Search

Through pyrolysis under a supercritical water (SCW) environment, the demetallization of Tsingtao vacuum residuum (VR) and Tahe atmospheric residuum (AR) with a total vanadium and nickel content above 300 ppm was studied. By introducing SCW, pyrolysis of heavy oil can be carried out in an emulsion structure in which heavy fractions rich in metals are concentrated in oil droplets. A metal removal rate higher than 90 % could be obtained in 2 h, which is faster than the pyrolysis under the nitrogen environment. Although two heavy oils have similar apparent properties, Tsingtao VR is characterized by the metal enrichment in the heaviest asphaltenes and the higher condensation activity of asphaltenes. Because of the preferential condensation of heavy fractions rich in metals, the liquid product yield of Tsingtao VR could be 15 wt% higher than that of Tahe AR at the metal removal rate of 70 to 90%.

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.

The visbreaking of heavy oil in supercritical benzene (SCbenzene) was investigated. By introducing SCbenzene, the visbreaking originally occurring in the oil phase is transferred into SCbenzene. The superior diffusivity in SCbenzene improves the efficiencies of the initiation and propagation of visbreaking network, by which the reaction could be run in the desired tandem structure. By mitigating diffusion limitation to reaction kinetics, the cracking of alkyl substitutes of aromatics vital to viscosity reduction is accelerated. Being the secondary reaction of the cracking, condensation could be terminated promptly at the shortened reaction time necessary for visbreaking. A comparison between the visbreaking in SCbenzene and supercritical water (SCH2O) confirms the effectiveness of improving diffusion for the optimization on heavy oil visbreaking. Nevertheless, the optimal operating conditions involved must be determined experimentally because of the complicated interaction between phase structure and reac...

The reduction of pour point of waxy crude oil by pyrolysis under high pressure N2 or supercritical methanol (SCMeOH) environment was experimentally studied at the temperatures ranging from 370 to 400 °C. During the pyrolysis under N2 environment, only a poor pour point reduction less than 5 °C, which is at the cost of the substantial condensation of saturates and aromatics to resins and asphaltenes, could be achieved. When the pyrolysis is transferred into the SCMeOH phase, the reaction consists primarily of the preferential cracking of wax fraction to gas. Benefiting from improved diffusivity, the cracking of wax fraction following the Fabuss-Satterfield-Smith mechanism is remarkably accelerated. Being the secondary reaction of the cracking of oil fractions at the moderate temperatures applied, the condensation of oil fractions is suppressed. Accordingly, an effective pour point reduction up to 22 °C could be obtained in 15 min of pyrolysis without sacrificing the quality of pyrolysis products.

The effect of coating Ru particles with a film of hydrophilic materials on the tetra-phase partial hydrogenation of benzene to cyclohexene was examined. By the sol–gel method, amorphous mesoporous TiO2, ZrO2, and SiO2 were coated on hexagonal Ru particles, by which Ru@XO2 (X = Ti, Zr or Si) catalysts were prepared. During the partial hydrogenation of benzene on Ru@XO2, the diffusion of benzene and cyclohexene dissolved in the water phase onto Ru particles is suppressed by the presence of mesoporous coating film. The diffusion of benzene is retarded further by the hydrogen bonding with the structural OH groups contained in hydrophilic materials. Because of the delicate diffusion behavior of benzene and cyclohexene through coating film, a decreasing rate of benzene conversion but a significantly increasing cyclohexene selectivity was observed in the partial hydrogenation on different Ru@XO2 catalysts. A maximum cyclohexene yield of 52.6 mol % occurs on Ru@TiO2 at the benzene conversion of 85.0%.

The visbreaking of heavy oil under high-pressure N2 or supercritical water (SCW) environment was experimentally investigated. Despite the difference in the reaction media, the visbreaking follows the same mechanism, that is, dealkylation and condensation of aromatics. The presence of SCW makes it possible that the visbreaking of heavy oil is transferred to the SCW phase with superior diffusivity by which the visbreaking tends to be controlled by intrinsic reaction kinetics rather than by diffusion. Accordingly, dealkylation occurring in the SCW phase, which is vital to the viscosity reduction of heavy oil, responds sensitively to the increase in reaction temperature. Being the secondary reaction of dealkylation at moderate temperatures, condensation is effectively suppressed with reduced reaction time required for dealkylation. By the introduction of SCW and the adoption of an appropriate reaction temperature, the visbreaking efficiency could be drastically improved together with guaranteed stability of v...

