Co-pyrolysis of residual oil and polyethylene in sub- and supercritical water

At the temperature of 693 K and water densities from 0.10 to 0.30 g/cm3, co-pyrolysis of residual oil and polyethylene in sub- and supercritical water (sub-CW and SCW) was experimentally investigated. With the increase in water density, the phase structure of the co-pyrolysis system may evolve from a liquid/liquid/solid three-phase structure to a liquid/solid two-phase one. By co-pyrolysis of polyethylene with residual oil, H-rich paraffins, the main pyrolysis product of polyethylene, are released continuously into the reaction system. At higher water densities with the favorable liquid/solid two-phase structure, the contact of aromatic radicals from the pyrolysis of residual oil and paraffins from that of polyethylene is promoted, ensuring the coupling between pyrolysis networks of residual oil and polyethylene. Consequently, dealkylation of aromatic radicals may follow the desired mechanism by which the production of coke-inducing components is effectively depressed. A significantly reduced coke yield is observed in the co-pyrolysis of residual oil and polyethylene in sub-CW and SCW.

Graphical abstractCo-pyrolysis of residual oil and polyethylene in sub- and supercritical water was investigated. The H-source is transferred from the pyrolysis network of polyethylene to that of residual oil, resulting in significantly depressed coke formation. The presence of sub-CW and SCW guarantees the coupling between pyrolysis networks.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Co-pyrolysis of residual oil and LDPE in sub-CW and SCW was experimentally investigated. ► The presence of LDPE establishes a sustaining H-source for the pyrolysis of residual oil. ► Phase structure of co-pyrolysis system can be tuned by adjusting water density. ► Co-pyrolysis applied in favorable phase structure may drastically depress the coke formation.