Energy Sources, Part A, 30:27–37, 2008

Copyright © Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/00908310600626705

Products from Lignocellulosic Materials

via Degradation Processes

A. DEMIRBAS1

1Sila Science, Trabzon, Turkey

Abstract Products from lignicellulosic materials by degradation processes are re-viewed based on the results of some investigations. Biomass provides a potential

source of added value chemicals, such as reducing sugars, furfural, ethanol andother products by using biochemical or chemical and thermochemical. The initial

degradation reactions include depolymerization, hydrolysis, oxidation, dehydration,and decarboxylation. The gas phase of pyrolitic degradation products contain mostly

carbon monoxide and carbon dioxide, and minor proportions of hydrogen, methane,ethane, and propane. The liquid fraction consists mainly of water, with small pro-

portions of acetaldehyde, propion aldehyde, butiraldehyde, acrolein, croton-aldehyde,furan, acetone, butanedione, and methanol. There are many studies on biomass con-

version methods because of energy problems and environmental pollution. Ethanol isan alcohol and is fermented from sugars, starches or from lignocellulosic biomass.

In order to produce bioethanol from lignocellulosic biomass, a pretreatment processis used to reduce the sample size, degrade the hemicelluloses to sugars, and open up

the structure of the cellulose component. The cellulose portion is hydrolyzed by acidsor enzymes into glucose sugar that is fermented to bioethanol. The sugars from the

hemicelluloses are also fermented to bioethanol.

Keywords biomass, biomass conversion processes, degradation

Introduction

Lignocellulosic materials include wood, grass, forestry waste, agricultural residues, and

municipal solid wastes. Wood is mainly composed of cellulose, hemicellulose and lignin.

Cellulose is a high molecular weight linear polymer of ˇ-1,4-linked D-glucose units

which can appear as a highly crystalline material (Fan et al., 1982). Hemicelluloses

are branched polysaccharides consisting of pentoses, hexoses and uronic acids (Saka,

1991). Softwood hemicelluloses have a higher proportion of mannose and glucose units

than hardwood hemicelluloses, which usually contain a higher proportion of xylose

units. Furthermore, hemicelluloses are more highly acetylated in hardwoods than in

softwoods (Fengel and Wenger, 1989). The relative abundance of individual sugars in

carbohydrate fraction of wood is shown in Table 1. Lignin is an aromatic polymer

synthesised from phenylpropanoid precursors (Adler, 1977). Lignins are divided into

two classes, namely “guaiacyl lignins” and “guaiacyl-syringyl lignins,” differing in the

substituents of the phenylpropanoid skeleton. Guaiacyl-lignins have a methoxy-group in

Address correspondence to Professor Ayhan Demirbas, P.K. 216, TR-61035 Trabzon, Turkey.E-mail: ayhandemirbas@hotmail.com

27

28 A. Demirbas

Table 1

Relative abundance of individual sugars in carbohydrate fraction

of wood (% by weight)

Sugar Softwoods

Softwood

bark Hardwoods

Hardwood

bark

Glucose 61–65 57–63 55–73 53–65

Xylose 9–13 11–15 20–39 18–36

Mannose 7–16 6–16 0.4–4 0.3–3

Galactose 6–17 1–5 1–4 1–6

Arabinose <3.5 4–11 <1 2–8

Rhamnose <1 <1 <1 <1

Uronic acids 4–7 — 4–7 —

Source: Goldstein, 1981.

the 3-carbon position, whereas syringyl-lignins have a methoxy-group in both the 3-

carbon and 5-carbon positions. Softwood and hardwood lignins belong to the first and

second category, respectively. Softwoods generally contain more lignin than hardwoods

(Saka, 1991).

