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.     

Simulation and optimization of an existing ethylbenzene dehydrogenation reactor

The dehydrogenation of ethylbenzene to styrene in an ideal, adiabatic reactor has been modelled using side reactions in addition to the main one. The differential equations describing the process were integrated on an IBM 7040 digital computer. A profit function ($ gained/hour) was chosen and for various combinations of process variables, which were subject to constraints, the single bed reactor was optimized by the method of Rosenbrock^(1,2). Studies of a proposed two-bed reactor were also carried out. Catalyst deactivation during the reaction was not considered because of a lack of data. The results showed that the existing reactor could be operated more efficiently if the present plant constraints were removed. Two beds in series gave still better results.     

Modeling of a novel membrane reactor to integrate dehydrogenation of ethylbenzene to styrene with hydrogenation of nitrobenzene to aniline

The catalytic dehydrogenation of ethylbenzene to styrene is coupled with the catalytic hydrogenation of nitrobenzene to aniline in a simulated integrated reactor formed of two fixed beds separated by a hydrogen-selective membrane, where both hydrogen and heat are transferred across the surface of membrane tubes. A pseudo-homogeneous model of the two fixed beds predicts the performance of this novel configuration first proposed by Moustafa and Elnashaie [Simultaneous production of styrene and cyclohexane in an integrated membrane reactor. Journal of Membrane Science 178 (1), 171-184]. Both co-current and counter-current operating modes are investigated and the simulation results are compared with corresponding predictions for an industrial adiabatic fixed bed reactor operated at the same feed conditions. The conversion of ethylbenzene and the yield of styrene in the membrane reactor are predicted to exceed by a wide margin those in the industrial adiabatic fixed bed reactor. Aniline is also produced as an additional valuable product in a favorable manner, and autothermality is achieved within the reactor. The results suggest that coupling of these reactions could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.     

基于径向基函数神经网络的乙苯催化脱氢转化率的软测量应用

针对乙苯催化脱氢过程的特点,选用历史生产数据即乙苯进料、一反温度、二反温度、二反出口压力、水比、脱氢选择性,利用改进的径向基函数神经网络（RBFNN）来构建乙苯催化脱氢过程模型,通过企业实际生产数据对该网络进行测试,其结果表明该模型可真实模拟实际乙苯脱氢生产过程,为后续乙苯催化脱氢系统实施先进控制优化技术奠定了基础.     

Optimal design of an autothermal membrane reactor coupling the dehydrogenation of ethylbenzene to styrene with the hydrogenation of nitrobenzene to aniline

Coupling the dehydrogenation of ethylbenzene to styrene with the hydrogenation of nitrobenzene to aniline in a catalytic fixed bed membrane reactor has the potential for significantly improving both processes (Abo-Ghander et al., 2008. Modeling of a novel membrane reactor to integrate dehydrogenation of ethylbenzene to styrene with hydrogenation of nitrobenzene to aniline. Chemical Engineering Science, 63 (7), 1817–1826). In a continuing effort to realize this potential, an optimal design is sought for a co-current coupled flow, catalytic membrane reactor configuration. To achieve this objective, two conflicting objective functions, namely: the yield of styrene on the dehydrogenation side and the conversion of nitrobenzene on the hydrogenation side, are considered. The total number of the decision variables considered in the optimization problem is 12, representing a set of operating and dimensional parameters. The problem is solved numerically by two deterministic multi-objective optimization approaches: the normalized normal constraint method and the normal boundary intersection method. It was found that the integrated reactor system can be operated to produce a maximum styrene yield of 97% when production of styrene is emphasized and, on the other hand, up to 80% of nitrobenzene conversion when nitrobenzene conversion is concentrated on. The resulting sets of Pareto optimal solutions obtained by both techniques are shown to be identical. Qualitative explanations are provided for the effect of the decision variables on both objectives.     

ZSM-5 型沸石膜反应器在乙苯脱氢反应中的模式

引言 沸石分子筛膜是近些年发展起来的和种新型的膜分离技术[1],它是通过分子筛孔道实现分子筛分,从而得到较高的分离因数.     

