Insight into catalytic effects of alkali metal salts addition on bamboo and cellulose pyrolysis

Abstract

Abstract Alkali metal compounds have vital influence on biomass pyrolysis conversion. In this study, bamboo and cellulose catalytic pyrolysis with different alkali metal salts catalysts (KCl, K2SO4, K2CO3, NaCl, Na2SO4, and Na2CO3) were investigated in the fixed-bed reaction system. The effect of cations (K+ and Na+) and anions (Cl−, SO42− and CO32−) on the evolution properties of biochar, bio-oil, and gas products was explored under both in-situ and ex-situ catalytic pyrolysis. Results showed that alkali metal salts facilitated the yields of biochar and gases at the expense of that of bio-oil. alkali metal-Cl, SO4 showed a weaker catalytic effect, while alkali metal-CO3 greatly promoted the generation of gas products and increased the condensation degree of biochar. With the addition of K2CO3 and Na2CO3, cyclopentanones content was over 50% from cellulose catalytic pyrolysis, and phenols content (mainly alky-phenols) reached over 80% from bamboo catalytic pyrolysis. Moreover, solid-solid catalytic reactions with K2CO3 and Na2CO3 catalysts had a more important role than gas-solid catalytic reactions for in-situ catalytic pyrolysis. The solid-solid and gas-solid catalytic reactions with alkali metal-CO3 catalysts were stronger than those with alkali metal-Cl, SO4 catalysts. Furthermore, the possible catalytic pyrolysis mechanism of alkali metal salts on biomass pyrolysis was proposed, which is important to the high-value utilization of biomass.