Biomass provides a potential source of added value chemicals, such as reducing

sugars, furfural, ethanol and other products, by using biochemical or chemical and

thermochemical. There are many studies on biomass conversion methods because of

energy problems and environmental pollution (Kucuk and Demirbas, 1997). Lignocel-

lulosic materials represent an important source of energy and chemicals. Before the

area of petrochemicals, various chemicals were produced from biomass by techniques

such as extraction, fermentation, and carbonization (Pakdel et al., 1997). Of the biomass

conversion processes, interest in pyrolysis has been growing (Bridgwater and Kuester,

1998; Grassi et al., 1990). Pyrolysis is a thermochemical process that converts biomass

into liquid, charcoal, and noncondensable gases by heating the biomass in the absence

of air (Demirbas, 2001a). Many biomass pyrolysis processes have been investigated

(Demirbas, 2000; Caballero et al., 2000; Demirbas, 2001b; Demirbas, 2005).

The liquid fraction of the pyrolysis products consists of 2 phases: an aqueous phase

containing a wide variety of organo-oxygen compounds of low molecular weight and a

non-aqueous phase containing insoluble organics of high molecular weight. This phase

is called tar and is the product of greatest interest. The oils are composed of a range of

oxygenated compounds, including cyclopentanone, methoxybenzene, acetic acid, furfural,

acetophenone, phenol, benzoic acid and their alkylated derivatives (Demirbas, 2002;

Gullu, 2003). Limited work has been conducted on the application of phenolic fraction

separated from pyrolysis liquid products.

Phenolics are valuable compounds and have been used as food aromas, pharma-

ceuticals and as intermediates for chemical synthesis. Significant amounts of phenolic

compounds frequently occur in foods such as fruits and vegetables and are routinely

consumed in our diet. Phenolics, including simple phenols (mostly phenolic acids),

flavonoids and anthocyanins, are hydrophilic compounds with antioxidant activity in vitro

(Ju and Bramlage, 1999; Santos-Gomes et al., 2002). Flavonoids represent a large group

of phenolic compounds found in plants (Vvedenskaya and Vorsa, 2004). Flavonoids and

phenolic acids are two large and heterogeneous groups of biologically active non-nutrients

Products from Lignocellulosics 29

(Hakkinen et al., 1999). Phenolic phytochemicals are important aromatic secondary

metabolites in plants, many of which are commonly substituted by sugar moieties such

as glucose, arabinose, xylose, rhamnose, and galactose (Kim et al., 2003). Flavonols

and phenolic acids have been proposed to have beneficial effects on health as antioxi-

dants (Rice-Evans et al., 1996; Natella et al., 1999) and anticarcinogens (Hakkinen and

Törrönen, 2000).

The phenolic compounds can be obtained from pyrolysis of lignin. The cleavage of

the lignin aromatic C–O bond led to the formation of one oxygen atom products, i.e.,

3-propylphenol, 4-propylphenol and methyl-4-propylphenols. The selectivity of the for-

mation of 3-propylphenol was higher than that of 4-propylphenol at all reaction temper-

ature and all reaction temperatures and all reaction times. The extent of conversion of

1-ethyl-4-hydroxybenzene (4-ethylphenol), as a model compound was relatively small

under both sets of reaction conditions. The main reaction products were diethyl phenol,

p-cresol, and phenol. The nature of these products shows that C–C cleavage occurred

between the aromatic ring and a-carbon atom. There was no indication of significant

formation of polymerized reaction products. The cleavage of the propyl side chain

C–C bonds gave minor products, i.e., 3-methylpyrocatechol, 4-methylpyrocatechol, 4-

methylguaiacol, guaiacol, cresols, and phenol. The nature of the products show that

cleavage occurred between the a- and b-carbon atoms, as well as between the ring and

alpha carbon atoms (Demirbas, 2002).

Degradation of Lignocellulosic Materials by Hydrolysis

Biomass provides a potential source of added-value chemicals, such as reducing sugars,

furfural, ethanol and other products, by using enzyme- or acid-catalyzed hydrolysis.