乙苯脱氢三叶型355催化剂的工业开发

开发成功了具有高活性、高选择性、低水同比、高侧压强及抗水性能好等特点的三叶型３５５催化剂。工业试生产和工业生产结果表明,在反应温度为６２０℃,流体空速为１．０ｈ,水油比为２．０的条件下,可使乙苯转化率大于８０％,苯乙烯收率大于７６％,苯乙烯选择性大于９５％。     

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.     

乙苯脱氢催化剂的发展现状

阐述了乙苯催化脱氢催化剂的发展历程和国内外比较知名的进行乙苯催化脱氢催化剂研发和生产的公司。针对当前乙苯脱氢制苯乙烯领域的发展现状,对乙苯脱氢-氢氧化工艺和乙苯氧化脱氢工艺进行了介绍,并对新工艺配套催化剂的研发进行了概括性总结。     

乙苯脱氢催化剂的发展动态

通过对乙苯脱氢制苯乙烯工业催化剂演变过程的分析。认为近年催化剂组成已经历由Ｆｅ－Ｋ－Ｃｒ系列向Ｆｅ－Ｋ－Ｃｅ系列以及由高钾含量向低钾含量的过渡。催化剂制备工艺也有诸多改进,颗粒形状由传统圆柱形向齿轮柱形及三叶柱形等异型颗粒演变。关于催化活性本质的研究渐趋活跃,多数研究者认为活性相是Ｋ２ｆｅ２Ｏ４钾流失是催化剂在正常操作条件下逐渐老化的根本原因。     

Comparison of diffusion models in the modeling of a catalytic membrane fixed bed reactor coupling dehydrogenation of ethylbenzene with hydrogenation of nitrobenzene

Coupling of dehydrogenation of ethylbezene with hydrogenation of nitrobenzene in a catalytic membrane reactor can lead to a significant improvement in the conversion of ethylbenzene and production of styrene. In this work, the homogeneous reactor model for a cocurrent flow configuration is compared to two heterogeneous models based on the Fickian diffusion model and the dusty gas model for both isothermal and non-isothermal pellets. It is observed that both heterogeneous models predict a significant drop in yield and conversion compared to the homogeneous model, indicating the importance of heterogeneity. This drop is generally less severe for the dusty gas model than for the Fickian diffusion model. The assumption of isothermality causes larger deviations than the assumption of Fickian diffusion. The deviations in the predictions of the homogenous model and the heterogeneous models from those of the dusty gas model for non-isothermal pellets are ∼6% and ∼11%, respectively.     

乙苯脱氢催化剂焙烧工艺的改进

以乙苯脱氢制苯乙烯催化剂为研究对象,对采用连续式回转炉和马弗炉焙烧的催化剂分别进行了物性分析和活性评价。结果表明,采用回转炉焙烧的催化剂样品在外观、强度、比表面积、孔容、孔径、晶粒形貌和催化活性等均优于马弗炉焙烧的催化剂,可用连续式回转炉代替马弗炉。     

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     

Screening of catalysts for the oxidative dehydrogenation of ethylbenzene

The oxidative dehydrogenation of ethylbenzene to styrene on various oxide catalysts has been investigated. The catalysts examined are classified into six types, considering their catalytic behavior. In general, acidic catalysts show high selectivity. The most effective catalyst has been found to be the SnO₂-P₂O₅ catalyst prepared from Sn(OH)₂ and phosphoric acid. The effects of partial pressures and reaction temperature have been studied and suitable reaction conditions for the SnO₂-P₂O₅ catalyst have been determined.     

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.     

Heterogeneous modeling of an autothermal membrane reactor coupling dehydrogenation of ethylbenzene to styrene with hydrogenation of nitrobenzene to aniline: Fickian diffusion model