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.

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 (SCbenzene) 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 SCbenzene 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.

Demetalization of heavy oil through pyrolysis in the presence of subcritical water or supercritical water (SCW) was experimentally investigated. At a high water-to-oil ratio and high water density, the occurrence of pyrolysis can be transferred to the SCW phase. Driven by the π–π attractive interaction between aromatic sheets and the superb diffusivity in SCW, the coke-like self-assembly of metal-containing heavy aromatics occurs spontaneously and rapidly. The self-assembly behavior of aromatics in SCW depends not only on the thermodynamic state of SCW but also on the average scale of aromatics. With the aid of self-assembly in dense SCW, the condensation of metal-containing heavy aromatics, distributed mainly in a vacuum residue, to coke is significantly accelerated, by which the rate of demetalization is improved simultaneously. Owing to the preferential self-assembly of metal-rich heavy aromatics, an increasing yield of liquid products can also be obtained under an optimized SCW environment.

The pyrolysis of asphaltenes under hydrothermal environments covering the subcritical and supercritical regions of water was applied, and the influence of the presence of H-donors was surveyed by a reaction kinetics analysis based on the lumping approach. Under hydrothermal environments, the pyrolysis of asphaltenes consisting mainly of condensation to coke and decomposition to maltenes is significantly faster than that under a N2 environment. The H-donors introduced, decalin or maltenes, may provide nonaromatic H atoms, capping the carbon radicals essential to pyrolysis. Accordingly, the apparent activation energies of the condensation and the decomposition of asphaltenes both increase to varying degrees. The pyrolysis of asphaltenes in the presence of a small quantity of decalin is seriously retarded in subcritical water but recovers rapidly in supercritical water owning to the promoted initiation efficiency at high temperature. Accompanied by a large amount of maltenes, the decomposition to maltenes in...

To understand the condensation during heavy oil thermal processing, the formation of aromatic carbon radicals by H-abstraction of methyl radicals ( CH3) or ethyl radicals ( C2H5) 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. CH3 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 CH3 and C2H5 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.

Under hydrothermal environments covering the subcritical and supercritical regions of water, the involvement of the carbonium mechanism in the dealkylation of aromatics and its resulting influence on the pyrolysis of heavy oil were surveyed. α-Olefin groups, as either a part of straight chain hydrocarbons or the terminal of alkyl substitutes of aromatics, are protonated spontaneously by hydronium ions into carboniums, followed by β-scission with similar reaction kinetic characteristics. The probability of the protonation of α-olefins under hydrothermal environments depends on the ionic product of water, so the occurrence of the β-scission in the carbonium mechanism is related to the thermodynamic state of water. With the aid of the carbonium mechanism at increasing water density, a recovered conversion rate and an increasing ratio of propene to ethylene in the product occur during the pyrolysis of a model α-olefin of dodecene under hydrothermal environments. Also, the dealkylation involved in the pyrolysi...

To improve the understanding of the condensation of asphaltenes in supercritical water (SCW), the solvation of asphaltenes under SCW environments was investigated with molecular dynamics simulation. The simulation results indicate that the repulsive van der Waals interaction has a primary influence on the nature and the magnitude of the interaction between asphaltenes and SCW. A cavity short-range solvent structure surrounding asphaltenes thus is formed, and the solvation free energy (Gsol) of asphaltenes in SCW has a positive sign in most cases. The scale of cavities and the value of Gsol both are determined mainly by the bulk density of water. By the repulsive asphaltenes/SCW interaction and the attractive π–π aromatic interaction, the aggregation of asphaltenes in SCW occurs spontaneously. The asphaltene clusters formed, containing asphaltene monomers and nanoaggregates, present a coke-like supramolecular structure. Benefiting from excellent diffusivity in SCW, the aggregation of asphaltenes in SCW can be accomplished rapidly.

