Influence of thermo-pressure synergistic effect on deoxygenation and aromatization reactions during extrusion pyrolysis of bagasse

Abstract

Biomass has the potential to replace coal, contributing to the mitigation of climate and energy challenges. The development of low-energy, high-quality biomass upgrading technologies is of significant importance. The biomass extrusion pyrolysis (EP) technology, which increases the pressure during the heating process of biomass pyrolysis, is anticipated to achieve the desired outcome. Pressure, temperature, and residence time were investigated for their effects on the physicochemical properties and structure of bagasse-derived biochar during EP. The volatile content of EP biochar decreased by 10.21∼12.63 % and the carbon fixation rate (CFR) increased by 23.04∼30.56 % compared with atmospheric pyrolysis (AP) biochar at the same temperature and residence time, below 6 MPa. A synergistic effect of pressure and temperature was observed, resulting in an approximately 10 % reduction in volatile content and a 10∼20 % increase in CFR of extruded pyrolysis products at 6 MPa, compared to AP above 240 °C. Below 240 °C, these values were lower. Comparing the pyrolysis product biochar of AP and EP, as well as those from low and high temperatures, FTIR and Raman analyses demonstrated that oxygen-containing functional groups decreased and the degree of aromatization increased, confirming that extrusion and temperature facilitated deoxygenation and aromatization. Extrusion caused pore structure contraction. In BET data, the specific surface area and pore volume decreased significantly. These, coupled with changes in the biochar's physicochemical properties, indicated that extrusion promoted volatile matter conversion into fixed carbon by gas-solid secondary reactions during pyrolysis.