Ind. Eng. Chem. Prod. Res. Dev. 1904, 23, 471-475
47 1
Application of Direct Thermal Liquefaction for the Conversion of Cellulosic Biomass Davld A. Nelson,' Peter M. Molton, Janet A. Russell, and Rlchard T. Hallen Chemical Technology Department, Baltelle, Pacific Northwest laboratory, Richland, Washington 99352
Direct thermochemical conversion of cellulosic biomass to useful products has been studied as en alternative to conventional biological processes. At temperatures of 250-400 O C and pressures up to 20.7 MPa in the presence of sodium carbonate, pure cellulose was converted to a mixture of phenols, cyclopentanones, and hydroquinones as well as other components. This liquefaction oil and others were examined for their use as fuel asphatt substitutes and wood adhesives. The product composition tended to change with liquefaction time. One major product of cellulose liquefaction, 2,5dimethyl-l,4benzenediol, was formed during a reduction-oxidation procedure involving acetoin and biacetyl. The use of alkaline catalysts under liquefaction at 300 O C was shown to shift the mechanism from one involving aqueous pyrolysis (predominant furan formation) to one incorporating aldol and related condensations.
Introduction Production of chemicals from renewable biomass and similar organic wastes is conventionally achieved by biological processes, via total gasification to carbon monoxide and hydrogen, or as byproducta of the wood products industry. Examples of each of these categories include ethanol from cellulose, methanol from gasification of biomass, and tall oil from wood pulping. An alternative chemical process which has received little attention as a way of making specialty chemicals is the thermochemical liquefaction route. This process originally attracted attention as a way of making an artificial coal (Bergius, 1928; Berl and Schmidt, 1932a,b) and subsequently with the addition of carbon monoxide and hydrogen as a way of making liquid fuels from biomass (Weiss, 1972; Gupta et al., 1976; Appell et al., 1975; Cavalier and Chornet, 1977; Waterman and Kortlandt, 1924). Work done on the determination of the reaction mechanisms of liquefaction, mainly with pure cellulose (Miller et al., 1981; Eager et al., 1983; Molton et al., 1979, Russell et al., 1983) suggests that the technique offers a potential alternative synthetic route to phenolics, furans, and other chemicals. Extension to actual organic waste materials should be possible. We have recently completed a study for the U S . Environmental Protection Agency (EPA) on production of a synthetic asphalt material from primary sewage sludge (Donovan et al., 1981a). Research is being continued both on the determination of fundamental reaction mechanisms for the U.S.Department of Energy and on the conversion of sewage for EPA. Experimental Section General. Nuclear magnetic resonance spectra ('H and I3C) were recorded with a Varian FT-80spectrophotometer. Gas chromatographic analyses were obtained with a Hewlett-Packard 5880A instrument using SE-54 and Superox capillary columns. A Hewlett-Packard Model 5992B gas chromatograph-mass spectrometer, equipped with a capillary column interface, was used for identification. One of the better columns for the GC-MS utilized Durabond 5 (0.32 mm X 30 m). Preparation of TMS-saccharides involved trimethylsilylimidazole in pyridine (Brittain, 1969). Alkaline Treatment of Cellulose. Although details of the experimental liquefaction procedure have been published elsewhere (Molton et al., 1981), a general sumQ796-4321/84/ 7223-0471$01.50/0
mary of that technique is presented for the 300 mL capacity autoclave. The 3WmL autoclave was charged with cellulose (Solka-floc, 30 g), anhydrous sodium carbonate (1.9 g), and 120 mL of distilled water. The autoclave was purged with nitrogen to exclude air, and the temperature was then raised to the desired level (heating time, 1h to reach 300 OC). The temperature was maintained for 1 h, then allowed to cool to 25 "C (3 h required). The pressure at 300 O C was 10.3 MPa. The gas was vented, and the autoclave was opened. The aqueous phase was decanted from the insoluble oil. The oil was extracted with acetone in a Soxhlet extraction apparatus until the solvent in the thimble became colorless (about 48 h). After removal of the acetone under reduced pressure, the oil yield was determined, and the oil was further analyzed to determine its composition. Faster heating and cooling times were achieved using a 3.0-mL capacity tubing autoclave (316 stainless steel). The tube was 0.6 X 9 cm and sealed with Swagelok fittings. The