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.     

Selective Oxidation of Methanol to Green Oxygenates – Feasibility Study of Fixed-Bed and Membrane Reactors

A feasibility study of a conventional fixed-bed reactor and a packed-bed membrane reactor (PBMR) in distributor configuration is carried out for the selective oxidation of methanol to the oxygenates dimethoxymethane and methyl formate on a VO_x/TiO₂ catalyst. Kinetic experiments provided the reaction network and a reliable kinetic model of six main reactions involved. The PBMR offers significant advantages and potential for the formation of both target products due to an effective kinetic coupling of the oxidative dehydrogenation of methanol and the consecutive reaction steps to dimethoxymethane and methyl formate in a broad range of operation conditions.     

Hydrogen production by methanol steam reforming carried out in membrane reactor on Cu/Zn/Mg-based catalyst

The methanol steam reforming (MSR) reaction was studied by using both a dense Pd-Ag membrane reactor (MR) and a fixed bed reactor (FBR). Both the FBR and the MR were packed with a new catalyst based on CuOAl₂O₃ZnOMgO, having an upper temperature limit of around 350 °C. A constant sweep gas flow rate in counter-current mode was used in MR and the experiments were carried out by varying the water/methanol feed molar ratio in the range 3/1–9/1 and the reaction temperature in the range 250–300 °C. The catalyst shows high activity and selectivity towards the CO₂ and the H₂ formation in the temperature range investigated. Under the same operative conditions, the MR shows higher conversions than FBR and, in particular, at 300 °C and H₂O/CH₃OH molar ratio higher than 5/1 the MR shows complete methanol conversion.     

Thermodynamic Analysis for Quantifying Fuel Cell Grade H2 Production by Methanol Steam Reforming

Steam reforming of methanol in fixed‐bed and hybrid reactors, namely, traditional fixed‐bed reactor (FBR1), fixed‐bed reactor with H₂‐selective membrane (FBR2), and fixed‐bed reactor with CO₂ adsorption (FBR3) is thermodynamically analyzed. The performance of these reactors is compared in terms of quality and quantity of H₂ production for fuel cell application. In FBR2 and FBR3, the contents of undesired products CO, CH₄, and carbon are highly reduced.     

Performance of a multi-slit packed bed microstructured reactor in the synthesis of methanol: Comparison with a laboratory fixed-bed reactor

The performance of a multi-slit Integrated Micro Packed Bed Reactor-Heat Exchanger (IMPBRHE) for methanol synthesis from synthesis gas over Cu/ZnO/support commercial catalyst was experimentally investigated from a reaction engineering perspective. Through establishment of a systematic comparison strategy, performance comparison with a laboratory scale tubular Fixed-Bed Reactor (FBR) with three different dilution ratios was made to evaluate the IMPBRHE. The productivity, thermal behavior, activity of body materials, pressure drop and residence time distribution (RTD) of the two reactor types were investigated. The IMPBRHE outperformed the undiluted FBR and gave CO conversions comparable to the diluted FBRs. The main difference is ascribed to superior heat exchange properties of the IMPBRHE, which can improve reactor performance for an exothermic reaction such as methanol synthesis. The results reveal advantages of the IMPBRHE for robust scale up.     

Determination of Optimum Conditions and the Kinetics of Methanol Oxidation

In this study, the catalytic oxidation of methanol to formaldehyde was investigated in a laboratory‐scale fixed‐bed catalytic reactor, under a large number of different conditions. Iron‐molybdate catalysts supported by silica or alumina with a molybdenium/iron (Mo/Fe) ratio of 1.5, 3 and 5 were studied for the gas phase reaction. In order to obtain the optimum conditions, six different temperatures in the range of 250–375 °C and three different space times of 50.63, 33.75 and 20.25 g/(mol/h) were investigated. After determining the optimum conditions for this reaction, experiments aimed at understanding the reaction kinetics, were carried out. These experiments were performed on the catalyst favoring the formation of formaldehyde, which has a (Mo/Fe) ratio of 5 on a silica support. Seven reaction models derived by the mechanisms cited in the literature were tested to elucidate the kinetics of the reaction and the surface reaction controlling model was found to be the most suitable reaction mechanism.     

