Experimental investigation on organic functional groups evolution in hydrogen production process by coal gasification in supercritical water

Supercritical water gasification (SCWG) of coal has great application prospect for converting coal into hydrogen-rich gas efficiently and cleanly. However, the previous study on the reaction mechanism for SCWG of coal is relatively macroscopic rather than reflects the reaction essence deeply. The evolution of organic functional groups in Zhundong lignite (ZD), Hongliulin bitumite (HLL) and Ningxia anthracite (NX) during SCWG, as well as the correlation with gaseous products were analyzed quantitatively in this paper. It was found that the lower rank coal contained more free radicals and produced more H₂ with SCW. H₂ yield of the three types of coal exceeded 2 times the hydrogen content in coal at 800 °C. The organic functional groups evolve in 2–4 stages during SCWG process. The decomposition and gasification of organic functional groups mainly took place in low or medium temperature range. About 95% of C=O groups and 90% of aromatic C=C groups cracked and were gasified. Aromatic ether (C_ar-O) groups were formed in high temperature range. The reasonable functional relationship between the parameters of gaseous products and organic functional groups was established, providing a new approach to predict organic functional groups through gaseous products. This research may lay the foundation for further optimization design of reactor.