INTEGRATED PROCESS FOR TOTAL UTILIZATION OF

WOOD COMPONENTS BY STEAM-EXPLOSION

PRETREATMENT

K. SHIMIZU*, K. SUDO$, H. ONO%, M. ISHIHARA*, T. FUJII* and S. HISHIYAMA*

*Wood Chemistry Division, Forestry and Forest Products Research Institute, P.O. Box 16,Tsukuba Science City, Ibaraki 305, Japan

$Gumma Women's College, 501 Nakaohrui-machi, Takasaki Gumma-Ken 370, Japan%Department of Forest Products, The University of Tokyo 1-1-1, Yayoi, Bunkyo-ku,

Tokyo 113, Japan

(Received 8 August 1994; accepted 1 September 1995)

AbstractÐVarious species of hardwood chips were subjected to steam-explosion at 180±2308C for 1±20 min. On steaming, hemicellulose was hydrolyzed partially becoming extractable with water, and lig-nin was degraded by extensive cleavage of a- and b-aryl ether linkages becoming extractable with or-ganic solvents and/or dilute alkali. The three main components, hemicellulose, lignin, and cellulose, ofsteam-exploded woods were fractionated by successive extraction with water and 90% dioxane. Thewater extracts were decolored and puri®ed by chromatography on synthetic adsorbents and ionexchange resins, yielding a mixture of xylose and xylooligosaccharides (DP2010). The xylooligosac-charides were hydrolyzed to xylose with hemicellulolytic enzymes immobilized on ceramics having con-trolled pore size. The yield of xylose was 10±20% based on starting materials. The extracted amountsof lignin were di�erent among wood species. Syringyl lignin became more soluble than guaiacyl ligninon steaming. The lignin extracted was converted to thermoplastic materials, lignin-pitch, by phenolysisfollowed by heat treatment under vacuum. The lignin-pitch was well spun into ®ne ®laments at a speedof 500±1000 m minÿ1 in the temperature range 150±1908C using the melt-spinning method. The ®la-ments were carbonized on heating from room temperature up to 10008C in a stream of nitrogen. Thecarbon ®ber was obtained in a yield of more than 40% based on the starting materials. The physicalproperties of the lignin- based carbon ®ber was equivalent to a commercial carbon ®ber made from pet-roleum pitch. The residual ®bers, mainly cellulose, were hydrolyzed with cellulase derived from Tricho-derma viride. Their enzymatic susceptibility was di�erent among wood species. It was higher in specieshaving lower contents of Klason lignin and guaiacyl lignin. Birch and Mollissima acasia were hydro-lyzed more than 90%. Finally, the economics of this process are discussed assuming a plant processing100 t of hardwoods per day. # 1998 Elsevier Science Ltd. All rights reserved

KeywordsÐCellulose; hemicellulose; lignin, carbon ®ber; xylooligosaccharide; cellulase, economics

1. INTRODUCTION

In Japan, the total area of broad-leaved forest

is 12 million ha and the store of hardwoods is

about 1.5 billion m3. Up to 30 years ago, we

annually used 30±40 million m3 of these hard-

woods as ®rewood and charcoal. Nowadays,

only one third is used as pulp and substrate

for mushroom cultivation. It is necessary to

activate the depressed forestry by developing a

new way to utilize the lesser used hardwoods.

Steam-explosion is an e�ective pretreatment

for enhancing the enzymatic susceptibility of

hardwoods and for fractionating three main

components, leading to total utilization of

wood components.1 This paper deals with the

integrated process for total utilization of woodcomponents by steam-explosion pretreatment.

2. PROCESS FOR TOTAL UTILIZATION OF WOODCOMPONENTS

Enzymatic sacchari®cation of wood wastehas received considerable interest with recentdevelopments in cellulase technology. It is wellknown that the susceptibility of some speciesof hardwoods to enzymatic attack is improvedremarkably by steam-explosion.1 It is necess-ary to develop an integrated processing, usingall of the components, to make the processeconomically feasible.

