Co-pyrolysis of oil sludge with hydrogen-rich plastics in a vertical stirring reactor: Kinetic analysis,emissions, and products

● Collaborative treatment of plastics and OS was established to improve oil quality. ● PE addition successfully improved OS pyrolysis process by deploying H/C_eff ratio. ● Higher H/C_eff ratio promoted cracking to obtain more gas and light oil fractions. ● The degradation of PE and OS was promoted each other under their temperature range. Pyrolysis is an effective method to treat oily sludge (OS) due to its balance between oil recovery and nonhazardous disposal. However, tank bottom OS contains a high content of heavy fractions, which creates obstacles for pyrolysis due to the high activation energy. The incomplete cracking of macromolecules and secondary polymerization decreases the oil quality and causes coking during the operation process. This study introduced polyethylene (PE) into OS to deploy the H/C_eff ratio of feedstocks for pyrolysis. A strong interaction between OS and PE during copyrolysis could be observed from the TG/DTG curves. PE tightly participated in OS degradation, while OS also promoted PE degradation at high temperature. Apparent pits were generated in solid residues from copyrolysis, which was attributed to the uniform and violent gas release. In addition to HCN, other nitrogenous and sulphurous pollutants were inhibited. Accordingly, more gas products were attained after PE addition with more value-added compositions of alkanes and alkenes. Although the oil yield decreased after PE addition, the oil products from copyrolysis possessed higher heating values and higher contents of light fractions with short chains as well as paraffins. Consequently, copyrolysis of OS and PE significantly improved the pyrolysis process and resulted in high oil quality.