Enzyme-catalyzed hydrolysis of biomass is a much slower reaction than acid hydroly-

sis. The recovery of the enzymes is difficult. Concentrated acid hydrolysis of biomass is

limited by corrosion and expensive acid recovery problems.

Various methods for the hydrolysis of lignocellulosic materials have recently been

described (Olsson and Hahn-Hagerdal, 1996). The dilute acid process is conducted under

high temperature and pressure, and has a reaction time in the range of seconds or minutes,

which facilitates continuous processing. As an example, using a dilute acid process with

1% sulfuric acid in a continuous flow reactor at a residence time of 0.22 minutes and

a temperature of 510 K with pure cellulose provided a yield over 50% sugars. In this

case, 1,000 kg of dry wood would yield about 164 kg of pure ethanol. Dilute acids

lead to a limited hydrolysis called prehydrolysis. Dilute-acid hydrolysis is carried out

using mineral acids such as H2SO4 or HCl, at temperatures between 395 K and 475 K

(Grethlein and Converse, 1991; Torget and Hsu, 1994). The chief advantages to using

hydrochloric acid over sulfuric acid are that HCI permeates the wood more easily than

H2SO4 and is a volatile compound, which assists in the crucial acid recovery steps. The

Udic-Rheinau process was an attempt to make the Bergius-Rheinau process economically

advantageous. In the improved process, the wood was first prehydrolyzed in 1% HCI

at 403 K to remove the hemicelluloses. The wood was then dried and subsequently

hydrolyzed with 40% HC1 at 295 K for 10 h. After washing the lignin residue with dilute

HC1, the HCI was recovered by vacuum distillation. This process was more economical

than the Bergius-Rheinau process (Kucuk and Demirbas, 1997). The biggest advantage of

dilute acid processes is their fast rate of reaction, which facilitates continuous processing.

Since 5-carbon sugars degrade more rapidly than 6-carbon sugars, one way to decrease

sugar degradation is to have a two-stage process. The first stage is conducted under mild

30 A. Demirbas

process conditions to recover the 5-carbon sugars while the second stage is conducted

under harsher conditions to recover the 6-carbon sugars.

Hydrolysis of lignocellulosic materials by concentrated sulfuric or hydrochloric acids

is a relatively old process. The concentrated acid process uses relatively mild tempera-

tures, and the only pressures involved are those created by pumping materials from vessel

to vessel. Reaction times are typically much longer than for dilute acid. This method

generally uses concentrated sulfuric acid followed by a dilution with water to dissolve

and hydrolyze or convert the substrate into sugar. This process provides a complete and

rapid conversion of cellulose to glucose and hemicelluloses to 5-carbon sugars with little

degradation. The critical factors needed to make this process economically viable are to

optimize sugar recovery and cost effectively recovers the acid for recycling.

Another basic method of hydrolysis is enzymatic hydrolysis. The chemical pretreat-

ment of the lignocellulosic biomass is necessary before enzymatic hydrolysis. The first

application of enzymatic hydrolysis was used in separate hydrolysis and fermentation

steps. Enzymatic hydrolysis is accomplished by cellulolytic enzymes. Different kinds

of “cellulases” may be used to cleave the cellulose and hemicelluloses. A mixture of

endoglucanases, exoglucanases, ˇ-glucosidases and cellobiohydrolases is commonly used

(Ingram and Doran, 1995; Laymon et al., 1996).

Figure 1 shows the main degradation products occurring during hydrolysis of lig-

nocellulosic material. When hemicelluloses are hydrolysed to xylose, mannose, acetic

acid, galactose, and glucose are liberated. Xylose is a hemicellulosic sugar mainly used

for its bioconversion to xylitol (Herrera et al., 2003). Hemicellulosic hydrolysis can be

generalized as

Hemicelluloses ! Xylan ! Xylose ! Furfural (1)

Acetyl groups ! Acetic acid (2)

Degradation of xylan yields eight main products: water, methanol, formic, acetic, and

propionic acids, hydroxy-1-propanone, hydroxy-1-butanone and 2-furfuraldeyde (Gullu,

2003). At high temperature and pressure, xylose is further degraded to furfural (Dun-

lop, 1948). Levulinic acid is formed by hydroxymethyl furfural degradation (Ulbricht

Figure 1. Main degradation products occurring during hydrolysis of lignocellulosic material.

