Isobutane dehydrogenation reaction in a packed bed catalytic membrane reactor

A packed-bed catalytic ceramic membrane reactor (PBCMR) was used for the isobutane dehydrogenation reaction. The experimental results have shown that through the use of the membrane reactor one can attain better conversions and yields than in a conventional reactor operating under the same outlet pressure and temperature, and feed composition conditions.     

Application of a carbon membrane reactor for dehydrogenation reactions

This research tests a membrane reactor, equipped with a molecular-sieve carbon membrane, using isobutane dehydrogenation on a chromia alumina catalyst as a model reaction. Most pores of the carbon membrane employed are 6- in size and previous independent transport studies show that the permeability ratio of hydrogen to isobutene is larger than 100. These features make the membrane an excellent highly selective low-cost candidate for application in a membrane reactor. The novelty of this study is in the proposed application at relatively high temperatures (450°C and 500°C); only a few studies have tested carbon membrane reactors.Two types of operation modes were studied, using either nitrogen as a sweeping gas in counter current flow or using vacuum as a driving force for membrane transport. As expected, higher conversions were achieved with decreasing feed flow rate. The conversion achieved in the counter-current flow operation method was higher than in all other modes achieving a maximum of 85% at 500°C. While this result is much higher than in the corresponding PFR, the obtained improvement is a result of nitrogen transport and dilution. The conversions obtained in the vacuum mode show modest gains above the ones received in the PFR (40% vs. 30% at 500°C). These results were compared with simulations that used the experimentally determined transport parameters.     

Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model

Methanol oxidative dehydrogenation to formaldehyde over a Fe-Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M < FBR < PBMR-O.     

Optimal conditions of isobutane dehydrogenation in radial flow moving bed hydrogen-permselective membrane reactors to enhance isobutene and hydrogen production

In the isobutane dehydrogenation process, coupling reaction and separation and optimization of the intensified process can improve the isobutane conversion and selectivity, reduce operational costs and lets to produce pure hydrogen. In this research, the radial flow moving bed reactors in the Olefex technology have been supported by Pd–Ag membrane plate to remove hydrogen from the reaction zone. The reactions occur in the tube side and the hydrogen is permeated from the reaction zone to the sweep gas stream. The proposed configuration has been modeled heterogeneously based on the mass and energy conservation laws considering reaction networks. To prove the accuracy of the considered model, the simulation results of the conventional process have been compared against available plant data. The Genetic algorithm as an effective method in the global optimization has been considered to optimize the operating condition of membrane reactors to enhance isobutene productivity. In this optimal configuration, the isobutene production has been enhanced about 3.7%.     

Oxidative dehydrogenation of isobutane over magnesium molybdate catalysts

A series of Mo-Mg-O catalysts with different crystalline phases (pure and mixtures) have been studied in the oxidative dehydrogenation of isobutane. X-ray diffraction, UV–Vis spectroscopy and temperature programmed reduction were applied to characterise the samples. In addition, the kinetics of the lattice oxygen exchange with labelled C¹⁸O₂ was measured for all samples. It has been found that the MgMoO₄ phase contains the surface active sites suitable for the adsorption of isobutane and for its dehydrogenation to isobutene with the minimum of cracking reaction. Moreover, for this reaction the migration of lattice oxygen ions is not a key parameter in the control of the catalytic properties of these materials.     

Pt系异丁烷脱氢催化剂研究进展

综述了Pt系异丁烷脱氢的研究状况,探讨了铂系催化剂的活性中心,重点总结了载体、助剂、失活这几方面对铂系催化剂的反应性能的影响,并对铂系催化剂的研究前景进行了展望.     

