Numerical investigation and experimental validation of the performance of a tubular packed bed reactor for hydrogenation of diene‐based polymers

A process which comprised a tubular reactor (that can be packed with different internal structures) has been modeled and theoretically analyzed for conducting the hydrogenation of nitrile butadiene rubber (NBR). The dynamics of the tubular reactor and the intrinsic hydrogenation kinetics are coupled, and detailed numerical simulations are performed under isothermal and isobaric conditions. The proposed model thus obtained involves coupled, nonlinear, partial differential equations (distributed parameter system). The effect of different reactor design parameters such as Peclet number, carbon–carbon double bond loading, mass transfer to reaction resistance, and solubility of hydrogen with respect to hydrogenation of the NBR has been investigated numerically. The conversions predicted using the proposed model for tubular packed bed reactor are compared with those possible in conventional plug flow reactor and continuous stirred tank reactor models. The optimal parameters and operating conditions for efficient production of hydrogenated NBR are suggested. Finally, the validity of the proposed model is confirmed by comparing the predicted and the experimental degree of hydrogenation obtained in a tubular reactor packed with Intalox saddles. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Investigation of multiphase hydrogenation in a catalyst‐trap microreactor

BACKGROUND: Multiphase hydrogenation plays a critical role in the pharmaceutical industry. A significant portion of the reaction steps in a typical fine chemical synthesis are catalytic hydrogenations, generally limited by resistances to mass and heat transport. To this end, the small‐scale and large surface‐to‐volume ratios of microreactor technology would greatly benefit chemical processing in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate mass transfer in a catalytic hydrogenation reaction. The reactor design is such that solid catalyst is suspended in the reaction channel by an arrangement of catalyst traps. The design supports the use of commercial catalyst and allows control of pressure drop across the bed by engineering the packing density. RESULTS: This paper discusses the design and operation of the reactor in the context of the liquid‐phase hydrogenation of o‐nitroanisole to o‐anisidine. A two‐phase ‘flow map’ is generated across a range of conditions depicting three flow regimes, termed gas‐dominated, liquid‐dominated, and transitional, all with distinctly different mass transfer behavior. Conversion is measured across the flow map and then reconciled against the mass transfer characteristics of the prevailing flow regime. The highest conversion is achieved in the transitional flow regime, where competition between phases induces the most favorable gas–liquid mass transfer. CONCLUSION: The results are used to associate a mass transfer coefficient with each flow regime to quantify differences in performance. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macro‐scale production reactors. Copyright © 2008 Society of Chemical Industry     

Dynamic modeling and validation of 2-ethyl-hexenal hydrogenation process

The paper evaluates, by modeling and simulation, 2-ethyl-hexenal hydrogenation process in catalytic trickle bed three-phase reactors. The mathematical model consists of balance equations for gas and liquid phases. Reaction rate equations, transport models and mass balances were coupled to generalized heterogeneous models which were solved with respect to time and space with algorithms suitable for partial differential equations. The importance of mass transfer resistance inside the catalyst pellets as well as the dynamics of the different phases being present in the reactor is revealed. The dynamic mathematical model presented can be used to analyze and understand the interaction of various processes that take place inside the hydrogenation reactor and also to make preliminary calculation of experimental parameters. Another important use of the mathematical model is to determine the optimal operation conditions and to design the control system. The model is implemented in Matlab and tested in simulations achieving successful results.     

