Effect of Ca–Fe composite catalysts on pyrolysis performance of demineralised anthracite and its char structure transformation

While catalytic pyrolysis with catalyst addition has been widely studied with a primary focus on optimising gas, tar and char yields, studies exploring the evolution of char structure during coal pyrolysis remain scarce. This knowledge gap potentially affects subsequent char gasification processes during coal conversion within gasifiers. This study presents demineralised anthracite (TM) prepared by HCl–HF acid washing. The pyrolysis performance of TM while adding Ca, Fe and Ca–Fe composite catalysts was investigated through thermogravimetric analysis. The char structure, morphology and functional groups in the obtained char samples were clarified through X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The results indicated that de-ashing by acid washing promoted the formation of C–O functional groups in coal due to the decomposition of C=O or a combination of oxygen with unsaturated carbon, or both. The TM sample exhibited improved thermal decomposition upon adding either Ca or Fe catalysts, which became more pronounced after adding the Ca–Fe composite catalyst under the same conditions. While the addition of Ca–Fe composite catalysts inhibited the crystalline carbon formation and char graphitisation degree compared to their individual additions, it led to enhanced decomposition of phenol C–O, thereby facilitating the thermal decomposition of TM.