Dehydrogenation of isobutane to isobutene over a Pt-Cu bimetallic catalyst in the presence of LaAlO3 perovskite

In this study, isobutane dehydrogenation to isobutene reaction was carried out in a series of Pt-Cu bimetallic catalysts prepared by co-impregnation method. The catalysts were characterized by means of several techniques, including XRD, N_2 adsorption–desorption, TEM, XPS, H_2-TPR and TG. The results show that the existence of LaAlO_3 perovskite can enhance the dispersion and sintering resistance of metal nanoparticles and facilitate the transfer of carbon deposits from active sites to the support. Interestingly,the perovskite nanoparticles can also inhibit the reduction of CuOxand the formation of PtCu alloys,resulting in the suitable interaction between Pt and Cu. The Pt-Cu/LaAlO_3/SiO_2 catalyst exhibits the optimal dehydrogenation performance with an isobutane conversion of 47% and isobutene selectivity of 92% after 310 min reaction, which was ascribed to the unique role of LaAlO_3 perovskite as well as the appropriate Pt-Cu interaction.     

Oxidative dehydrogenation of isobutane over pyrophosphates catalytic systems

The catalytic effect of metal pyrophosphates (i.e., Mn₂P₂O₇, Ni₂P₂O₇, CeP₂O₇, Mg₂P₂O₇, ZrP₂O₇, Ba₂P₂O₇, V₄(P₂O₇)₃ and Cr₄(P₂O₇)₃) on the oxidative dehydrogenation of isobutane to isobutene in the reaction temperature range of 400–600 °C has been investigated. CeP₂O₇ gives the highest isobutene yield and selectivity (71%), however, V₄(P₂O₇)₃ is the most active catalyst with an isobutane conversion of 33.5% at 500 °C. Increasing the reaction temperature results in higher isobutane conversions and lower isobutene selectivity. Reaction by-products are propylene, CO, CO₂ and traces of methane and ethylene. No oxygenate products are formed under the used reaction conditions. The sum of selectivities of CO, CO₂ and methane is approximately equal to that of propylene, indicating their formation from total oxidation of C₁ species accompanying the isobutane crack reactions. Working at temperatures higher than 550 °C, the homogeneous gas phase reactions become significant and the oxygen conversion reaches 100%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-isothermal simulation of cyclohexane dehydrogenation in an inert membrane reactor with catalytic pellets in the feed-side chamber

A mathematical model is presented to simulate the performance of a non-isothermal inert membrane reactor with catalytic pellets in the feed-side chamber (IMRCF). The simulation takes into account the various heat exchanges that take place inside the reactor. The model consists of the full set of partial difference equations that describe the conservation of mass, momentum, energy and chemical species, coupled with chemical kinetics and appropriate boundary conditions for the physical problem. The set of equations is solved by finite difference method. The model is applied to investigate the endothermic dehydrogenation of cyclohexane in the IMRCF, where a permselective Vycor glass membrane is used. The simulation results show that the conversion of cyclohexane for non-isothermal IMRCF at the temperature of 550 K and below is higher than the equilibrium conversion. On the contrary, when the temperature is 570 K and above, the conversion will be lower than the equilibrium conversion. The heat effects have a greater influence on the IMRCF.     

On the link between intrinsic catalytic reactions kinetics and the development of catalytic processes: Catalytic dehydrogenation of ethylbenzene to styrene

A procedure linking kinetic modeling of catalytic reactions to reactor modeling for different configurations is developed and applied to the catalytic dehydrogenation of ethylbenzene to styrene. The procedure is applied to four configurations, namely fixed bed with/without hydrogen selective membranes and bubbling fluidized beds with/without selective membranes. The kinetic data for the industrial catalyst are extracted from industrial fixed bed data using a rigorous heterogeneous model. The kinetic data for the three in-house prepared catalysts are obtained from the laboratory scale experiments using pseudo-homogeneous models.     