Products from Lignocellulosics 31

et al., 1984). Cellulose is hydrolysed to glucose. The following reaction is proposed for

hydrolysis of cellulose:

Cellulose ! Glucan ! Glucose ! Decomposition products (3)

The residual lignin after acid hydrolysis can be a raw material for producing phenol,

benzene, toluene, xylene, and other aromatics through hydrocracking and related pro-

cesses. The rational upgrading of this fraction plays an important role in the economic

utilization of two-stage biomass hydrolysis (Kucuk and Demirbas, 1997). Phenolic com-

pounds are generated from partial breakdown of lignin (Bardet et al., 1985; Lapierre et al.,

1983; Sears et al., 1971), and have also been reported to be formed during carbohydrate

degradation (Popoff and Theander, 1976; Suortti, 1983). The furan derivatives such as

furfural and low molecular phenolic compounds will react further to form some polymeric

material.

Biochemical Degradation of Lignocellulosic Materials

Biochemical degradation is the process by which biomass is converted to gas (methane/

carbon dioxide), waste (compost or fertilizer) and water by using microorganisms. The

biochemical processes refer mainly to (1) aerobic fermentation, which produces compost,

carbon dioxide, and water; (2) anaerobic fermentation which produces fertilizer and gas

(methane/carbon dioxide), and (3) alcoholic fermentation which produces ethanol, carbon

dioxide, and waste.

Anaerobic decomposition is a complex process. The process by which anaerobic

bacteria decompose organic matter into methane, carbon dioxide, and a nutrient-rich

sludge involves a step-wise series of reactions requiring the cooperative action of several

organisms. A variety of factors affect the rate of digestion and biogas production. The

most important is temperature.

In a process of manure and straw mixture digestion, for the first 3 days, methane

yield was almost 0% and carbon dioxide generation was almost 100%. In this period,

digestion occurred as aerobic fermentation to carbon dioxide. The yields of methane and

carbon dioxide gases were fifty-fifty at the 11th day. At the end of the 20th day, the

digestion reached the stationary phase. The methane content of the biogas was in the

range of 73–79% for the runs, the remainder being principally carbon dioxide. During a

30-day digestion period, �80–85% of the biogas was produced in the first 15–18 days.

This implies that the digester retention time can be designed to 15–18 days instead of

30 days (Demirbas and Ozturk, 2004).

Another anaerobic method is to produce landfill gas (a mixture of methane and

other gases). The degradation of the organic component of refuse in landfills is a process

carried out by a succession of microbial populations.

Thermochemical Degradation of Lignocellulosic Materials

Thermochemical degradation can be subdivided into direct liquefaction, gasification,

and pyrolysis. In the case of liquefaction, feedstock macro-molecule compounds are

decomposed into fragments of light molecules in the presence of a suitable catalyst. With

pyrolysis, on the other hand, a catalyst is usually unnecessary, and the light decomposed

fragments are converted to oily compounds through homogeneous reactions in the gas

phase.

32 A. Demirbas

Liquefaction

The degradation of biomass into smaller products mainly proceeds by depolymerization

and deoxygenation. During these reactions, however, some condensation and repolymer-

ization of intermediate products also do proceed. To prevent these undesirable reactions

of intermediates, various methods have been attempted. The use of hydrogen is believed

to be one of the highly effective methods. When hydrogen is not used, another stabilizer

is needed.