Figure 1 shows our process for total utiliz-ation of hardwood components. Wood chips

Biomass and Bioenergy Vol. 14, No. 3, pp. 195±203, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0961-9534/98 $19.00+0.00PII: S0961-9534(97)10044-7

195

were subjected to steaming at 180±2308C for2±20 min and ®berized by explosion or by useof a re®ner. The ®bers obtained are extractedsuccessively with water and 90% dioxane. Theresidual cellulose is hydrolyzed with a commer-cial cellulase preparation ``Meicelase'' derivedfrom Trichoderma viride.1,2 From the waterextracts, xylose and xylooligosaccharides areisolated and can be used as a sweetener and/orfood additive. The lignin fragments isolatedform the dioxane extract are converted to car-

bon ®ber and adhesives as described below.The enzymatic hydrolyzate of cellulose can befermented to single cell protein and/or alcohol.

Table 1 shows the results of analyses ofbirch wood (Betula platyphylla) steamed atvarious conditions. The steaming treatmentresulted in a weight loss of 4±27%. Most ofthe hemicellulose and lignin were modi®ed,becoming soluble in water and 90% dioxane,respectively. The residual cellulose was com-pletely hydrolyzed with the enzyme.

Fig. 1. Process for total utilization of wood components by steam explosion.

Table 1. Analysis of birch woods steamed at various condition

Steamingpressure MPa Time (min) Yield (%)

Klason lignin(%)

Water extract(%)

Dioxane extract(%)

Enzymaticsusceptibility

(%)

0.98 20 73.4 28.6 23.7 10.3 1001.47 5 84.9 29.9 19.2 8.1 98.0

10 75.0 28.2 15.6 9.1 96.015 73.7 32.1 14.5 10.6 100

1.96 3 96.0 29.5 25.4 14.0 96.26 76.5 37.1 23.9 29.9 1009 80.3 35.3 25.7 34.5 100

2.45 2 83.5 30.0 34.2 20.4 99.34 82.5 32.3 27.1 25.7 100

2.94 1 93.7 30.1 33.5 17.5 1002 81.3 31.3 34.5 21.9 100

K. SHIMIZU et al.196

3. STEAM-EXPLOSION OF VARIOUS SPECIES OFWOODS

Chips of various species of woods including

hardwoods (44 spceies) and softwood (6

species) were treated with saturated steam at

1808C for 15 min and ®berized for 1 min in a

de®brator.1 A sample of the ®ber obtained

was hydrolyzed with the enzyme without any

extraction, yielding a hydrolyzate consisting

mainly of glucose (50±60%) and xylose (30±

40%). the extent of enzymatic hydrolysis of

the residual polysaccharides in the ®ber varied

from 80 to 17% depending upon the species.

The steamed and de®bratd ®bers were

extracted successfully with hot water and 90%

dioxane. The amounts of hemicellulose and

lignin extracted ranged from 10±18% and 5 to

10%, respectively, based on the weight of the

®bers. Most of the hemicellulose was removed

on steaming, followed by extraction with hot

water in all of the hardwoods, but the extrac-

table lignin ranged form 57.4 to 16.1%

depending upon the species. The di�erences in

the extractability of lignin are probably at-

tributable to the di�erences in the chemical

structure of the lignin among the hardwood

species.

4. MORPHOLOGICAL CHANGES OF CELL WALLON STEAMING

The morphological changes in the distri-bution of the cell wall components uponsteaming followed by successive extractionwith water and 90% dioxane, and enzymaticsusceptibility of cellulose were studied. Upon

steaming, lignin of the secondary wall middlelayer (S2) was degraded becoming moreextractable than that from other parts.However, the amount of lignin remaining afterextraction with 90% dioxane was quite di�er-

ent among the wood species. The enzymaticsusceptibility increased as the amount of ligninremaining decreased. 2 Lignin in the secondarywall of ray and axial parenchyma cells becamemore extractable than that of ®bers and

vessels. Lignin in the vessel walls was most re-sistant.