tube was charged with 0.5 g of cellulose and 2 mL of 0.2 M Na2C03. The void space was swept with nitrogen. The tubing autoclave was plunged into a sand bath held at 315 "C. Only 2.5 min were required to reach 300 "C, while cooling to less than 100 "C required 0.1 min. The nonaqueous contents of the autoclave were extracted with acetone. Alkaline Treatment of Biacetyl and Acetoin. The liquefaction procedure discussed above was applied to 3-hydroxy-2-butanone (acetoin) and 2,3-butanedione (biacetyl). To a 180 mL capacity autoclave were added 11.5 g of an 85% solution of acetoin in water, sodium carbonate (0.219 g), and distilled water (5.75 g). The biacetyl reaction was performed with 9.8 g of this intermediate. The autoclave was sealed and flushed with nitrogen for 5 min. The temperature of the autoclave was then raised to the desired level (heating time, 1h to reach 300 "C) and kept there for 1h. The mixture was cooled during 3 h, the gas was vented, and the autoclave was opened. The mixture (1.4 was filtered to remove 2,5-dimethyl-1,4-benzenediol g) that was present during acetoin reactions. The crystalline dimethylbenzenediol was washed with water and dichloromethane. Only a tar-like product was recovered from the biacetyl reaction mixture. Alkaline Treatment of Other Precursors. The 3.0 mL capacity tube autoclave was used for alkaline liquefaction of 2,3-dihydroxypropanal (glyceraldehyde), 10 1984 American Chemical Society
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Table I. Representative Liquefaction Oil Yields temp, time, yield, wt alkali feedstock "C ha %b M NaeCOl ce11u 1ose 291 0.33 4 2.0 279 1.67 17 2.0 324 0.33 27 2.0 295 1.0 10 2.0 1.0 37 2.0 300 407 1.0 23 2.0 Hawaiian sewage sludge' 320 1.0 31 2.0 37 2.0 345 1.0 250 0.33 3 2.0 Washington hop residues 250 0.33 41 1.2 300 0.33 35 0.6 "Does not include time to reach temperature or cooling time. Yield of acetone soluble oil, char weight not included. Based on pure cellulose, the theoretical yield is 53 wt ?'& for the oil. 'The primary sewage sludge was undigested and dewatered.
hydroxy-2-propanone (hydroxyacetone), 1,3-dihydroxy-2propanone (dihydroxyacetone),erythrose, and erythritol. The tube was charged with 0.5 g of compound and 2 mL of 0.2 M Na2C03. Each sample was exposed to 5 min of total heating. The oil product was examined by GC-MS.
Results Product Oil Composition. The liquefaction reaction proceeded smoothly with a variety of starting materials, at temperatures of 290 "C and above, although there was little reaction of cellulose and biomass feedstocks below 270 "C. Feedstock conversion was essentially complete above 300 "C, with oil yields typically between 20 and 50% on a weight basis (Table I). The remainder of the carbon was present in the "char" fraction which had an elemental composition similar to the product oils (Table 11). The "char" fraction was friable when dry. Most of the inorganic ash was present in the char, which burned well and should be suitable as a fuel source for the liquefaction reaction, or may be used with some of the heavier portions of the oil as a synthetic asphalt. For cellulose, the average oil yield was 25% ,expressed as wt % of cellulose converted to acetone soluble oil. In general, the char was about 10 wt %, and the aqueous phase contained up to 5 wt % oil (dichloromethane extraction). The gas, which represented the remaining carbon, was predominantly C02 with 0.1% when 1968). Similarly, we found that alkaline liquefaction of glyceraldehyde, hydroxyacetone, and dihydroxyacetone these conditions were applied to biacetyl. However, exproduced 1-5% of biacetyl and a range of products inposure of acetoin to the same conditions was considerably cluding 1,2-dihydroxybenzeneand 2-hydroxy-3-methyl-2more successful; yields of 18% of 2 and 0.1% of 1 were cyclopent-2-en-1-one. Trioses, such as glyceraldehyde and obtained. In neither case was acetic acid detected. Howdihydroxyacetone, have been shown to form hexoses when ever, a minute amount of biacetyl was present in the exposed to aldol conditions (Gutsche et ai., 1967). It is acetoin and could not be removed. The presence of biCH3
0
OH
CH3
OH