To understand the partial hydrogenation of benzene on Ru particles coated with hydrophilic materials, the diffusion of benzene through the water film confined in silica mesopores was studied by molecular dynamics simulation. There is an unconventional hydrogen bond between benzene and the surface hydroxyl group, which was previously supposed to retard benzene diffusion in hydrophilic mesopores. Driven by stronger hydrogen bonding, solvent water, however, is preferentially adsorbed onto the hydroxylated silica surface. Benzene dissolved in the water film has to diffuse away from the interfacial region, thereby weakening its interaction with the surface. Benzene may diffuse faster in hydroxylated mesopores than in bare mesopores, and the difference depends on the pore diameter. With a pore diameter of 4 to 6 nm, the diffusion coefficient of benzene along the pore axis, varying from 0.04 × 10−8 to 0.12 × 10−8 m2/s, could be adjusted by surface hydroxylation.

Asphaltenes derived from the condensation of maltenes under high-pressure N2 and supercritical water (SCW) environments were characterized with various approaches. The reaction kinetics of the condensation of asphaltenes under hydrothermal environments were also measured. By improving the diffusivity of hydrocarbon species and the isolation of aromatic carbon radicals from hydrogen donors in the SCW phase, the dealkylation of alkyl substitutes and the condensation of aromatic rings involved in the condensation of maltenes are promoted. Consequently, asphaltenes formed in the SCW phase (As-SCW) have a higher aromaticity and lower alkyl and naphthenic fractions than asphaltenes formed in the oil phase (As-oil). Nevertheless, As-SCW and As-oil both present a cokelike supermolecular structure with the stacking of polycyclic aromatic rings. Benefitting from the highly fused aromatic molecular structure and the cokelike supermolecular structure, the condensation of As-SCW to coke occurs readily under hydrotherm...

The reaction kinetics of the pyrolysis of heavy oil in the presence of supercritical water (SCW) and high pressure N2 were measured. At any reaction temperature applied, the pyrolysis under SCW environments is faster than that under N2 environments. Meanwhile, at lower temperatures the pyrolysis under both environments is accelerated by the introduction of coke into the feedstock. On the basis of a first-order four-lump reaction network consisting of the sequential condensation of maltenes and asphaltenes, the pyrolysis in whichever medium can be preferably described either by the lumped reaction kinetic model modified with autocatalysis and pseudoequilibrium or by the model modified solely with pseudoequilibrium. Benefited from the reduced limitation of diffusion to reaction kinetics, the pyrolysis in the SCW phase is more sensitive to the increase in reaction temperature than that in the oil phase, disengaging readily from the dependence on autocatalysis at a lower temperature. © 2015 American Institute of Chemical Engineers AIChE J, 62: 207–216, 2016

Multiscale molecular modeling and dissolution behavior measurement were both used to evaluate the factors conclusive on the CO2-philicity of poly(vinyl acetate) (PVAc) homopolymer and poly(vinyl acetate-alt-maleate) copolymers. The ab initio calculated interaction energies of the candidate CO2-philic molecule models with CO2, including vinyl acetate dimer (VAc), dimethyl maleate (DMM), diethyl maleate (DEM), and dibutyl maleate (DBM), showed that VAc was the most CO2-philc segment. However, the cohesive energy density, solubility parameter, Flory-Huggins parameter, and radial distribution functions calculated by using the molecular dynamics simulations for the four polymer and polymer-CO2 systems indicated that poly(VAc-alt-DBM) had the most CO2-philicity. The corresponding polymers were synthesized by using free radical polymerization. The measurement of cloud point pressures of the four polymers in CO2 also demonstrated that poly(VAc-alt-DBM) had the most CO2-philicity. Although copolymerization of maleate, such as DEM or DBM, with PVAc reduced the polymer-CO2 interactions, the weakened polymer-polymer interaction increased the CO2-philicity of the copolymers. The polymer-polymer interaction had a significant influence on the CO2-philicity of the polymer. Reduction of the polymer-polymer interaction might be a promising strategy to prepare the high CO2-philic polymers on the premise that the strong polymer-CO2 interaction could be maintained.

