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To overcome the heat removal problem encountered in methanol synthesis at high syngas concentrations in the gas phase, a three-phase nonwetted catalytic system was established by introducing an inert liquid medium into a fixed-bed reactor. To form a repellent interface between the liquid and the catalyst, the catalyst was modified into hydrophobic, while the liquid medium was chosen as a room temperature ionic liquid with hydroxyl groups. The liquid-solid contact angle was measured to be 115°, and only 20% of the catalyst external surface was wetted by the liquid. Under three-phase condition, the reaction rate was measured to be 60%-70% of gas-phase reaction, while it was merely 10%-20% for the fully wetted catalyst. From the resistance analysis on the mass transfer and reaction steps, the overall reaction rate is expected to increase further if the surface could be more wet proofed. © 2016 American Institute of Chemical Engineers AIChE J, 63: 226-237, 2017 [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

A stochastic model was developed to describe the liquid radial dispersion in a trickle-bed reactor, which has conventionally been modeled by the effective diffusion model. To establish the stochastic model, the column was divided into some layers of particles in the axial direction and several annulus rings in each layer in the radial direction. The liquid spreading was regarded as a fluid transport process and the matrix of transfer probability was derived based on the coordinates of the particle network in the cross-section of the column. With this transfer probability matrix and the initial liquid distribution, the liquid distribution in the downstream was predicted. In order to evaluate the model parameters, experimental data of the liquid dispersion were obtained from electrical capacitance tomography images and tracer injection. Good agreement was obtained between the stochastic model and the experimental liquid distribution data. [ABSTRACT FROM AUTHOR]

The radial profiles of axial liquid velocity and gas hold-ups are investigated in the riser of a pilot plant scale external loop airlift reactor (ELAR) using a modified Pavlov tube and differential pressure technique. The experimental investigation reveals that there exist two different kinds of liquid circulation structures in an ELAR, which has rarely been reported in the literature, namely internal liquid circulation, which exists only in the riser and external liquid circulation, which circulates through the downcomer. A power-law relationship is used to correlate the gas hold-up and superficial gas velocity, which gives good agreement with experimental data. Experiments for axial liquid velocity profiles are analysed in analogy to a model described for a conventional bubble column. The results predicted by the model are in excellent agreement with the experimental data obtained under various operating conditions. © 2011 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]

A three-region model was proposed, which considers the bed cross section being composed of a stagnant liquid region, a liquid film region, and a rivulet flow region. To estimate the fractions of the three regions, the fraction of film flow was evaluated first, by transforming the complex trickling flow texture into pure liquid film flow. Through the measurements of liquid holdup and pressure drop for the film flow, a relationship between relative permeability and gas saturation was established, and from which the fraction of film flow region was obtained. It shows packing size is most important to the faction of rivulet flow. The external wetting efficiency of the packing was correlated as the sum of two-third power of the liquid film fraction and the rivulet flow fraction, besides, a correlation based on Reynolds and Galileo numbers of the two phases in the form of [ABSTRACT FROM AUTHOR]

In reduction of liquid backmixing in bubble columns,Wu et al.[Wu, Y; Cheng, Z. M.; Huang, Z. B. Backmixing reduction of a bubblecolumn by interruption of the global liquid circulation. Ind.Eng. Chem. Res.2009, 48, 6558–6563]have shown that the backmixing could be substantially reduced by interruptingthe global liquid circulation using four identical short Venturi throats(SVTs). Considering the advantages of such structures, it is necessaryto further investigate the backmixing characteristics of a bubblecolumn with SVTs. In the present work, a multipoint tracer injectionand detection device was employed to enhance the insight into whereand how the liquid tracer was backmixed in different stages of a 50-cmdiameter column. Tracer response profiles were measured to track theliquid backmixing trajectory in different stages at various operatingconditions. The results showed that the backmixing of the column wassensitive to the throat diameter of SVTs. Based on the observed physicalphenomena, a tanks-in-series with backflow (TISB) model was adoptedto interpret the tracer experiment data, which shows an excellentagreement between the prediction and experimental measurements. [ABSTRACT FROM AUTHOR]

To experimentally verify the existence of reaction rate hysteresis in the gas phase operation due to capillary condensation, benzene hydrogenation was carried out in a fixed bed under isothermal condition. Through changing the flow rate of benzene and cyclohexane mixture in a sequence from low to high and then vice versa, a group of distinctive conversion profiles was obtained. By plotting the reaction rate against the relative vapor pressure, hysteresis loops in reaction rate are confirmed to exist. It was observed the reaction rate kept nearly constant in the region of p/p0 0.8. In providing an intrinsic understanding on the influence of vapor condensation on the reaction rate of a partially wetted catalyst, the reaction rate and internal effectiveness factor are plotted against the catalyst wetting fraction, from which a new correlation between the overall reaction rate and catalyst wetting fraction was proposed. [ABSTRACT FROM AUTHOR]

A two-stage reactor composed of a slurry bubble column and a fixed bed was proposed. The slurry column, installed with a radio frequency conductance liquid level controller, was considered not only as a preliminary reactor for the vaporization of the liquid reactants, but also as a protector to prevent liquid flooding in the fixed bed. Preliminary experiments were carried out to investigate the effects of different operating factors on the reactor performance, and the results showed that even under the optimal condition the benzene concentration should be kept at a low level of 21.9% to avoid high temperature rise. Therefore, side stream injection of cyclohexane into the fixed bed was proposed, and benzene conversion of 99.82% was reached even at a much higher concentration of 32.8%. To verify whether capillary condensation inside the catalyst particle in the fixed bed would exist in the presence of coolant injection, a criterion was proposed which is based on the understanding that once vapor condensation is occurring it will lead to multiplicity in reaction rate, which will consequently result in hysteresis in temperature profile under adiabatic condition. [ABSTRACT FROM AUTHOR]

Abstract: Citric acid complexation under mild condition was proposed to prepare monophasic and well crystallized Mg3(VO4)2 particle to be used as an active catalyst for the oxidative dehydrogenation of cyclohexane to cyclohexene. The catalyst prepared above was characterized by N2-physisorption, X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis. The characterization results displayed that the Mg3(VO4)2 particle was typically 100–160 nm and the specific surface area was 12.0–26.7 m2/g. Moreover, it showed that the purity and the structure of the catalyst were principally subjected to the calcination temperature and the amount of citric acid used in the sol–gel procedure. The Mg3(VO4)2 catalyst calcined at 823 K for 6 h with a molar ratio of (Mg+V):citric acid=1:1.2 exhibited the best catalytic performance with an excellent thermal stability. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]