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Integrated process for total utilization of wood components by steam-explosion pretreatment
PII:
Biomass and Bioenergy Vol. 14, No. 3, pp. 195±203, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0961-9534/98 $19.00 + 0.00 S0961-9534(97)10044-7
INTEGRATED PROCESS FOR TOTAL UTILIZATION OF WOOD COMPONENTS BY STEAM-EXPLOSION PRETREATMENT K. SHIMIZU*, K. SUDO$, 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 lignin was degraded by extensive cleavage of a- and b-aryl ether linkages becoming extractable with organic solvents and/or dilute alkali. The three main components, hemicellulose, lignin, and cellulose, of steam-exploded woods were fractionated by successive extraction with water and 90% dioxane. The water extracts were decolored and puri®ed by chromatography on synthetic adsorbents and ion exchange resins, yielding a mixture of xylose and xylooligosaccharides (DP2010). The xylooligosaccharides were hydrolyzed to xylose with hemicellulolytic enzymes immobilized on ceramics having controlled pore size. The yield of xylose was 10±20% based on starting materials. The extracted amounts of lignin were dierent among wood species. Syringyl lignin became more soluble than guaiacyl lignin on steaming. The lignin extracted was converted to thermoplastic materials, lignin-pitch, by phenolysis followed by heat treatment under vacuum. The lignin-pitch was well spun into ®ne ®laments at a speed of 500±1000 m minÿ1 in the temperature range 150±1908C using the melt-spinning method. The ®laments were carbonized on heating from room temperature up to 10008C in a stream of nitrogen. The carbon ®ber was obtained in a yield of more than 40% based on the starting materials. The physical properties of the lignin- based carbon ®ber was equivalent to a commercial carbon ®ber made from petroleum pitch. The residual ®bers, mainly cellulose, were hydrolyzed with cellulase derived from Trichoderma viride. Their enzymatic susceptibility was dierent among wood species. It was higher in species having lower contents of Klason lignin and guaiacyl lignin. Birch and Mollissima acasia were hydrolyzed more than 90%. Finally, the economics of this process are discussed assuming a plant processing 100 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 hardwoods 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 eective 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 195
integrated process for total utilization of wood components by steam-explosion pretreatment. 2. PROCESS FOR TOTAL UTILIZATION OF WOOD COMPONENTS
Enzymatic sacchari®cation of wood waste has received considerable interest with recent developments in cellulase technology. It is well known that the susceptibility of some species of hardwoods to enzymatic attack is improved remarkably by steam-explosion.1 It is necessary to develop an integrated processing, using all of the components, to make the process economically feasible. Figure 1 shows our process for total utilization of hardwood components. Wood chips
K. SHIMIZU et al.
196
Fig. 1. Process for total utilization of wood components by steam explosion.
were subjected to steaming at 180±2308C for 2±20 min and ®berized by explosion or by use of a re®ner. The ®bers obtained are extracted successively with water and 90% dioxane. The residual cellulose is hydrolyzed with a commercial cellulase preparation ``Meicelase'' derived from Trichoderma viride.1,2 From the water extracts, xylose and xylooligosaccharides are isolated and can be used as a sweetener and/or food additive. The lignin fragments isolated form the dioxane extract are converted to car-
bon ®ber and adhesives as described below. The enzymatic hydrolyzate of cellulose can be fermented to single cell protein and/or alcohol. Table 1 shows the results of analyses of birch wood (Betula platyphylla) steamed at various conditions. The steaming treatment resulted in a weight loss of 4±27%. Most of the hemicellulose and lignin were modi®ed, becoming soluble in water and 90% dioxane, respectively. The residual cellulose was completely hydrolyzed with the enzyme.
Table 1. Analysis of birch woods steamed at various condition Steaming pressure MPa 0.98 1.47 1.96 2.45 2.94
Time (min) 20 5 10 15 3 6 9 2 4 1 2
Yield (%)
Klason lignin (%)
Water extract (%)
Dioxane extract (%)
73.4 84.9 75.0 73.7 96.0 76.5 80.3 83.5 82.5 93.7 81.3
28.6 29.9 28.2 32.1 29.5 37.1 35.3 30.0 32.3 30.1 31.3
23.7 19.2 15.6 14.5 25.4 23.9 25.7 34.2 27.1 33.5 34.5
10.3 8.1 9.1 10.6 14.0 29.9 34.5 20.4 25.7 17.5 21.9
Enzymatic susceptibility (%) 100 98.0 96.0 100 96.2 100 100 99.3 100 100 100
Total utilization of wood by steam-explosion pretreatment
197
3. STEAM-EXPLOSION OF VARIOUS SPECIES OF WOODS
4. MORPHOLOGICAL CHANGES OF CELL WALL ON STEAMING
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 extractable lignin ranged form 57.4 to 16.1% depending upon the species. The dierences in the extractability of lignin are probably attributable to the dierences in the chemical structure of the lignin among the hardwood species.
The morphological changes in the distribution of the cell wall components upon steaming followed by successive extraction with water and 90% dioxane, and enzymatic susceptibility of cellulose were studied. Upon steaming, lignin of the secondary wall middle layer (S2) was degraded becoming more extractable than that from other parts. However, the amount of lignin remaining after extraction with 90% dioxane was quite dierent among the wood species. The enzymatic susceptibility increased as the amount of lignin remaining decreased. 2 Lignin in the secondary wall of ray and axial parenchyma cells became more extractable than that of ®bers and vessels. Lignin in the vessel walls was most resistant. To explain why the degradation extent of lignin on steaming and the enzymatic susceptibility of cellulose in steamed woods is dierent among wood species and also cell types, the nature of secondary-wall lignin was investigated in various wood species and cell types by means of ultraviolet microspectrometry and chemical analysis.3 Furthermore, the enzymatic susceptibility of cellulose in cell walls was investigated on ultrathin sections (100 nm)
Fig. 2. Electron micrograph of an ultrathin cross section of an untreated Beech (F. crerata) chip after incubation in the enzyme solution for 4 h.