In the presence of supercritical water (SCW) and N2, the pyrolysis of heavy oil was investigated to distinguish the difference in the reaction kinetics between the upgrading in the SCW and oil phases. The pyrolysis in the SCW phase is faster than that in the oil phase, but the reaction in whichever phase is retarded by vigorous stirring. The pyrolysis can be preferably described by a four-lump kinetic model consisting of the condensation of maltenes and asphaltenes in series. In the SCW phase, highly dispersed asphaltenes are isolated by water clusters from maltenes dissolved in SCW surroundings, by which the condensation of asphaltenes is drastically accelerated. Benefited from excellent mass transfer environments in SCW, the condensation of maltenes is promoted simultaneously. The introduction of SCW into the pyrolysis of heavy oil results in an effectively increased upgrading efficiency, but its influence on the properties of equilibrium liquid products is minor. © 2014 American Institute of Chemical Engineers AIChE J, 61: 857–866, 2015

At 693 K and water density of 0.30 g/cm 3 , 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.

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 H β 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 653 K and water density of 0.30 g/cm 3 , it was experimentally confirmed that the introduced DTBP was capable of initiating the pyrolysis of heavy oil. After 15 min's reaction, the pyrolysis products centered toward the fraction of aromatics whose weight proportion in the liquid product increased drastically by ca . 25.0 wt.%. Meanwhile, only a negligible coke yield of 0.5 wt.% was collected.

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.

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 713 K and water densities of 0.05 to 0.20 g/cm 3 . 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.

The acid properties of WOx/t-ZrO2 under hydrothermal environments were theoretically investigated with density functional theory calculations. The calculations indicate that water molecules can be readily chemisorbed on t-Zr (1 1 0), followed by spontaneous dissociation to form a fully hydrated surface. The structural parameters of the WOx species anchored on t-Zr (1 1 0) are determined mainly by the coordination of central W atoms, and surface hydration has no essential effect on the configuration of WOx species. The thermodynamic equilibrium among WOx species is found to be closely relevant to the applied hydrothermal environments. The transformation of WOx species to the condensated configurations with higher Lewis acidity tends to occur at high temperature and low partial pressure of water, while the configurations with multiple Bronsted sites are preferentially formed at moderate temperature and high partial pressure of water.

Solvation of methyl radicals in subcritical and supercritical water was investigated with the ab initio MD simulation to increase the understanding of the thermal cracking of hydrocarbons under the severe hydrothermal environments. The calculation results show that water clusters around the radical could be formed with the following prerequisites: the bulk density of water is close to liquid phase, and the state point of water on its phase diagram is far away from the critical point and from the vapor–liquid equilibrium boundary. The occurrence of water clusters superimposes a negative influence on the originally depressed diffusivity of the radical under the dense hydrothermal environments, and the interference from the immediately adjacent water molecules with the frontier orbitals of the radical results in randomly reduced activity of the radical. Regardless of whether there are water clusters around the radical or not, in subcritical and supercritical water the bimolecular reactions participating via hydrocarbon radicals should be partially suppressed by the reduced diffusivity and lower activity of the radical.

WO x /ZrO 2 catalyzed hydration of cyclohexene in sub-critical water was experimentally investigated. The migration of reaction zone into sub-critical water makes it possible to run the hydration in a single liquid phase, and the reaction is free from the limitation of liquid–liquid phase mass transfer to hydration kinetics. The severe hydrothermal environments favor the transformation of surface active sites on WO x –ZrO 2 catalysts to Bronsted acid centers of stronger acidity, which are highly effective for the hydration of cyclohexene to the desired product cyclohexanol.

In this work, hydrophilic property of Ru (0 0 0 1) with and without H adatoms was theoretically studied to increase the understanding of the partial hydrogenation of benzene to cyclohexene over ruthenium catalysts. Density functional theory based calculations suggest that formation of hydrogen bonding among the adsorbed H 2 O molecules results in a weakened interaction between the water adlayer and Ru (0 0 0 1), while the calculated heat of adsorption containing the contribution of hydrogen bonding is no longer suitable for evaluating the hydrophilic property of the metal surface. The presence of H adatoms exerts an electrostatic repulsion on the adsorbed H 2 O molecules; thereby the latter can be in the state of chemisorption or physisorption on the Ru metal depending on the number of immediately adjacent H adatoms and on the relative distance to the H adatoms. By tuning the coverage of H adatoms, the surface hydrophilic/hydrophobic balance of the Ru metal can be effectively adjusted, which provides an approach to improve the selectivity to cyclohexene in the partial hydrogenation of benzene.

