Fixed-bed Membrane Reactor Research Articles

Simultaneous isobutane dehydrogenation and hydrogen production in a hydrogen-permselective membrane fixed bed reactor

In this study, performance of hydrogen-permselective membrane fixed bed reactors to produce isobutene is studied at steady state condition. The proposed reactors have been modeled heterogeneously based on the mass and energy conservation laws. The considered reaction networks in the model are isobutene dehydrogenation as the main reaction, and hydrogenolysis, propane dehydrogenation as well as coke formation as side reactions that all occur on the catalyst surface. The coke deposition on the catalyst surface results an activity profile along reactors. The reactions occur in the tube side and the hydrogen permeates from the reaction zone to the sweep gas stream. Decreasing the hydrogen concentration over the catalyst pellets improves isobutane conversion and isobutene selectivity. To prove the performance of the proposed configuration, simulation results for membrane process are compared with the conventional process at the same operating condition. In this configuration, the isobutene production rate is enhanced about 10.81% compared to the conventional process at the same catalyst loading.

Computational study of Pd-membrane CH4 steam reformer with fixed catalyst bed: Searching for a way to increase membrane efficiency

This paper focuses on the feasibility of coupling a Pd-alloy composite membrane with specially structured catalytic bed for SMR at realistic operating and design conditions. The practical aim is computational design of a compact fuel processor, capable to produce 3–4 kg/h of high purity hydrogen (100–130 kW total power) for PEM FC applications. The research goal is searching for a way to increase membrane efficiency by facilitating hydrogen transport across the catalyst bed (suppressing concentration polarization phenomena) that greatly deteriorates fixed-bed membrane reactor (MR) performance. A pseudo-2D model is developed to analyze the operation of different MR types: tube-in-tube or sandwich-type, granular or structured catalyst with Ni or Rh as active component. In order to overcome mass and heat transport limitations a novel type of catalyst support, closed-cross-flow-structure (CCFS) was incorporated in the MR model. The significant increase of MR efficiency was predicted after replacement of 8%Ni/Al2O3 coating by 1%Rh/Al2O3 catalyst. The potential advantages of the suggested MR type are shown to be effectively realized in case of ultra-thin Pd membrane 4.5 μm with extremely high MR output productivity >4 kg(H2)/h/m2.

Enhancement of pure hydrogen production through the use of a membrane reactor

Pure hydrogen production is of great interest as it is an energy carrier which can be used in PEM fuel cells for power production. Methane Steam Reforming (MSR) is commonly used for hydrogen production although the produced hydrogen is not free of other components. Membrane Reactors (MR) enable a pure hydrogen product stream and allows the reaction to take place at significantly lower temperatures (lower than 550 °C) than in conventional reactors (greater than 800 °C) with comparable methane conversion. This is achieved by hydrogen removal through a permselective Pd–Ag based membrane that cause a favorable shift in chemical equilibrium towards hydrogen production. In the present study, a two-dimensional, nonlinear, and pseudo-homogeneous mathematical model of a catalytic fixed-bed membrane reactor for methane steam reforming over a nickel-based foam supported catalyst is presented. Simulated results referring to the distribution of species, methane conversion, temperature and hydrogen flowrate along the reactor for different radial positions are obtained and analyzed. The performance of structured catalyst and catalyst supported on foam configurations under the same operating conditions is also studied. Experimental results for the membrane facilitate the identification of suitable operating conditions.

Simultaneous Isobutane Dehydrogenation and Hydrogen Production in a Hydrogen–Permselective Membrane Fixed Bed Reactor

Simultaneous Isobutane Dehydrogenation and Hydrogen Production in a Hydrogen–Permselective Membrane Fixed Bed Reactor

A fixed-bed reactor modeling study on the methanation of CO2

The methanation of carbon dioxide has gained renewed interest during the last years as a possible technology to synthesize a feasible chemical energy carrier. This modeling study aims at a basic understanding of the aspects relevant for designing an externally cooled fixed-bed reactor for the methanation of a pure, stoichiometric feed gas. It is shown that the reaction rates and the exothermicity (ΔH°=−165kJ/mol) prevent a fixed-bed reactor of technical dimensions to be operated at high conversions without runaway of the reactor. The model predictions of differently detailed pseudo-homogeneous reactor models and a heterogeneous reactor model where the intraparticle transport of mass is described according to a dusty-gas approach are compared to assess the needed level of detail in terms of modeling the heat transfer, fluid flow characteristics and transport resistances on the pellet scale. Under specific conditions, intraparticle mass transfer and external heat transfer need to be considered for describing the temperature and concentration profiles adequately. The study is completed by modeling a fixed-bed membrane reactor as an example of a structured reactor that offers improved temperature control by separated and controlled feeding of hydrogen and carbon dioxide.