To explain why the degradation extent of

lignin on steaming and the enzymatic suscepti-bility of cellulose in steamed woods is di�erentamong wood species and also cell types, thenature of secondary-wall lignin was investi-

gated in various wood species and cell typesby means of ultraviolet microspectrometry andchemical analysis.3 Furthermore, the enzy-matic susceptibility of cellulose in cell wallswas investigated on ultrathin sections (100 nm)

Fig. 2. Electron micrograph of an ultrathin cross section of an untreated Beech (F. crerata) chip afterincubation in the enzyme solution for 4 h.

Total utilization of wood by steam-explosion pretreatment 197

to obtain some clues for understanding theultrastructural organization of ligni®ed cell-walls.3

The ultrathin sections were cut fromuntreated wood (air- dried) and treated withcellulase. Figure 2 shows an electron micro-graph of an untreated beech (Fagus crenata)chip after incubation in the cellulase solutionfor 4 h. The ®ber S2 layer was eroded remark-ably by the enzymatic attack, whereas the®ber secondary wall outer layer (S1) was not.The secondary wall of axial parenchyma cellswas eroded a little, but the secondary wall ofvessel was most resistant.2

The chemical nature and content of ligninwere di�erent from wood to wood. In thewood species with lower Klason-lignin con-tents, the S2 lignin of wood ®bers was syringyltype, and the cellulose of the ultrathin sectionswas susceptible to enzymatic attack indicatingthat cellulose is loosely packed with lignin. Inthe wood species with higher Klason-lignincontents, the S2 lignin of wood ®bers was richin guaiacyl residues, and the cellulose was notsusceptible to enzymatic attack.

The S2 lignin of vessels consisted predomi-nantly of guaiacyl residues in all species, andthe enzyme was not able to attack the celluloseof ultrathin sections. The S2 lignin of xylemparenchyma was richer in guaiacyl residuesthan was the lignin of wood ®bers, althoughthe former was not as rich as the vessels, andthe enzyme could not reach the cellulose.

5. WATER EXTRACTS

The water extracts of steam-exploded chipsbeing brown in color were decolored and puri-®ed by use of synthetic adsorbents (AmberliteXAD 2 and 7) and various types of ion

exchange resins. The sugars in the extracts

were separated into neutral and acidic frac-tions in the usual way.4 The neutral sugars

mainly consisted of xylose and xylooligosac-

charides having DP 2±10 and were fractio-

nated preparatively by GPC on cellulo®ne

(10 cm� 2 m) (Table 2). The amounts of

sugars having lower DP increased with

increased steaming time.

The mixtures of these sugars were reduced

to sugar alcohols by hydrogenation under H2

pressure of 14.7 MPa at 100±1308C for 2 h

using Raney±Ni as a catalyst. They were hy-

droscopic and sweet. They gave viscous syrups

when dissolved in water and can be used asfood additives and/or as sweetener.

The acidic sugars were fractionated by ion

exchange chromatography on Diaion

(2� 90 cm) (Table 3). Aldo-(bio- ±pentao-)

uronic acids, consisting of xylose and 4-0-Me-

GlcAp residues were found to be present. Thealdo-(trio- ±pentao-) uronic acid fractions

were mixtures of possible isomers and

unknown substances.

In order to produce xylose and/or xylitol,

the oligosaccharides in the extract were hydro-

lysed with commercial cellulases usingeither T. viride or Aspergillus niger. These

enzymes were immobilized on porous silica

glass and ceramics such as alumina and titania

activated with TiCl4 and on their silanized de-

rivatives with glutaraldehyde as reported pre-

viously.5 The amounts of the immobilized

enzymes were in the range 10±50 mg gÿ1 car-rier (dry) depending on the kind of carrier and

immobilization method. their activities toward

carboxymethyl cellulose (CMC), xylan, aryl-b-glucoside, and aryl-b-xyloside were 3±53% of

those with native enzymes. The optimum pH

of the enzymes shifted to the acidic side in

Table 2. Composition of neutral sugars in water extractfrom birch steamed at 1.47 MPa for 10 min