在Pb-Bi-La-Mo/SiO_2催化剂上甲醇氧化的内扩散影响及甲醇扩散系数和催化剂曲折因子的测定

在30-40目的Pb_(0.88)Bi_(0.06)La_(0.02)Mo/SiO_2催化剂上甲醇氧化制甲醛的反应在动力学区域进行,其速度规律服从二步骤Redox机理动力学方程.当催化剂增大到3mm时,其动力学方程受内扩散影响严重,实验上测定了催化剂有效因子在0.28—0.12之间.作者对甲醇内扩散控制时的Redox机理动力学方程进行了理论上的推导和实验上的验证.实验上测定了受内扩散控制时的反应活化能,并从理论上指出动力学区域与内扩散区域活化能的关系.用动力学方法测定了甲醇在给定反应条件下的扩散系数和曲折因子.     

Kinetics of the catalytic oxidation of methanol to formaldehyde

The kinetics of the oxidation of methanol to formaldehyde, over iron molybdate as catalyst, have been studied. The kinetic runs have been performed with a CSTR reactor.The results can be described with a kinetic model derived on the basis of a redox mechanism partially hindered by the adsorption of water. The low temperatures used in the reactor (200–250°C) favour the formation of by-products, as dimetoxymethane, dimethyl ether and methylformate.     

Hydrogen generation and purification in a composite Pd hollow fiber membrane reactor: Experiments and modeling

“Pd nanopore” composite membranes are a novel class of H₂ permselective membranes in which a thin layer of Pd is grown within the pores of a supported nanoporous layer. In this work, Pd nanopore membranes and conventional Pd top-layer membranes were used in the generation of high-purity H₂ from the catalytic decomposition of anhydrous NH₃. An effective 4 μm thick Pd nanopore membrane and 13 μm thick Pd top-layer membrane were synthesized on 2 mm O.D. α-Al₂O₃ hollow fibers. The permeation features of the membranes were determined and the membranes were then employed in a single fiber packed-bed membrane reactor in which Ni-catalyzed NH₃ decomposition served as the test reaction, with conditions spanning a range of conditions (500–600 °C; 3–5 bar total retentate pressure; 60–1200 scc/h g cat space velocity). The NH₃ conversions in both the PBMRs were approximately 10% higher than in a packed-bed reactor (PBR) under similar conditions. The increase in conversion with the PBMR was attributed to the removal of H₂, which has an inhibitory effect on the forward kinetics of the reaction as per the Temkin-Pyzhev type rate mechanism. Reactor productivities in the range of 2 mol/s m³ (at 85% H₂ utilization) to 7 mol/s m³ (at 50% H₂ utilization) were obtained. The permeate stream purity exceeded 99.2% H₂. A two-dimensional pseudo-homogeneous model was successfully used to simulate the experimental results and to interpret the findings. Permeation and kinetic parameters were estimated in permeation and PBR experiments, respectively. Without any data fitting the PBMR model predictions demonstrated very good agreement with experimental trends. Together with an analysis of the characteristic times, the model determined that transverse transport of hydrogen in the catalyst bed limited PBMR performance. The model was used to determine the rate limiting step and to suggest ways in which the reactor productivities could be further improved.     

A comparative study of a fluidised bed reactor and a gas lift loop reactor for the ibe process: Part III. Reactor performances and scale Up

Continuous fermentations using Clostridium spp. DSM 2152 immobilised in calcium alginate beads to produce butanol and isopropanol from glucose were carried out in a fluidised bed reactor with liquid recycle (FBR, 10.9 dm³ working volume, 41 % solids) and in a gas lift loop reactor (GLR, 11.4 dm³ working volume, 32% solids). In the FBR in-situ produced non-coalescing gas bubbles had a negligible influence on the fluidisation pattern and the steady state results of the fermentation were in accordance with those predicted by a reactor model. The FBR was operated reliably for 5 weeks without decrease of activity. The GLR behaved as a three phase reactor because of the recycled fermentation gas. The steady state fermentation results were as predicted by the GLR model. Scale up to a 50 m³ FBR and a 65 m³ GLR led to development of a plug flow with recycle model for the FBR and a stirred tank model for the GLR. On the basis of overall reactor performance and ease of integration with a simultaneous product recovery the FBR is preferred to the GLR for application in a large scale butanol/isopropanol process using immobilised Clostridia spp.     