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presumed that the retro-aldol reaction of glucose can produce trioses as well as a tetrose (erythrose). The trioses can just as readily undergo aldol condensation to hexoses. It appears that complex series of reactions may occur during the alkaline liquefaction of glucose (and cellulose) involving both retro-aldolization and reformation of hexoses. We are currently investigating the presence of saccharides in the aqueous phase of the liquefaction products to substantiate Scheme 111. During the liquefaction of cellulose and many of its derivatives, it was noted that the pH of the reaction mixture decreased from 11 to 4.0. Acetaldehyde was exposed to liquefaction conditions to confirm that aldol condensation could occur through the changing pH range. The assumed product, 2-butenal, was obtained in excellent yield. Cellulose liquefaction was performed with 0.2 M NaOH (pH 13.3), 0.2 M sodium acetate (pH 8.1) and NaHC03 (pH 8.2). At the end of 5 min in the tube autoclave (300 "C), the pH of each of the mixtures was 4.1-4.2. In each case the mixture of products was similar to that obtained with 0.2 M Na2C03. Without Na2C03the final pH of an aqueous cellulose mixture was 2.8. Thus, it appears that the wide variance of the initial pH makes little difference in liquefaction as long as it remains above 4.0. This pH requirement probably is associated with the ability to catalyze aldol and Michael reactions. That the pH dictates the predominant mechanism in this type of liquefaction was shown by exposing 2,5-hexanedione to 0.2 M acetic acid and 0.2 M Na2C03in tube autoclaves at 300 OC for 5 min. The major product of the acetic acid catalyzed liquefaction was 2,5-dimethylfuran, while that of the Na2C0, catalyzed reaction was 3-methylcyclopent-2-enl-one. Product Oil Application. It was noted previously (Miller et al., 1981) that the liquid products of cellulose liquefaction contain about 62% of the energy of the starting material although they represent a third of the mass. The average heat of combustion for this material is 32.6 kJ g-l (Donovan et al., 1981b) compared to no. 6 fuel oil at 42.3 k J g-' (Paber and Bauer, 1977). However, the values for the heat of combustion of cellulose oil do increase with the liquefaction temperature. This presumably is due to further conversion of the char fraction to lower molecular weight components. Boiler-firing tests were performed with whole wood oil (PERC and LBL processes), and both gave satisfactory efficiencies and emission levels (Elliott, 1981a). One impediment to the use of cellulose liquefaction oil as a fuel may involve an increase in viscosity with time. This is especially observed with dry cellulose oil prepared at 300 "C and with less than two weeks of aging. Distillates of this material tend to darken with age when exposed to air. These observations were not made with whole wood oil (LBL or PERC processes) since those oils were well aged and processed at higher temperatures. Further, whole wood oil generally contained about 7% water, whereas the cellulose oil (after extraction) usually contained less than 0.5% water. Typically, the acetone or dichloromethane fractions of cellulose oil had an initial viscosity of about 750 CP (0.75 N s mP2). After 2 weeks the viscosity was measured at over lo4 CP (1.0 N s m-9. Neither IR nor NMR could distinguish any gross differences due to aging (Russell et al., 198313). However, preliminary gel-permeation chromatography of the aging cellulose oil suggests an increasing average molecular weight over the first month of exposure to air. This "oligomerization" may be due to autoxidation (radical initiation). Further, the presence of quinones, and most likely semiquinones, in the
cellulose oil suggests that these components may be the intiators for radical induced oligomerization. Elimination of the aging phenomenon can probably be achieved by conducting cellulose liquefaction at temperatures above 300 "C. Catalytic hydrotreating (Gupta et al., 1976; Elliott and Baker, 1983) of cellulose oil would certainly decrease the effects of aging as well as provide an up-graded transportation fuel. Pyrolytic processes have already utilized solid organic wastes as feedstock for the production of asphaltic materials (Espenscheid, 1979). Milder conditions using alkaline liquefaction have also provided an asphalt-like material from sewage sludge (Donavan et al., 1981). In this latter work ten samples of the liquefaction oil from Honolulu sewage sludge were vacuum distilled after acetone extraction, yielding a light oil with 90% of the heating value of diesel fuel and a bottoms fraction which constituted the synthetic asphalt (designated SA). The materials were examined by a series of tests for asphalt quality and compared to an AC-10 petroleum asphalt. Tests applied included determination of pouring temperature, hot water leaching, brittleness, tackiness as a thin film exposed to freezing temperatures, odor, mixing with petroleum asphalt, mixing