D -lyxo-2-hep-2 tulosaric acid

β- D -Galactopyranose α- D -Galactopyranosyluronic acid β- D -Galactopyranosyluronic acid

Fig 1.10 Sugars found in hemicellulose

cellulose and lignin via ether or ester bonds In the case of lignin, the most frequentbond is between the phenol group of lignin and an arabinose or a 4-o-methylglucuronic acid unit of hemicellulose Structurally, xylans are the most abun-dant type of hemicellulose in nature and are typical of hardwood They are also found

in large quantities in crop residues (e.g., leaves and stalks of maize) and in paper duction wastes This class includes all polysaccharides containing high percentages of

pro-D-xylose In hardwood, the most common xylan is a linear chain consisting solely ofxylose, 70% of which is acetylated Structurally, the xylan chain can be considered thesame as that of cellulose except for the absence of the dCH2OH group in equatorialposition on C5, which imparts less steric hindrance and therefore a greater possibility

of rotation at the glycosidic bond

Solid-state polymer structure has been reconstructed by X-ray diffraction analysis

of crystal structure The chain forms a tight left-handed helix (three xylose residuesper turn) with a repetition distance of 15 A˚ and an angle of rotation of 120 degreesbetween residues (Fig 1.11)

1.2.4 Mannans

Together with xylans, mannans are major constituents of hemicelluloses observed inthe walls of higher plants Mannans show great affinity for cellulose, to which they areoften bound in wood (Preston, 1968; Brennan et al., 1996; Liepman et al., 2007) Theyare classified in four families: linear mannans, glucomannans, galactomannans, andgalactoglucomannans (Petkowicz et al., 2001;Fig 1.12) Linear mannans are linearpolymers composed essentially of 1,4-linkedβ-D-mannopyranosyl units; they containtraces of other sugar units, mainly galactose Other mannans have a backbone based onmannose units or occasionally glucose and mannose bound by β-(1–4) glycosidebonds (Liepman et al., 2007) Glucomannans have a backbone consisting of (1,4)-linked β-D-mannopyranosyl residues containing D-glucose in 3:1 ratio (Northcote,1972; Popa and Spiridon, 1998) They have branches due toα-1,6 links with galactoseresidues These polymers are the prevalent hemicelluloses in softwoods Acetylgroups can often be identified distributed in an irregular manner in the chains ofthe carbohydrate backbone

Galactomannans are branched polymers that are soluble in water, with a backboneconsisting of 1,4-linkedβ-D-mannopyranosyl residues with side chains containing sin-gle 1,6-linkedα-D-galactopyranosyl groups (McCleary and Matheson, 1986; Shobha

et al., 2005; Parvathy et al., 2005) Galactoglucomannans have a backbone like that ofglucomannans with branches containing D-galactose residues linked with alpha-1,-6- bonds toD-glucosyl andD-mannosyl units Structurally, the galactosidic side chainforms intramolecular hydrogen bonds with mannose and/or glucose units of the back-bone, creating a compact and rather rigid structure The different types of mannans are

of great industrial interest for their aggregating and gelling properties, which are ful in food technology

use-As in the case of cellulose, enzyme complexes consisting of β-mannanase,β-glucosidase, β-mannosidase, acetyl mannan esterase, and α-galactosidase have been

identified that can hydrolyze these polymers to simple sugars They can be used inindustrial processes or for fermentation in biofuel production.

1.2.5 Galactans

Galactans are a relatively less abundant class of polysaccharides and are mainly found

in larch trees in the form of arabinogalactans, the main structure of which is terized by a chain of galactose units linked by 1–6 and 1–3 bridges (Pomin andMoura´o, 2008)

charac-1.836 nm

Fig 1.11 Structure of a repeat unit of xylose polymer The repeat unit includes three xylosemolecules linked by aβ-(1–3) bond, rotated at 120 degrees with respect to each other Theresulting structure is almost cylindrical with hydroxyls disposed uniformly on the outer surface.This disposition imparts greater solubility than in the case of cellulose