Selective Oxidation of Methanol to Formaldehyde Using Modified Iron-Molybdate Catalysts

Methanol selective oxidation to formaldehyde over a modified Fe-Mo catalyst with two different stoichiometric (Mo/Fe atomic ratio = 1.5 and 3.0) was studied experimentally in a fixed bed reactor over a wide range of reaction conditions. The physicochemical characterization of the prepared catalysts provides evidence that Fe₂(MoO₄)₃ is in fact the active phase of the catalyst. The experimental results of conversion of methanol and selectivity towards formaldehyde for various residence times were studied. The results showed that as the residence time increases the yield of formaldehyde decreases. Selectivity of formaldehyde decreases with increase in residence time. This result is attributable to subsequent oxidation of formaldehyde to carbon monoxide due to longer residence time.     

Formaldehyde biodegradation in the presence of methanol under denitrifying conditions

Simultaneous formaldehyde and methanol biodegradation and also denitrification were studied in batch assays and in a continuous laboratory‐scale reactor. In batch assays, high formaldehyde concentrations (up to 1360 mg dm^?3) were removed under anoxic conditions in the presence of methanol. It was found that formaldehyde biodegradation produced methanol and formic acid as products. The denitrification process was affected by the initial formaldehyde concentration. In the continuous reactor, the biodegradation of different concentrations of formaldehyde (1500–275 mg dm^?3) and methanol (153–871 mg dm^?3) took place, maintaining the organic loading rate at 0.84 g COD dm^?3 d^?1 (COD/N 4). However, each increase in the methanol concentration in the influent caused a decrease in the denitrification level. An adaptation period to methanol was necessary before the denitrification percentage could be recovered. In contrast with batch assays, in the continuous reactor methanol and formic acid were not detected in the effluent. Moreover, in the continuous reactor the denitrification percentages were higher and the nitrite accumulation was lower. Copyright © 2005 Society of Chemical Industry     

Modeling and process simulation of hollow fiber membrane reactor systems for propane dehydrogenation

We report a detailed modeling analysis of membrane reactor systems for propane dehydrogenation (PDH), by integrating a two‐dimensional (2‐D) nonisothermal model of a packed bed membrane reactor (PBMR) with ASPEN process simulations for the overall PDH plant including downstream separations processes. PBMRs based on ceramic hollow fiber membranes—with catalyst placement on the shell side—are found to be a viable route, whereas conventional tubular membranes are prohibitively expensive. The overall impact of the PBMR on the PDH plant (e.g., required dimensions, catalyst amount, overall energy use in reaction and downstream separation) is determined. Large savings in overall energy use and catalyst amounts can be achieved with an appropriate configuration of PBMR stages and optimal sweep/feed ratio. Overall, this work determines a viable design of a membrane reactor‐based PDH plant and shows the potential for miniaturized hollow‐fiber membrane reactors to achieve substantial savings. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4519–4531, 2017     

Acetaldehyde dimethylacetal synthesis with Smopex 101 fibres as catalyst/adsorbent

The synthesis of dimethylacetal using acetaldehyde and methanol as raw material in the presence of Smopex 101 fibres as catalyst and adsorbent in batch reactor and in a fixed bed adsorptive reactor, respectively, was studied. In the batch reactor the determination of thermodynamic and reaction kinetics data for acetalization reaction was presented. A kinetic model based on a pseudo-homogeneous rate expression using activities was proposed to describe the experimental kinetic results. The dynamic binary adsorption experiments were carried out in the absence of reaction at 293.15 K in a laboratory scale column. The experimental results of the adsorption of binary non-reactive mixtures are reported and used to obtain multi-component adsorption equilibrium isotherms of Langmuir type. The mathematical model was proposed to describe the adsorptive reactor dynamic behaviour. The experimental results obtained for the reaction and regeneration experiments were compared with the model proposed. Model equations were solved by orthogonal collocation on finite elements (OCFE) implemented by the PDECOL package, using the measured model parameters and was validated for both reaction and regeneration steps.     

Influence of the process parameters on temperature conditions and productivity of multitubular reactor for methanol to formaldehyde oxidation

The results of the parametric analysis of the methanol oxidation to formaldehyde on the basis of the kinetic model of reactions on an iron-molybdenum oxide catalyst and the two-dimensional model of a multitubular reactor were reported in the paper. The results of kinetic experiments on an industrial Fe-Mo granular catalyst were given. Calculation results were compared with industrial data. The possibilities of controlling the methanol oxidation to formaldehyde in multitubular reactors at varied plant unit productivity with consideration for process restrictions were theoretically studied. The effect of parameters on the temperature and concentration conditions in reactors at different ratios of catalyst and inert material loads was studied.     