with mineral aggregate, and determination of the effect of water on the bending/pulling ductility characteristics of the SA-aggregate mixtures after consolidation. All of the SA samples were relatively odorous, but some of the odor could be removed with hot water extraction. When mixed with petroleum asphalt, the SA tended to cause gel formation and weaken the binding properties of the mixture. On the positive side, the SA samples mixed with and coated the mineral aggregate. Three of the SA samples compared well with petroleum asphalt, meeting or exceeding most of the desired property test values. It was concluded that some of the heavier fractions of the sewage sludge-derived oil would be useful as asphalt substitutes. Another application for the biomass-derived oil is its use as an adhesive intermediate. This potential exists due to the phenol and furan content of the oils, which are in principle capable of cross-linkingwith formaldehyde. Such an adhesive would be similar to the phenol-formaldehyde resins now in use commercially. Pine waste, pyrolytic tar phenolics have been found useful as extenders of phenolieformaldehyde resins (Soltes and Lin, 1983). Similar results were observed with biomass liquefaction oil fractions as substitutes in molding compositions (Elliott, 1981a). To further exploit this work, liquefaction oil (PERC process) was examined as a wood adhesive. This oil had been obtained from the Biomass Liquefaction Experimental Facility (DOE) in Albany, OR (Elliott, 1984). Whole wood oil was extracted with a series of solvents to generate a phenol-rich fraction. The extract contained 25.3 wt % of acidic components, i.e., caustic extractable material. Based on this information, a formulation was prepared containing 5 g of the phenolic extract, 66.5 mL of 37% formaldehyde, 33 mL of water, and 23 g sodium hydroxide. The mixture was heated to 70-80 "C for 6 h. The resulting resin was mixed in 100-mL batches with 15 g of powdered bark, 6 mL of 50% aqueous sodium hydroxide, and 3 g of sodium carbonate, stirred for 30 min, and cooled. The compounded adhesive spread easily at room temperature. It was also water soluble before curing which allowed easy equipment cleaning. Squares of birch veneer were spread with this glue and cured in a Carver laboratory press at 140 "C and 85 psi for 5-6 min. In five of six samples examined, commercial adhesive between the veneer and the core failed before the wood-oil derived
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 3, 1984 475 Table IV. Tensile Strength of Wood Oil-Derived Adhesive sample
1 2 3 4 5
n0.O
u l t i m a t e tensile strength, lb./in.2
failure
85.4 46.2 142 121 174 235 133
substrate adhesive substrate substrate substrate 6 substrate 7 adhesive OAdhesive preparation i s described in t h e text. Sample 7 was soaked in water a t 80 OC f o r 24 h p r i o r t o testing. T h e veneer squares were glued cross-grained t o each other.
synthetic glue, showing the wood oil product to be superior in tensile strength. Table IV shows the ultimate tensile strengths for the seven samples tested. Conclusions It is apparent that a more detailed understanding is required of the basic reaction mechanisms involved in the conversion of cellulosic biomass before further product applications can be made. The reduction of heating and cooling times with this procedure (similar to that achieved in aqueous pyrolysis) has provided an insight into the mechanisms of cellulose liquefaction under alkaline conditions. Faster heating rates would be useful to reduce the inevitable degradation and recombination of the initial produds. It has been shown in this study and others that many of the reactive intermediates formed during liquefaction act as precursors for other products with time. An example of this is the formation of 2,5-dimethyl-1,4benzenediol from acetoin and biacetyl. The use of alkaline catalysts under liquefaction conditions at 300 “C was shown to shift the mechanism from one involving aqueous pyrolysis (predominant furan formation) to one incorporating aldol and related condensations. Incomplete mixing of the alkaline catalyst allowed both mechanisms to operate during liquefaction with fast heating and cooling rates. Acknowledgment The work reported here was supported in part by the Department of Energy, Division of Chemical Sciences, Office of Basic Energy Sciences, under Contract No. EY76-C-06-1830 (basic research), and by the Environmental Protection Agency under Grant No.R-806790-01(synthetic asphalt research). Assistance from these sources is gratefully acknowledged.
