Effect of acid washing and K/Ca loading on corn straw with the characteristics of gas-solid products during its pyrolysis

Abstract

Alkali and alkaline earth metallic species (AAEMs) significantly affect the thermal conversion and utilization of biomass. However, the bonding mechanism between AAEMs and biomass carbon substrates is still unclear. In this paper, corn straw with different AAEMs contents were prepared by acid washing and K/Ca loading with impregnation method. A horizontal furnace was used to conduct the fast pyrolysis experiment at 800 °C. The Fourier transform infrared spectroscopy (FTIR) was used to analyse the chemical structural characteristics of corn straw and biochar. The production of pyrolysis gases was online monitored by a synthetic gas analyzer. The main conclusions are as follows: the K/Ca loading promotes the conversion of C–O–C and CO to COO- and C–O in corn straw. K is linked to corn straw mainly through COO- group, and Ca is linked to corn straw mainly through C–O group. Both K/Ca elements are effective in inhibiting the consumption of C–O–C group during corn straw pyrolysis. Besides, K element can catalyze the depletion and decomposition of C–O group during pyrolysis. The K element inhibits the decomposition of the unstable carbon matrix and CO group during pyrolysis, thereby reducing the emission levels of CH4 and CO. K can promote the release of CO2 during pyrolysis, while Ca has no obvious effect. The pyrolysis reactivity of K-loaded corn straw is extremely low, while that of H-form corn straw and Ca-loaded corn straw is at a high level. AAEMs promote the release of H/O elements during corn straw pyrolysis, and the role of K is significantly stronger than that of Ca.