Reproduced with permission from Buliga, G.S., Brant, D.A., Fincher, G.B., 1986 The sequencestatistics and solution conformation of a barley (1–3, 1–4)-β-D-glucan Carbohydr Res 157,139–156

Red seaweeds contain sulfated galactans, such as carrageenans or agarans, whichare the main matrix polysaccharides These polymers consist of linear chains withalternation of 3-β-D-galactopyranosyl and 4-α-galactopyranosyl (or anhydrogalactosepyranosyl) residues Galactans are polysaccharides found in seeds, algae, and certainbuds The best known galactans are those isolated from algae (agar), larch (ε-galac-tan), alfalfa seeds (α-galactan), and yellow lupin seeds (β-galactan).

1.2.6 Chitin and peptidoglycan

Chitin is a large polysaccharide composed of many N-acetylglucosamine subunitslinked together viaβ-1,4 bonds, the same bond as is found between the glucose unitsthat form cellulose Chitin can be considered a cellulose in which the hydroxyl group

at C2 on each unit is replaced with an acetylamine group Along with chitosan, chitin

is also the main component of the cell wall of fungi In fungi, chitin is often associated

O O

O

O

Mannan

Galactomannan

Gal α(1, 6)

HO HO

HO HO

withβ-glucan polysaccharides linked to proteins to form a sometimes stratified saccharide matrix.

poly-Peptidoglycan is a polymer that imparts rigidity to cells and in fact forms a layer in thecell wall of bacteria The main constituents of peptidoglycan are N-acetylglucosamineand N-acetylmuramic acid that form the polysaccharide part of peptidoglycan knownalso as glycan N-acetylglucosamine and N-acetylmuramic acids are linked byβ-(1,4)glycosidic bonds, alternating to form chains varying from 10 to 80 disaccharide repeats

in length The peptide chain can be cross-linked to the peptide chain of another strandforming the 3D mesh-like layer Peptidoglycan serves a structural role in the bacterialcell wall, giving structural strength and counteracting the osmotic pressure of thecytoplasm It is also involved in binary fission during bacterial cell reproduction

1.2.7 Reserve polysaccharides

The differences in function between reserve and skeletal polysaccharides do not reside

in the nature of the component monosaccharide units but in the position of interunitattachment and linkage configurations These factors influence the flexibility ofglycosidic linkages

Storage polysaccharides are generally more flexible than fibrous polymers due toless steric hindrance on torsional rotations In these polymers, the 1–6 linkage isextremely flexible Weak interchain bonding can be readily disrupted to facilitateaccess by catabolic hydrolases, which release the stored material

Another common feature of reserve polysaccharides is extensive branching Theside chains, which are long and themselves branched, further hinder packing of thechains into a regular structure, confer the functional advantage of compactness,and provide more end groups for enzymes

1.2.7.1 Starch

Starch is a reserve polysaccharide, and its production is the simplest and most generalmethod of energy storage in plants The molecule is complex and consists of two com-ponents: amylose and amylopectin Amylose accounts for about 15%–25% of starch,and amylopectin accounts for 75%–85% Structurally, amylose consists of linearchains ofD-glucose units linked byα-(1–4) glycoside bonds; amylopectin has a similarbackbone to amylose, but its branches are made up of glucose units linked byα-(1–6)glycoside bonds Amylose is almost insoluble in water It is possible to prepare aque-ous suspensions in which the structural properties of the solid phase are maintained

Amylose

Amylose has structural characteristics similar to cellulose because both are linearpolymers of glucose, but cellulose has β-(1–4) glycosidic bonds, whereas amylosehasα-(1–4) bonds Thus, cellulose forms long linear chains, while amylose organizes

in three-dimensional helical structures (Buleon, et al., 1998;Fig 1.13) At least helix conformations of amylose, A, B, and V, are known The A and B helix forms aresimilar, being left-handed with six glucose units per turn The V helix form is

three-interesting because it is generated by a cocrystallization process with apolar and/orlipid molecules such as iodine, solvents, and fats Double helixes are possible Amy-lose is completely hydrolyzed to glucose byβ-glucosidase In the case of amylopectin,the backbone is hydrolyzed, while the side chains give rise to dextrin residues(Rappenecker and Zugenmaier, 1981; Godet, et al., 1995).

