Experimental Investigation on Supercritical Water Gasification of Organic-Rich Shale with Low Maturity for Syngas Production

Shale oil and gas reserves are abundant enough to meet the growing demand for energy, but the exploitation of organic-rich shale with low maturity is still a challenging work due to its high kerogen content. As both a heat carrier and an organic solvent, supercritical water has been found to be an excellent working medium for hydrogen production by biomass or coal gasification. This study is an initial attempt to determine the candidacy of organic-rich shale as a feedstock for hydrogen-rich gas generation by supercritical water gasification. The effects of temperature (500–700 °C), pressure (22–28 MPa), time (0–12 h), water/shale mass ratio (1:1–10:1), and shale particle size (5–150 mesh) were investigated in a batch reactor. The results showed that the gas products were mainly consisted of hydrogen, carbon dioxide, and methane, which were produced by the reactions of steam reforming, water–gas shift, methanation, and carbonate hydrolysis. The abundant inorganic minerals in the shale, especially carbonate, could act as the catalyst for gasification reactions and contribute a lot to carbon dioxide formation. It was found that temperature and time were dominant factors to gas yield and selectivity. Increasing the temperature promoted the endothermic reactions of steam reforming and pyrolysis and accelerated the water–gas shift reaction. Pressure increase has a less negative but negligible effect on gasification. The carbon gasification efficiency and hydrogen selectivity all first increased and then stabilized when the reaction time was prolonged, and the water–shale mass ratio was increased and (or) the shale particle size was decreased. Overall, the suggested conditions were a temperature of 700 °C, a pressure of 22.1 MPa, a water/shale mass ratio of 5:1, a time of 4 h, and the particle size range of 10–20 mesh.