In-situ pyrolysis of oil shale in pressured semi-closed system: Insights into products characteristics and pyrolysis mechanism

In-situ conversion of oil shale involving kerogen cracking and hydrocarbon migration occurred in a semi-closed system under high pressure. Due to the insufficient understanding of the pyrolysis characteristics and mechanism of oil shale under these conditions, this study presented a systematic investigation of the coupling effects of temperature and pressure on oil shale pyrolysis within a semi-closed system. At 500 °C, the shale oil yield of 8 MPa declined by 65.7 %, while the gas yield increased by 93.7 % when compared to atmospheric pressure. The trend of shale oil yield exhibited variations with increasing temperature, depending on the pressure, and a demarcation point was observed at 2 MPa. The GC-MS and simulated distillation results of shale oil revealed that pressure promoted the generation of light components and accelerated the conversion of alkenes to alkanes and aromatics. The release temperature of gases increased under pressure, encouraging the production of alkane gas while reducing the hydrogen yield. Additionally, the pressure enhanced the combustion performance of semi-coke. As the pyrolysis temperature increased, the combustion performance of semi-coke deteriorated under low pressure, whereas the trend was reversed under high pressure. Finally, the pyrolysis mechanism for oil shale coupling of temperature and pressure was proposed.