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Ind. Eng. Chem. Res. 1996, 35, 2709-2715
2709
Fractionation of Sugar Cane with Hot, Compressed, Liquid Water Stephen Glen Allen, Lance Cameron Kam, Andreas Joseph Zemann,† and Michael Jerry Antal, Jr.* Hawaii Natural Energy Institute and the Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii 96822
Sugar-cane bagasse and leaves (10-15 g oven-dry basis) were fractionated without size reduction by a rapid (45 s to 4 min), immersed percolation using only hot (190-230 °C), compressed (P > Psat), liquid water (0.6-1.2 kg). Over 50% of the biomass could be solubilized. All of the hemicellulose, together with much of the acid-insoluble lignin in the bagasse (>60%), was solubilized, while less than 10% of the cellulose entered the liquid phase. Moreover, recovery of the hemicellulose as monomeric sugars (after a mild posthydrolysis) exceeded 80%. Less than 5% of the hemicellulose was converted to furfural. Percolation beyond that needed to immerse the biomass in hot liquid water did not result in increased solubilization. The yield of lignocellulosic residue was also not sensitive to the form of the sugar cane used (bagasse or leaves) or its moisture content (8-50%). Commercial applications for this fractionation process include the pretreatment of lignocellulosics for bioconversion to ethanol and the production of pulp and paper products. Introduction Biomass needs to be separated into its components for the complete conversion of this resource to the highest value products. As is evident from Table 1, a variety of aqueous processes have been developed to separate cellulose, hemicellulose, and lignin from whole biomass. Unfortunately, an aqueous process capable of producing these components in high yields and purity on a practical scale has remained elusive. For example, an extract of solubilized lignin together with all of the hemicellulose (90% recoverable as pentosans) and a fibrous cellulose-enriched residue was produced after less than 15 min of treatment by a simple percolation of biomass with hot, compressed, liquid water at 190230 °C (Mok and Antal, 1992). Unfortunately, this work was perceived to have little industrial application, because Mok and Antal only processed a few hundred milligrams of biomass powder in a microreactor. In earlier studies employing liquid water, solubilization profiles for the main components of both aspen and jack pine were obtained at 100-186 °C (Aronovsky and Gortner, 1930), but at these lower temperatures, reaction times of up to 12 h were required. A percolation/ recirculation reactor (50 L) employing higher temperatures (180-240 °C) and shorter residence times (3 h) was later developed by Bobleter and co-workers (Bobleter and Paper, 1968; Bobleter and Binder, 1980). This liquid “hydrothermolysis” process solubilizes 50% of the biomass (35-50% of the lignin) but requires large amounts of water and time to effect the separation. A continuous (100 kg h-1) tubular reactor was later developed by Montane´ et al. (1993) from batch autoclave studies (Koeberle et al., 1985). Short reaction times were possible, but the system was limited to slurries. Although steam treatment can also fractionate biomass, the recovery of hemicellulose sugars (pentosans) is low, especially when compared to liquid systems (Table 1). Vapor systems such as steam explosion and steam extraction (Brownell and Saddler, 1987) derive from the * To whom correspondence should be addressed. E-mail:
[email protected]. † Permanent address: Institute for Analytical Chemistry and Radiochemistry, University of Innsbruck, A-6020 Innsbruck, Austria.