Methylcyclohexane dehydrogenation for hydrogen production via a bimodal catalytic membrane reactor

The dehydrogenation of methylcyclohexane (MCH) to toluene (TOL) for hydrogen production was theoretically and experimentally investigated in a bimodal catalytic membrane reactor (CMR), that combined Pt/Al₂O₃ catalysts with a hydrogen‐selective organosilica membrane prepared via sol‐gel processing using bis(triethoxysilyl) ethane (BTESE). Effects of operating conditions on the membrane reactor performance were systematically investigated, and the experimental results were in good agreement with those calculated by a simulation model with a fitted catalyst loading. With H₂ extraction from the reaction stream to the permeate stream, MCH conversion at 250°C was significantly increased beyond the equilibrium conversion of 0.44–0.86. Because of the high H₂ selectivity and permeance of BTESE‐derived membranes, a H₂ flow with purity higher than 99.8% was obtained in the permeate stream, and the H₂ recovery ratio reached 0.99 in a pressurized reactor. A system that combined the CMR with a fixed‐bed prereactor was proposed for MCH dehydrogenation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1628–1638, 2015     

Oxidative dehydrogenation of isobutane over LaBaSm oxide catalyst: Influence of the addition of CO2 in the feed

Oxidative dehydrogenation (ODH) of isobutane over LaBaSm oxide catalyst in the temperature range 450–600°C, and the influence of the addition of CO₂ into the feed were investigated. It was found that LaBaSm oxide is an active and stable catalyst for ODH of isobutane. Upon reaction conditions the specific surface area decreases and a new phase, La₂O(CO₃)₂, is formed, which causes an increase in the surface specific conversion. The selectivity to isobutene as well as isobutane conversion can be improved by adding CO₂ into the feed. These effects may be explained as due to the combined effects of improvement of the active phase formation and the competition between molecular O₂ and CO₂ adsorption on the sites which are responsible for total oxidation.     

Vapor phase dehydrogenation of methanol to methyl formate in the catalytic membrane reactor with Cu/SiO2/ ceramic composite membrane

The Cu/SiO₂/ceramic composite membrane was prepared on the SiO₂/ceramic mesoporous membrane by an ion exchange method, and vapor phase dehydrogenation of methanol to methyl formate in the catalytic membrane reactor was investigated. It showed much better performance in the catalytic membrane reactor than that in the fixed-bed reactor under the same reaction conditions. At 240 °C, 57.3% conversion of methanol and 50.0% yield of methyl formate were achieved in the catalytic membrane reactor and only 43.1% conversion of methanol and 36.9% yield of methyl formate were achieved in the fixed-bed reactor.     

Simulation of a catalytic membrane reactor for the oxidative dehydrogenation of butane

A two-dimensional model has been used to simulate the oxidative dehydrogenation of butane on a two-layer catalytic membrane (diffusion layer and V/MgO active layer) operating with segregated reactant feeds. The model considers plug flow on both sides of the membrane, uses an extended Fick's law expression to describe multi-component diffusion in the radial direction, and a complex kinetic scheme to account for the reaction network. The simulation study shows that different feed configurations lead to marked differences on the partial pressure profiles of the different species across the membrane, and explains the performance order (in terms of the selectivity-conversion behaviour) that was observed experimentally. Similarly, the behaviour observed for membranes with catalytic layers of different width was justified by taking into account the variation of the oxygen partial pressure across the active zone of the membrane.     

A composite catalytic polymer membrane reactor using heteropolyacid-blended polymer membrane

The vapor-phase MTBE decomposition was examined in a shell and tube-type catalytic membrane reactor (CMR). 12-Tungstophosphoric acid (PW) was used as a catalyst and poly-2,6-dimethyl-1,4-phenylene oxide (PPO) was used as a polymer material. A single-phase CMR (PW-PPO/Al₂O₃, type-1) and a composite CMR (PW-PPO/ PPO/ Al₂O₃, type-2) were successfully designed and characterized. It was revealed that the single-phase PW-PPO/ Al₂O₃ showed perm-selectivities for reaction products. The selective removal of methanol through the catalytic membrane shifted the chemical equilibrium toward the favorable direction in the MTBE decomposition. The PWPPO/ PPO/ Al₂O₃ showed the better performance than PW-PPO/ Al₂O₃. The enhanced performance of PW-PPO/ PPO/ Al₂O₃ CMR was due to the intrinsic perm-selectivity of PW-PPO and the additional separation capability of sub-layered PPO membrane.     

