A sustainable strategy for the production of 1,4:3,6-dianhydro-α-d-glucopyranose through oxalic acid-assisted fast pyrolysis of cellulose

Abstract

Selective preparation of value-added products via fast pyrolysis is a sustainable way for biomass utilization. We developed a novel strategy, oxalic acid-assisted fast pyrolysis (OAFP) of cellulose, which achieved the selective production of a promising anhydrosugar, 1,4:3,6-dianhydro-α-d-glucopyranose (DGP), for the first time. Effects of temperature and the mass ratio of cellulose-to-oxalic acid (Cell/OA) in their solid mixture were explored. The yield of DGP could be up to 14.0 wt% (based on cellulose) at 400 °C and the Cell/OA mass ratio of 1:9 with a lab-scale setup, about 200 times higher than that from fast pyrolysis of pure cellulose. According to the experiments and density functional theory (DFT) calculations, it was OA rather than its pyrolysis vapors (mainly formic acid) that played the predominant role in the selective generation of DGP, where OA acted as a reactant and a catalyst-like material at the same time. The formation of DGP competed with that of levoglucosan (LG), the most typical product in the fast pyrolysis of pure cellulose, and a small amount of DGP came from the secondary conversion of LG. The esterification of free hydroxyl at C3 or C6 position with OA determined the selective generation of DGP by promoting the formation of the C1 = C2 bond and the 3,6-acetal ring, and the generation of the 1,6-acetal ring was inhibited correspondingly which led to the decrease of LG. In addition, the OAFP process also showed the potential for poly-generation of value-added chemicals, syngas, and char.