SynopsisIt has been shown that the pyrolysis of cellulose at low pressure (1.5 Torr) can be described by a three reaction model. In this model, it is assumed that an "initiation reaction" leads to formation of an "active cellulose" which subsequently decomposes by two competitive first-order reactions, one yielding volatiles and the other char and a gaseous fraction. Over the temperature range of 259-341°C, the rate constants of these reactions, k; (for cellulose -"active cellulose"), k, (for "active cellulose" -"volatiles"), and k , (for "active cellulose" -char + the gaseous fraction) are given by min-', respectively. ki = 1.7 x 1021e-(58,000/RT) min-1, k, = 1.9 x 1016~-(47,300/RT) min-l, and k , = 7.9 x 1Olle-(36,600/RT)

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Thermal analysis and kinetic studies have shown that oxidative reactions are responsible for acceleration in the rates of weight loss and depolymerization of cellulose on pyrolysis in air at temperatures below 300°C. The oxidative reactions include production of hydroperoxide, carbonyl, and carboxyl groups, which have been investigated at lower temperatures along with the rates of depolymerization and production of carbon monoxide and carbon dioxide. The experimental results are consistent with an autoxidation mechanism involving initiation, propagation, and decomposition reactions. At temperatures above 300°, the rate of pyrolysis is essentially the same in both air and nitrogen, indicating that thermal degradation is independent of the oxidative reactions.

SynopsisVacuum pyrolysis of cellulose within the temperature range of 300-50O0C provides a tar fraction containing mainly levoglucosan and glucose condensation products. It was found that pyrolysis proceeds at a much faster rate at the higher temperatures without detrimental effect on the yields. At 400OC the reaction was essentially conlplete within 3 min yielding a tar that contained 39% levoglucosan and, upon mild acid hydrolysis, gave 49% D-glucose. The yields could be further improved by washing or treatment of cellulosic sobstrates with acids. Cotton hydrocellulose provided up to 58% levoglucosan or 77% D-glucose. This is the highest yield determined by unequivocal methods. Commonly available cellulosic materials such as wood and newsprint give very poor yields of levoglucosan. However, the yields could be improved substantially by acid washing or prehydrolysis to the extent that pyrolysis of these substrates may become an attractive industrial process. The data in this report provide the technical basis for such a process and resolve the existing controversies on the reported yields. INTRODUCTIONCurrent efforts for development of alternative sources of energy and chemical feedstock have focused considerable interest on more intensive utilization of renewable cellulosic materials. These materials can be converted to glucose and sugar derivatives by acidic, enzymic, and pyrolytic methods. However, commercial applications are hampered by economic considerations. Acid hydrolysis is slow and cumbersome, while enzymic hydrolysis requires costly pretreatment to increase the accessibility and susceptibility of the substrate. Pyrolytic depolymerization is hampered by a lack of specificity; however, this process deserves special consideration because of its inherent efficiency and compatibility with modern engineering technology including fluidized bed processes.Pyrolysis of cellulose to levoglucosan (1,6-anhydro-~-D-glucopyranose) was reported 60 years ago by Pictet and Sarasin.l However, the yield of levoglucosan that could be obtained from pure cellulose was indefinite and contr~versial.~-~ Pyrolyzates from commonly available cellulosic materials such as paper and wood contained very little l e v o g l u~o s a n~~ and were better suited for fuel rather than chemical feedstock for sugar derivatives. Furthermore, reliable kinetic data were missing to indicate the optimal pyrolytic conditions. Detailed studies at this laboratory to unravel the pyrolytic r e a c t i~n s~J~-~~ indicated that at temperatures above 300°C, the glycosidic bond in cellulose is substituted by one of the free hydroxyl groups. This intramolecular transglycosylation provides anhydrosugars which are subsequently interconverted and partially repolymerized by intermolecular transglycosylation to provide a tarry mixture of levoglucosan, its furanose isomer (1,6-anhydro-~-D-glucofuranose), and randomly linked oligo-and polysaccharides.'O The tar fraction also contains a variety of minor products resulting from competing dehydration, elimination, an...

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