Hierarchically macro–mesoporous titania was synthesized by the simple dropwise addition of tetrabutyl titanate to an ammonia solution in the absence of surfactant molecules, and then calcined at different temperatures. The as-prepared titania was characterized by X-ray diffraction, N2 adsorption–desorption analysis and scanning electron microscopy. The results showed that the hierarchically marcro–mesoporous structure of the titania was well preserved after calcination at 650 °C, indicating high thermal stability. The 500 °C calcined titania with the hierarchically bimodal pore network was impregnated with 0.5 wt.% of palladium and compared with 0.5 wt.% Pd/TiO2 catalyst without such macrochannels. The novel macro–mesostructured Pd/TiO2 catalyst exhibited higher catalytic activity for styrene hydrogenation due to the lower diffusion resistance of species inside the catalyst caused by the hierarchically macro–mesoporous bimodal structure.

From the adsorption point of view, partial hydrogenation of benzene to cyclohexene over the metallic Zn modified Ru-based catalyst was experimentally and theoretically investigated. A decreased hydrogenation activity but increased selectivity to cyclohexene over the prepared Ru-Zn/ZrO 2 catalyst was observed in the partial hydrogenation of benzene. Theoretical calculations suggest that the above phenomena are mainly resulted from the depression of the chemisorption of benzene and cyclohexene on the modified catalyst, especially for the latter. Undesired deep hydrogenation from cyclohexene to cyclohexane in the middle and late reaction stage therefore is effectively retarded, by which an improved cyclohexene yield is guaranteed. An optimal Zn content of 2.72 wt.% in the Ru-based catalyst was proposed by both the experiment and calculation for the partial hydrogenation of benzene, and a cyclohexene yield up to 44% was obtained over Ru-Zn/ZrO 2 catalyst.

To disperse the unreacted overhead gas phase into the liquid in an agitated reactor without gas outlet, a gas-inducing impeller is usually employed. To determine the lowest critical rotating speed, the gas-induction mechanism was reconsidered by constituting a mechanical energy conservation equation between the gas inlet orifice in the gas phase and the gas outlet orifice in the liquid phase under a certain rotational speed. According to this model, the critical speed of the gas-inducing impeller could be basically determined by the submersion depth and the radial position of the gas outlet, and a novel design was proposed by introduction of six short pipes stretched radially from the axis of the impeller. The final design of the gas-inducing impeller was obtained by an optimal combination of the gas-inducing pipes, the blades of the impeller and the baffle dimension.

Vacuum residue (VR) upgrading was conducted in the environment of supercritical water (SCW) without oxygen addition in an attempt to yield a maximum of light oil. Simulated distillation of the liquid products from a set of orthogonal experiments shows that temperature should not be too high to restrict coke formation, and the most beneficial condition is found at (1) 420 °C for the temperature, (2) 0.15 g/cm3 for the water density, (3) 2 g/g for the H2O/oil ratio, and (4) 1 h for the reaction time. A simultaneous increase of the water density and H2O/oil would significantly improve the cracking behavior and the yield in light oil. Scattered coke particles between 10 and 100 μm were generated from VR cracking, which suggests the dispersion effect of SCW. The infrared spectrum analysis has indicated an increase in the H/C atomic ratio in the liquid product, which implies that hydrogen is generated from the condensation reactions rather than from water because no oxygen-containing group was detected.

