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Graphical abstract By the differences in heavy oil composition and thermodynamic state of water applied, the oil-in-water emulsion structure of heavy oil/SCW systems may transit to the condensed emulsion or pseudo single-phase structure, determining their feasible application in upgrading of heavy oil. Highlights • MD simulation on dissolution of PAHs or PAH mixtures in sub-CW/SCW was applied. • Dissolution of heavy PAHs in sub-CW/SCW is sensitive to thermodynamic state of water. • Preferential dissolution of light PAHs occurs during dissolution of PAH mixtures. • Electrostatic interaction promotes the dissolution of PAHs in sub-CW/SCW. • Heavy oil/SCW could exist in condensed emulsion or pseudo single-phase structure. Abstract To get a better understanding of the upgrading of heavy oil under severe hydrothermal environment, a molecular dynamics simulation on the dissolution of oil droplets containing polycyclic aromatic hydrocarbons (PAHs) or PAH mixtures in subcritical or supercritical water (sub-CW/SCW) was applied. Being the representative of light PAHs, naphthalene dissolves readily into sub-CW/SCW. The dissolution of heavy PAHs, like benzo[α]pyrene and benzo[ghi]perylene however is sensitive to the thermodynamic state of water. During the dissolution of PAH mixtures, a preferential dissolution of light PAHs into the water phase occurs, leaving heavy PAHs concentrated in the oil droplets. With the simultaneous increase in water density and temperature, the miscibility of PAHs with sub-CW/SCW is improved by the enhanced attractive electrostatic interaction between PAHs and hydrothermal environment and the weakened interaction between PAHs. By the differences in heavy oil composition and the thermodynamic state of water, the upgrading of heavy oil in sub-CW/SCW could be run in the condensed emulsion or pseudo single-phase structure. [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]

• ASA with the different Al/Si ratio were synthesized by a simple co-precipitation method. • The Al/Si ratio affects the Al coordination state, pore structure, acidity and surface properties of ASA. • Mo/ASA-4 with the largest amount of Mo atoms located at edge sites can provide the most amount of exposure Mo active sites. • Mo/ASA-4 catalyst achieves the highest yield of value light oil and the lowest yield of gas and coke due to its excellent hydrogenation activity. To deeply illuminate the effect of ASA composition on its corresponding Mo catalyst properties and performance for the slurry-phase hydrocracking of vacuum residue, the amorphous silica-alumina (ASA) samples with the various ratios of Al to Si were successfully synthesized by a simple co-precipitation method, which have the different acid properties and pore structure, especially ASA-1 with lowest ratio of Al to Si owning the largest number of B acid sites and the highest volume of mesoporous. Additionally, the Mo catalyst supported on ASA-4 possesses the highest dispersion of MoS 2 slabs and largest amount of Mo atoms located at the edge sites among all the catalyst, possibly due to the appropriate surface properties of ASA-4 derived from the ratio of Al to Si, it demonstrates that the most exposure Mo active sites are present on Mo/ASA-4 catalyst. The hydrocracking evaluation results show that the VR conversion over the different catalysts are similar, it may be ascribed to the variation of acid properties and pore structure insufficient to change VR cracking pathway because of the low catalyst dosage. Furthermore, the Mo/ASA-4 catalyst exhibits the higher yield of naphtha and middle distillate and inversely the lower yield of gas and coke in comparison with other catalysts, it should be attributed that the higher hydrogenation activity derived from the more exposure Mo active sites can efficiently restrain the over-cracking of the intermediate product and aggregation of the polycyclic aromatic hydrocarbon in the hydrocracking process. [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]