Production of levoglucosan and glucose from pyrolysis of cellulosic materials

Abstract

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...

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Levoglucosan, a sixcarbon 1,6-anhyrosugar (see Figure 1), was identified as the main product of cellulose pyrolysis nearly a century ago (Pictet and Sarasin, 1918). Levoglucosan is formed alongside other smaller decomposition products, with maximum levoglucosan production occurring at 500°C (Shafizadeh et al, 1979). Minor products of cellulose pyrolysis are dominated by other anhydrosugars that retain all six carbons of glucose, such as 1,6-anhydroglucofuranose and 5-hydroxymethyl furfural, but also smaller molecules, like furfural (5, Figure 1), formic acid, and glycolaldehyde, among others (Patwardhan et al, 2011b).…”

Is the Broido-Shafizadeh Model for Cellulose Pyrolysis True?

“…Depending upon the purity and size of the sample, cellulose pyrolysis can result in the formation of either the monomeric anhydrosugar levoglucosan and related species 1 , or char 2 and light volatile fragmentation products such as glycolaldehyde [3][4][5][6] . In this paper we deal only with the pyrolysis kinetics of pure, ash-free cellulose under conditions where secondary reactions and transport processes do not obfuscate the primary solid-phase decomposition reactions.…”

Advances in Thermochemical Conversion of Biomass—Introduction

“…The thermal decomposition studies of biomass samples started several decades ago. Among the early publications, the pioneering work of F. Shafizadeh and his coworkers must be mentioned [2,3,6,7]. They applied thermogravimetry and furnace pyrolysis and analyzed the volatile products off-line by various analytical techniques.…”