Role of different chain end types in pyrolysis of glucose-based anhydro-sugars and oligosaccharides

Abstract

This study investigates the pyrolysis characteristics of glucose-based anhydro-sugars (maltosan and levoglucosan) and oligosaccharides (cellobiose, cyclodextrin and cellulose) using TG-FTIR-MS and the role of the reducing and levoglucosan ends in cellulose pyrolysis. During the slow pyrolysis of two disaccharides (cellobiose and maltosan), dehydration reactions were strongly promoted at low temperatures due to the polymerization, which led to the earlier decomposition of maltosan and cellobiose compared with other carbohydrates. Compared with the reducing end in cellobiose, the levoglucosan end in maltosan enhanced the cleavage of glycosidic bonds, which led to the maximum weight loss of maltosan at a lower temperature (i.e. 232 °C) than that of cellobiose (i.e. 299 °C). Furthermore, because of the stability of the levoglucosan end, a significantly higher char yield was obtained after an obvious carbonization process at the expense of gaseous volatiles. Fast pyrolysis of these samples at 500 °C was also conducted on Py-GC/MS and yields based on carbon of 28 products were identified. The results show that the reducing end prompted the rupture of pyran rings for furan species, while the stable structure of the levoglucosan end strongly promoted the formation of pyrans such as levoglucosenone. Finally, a mechanism for cellulose pyrolysis is proposed, which takes into consideration the effects of the different chain ends.