Effect of hydrothermal process on the pyrolysis of oily sludge: Characterization and analysis of pyrolysis products

In this paper, the effect of the pretreatment method combined with hydrothermal treatment and in situ mechanical compression (HT-MC) on the pyrolysis characteristics of oily sludge (OS) was investigated. The results of the thermal analysis showed that the temperature range in different pyrolysis stage intervals shifted to a lower level and the weight loss rate decreased significantly after HT-MC. Isoconversional methods were employed with an estimated apparent activation energy of 92.66 –198.21 kJ·mol⁻¹ for the pyrolysis of OS after HT-MC. As the hydrothermal temperature increased to 240 °C, the yield of char increased from 80.44 to 86.08 wt%, and the yield of oil decreased from 16.03 to 11.23 wt%. Compared to the raw material, the gas products from the pyrolysis of OS after HT-MC had a higher H₂ concentration and yield. The analysis results of GC-MC showed that, compared with the pyrolysis oil obtained by direct pyrolysis, the content of olefins in pyrolysis oil obtained in pyrolysis of OS after hydrothermal treatment increased from 0.86 % to 5.73 %. Furthermore, the relative content of alkanes in pyrolysis oil increased from 76.12 % to 87.40 % with the rise of hydrothermal temperature from 160 to 240 °C.