Biodiesel Production from Soybean Oil in a Membrane Reactor over Hydrotalcite Based Catalyst: An Optimization Study

Transesterification of soybean oil to produce biodiesel was performed in a membrane reactor packed with shaped KF/Ca–Mg–Al hydrotalcite solid base. The microfiltration ceramic membrane (length: 20 cm, inner/outer diameter: 6/10 mm) was used to retain the oil during the transesterification reaction. High quality biodiesel was produced in the fixed bed membrane reactor by coupling heterogeneous alkali catalyzed transesterification and separation process. The response surface methodology (RSM) was employed to evaluate the effects of such factors as reaction temperature, catalyst amount, and circulation velocity on biodiesel production. 70 °C reaction temperature, 0.531 g/cm3 catalyst amount and 3.16 mL/min circulation velocity was found to be the optimum condition, achieving a 0.1820 g/min biodiesel yielding rate during 150 min of circulation time.

A comparison of co-current and counter-current modes for Fischer–Tropsch synthesis in two consecutive reactors of oxidative coupling of methane and Fischer–Tropsch

The results of three cases of two consecutive reactors are studied in two types of co-current and counter-current flow in second reactor where two consecutive reactors are oxidative coupling of methane (OCM) and Fischer–Tropsch (FT) reactors. FT reactor can be fixed bed or membrane fixed bed reactor with a hydrogen perm-selective membrane. Effect of CH4/O2 ratio, contact time, inlet temperature, and amount of N2 in OCM feed on C2 to C5+ hydrocarbons produced in FT reactor were studied. Results show that use of counter-current hydrogen-perm selective membrane FT reactor that sequenced after OCM reactor improves the C5+ yield as a desirable product and reduces the amount of CH4 and CO2 as byproducts of FT reactor in comparison to co-current and conventional reactor. This phenomenon can be explained with more H2 diffusion through the membrane and more CO conversion and more hydrocarbons productions, briefly. As compared to the conventional reactor, in co-current and counter-current reactors, yield of C5+ has increased almost 3% and 4% alternatively when using these systems.

Dynamic modeling of a H2O-permselective membrane reactor to enhance methanol synthesis from syngas considering catalyst deactivation

In this paper, the effect of water vapor removal on methanol synthesis capacity from syngas in a fixed-bed membrane reactor is studied considering long-term catalyst deactivation. A dynamic heterogeneous one-dimensional mathematical model that is composed of two sides is developed to predict the performance of this configuration. In this configuration, conventional methanol reactor is supported by an alumina-silica composite membrane layer for water vapor removal from reaction zone. To verify the accuracy of the considered model and assumptions, simulation results of the conventional methanol reactor is compared with the industrial plant data under the same process condition. The membrane reactor improves catalyst life time and enhances CO2 conversion to methanol by overcoming the limitation imposed by thermodynamic equilibrium. This configuration has enhanced the methanol production capacity about 4.06% compared with the industrial methanol reactor during the production time.

Fixed bed membrane reactors for WGSR-based hydrogen production: Optimisation of modelling approaches and reactor performance

The production of high-purity hydrogen using the water–gas-shift reaction in both conventional fixed bed reactor and hydrogen perm-selective membrane reactor at low to medium scale is studied in this work by developing and comparing models with different complexity levels. A two-dimensional rigorous reactor model considering radial and axial variations of properties (including bed porosity), setting mass, energy and momentum differential balances, and nesting a rigorous model for mass transfer within the porous catalyst was considered as reference for comparison. Different simplifications of this model for taking into account mass-transfer effects within the catalyst pellet (Thiele modulus, evaluation of apparent kinetic constants, empirical correlation for effectiveness factors or just neglecting these effects) were tested, being observed that these effects are not negligible and that the first two approaches are accurate enough for taking into account mass transfer within catalyst pellets. Regarding to the reactor model, it was observed that one-dimensional models are not adequate, especially for the membrane reactor. Analogously, neglecting the momentum balances in the reactor (as made is most simulations reported in the literature) leads to important misspredictions in the behaviour of the membrane reactor performance. Finally, the influence of the main operation parameters (inlet temperature, pressure, space velocity, etc.) was studied using the detailed reactor model, concluding that space velocity and pressure are the most important parameters affecting reactor performance for membrane reactors.

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.