连续微反应加氢技术在脱保护反应中的应用

保护与脱保护是医药中间体等精细化工领域中较为常见的一种有机合成策略。常用的保护基主要有苄基与苄氧羰基,通常可利用催化加氢法将其脱除。采用高压加氢间歇釜工艺存在气液传质效率低,操作安全性差,氢解效率低等问题。采用连续微反应加氢技术进行非均相催化加氢脱保护,可以利用其较高的气液传质效率和平推流特性实现高选择性脱保护,并显著缩短反应时间。本文阐述了连续微反应加氢技术在脱保护反应中的优点及其在药物中间体合成中的实际应用,并介绍了催化剂与溶剂对脱保护反应的影响。最后对连续微反应加氢技术在脱保护中的应用进行了展望。     

CFD modeling of gas flow in porous medium and catalytic coupling reaction from carbon monoxide to diethyl oxalate in fixed-bed reactors

A comprehensive two-dimensional heterogeneous reactor model was developed to simulate the flow behavior and catalytic coupling reaction of carbon monoxide (CO)–diethyl oxalate (DEO) in a fixed-bed reactor. The two-temperature porous medium model, which was revised from a one-temperature porous medium model, as well as one equation turbulent model, and exponent-function kinetic model was constructed for the turbulent velocity scale comparing with laminar flow and simulation of the catalytic coupling reaction. The simulation results were in good agreement with the actual data collected from certain pilot-plant fixed bed reactors in China. Based on the validated approach and models, the distributions of reaction parameters such as temperature and component concentrations in the reactor were analyzed. The simulations were then carried out to understand the effects of operating conditions on the reactor performance which showed that the conduction oil temperature in the reactor jacket and the CO concentration are the key impact factors for the reactor performance.     

A porous carbon membrane reactor for the homogeneous catalytic hydration of propene

A porous carbon membrane contactor was studied to determine whether such a reactor could be used for homogeneous catalytic reactions. The hydration of propene, catalysed by an aqueous solution of phosphoric acid, was selected as a suitable model reaction. Experiments at high pressure and temperature were conducted in a laboratory-scale gas phase continuous reactor equipped with a flat carbon membrane contactor. It was shown that reasonably stable operation of the reactor could be achieved at high operating pressures by tailoring the porous structure of the carbon membrane and coupling the reactor with an on-line feedback pressure controller. The reactor operated in a mass transfer limited regime due to mass transfer resistance in the liquid filled membrane pores. Periodic oscillation of transmembrane pressure was shown to reduce mass transfer resistance and considerably improve the overall reactor performance.A dynamic model of the reactor was developed and the results of simulations compared favourably with experiments and the performance of a commercially operated conventional reactor employing a supported liquid phase (SLP) catalyst.     

Process intensification of catalytic hydrogenation of ethylanthraquinone with gas‐liquid microdispersion

In this article, to miniaturize the hydrogenation reactor and make the H₂O₂ production with more safety a gas‐liquid microdispersion system was generated to intensify the process of catalytic hydrogenation of ethylanthraquinone by passing the gas‐liquid microdispersion system through a generally packed bed reactor. A microdispersion device with a 5 μm pore size microfiltration membrane as the dispersion medium has been developed and microbubbles in the size of 10–100 μm were successfully generated. The reaction and mass transfer performance was evaluated. The conversion of ethylanthraquinone as much as 35% was realized in less than 3.5 s. The overall volume mass transfer coefficient in the microdispersion reaction system reached in the range of 1–21 s^?1, more than two orders of magnitude larger than the values in normal gas‐liquid trickle‐bed reactors. A mathematical model in the form of Sh = 2.0 + 54.7Sc^1/3We^1/2?^1/10 has been firstly suggested, which can well predict the overall mass transfer coefficient. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Membrane reactor immobilized with palladium‐loaded polymer nanogel for continuous‐flow Suzuki coupling reaction

A catalytic membrane reactor, which was immobilized with palladium‐loaded nanogel particles (NPs), was developed for continuous‐flow Suzuki coupling reaction. Palladium‐loaded membranes were prepared by immobilization of NPs, adsorption of palladium ions, and reduction into palladium(0). The presence of palladium in the membrane was confirmed by the scanning electron microscopy; palladium aggregation was not observed. The catalytic activity of the membrane reactor in continuous‐flow Suzuki coupling reaction was approximately double that of a comparable reactor in which palladium ions were directly adsorbed onto an aminated membrane. This was attributed to the formation of small palladium particles. The reusability in the continuous‐flow system was higher than that in a batch system, and the palladium‐loaded membrane reactor had high long‐term stability. © 2014 American Institute of Chemical Engineers AIChE J, 61: 582–589, 2015     

