The Competitive Evolution of Oxygen-Containing Functional Groups during Pressure-Controlled Pyrolysis of Oil Shale

Oil shale serves as a vital strategic alternative fossil energy resource for China. Uncovering how graded pressures govern the cleavage and conversion of diverse oxygen-bearing structures helps to understand pressure-modulated kerogen transformation at the chemical-bond level and enriches the microscopic theoretical framework of pressure-regulated oil-generation processes. This work focuses on competitive evolution of oxygen-containing functional groups in solid-phase pyrolysis residues. In this work, continental Type II1–I oil shale sampled from Huadian, Jilin Province was subjected to pressure-controlled pyrolysis at 400 °C for 240 min under pressures ranging from atmospheric pressure to 8.0 MPa. A combined characterization platform integrating Gaussian peak-fitting Fourier Transform Infrared Spectroscopy(FTIR), Thermogravimetry (TG) and Gas Chromatography–Mass Spectrometry (GC-MS) was adopted to characterize evolutionary behaviors of three typical oxygen-containing functional group bands. Combined with TG-DTG and GC-MS auxiliary evidence, carbonyl-related structures show a tendency of enhanced retention near 2 MPa. High-pressure treatment preserves aliphatic oil-generating precursors and elevates thermal stability of pyrolysis residues, accompanied by an increasing relative abundance of medium-long-chain alkanes within collected liquid shale-oil fractions. This study establishes correlations among solid-phase microstructures, macroscopic thermal weight-loss behaviors and relative compositional features of liquid pyrolytic products, providing fundamental microscale experimental observations and mechanistic references for laboratory-scale pressurized oil-shale pyrolysis research.