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.     

Oxidative dehydrogenation of propane to propene, 1: Kinetic study on V/MgO

The reaction kinetics of the oxidative dehydrogenation of propane to propene over a V/MgO catalyst were studied. Both propane and propene oxidation kinetics were measured independently to quantify the rates of the parallel and consecutive reactions to propene and carbon oxides. Specific experiments to evaluate reaction products effects showed that water inhibited reaction rates but co‐feeding CO₂ or propene had no measurable effect on selectivity or conversion. Kinetic data generated under integral reactor conditions and over an inert membrane reactor have also been used to estimate the kinetic parameters. Selectivity decreased as the oxygen partial pressure increased; however, propene yield was relatively insensitive to oxygen concentration. A dual site Mars‐van Krevelen model characterizes the reaction kinetics well. The role of lattice oxygen was established by alternating pulses of propane and oxygen. This redox model is able to predict the experimental tendencies observed in the three types of reactor studied.     

Selective oxidation of ethane and propane over sulfated zirconia‐supported nickel oxide catalysts

The oxidative dehydrogenations of ethane and propane were investigated over a series of zirconia and nickel‐oxide supported on zirconia catalysts. It was found that zirconia, sulfated zirconia as well as NiO‐based zirconia catalysts showed high catalytic activities for oxidative dehydrogenation of ethane and propane. However, conversion and selectivity differed depending on the nature of the catalysts. Zirconia, sulfated zirconia (SZ) and their supported NiO catalysts showed high ethane conversions but lesser selectivities to olefins while NiO/Li₂ZrO₃ exhibited high selectivities to ethylene and propylene. Addition of an LiCl promoter in the NiO/SZ catalyst increased the catalytic activity and olefin selectivity, thus resulting in a higher olefin yield. In the oxidative dehydrogenations of ethane and propane NiO–LiCl/SZ exhibited 79% ethylene selectivity at 93% ethane conversion at 650 °C and 52% selectivity to propylene at 20% propane conversion at 600 °C, respectively. Characterization showed that the physico‐chemical properties of the catalysts determine the catalytic activity and selectivity. © 2001 Society of Chemical Industry     

Material properties and operating configurations of membrane reactors for propane dehydrogenation

A modeling‐based approach is presented to understand physically realistic and technologically interesting material properties and operating configurations of packed‐bed membrane reactors (PBMRs) for propane dehydrogenation (PDH). PBMRs composed of microporous or mesoporous membranes combined with a PDH catalyst are considered. The influence of reaction and membrane transport parameters, as well as operating parameters such as sweep flow and catalyst placement, are investigated to determine desired “operating windows” for isothermal and nonisothermal operation. Higher Damköhler (Da) and lower Péclet (Pe) numbers are generally helpful, but are much more beneficial with highly H₂‐selective membranes rather than higher‐flux, lower‐selectivity membranes. H₂‐selective membranes show a plateau region of conversion that can be overcome by a large sweep flow or countercurrent operation. The latter shows a complex trade‐off between kinetics and permeation, and is effective only in a limited window. H₂‐selective PBMRs will greatly benefit from the fabrication of thin (～1 µm or less) membranes. © 2014 American Institute of Chemical Engineers AIChE J, 61: 922–935, 2015     

Efficient tuning of microstructure and surface chemistry of nanocarbon catalysts for ethylbenzene direct dehydrogenation