异丁烷催化脱氢反应机理与失活动力学研究进展

异丁烯是化工行业重要的基础原料,国内外对异丁烯的需求量逐年递增。仅靠石油催化裂解已无法满足对异丁烯的需求,开展异丁烷脱氢制异丁烯工艺的研究备受关注。综述Cr系异丁烷脱氢催化剂的研究进展,探讨Cr系催化剂的活性中心以及发生在活性中心上的多种反应机理和相应的动力学模型,详述催化剂的失活机理,总结积炭的形成过程,指出Cr系异丁烷催化脱氢反应和失活机理以及相关动力学方面研究的不足,并对未来研究前景进行展望。     

Steam reforming of methanol over a CuO/ZnO/Al2O3 catalyst part II: A carbon membrane reactor

The reaction of methanol steam reforming was studied in a carbon membrane reactor over a commercial CuO/ZnO/Al₂O₃ catalyst (Süd-Chemie, G66 MR). Carbon molecular sieve membranes supplied by Carbon Membranes Ltd. were tested at 150 °C and 200 °C. The carbon membrane reactor was operated at atmospheric pressure and with vacuum at the permeate side, at 200 °C. High methanol conversion and hydrogen recovery were obtained with low carbon monoxide permeate concentrations. A sweep gas configuration was simulated with a one-dimensional model. The experimental mixed-gas permeance values at 200 °C were used in a mathematical model that showed a good agreement with the experimental data. The advantages of using water as sweep gas were investigated in what concerns methanol conversion and hydrogen recovery. The concentration of carbon monoxide at the permeate side was under 20 ppm in all simulation runs. These results indicate that the permeate stream can be used to feed a polymer electrolyte membrane fuel cell.     

Concentration and residence time effects in packed bed membrane reactors

A fixed bed reactor (FBR) and a packed bed membrane reactor (PBMR) were compared with respect to their performance in the oxidative dehydrogenation of ethane over VO_x/γ-Al₂O₃ catalyst. The experiments were carried out at high space velocities and under oxygen excess conditions. In the PBMR, the oxidant air was distributed from the shell side of the membrane.

At similar overall feed configurations, the conversion of ethane was found to be higher in the PBMR. This effect was most pronounced at the highest space velocity. Mostly ethylene yield was higher in the PBMR than in the FBR. However, the yield of carbon oxides increased more. Thus, an improvement of olefin selectivity was not observed. There were even sets of experimental conditions, where the ethylene yield in the PBMR fell below the corresponding value for the FBR. In the PBMR under oxygen excess conditions, the consecutive oxidation of ethylene is more favoured than in the FBR.

Two essential reasons for the observed differences in the reactor performances are discussed. At first, there are different local reactant concentrations. Secondly, there are essential differences in the residence time behaviour of the reactants in the FBR and PBMR. In order to exemplify the latter aspect additional experiments have been carried out using a cascade of three identical PBMRs. Varying the specific oxygen flow rates over the individual membrane segment walls different dosing profiles were implemented. The results obtained in this study emphasise the general potential, but also the limits of membrane reactors compared to the FBR.     

Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction, removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production. For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used. Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogena-tion method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and significant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.     

Optimal design conditions for dehydrogenation of cyclohexane in a membrane reactor

The design variables of a membrane reactor, such as the permeation rate through the membrane and catalyst loading in the membrane, have received little attention in comparison with the operating conditions. A non-dimensionalized model for a membrane reactor was developed to account for the effects of permeation rate and catalyst loading. The increased permeation rate did not always increase the exit conversion and there existed a maximum point of exit conversion. At isothermal conditions, the exit conversion was saturated as catalyst loading was increased; however, when the reactor was under non-isothermal condition along the axial direction, there existed an optimum catalyst loading at which the exit conversion was maximum. With this model, the optimal configuration of permeation rate and catalyst loading could be determined.