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198
The water extracts of steam-exploded chips being brown in color were decolored and puri®ed by use of synthetic adsorbents (Amberlite XAD 2 and 7) and various types of ion
exchange resins. The sugars in the extracts were separated into neutral and acidic fractions in the usual way.4 The neutral sugars mainly consisted of xylose and xylooligosaccharides having DP 2±10 and were fractionated 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 hydroscopic and sweet. They gave viscous syrups when dissolved in water and can be used as food 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-MeGlcAp residues were found to be present. The aldo-(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 hydrolysed with commercial cellulases using either 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 derivatives with glutaraldehyde as reported previously.5 The amounts of the immobilized enzymes were in the range 10±50 mg gÿ1 carrier (dry) depending on the kind of carrier and immobilization method. their activities toward carboxymethyl cellulose (CMC), xylan, aryl-bglucoside, 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 extract from birch steamed at 1.47 MPa for 10 min
Table 3. Acidic sugars in water extract (1 g) from birch steamed at 15 Kgf cmÿ1 for 10 min
to obtain some clues for understanding the ultrastructural organization of ligni®ed cellwalls.3 The ultrathin sections were cut from untreated wood (air- dried) and treated with cellulase. Figure 2 shows an electron micrograph of an untreated beech (Fagus crenata) chip after incubation in the cellulase solution for 4 h. The ®ber S2 layer was eroded remarkably by the enzymatic attack, whereas the ®ber secondary wall outer layer (S1) was not. The secondary wall of axial parenchyma cells was eroded a little, but the secondary wall of vessel was most resistant.2 The chemical nature and content of lignin were dierent from wood to wood. In the wood species with lower Klason-lignin contents, the S2 lignin of wood ®bers was syringyl type, and the cellulose of the ultrathin sections was susceptible to enzymatic attack indicating that cellulose is loosely packed with lignin. In the wood species with higher Klason-lignin contents, the S2 lignin of wood ®bers was rich in guaiacyl residues, and the cellulose was not susceptible to enzymatic attack. The S2 lignin of vessels consisted predominantly of guaiacyl residues in all species, and the enzyme was not able to attack the cellulose of ultrathin sections. The S2 lignin of xylem parenchyma was richer in guaiacyl residues than was the lignin of wood ®bers, although the former was not as rich as the vessels, and the enzyme could not reach the cellulose.
5. WATER EXTRACTS
Fr.
Sugar
Weight (%)
1 2 3 4 5 6 7 8 9 10 11
Others Xyl10 Xyl9 Xyl8 Xyl7 Xyl6 Xyl5 Xyl4 Xyl3 Xyl2 Xyl
12.8 4.0 2.3 2.9 3.5 6.0 7.1 9.8 12.0 16.3 23.2
Fraction 1 2 3 4 5 6 7 8 9 10
Compound 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl4 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl3 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl2 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl 4-O-GalA-D-Xyl Unknown 4-O-Me-D-GlcA Unknown GalA Unknown
Amount (mg) 73 74.2 137.7 14.6 11.3 28.5 6.9 5.9 6.5 3.2
Total utilization of wood by steam-explosion pretreatment
most cases, whereas the optimum temperatures were nearly the same as those of native ones. The activity of immobilized enzyme preparations toward CMC did not change signi®cantly during continuous operation over a period of 60 days. The immobilized enzymes were packed in glass columns (2 30 cm) and the water extracts (Brix 10%) were applied continuously to the columns at a ¯ow rate of 0.5 m, minÿ1. Gel permeation chromatography showed that xylose was a main sugar formed in addition to a trace amount of xylobiose.
199
were analysed by gas chromatograph (GC) and gas chromatograph±mass spectrometer (GC±MS).7 Among the degraded compounds, guaiacyl acetone, vanilloyl acetyl and their syringyl analogies were identi®ed. The amount of syringaresinol liberated was much less than that expected based on the proportional content of these structural units in the original lignin. These facts suggest that the lignin is mainly decomposed by acid catalyzed hydrolysis during the steam treatment. 7. LIGNIN CARBON FIBER
6. MECHANISM OF LIGNIN DEGRADATION ON STEAMING
In order to elucidate chemical properties of steamed wood lignin (STWL), beech wood (F. crenata) was treated at 183±2308C with saturated steam for various periods of time. The amount of lignin extractable with 90% dioxane increased remarkably as the steaming temperature was elevated and the time extended. It is possible to extract more than 70% of the lignin in certain hardwoods such as birch, beech, acacia, and aspen by steaming at 2308C for 2 min.1,2 The lignins from woods treated under various steaming conditions were investigated by elementary and functional analyses, gel permeation chromatography, infrared spectroscopy, 13C-NMR and nitrobenzene oxidation.6 For comparison, beech milled-wood lignin (MWL) was also investigated in the same manner. The lignins extracted had smaller molecular weights and higher contents of methoxyl, syringyl, and hydroxyl groups than those of MWL, indicating that syringyl-type lignin is depolymerized more preferentially than guaiacyl-type lignin. Lignin was broken down by extensive cleavage of b-aryl ether linkages during the steaming process, resulting to STWL of high phenolic hydroxyl content. At the same time, the aliphatic hydroxyl group content decreased. The chemical properties of STWL were found to depend on the steaming temperature. Namely, lignin from wood steamed at relatively low temperature (183± 2158C) was rich in syringyl units and only slightly modi®ed. By treatment at higher temperature (2308C) STWL most likely consisted of heavily condensed type of structures and modi®ed functionality. In order to clarify the mechanism of lignin degradation brought about by a steam explosion of wood the lignin fractions seperated from the reaction liquor,
A new carbon ®ber was prepared in two ways from STWL (lignin A in Fig. 1) isolated from steam-exploded birch wood.8,9 STWL was modi®ed to a thermoplastic by hydrogenation using Raney±Ni as a catalyst in 0.5 N NaOH under an initial H2 pressure of 2.92 MPa at 2508C for 60 min. The reaction mixture was extracted with CHCl3 after acidi®cation with 2 N HCl. The CHCl3 extracts were further extracted with CS2 to remove monoand di-meric products. The yield of CHCl3 soluble and CS2 insoluble fraction was 50.9%. This fraction was heated at 300±3508C for 30 min in a stream of N2, giving a pitch like substance (lignin pitch) in yields of 78%. This lignin pitch was spun into ®ne ®laments through a pinhole (diameter: 0.3 mm) from the molten state in the temperature range of 155± 1808C at speeds of 100±500 m minÿ1 under N2 pressure. The lignin-based ®lament was thermoset on heating in air up to 2108C at a rate 1± 28C minÿ1 and then carbonized at a heating rate of 58C minÿ1 up to 10008C in a stream of N2. The yield of carbon ®ber was 70% on the basis of the ®lament. Accordingly, the yield of lignin based carbon ®ber was about 27±28% based on extracted lignin. By another process, STWL was ®rst reacted with phenol in the presence of p-toluene sulfonic acid at 1808C for 4 h, heated for 10 min in a vacuum, and then converted into carbon ®ber by the process described above. The lignin-pitch obtained had excellent spinnability in the melt state to form a ®ne ®lament. It was spun into ®ne ®laments at a speed of 500± 1000 m minÿ1 in the temperature range 150± 1908C. The green ®bers were easily made infusible when heated in air at a relatively high heating rate (5±608C hÿ1). The lignin-based carbon ®ber was produced in 43.7% yield based on the starting material by the process