A New Process for Synthesis of γ‐Butyrolactone and Cyclohexanone

A new process through the coupling of maleic anhydride hydrogenation and cyclohexanol dehydrogenation has been studied for the simultaneous synthesis of γ‐butyrolactone and cyclohexanone. The possibility of the coupling process has been investigated thermodynamically. The separated hydrogenation of maleic anhydride, the dehydrogenation of cyclohexanol, and the coupling process over the same Cu‐Zn‐Al catalyst have been carried out in a fixed‐bed reactor. Compared to conventional processes, the coupling process has several advantages, e.g., improved γ‐butyrolactone and cyclohexanone yields, good energy efficiency, and optimal hydrogen utilization. The effects of reaction temperature, n(H₂)/n (reactants) and liquid hourly space velocity on the coupling process are investigated. One thousand hours of stability testing shows that the Cu‐based catalyst has relatively high activity and good stability in the coupling process.     

连续微反应加氢技术在有机合成中的研究进展

加氢反应是有机合成中很常见的一种反应类型,采用常规的间歇加氢釜具有反应效率低、操作烦琐和安全性差等问题。而连续加氢微反应器进行非均相催化加氢反应能提供更高的传质性能,催化剂的回收利用与产物的纯化也更为方便,能极大地提高生产效率,减少贵金属催化剂的损失。因为这些优点,连续微反应加氢技术得到了越来越多的关注。本文阐述了连续微反应加氢技术中常用的微反应器与固体金属催化剂类型,以及不同官能团非均相高效催化加氢的研究进展,在此基础,对该技术在精细化工领域的应用进行了展望。连续微反应加氢技术使得加氢过程可以在更安全、更高效、更环保的条件下完成,具有很高的工业应用价值,是未来化学化工领域重点发展的方向之一。     

Optimization and simulation of the Sabatier reaction process in a packed bed

The Sabatier reaction in a testing packed bed was investigated experimentally and theoretically, and was used to convert waste carbon dioxide and hydrogen to provide needed water for closing the life‐support loop on orbit in space. A three‐dimensional model including fluid flow, gas dispersion, heat and mass transfer, and chemical reaction was developed by coupling some semi‐empirical correlated equations in chemical engineering science into computational fluid dynamics theory. Good agreements between the simulating results and experimental data for the effect of some parameters on reaction verified this model, for example, heat exchange between reactor and atmosphere, the material property of reactor, the catalyst deactivated and gas mass flux and so on. By using this model as the designing tools, an optimized packed bed is proposed. Compared with the testing packed bed, the relevant reactor length can be reduced from 220 to 150 mm with the same hydrogen conversion and lower pressure drop. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2879–2892, 2016     

Parallel hydrogenation for the quantification of wetting efficiency and liquid–solid mass transfer in a trickle‐bed reactor

A novel method for the measurement of wetting efficiency in a trickle‐bed reactor under reaction conditions is introduced. The method exploits reaction rate differences of two first‐order liquid‐limited reactions occurring in parallel, to infer wetting efficiencies without any other knowledge of the reaction kinetics or external mass transfer characteristics. Using the hydrogenation of linear‐ and isooctenes, wetting efficiency is measured in a 50‐mm internal diameter, high‐pressure trickle‐bed reactor. Liquid–solid mass transfer coefficients are also estimated from the experimental conversion data. Measurements were performed for upflow operation and two literature‐defined boundaries of hydrodynamic multiplicity in trickle flow. Hydrodynamic multiplicity in trickle flow gave rise to as much as 10% variation in wetting efficiency, and 10–20% variation in the specific liquid–solid mass transfer coefficient. Conversions for upflow operation were significantly higher in trickle‐flow operation, because of complete wetting and better liquid–solid mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011.     

