Kinetics comparison and insight into structure-performance correlation for leached biochar gasification

Abstract

• Isothermal prediction based on model-free method was established. • Kinetic parameters form model-free and model-fitting method were compared. • Gasification mechanism was revealed from carbon and pore structure evolution. • The fractal dimension D 1 was related with amorphous structure. • Mesopore SSA increased by hundred times whereas active sites changed insignificantly. Biomass gasification integrated with leaching pretreatment can be conducive to the sustainable energy system. In this work, the biochar gasification was studied from structure to reactivity with the consideration of leaching pretreatment. The biochar was prepared from raw and leached corn straw (CS) and corncob (CC) in a fixed bed reactor. The gasification was performed in thermogravimetric analyzer with the emphasis on kinetic parameters comparison and reactivity prediction. The carbon and pore structure were investigated to reveal gasification mechanism. The prediction procedure based on model-free method was proposed. From the results, compared with CS, leaching pretreatment reduced gasification reactivity of CC considerably according to reactivity index and reactivity prediction. The random pore model showed the best fitting performance. Furthermore, the leaching pretreatment reduced inorganics (mainly K) in CS and CC, and removed water-soluble organics (pectin) in CC. The active sites and surface roughness in leached biochar decreased accordingly. The CO 2 gasification can activate initial biochar after pyrolysis. Specifically, the specific surface area of mesopore increased by hundred times and more active sites were also generated. However, as the gasification proceeding, the active sites and the fractional dimensions changed insignificantly for both raw and leached biochar. The leaching pretreatment mainly promoted the micropore development during gasification. The pore structure evolution was consistent with the carbon structure, which appeared to be correlated with the kinetic analysis. The research gives new insight into structure-performance correlation of biomass gasification and provides the implication for sustainable energy system based on gasification technology.