Concerning the catalytic effect of alkali metal salts, there has been little description

about the roles that a catalyst plays in the liquefaction with some exceptions. Appell

(1967) proposed the mechanism for sodium carbonate-catalyzed liquefaction of carbohy-

drate in the presence of carbon monoxide. According to this mechanism, deoxygenation

occurs through decarboxylation from esterm formed by the hydroxyl group and formate

ion derived from the carbonate. Alkali salts, such as sodium carbonate and potassium

carbonate, can act as catalysts for hydrolysis of macromolecules, such as cellulose and

hemicellulose, into smaller fragments (Chornet and Overend, 1985).

The micellar-like broken down fragments produced by hydrolysis are then degraded

to smaller compounds by dehydration, dehydrogenation, deoxygenation and decarboxy-

lation. These compounds, once produced, rearrange through condensation, cyclization,

and polymerization, leading to new compounds (Chornet and Overend, 1985).

Lignin is a macromolecule, which consists of alkylphenols and has a complex three-

dimensional structure. It is generally accepted that free phenoxyl radicals are formed

by thermal decomposition of lignin above 525 K and that the radicals have a random

tendency to form a solid residue through condensation or repolymerization. The yield of

heavy oil decreased as the holding time was prolonged, owing to the formation of solid

residue by repolymerization of heavy oils, once produced. In the case of barks containing

larger amounts of lignin than woods, the yields of heavy oil could be lower, attributed

to repolymerization of the primary heavy oils (Demirbas, 2000).

The heavy oil obtained from the liquefaction process was a viscous tarry lump,

which sometimes caused troubles in handling. For this purpose, some organic solvents

were added to the reaction system. When only glycerol was used as a reaction solvent,

in the presence of alkaline, the polymers, polyglyceride, are formed on under heating,

and the glycerol is spent entirely (Demirbas, 1985).

Pyrolysis

Liquid, solid, and gaseous products were obtained from lignocellulosic materials by

pyrolysis. The liquid fraction of the pyrolysis products consists of two phases: an aque-

ous phase containing a wide variety of organo-oxygen compounds of low molecular

weight and a non-aqueous phase containing insoluble organics (mainly aromatics) of

high molecular weight. This phase is called bio-oil or tar, and is the product of greatest

interest. The ratios of acetic acid, methanol, and acetone of aqueous phase were higher

than those of the non-aqueous phase. It has been reported that the first runs in the

pyrolysis of the pyroligneous acid consists of about 50% methanol, 18% acetone, 7%

esters, 6% aldehydes, 0.5% ethyl alcohol, 18.5% water, and small amounts of furfural

(Wenzl et al., 1970). Table 2 shows the gas chromatographic analysis of the liquid fraction

of pyrolysis products from beech wood (Demirbas, 2006). The bio-oil formed at 725 K

contained high concentrations of compounds such as acetic acid, 1-hydroxy-2-butanone,

1-hydroxy-2-propanone, methanol, 2,6-dimethoxyphenol, 4-methyl-2,6-dimetoxyphenol

Products from Lignocellulosics 33

Table 2

Gas chromatographic analysis of the liquid fraction of pyrolysis products

from beech wood (wt% dry basis)

Reaction temperature (K)

