Valorisation of cotton stalk toward bio-aromatics: Effect of wet torrefaction deoxygenation and deminerization pretreatment on catalytic fast pyrolysis using Ga modified hierarchical zeolite

Abstract

Wet torrefaction pretreatment (WTP) can upgrade the property of biomass by synergistic effect of deoxygenation and deminerization (e.g. K, Ca, Na, Mg). In this work, valorisation of cotton stalk (CS) was performed by using combined approaches of WTP and catalytic fast pyrolysis (CFP) to produce bio-aromatics. First, the maximum deoxygenation and deminerization rates were 53.84 % and over 90 %, respectively, at the WTP temperature of 260 °C. Second, the bifunctional catalyst of Ga modified hierarchical HZSM-5 with micro-mesopore structure allowed more oxygenates diffusing into the channel of catalyst and increased the reaction rates of deoxygenation and aromatization reactions which highly improved the yield of bio-aromatics. Third, higher CFP temperature was favored for the formation of aromatics. The yield of aromatics increased first with the raise of catalyst-to-biomass (C/B) ratio from 1:1 to 1:3, then decreased slightly at the highest C/B of 1:5. At last, the operation parameter of WTP and SS-CFP was optimized which the maximum yield of light aromatics was 1.08 × 108 a.u./mg at WTP temperature of 220 °C, biomass-to-catalyst ratio of 3:1, and CFP temperature of 850 °C.