Evolution of gas and shale oil during oil shale kerogen pyrolysis based on structural characteristics

Abstract

Kerogen thermal chemical conversion has a significant role on oil shale utilization and is affected by its chemical structural characteristics. In this work, three oil shale kerogen from Huadian Dachengzi (DCZ), Gonglangtou (GLT) and Gonghe (GH) are studied by TG-FTIR-MS and fixed bed pyrolysis system to analyze evolution characteristics of gas and shale oil. Typical gaseous products, CH4, H2, CO2 and CO, were analyzed by deconvolving their evolution curves. GCMS was employed to analyze the distribution of components in shale oils. Results show that studied four gases are related to several precursor structures and shale oil is mainly obtained from cracking of aliphatic structure in kerogen. Structural characteristics of kerogen affects its product distribution, resulting in higher yields of oil and hydrocarbon gases from kerogen DCZ and GH, while higher yields of char, aromatics and oxygen-containing products from kerogen GLT. Evolution behaviors of oil and gas products at different temperatures are related to cleavage of chemical bonds in kerogen. Labile CalO bonds crack below 350 ℃ causing removal of oxygen-containing functional groups and formation of CO2 and CO. Cleavage of CalCal/H bonds at 400–500 ℃ causes acute decomposition of kerogen and formation of abundant products. Incomplete decomposition of kerogen at low temperature results in low yields of oil and gas. At high temperature above 500 ℃, cleavage of CarCal/O/H bonds occurs and secondary reactions of oil products are intensified, causing reduction of oil yield and increases of gas yield.