In this work, the hydrogenation of cyclohexene over Ru–Zn/Ru(0 0 0 1) surface alloy was investigated by a DFT study so as to improve the understanding of the catalytic mechanism of the partial hydrogenation of benzene to cyclohexene over Ru–Zn alloy catalyst. Calculation results show that the presence of Zn atoms on the surface alloy results in not only a direct decrease in sites for the chemisorption of cyclohexene but also a depressed adsorption capability of the neighboring surface Ru sites. For an adsorbed cyclohexene molecule, whether the subsequent hydrogenation can be readily performed actually is determined by the relative position among the Zn atom, the H atom, and the adsorbed cyclohexene molecule. In most cases, the hydrogenation is forbidden because of the repulsion from Zn atoms to the nearby H atoms. Only in the specific situations in which the H atom participating in the reaction is not immediately close to the Zn atom, can the hydrogenation be accomplished with a relatively lower activation energy compared with the reactions on the Ru(0 0 0 1) surface. From the perspectives of adsorption and reaction kinetics, Ru-based catalyst modified by metallic Zn is no longer suitable for the hydrogenation of cyclohexene, which is supposed to be crucial to the improvement of cyclohexene yield in the partial hydrogenation of benzene over Ru–Zn alloy catalyst.

Molecular dynamics simulation and Density Functional Theory were used to investigate the adsorption of two kinds of anti-scalant, ethane diphosphonic acid (EDPA) and polyether polyamino methylene phosphonate (PAPEMP), on the calcite (104) surface in order to increase the level of understanding of the anti-scaling mechanism in membrane processes for water desalination. Calculation results show that the performance of an anti-scalant is mainly determined by the negative electrostatic potential presented on the anti-scalant modified scale surface. A negative electrostatic potential on the scale surface can prevent not only the agglomeration of scale nuclei in the concentrate but also the precipitation of scale nuclei on the membrane surface. Phosphonate groups in 1,1-EDPA are bifunctional since they simultaneously satisfy the requirements for the electrostatic potential distribution and for the adsorption stability on the scale surface. As concerns PAPEMP, the above requirements are fulfilled respectively by different functional groups, i.e. ether groups and phosphonate groups. To simplify the role of functional groups in the anti-scaling mechanism means that the performance of an anti-scalant can be optimized by the combination of specific functional groups; furthermore, these functional groups can also be adjusted with respect to different scale surfaces.

With the view of increasing the understanding to the anti-scaling mechanism in the membrane process, zeta potential on the anti-scalant (Calgon and PAA) modified sub-micro calcite surface was measured and was further characterized with a molecular simulation. Experimental results show that the original positively charged calcite in an aqueous solution is reversed to be negatively charged by introducing anti-scalants at a dosage of ppm level. On the basis of theoretical calculation, the observed reversal is resulted from the statistically predominant orientation of negative potential-determining groups in the adsorbed anti-scalant molecules, i.e. P O and C O, stretching against the calcite surface. A negative zeta potential prevailing on the calcite surface can effectively prevent the calcite from precipitating on the membrane surface. In the presence of anti-scalants, zeta potential on the sub-micro calcite surface is a sensitive function of calcite content, anti-scalant concentration, salt concentration, and pH of the suspension.

For the sake of improving the performance of Ru-based catalyst used in partial hydrogenation of benzene to cyclohexene, the effect of Zn2+/Zn layer on the adsorption and dissociation of H2 on Ru (0001) surface was investigated by applying density function theory (DFT) calculations. Calculation results show that the dissociation of H2 occurs only after its being chemisorbed horizontally at atop site. Because of the influence of Zn2+ on the electron delocalization between molecular orbit of H2 and valence orbits of atop Ru atom, a remarkable increase in the H2 dissociation barrier is noticed, which results in zones of sparse chemisorbed H around Zn2+. Adsorbed Zn2+ can be reduced by chemisorbed H, and the H2 dissociation kinetics varies little in the presence of Zn atoms at adjacent sites. Split zones of chemisorbed H are formed at a high coverage of Zn layer. The consecutive or synchronous hydrogenation of benzene is disturbed when benzene is adsorbed in zones of sparse chemisorbed H or split zones of chemisorbed H. It is therefore deducted that a high coverage layer of some transition metal atoms on catalyst surface should be helpful for maintaining the hydrogenation activity of the catalyst and improving the cyclohexene yield.

