Experimental and modeling study of potassium catalyzed gasification of woody char pellet with CO2

Abstract

Understanding the catalytic effect of potassium on CO2 gasification of biochar can help clarify the complex catalytic conversion mechanism of biochar. In this study, effects of temperature and KOH content on conversion performance and reaction kinetics of gasification of biochar pellet were investigated by using a macro-thermogravimetric analysis (MTGA) unit. Results showed that the increase of gasification temperature and KOH content promoted the conversion of biochar pellet and enhanced the gasification rate (dX/dt). With the reaction proceeded, dX/dt increased initially then decreased, and reached the peak values at X of about 0.15–0.40. A faster expansion of pore structure at both higher temperature and higher KOH content would contribute to the shift of peak values to lower X. Phase boundary-controlled model fitted well to the gasification of biochar pellet with added KOH at 750 and 800 °C, while the possible melting of K species at 850 °C would change the gasification reaction to phase change model. The inferred catalytic role of K in pellet gasification is that it reduced the activation energy and increased the active sites for carbon to react with CO2, and the activation energy was reduced with the increase in K content (0–20 wt. %).