Fr. Sugar Weight (%)

1 Others 12.82 Xyl10 4.03 Xyl9 2.34 Xyl8 2.95 Xyl7 3.56 Xyl6 6.07 Xyl5 7.18 Xyl4 9.89 Xyl3 12.010 Xyl2 16.311 Xyl 23.2

Table 3. Acidic sugars in water extract (1 g) from birchsteamed at 15 Kgf cmÿ1 for 10 min

Fraction CompoundAmount(mg)

1 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl4 732 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl3 74.23 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl2 137.74 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl 14.65 4-O-GalA-D-Xyl 11.36 Unknown 28.57 4-O-Me-D-GlcA 6.98 Unknown 5.99 GalA 6.510 Unknown 3.2

K. SHIMIZU et al.198

most cases, whereas the optimum temperatureswere nearly the same as those of native ones.The activity of immobilized enzyme prep-arations toward CMC did not change signi®-cantly during continuous operation over aperiod of 60 days. The immobilized enzymeswere packed in glass columns (2� 30 cm) andthe water extracts (Brix 10%) were appliedcontinuously to the columns at a ¯ow rate of0.5 m, minÿ1. Gel permeation chromatographyshowed that xylose was a main sugar formedin addition to a trace amount of xylobiose.

6. MECHANISM OF LIGNIN DEGRADATION ONSTEAMING

In order to elucidate chemical properties ofsteamed wood lignin (STWL), beech wood (F.crenata) was treated at 183±2308C with satu-rated steam for various periods of time. Theamount of lignin extractable with 90% diox-ane increased remarkably as the steaming tem-perature was elevated and the time extended.It is possible to extract more than 70% of thelignin in certain hardwoods such as birch,beech, acacia, and aspen by steaming at 2308Cfor 2 min.1,2 The lignins from woods treatedunder various steaming conditions were inves-tigated by elementary and functional analyses,gel permeation chromatography, infrared spec-troscopy, 13C-NMR and nitrobenzene oxi-dation.6 For comparison, beech milled-woodlignin (MWL) was also investigated in thesame manner. The lignins extracted had smal-ler molecular weights and higher contents ofmethoxyl, syringyl, and hydroxyl groups thanthose of MWL, indicating that syringyl-typelignin is depolymerized more preferentiallythan guaiacyl-type lignin. Lignin was brokendown by extensive cleavage of b-aryl ether lin-kages during the steaming process, resulting toSTWL of high phenolic hydroxyl content. Atthe same time, the aliphatic hydroxyl groupcontent decreased. The chemical properties ofSTWL were found to depend on the steamingtemperature. Namely, lignin from woodsteamed at relatively low temperature (183±2158C) was rich in syringyl units and onlyslightly modi®ed. By treatment at higher tem-perature (2308C) STWL most likely consistedof heavily condensed type of structures andmodi®ed functionality. In order to clarify themechanism of lignin degradation broughtabout by a steam explosion of wood the ligninfractions seperated from the reaction liquor,

were analysed by gas chromatograph (GC)and gas chromatograph±mass spectrometer(GC±MS).7 Among the degraded compounds,guaiacyl acetone, vanilloyl acetyl and their syr-ingyl analogies were identi®ed. The amount ofsyringaresinol liberated was much less thanthat expected based on the proportional con-tent of these structural units in the original lig-nin. These facts suggest that the lignin ismainly decomposed by acid catalyzed hydroly-sis during the steam treatment.