K. SHIMIZU et al.
200
Table 4. Physical properties of lignin based carbon ®bers Fiber width (mm) Tensile strength (MPa) Elongation (%) Modulus of elasticity (t mmÿ2)
7.622.7 6622232 1.6320.19 4.1520.64
described above. The physical properties of these lignin-based carbon ®bers are shown in Table 4. The lignin-based carbon ®bers were classi®ed as a general purpose grade.9 8. LIGNIN ADHESIVES
Wood adhesives have also been studied as feasible products from (STWL).10 STWL (lignins A and B in Fig. 1) were reacted with two times excess amount of phenol in the presence of H2SO4 at 1708C for 3 h and the unreacted phenol was removed under reduced pressure. The degree of phenolation was calculated to be in excess of one mol/lignin (C9) unit on the basis of 13C NMR measurements. The phenolated lignin was methylolated in order to prepare adhesive resins. The cure behavior of the adhesive resins was examined by Torsional Braid Analysis (TBA). It was revealed that the phenolated STWL-based resins had intrinsic retardation in cure as compared to a commercial phenolic resin. This defect, however, was partly overcome by increasing the pH values of the steam-exploded lignin resins. The adhesive from these resins generally provides excellent bond strength comparable to a commercial phenolic resin (Table 5). 9. ENZYMATIC HYDROLYSIS OF CELLULOSE
The residual ®bers were hydrolyzed with cellulase derived from T. viride. The enzymatic susceptibility was dierent among wood species, and was higher in species having lower contents of Klason lignin and lower contents Table 5. Tensile shear bond strength of adhesives from phenolysis lignin
Adhesive PLAFf PLAF PLBFf PLBF Commercial phenolic resin
Bond strength (MPa) at After cyclic normal state boil 48.1 29.0 66.6 29.8 58.7 24.3 75.3 27.7 63.8 26.8
53.926.3 44.323.4 55.728.1 37.727.9 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 lignocellulose.
of non-extractable lignin after steaming.3 The hydrolysis extents of birch and mollissima acacia were more than 90% (Table 1). Cellulosic ®bers were semicontinuously hydrolyzed on a large scale [2±2.5 kg of substrate vs 20,000 IU ®lterpaperase (FPase)] using a 10-l hydrolysis reactor with an ultra®ltration unit for the recovery and reuse of cellulases (Fig. 3).11 Substrates were added to the reactor at appropriate intervals to keep a solids concentration of approx. 5% (W/V) (Fig. 4). All of the enzyme was added at the beginning and no further addition was done. The ultra®ltration unit was operated intermittently. In this experiment, two substrates were used as shown in Fig. 4. One was the birch wood steamed at 1.27 MPa for 15 min and then extracted with water. This steamed birch wood contained lignin 34.7%. Another substrate was a commercial bleached hardwood pulp of which lignin content was less than 2%. The enzyme required to produce one gram of reducing sugar in this reactor amounted to 27.3 FPase IU gÿ1 reducing sugar (RS) for steamed birch wood, and 7.4 FPase IU gÿ1 RS for hardwood Kraft pulp. The loss of enzyme is attributed to several causes: irreversible enzyme adsorption to insoluble residue, especially in case of the substrate containing lignin, physical deterioration of enzyme in the tubular UF membrane module and proteolytic modi®cation of original enzyme. The enzyme should have a considerable shearing stress in the tubular UF membrane module in operating the ultra®ltration unit because the reaction mixture is pumped
Total utilization of wood by steam-explosion pretreatment
201
Fig. 4. Balance of substrate and enzyme (FPase) in semi continuous enzymatic hydrolysis of lignocellulosic materials.
through the tube (cross-sectional area of approx. 1 cm2 and length of 1.31 m) at a velocity of 10 l minÿ1. In the case of the steamed birch wood, the hydrolysis residue accumulated in the reactor had to be removed intermittently as shown in Fig. 4(a). The accumulation of unhydrolyzable residue reduced the reaction eciency. The yield of reducing sugar was considerably lower than in the case of the lignin-free kraft pulp. Table 6. Material balance in process of total utilization of wood components Day (t) Hardwood chips Steam-exploded ®ber Hemicellulose Xylooligosaccharides Reduced xylooligosaccharides Lignin Carbon ®ber Residual Cellulose Glucose 96% Ethanol Residual lignin
The sugar composition of the hydrolyzate remained virtually constant from beginning to end of the hydrolysis in spite of progressive loss of enzyme activity. The analysis of the enzyme composition in the hydrolyzate during hydrolysis revealsed that an exo-b-D-glucanase component was adsorbed selectively at the stages of advanced hydrolysis extent.11 The sugars in the hydrolyzate were converted to the single cell protein of Candida utilis in a yield of 46.7% (percentage of the amount of dried mycelium based on the sugars consumed).1
Year (t)
100.0 30,000 85.0 25,500 17.0 5100 15.0 4600 15.0 4500 12.0 3600 5.1 1542 51.0 15300 39.4 11808 18.0 5412 (22.2 kl) (6685 kl) 10.0 3000
Table 7. Initial investiment
Process Steam-explosion and fractionation Puri®cation of xylooligosaccharides Reduction of xylooligosaccharides Production of carbon ®ber Production of cellulose Hydrolysis of cellulose Alcohol fermentation Sum
Price (X***** 1000) 2,158,000 1,500,000 1,000,000 4,121,000 710,000 1,014,000 760,000 11,263,000