Masonite process of the early 1930s (Mason, 1929) and the more recent Iotech (steam-explosion) process (Delong, 1981). Regardless of whether a steam or liquid water process is used, the unique properties of hot, compressed, liquid water need to be exploited to fractionate biomass. This breaking of chemical bonds may be enhanced by the increased disproportionation of water at elevated temperatures. At 220 °C the ion product of liquid water is 10-11 (Marshall and Franck, 1981). Thus, the pH of water at this temperature is 5.5, as compared to 7.0 at 25 °C. Although hemicellulose is partially deacetylated as well as depolymerized under these conditions (Bouchard et al., 1991), some evidence suggests that the cleavage of glycosidic bonds may not depend on the presence of hemicellulose-derived organic acids. A mechanism other than acid hydrolysis may be followed (Bobleter et al., 1986). Isolated lignin can also be depolymerized with only water (Bobleter and Concin, 1979; Chua and Wayman, 1979). During steam explosion, the internal cavities of biomass must be well wetted with liquid water to enhance the hydrolytic reactions responsible for fractionation (Overend and Chornet, 1987). The rapid decompression (“explosion”) is a physical process which disrupts the ultrastructure of the biomass but has little chemical effect (Tanahashi et al., 1990; Law et al., 1991). Similarly, using mechanical devices such as homogenizing valves does not necessarily leads to the increased fractionation of biomass in liquid systems (Montane´ et al., 1993; Abatzoglou et al., 1990). There is evidence, however, that changes in the microstructure of cellulose can be mechanically induced by these devices (Turbak et al., 1983). Mok and Antal (1992) took advantage of the properties of hot, compressed, liquid water in an inherently simple fractionation process. Of all the aqueous fractionation systems listed in Table 1, only that of Mok and Antal (1992) was able to completely solubilize the hemicellulose in a recoverable form, together with the majority of the lignin, within a few minutes. In addition, this separation was achieved without using mechanical mixing devices or slurries, as needed in other systems (Montane´ et al., 1993; Koeberle et al., 1985). The goal of this study was to determine if reaction
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2710 Ind. Eng. Chem. Res., Vol. 35, No. 8, 1996 Table 1. Solubilization Profiles for Aqueous Fractionation of Biomassa reaction conditions
solubilized material (wt %)
reactor type
feed material
temp (°C)
time (min)
severity (log Ro)b
biomass
lignin
cellulose
hemicellulose
pentosan recovery
ref
percolation batch autoclave flow steam explosion percolation percolation steam explosion percolation steam explosion
aspen aspen aspen aspen sugar cane sugar cane sugar cane wheat straw wheat straw
230 170 220 220 195 230 210 195 220
2 120 2 2 65 2 2 25 2
4.1 4.1 3.8 3.8 4.6 4.1 3.5 4.2 3.8
47 29 26 25 50 41 28 50 44
37 25 15 ndc 68 38 ndc Psat). The solubilization of over 50% of the sugar cane is possible at the most severe conditions tested (log Ro > 4.0). 2. All of the hemicellulose, together with much (>60%) of the acid-insoluble lignin in the bagasse can be solubilized with less than 10% of the cellulose entering the liquid phase. 3. Degradation of the carbohydrates during the fractionation process is low. Complete recovery of hemicellulose as monomeric sugars (after a mild posthydrolysis) is possible after the fractionation of bagasse at 190 °C. Hemicellulose recovery exceeds 90% after fractionation at 220 °C. Furfural (but no hydroxymethylfurfural) can be detected but accounts for less than 1% of the biomass (5% of the hemicellulose). 4. Percolation beyond that needed to immerse the biomass in hot, compressed, liquid water does not change the yield of lignocellulosic residue. 5. Recondensation reactions are not prevalent during the fractionation process. As the reaction severity increases, the yield of lignocellulosic residue monotonically approaches a limiting value rather than passing through a minimum. 6. The yield of lignocellulosic residue is not sensitive to the form of the sugar cane used. Sugar-cane bagasse and leaves provide similar solubilization data. The yield of lignocellulosic residue is also independent of the moisture content of the bagasse (8-50%). 7. Possible applications for the lignocellulosic residue produced by the Aquasolv process described above include bioconversion to ethanol and the production of pulp and paper products. Acknowledgment This work was supported by the National Renewable Energy Laboratory (NREL) as part of the Hawaii Integrated Biofuels Research Program (Contract No. F-212-F-470-B207). The authors thank Dr. Esteban Chornet (NREL) and Dr. Ralph Overend (NREL) for insightful discussions. We also thank Francis Keany (Hawaiian Commercial & Sugar) for supplying feed materials and his interest in this work, William Mok for assistance in the design of the process equipment, Eric Croiset, Lance Kam, and Ben Respicio for construction of the apparatus, and Michael Onuma and Mark Spencer for help in conducting experiments (all affiliated with the University of Hawaii). Last, the helpful suggestions of an anonymous reviewer are acknowledged. Literature Cited Abatzoglou, N.; Koeberle, P. G.; Chornet, E.; Overend, R. P.; Koukios, E. G. Dilute Acid Hydrolysis of Lignocellulosics: An Application to Medium Consistency Suspensions of Hardwoods Using a Plug Flow Reactor. Can. J. Chem. Eng. 1990, 68, 627638. Aronovsky, S. I.; Gortner, R. A. The Cooking Process. I. The Role of Water in the Cooking of Wood. Ind. Eng. Chem. 1930, 22, 264-274. Bobleter, O.; Pape, G. Method to Degrade Wood, Bark and Other Plant Materials. Austrian Patent 263,661, 1968. Bobleter, O.; Concin, R. Degradation of Poplar Lignin by Hydrothermal Treatment. Cell. Chem. Technol. 1979, 13, 583-593.
