Thermolysis of crude oil sludge using CO2 as reactive gas medium

•Simultaneous crude oil sludge disposal and energy recovery via the pyrolysis process.•CO2 was used as reactive gas medium to modify the pyrogenic products.•CO2 significantly expedited thermal cracking and dehydrogenation of crude oil sludge.•CO2 served a role to provide the O source, which resulted in the formation of CO. Up to date, despite the massive generation of crude oil sludge (COS), the technical completeness for disposing COS has not been fully achieved. Considering its harmfulness and the high content of hydrocarbon species, establishing an environmentally benign platform for the simultaneous waste disposal and energy recovery will be greatly important. To this end, this study mainly focuses on pyrolysis of COS. To develop the more sustainable pyrolytic platform for COS, this study particularly employed carbon dioxide (CO2) as reactive gas medium. To chase the thermolytic behaviors of COS in the presence of CO2, a series of the TGA tests of COS was conducted, and the TGA tests confirmed that CO2 did not change the thermolytic behaviors, such as onset and end temperature for the thermolysis of COS. Nevertheless, CO2 greatly influenced the pyrogenic products via the heterogeneous reactions (i.e., volatilized hydrocarbons and CO2). In detail, CO2 expedited the thermal cracking and dehydrogenation of volatilized hydrocarbons evolved from COS, thereby resulting in the enhanced generation of H2, CH4, C2H6, C2H4, and C2H2. Despite the fact that the enhanced thermal cracking and dehydrogenation generally enhances the aromaticity in pyrolytic oil, the enhanced generation of CO was observed only from pyrolysis of COS in CO2, of which enhanced generation of CO effectively decreased the aromaticity by restricting the formation of benzene derivatives.