Enhancing the production of small molecular products from pubescens via stepwise pyrolysis process

Abstract

Pyrolysis of pubescens pretreated by torrefaction was investigated by one-step and stepwise processes. The cumulative yield of small molecular compounds reached up to 19.6 wt% via stepwise processing, yielding monosaccharides (1.49 wt%), carboxylic acids (5.20 wt%), furans (3.97 wt%) and monophenols (8.94 wt%), which is higher than the corresponding value of 12.39 wt%, with 0.65 wt%, 6.15 wt%, 1.05 wt% and 4.54 wt% of the four kinds of species obtained respectively, from one-step pyrolysis. Production of carboxylic acids could be enhanced in the temperature range of 200–320 °C via dehydration of holocellulose and cleavage of acetyl group in lignin, while the acquisition of furans could be promoted in the range of 240–360 °C via further dehydration of the units of holocellulose. In the temperature range of 240–440 °C, the cleavage of β-1,4-glycosidic linkages in cellulose and glycosidic bonds in hemicellulose enhanced the yield of monosaccharides. Furthermore, the formation of monophenols from the decomposition of H, G, and S units of lignin was enhanced via cleavage of C1-Cα, Cα-Cβ, Cβ-Cγ, Cα-OH, C-O-H(R), etc. in saturated and unsaturated regions, accompanied by elimination, dehydration reactions. With stepwise processing, the corresponding carbon content in the pyrolyzed residue was enriched, resembling the elemental composition of Bituminous coal. Moreover, the relationship between small molecular weight compounds and oligomers has been probed.