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Based on theoretical calculations and experimental characterizations, the extraction of heavy oil components using subcritical water (Sub-CW) as an extraction solvent was studied in the temperature range of 250–325 °C. According to theoretical calculations, small-scale polycyclic aromatic hydrocarbons (PAHs) are preferentially dissolved in Sub-CW. Meanwhile, the dissolution of heavy oil molecules with large-scale aromatic structures and heterocyclic rings in Sub-CW is hindered. The increase in temperature reduces the hydrogen bonding force between water molecules and the van der Waals repulsion between Sub-CW and PAHs, promoting the dissolution of PAHs in Sub-CW. Extraction experiments applied in a semi-continuous device confirm that Sub-CW selectively extracts aromatic hydrocarbons from heavy oil. Increasing extraction temperature increases the yield of the extract. The aromatic hydrocarbon content in the extract at 325 °C reaches 80 wt%, which is 27 wt% higher than feedstock value. In addition, the asphaltene content in the extract is reduced from the feedstock value of 14 wt% to 2 wt%. • Sub-CW was used as a property-tunable solvent for extracting heavy oil components. • Sub-CW selectively extracts aromatic hydrocarbons from heavy oil. • The yield and composition of the extract are sensitive to extraction temperature. • Opposite distribution of HSP hinders dissolution of PAHs/hetero-PAHs in Sub-CW. • Destruction of hydrogen bonds promotes dissolution of PAHs/hetero-PAHs in Sub-CW. [ABSTRACT FROM AUTHOR]

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 strategy of adding tetralin as a H-donor in the thermal processing of heavy oil was investigated by experimental characterization and theoretical calculations. According to the experiments, the timing of adding 1 wt% of tetralin has a great influence on the visbreaking performance of heavy oil. Calculations based on density functional theory showed that benzyl radicals released from the thermal cracking of tetralin accelerate the dealkylation that determines the heavy oil upgrading. Meanwhile, H α provided by tetralin is able to selectively saturate aromatic C radicals which are essential for condensation. Compared with the conventional H-donor addition, i.e., pre-mixing of tetralin with heavy oil, a similar viscosity reduction rate of about 98% can be obtained during the visbreaking with delayed tetralin addition. Furthermore, the addition of tetralin before the significant occurrence of condensation further increases the conversion of vacuum residue fraction by 3.4% and reduces the asphaltene content of the product by 2.6 wt%. [Display omitted] • Tetralin cracking releases benzyl radicals which accelerate heavy oil upgrading. • H α provided by tetralin selectively saturates aromatic C radicals. • Pre-mixing of tetralin with heavy oil affects sufficient condensation inhibition. • In visbreaking tetralin should be added before apparent occurrence of condensation. • In delayed coking the addition of tetralin is not recommended. [ABSTRACT FROM AUTHOR]

• The mesoporous iron oxide was successfully synthesized by using the waste wood powder as a template. • The alkali concentration had an effect on the physicochemical properties and performance of the synthesized iron oxides. • The iron oxide catalyst with larger surface area and pore volume exhibited higher yield of gasoline and diesel distillates. • The perfect performance of mesoporous iron oxide catalyst is ascribed to the presence of more exposure Fe active sites. In order to develop a high-efficiency iron oxide catalyst for the slurry-phase hydrocracking of poor heavy oil, the mesoporous iron oxide was successfully synthesized by using the waste wood powder as a template, and the influence of alkali concentration in the resulting solution on crystal phase, morphology and pore structure of the synthesized samples was investigated. The crystal phase of the synthesized iron oxide transfers from α-Fe 2 O 3 to γ-Fe 2 O 3 , and their crystal sizes gradually decrease with an increase of alkali concentration based on the XRD and HRTEM results. Additionally, the iron oxide with mesoporous structure, larger surface area and pore volume is obtained at the higher concentration of alkali in solution confirmed by N 2 adsorption-desorption analysis. The assessment result of the iron oxide catalyst employed in the slurry-phase hydrocracking of vacuum residue (VR) illustrates that the yields of gasoline and diesel distillates obtained over Fe-O-B 20 , Fe-O-B 24 and Fe-O-B 30 catalysts are higher compared with those over Fe-O-B 2 and Fe-O-B 14 catalysts, it can be attributed that more exposure Fe active sites derived from their larger surface area and pore volume availably improve the catalyst hydrogenation activity, which can inhibit the over-cracking reaction of intermediate products and the condensation of polycyclic aromatic hydrocarbon in VR to enhance the yields of gasoline and diesel distillates. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were applied to characterize the dissolution of subcritical water (Sub-CW) in polycyclic aromatic hydrocarbons (PAHs). The phase equilibria of Sub-CW/PAHs are characterized by the dissolution of Sub-CW in PAHs. The solubility of Sub-CW increases with temperature but is relatively insensitive to pressure changes. Furthermore, an increase in PAH scale leads to a decrease in Sub-CW solubility. The PAH-rich phase can be divided into an interface region and a bulk region, and the water concentrations in the two regions differ greatly. The Hansen solubility parameters of PAHs and Sub-CW exhibit opposite distributions, hindering the mutual solubility between the two. The dissolution of Sub-CW is promoted by the destruction of intermolecular hydrogen bonds of water at increasing temperature, but is ultimately inhibited by the difference in dispersion properties between PAHs and Sub-CW. According to the Gibbs solvation free energy, the electrostatic interaction between PAHs and Sub-CW favors the dissolution of Sub-CW. Meanwhile, the van der Waals interaction shows different effects. • Phase equilibria of PAHs and Sub-CW were studied by MD simulation. • Phase equilibria of PAHs and Sub-CW feature dissolution of Sub-CW in PAHs. • Solubility of Sub-CW in PAHs is sensitive to temperature change. • Opposite distributions of Hansen HSP hinder dissolution of Sub-CW in PAHs. • Electrostatic interaction promotes dissolution of Sub-CW in PAHs. [ABSTRACT FROM AUTHOR]

