The oxalic acid-assisted fast pyrolysis of biomass for the sustainable production of furfural

Abstract

Pyrolysis is a promising thermal conversion technique of biomass to tackle the energy crisis and environmental pollution. Furfural (FF) is an important pyrolysis product from biomass-based materials and a crucial platform compound for energy and fuels. In the present study, we developed a new and green approach to selectively produce FF through the oxalic acid-assisted fast pyrolysis (OAFP) of corncob (CC). The FF yield was up to 16.5 wt% (based on raw CC) through the fast pyrolysis of the solid mixture of CC and OA with a ratio of 1:4 (CC/OA) at 400 °C during the micro-pyrolysis coupled with online-detection experiments. The corresponding FF selectivity was 56.5% (based on raw CC). Under similar experimental parameters, a yield of 10.0 wt% (based on raw CC) was achieved with a lab-scale setup. Experiment and density functional theory (DFT) calculation results suggested that OA played a catalyst-like role in the selective formation of FF from hemicellulose (mainly xylose units) of CC and meanwhile decomposed during the pyrolysis process. The formic acid (FA) decomposed from OA had a similar but lighter effect than OA. With the assistance of OA, the energy barriers of the FF formation reactions decrease dramatically and the competitiveness of the pathways is also altered, which contributes a lot to the FF selective generation. FF is mainly generated in a chain propagation pattern from the acyclic reducing end and unsaturated (C4C5 bond) non-reducing end of the xylan chain.