Bobleter, O.; Binder, H. Dynamic Hydrothermal Degradation of Wood. Holzforschung 1980, 34, 48-51. Bobleter, O.; Schwald, W.; Concin, R.; Binder, H. Hydrolysis of Cellobiose in Dilute Sulfuric Acid and Under Hydrothermal Conditions. J. Carbohydr. Chem. 1986, 5, 387-399. Bobleter, O.; Vidotti, R.; Zemann, A.; Prutsch, W. Hydrothermal Pretreatment of Bagasse and Wheat Straw. Biomass for Energy and Industry; 5th E.C. Conference Volume 2 Conversion and Utilisation of Biomass; Grassi, G., Gosse, G., dos Santos, G., Eds.; Elsevier Applied Science: London, 1990; pp 2.31-2.37. Bouchard, J.; Nguyen, T. S.; Chornet, E.; Overend, R. P. Analytical Methodology for Biomass Pretreatment. Part 1: Solid Residues. Biomass 1990, 23, 243-261. Bouchard, J.; Nguyen, T. S.; Chornet, E.; Overend, R. P. Analytical Methodology for Biomass Pretreatment. Part 2: Characterization of the Filtrates and Cumulative Distribution as a Function of Treatment Severity. Biores. Technol. 1991, 36, 121-131. Brownell, H. H.; Saddler, J. N. Steam Pretreatment of Lignocellulosic Material for Enhanced Enzymatic Hydrolysis. Biotechnol. Bioeng. 1987, 29, 228-235. Chornet, E. (National Renewable Energy Laboratory, Golden, CO). Personal communication, 1994. Chua, M. G. S.; Wayman, M. Characterization of Autohydrolysis Aspen (P. Tremuloides) Lignins. 1. Composition and Molecular Weight Distribution of Extracted Autohydrolysis Lignin. Can. J. Chem. 1979, 57, 2603-2611. Delong, E. A. Method of Rendering Lignin Separable From Cellulose and Hemicellulose in Lignocellulosic Material and the Product so Produced. Canadian Patent 1,096,374, 1981. Goring, D. A. I. The Lignin Paradigm. ACS Symp. Ser. 1989, 397, 2-10. Heitz, M.; Capek-Menard, E.; Koeberle, P. G.; Gange, J.; Chornet, E.; Overend, R. P.; Taylor, J. D.; Yu, E. Fractionation of Populus tremuloides at the Pilot Plant Scale: Optimization of Steam Pretreatment Conditions using the STAKE II Technology. Biores. Technol. 1991, 35, 23-32. International Energy Association Pre-Symposium, Modern Methods of Analysis of Wood, Annual Plants and Lignins, New Orleans, LA, 1991. Jollez, P.; Chornet, E.; Overend, R. P. Steam-Aqueous Fractionation of Sugar Cane Bagasse: An Optimization study of Process Conditions at the Pilot Plant Level. Advances in Thermochemical Biomass Conversion; Bridgwater, A. V., Ed.; Chapman & Hall Publishers: London, 1994; Vol. 2, pp 1659-1669. Kempthorne, O. The Design and Analysis of Experiments; John Wiley & Sons, Inc.: New York, 1952; pp 237-241. Koeberle, P.; Meloche, F.; Chauvette, G.; Me´nard, H.; Chornet, E.; Jaulin, L.; Heitz, M.; Overend, R. P. Pre´traitement du Mate´rial Lignocellulosique par Voie Thermo-Me´cano-Chimique en Phase Aqueuse. In Fifth Canadian Bioenergy R&D Seminar; Hasnain, S., Ed.; Elsevier Applied Science Publ.: Oxford, U.K., 1985; pp 263-267. Law, K. N.; Zhou, W. X.; Valade, J. L. Vapor-Phase Chemimechanical Pulping of AspensExplosion vs. No