Mechanistic insights into the primary reactions during acid-catalysed pyrolysis of levoglucosan at 80–140 °C

Abstract

This paper reports an experimental investigation into the pyrolysis of acid-impregnated levoglucosan at 80–140 °C to understand the fundamental reaction mechanism of acid-catalysed levoglucosan pyrolysis. Glucose, anhydro-disaccharides and disaccharides of various linkages have been successfully identified as major primary products during acid-catalysed levoglucosan pyrolysis at such low temperatures. Among all identified primary products, glucose has the highest initial selectivity of ~20%, indicating hydrolysis reaction plays an important role during acid-catalysed levoglucosan pyrolysis. The formation of anhydro-disaccharides of various α and β linkages (including 1,4-, 1,3-, and 1,2-glycosidic bond) clearly demonstrates the importance of polymerisation reactions during acid-catalysed levoglucosan pyrolysis. In addition, disaccharides of various α and β linkages (including 1,6-, 1,4-, 1,3-, 1,2-, 1,1-glycosidic bond) are also minor primary products from acid-catalysed levoglucosan pyrolysis. Once those primary products are formed, they are easily polymerised into high-DP anhydro-sugar and sugar oligosaccharides, with a highest DP of up to ~10 at 120 °C. At 140 °C, the oligosaccharides are also easily condensed to form char, as evidenced by post-hydrolysis results. Increasing acid loading level enhances the formation of glucose and disaccharides, but has negligible effect on the formation of anhydro-disaccharides. These results provide new insights into the fundamental mechanism of acid-catalysed levoglucosan pyrolysis for producing biofuels and biochemicals.