The effect of nanoparticle morphology in the filtration efficiency and saturation of a silicon beads fluidized bed

Polysilicon is a key commodity required for both electronics and solar photovoltaic modules. The traditional route to produce polysilicon involves the Siemens reactor, an energy intensive batch process. A more efficient, but more complex alternative process is the fluidized bed reactor (FBR). In an FBR silane is pyrolysed producing chemical vapor deposition (CVD) and aerosols. Efficient FBR operation requires yield optimization together with continuous and stable operation of the reactor. Such optimization is not straightforward because the aerosol formation mechanisms and incorporation into the FBR beads are not completely understood. In this work, two model aerosols with different morphology were tested and their filtration efficiency between 20 and 800 nm was determined. Bead saturation at different times was determined for each morphology and the scavenging factor over time for each case is reported. Such information can be of interest for establishing bed recirculation needs in a silicon FBR.     

Synthesis of methylal by catalytic distillation

Methylal is an important raw material and an excellent solvent in industry. The conventional methods for the synthesis of methylal have drawbacks such as corrosion to the equipments, catalyst isolation, high molar ratio of methanol to formaldehyde and high cost of equipments. To overcome these drawbacks, the synthesis of methylal was investigated in a pilot scale catalytic distillation column using Sulzer BX and the structured catalytic packing Katapak-SP 12 in the present study. The reaction was catalyzed by polystyrene based macroporous cation exchange resin (D72) which was filled in the catalystic layers of the structured packings. The effects of operating parameters such as reflux ratio, total feed rate, molar ratio of methanol to formaldehyde, catalyst weight, aqueous formaldehyde concentration were studied experimentally. The appropriate operating parameters obtained in the present study include: reflux ratio is 5; total feed rate is 3.10 kg/h; molar ratio of methanol to formaldehyde is 2.5, catalyst weight is 0.51 kg, aqueous formaldehyde concentration is 35.3%. Under the above operating conditions the average conversion of formaldehyde is 99.6% while the average methylal purity is 92.1%. In order to achieve higher purity of methylal at the top of the column, two different configurations: feeding aqueous formaldehyde and feeding water at mid-way of rectifying section, was tried in the experiments. The experimental results show that the former configuration surpasses the latter, under which the average conversion of formaldehyde is 99.8% and the average methylal purity is 99.1%.     

Dynamic modelling of a gas phase catalytic fixed-bed reactor—I: Experimental apparatus and determination of reaction kinetics

A large scale fixed bed pilot reactor for performing dynamic experiments is described. The reactor system is especially designed to suppress secondary dispersion effects not characteristic for the packed bed itself.As a model reaction the reaction between oxygen (<1%) and hydrogen on a platinum catalyst supported by alumina has been used.Differential reactor experiments disclosed a hysteresis phenomenon in the catalyst activity. The catalyst is generally more active when going from high to low temperatures than vice versa.A global first order reaction rate expression with Arrhenius temperature dependency fits the fixed-bed reactor profiles well but the static gains badly. However by simultaneous estimation of frequency factor and activation energy in several axial segments a much better approximation to the static gains was obtained. This result indicates that the reaction kinetics is more complicated than first assumed. However for dynamic modelling the exact reaction mechanism is not needed.     

Synthesis of MTBE in zeolite membrane reactors

A zeolite membrane was employed to selectively remove water from the reaction atmosphere during the gas-phase synthesis of methyl-tert-butyl ether (MTBE) from tert-butanol and methanol. This reaction was carried out over a bed of Amberlyst™ 15 catalyst packed on the inside of a zeolite tubular membrane. The results obtained with different hydrophilic membranes (mordenite or NaA zeolite) are presented. Prior to reaction, the zeolite membranes were characterized by measuring their performance in the separation of the equilibrium mixture containing water, methanol, tert-butanol, MTBE and isobutene. The results obtained with zeolite membrane reactors (ZMR) were compared with those of a fixed bed reactor (FBR) under the same operating conditions. MTBE yields obtained with the ZMR at 334 K reached 67.6%, under conditions where the equilibrium value without product removal (FBR) would be 60.9%.     

具有基质抑制的流加反应器计算机模拟和优化

以单位时间内获得尽可能多的细胞生物量为目标函数,建立了流加反应器最优化模型。通过引入哈密尔顿函数和庞特雅金最小值原理,求解了这个最优化模型。此外,以安德鲁方程为例,还对几种特殊的流加反应器进行了计算机模拟,并给出了最优化计算结果。