Catalytic effects of inherent AAEM on char gasification: A mechanism study using in-situ Raman

Despite a small proportion of mineral in coal, inherent alkali and alkaline earth metals (AAEM) catalytically affected thermal conversion of coal. The gasification of raw and leached coal char was investigated by using an operando microscopic Raman spectroscopy to explore the effect of content and chemical form of the inherent AAEM on morphology and carbon structure evolution of a single particle during in-situ char gasification. The removal of water-soluble and ion-exchangeable AAEM reduced the R-0.5 of SF, NM and YN char by 53.31%, 49.09% and 35.02%, respectively. As a result, the shrinkage of leached coal char progressed slower than that of the raw coal char. Besides, both water-soluble and ion-exchangeable AAEM accelerated char gasification because of an inhibition of the orderly evolution of carbon structure. Higher gasification temperature weakened the catalytic performance of ion-exchangeable AAEM. With the consumption of carbon, carbon microcrystalline structure of the residual char tended to be ordered, which led to a decrease in active free carbon sites for gasification reaction. Kinetic analysis indicated both water-soluble and ion-exchangeable AAEM reduced the activation energy of SF, NM and YN char by 20.97, 20.82 and 9.38 kJ.mol(-1), respectively, and the effect of ion-exchangeable AAEM was more significant. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the catalytic effects of inherent alkali and alkaline earth metals (AAEM) on the thermal conversion of coal. The presence of water-soluble and ion-exchangeable AAEM was found to significantly affect char gasification, slowing down carbon structure evolution and decreasing active free carbon sites. Kinetic analysis demonstrated that both types of AAEM reduced the activation energy of char gasification, with ion-exchangeable AAEM having a more significant impact.