Comparative study on carbon dioxide-cofed catalytic pyrolysis of grass and woody biomass

This study investigated the mechanistic functions of CO₂ on the pyrolysis of two different biomasses to elucidate the effect of CO₂ on syngas formations during pyrolysis. To this end, CO₂-assisted pyrolysis of cellulosic biomass (barnyard grass, Echinochloa) and lignin-rich woody biomass (retinispora, Chamaecyparis obtusa) were compared. The confirmed mechanistic effectiveness of CO₂ on pyrolysis of biomass was gas phase reactions between CO₂ and volatile matters from biomass pyrolysis. Lignin-rich biomass had more CO₂ susceptibility, resulting in more enhanced CO formation via the gas phase reactions. To expedite the slow reaction rate of the gas phase reactions during biomass pyrolysis, earth-abundant catalysts (Co/SiO₂ and Ni/SiO₂) were employed for pyrolysis of two biomass substrates. With Co and Ni catalysts, the syngas formations were 2 and 3 times higher comparing to the pyrolysis of without catalyst. The cumulative formations of syngas from lignin-rich biomass was nearly doubled than that from cellulosic biomass.