Registry No. Na2C03,497-19-8; cellulose, 9004-34-6; 2,5-di615-90-7; biacetyl, 431-03-8;acetoin, 51386-0. methylhydroquinone,
Literature Cited Appell. H. R.; Fu, Y. C.; Friedman, S.; Yavorsky, P.; Wender, I. U.S. Bur. Mines rept. Invest. 1975, 8013. Bergius, F. Mining J . 1928, 163, 1067. Berl, E.; Schmldt, A. Justus Liebigs Ann. Chlm. 1932, 493, 97. Berl, e.; Schmidt. A. Justus Liebigs Ann. Chlm. 1932, 496, 283. Bobleter, 0.; Niesner, R.; Rohr, M. J . Appi. fo/ym. Sci. 1978, 20, 2083. Brittain, G. D. Am. Lab. 1969, (5), 57. Cavalier, J.; Chornet, E. fuei 1977, 56, 57. Donovan, J.; Miller, R.; Batter, T.; Lottman, R. €PA Rept. 6092-810242, 1981, NTIS PB82-119082. Donovan, J.; Mokon, P.; Demmitt, T. fuel 1981, 60, 898. Eager, R. L.; Pepper, J. M.; Roy, J. C.; Mathews, J. F. Can. J . Chem. 1983, 6 1 , 2010. Elliott D. C. Biotech. Bloeng. Symp. No. 1 1 1981, 187. Elliott, D. C. I n “Fuels from Biomass and Wastes”, Klass, D. L.; Emert, G. H., Ed.; Ann Arbor Publishers: Ann Arbor, MI, 1981; p 435. Elllott, D. C. I n “Proceedings, International Conference on Fundamentals of Thermochemical Biomass Converslon”, Overend, R.; Milne, T. A,; Mudge, L. K., Ed.; Applied Science Publishers: Essex, 1984 in press. Elllott, D. C.; Baker, E. 0. “Biomass Liquefaction Product Analysis and Upgrading”; presented at Meetlng of Biomass Liquefaction Experts, Sherbrooke, Quebec, Sept 29-30, 1983. Epenscheid, W. F. U.S. Patent 4 177 079, 1979. Forsskahl. I.; Popoff, T.; Theander, 0. Carbohydr. Res. 1978, 48, 13. Gupta, D. V.; Kranlch, W.L.; Welss, A. H. Ind. Eng. Chem. Process Res. Dev. 1978, 15, 256. Gutsche, C. D.; Redmore, D.; Burlks, R. S.; Nowotny, K.; Grassner, H.; Armbruster, C. W. J . Am. Chem. SOC. 1987, 8 9 , 1235. Heyns, K.; Kller, M. Carbohydr. Res. 1988, 6 , 436. Kato, M.; Mizushlma, M.; Kurata, T.; Fujlmaki, M. Agr. Biol. Chem. 1973, 3 7 , 2877.
Miller, R.; Molton. P.; Russell, J. I n “Fuels from Blomass and Wastes”, Klass. D. L.; Emert, G. H., Ed.; Ann Arbor Science Publishers: Ann Arbor, M I 1981; p 451. Molton, P.; Miller, R.; Donovan, J.; Demmitt, T. Carbohydr. Res. 1979, 75, 199.
Mokon, P.; Miller, R.; Russell, J.; Donovan, J. I n “Biomass as a Nonfossll Fuel Source”, Klass, D. L., Ed.; American Chemical Soclety; Washington, DC, 1981; ACS Symp. Ser. No. 144, 1981, 137. Nelson, D. A.; Landsman, S. D.; Molton, P. M. Carbohydr. Res. 1984, 128, in press. Paber, K. W.; Bauer, H. F. I n “Fuels from Waste”, Anderson, L. L.; Tlllman, D. A., Ed.; Academlc Press: New York, 1977; p 73. von Pechmann, H. Chem. Ber. 1888, 2 1 , 1411. Russell, J. A.; Miller, R. K.; Molton, P. M. Biomass 1983, 3, 43-57. Russell, J. A.; Hanson, K. R.; Mokon, P. M.; Landsman, S. D.; Nelson, D.A. I n “Symposium Papers of Energy from Biomass and Wastes VII”, Klass, D. L.; Elliott, H. H., Ed.; Institute of Gas Technology: Chicago, 1983; p 1199. Shaflzadeh, F.; Lai, Y. J . Org. Chem. 1972, 3 7 , 278. Shaflzadeh, F.; Phllpot. C.; Ostojlc, N. Carbohydr. Res. 1971, 16, 279. Soltes. E. J.; Lln, S. -C. K. “Vehicular Fuels and Oxy-Chemicals from Biomass Thermochemlcal Tars”; presented at Flfth Symposium on Biotechnology for Fuels and Chemlcals: Gatlinburg, TN, May 1983. Waterman, H.; Kortlandt, F. R e d . Trav. Chim. fays-Bas 1924, 43, 691. Weiss, A. H. Text. Res. J . 1972, 42, 526.
Receiued for reuiew D e c e m b e r 1, 1983 Accepted M a y 3, 1984
