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Continuous visbreaking of heavy oil in a tubular reactor was studied under pressurized steam environments at 10 MPa (MPS) and 18 MPa (HPS). Within the operating range considered, heavy oil and pressurized steam exhibit a liquid-vapor two-phase structure. During the transition from the MPS environment to the HPS environment, the dissolution of water into the oil phase is promoted, thereby reducing the viscosity of the oil phase. According to the lumped reaction kinetics analysis, the reaction behavior of the lumped component VR2 with a boiling point higher than 700 °C determines the visbreaking efficiency in the early visbreaking stage to a large extent. Dealkylation of VR2 and condensation of the lightest lumped component show sensitive responses to improved diffusion in the oil phase. At 400 °C and a space time of 37 min, visbreaking in HPS environment can achieve a viscosity reduction rate of 90%. Meanwhile, the asphaltene content of the product is lower than the feedstock value. • Continuous heavy oil visbreaking was investigated in pressurized steam environments. • Visbreaking products with reduced viscosity and asphaltene content can be obtained. • Dissolution of water in heavy oil reduces the viscosity of the oil phase. • Reaction kinetics of visbreaking respond sensitively to diffusion improvement. • Dealkylation of heaviest components determines initial visbreaking efficiency. [ABSTRACT FROM AUTHOR]

The effect of the timing of adding 1 wt% decalin as a hydrogen donor on heavy oil visbreaking was studied. Experiments show that either premixing decalin with heavy oil or adding decalin during the reaction accelerates the formation of light distillates and improves the efficiency of viscosity reduction. Premixing with heavy oil is an appropriate way to add decalin. After 10 min of reaction at 400 ℃, the viscosity reduction rate of the product reaches 90% and the asphaltene content of the product is 1.8 wt% lower than that of the raw heavy oil. According to theoretical calculations, the active hydrogens of decalin preferentially saturate the aromatic C radicals that are critical for condensation. The equilibrium constant of the H-donation reaches the order of 105, while the activation energy of the reaction is only about 26 kJ/mol. The thermal cracking of decalin itself releases active and small-sized radicals, which accelerate visbreaking by participating in the dealkylation network of heavy oil molecules. • Decalin cracking releases radicals with high activity and diffusivity. • Addition of decalin in visbreaking greatly accelerates viscosity reduction. • Decalin selectively saturates aromatic C radicals vital for condensation. • Premixing decalin with heavy oil inhibits condensation in early reaction stage. • Premixing decalin as a hydrogen donor with heavy oil in visbreaking is recommended. [ABSTRACT FROM AUTHOR]

The performance of introducing a free radical initiator into dealkylation-based visbreaking of heavy oil in the N 2 or supercritical benzene (SC benzene) medium was investigated. Calculations based on density functional theory show that the introduction of di-tert-butyl peroxide (DTBP) into heavy oil visbreaking results in the formation of alkyl C radicals similar to those naturally formed in high temperature initiation. The visbreaking in SC benzene environment is sensitive to the introduction of DTBP, which is different from the visbreaking in N 2 environment. According to reaction kinetics analysis, the presence of SC benzene solvent and the introduction of DTBP greatly accelerate the dealkylation related lumped reactions. Benefiting from improved diffusion environment, the superimposed radicals resulting from DTBP introduction effectively participate in visbreaking and selectively accelerate dealkylation. After only 10–20 min of reaction at 380 °C, visbreaking products with satisfactory viscosity reduction, reduced asphaltene content and improved light component yield can be obtained. • Initiator-introduced heavy oil visbreaking in supercritical benzene was examined. • DTBP introduction results in rapid superposition of alkyl C radicals. • The presence of supercritical benzene accelerates visbreaking. • Superimposed radicals effectively participate in visbreaking in SC benzene. • Best upgrading is obtained in DTBP-introduced visbreaking in SC benzene. [ABSTRACT FROM AUTHOR]

• Visbreaking of heavy oil with high metal and asphaltene content was investigated. • Coupling of porphyrin metals with asphaltenes promotes asphaltene aggregation. • Asphaltene condensation is accelerated by high content and aggregation. • Asphaltenes with highest metal content participate in condensation to coke first. The visbreaking of Canadian oil sands bitumen (OSB) and Tahe atmospheric residue (AR) with high metal and asphaltene content was studied to deepen the understanding of the utilization of ultra-inferior heavy oil. The total content of nickel and vanadium in the asphaltenes contained in Canadian OSB reaches 1300 ppm, promoting large-scale aggregation of asphaltenes. Driven by high asphaltene content of 19.3 wt% and large-scale aggregation of asphaltenes, Canadian OSB with an initial boiling point (IBP) of 500 °C exhibits rapid condensation during visbreaking. Furthermore, those asphaltenes with the highest metal content participate in condensation first, producing metallic nickel in the formed coke. By changing cutting strategy, the group composition and metal distribution of Canadian OSB can be adjusted. A viscosity reduction rate above 99 % is obtained during the visbreaking of Canadian OSB with an IBP of 350 °C, similar to the visbreaking of Tahe AR with an asphaltene content of 15.4 wt% and a total metal content of 300 ppm. [ABSTRACT FROM AUTHOR]

• Reaction kinetics analysis of heavy oil visbreaking in SC benzene was applied. • SCF visbreaking features low reaction temperature and shortened reaction time. • Competition between dealkylation and condensation exists throughout visbreaking. • Dealkylation-based visbreaking is accelerated by reducing diffusion limitation. • Condensation-based lumped reactions respond sensitively to temperature variation. To understand the reaction behavior of heavy oil visbreaking with reduced diffusion limitation, the visbreaking of an atmospheric residual oil in the solvent of supercritical benzene (SC benzene) was applied, followed by a reaction kinetics analysis based on a hybrid lumping with combination of boiling point distribution and group composition of oil components. The visbreaking under SC benzene environment was found to be much faster than that under nitrogen environment, proceeding effectively even at a temperature lower to 350 °C. Although the dealkylation-based lumped reactions responsible for light component production and viscosity reduction are supposed to dominate the visbreaking, a competition between dealkylation and condensation exists throughout the visbreaking. Because of the reduced diffusion limitation to reaction kinetics, the condensation-based lumped reactions with a higher activation energy up to 306 kJ.mol−1 respond more sensitively to the variation of reaction temperature, greatly shortening the reaction time window for the visbreaking at high temperatures. [ABSTRACT FROM AUTHOR]