A facile and scalable approach to efficiently tune microstructure and surface chemical properties of N‐doped carbocatalysts through the controlled glucose hydrothermal treatment with diverse parameters and subsequent pyrolysis of pretreated carbonaceous materials with melamine (GHT‐PCM) was presented. Various characterization techniques including high resolution transmission electron microscopy (HRTEM), N₂ adsorption desorption (BET), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and fourier transform infrared spectroscopy (FTIR) were employed to investigate the effect of prior GHT on the microstructure and surface chemical properties of N‐doped carbocatalysts, as well as to reveal the relationship between catalyst nature and catalytic performance in oxidant‐ and steam‐free direct dehydrogenation (DDH) of ethylbenzene for styrene production. It was found that the GHT process and its conditions significantly affect microstructure and surface chemical properties of the N‐doped carbocatalysts, which subsequently influences their catalytic performance in DDH reaction dramatically. Interestingly, the prior GHT can remove the carbon nitride layer formed on parent nanocarbon in the process of melamine pyrolysis, produce structural defects, and tune surface element component, through the “detonation” of polysaccharide coating on nanocarbon. The as‐prepared N‐doped CNT (M‐Glu‐CNT) by the established GHT‐PCM approach demonstrates higher catalytic performance (4.6 mmol g^?1h^?1 styrene rate with 98% selectivity) to the common N‐doped CNT (M‐CNT, 3.4 mmol g^?1 h^?1 styrene rate with 98.2% selectivity) as well as to pristine CNT (2.8 mmol g^?1 h^?1 styrene rate with 96.8% selectivity), mainly ascribed to increased structural defects, enriched surface ketonic C?O groups, and improved basic properties from N‐doping on the M‐Glu‐CNT, those strongly depend on GHT conditions. The excellent catalytic performance of the developed M‐Glu‐CNT catalyst endows it with great potential for future clean production of styrene via oxidant‐ and steam‐free conditions. Moreover, the directed GHT‐PCM strategy can be extended to the other N‐doped carbonaceous materials with enhanced catalytic performance in diverse reactions by tuning their microstructure and surface chemistry. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2543–2561, 2015     

PtZn‐ETS‐2: A novel catalyst for ethane dehydrogenation

Catalysts having unprecedented selectivity toward ethane dehydrogentation were prepared by combining platinum and zinc on the surface of the titanate ETS‐2. This high surface area, sodium titanate ion exchanger affords high metal dispersion, presents many active sites to the gas stream, and is free of any pore structure that can influence mass transfer to and away from the active sites. It was determined that the addition of zinc to platinum‐loaded ETS‐2 changes the electronic properties of the metals and significantly improves the specificity of the catalyst. By changing the zinc‐to‐platinum ratio, and by manipulating the space velocity of the gas, the production of side products and coke can be suppressed or eliminated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4367–4376, 2015     

Simulation of Propane Dehydrogenation to Propylene in a Radial‐Flow Reactor over Pt‐Sn/Al2O3 as the Catalyst

Catalytic paraffin dehydrogenation for manufacturing olefins is considered to be one of the most significant production routes in the petrochemical industries. A reactor kinetic model for the dehydrogenation of propane to propylene in a radial‐flow reactor over Pt‐Sn/Al₂O₃ as the catalyst was investigated here. The model showed that the catalyst activity was highly time dependent. In addition, the component concentrations and the temperature varied along the reactor radius owing to the occurring endothermic reaction. Moreover, a similar trend was noticed for the propane conversion as for the propylene selectivity, with both of them decreasing over the time period studied. Furthermore, a reversal of this trend was also revealed when the feed temperature was enhanced or when argon was added into the feed as an inert gas.     

丁烯氧化脱氢铁系催化剂绿色制备关键因素的考察

丁烯氧化脱氢是工业生产丁二烯常用的工艺,其中,铁系催化剂是丁烯氧化脱氢工业使用的主流催化剂,为满足清洁生产的需要,了解催化剂制备过程中产生的NOx及废水等排放物的组成尤为重要。对铁系催化剂生产过程中前驱体制备步骤的气体生成及组成进行研究,同时对沉淀洗涤步骤产生的废液成分进行检测。通过XRD、TG-DSC、ICP和TPC等技术对催化剂性质及制备排放物进行分析,考察制备条件对催化剂结构和性能的影响及废物排放的变化规律。结果表明,在前驱体制备溶铁过程中,空气气氛下提高硝酸浓度可有效抑制氢气的产生;不同焙烧温度阶段,生成NOx种类有较大差别;排放废水中含有较多的Zn离子。焙烧条件试验表明,最佳焙烧温度为(650~700)℃,焙烧时间低于9 h。     

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.