% 19.2 13.3 8.9 36.6 6.3 9.0 6.7 100.0
K. SHIMIZU et al.
202
Table 8. Cost analysis of process for utilization of wood components by steam-explosion Item
Unit cost
Labor Utilities Water Electricity Crude oil Maintenance of environment Chemicals NaCl 35% HCl 50% NaOH N2 H2 Catalyst Phenol Enzyme Others Wood Chips Initial cost Depreciation Interest Maintenance Others Taxes Interest Sum
Sum ***** 1000
49 persons 12,000
[588,000] [1,487,702] 190,854 743,348 542,300 11,200 [1,861,466] 32,400 56,346 79,158 339,240 67,100 116,250 160,200
ÿ3
***** 150 m ***** 15 kWhÿ1 ***** 50 kgÿ1 ***** 30 kgÿ1 ***** 22 kgÿ1 ***** 30 kgÿ1 ***** 55 Nmÿ3 ***** 100 Nmÿ3 ***** 2,500 kgÿ1 ***** 200 kgÿ1 ***** 1,655 kgÿ1
[1,002,210] [900,000] [1,899,540]
***** 30 kg 30,000 t 10%, 10 years Initial cost 7%/year Initial cost 2.0%/year
[253,227]
Initial cost 1.4%/year Initial cost 7%/year
The adsorption behavior of T. viride cellulases on steamed birch wood was studied previously.12 Substrate/enzyme (S/E) ratio, hydrolysis time and sacchari®cation extent as well as the presence of absence of lignin in the substrate were taken into consideration as factors aecting the enzyme adsorption. FPase components were adsorbed more selectively than other cellulase components on the substrate. The presence of lignin in the steamed hardwood tended to slow down the enzyme adsorption, but it did not appear to restrict the extent of hydrolysis of the carbohydrate moiety. The changes in the composition of the enzyme preparation during the course of hydrolysis were analyzed by fast protein liquid chromatography
6,981,303
(FPLC). The irreversible adsorption of speci®c cellulase components was not observed in the prolonged hydrolysis of steamed birch wood containing abundant lignin.12
10. ECONOMICS OF PROCESS
The economics of the process shown in Fig. 1 was evaluated by assuming a plant processing 30,000 t of birch wood chips per year (100 t per day) dry basis. Table 6 shows the material balance in the process. The annual production of the reduced xylooligosaccharides, carbon ®ber, and alcohol is 4,500 t, 1,542 t and 6,658 kl, respectively.
Table 9. Production cost Goods
Output (t/year)
Cost ( ***** 1000)
Crude oligosaccharide Xylooligosaccharide Reduced xylosugars
5100 4600 4500
Lignin Carbon ®ber
3600 1542
453,900 687.872 823,340 1,965,112 320,400 2,803,603 2,404,003 1,361,700 (534,574) 982,744 267,744 2,612,188
Cellulose Enzymes Glucose Ethanol Residual lignin
15,300 11,750 5412 3000
6,981,303
Unit cost ( ***** kgÿ1)
Market price ( ***** kgÿ1)
437
450 2,025,000
1559
2500 3,855,000
482
172 930,864 33 99,000 6,909,864
Total utilization of wood by steam-explosion pretreatment
The capital investment is more than $100 million (US. $ 1 equivalent to 100 yen) as shown in Table 7. The production facilities for carbon ®ber occupies 37%. The cost for labor, utilities, chemicals, wood chips, and so on are listed in Table 8. The cost for steam-explosion followed by extraction with water and aqueous alkali amounts to $ 21 million, producing hemicellulose (5100 t), lignin (3600 t), and cellulose (15300 t) annually. The total cost of production amounts to $ 70 million as shown in 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 in Table 9, the total income amounts to 69 million. It is necessary to lower the costs of production, especially the processes for steamexplosion-fractionation and the enzymatic hydrolysis of cellulose. AcknowledgementÐThis work was supported by the Biomass Conversion Program of the Ministry of Agriculture, Forest and Fisheries.
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spectra of Japanese hardwoods and softwoods, Mokuzai Gakkaishi, 1987, 33(5), 400±407. Fujii, T., Shimizu, K., Sudo, K. and Yamamoto, K., Ultra structural changes of three diuse-porous hardwoods upon autohydrolysis and enzymatic sacchari®cation, Mokuzai Gakkaishi, 1985, 31(5), 366±374. Shimizu, K., Ishihara, M. and Ishihara, T., Hemicelluloses of brown rotting fungus, Tyromyces palustris II, Mokuzai Gakkaishi, 1976, 22, 618±625. Shimizu, K. and Ishihara, M., Immobilization of cellulolytic and hemicellulolytic enzymes on inorganic supports, Biotechnology and Bioengineering, 1987, 26, 236±241. Sudo, K., Shimizu, K. and Sakurai, K., Characterization of steamed wood lignin from beech wood, Hozforschung, 1985, 39, 281±288. Hishiyama, S. and Sudo, K., Degradation mechanism of lignin by steam-explosion, Mokuzai Gakkaishi, 1992, 38, 944±949. Sudo, K. and Shimizu, K., A new carbon ®ber from lignin, Journal of Applied Polymer Science, 1992, 44, 127±134. Sudo, K., Shimizu, K., Nakashima, N. and Yokoyama, A., A new modi®cation method of exploded lignin for the preparation of a carbon ®ber precursor, Journal of Applied Polymer Science, 1993, 48, 1485±1491. Ono, H. and Sudo, K., Wood adhesives from phenolysis lignin, ACS Symposium Series, 1989, 397, 334±335. Ishihara, M., Uemura, S., Hayashi, N. and Shimizu, K., Semi continuous enzymatic hydrolysis of lignocelluloses, Biotechnology and Bioengineering, 1991, 37, 948±954. Ishihara, M., Uemura, S., Hayashi, N., Jellison, J. and Shimizu, K., Adsorption and desorption of cellulase compnents during enzymatic hydrolysis of steamed shirakamba (Betula platyphylla Skatchev) wood, Journal of Fermentation Bioengineering, 1991, 72, 96±100.