The phase equilibria of subcritical water (Sub-CW) and four-ring N-, S-containing heterocyclic aromatic hydrocarbons (hetero-PAHs) were investigated by molecular dynamics simulation. In a temperature range of 250–350 °C and a pressure range of 4.2–21 MPa, the mixture of hetero-PAHs and Sub-CW shows an equilibrium between water-rich and oil-rich liquid phases, characterized by a significant dissolution of water in the oil phase. The solubility of Sub-CW is 1.9–3.8 wt% in N-containing hetero-PAHs and 1.0 to 2.7 wt% in S-containing hetero-PAHs. Compared with polycyclic aromatic hydrocarbons (PAHs) with the same ring number, the presence of the thiophenic ring in hetero-PAHs leads to a decrease in the solubility of Sub-CW. The particularity of N-containing hetero-PAHs lies in the hydrogen bond between the pyridinic ring and water molecules, which increases the solubility of Sub-CW at temperatures below 300 °C. The solubility of Sub-CW in hetero-PAHs/PAHs can be correlated with the Gibbs solvation free energy of water dissolved in the oil phase and the cohesive energy density of the oil phase as parameters. • Phase equilibria of hetero-PAHs and Sub-CW were studied by MD simulation. • Phase equilibria feature dissolution of Sub-CW in hetero-PAHs rich phase. • The presence of thiophenic rings in hetero-PAHs decreases Sub-CW solubility. • The presence of pyridinic rings in hetero-PAHs increases Sub-CW solubility. • Hydrogen bonds play vital roles in Sub-CW solubility in N-containing hetero-PAHs. [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]

The difficulty of the H-abstraction of alkyl radicals from PAHs or hetero-PAHs follows the order: S-containing heterocycles > PAHs > N-containing heterocycles. • H-abstraction of CH 3 or C 2 H 5 from PAHs or hetero-PAHs was investigated. • CH 3 instead of C 2 H 5 is responsible for aromatic C radical formation on PAHs. • Activation entropy determines the difference in k T S T of H-abstraction on PAHs. • H-abstraction difficulty: S-containing heterocycles > PAHs > N-containing heterocycles. To understand the condensation during heavy oil thermal processing, the formation of aromatic carbon radicals by H-abstraction of methyl radicals (CH 3) or ethyl radicals (C 2 H 5) from polycyclic aromatic hydrocarbons (PAHs) or heterocyclic aromatic hydrocarbons (hetero-PAHs) was studied by density functional calculation. The H-abstraction from different PAHs all has a positive standard state Gibbs free energy change, while increasing reaction temperature or radical concentration promotes the reaction to proceed spontaneously. CH 3 mainly contributes to the formation of aromatic carbon radicals on PAHs, and the activation entropy of H-abstraction determines the difference in reaction rate constants. The particularity of H-abstraction from hetero-PAHs is reflected at the α-site of heterocycles. The H-abstraction from N-containing hetero-PAHs occurs preferentially at the α-site of heterocycles, and both CH 3 and C 2 H 5 could participate in abstracting the α-H. The H-abstraction from S-containing hetero-PAHs occurs preferentially on coupled aromatic rings, showing reaction behavior similar to the H-abstraction on PAHs. [ABSTRACT FROM AUTHOR]