Explosion. Tappi J. 1991, 4, 263-267. Marshall, W. L.; Franck, E. U. Ion Product of Water Substance, 0-1000 °C, 1-10,000 BarssNew International Formulation and Its Background. J. Phys. Chem. Ref. Data 1981, 10, 295304. Mason, W. H. Apparatus for and Process of Explosion Fibration of Lignocellulosic Material. U.S. Patent 1,655,618, 1929. Masselter, S.; Zemann, A.; Bobleter, O. Analysis of Lignin Degradation Products by Capillary Electrophoresis. Chromatographia 1995, 40, 51-57. Mok, W. S.-L.; Antal, M. J., Jr. Uncatalyzed Solvolysis of Whole Biomass Hemicellulose by Hot Compressed Liquid Water. Ind. Eng. Chem. Res. 1992, 31, 1157-1161. Montane´, D.; Salvado´, J.; Farriol, X.; Chornet, E. The Fractionation of Almond Shells by Thermo-Mechanical Aqueous-Phase (TMAV) Pretreatment. Biomass Bioenergy 1993, 4, 427-437. Montane´, D.; Farriol, X.; Salvado´, J.; Jollez, P.; Chornet, E. Fractionation of Wheat Straw (Triticum aestivum) via Steam-Explosion: Product Distribution and Chemical Characteristics of the Cellulose Pulp Obtained. Biomass Bioenergy 1994, submitted for publication. Moore, J. F.; Johnson, D. B. Procedures for the Chemical Analysis of Wood and Wood Products; Forest Products Laboratory, Forest Service, U.S. Department of Agriculture: 1967.
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Ind. Eng. Chem. Res., Vol. 35, No. 8, 1996 2715 Overend, R. P.; Chornet, E. Fractionation of Lignocellulosics by Steam/Aqueous Pretreatments. Philos. Trans. R. Soc. London 1987, A321, 523-536. Patel, R. J.; Angadiyavar, Y. Srinvasa, R. Nonwood Plant Fiber Pulping: Progress Report No. 15; Technical Association of the Pulp and Paper Industry (TAPPI) Press: Atlanta, GA, 1984. Spencer, M. J. An Investigation into Chemical-Free Pulping of Biomass Using Only Hot Liquid Water. M.Sc. Thesis, University of Hawaii, Honolulu, HI, 1995. Tanahashi, M.; Karina, M.; Higuchi, T. Degradation Mechanism of Lignin Accompanying Steam Explosion II. High-Pressure Steam Treatment of Guaiacylglycerol-β-Guaiacyl Ether. Mokuzai Gakkaishi 1990, 36, 380-388. Turbak, A. F.; Snyder, F. W.; Sandberg, K. R. Microfibrilated Cellulose; A New Cellulose Product: Properties, Uses and Commercial Potential: J. Appl. Polym. Sci. 1983, 37, 815-827. van Walsum, P. G.; Allen, S. G.; Spencer, M. J.; Laser, M. S.; Antal, M. J., Jr.; Lynd, L. R. Conversion of Lignocellulosics Pretreated
with Liquid Hot Water to Ethanol. Appl. Biotechnol. Bioeng. 1995, accepted for publication. Zemann, A.; Bobleter, O.; Prutsch, W. HydrothermolysissA Pretreatment Process for Pulp Production. In Lignocellulosics: Science, Technology, Development and Use; Kennedy, J. F., Philips, G. O.; Williams, P. A., Eds.; Ellis Horwood Series in Polymer Science and Technology; Ellis Horwood: Chichester, U.K., 1992; pp 213-226.
Received for review September 25, 1995 Accepted January 9, 1996X IE950594S
X Abstract published in Advance ACS Abstracts, May 1, 1996.