Biomass and Bioenergy Vol. 14, No. 3, pp. 195±203, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0961-9534/98 $19.00 + 0.00 S0961-9534(97)10044-7
INTEGRATED PROCESS FOR TOTAL UTILIZATION OF WOOD COMPONENTS BY STEAM-EXPLOSION PRETREATMENT K. SHIMIZU*, K. SUDO$, 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 lignin was degraded by extensive cleavage of a- and b-aryl ether linkages becoming extractable with organic solvents and/or dilute alkali. The three main components, hemicellulose, lignin, and cellulose, of steam-exploded woods were fractionated by successive extraction with water and 90% dioxane. The water extracts were decolored and puri®ed by chromatography on synthetic adsorbents and ion exchange resins, yielding a mixture of xylose and xylooligosaccharides (DP2010). The xylooligosaccharides were hydrolyzed to xylose with hemicellulolytic enzymes immobilized on ceramics having controlled pore size. The yield of xylose was 10±20% based on starting materials. The extracted amounts of lignin were dierent among wood species. Syringyl lignin became more soluble than guaiacyl lignin on steaming. The lignin extracted was converted to thermoplastic materials, lignin-pitch, by phenolysis followed by heat treatment under vacuum. The lignin-pitch was well spun into ®ne ®laments at a speed of 500±1000 m minÿ1 in the temperature range 150±1908C using the melt-spinning method. The ®laments were carbonized on heating from room temperature up to 10008C in a stream of nitrogen. The carbon ®ber was obtained in a yield of more than 40% based on the starting materials. The physical properties of the lignin- based carbon ®ber was equivalent to a commercial carbon ®ber made from petroleum pitch. The residual ®bers, mainly cellulose, were hydrolyzed with cellulase derived from Trichoderma viride. Their enzymatic susceptibility was dierent among wood species. It was higher in species having lower contents of Klason lignin and guaiacyl lignin. Birch and Mollissima acasia were hydrolyzed more than 90%. Finally, the economics of this process are discussed assuming a plant processing 100 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 hardwoods 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 eective 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 195
integrated process for total utilization of wood components by steam-explosion pretreatment. 2. PROCESS FOR TOTAL UTILIZATION OF WOOD COMPONENTS
Enzymatic sacchari®cation of wood waste has received considerable interest with recent developments in cellulase technology. It is well known that the susceptibility of some species of hardwoods to enzymatic attack is improved remarkably by steam-explosion.1 It is necessary to develop an integrated processing, using all of the components, to make the process economically feasible. Figure 1 shows our process for total utilization of hardwood components. Wood chips
K. SHIMIZU et al.
196
Fig. 1. Process for total utilization of wood components by steam explosion.
were subjected to steaming at 180±2308C for 2±20 min and ®berized by explosion or by use of a re®ner. The ®bers obtained are extracted successively with water and 90% dioxane. The residual cellulose is hydrolyzed with a commercial cellulase preparation ``Meicelase'' derived from Trichoderma viride.1,2 From the water extracts, xylose and xylooligosaccharides are isolated and can be used as a sweetener and/or food additive. The lignin fragments isolated form the dioxane extract are converted to car-
bon ®ber and adhesives as described below. The enzymatic hydrolyzate of cellulose can be fermented to single cell protein and/or alcohol. Table 1 shows the results of analyses of birch wood (Betula platyphylla) steamed at various conditions. The steaming treatment resulted in a weight loss of 4±27%. Most of the hemicellulose and lignin were modi®ed, becoming soluble in water and 90% dioxane, respectively. The residual cellulose was completely hydrolyzed with the enzyme.
Table 1. Analysis of birch woods steamed at various condition Steaming pressure MPa 0.98 1.47 1.96 2.45 2.94
Time (min) 20 5 10 15 3 6 9 2 4 1 2
Yield (%)
Klason lignin (%)
Water extract (%)
Dioxane extract (%)
73.4 84.9 75.0 73.7 96.0 76.5 80.3 83.5 82.5 93.7 81.3
28.6 29.9 28.2 32.1 29.5 37.1 35.3 30.0 32.3 30.1 31.3
23.7 19.2 15.6 14.5 25.4 23.9 25.7 34.2 27.1 33.5 34.5
10.3 8.1 9.1 10.6 14.0 29.9 34.5 20.4 25.7 17.5 21.9
Enzymatic susceptibility (%) 100 98.0 96.0 100 96.2 100 100 99.3 100 100 100
Total utilization of wood by steam-explosion pretreatment
197
3. STEAM-EXPLOSION OF VARIOUS SPECIES OF WOODS
4. MORPHOLOGICAL CHANGES OF CELL WALL ON STEAMING
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 extractable lignin ranged form 57.4 to 16.1% depending upon the species. The dierences in the extractability of lignin are probably attributable to the dierences in the chemical structure of the lignin among the hardwood species.
The morphological changes in the distribution of the cell wall components upon steaming followed by successive extraction with water and 90% dioxane, and enzymatic susceptibility of cellulose were studied. Upon steaming, lignin of the secondary wall middle layer (S2) was degraded becoming more extractable than that from other parts. However, the amount of lignin remaining after extraction with 90% dioxane was quite dierent among the wood species. The enzymatic susceptibility increased as the amount of lignin remaining decreased. 2 Lignin in the secondary wall of ray and axial parenchyma cells became more extractable than that of ®bers and vessels. Lignin in the vessel walls was most resistant. To explain why the degradation extent of lignin on steaming and the enzymatic susceptibility of cellulose in steamed woods is dierent among wood species and also cell types, the nature of secondary-wall lignin was investigated in various wood species and cell types by means of ultraviolet microspectrometry and chemical analysis.3 Furthermore, the enzymatic susceptibility of cellulose in cell walls was investigated on ultrathin sections (100 nm)
Fig. 2. Electron micrograph of an ultrathin cross section of an untreated Beech (F. crerata) chip after incubation in the enzyme solution for 4 h.