Amylopectin

Amylopectin is a highly branched polymer structurally similar to glycogen, formed bynonrandom α-(1–6) branching of the amylose-type α-(1–4)-D-glucose It has beenreported that native amylopectin mainly presents three forms of crystalline structures:A-chain and B-chain, outer and inner unbranched chains, respectively, and C-chaincontaining the reducing group (Zobel, 1988) The A-chains usually consist of

13–23 residues, whereas the B-chains can show longer arrangement up to about

23–35 residues and shorter internal chains similar to the A-chains The branching

is determined by enzymes, and a single molecule of amylopectin contains abouttwo million glucose residues in a compact structure with hydrodynamic radius

21–75 nm (Parker and Ring, 2001) The molecules are radially oriented, and the phous and crystalline regions produce concentric layers (Fig 1.14)

amor-1.2.8 Lignin

Plant cell walls mainly contain three structural polymers: cellulose, hemicellulose,and lignin Lignin is a term used for a large group of aromatic polymers resulting fromoxidative radical polymerization of three hydroxycinnamyl alcohols (Fig 1.15) thatdiffer in degree of methoxylation: p-coumaryl, coniferyl, and sinapyl alcohols(Higuchi, 1990; Higuchi, 2003; Boerjan et al., 2003; Ralph et al., 2004) These mol-ecules are called monolignols and are formed in plastids via the phenylalanine met-abolic pathway (Rippert et al., 2009) When incorporated into the polymer,

Fig 1.13 Structure of the amylose chain, assumed to be a left-handed spiral due toα-(1,4)glycosidic bonds (n¼500–6000 α-D-glucopyranosyl units)

Reproduced with permission from Miguel, A.S.M., Martins-Meyer, T.S., da Costa

Figueiredo, E.V., Lobo, B.W.P., Dellamora-Ortiz, G.M., 2013 Enzymes in Bakery: Current andFuture Trends In: Muzzalupo, I (Ed.), Future Trends, Food Industry InTech Publisher

monolignols give rise to different types of lignin unit: guaiacyl,p-hydroxyphenyl, andsyringyl units, respectively The major monolignols in dicotyledonous angiospermlignin are monomethylated guaiacyl units derived from coniferyl alcohol anddimethylated syringyl units derived from sinapyl alcohol (Dixon et al., 2001).Together with cellulose and hemicellulose, lignin polymer provides mechanicalsupport in plants, constituting wood and lignified elements Its radical-inducedpolymer synthesis makes the precise chemical structure of lignin impossible todefine Lignins from different sources show wide variations in chemical composi-tion and above all spatial conformation This is due to the fact that radical-inducedpolymerization reactions depend on the statistical distribution of limit forms, theprobability of which depends on the energy of the radical species As a result,all thermodynamically and kinetically possible links are present but are not

A chains

B chains

C chains Reducing end

Amorphous regions

Crystalline regions

6 glucose units Hilum

(D)(C)

a-1 ®6 branchpoints

Fig 1.14 (A) General structure of amylopectin; (B) amorphous and crystalline regions of theamylopectin structure; (C) orientation of the amylopectin molecules in a cross section of anidealized granule; (D) double helix structure that produce the extensive degree of crystallinity ingranule

Reproduced with permission from Coultate, T., 2009 Food The chemistry of its components,fifth ed RSC Publishing (Chapter 3)

expressed with the same probability The most elegant way to define this molecule

is as follows: lignin is a three-dimensional polymer with interconnected dendriticstructure, consisting of phenylpropene structural units Fig 1.16 shows a two-dimensional structural model of lignin in which almost all the different types ofchemical bond are indicated

