Product distribution and coke formation during catalytic pyrolysis of oil shale with zeolites

Catalytic pyrolysis is useful for product regulation of fuel. In this work, we studied oil shale catalytic pyrolysis with HZSM-5 and HUSY by experiments and DFT calculation. We discussed the catalytic pyrolysis in detail by analyzing product distribution, coke characteristics and adsorption of hydrocarbons in zeolites. Catalytic cracking of long-chain aliphatics and formation of light aromatics increase light fraction in shale oil. Coke comes from growth of coke precursors and deposition of long-chain compounds. In comparison, catalytic pyrolysis with HZSM-5 has higher yield of hydrocarbon gases, less content of alkenes in shale oil and low coke yield, while catalytic pyrolysis with HUSY has high content of aromatics in shale oil and high coke yield. Product distribution is affected by zeolite characteristics and pyrolysis conditions. Pore size of zeolites affects the diffusion and conversion of compounds and formation of coke, which makes two zeolites show different shape-selective effects. Competition between alkanes, alkenes and aromatics for Brønsted acid and coke species deposited in zeolites was analyzed by DFT calculation. Increasing temperature from 490 to 520 ℃ significantly promotes cracking in catalytic pyrolysis with HZSM-5 and aromatization in catalytic pyrolysis with HUSY. This study indicates optimizing zeolite characteristics and catalytic pyrolysis condition could realize directional regulation of volatile products and improvement of quality of shale oil.