Enhancing oil shale pyrolysis through swelling Pretreatment: Mechanisms and product distribution

This study presented a novel investigation into the solvent swelling-pyrolysis mechanisms of high- and low-grade oil shale, with a particular focus on the role of high electron donor numbers (EDN) solvents in enhancing pyrolysis oil quality. By employing N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and tetrahydrofuran (THF) as swelling solvents, the different swelling mechanisms of low-grade Fushun oil shale (FOS) and high-grade Nantun oil shale (NOS) were systematically revealed from the perspective of swelling samples, extracts and pyrolysis products. The functional groups of organic matter were semi-quantitatively characterized by Fourier transform infrared spectroscopy (FTIR) combined with curve fitting analysis. The specific compounds in pyrolytic oil were identified using gas chromatography-mass spectrometry (GC–MS). The results indicate that the solvents effectively disrupt hydroxyl hydrogen bonds. The swelling-pyrolysis mechanism in the pyrolysis of low-grade oil shale is to enhance the self-hydrogen supply capacity of oil shale, thereby increasing the pyrolysis oil saturation. For high-grade oil shale, it promotes bond breaking, thereby increasing the content of light aromatic hydrocarbons in pyrolysis oil. These demonstrate that swelling pretreatment effectively modifies oil shale structure and pyrolysis process, offering references for optimizing solvent selection based on shale grade and desired product distributions.