Evolution of S/N containing compounds in pyrolysis of highly oily petroleum sludge

[Display omitted] •The thermal transformation behavior of oily sludge was investigated.•The oil composition was investigated in detail.•Distribution of S/N compounds in oily sludge were studied.•The existing forms of S/N compounds in char was discussed. Pyrolysis of oily sludge in inert environment has a strong potential for energy recovery, in which the transformation of S/N containing compounds is a key to influence the quality of various products. This work addresses the evolution of S/N containing compounds in pyrolysis process of two oily sludge samples with high oil content by comparing the species and distribution of S/N containing compounds in origin samples and char. The results demonstrate that aromatic and saturated completed volatilize or react completely at 500 °C while the resin completed the reaction at 750 °C–800 °C. The S-containing compounds are mainly Sulfate-S. At 500 °C, most sulfate remained unchanged, and continued heating led to a large-scale decomposition. After condensation and cyclization, the S/N compounds were transformed into components with high thermal stability. Sulfoxide-S, Thiophenic-S and Aromatic-S with more stable thermal stability held the main position at higher temperature. The transformation of N-containing compounds was almost based on Proteins-N. As the temperature rising from 500 °C to 700 °C and 900 °C, the content of protein-N decreased continuously and transformed into high thermal stability Pyridine-N, Pyrrole-N and Quaternary graphic-N, which could account for more than 90%. This work provides a theoretical basis for the distribution and transformation of S/N in char, the deep application of char and the pollution prevention in subsequent treatment.