Compound 625 675 725 775 825 875

Acetic acid 16.8 16.5 15.9 12.6 8.42 5.30

Methyl acetate 0.47 0.35 0.21 0.16 0.14 0.11

1-hydroxy-2-propanone 6.32 6.84 7.26 7.66 8.21 8.46

Methanol 4.16 4.63 5.08 5.34 5.63 5.82

1-hydroxy-2-butanone 3.40 3.62 3.82 3.88 3.96 4.11

1-hydroxy-2-propane acetate 1.06 0.97 0.88 0.83 0.78 0.75

Levoglucosan 2.59 2.10 1.62 1.30 1.09 0.38

1-hydroxy-2-butanone acetate 0.97 0.78 0.62 0.54 0.48 0.45

Formic acid 1.18 1.04 0.84 0.72 0.60 0.48

Guaiacol 0.74 0.78 0.82 0.86 0.89 0.93

Crotonic acid 0.96 0.74 0.62 0.41 0.30 0.18

Butyrolactone 0.74 0.68 0.66 0.67 0.62 0.63

Propionic acid 0.96 0.81 0.60 0.49 0.41 0.34

Acetone 0.62 0.78 0.93 1.08 1.22 1.28

Valeric acid 0.72 0.62 0.55 0.46 0.38 0.30

Isovaleric acid 0.68 0.59 0.51 0.42 0.35 0.26

Furfural 2.52 2.26 2.09 1.84 1.72 1.58

5-methyl-furfural 0.65 0.51 0.42 0.44 0.40 0.36

Butyric acid 0.56 0.50 0.46 0.39 0.31 0.23

Valerolactone 0.51 0.45 0.38 0.32 0.34 0.35

Propanone 0.41 0.35 0.28 0.25 0.26 0.21

2-butanone 0.18 0.17 0.32 0.38 0.45 0.43

Crotonolactone 0.12 0.19 0.29 0.36 0.40 0.44

Acrylic acid 0.44 0.39 0.33 0.25 0.19 0.15

2-cyclopenten-1-one 1.48 1.65 1.86 1.96 2.05 2.13

2-methyl-2-cyclopenten-1-one 0.40 0.31 0.24 0.17 0.13 0.14

Cyclopentenone 0.10 0.14 0.16 0.23 0.27 0.31

Methyl-2-furancarboxaldehyde 0.73 0.65 0.58 0.50 0.44 0.38

Phenol 0.24 0.30 0.36 0.43 0.54 0.66

2,6-dimethoxyphenol 2.28 2.09 1.98 1.88 1.81 1.76

Methyl phenol 0.32 0.38 0.44 0.50 0.66 0.87

4-methyl-2,6-dimetoxyphenol 2.24 2.05 1.84 1.74 1.69 1.58

Source: Demirbas, 2006.

and 2-cyclopenten-1-one, etc. A significant characteristic of the bio-oils was the high

percentage of alkylated compounds especially methyl derivatives.

The destructive reaction of cellulose is started at temperatures lower than 325 K and is

characterized by a decreasing polymerization degree. The glucose chains in cellulose are

first cleaved to glucose and from this, in a second stage, glucosan is formed by the splitting

off of one molecule of water. The isothermal pyrolysis of cellulose in air and milder

34 A. Demirbas

conditions, in the temperature range 625–645 K, was investigated (Fengel and Wegener,

1983). The decreased formation of char at the higher rate of heating was accompanied by

an increased formation of tar. The liquid fraction consisted mainly of water, with small

proportions of acetaldehyde, propion aldehyde, butiraldehyde, acrolein, crotonaldehyde,

furan, acetone, butanedione, and methanol. The net effect is a decrease in the volatile

fuel production and an increased yield of char cellulose converted to levoglucosan at

above 535 K temperatures (Freudenberg and Neish, 1968). Rapid depolymerization of

the cellulose by pyrolysis can lead to the recovery of free sugars from both levoglucosan

and its condensation products in the tar.

The hemicelluloses, which are present in deciduous woods chiefly as pentosans and

in coniferous woods almost entirely as hexosanes, undergo thermal decomposition very

readily. It was therefore to be expected that furan derivatives would readily be found

among the decomposition products. The thermal degradation of hemicelluloses begins

above 373 K during heating for 48 h; hemicelluloses and lignin are depolymerized by

steaming at high temperature for a short time. The metoxyl content of wet meals decreased

at 493 K. Therefore, the decrease of metoxyl contents below 473 K is mainly attributed

to the loss of metoxyl groups from the hemicelluloses (Demirbas, 2000).

