Insight into the relationship between CO2 gasification characteristics and char structure of biomass

Abstract

Biomass gasification consists of three thermochemical stages: drying, pyrolysis, and char gasification, of which char gasification is the rate-limiting step. This study compared the char structure of biomass components (cellulose, hemicellulose, lignin, starch, and pectin) and revealed its quantitative relationship with the CO2 gasification reaction rate. Gasification experiments were performed in a self-built macro-thermogravimetric analyzer (Macro-TGA), and the char was characterized by proximate analysis, ultimate analysis, Fourier transform infrared (FTIR) spectroscopy, N2 adsorption/desorption isotherm, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The char gasification starting temperature from low to high was pectin ≈ starch < lignin < xylan. SEM revealed that the cellulose and starch chars had larger block structures. According to the FTIR results, the hydroxyl groups in the char enhanced the reactivity of char gasification. C–C/C=C was the dominant functional group in char, and O-containing groups, especially C–O, positively affected char gasification reactivity. It was found that the relationship between the gasification mass loss rate r and the char structure was r = 0.384 × surface area0.12 × ash content0.24. This study helps understand the relationship between biomass char gasification and its structure.