7. LIGNIN CARBON FIBER

A new carbon ®ber was prepared in twoways from STWL (lignin A in Fig. 1) isolatedfrom steam-exploded birch wood.8,9 STWLwas modi®ed to a thermoplastic by hydrogen-ation using Raney±Ni as a catalyst in 0.5 NNaOH under an initial H2 pressure of 2.92MPa at 2508C for 60 min. The reaction mix-ture was extracted with CHCl3 after acidi®ca-tion with 2 N HCl. The CHCl3 extracts werefurther extracted with CS2 to remove mono-and di-meric products. The yield of CHCl3soluble and CS2 insoluble fraction was 50.9%.This fraction was heated at 300±3508C for30 min in a stream of N2, giving a pitch likesubstance (lignin pitch) in yields of 78%. Thislignin pitch was spun into ®ne ®lamentsthrough a pinhole (diameter: 0.3 mm) from themolten state in the temperature range of 155±1808C at speeds of 100±500 m minÿ1 under N2

pressure. The lignin-based ®lament was ther-moset on heating in air up to 2108C at a rate1± 28C minÿ1 and then carbonized at a heatingrate of 58C minÿ1 up to 10008C in a stream ofN2. The yield of carbon ®ber was 70% on thebasis of the ®lament. Accordingly, the yield oflignin based carbon ®ber was about 27±28%based on extracted lignin.

By another process, STWL was ®rst reactedwith phenol in the presence of p-toluene sulfo-nic acid at 1808C for 4 h, heated for 10 min ina vacuum, and then converted into carbon®ber by the process described above. The lig-nin-pitch obtained had excellent spinnabilityin the melt state to form a ®ne ®lament. Itwas spun into ®ne ®laments at a speed of 500±1000 m minÿ1 in the temperature range 150±1908C. The green ®bers were easily made infu-sible when heated in air at a relatively highheating rate (5±608C hÿ1). The lignin-basedcarbon ®ber was produced in 43.7% yieldbased on the starting material by the process

Total utilization of wood by steam-explosion pretreatment 199

described above. The physical properties ofthese lignin-based carbon ®bers are shown inTable 4. The lignin-based carbon ®bers wereclassi®ed as a general purpose grade.9

8. LIGNIN ADHESIVES

Wood adhesives have also been studied asfeasible products from (STWL).10 STWL (lig-nins A and B in Fig. 1) were reacted with twotimes excess amount of phenol in the presenceof H2SO4 at 1708C for 3 h and the unreactedphenol was removed under reduced pressure.The degree of phenolation was calculated tobe in excess of one mol/lignin (C9) unit on thebasis of 13C NMR measurements. The pheno-lated lignin was methylolated in order to pre-pare adhesive resins. The cure behavior of theadhesive resins was examined by TorsionalBraid Analysis (TBA). It was revealed that thephenolated STWL-based resins had intrinsicretardation in cure as compared to a commer-cial phenolic resin. This defect, however, waspartly overcome by increasing the pH valuesof the steam-exploded lignin resins. The ad-hesive from these resins generally providesexcellent bond strength comparable to a com-mercial phenolic resin (Table 5).

9. ENZYMATIC HYDROLYSIS OF CELLULOSE

The residual ®bers were hydrolyzed with cel-lulase derived from T. viride. The enzymaticsusceptibility was di�erent among woodspecies, and was higher in species having lowercontents of Klason lignin and lower contents

of non-extractable lignin after steaming.3 Thehydrolysis extents of birch and mollissima aca-cia were more than 90% (Table 1).

Cellulosic ®bers were semicontinuouslyhydrolyzed on a large scale [2±2.5 kg of sub-strate vs 20,000 IU ®lterpaperase (FPase)]using a 10-l hydrolysis reactor with an ultra-®ltration unit for the recovery and reuse ofcellulases (Fig. 3).11 Substrates were added tothe reactor at appropriate intervals to keep asolids concentration of approx. 5% (W/V)(Fig. 4). All of the enzyme was added at thebeginning and no further addition was done.The ultra®ltration unit was operated intermit-tently.