Due to its strongly hydrophobic chemical composition, lignin constitutes a barrieragainst penetration of water into lignified parts of plants This property contrasts withthe hydrophilic characteristics of the polysaccharide polymers, cellulose and hemicel-lulose, which are highly water permeable By bonding covalently to hemicellulose,lignin builds a stable structural network with high mechanical resistance and elastic-ity, typical of woody systems Lignin is the most abundant polymer on the planet.About 50 million tons/year of lignin-based residues are not used due to the difficulty

of collecting them and limited processing capacity

1.3 Agriculture and forestry biomass for energy

production

The Earth has a great variety of agriculture biomass that could be used for energy duction Biomass includes organic residues, grassy starch crops, sugar crops, lignocel-lulose crops, lignocellulose residues, oil crops, and marine biomass The mainclassification of agricultural and forestry biomass used for energy production is shown

pro-inTable 1.1

The difficulty of defining the complex term biomass induced the European mittee for Standardization (CEN) to differentiate technical specifications for solidbiomass Classification of biomass into different categories helps delineate biomassorigin and possible treatments for energy production These classifications became

Com-EN standards for European countries (particularly Com-EN 14961)

Solid biomass is classified in four categories:

(a) Woody biomass

2 5

6

1 α β γ

Coumaryl alcohol Coniferyl alcohol Sinapyl alcohol

OH

OH OMe

OH

OH

OMe MeO

Fig 1.15 The three common monolignols,p-coumaryl alcohol, coniferyl alcohol, and sinapylalcohol

Tables 1.2–1.4show classifications of woody, herbaceous, fruit, and mixed biomass.The biomass composition of wood and herbaceous biomass (Table 1.5) shows thatmoisture is more abundant in wood, whereas ash and volatile components have ahigher concentration in herbaceous residues.

Biomass processing allows conversion of the raw materials of biomass into energy,organic residues of reduced complexity, and inorganic components Considering allavailable biomass sources and the different conversion options, it is quite difficult

to generalize a unified model for biomass treatment The main processes involve mochemical, biochemical, and physicochemical conversion

ther-Thermochemical treatment of solid biomass includes combustion, gasification, andpyrolysis The outputs of thermal transformation are thermal energy and a range ofsolid, liquid, and gaseous fuels that can be used for other purposes, including trans-portation, thermal and electric energy generation, and basic products for the chemicalindustry

O HC

HC OH

HC O

CH3O OCH3

HCOH HC HO

O

HCOH CH

Table 1.1 Agricultural and forestry biomass for energy production

Straw (maize, cereal, rice)Sugar beet leavesResidues flows from bulb sectorLivestock waste Solid manure (chicken manure)

Liquid manure (cattle, pig, sheep manure)Dedicated

energy crops

Dry lignocellulosicwoody energy crops

SRW-willow, SRC-poplar, eucalyptusDry lignocellulosic

herbaceous energycrops

Miscanthus, switch grass, common reed, reedcanary grass, giant reed,Cynara cardunculus,Indian shrub

Sugar energy crops Sugar beet, cane beet, sweet sorghum,

Jerusalem artichoke, sugar milletStarch energy crops Wheat, potatoes, maize, barley, triticae, corn

(cob), amaranthOthers Flax (Linum), hemp (Cannabis), tobacco

stems, aquatic plants (lipids from algae), cottonstalks, kenaf

Forestry Forestry by-products Bark, wood blocks, wood chips from tops and

branches, wood chips from thinning, logs fromthinning

Industry Wood industry

residues

Industrial waste wood from swamills andindustrial waste wood from timber mills (bark,sawdust, wood chips, slabs, off-cuts)

Fibrous vegetable waste from virgin pulpproduction and from production of paper frompulp, including black liquor

Food industryresidues

Wet cellulosic material (beet root tails), fats(used cooking oils), tallow, yellow grease,proteins (slaughter house waste)

Industrial products Pellets from sawdust and shavings, briquettes

from sawdust and shavings, bio-oil (pyrolysisoil), ethanol, biodiesel

Parks and

gardens

Waste Contaminate waste Demolition wood, biodegradable, municipal

waste, sewage sludge, landfill gas, sewage gas

Husks/shells Almond, olive, walnut, palm pit, cacaoFrom Loo Van, S., Koppejan, J., 2004 Handbook of Biomass Combustion of Co-firing Prepared by Task 32 of the Implementing Agreement on Biomass under the Auspices of the Int Energy Agency Tent University Press.