K. SHIMIZU et al.
198
The water extracts of steam-exploded chips being brown in color were decolored and puri®ed by use of synthetic adsorbents (Amberlite XAD 2 and 7) and various types of ion
exchange resins. The sugars in the extracts were separated into neutral and acidic fractions in the usual way.4 The neutral sugars mainly consisted of xylose and xylooligosaccharides having DP 2±10 and were fractionated 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 hydroscopic and sweet. They gave viscous syrups when dissolved in water and can be used as food 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-MeGlcAp residues were found to be present. The aldo-(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 hydrolysed with commercial cellulases using either 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 derivatives with glutaraldehyde as reported previously.5 The amounts of the immobilized enzymes were in the range 10±50 mg gÿ1 carrier (dry) depending on the kind of carrier and immobilization method. their activities toward carboxymethyl cellulose (CMC), xylan, aryl-bglucoside, 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 extract from birch steamed at 1.47 MPa for 10 min
Table 3. Acidic sugars in water extract (1 g) from birch steamed at 15 Kgf cmÿ1 for 10 min
to obtain some clues for understanding the ultrastructural organization of ligni®ed cellwalls.3 The ultrathin sections were cut from untreated wood (air- dried) and treated with cellulase. Figure 2 shows an electron micrograph of an untreated beech (Fagus crenata) chip after incubation in the cellulase solution for 4 h. The ®ber S2 layer was eroded remarkably by the enzymatic attack, whereas the ®ber secondary wall outer layer (S1) was not. The secondary wall of axial parenchyma cells was eroded a little, but the secondary wall of vessel was most resistant.2 The chemical nature and content of lignin were dierent from wood to wood. In the wood species with lower Klason-lignin contents, the S2 lignin of wood ®bers was syringyl type, and the cellulose of the ultrathin sections was susceptible to enzymatic attack indicating that cellulose is loosely packed with lignin. In the wood species with higher Klason-lignin contents, the S2 lignin of wood ®bers was rich in guaiacyl residues, and the cellulose was not susceptible to enzymatic attack. The S2 lignin of vessels consisted predominantly of guaiacyl residues in all species, and the enzyme was not able to attack the cellulose of ultrathin sections. The S2 lignin of xylem parenchyma was richer in guaiacyl residues than was the lignin of wood ®bers, although the former was not as rich as the vessels, and the enzyme could not reach the cellulose.
5. WATER EXTRACTS
Fr.
Sugar
Weight (%)
1 2 3 4 5 6 7 8 9 10 11
Others Xyl10 Xyl9 Xyl8 Xyl7 Xyl6 Xyl5 Xyl4 Xyl3 Xyl2 Xyl
12.8 4.0 2.3 2.9 3.5 6.0 7.1 9.8 12.0 16.3 23.2
Fraction 1 2 3 4 5 6 7 8 9 10
Compound 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl4 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl3 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl2 2-O-(4-O-Me-a-D-GlcAp)-D-Xyl 4-O-GalA-D-Xyl Unknown 4-O-Me-D-GlcA Unknown GalA Unknown
Amount (mg) 73 74.2 137.7 14.6 11.3 28.5 6.9 5.9 6.5 3.2
Total utilization of wood by steam-explosion pretreatment
most cases, whereas the optimum temperatures were nearly the same as those of native ones. The activity of immobilized enzyme preparations toward CMC did not change signi®cantly during continuous operation over a period of 60 days. The immobilized enzymes were packed in glass columns (2 30 cm) and the water extracts (Brix 10%) were applied continuously to the columns at a ¯ow rate of 0.5 m, minÿ1. Gel permeation chromatography showed that xylose was a main sugar formed in addition to a trace amount of xylobiose.
199
were analysed by gas chromatograph (GC) and gas chromatograph±mass spectrometer (GC±MS).7 Among the degraded compounds, guaiacyl acetone, vanilloyl acetyl and their syringyl analogies were identi®ed. The amount of syringaresinol liberated was much less than that expected based on the proportional content of these structural units in the original lignin. These facts suggest that the lignin is mainly decomposed by acid catalyzed hydrolysis during the steam treatment. 7. LIGNIN CARBON FIBER
6. MECHANISM OF LIGNIN DEGRADATION ON STEAMING
In order to elucidate chemical properties of steamed wood lignin (STWL), beech wood (F. crenata) was treated at 183±2308C with saturated steam for various periods of time. The amount of lignin extractable with 90% dioxane increased remarkably as the steaming temperature was elevated and the time extended. It is possible to extract more than 70% of the lignin in certain hardwoods such as birch, beech, acacia, and aspen by steaming at 2308C for 2 min.1,2 The lignins from woods treated under various steaming conditions were investigated by elementary and functional analyses, gel permeation chromatography, infrared spectroscopy, 13C-NMR and nitrobenzene oxidation.6 For comparison, beech milled-wood lignin (MWL) was also investigated in the same manner. The lignins extracted had smaller molecular weights and higher contents of methoxyl, syringyl, and hydroxyl groups than those of MWL, indicating that syringyl-type lignin is depolymerized more preferentially than guaiacyl-type lignin. Lignin was broken down by extensive cleavage of b-aryl ether linkages during the steaming process, resulting to STWL of high phenolic hydroxyl content. At the same time, the aliphatic hydroxyl group content decreased. The chemical properties of STWL were found to depend on the steaming temperature. Namely, lignin from wood steamed at relatively low temperature (183± 2158C) was rich in syringyl units and only slightly modi®ed. By treatment at higher temperature (2308C) STWL most likely consisted of heavily condensed type of structures and modi®ed functionality. In order to clarify the mechanism of lignin degradation brought about by a steam explosion of wood the lignin fractions seperated from the reaction liquor,
A new carbon ®ber was prepared in two ways from STWL (lignin A in Fig. 1) isolated from steam-exploded birch wood.8,9 STWL was modi®ed to a thermoplastic by hydrogenation using Raney±Ni as a catalyst in 0.5 N NaOH under an initial H2 pressure of 2.92 MPa at 2508C for 60 min. The reaction mixture was extracted with CHCl3 after acidi®cation with 2 N HCl. The CHCl3 extracts were further extracted with CS2 to remove monoand di-meric products. The yield of CHCl3 soluble and CS2 insoluble fraction was 50.9%. This fraction was heated at 300±3508C for 30 min in a stream of N2, giving a pitch like substance (lignin pitch) in yields of 78%. This lignin pitch was spun into ®ne ®laments through a pinhole (diameter: 0.3 mm) from the molten state in the temperature range of 155± 1808C at speeds of 100±500 m minÿ1 under N2 pressure. The lignin-based ®lament was thermoset on heating in air up to 2108C at a rate 1± 28C minÿ1 and then carbonized at a heating rate of 58C minÿ1 up to 10008C in a stream of N2. The yield of carbon ®ber was 70% on the basis of the ®lament. Accordingly, the yield of lignin based carbon ®ber was about 27±28% based on extracted lignin. By another process, STWL was ®rst reacted with phenol in the presence of p-toluene sulfonic acid at 1808C for 4 h, heated for 10 min in a vacuum, and then converted into carbon ®ber by the process described above. The lignin-pitch obtained had excellent spinnability in the melt state to form a ®ne ®lament. It was spun into ®ne ®laments at a speed of 500± 1000 m minÿ1 in the temperature range 150± 1908C. The green ®bers were easily made infusible when heated in air at a relatively high heating rate (5±608C hÿ1). The lignin-based carbon ®ber was produced in 43.7% yield based on the starting material by the process