In this experiment, two substrates were usedas shown in Fig. 4. One was the birch woodsteamed at 1.27 MPa for 15 min and thenextracted with water. This steamed birch woodcontained lignin 34.7%. Another substrate wasa commercial bleached hardwood pulp ofwhich lignin content was less than 2%. Theenzyme required to produce one gram of redu-cing sugar in this reactor amounted to 27.3FPase IU gÿ1 reducing sugar (RS) for steamedbirch wood, and 7.4 FPase IU gÿ1 RS forhardwood Kraft pulp.

The loss of enzyme is attributed to severalcauses: irreversible enzyme adsorption to inso-luble residue, especially in case of the substratecontaining lignin, physical deterioration ofenzyme in the tubular UF membrane moduleand proteolytic modi®cation of originalenzyme. The enzyme should have a consider-able shearing stress in the tubular UF mem-brane module in operating the ultra®ltrationunit because the reaction mixture is pumped

Table 4. Physical properties of lignin based carbon ®bers

Fiber width (mm) 7.622.7Tensile strength (MPa) 6622232Elongation (%) 1.6320.19Modulus of elasticity (t mmÿ2) 4.1520.64

Table 5. Tensile shear bond strength of adhesives fromphenolysis lignin

Adhesive

Bond strength(MPa) at

normal stateAfter cyclic

boil

PLAFf 48.129.0 53.926.3PLAF 66.629.8 44.323.4PLBFf 58.724.3 55.728.1PLBF 75.327.7 37.727.9Commercial phenolic resin 63.826.8 48.3211.8

Specimens were cured at 1408C for 6 min. PL-A,PL-B:Adhesives from phenolysis lignin A and B, respectively. F:methylolated. f: wheat ¯our was added as extender

Fig. 3. Apparatus for continuous hydrolysis of ligno-cellulose.

K. SHIMIZU et al.200

through the tube (cross-sectional area ofapprox. 1 cm2 and length of 1.31 m) at a vel-ocity of 10 l minÿ1.

In the case of the steamed birch wood, thehydrolysis residue accumulated in the reactorhad to be removed intermittently as shown inFig. 4(a). The accumulation of unhydrolyzableresidue reduced the reaction e�ciency. Theyield of reducing sugar was considerably lowerthan in the case of the lignin-free kraft pulp.

The sugar composition of the hydrolyzateremained virtually constant from beginning toend of the hydrolysis in spite of progressiveloss of enzyme activity. The analysis of theenzyme composition in the hydrolyzate duringhydrolysis revealsed that an exo-b-D-glucanasecomponent was adsorbed selectively at thestages of advanced hydrolysis extent.11 Thesugars in the hydrolyzate were converted to thesingle cell protein of Candida utilis in a yield of46.7% (percentage of the amount of dried my-celium based on the sugars consumed).1

Fig. 4. Balance of substrate and enzyme (FPase) in semi continuous enzymatic hydrolysis of lignocellu-losic materials.

Table 6. Material balance in process of total utilization ofwood components

Day (t) Year (t)

Hardwood chips 100.0 30,000Steam-exploded ®ber 85.0 25,500Hemicellulose 17.0 5100Xylooligosaccharides 15.0 4600Reduced xylooligosaccharides 15.0 4500Lignin 12.0 3600Carbon ®ber 5.1 1542Residual Cellulose 51.0 15300Glucose 39.4 1180896% Ethanol 18.0 5412

(22.2 kl) (6685 kl)Residual lignin 10.0 3000

Table 7. Initial investiment

Process

Price(X*****1000) %

Steam-explosion and fractionation 2,158,000 19.2Puri®cation of xylooligosaccharides 1,500,000 13.3Reduction of xylooligosaccharides 1,000,000 8.9Production of carbon ®ber 4,121,000 36.6Production of cellulose 710,000 6.3Hydrolysis of cellulose 1,014,000 9.0Alcohol fermentation 760,000 6.7Sum 11,263,000 100.0