Hydrocarbon CO2-philes are of great interest for use in expanding CO2 applications as a green solvent. In this work, multiscale molecular modeling and dissolution behavior measurement were both applied to explore CO2-philicity of the poly(vinyl acetate) (PVAc)-based copolymer. Introduction of a favorable comonomer, i.e., vinyl ethyl ether (VEE), could significantly reduce the polymer-polymer interaction on the premise that the polymer-CO2 interaction was not weakened but enhanced. The ab initio calculated interaction of the model molecules with CO2 demonstrated that the ether group in VEE or VBE was the suitable CO2-philic segment. From the molecular dynamics (MD) simulations of polymer/CO2 systems, the interaction energy and Flory-Huggins parameter (χ12) of poly(VAc-alt-VEE)/CO2 supported that poly(VAc-alt-VEE) possessed better CO2-philicity than PVAc. The dissolution behaviors of the synthesized poly(VAc-co-alkyl vinyl ether) copolymers in CO2 showed the best CO2-phile had the VEE content of about 34 mol %. The MD simulations also indicated that the interaction of random poly(VAc-co-VEE) containing about 30 mol % VEE with CO2 was the strongest and the χ12 was the smallest in these polymer/CO2 systems. Not only could the VEE monomer reduce the polymer-polymer interaction, but it could also enhance the polymer-CO2 interaction with an optimized composition. Introducing a suitable comonomer with a certain composition might be a promising strategy to form the synergistic effect of polymer-polymer interaction and polymer-CO2 interaction for screening the hydrocarbon CO2-philes.

Vacuum residuum (VR) upgrading through pyrolysis in supercritical water was investigated in a bomb reactor and a batch autoclave. The experiments were carried out in the temperature range of 380−460 °C at 25.0 MPa for 5−120 min with a water/VR ratio of 0.78:1−4:1 by weight. The upgrading leads to a reduction of 30.9% in resins and asphaltenes, a reduction of 22.8% in aromatics, and an increase of 98.6% in saturates. The viscosity of the product was reduced from 116 mPa s of the feedback to 6.2 mPa s, which is approximately 179 times. Besides, the average molecular weight was reduced from 1860 to 646 g mol-1, and S, N, Ni, and V contents were reduced by 32, 15, 83, and 85%, respectively. The upgrading mechanism was proposed as ionic and radical reactions in parallel.

In this work, the denitrogenation of hydrocarbons under supercritical water oxidation environment was investigated in a rotated bomb reactor at 623–723 K and 25–35 MPa over sulfided NiMo catalyst. Quinoline was used as a model nitrogen-containing compound. A high reduction of total nitrogen up to about 85% was obtained. The denitrogenation pathway is composed of two consecutive steps: in situ H 2 generation and the hydrogenation of quinoline. The hydrogenation mechanism of quinoline varies with reaction temperature because of the participation of supercritical water in HDN step. The strong adsorption of quinoline and its hydrogenation intermediates on catalyst surface has an adverse influence on total nitrogen reduction rate.

Catalytic desulfurization of a model sulfur-containing compound benzothiophene (BT) through partial oxidation in supercritical water (SCW) was investigated in a bomb reactor at 623–723 K and 30–40 MPa over sulfided CoMo/γ-Al 2 O 3 . Vacuum residuum was used to confirm the desulfurization rate and efficiency, and the desulfurization mechanism of vacuum residuum was determined by the pyrolysis temperature ( T R ) of the vacuum residuum (VR). For T > T R , obvious reduction of sulfides up to 67% was obtained. The thermodynamic equilibrium of in situ H 2 generation was a controlling factor of the desulfurization pathway.

An industrial trickle bed reactor was simulated for pyrolysis gasoline selective hydrogenation. The operation was recognised in the upper limit of pulsing flow regime by the Charpentier-Tosun flow pattern diagram at a very low hydrogen to oil volumetric ratio. Hydrodynamic parameters in the pulsing flow regime were calculated from the literature correlations which apply to the hydrogen-paraffin system. The external wetting efficiency which should be no higher than 100% was found to be 147% according to the correlation of Al-Dahhan and Dudukovic (1995), due to the undefined upper limit of their equation. The reactor simulation shows the gas-liquid and liquid-solid mass transfer rates were large enough for the active Pd hydrogenation catalyst. By comparing with the mass transfer rate in the Taylor flow regime in a monolithic structure, it shows the hydrogen concentration in the liquid phase in an industrial trickle reactor is more than two times of that in the monolith, which implies the substitution of the conventional catalyst pellet by the monolith is not required.