Thermal degradation of type I sulfur-rich kerogen: pyrolyzate evolution and kinetic parameters

• First integrated CP-Py-GC-MS and TG-FTIR-GC-MS study on lacustrine Type I sulfur-rich (I-S) kerogen. • Pyrolyzate composition shifts from aliphatic and organosulfur compounds to aromatic compounds with increasing temperature. • Heating rate exerts a non-monotonic control on yields of aliphatics, alkenes, aromatics, and heteroatomic compounds. • Left-skewed activation energy distribution (∼53 kcal/mol peak) reveals kinetic complexity related to sulfur bonds. The thermal degradation of type I sulfur-rich (I-S) kerogen, a lacustrine type of hydrogen-rich organic matter with significant petroleum potential, remains poorly constrained. This study employs integrated analytical techniques, Curie-Point Pyrolysis-Gas Chromatography-Mass Spectrometry (CP-Py-GC–MS) at multiple temperatures and Thermogravimetry-Fourier Transform Infrared Spectroscopy-Gas Chromatography-Mass Spectrometry (TG-FTIR-GC–MS) at varying heating rates to systematically investigate the pyrolyzate composition and kinetic characteristics of an immature type I-S kerogen from the Miocene Nördlinger Ries Basin, Germany. Curie-Point Pyrolysis reveals that pyrolyzates are dominated by aliphatic compounds (51–87%), followed by sulfur-containing compounds (7–35%), aromatics (3–16%), and minor oxygen-containing species. With increasing pyrolysis temperature, the relative abundance of aliphatics decreases while aromatics and organosulfur compounds (OSCs) increase. Short-chain n -alkanes rise at the expense of longer chain n -alkanes and acyclic isoprenoids, indicating enhanced cracking and cyclization at higher thermal stress. Sulfur and oxygen groups exhibit correlated release patterns, suggesting inherent S–O bonded structures in the kerogen matrix. Heating rates significantly influence product distribution: faster rates (up to 50 °C/min) promote higher yields of aliphatics and aromatics at elevated temperatures, while slower rates favor heteroatom release at lower temperatures. Hydrocarbon generation occurs mainly between 200 and 600 °C, with CH 4 and aliphatics showing unimodal yield profiles. The activation energy distribution, derived from non-isothermal kinetics, is left-skewed with a dominant peak at ∼ 53 kcal/mol, reflecting chemical complexity induced by sulfur incorporation. These findings provide new insights into the pyrolysis pathways and kinetic parameters of type I-S kerogen, supporting the optimization of in-situ conversion processes for sulfur-rich oil shales and refining petroleum generation models in analogous lacustrine settings.