Composition and Distribution Characteristics of Volatile Products from the Rapid Pyrolysis of Refinery Water Treatment Sludge

Refinery water treatment sludge (RWTS) is a hazardous organic waste that requires effective treatment prior to disposal, yet its resource potential remains underexplored. In this work, the physicochemical properties and pyrolysis product distribution of RWTS collected from a refinery in Xinjiang, China, were systematically investigated using Fourier transform infrared (FTIR), thermogravimetric and derivative thermogravimetric (TG-DTG) analysis, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Proximate analysis revealed a high volatile matter content (64.69%), while ultimate analysis showed a carbon content of 49.18% and an H/C molar ratio of 1.80, indicating that RWTS is a hydrocarbon-rich feedstock. FTIR analysis demonstrated that aliphatic C-H groups dominate the organic structure, while aromatic C=C and oxygen-containing functional groups are present in minor proportions. TG-DTG profiles revealed three distinct decomposition stages, with maximum weight-loss rates at 305, 445, and 655 °C, corresponding to the staged release of volatile compounds and the progressive cleavage of organic structures. Py-GC/MS analysis further showed a pronounced temperature dependence of the pyrolysis products. At 305 °C and 445 °C, the products were mainly alkanes, with relative contents of 84.9% and 89.1%, respectively, mainly distributed in the C11–C30 carbon-number range. In contrast, at 655 °C, extensive thermal cracking of long-chain aliphatic hydrocarbons generated large amounts of light hydrocarbons (C4–C10, 42.20%) and alkenes (56.0%), accompanied by the formation of monocyclic aromatic hydrocarbons. Results demonstrate that increasing the pyrolysis temperature shifts the dominant conversion pathway from the volatilization of indigenous hydrocarbons to the thermal cracking of long-chain aliphatic structures, providing new insights into the thermal conversion mechanism and resource utilization of RWTS.