Oil shale in-situ upgrading with natural clay-based catalysts: Enhancement of oil yield and quality

Abstract

Abundant oil shale reserves in China provide great potential for solving the energy crisis and increasing the energy supply. Natural clay-based catalysts were prepared for oil shale in-situ upgrading, and the catalytic behavior was thoroughly investigated. Through the exploration of the hydrocarbon yield in the oil shale catalytic conversion products, the best catalyst was selected as SO3H-APG that was prepared by facile ball-milling of a natural clay, attapulgite, and 3-mercaptopropyltrimethoxysilane (MPTMS) and followed H2O2 oxidation. The highest oil generation ability of SO3H-APG was obtained when the –SO3H dosage was 4 mmol/g and the acid amount was 1.52 mmol/g. The oil yield reached 54.93%. The apparent activation energy Ea of oil shale pyrolysis on SO3H-APG catalyst was 61.43 kJ⋅mol−1, which was roughly 44 kJ⋅mol−1 lower than thermal cracking. In the catalytic conversion reaction of oil shale, this type of clay-based catalyst also showed good hydrocarbon generation ability and stability due to its abundant acid sites. The complexity of the catalytic conversion products was reduced, and the carbon number distribution was mainly concentrated between C6-C14. There was no compound of the boiling point above 300 °C detected in liquid products, mainly concentrated between 140 and 280 °C, and moved toward a lower boiling point. Compared with noncatalytic shale oil, the SO3H-APG catalyst enhanced the hydrocarbon yield in the product from 57.01% to 70.30%, reduced oxygen-containing compounds and nitrogen-containing substances to 22.16% and 5.54%, respectively. Meanwhile, under the action of SO3H-APG catalytic decarboxylation, the H/C ratio of shale oil inclined to 1.78, the O/C ratio dropped to about 0.03, and the HHV value of shale oil generated by the catalytic conversion reached 45.24 MJ/kg. The development of SO3H-APG catalysts provided a promising approach to enhance the oil recovery and process feasibility for oil shale in-situ catalytic upgrading.