Acetic acid is formed in the thermal decomposition of all three main components

of wood. When the yield of acetic acid originating from the cellulose, hemicelluloses,

and lignin is taken into account, the total is considerably less than the yield from to

wood itself (Wenzl et al., 1970). This can be explained by the fact that the main source

of acetic acid is the acetyl groups which are split of during the isolation of the single

components. Undoubtedly, most of the acetyl groups are attached to the pentosans. The

acetyl derivatives of xylose and arabinose are found in the products of a mild acid

hydrolysis.

The pyrolysis of lignin has been studied widely (Adler, 1977; Pakdel et al., 1997;

Demirbas, 2000). Pyrolysis seems to produce the most substituted phenols on a selective

basis. Lignin is broken down by extensive cleavage of ˇ-aryl ether linkages during

steaming of wood under 488 K (March, 1977). The cleavage of the aromatic C–O bond

led to the formation of one oxygen atom products, i.e., 3-propylphenol, 4-propylphenol,

and methyl-4-propylphenols. The extent of conversion of 1-ethyl-4-hydroxybenzene (4-

ethylphenol), as a model compound, was relatively small under both sets of reaction

conditions. The nature of these products shows that C–C cleavage occurred between the

aromatic ring and ˛-carbon atom. There was no indication of significant formation of

polymerized reaction products. The cleavage of the propyl side chain C–C bonds gave

minor products, i.e., 3-methylpyrocatechol, 4-methylpyrocatechol, 4-methylguaiacol, gua-

iacol, cresols, and phenol (Demirbas, 2000).

The phenol content increased to 52% and the yield of neutral oils increased from 18 to

33% with increasing temperature, while the methoxyl content decreased. The methoxyl

content at 675 K amounted to 11.8%, at 875 K to only 5%. The coke formed could be

briqueted without the addition of a binder (Demirbas, 1999).

Gasification

Some solids, liquids, and gases are produced in every thermal degradation process,

including gasification. However, pyrolysis differs from gasification in that the products

of interest are the char and liquids. Gasification is the process by which lignocellulosic

matter is converted to gas through thermal decomposition in an oxygen deficient envi-

ronment, followed by secondary reactions of the resulting volatiles. The gas phase of

Products from Lignocellulosics 35

Figure 2. Main themochemical degradation products from lignocellulosic material.

thermal degradation products contains mostly carbon monoxide and carbon dioxide, and

minor proportions of hydrogen, methane, ethane, and propane. The yield of produced

gas increased linearly with an increase in the temperature, and the concentrations of H2,

CH4, and C2H4 increased linearly with an increase in the temperature.

Hydro-gasification conversion of biomass to liquids has been demonstrated with the

use of a number of processing configurations. Generally, wood or biomass is injected as

slurry into a high pressure reactor, using a water or synthetic oil carrier. The reaction

occurs in reducing hydrogen phase. The reaction temperature varies from 625 to 695 K

and the pressure from 5 to 28 MPa. Sodium carbonate or nickel carbonate catalysts are

used in some cases.

Figure 2 shows main themochemical degradation products from lignocellulosic

material.

Conclusion

Lignicellulosic materials provides a potential source of added value chemicals, such as

reducing sugars, furfural, ethanol and other products, by using biochemical or chemical

and thermochemical. The initial degradation reactions include depolymerization, hydrol-

ysis, oxidation, dehydration, and decarboxylation. There are many studies on biomass

conversion methods because of energy problems and environmental pollution.

In the pyrolysis reactions of biomass: water is formed by dehydration; acetic acid

comes from the elimination of acetyl groups originally linked to the xylose unit; furfural

is formed by dehydration of the xylose unit; formic acid proceeds from carboxylic groups

of uronic acid; and methanol arises from methoxyl groups ofuronic acid.

Pyroligneous acids disappear in high-temperature pyrolysis. Levoglucosan is also

sensitive to heat and decomposes to acetic acid, acetone, phenols, and water. Methanol

arises from the methoxyl groups of aronic acid.

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