Biochemical conversion of biomass includes all processes performed by yeasts andbacteria or enzymes Two main transformation routes are generally considered: bio-ethanol production by fermentation and biogas production by anaerobic digestion Inthe latter case, larger commercial plants involve ethanol production by fermentation ofboth sugar and starch crops More recently, cellulosic biomass has been used toproduce ethanol by a second-generation process, which first involves hydrolysis ofcellulose to glucose by a pool of enzymes known as “cellulase.” Several other bio-chemical processes are involved and are based on the availability of specific biomass

to produce end products or intermediates for industrial applications, such as (i) lacticacid produced by bacterial fermentation of sugar substrates, (ii) acetone-butanol as

Table 1.2 Woody biomass (EN 14961-1)

Forest plantation and

other virgin wood

Whole trees withoutroots

Broadleaf, coniferous, shortrotation coppice, bushes, blendsand mixture

Whole trees with roots Broadleaf, coniferous, short

rotation coppice, bushes, blendsand mixture

Stemwood Broadleaf, coniferous, blends and

mixtureLogging residues Fresh/green broadleaf (including

needles), stored broadleaf, storedconiferous, blends and mixtureStems/roots Broadleaf, coniferous, short

rotation coppice, bushes, blendsand mixture

Bark (from forestry operations)Segregated wood from gardens, parks, roadside maintenance,vineyards, and fruit orchards

Blends and mixturesBy-products and

residues from wood

processing industry

Chemically untreatedwood residues

Broadleaf with and without bark,coniferous with and without bark,bark (from industry operations)Chemically treated wood

residues, fibers andwood constituents

With and without bark, bark (fromindustry operations), fibers andwood constituents

Blends and mixture

wood

With and without bark, barkChemically treated wood With and without bark, barkBlends and mixture

Blends and mixture

Table 1.3 Herbaceous biomass (EN 14961-1)

Herbaceous biomass Cereal crops Whole plant, straw parts, grain or seeds,

husks or shells, blends and mixtureGrasses Whole plant, straw parts, seeds, shells,

blends and mixtureOil seed crops Whole plant, stalk and leaves, seeds,

husks or shells, blends and mixtureRoot crops Whole plant, stalk and leaves, root,

blends and mixtureLegume crops Whole plant, stalk and leaves, fruit,

pods, blends and mixtureFlowers Whole plant, stalk and leaves, seeds,

blends and mixtureSegregated herbaceous biomass from gardens, parks, roadsidemaintenance, vineyards, and fruit orchards

Blends and mixturesBy-products and

residues from fruit

processing industry

Chemicallyuntreatedherbaceousresidues

Cereal crops and grasses, oil seed crops,root crops, legume crops, flowers,blends and mixture

Chemicallytreatedherbaceousresidues

Cereal crops and grasses, oil seed crops,root crops, legume crops, flowers,blends and mixture

Table 1.4 Fruit biomass (EN 14961-1)

Orchard and horticulture

fruit

Berries Whole berries, flesh, seeds, blends and

mixtureStone/kernel

fruits

Whole fruit, flesh, stone/kernel, blendsand mixture

Nuts and acorns Whole nuts, shells and husks, kernels,

blends and mixtureBlend and

mixtureBy-products and residues

from fruit processing

industry

Chemicallyuntreated fruitresidues

Berries, stone/kernel fruits, nuts andacorns, crude olive cake, blends andmixture

Chemicallytreated fruitresidues

Stone/kernel fruits, nuts and acorns,crude olive cake, blends and mixtureBlend and mixture