Study on the hydrothermal pyrolysis of oil shale catalyzed by La/HZSM-5

Aiming at the problems of long pyrolysis time and poor shale oil quality in in-situ mining of oil shale, La-loaded HZSM-5 molecular sieve was used to catalyze the hydrothermal pyrolysis of oil shale. The experimental results showed that La could be uniformly dispersed on the surface of the HZSM-5 molecular sieve synthesized by the incipient wetness impregnation method. When the La loading was 4 wt%, it had the highest population of strong acid sites. The pyrolysis experiment of oil shale was carried out in a subcritical water environment at 350 °C. The experimental results showed that the oxygen-containing structure and the hydrogen-rich structure in the kerogen would be preferentially cracked, while the hydrogen-poor structure was difficult to cleave and continuously condensed. Compared with the non-catalytic experiment, after adding 4 wt% La/HZSM-5, the yield of discharged bitumen increased from 9.05 wt% to 12.39 wt% at 20 h, and the time to obtain the highest discharged bitumen yield was shortened from 120 h to 60 h. On the one hand, the 4 wt% La/HZSM-5 effectively facilitated the participation of hydrogen in water in the pyrolysis of kerogen, promoted the destruction of aromatic structure, maintained a high H/C atomic ratio of kerogen, inhibited the growth of aromaticity and aromatic bridge carbon ratio, and slowed down the attenuation of oil generation potential of kerogen. On the other hand, it significantly aggravated the decomposition of bitumen products to produce more small molecule compounds, and thus elevated the content of hydrocarbon gases in pyrolysis gas.