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Abstract: At 693K and water density of 0.30g/cm3, the co-pyrolysis of heavy oil and low density polyethylene (LDPE) in the presence of supercritical water (SCW) was investigated with the emphasis on the coking mechanism involved. The co-pyrolysis in SCW was found to have the significant advantages of the decreasing yield of coke and the increasing yield of aromatics over the pyrolysis of heavy oil alone in SCW. With the increase in the loading of LDPE, the suppression of condensation in co-pyrolysis is gradually intensified, suggesting the essential role of LDPE as an external H-source in co-pyrolysis. Only in the continuous SCW phase can the H-donation between the pyrolysis networks of heavy oil and LDPE be effectively accomplished, by which the condensation of light oil fractions to heavy oil fractions and the deep condensation of asphaltenes to coke are partly suppressed. [Copyright &y& Elsevier]

Abstract: The initiated pyrolysis of heavy oil in the presence of near-critical water (near-CW) was investigated with density functional theory (DFT) calculation and experimental characterization. Theoretical calculation indicated the thermodynamic feasibility of forming hydrocarbon radicals in heavy oil with the aid of appropriate radical initiators. By introducing ditertbutyl peroxide (DTBP) into heavy oil, the H-abstraction of Hβ atoms distributed mainly in the fractions of saturates, resins, and asphaltenes occurs, forming hydrocarbon radicals located on aliphatic chains with priority. At the temperature of 653K and water density of 0.30g/cm3, it was experimentally confirmed that the introduced DTBP was capable of initiating the pyrolysis of heavy oil. After 15min''s reaction, the pyrolysis products centered toward the fraction of aromatics whose weight proportion in the liquid product increased drastically by ca. 25.0wt.%. Meanwhile, only a negligible coke yield of 0.5wt.% was collected. [Copyright &y& Elsevier]

Abstract: At the temperature of 693K and water densities from 0.10 to 0.30g/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. [Copyright &y& Elsevier]

Abstract: To increase the understanding of the reaction behavior of heavy hydrocarbons in the presence of sub- and supercritical water, upgrading of residual oil was applied in a batch reactor at temperatures of 653 to 713K and water densities of 0.05 to 0.20g/cm3. It is confirmed that upgrading of residual oil in sub- and supercritical water is still dominated by the free radical mechanism based thermal cracking. The ion mechanism based hydrolysis only has an extremely limited influence on the upgrading performance. With the increase in water density, the upgrading system may evolve from a partially miscible two-phase structure to a pseudo single-phase structure in which asphaltenes are highly dispersed in the continuous water phase. Prompt diffusion of aromatic radicals from asphaltenes into the water phase both depresses the coke formation and improves the liquid product distribution. [Copyright &y& Elsevier]