Thermal decomposition mechanism of Chang 7 sulfur-rich lacustrine kerogen: insights from combined thermogravimetric and pyrolysis mass spectrometric analysis

Studying the pyrolysis behavior of oil shale provides important guidance for its in-situ or external conversion. The pyrolysis characteristics of Chang 7 sulfur-rich lacustrine shale kerogen were investigated using coupled thermogravimetric analysis, Fourier-transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses. The TG results revealed four distinct stages: desorption, kerogen conversion, bitumen cracking, and aromatization, with major weight loss occurring between 400 and 600 °C. FTIR and MS analyses indicated that SO2 is generated within 200–700 °C, primarily originating from the decomposition of organic sulfur, while the formation of H2S dominates above 500 °C under a hydrogen radical environment accompanied by substantial hydrocarbon production. Py-GC/MS results showed a temperature-dependent evolution of products from long-chain alkanes to olefins and aromatics, with fatty acids indicating algal-derived kerogen. By integrating real-time gas evolution with temperature-resolved product composition, a multistage pyrolysis mechanism was proposed, demonstrating the coupled evolution of organic matter and sulfur species. This study provides mechanistic insight into the thermal decomposition pathways and differentiated sulfur gas release behavior of sulfur-rich kerogen, which is relevant for understanding sulfur behavior during oil shale thermal conversion. Pyrolysis of sulfur-rich lacustrine kerogen by TG-IR-MS and Py-GC/MS was studied.SO2 and H2S from organic sulfur and pyrite were identified at different temperatures.Product shift from alkanes to olefins and aromatics with heating was observed.Pyrolysis mechanism in distinct stages was summarized. Pyrolysis of sulfur-rich lacustrine kerogen by TG-IR-MS and Py-GC/MS was studied. SO2 and H2S from organic sulfur and pyrite were identified at different temperatures. Product shift from alkanes to olefins and aromatics with heating was observed. Pyrolysis mechanism in distinct stages was summarized.