Study on the effect of inherent AAEM on char structure evolution during coal pyrolysis by in-situ Raman and TG

Inherent minerals, especially alkali and alkaline earth metals (AAEM), are reactive constituents that interact with organic matter during pyrolysis and have significant effects on thermal characteristics and carbon structure evolution of char. The pyrolysis of raw and leached coal samples was conducted by using thermogravimetric analyzer and in-situ Raman system to explore the effects of content and chemical form of AAEM on pyrolysis characteristics and carbon structure evolution of single char particle. The water-soluble and ion-exchangeable AAEM promoted continuous breaking/reforming of bonds between alkyl substitutional groups and aromatic ring systems, resulting in the delay of volatiles release and orderly evolution of carbon structure during pyrolysis. The effects of water-soluble AAEM was more severe, because the divalent alkaline earth metal bonds to carbon was much more stable than the monovalent alkali metal for the inherent AAEM participated in the polycondensation reaction. Besides, the ion-exchangeable AAEM inhibited the generation of cross-linked structures more effectively than water-soluble AAEM, because ion-exchangeable AAEM existed in the form of AAEMcarboxylates and delayed the thermal decomposition. Moreover, the inherent AAEM promoted the miniaturization of carbon crystal structure in the carbon matrix, forming char with disordered carbon structure.

Automated summary

This study investigates the effects of inherent minerals, especially alkali and alkaline earth metals (AAEM), on the thermal characteristics and carbon structure evolution of char during pyrolysis. Water-soluble and ion-exchangeable AAEM promote the breaking/reforming of bonds between alkyl substitutional groups and aromatic ring systems, delaying volatiles release and orderly evolution of carbon structure. Water-soluble AAEM have more severe effects due to stable bonds between divalent alkaline earth metal and carbon, while ion-exchangeable AAEM inhibit cross-linked structures generation effectively.