Three-stage behaviors of K2CO3 catalyst during CO2 catalytic gasification of coal

Abstract

Interactions between minerals in coal and alkali metals heavily influence the deactivation of alkali metal catalyst and induce several ash-related problems, seriously hindering the industrialization of catalytic gasification. Therefore, it’s essential to figure out the behaviors of catalyst throughout the catalytical gasification process. In this study, the diffusion, deactivation and catalytic behaviors of the catalyst, as well as the intricate interaction patterns between these sections were comprehensively investigated. The results reveal a three-stage behavior for K catalyst during the gasification process, a diffusion process, a rapid deactivation process, and then followed by a catalytic gasification process. In the initial diffusion stage, K2CO3 evenly disperses onto coal particles due to recrystallization effects. Subsequently, K2CO3 undergoes rapid deactivation by Si/Al minerals, forming KAlSi3O8. Owing to the rapid nature of this deactivation process, K2CO3 exhibits minimal catalytic activity during the second stage. In the catalytic gasification stage, the deactivation of the catalyst doesn’t cease, K2CO3 will continues to react with Si/Al minerals, leading to the formation of KAlSiO4 and subsequently deactivation. However, the deactivation speed is slower than that of the second stage, allowing for the generation of active intermediate Kn-O-C for catalytic gasification. The boundary between fast and slow deactivation establishes a threshold value for the catalyst loading amount, which was determined to 5 wt% in this study. Furthermore, a model for predicting the threshold value of K2CO3 loading amount for different coals was proposed. The boundary is crucial in understanding the balance between catalytic activity and deactivation, providing valuable insights for optimizing the gasification process.