Total utilization of wood by steam-explosion pretreatment 201

The adsorption behavior of T. viride cellulaseson steamed birch wood was studiedpreviously.12 Substrate/enzyme (S/E) ratio,hydrolysis time and sacchari®cation extent aswell as the presence of absence of lignin in thesubstrate were taken into consideration as fac-tors a�ecting the enzyme adsorption. FPasecomponents were adsorbed more selectivelythan other cellulase components on the sub-strate. The presence of lignin in the steamedhardwood tended to slow down the enzymeadsorption, but it did not appear to restrict theextent of hydrolysis of the carbohydrate moiety.The changes in the composition of the enzymepreparation during the course of hydrolysis wereanalyzed by fast protein liquid chromatography

(FPLC). The irreversible adsorption of speci®ccellulase components was not observed in theprolonged hydrolysis of steamed birch woodcontaining abundant lignin.12

10. ECONOMICS OF PROCESS

The economics of the process shown inFig. 1 was evaluated by assuming a plant pro-cessing 30,000 t of birch wood chips per year(100 t per day) dry basis. Table 6 shows thematerial balance in the process. The annualproduction of the reduced xylooligosacchar-ides, carbon ®ber, and alcohol is 4,500 t,1,542 t and 6,658 kl, respectively.

Table 8. Cost analysis of process for utilization of wood components by steam-explosion

Item Unit cost Sum�***** 1000

Labor 49 persons�12,000 [588,000]Utilities [1,487,702]Water ***** 150 mÿ3 190,854Electricity ***** 15 kWhÿ1 743,348Crude oil ***** 50 kgÿ1 542,300Maintenance of environment 11,200

Chemicals [1,861,466]NaCl ***** 30 kgÿ1 32,40035% HCl ***** 22 kgÿ1 56,34650% NaOH ***** 30 kgÿ1 79,158N2 ***** 55 Nmÿ3 339,240H2 ***** 100 Nmÿ3 67,100Catalyst ***** 2,500 kgÿ1 116,250Phenol ***** 200 kgÿ1 160,200Enzyme ***** 1,655 kgÿ1

Others [1,002,210]Wood Chips ***** 30 kg� 30,000 t [900,000]Initial cost [1,899,540]Depreciation 10%, 10 yearsInterest Initial cost� 7%/yearMaintenance Initial cost� 2.0%/year

Others [253,227]Taxes Initial cost� 1.4%/yearInterest Initial cost� 7%/year

Sum 6,981,303

Table 9. Production cost

Goods Output (t/year) Cost�( ***** 1000)Unit cost ( *****

kgÿ1) Market price ( ***** kgÿ1)

Crude oligosaccharide 5100 453,900Xylooligosaccharide 4600 687.872Reduced xylosugars 4500 823,340 437 450

1,965,112 2,025,000Lignin 3600 320,400Carbon ®ber 1542 2,803,603 1559 2500

2,404,003 3,855,000Cellulose 15,300 1,361,700Enzymes (534,574)Glucose 11,750 982,744Ethanol 5412 267,744 482 172

2,612,188 930,864Residual lignin 3000 33

99,0006,981,303 6,909,864

K. SHIMIZU et al.202

The capital investment is more than $100million (US. $ 1 equivalent to 100 yen) asshown in Table 7. The production facilities forcarbon ®ber occupies 37%. The cost for labor,utilities, chemicals, wood chips, and so on arelisted in Table 8. The cost for steam-explosionfollowed by extraction with water and aqueousalkali amounts to $ 21 million, producinghemicellulose (5100 t), lignin (3600 t), and cel-lulose (15300 t) annually. The total cost ofproduction amounts to $ 70 million as shownin Table 9. The reduced xylooligosaccharides,carbon ®ber, and alcohol can be calculated as$ 4.4, 16 and 4.8 kgÿ1, respectively.

If market prices are assumed as shown inTable 9, the total income amounts to 69million. It is necessary to lower the costs ofproduction, especially the processes for steam-explosion-fractionation and the enzymatic hy-drolysis of cellulose.

AcknowledgementÐThis work was supported by the Bio-mass Conversion Program of the Ministry of Agriculture,Forest and Fisheries.

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Total utilization of wood by steam-explosion pretreatment 203