K. SHIMIZU et al.
200
Table 4. Physical properties of lignin based carbon ®bers Fiber width (mm) Tensile strength (MPa) Elongation (%) Modulus of elasticity (t mmÿ2)
7.622.7 6622232 1.6320.19 4.1520.64
described above. The physical properties of these lignin-based carbon ®bers are shown in Table 4. The lignin-based carbon ®bers were classi®ed as a general purpose grade.9 8. LIGNIN ADHESIVES
Wood adhesives have also been studied as feasible products from (STWL).10 STWL (lignins A and B in Fig. 1) were reacted with two times excess amount of phenol in the presence of H2SO4 at 1708C for 3 h and the unreacted phenol was removed under reduced pressure. The degree of phenolation was calculated to be in excess of one mol/lignin (C9) unit on the basis of 13C NMR measurements. The phenolated lignin was methylolated in order to prepare adhesive resins. The cure behavior of the adhesive resins was examined by Torsional Braid Analysis (TBA). It was revealed that the phenolated STWL-based resins had intrinsic retardation in cure as compared to a commercial phenolic resin. This defect, however, was partly overcome by increasing the pH values of the steam-exploded lignin resins. The adhesive from these resins generally provides excellent bond strength comparable to a commercial phenolic resin (Table 5). 9. ENZYMATIC HYDROLYSIS OF CELLULOSE
The residual ®bers were hydrolyzed with cellulase derived from T. viride. The enzymatic susceptibility was dierent among wood species, and was higher in species having lower contents of Klason lignin and lower contents Table 5. Tensile shear bond strength of adhesives from phenolysis lignin
Adhesive PLAFf PLAF PLBFf PLBF Commercial phenolic resin
Bond strength (MPa) at After cyclic normal state boil 48.1 29.0 66.6 29.8 58.7 24.3 75.3 27.7 63.8 26.8
53.926.3 44.323.4 55.728.1 37.727.9 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 lignocellulose.
of non-extractable lignin after steaming.3 The hydrolysis extents of birch and mollissima acacia were more than 90% (Table 1). Cellulosic ®bers were semicontinuously hydrolyzed on a large scale [2±2.5 kg of substrate vs 20,000 IU ®lterpaperase (FPase)] using a 10-l hydrolysis reactor with an ultra®ltration unit for the recovery and reuse of cellulases (Fig. 3).11 Substrates were added to the reactor at appropriate intervals to keep a solids concentration of approx. 5% (W/V) (Fig. 4). All of the enzyme was added at the beginning and no further addition was done. The ultra®ltration unit was operated intermittently. In this experiment, two substrates were used as shown in Fig. 4. One was the birch wood steamed at 1.27 MPa for 15 min and then extracted with water. This steamed birch wood contained lignin 34.7%. Another substrate was a commercial bleached hardwood pulp of which lignin content was less than 2%. The enzyme required to produce one gram of reducing sugar in this reactor amounted to 27.3 FPase IU gÿ1 reducing sugar (RS) for steamed birch wood, and 7.4 FPase IU gÿ1 RS for hardwood Kraft pulp. The loss of enzyme is attributed to several causes: irreversible enzyme adsorption to insoluble residue, especially in case of the substrate containing lignin, physical deterioration of enzyme in the tubular UF membrane module and proteolytic modi®cation of original enzyme. The enzyme should have a considerable shearing stress in the tubular UF membrane module in operating the ultra®ltration unit because the reaction mixture is pumped
Total utilization of wood by steam-explosion pretreatment
201
Fig. 4. Balance of substrate and enzyme (FPase) in semi continuous enzymatic hydrolysis of lignocellulosic materials.
through the tube (cross-sectional area of approx. 1 cm2 and length of 1.31 m) at a velocity of 10 l minÿ1. In the case of the steamed birch wood, the hydrolysis residue accumulated in the reactor had to be removed intermittently as shown in Fig. 4(a). The accumulation of unhydrolyzable residue reduced the reaction eciency. The yield of reducing sugar was considerably lower than in the case of the lignin-free kraft pulp. Table 6. Material balance in process of total utilization of wood components Day (t) Hardwood chips Steam-exploded ®ber Hemicellulose Xylooligosaccharides Reduced xylooligosaccharides Lignin Carbon ®ber Residual Cellulose Glucose 96% Ethanol Residual lignin
The sugar composition of the hydrolyzate remained virtually constant from beginning to end of the hydrolysis in spite of progressive loss of enzyme activity. The analysis of the enzyme composition in the hydrolyzate during hydrolysis revealsed that an exo-b-D-glucanase component was adsorbed selectively at the stages of advanced hydrolysis extent.11 The sugars in the hydrolyzate were converted to the single cell protein of Candida utilis in a yield of 46.7% (percentage of the amount of dried mycelium based on the sugars consumed).1
Year (t)
100.0 30,000 85.0 25,500 17.0 5100 15.0 4600 15.0 4500 12.0 3600 5.1 1542 51.0 15300 39.4 11808 18.0 5412 (22.2 kl) (6685 kl) 10.0 3000
Table 7. Initial investiment
Process Steam-explosion and fractionation Puri®cation of xylooligosaccharides Reduction of xylooligosaccharides Production of carbon ®ber Production of cellulose Hydrolysis of cellulose Alcohol fermentation Sum
Price (X***** 1000) 2,158,000 1,500,000 1,000,000 4,121,000 710,000 1,014,000 760,000 11,263,000