下行床反应器内催化裂化过程的CFD模拟

耦合湍流气粒多相流模型和催化裂化集总动力学模型,建立了描述下行床内多相流动和催化裂化过程的反应器数学模型,并利用计算流体力学单元模拟软件CFX4.3对下行床内的催化裂化过程进行了数值模拟及分析.模型能预测出在工业应用中反应器内最受关注的诸多参数,如固含率、相间滑移速度、压降、气固相的加速区以及各组分浓度的分布情况.预测结果表明,气相反应的进行将导致反应器内的气粒流动行为发生较大变化,充分考虑反应与流动行为的耦合十分重要;而反应器床径的增大将导致转化率和各产物收率的下降.     

Kinetics and slurry-type reactor modelling during catalytic hydrogenation of o-cresol on Ni/SiO2

The effect of kinetic parameters (reactant concentrations, temperature) was investigated on the initial reaction rate for the catalytic hydrogenation of o-cresol on Ni/SiO₂, carried out in a batch or semi-batch agitated slurry-type reactor.

The data were interpreted by a kinetic model based on the Langmuir-Hinshelwood mechanism with non-dissociative and non-competitive adsorption of o-cresol and hydrogen on different sites, where the limiting step is due to the reaction of adsorbed reactants. The activation energy (E_a = 82 kJ/mol) is in good agreement with previous literature values reported for the catalytic hydrogenation of phenol.

Taking into account thermodynamic (solubilities) and mass transfer kinetics (k_La) data measured in situ, the integral reactor conversion rate of this three-phase catalytic reaction was simulated accurately in the physical regime by taking into account external and internal mass transfer resistances.     

Modeling for the catalytic coupling reaction of carbon monoxide to diethyl oxalate in fixed-bed reactors: Reactor model and its applications

A two-dimensional (2D) pseudo-homogeneous reactor model was developed to simulate the performance of fixed-bed reactors for catalytic coupling reaction of carbon monoxide to diethyl oxalate. Reactor modeling was performed using a comprehensive numerical model consisting of two-dimensional coupled material and energy balance equations. A power law kinetic model was applied for simulating the catalytic coupling reaction with considering one main-reaction and two side-reactions. The validity of the reactor model was tested against the measured data from different-scale demonstration processes and satisfactory agreements between the model prediction and measured results were obtained. Furthermore, detailed numerical simulations were performed to investigate the effect of major operation parameters on the reactor behavior of fixed bed for catalytic coupling reaction of carbon monoxide to diethyl oxalate, and the result shows that the coolant temperature is the most sensitive parameter.     

Toward a Continuous‐Flow Synthesis of Boscalid®

A two‐step continuous‐flow protocol for the synthesis of 2‐amino‐4′‐chlorobiphenyl, a key intermediate for the industrial preparation of the fungicide Boscalid^® is described. Initial tetrakis(triphenylphosphine)palladium‐catalyzed high‐temperature Suzuki–Miyaura cross‐coupling of 1‐chloro‐2‐nitrobenzene with 4‐chlorophenylboronic acid in a microtubular flow reactor at 160 °C using the tert‐butanol/water/potassium tert‐butoxide solvent/base system provides 4′‐chloro‐2‐nitrobiphenyl in high yield. After in‐line scavenging of palladium metal with the aid of a thiourea‐based resin, subsequent heterogeneous catalytic hydrogenation is performed over platinum‐on‐charcoal in a dedicated continuous‐flow hydrogenation device. The overall two‐step homogeneous/heterogeneous catalytic process can be performed in a single operation providing the desired 2‐amino‐4′‐chlorobiphenyl in good overall yield and high selectivity.     

