Hydrogen production from low-rank coal by a two-step method combined subcritical depolymerization with supercritical gasification

Abstract

High efficiency gasification of inferior brown coal to produce hydrogen is a research focus and difficulty for clean utilization of coal resources. Abundant intermolecular hydrogen bonds in brown coal induce cross-linking side reactions of coal molecules in the pyrolysis process, which inhibits the efficient gasification of lignite. Based on the high temperature and pressure visualization reactor, it was found that alkaline subcritical liquid water would destroy the hydrogen bond structure in lignite, thus leading to the depolymerization of lignite particles. Based on this phenomenon, the crosslinking side reaction in the pyrolysis process can be suppressed at the molecular level. Therefore, a two-step method combined subcritical depolymerization with supercritical gasification was proposed to achieve high-efficiency gasification of brown coal for hydrogen production (the carbon gasification efficiency reached 98 % at 650 ∼ 700 °C). This provides a theoretical basis for the scheme design of clean and efficient gasification hydrogen production from inferior brown coal in supercritical water.