% 19.2 13.3 8.9 36.6 6.3 9.0 6.7 100.0
K. SHIMIZU et al.
202
Table 8. Cost analysis of process for utilization of wood components by steam-explosion Item
Unit cost
Labor Utilities Water Electricity Crude oil Maintenance of environment Chemicals NaCl 35% HCl 50% NaOH N2 H2 Catalyst Phenol Enzyme Others Wood Chips Initial cost Depreciation Interest Maintenance Others Taxes Interest Sum
Sum ***** 1000
49 persons 12,000
[588,000] [1,487,702] 190,854 743,348 542,300 11,200 [1,861,466] 32,400 56,346 79,158 339,240 67,100 116,250 160,200
ÿ3
***** 150 m ***** 15 kWhÿ1 ***** 50 kgÿ1 ***** 30 kgÿ1 ***** 22 kgÿ1 ***** 30 kgÿ1 ***** 55 Nmÿ3 ***** 100 Nmÿ3 ***** 2,500 kgÿ1 ***** 200 kgÿ1 ***** 1,655 kgÿ1
[1,002,210] [900,000] [1,899,540]
***** 30 kg 30,000 t 10%, 10 years Initial cost 7%/year Initial cost 2.0%/year
[253,227]
Initial cost 1.4%/year Initial cost 7%/year
The adsorption behavior of T. viride cellulases on steamed birch wood was studied previously.12 Substrate/enzyme (S/E) ratio, hydrolysis time and sacchari®cation extent as well as the presence of absence of lignin in the substrate were taken into consideration as factors aecting the enzyme adsorption. FPase components were adsorbed more selectively than other cellulase components on the substrate. The presence of lignin in the steamed hardwood tended to slow down the enzyme adsorption, but it did not appear to restrict the extent of hydrolysis of the carbohydrate moiety. The changes in the composition of the enzyme preparation during the course of hydrolysis were analyzed by fast protein liquid chromatography
6,981,303
(FPLC). The irreversible adsorption of speci®c cellulase components was not observed in the prolonged hydrolysis of steamed birch wood containing abundant lignin.12
10. ECONOMICS OF PROCESS
The economics of the process shown in Fig. 1 was evaluated by assuming a plant processing 30,000 t of birch wood chips per year (100 t per day) dry basis. Table 6 shows the material balance in the process. The annual production of the reduced xylooligosaccharides, carbon ®ber, and alcohol is 4,500 t, 1,542 t and 6,658 kl, respectively.
Table 9. Production cost Goods
Output (t/year)
Cost ( ***** 1000)
Crude oligosaccharide Xylooligosaccharide Reduced xylosugars
5100 4600 4500
Lignin Carbon ®ber
3600 1542
453,900 687.872 823,340 1,965,112 320,400 2,803,603 2,404,003 1,361,700 (534,574) 982,744 267,744 2,612,188
Cellulose Enzymes Glucose Ethanol Residual lignin
15,300 11,750 5412 3000
6,981,303
Unit cost ( ***** kgÿ1)
Market price ( ***** kgÿ1)
437
450 2,025,000
1559
2500 3,855,000
482
172 930,864 33 99,000 6,909,864
Total utilization of wood by steam-explosion pretreatment
The capital investment is more than $100 million (US. $ 1 equivalent to 100 yen) as shown in Table 7. The production facilities for carbon ®ber occupies 37%. The cost for labor, utilities, chemicals, wood chips, and so on are listed in Table 8. The cost for steam-explosion followed by extraction with water and aqueous alkali amounts to $ 21 million, producing hemicellulose (5100 t), lignin (3600 t), and cellulose (15300 t) annually. The total cost of production amounts to $ 70 million as shown in 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 in Table 9, the total income amounts to 69 million. It is necessary to lower the costs of production, especially the processes for steamexplosion-fractionation and the enzymatic hydrolysis of cellulose. AcknowledgementÐThis work was supported by the Biomass Conversion Program of the Ministry of Agriculture, Forest and Fisheries.
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4. 5.
6. 7. 8. 9.
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spectra of Japanese hardwoods and softwoods, Mokuzai Gakkaishi, 1987, 33(5), 400±407. Fujii, T., Shimizu, K., Sudo, K. and Yamamoto, K., Ultra structural changes of three diuse-porous hardwoods upon autohydrolysis and enzymatic sacchari®cation, Mokuzai Gakkaishi, 1985, 31(5), 366±374. Shimizu, K., Ishihara, M. and Ishihara, T., Hemicelluloses of brown rotting fungus, Tyromyces palustris II, Mokuzai Gakkaishi, 1976, 22, 618±625. Shimizu, K. and Ishihara, M., Immobilization of cellulolytic and hemicellulolytic enzymes on inorganic supports, Biotechnology and Bioengineering, 1987, 26, 236±241. Sudo, K., Shimizu, K. and Sakurai, K., Characterization of steamed wood lignin from beech wood, Hozforschung, 1985, 39, 281±288. Hishiyama, S. and Sudo, K., Degradation mechanism of lignin by steam-explosion, Mokuzai Gakkaishi, 1992, 38, 944±949. Sudo, K. and Shimizu, K., A new carbon ®ber from lignin, Journal of Applied Polymer Science, 1992, 44, 127±134. Sudo, K., Shimizu, K., Nakashima, N. and Yokoyama, A., A new modi®cation method of exploded lignin for the preparation of a carbon ®ber precursor, Journal of Applied Polymer Science, 1993, 48, 1485±1491. Ono, H. and Sudo, K., Wood adhesives from phenolysis lignin, ACS Symposium Series, 1989, 397, 334±335. Ishihara, M., Uemura, S., Hayashi, N. and Shimizu, K., Semi continuous enzymatic hydrolysis of lignocelluloses, Biotechnology and Bioengineering, 1991, 37, 948±954. Ishihara, M., Uemura, S., Hayashi, N., Jellison, J. and Shimizu, K., Adsorption and desorption of cellulase compnents during enzymatic hydrolysis of steamed shirakamba (Betula platyphylla Skatchev) wood, Journal of Fermentation Bioengineering, 1991, 72, 96±100.