Experimental study on optimizing reaction path for promoting the gasification of coal in supercritical water

Coal gasification in supercritical water (SCW) has great potential in industrial application for converting coal into hydrogen-rich gas in a clean and efficient manner. However, when the reaction conditions are improperly coupled with reaction path, undesirable side reactions would take place, which is prone to reduce the efficiency of converting coal into hydrogen-rich gas. It is revealed that the condensation of aromatic structures and the formation of aromatic ether (C_ar-O) groups are the restrained reactions according to the reaction path obtained by studying the variation of gas–liquid-solid products during supercritical water gasification (SCWG) of coal. Methanol, Fe₂O₃ and Ni(CH₃COO)₂·4H₂O are added to inhibit the restrained reactions. It is found that these all facilitate the cracking and gasification of aromatic structures. Fe₂O₃ and Ni(CH₃COO)₂·4H₂O except methanol, reduce the formation of C_ar-O groups effectively. The optimal concentration of these corresponding to the greatest promotion is 7.5 wt% (methanol), 2.5 wt% (Fe₂O₃) and 2.5 wt% (Ni(CH₃COO)₂·4H₂O), respectively. Ni(CH₃COO)₂·4H₂O (2.5 wt%) has the highest promotion on the production of H₂ and CO, as well as the cracking and gasification of aromatic structures. The corresponding maximum yields of H₂ and CO increase by 0.29 and 1.85 times, respectively. Fe₂O₃ (2.5 wt%) has the greatest promotion on the decomposition of C_ar-O groups, and the relative content of C_ar-O groups decreases by 80.86%. This research provides the theoretical basis for regulating the ordered conversion of coal into hydrogen-rich gas during SCWG of coal.