Coupling of reactions in catalytic membrane reactors provides a route to process intensification. Dehydrogenation of ethylbenzene and hydrogenation of nitrobenzene form a promising pair of processes to be coupled in a membrane reactor. The heat released from the hydrogenation side is utilized to break the endothermality on the dehydrogenation side, while hydrogen produced on the dehydrogenation side permeates through the hydrogen-selective membranes, enhances the equilibrium conversion of ethylbenzene and reacts with nitrobenzene on the permeate side to produce aniline. Mathematical reactor models are excellent tools to evaluate the extent of improvement before experiments are set up. However, a careful selection of phenomena considered by the reactor model is needed in order to obtain accurate model predictions.To investigate the effect of the intraparticle resistances on the performance of the cocurrent configuration of the coupling reactor, a heterogeneous fixed bed reactor model is developed with Fickian diffusion inside the catalyst pellets. For the condition of interest, the styrene yield is found to be 82% by the homogenous model, 73% by the heterogeneous model for isothermal pellets, and 69% by the heterogeneous model with non-isothermal pellets. Hence, the homogeneous model overestimates the yield by 5–15% of their actual values.     

A novel inorganic hollow fiber membrane reactor for catalytic dehydrogenation of propane

A novel inorganic hollow fiber membrane reactor (iHFMR) has been developed and applied to the catalytic dehydrogenation of propane to propene. Alumina hollow fiber substrates, prepared by a phase inversion/sintering method, possess a unique asymmetric structure that can be characterized by a very porous inner surface from which finger-like voids extend across ∼80% of the fiber cross-section with the remaining 20% consisting of a denser sponge-like outer layer. In contrast to other existing Pd/Ag composite membranes, where an intermediate γ-Al₂O₃ layer is often used to bridge the Pd/Ag layer and the substrate, the Pd/Ag composite membrane prepared in this study was achieved by coating the Pd/Ag layer directly onto the outer surface of the asymmetric substrate. After depositing submicron-sized Pt (0.5 wt %)/γ-alumina catalysts in the finger-like voids of the substrates, a highly compact multifunctional iHFMR was developed. Propane conversion as high as 42% was achieved at the initial stage of the reaction at 723 K. In addition, the space-time yields of the iHFMR were ∼60 times higher than that of a fixed bed reactor, demonstrating advantages of using iHFMR for dehydrogenation reactions. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

PED-01乙苯脱氢催化剂的评价试验

自主开发的PED-01乙苯脱氢催化剂在100 mL等温评价装置上进行了重复试验和稳定性试验,在反应温度620 ℃、空速1.0 h^-1、水蒸汽与乙苯质量比2∶1和常压条件下,催化剂的乙苯平均转化率为79.51%,苯乙烯平均选择性为95.91%,苯乙烯平均收率为76.25%。侧线装置上条件试验和稳定性试验结果表明,PED-01催化剂的乙苯转化率和苯乙烯平均收率均优于进口催化剂,失活速率比进口催化剂慢,具有更好的稳定性。     

The oxidative dehydrogenation of ethylbenzene to styrene

The results of a kinetic study of the oxidative dehydrogenation of ethylbenzene to styrene over an organic catalyst (pyrolyzed polymerized acrylonitrile) are reported. The reaction is found to be second order in ethylbenzene and zero order in oxygen with an activation energy of 76.5 kJ/mol. The rate equation is: \documentclass{article}\pagestyle{empty}\begin{document}$ - r(mol/\min .g\,catalyst) = 3.2 \times 10^9 \exp [ - 76,500/RT] \cdot C_{EtB}^2 \cdot C_{O_2 }^0 $\end{document} where R = 8.31 J/niol.K and concentration (CEtB) is expressed as mol/L. The catalyst is more active than conventional metal oxide catalysts and appears to be quite stable under reaction conditions. The results suggest that, using the PPAN catalyst, it may be possible to reduce the operating temperature of the oxidative dehydrogenation of ethylbenzene to about 250-300°C, thereby avoiding some of the problems of the present high temperature process.     

SO2 promoted oxidative dehydrogenation of ethylbenzene

It has been demonstrated that SO₂ acts as an efficient dehydrogenation agent in the conversion of ethylbenzene to styrene in the presence of alkali and alkaline earth metal oxide doped alumina and titania catalysts. Development of these catalysts, which give styrene yields of greater than 80% per pass, is described in the paper. The catalysts allow the use of close to stoichiometric amounts of sulphur dioxide, are active in the presence of steam diluent and show low deactivation with time. The effect of varying process conditions such as temperature, reactant concentration and diluent amount is also described.