Modelling of kinetics and mass transfer in the hydrogenation of xylose over Raney nickel catalyst

This paper discusses the modelling of xylose hydrogenation kinetics over Raney nickel in aqueous solutions, the determination of the hydrogen solubility in the reaction mixture as well as evaluation of mass transfer effects in the reaction system. The hydrogenation experiments were carried out batchwise in an automatic laboratory‐scale reactor. The reactor system operated at a pressure range of 40–70 bar and at temperatures between 80 and 140 °C. The catalyst‐to‐xylose ratio was approximately 5 wt‐% of the xylose weight normally. The reactor contents were analysed off‐line with a high performance liquid chromatograph. Hydrogen solubility in the reaction medium was determined with a gas‐chromatographic system. The solubility was found to remain fairly constant during the hydrogenation. Only a slight increase in the hydrogen solubility was detected as xylose was hydrogenated to xylitol. The overall hydrogen solubility in the reaction mixture was significantly lower than in pure water, as expected. The main hydrogenation product was xylitol, but small amounts of xylulose and arabinitol were detected as by‐products. A semi‐competitive kinetic model, based on hydrogen and xylose adsorption, was developed. The model accounts for the very different areas covered by a hydrogen atom and an organic species on the catalyst surface. The parameters of the kinetic model were determined with non‐linear regression analysis. It turned out that the kinetic model is able to describe the formation of both xylitol and the by‐products. The mass transfer effects in the batch hydrogenation were evaluated by using measured viscosities and estimated diffusion and mass transfer coefficients. A process simulator, utilizing the kinetic and mass transfer effects, was developed to predict the behaviour of industrial reactors. © 1999 Society of Chemical Industry     

Three‐Phase Nitrobenzene Hydrogenation over Supported Glass Fiber Catalysts: Reaction Kinetics Study

The catalytic properties of Pd and Pt supported on woven glass fibers (GF) were investigated in the three‐phase hydrogenation of nitrobenzene (NB). Over all catalysts, a 100 % yield of aniline was attained. The catalytic activity for the best catalysts was two times higher than the activity of commercial Pt/C catalyst traditionally used for liquid–phase hydrogenation. The intrinsic reaction kinetics were studied and a reaction scheme is suggested. The direct formation of aniline from NB was observed over Pd/GF with traces of intermediates. Four intermediate products were detected during aniline formation over Pt/GF: nitrosobenzene, phenylhydroxylamine, azoxybenzene, and azobenzene. The Eley‐Rideal kinetic model fits the experimental data well. The parameters of the model were determined as a function of initial NB concentration and hydrogen pressure. Pt and Pd supported on GF in woven fabrics are suggested as suitable materials for reactors with a structured catalytic bed in multi‐phase reactor performance.     

The hydrogenation of isophorone to trimethyl cyclohexanone using the downflow single capillary reactor

Despite many innovations in the intensification of catalytic multiphase reactors for the small and medium scale manufacture of chemicals, there have as yet been relatively few commercial successes. One reason for this might be that many of these developments inherently incorporate a fixed catalyst, which may not suit an industry that is based on principles of batch manufacture and multi-product plant. This study evaluates an intensified reactor that encompasses the opportunities demonstrated from structured flows and thin channels, together with a mobile, slurry catalyst, namely a capillary reactor with gas/liquid/suspended catalyst flow. A downflow single capillary reactor (SCR) was designed, built and evaluated for the selective hydrogenation of isophorone to trimethyl cyclohexanone using commercial Pd- and Rh-based catalysts. Using the single capillary arrangement, the reaction was shown to be operating under kinetic control.

Comparison of the rate of hydrogenation with autoclave showed a significant increase of the reaction rate when capillary reactor was used. The temperature of reaction is a crucial factor in tuning the reaction towards different products. The constant relative reaction rate obtained for different catalyst loading as well as the calculated value of the apparent activation energy show that the reaction of hydrogenation of isophorone is not mass transfer limited in the single capillary reactor.