Characterization of Water-Soluble Intermediates and Solid Residues from Fast Pyrolysis of Cellulose in a Wire-Mesh Reactor

Abstract

The fast pyrolysis characteristics of cellulose were investigated in a wiremesh reactor, which minimized the secondary reactions between the solid residues and the evolved volatiles during pyrolysis and facilitated the collection of the primary intermediates and volatiles. The main component of the water-soluble intermediates was anhydrooligosaccharides with various degrees of polymerization (DP). The yields of cellotriosan and cellotetraosan in the intermediates were much higher than those of levoglucosan and cellobiosan in the early pyrolysis stage, indicating that the depolymerization of the cellulose chain occurred during a random cleavage process. Anhydro-oligosaccharides with DP up to 3, and partially decomposed sugar-ring-containing oligomers, were identified in the primary volatiles. Among the sugar-ring-containing oligomers, the compound with a relative molecular weight of 222 was considered to be the product of a reverse aldolization reaction. An analysis of the solid residues confirmed the occurrence of intramolecular dehydration during the cellulose pyrolysis.

Activation of Cellulose via Cooperative Hydroxyl-Catalyzed Transglycosylation of Glycosidic Bonds

“…Anhydropolysaccharides, which are small-chain glucose-based oligomers with anhydrous LGA end groups, are known intermediates in the conversion of cellulose. Small anhydrosugars with negligible volatility such as cellobiosan and cellotriosan have been observed in products of cellulose conversion, likely formed through the aerosol ejection mechanism. ,, Also, Xu et al detected anhydropolysaccharides with a degree of polymerization up to seven in the water-soluble fraction of cellulose pyrolysis intermediates. For this reason, anyhydrosugars have previously been selected as one of many possible intermediates for experimental evaluation.…”

“…LGA (1,6-anhydro-β- d -glucopyranose), a six-carbon anhydrosugar, is the most abundant product of cellulose pyrolysis with yields as high as 70% . Studies also report that captured intermediate of cellulose decomposition contains short-chain (2–8 monomer) anhydro-oligomers with LGA end groups. , This indicates that transglycosylation is a probable reaction mechanism in cellulose activation. Mechanisms by which LGA forms from cellulose reactive intermediates are depicted in Scheme including radical (Scheme A), ionic (Scheme B), and concerted (Scheme D) mechanisms.…”