Enhancement of DME Production in an Optimized Membrane Isothermal Fixed-Bed Reactor

Dimethyl ether is a colorless gas at the ambient condition that is easily liquefied under light pressure. Currently, DME as a green fuel has been suggested as one of the most promising candidates for substitution of LPG and diesel fuel. In this paper, a water cooled membrane fixed bed reactor is proposed and modeled heterogeneously for large scale production of DME from methanol dehydration. The proposed reactor is modeled one-dimensionally based on mass and energy conservation laws at steady state condition. Also, the efficacy of the proposed membrane reactor is investigated and the results of the proposed reactor are compared with an isothermal and commercial adiabatic reactor. The simulation results of the proposed membrane reactor indicate that the methanol conversion is improved about 6.2 percent compared to the conventional industrial reactor. Also, water vapor removal from reaction zone in the membrane reactor yields lower water concentration over the catalyst pellets and higher quality of outlet product. These can lead to higher catalyst lifetime and lower cost in purification stage.

Enhancement of DME Production in an Optimized Membrane Isothermal Fixed-Bed Reactor

Dimethyl ether is a colorless gas at the ambient condition that is easily liquefied under light pressure. Currently, DME as a green fuel has been suggested as one of the most promising candidates for substitution of LPG and diesel fuel. In this paper, a water cooled membrane fixed bed reactor is proposed and modeled heterogeneously for large scale production of DME from methanol dehydration. The proposed reactor is modeled one-dimensionally based on mass and energy conservation laws at steady state condition. Also, the efficacy of the proposed membrane reactor is investigated and the results of the proposed reactor are compared with an isothermal and commercial adiabatic reactor. The simulation results of the proposed membrane reactor indicate that the methanol conversion is improved about 6.2 percent compared to the conventional industrial reactor. Also, water vapor removal from reaction zone in the membrane reactor yields lower water concentration over the catalyst pellets and higher quality of outlet product. These can lead to higher catalyst lifetime and lower cost in purification stage.

Modeling and simulation of an integrated multi-shell fixed bed membrane reactor with well-mixed catalyst pattern for production of styrene and cyclohexane

A rigorous two-dimensional steady state mathematical model based on the dusty gas model is implemented to investigate the performance of a bench-scale integrated multi-shell fixed bed membrane reactor with well-mixed catalyst pattern for simultaneous production of styrene and cyclohexane. Since the styrene producing reaction is equilibrium limited, significant displacement of the thermodynamic equilibrium is achieved by three simultaneous actions of an auxiliary hydrogenation reaction of benzene using a well-mixed catalyst pattern, the membrane and the multi-shell reactor configuration. The simulation results show that the complete conversion of ethylbenzene is possible at relatively low temperature and shorter reactor length. Effective operating regions with optimal conditions are observed and explanations offered. An effective length criterion for the optimal conditions is presented. The effective operating regions are found to be sensitive to changes of catalyst bed composition, feed temperature, feed pressure and shells ratio. It is also found that the multi-shell configuration is superior to the single shell configuration. Although this investigation is restricted to two catalysts and two shells, some of the rich characteristics of this system have been uncovered.

Application of water vapor and hydrogen-permselective membranes in an industrial fixed-bed reactor for large scale methanol production

Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the next stages. In this work a novel reactor consisting two membrane layers has been proposed for simultaneous hydrogen permeation to reaction zone and water vapor removal from reaction zone in the methanol synthesis reactor. In this configuration conventional methanol reactor is supported by a Pd/Ag membrane layer for hydrogen permeation and alumina–silica composite membrane layer for water vapor removal from reaction zone. In this reactor syngas is fed to the reaction zone that is surrounded with hydrogen-permselective membrane tube. The water vapor-permselective membrane tube is placed in the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed for simulation of the proposed reactor. To verify the accuracy of the model, simulation results of the conventional reactor is compared with the available plant data. The membrane fixed bed reactor benefits are higher methanol production rate, higher quality of outlet product and consequently lower cost in product purification stage. This configuration has enhanced the methanol yield by 10.02% compared with industrial reactor. Experimental proof-of-concept is needed to establish the safe operation of the proposed configuration.

A novel water perm-selective membrane dual-type reactor concept for Fischer–Tropsch synthesis of GTL (gas to liquid) technology

Abstract The present study proposes a novel configuration of Fischer–Tropsch synthesis (FTS) reactors in which a fixed-bed water perm-selective membrane reactor is followed by a fluidized-bed hydrogen perm-selective membrane reactor. This novel concept which has been named fixed-bed membrane reactor followed by fluidized-bed membrane reactor (FMFMDR) produces gasoline from synthesis gas. The walls of the tubes of a fixed-bed reactor (water-cooled reactor) of FMFMDR configuration are coated by a high water perm-selective membrane layer. In this new configuration, two membrane reactors instead of one membrane reactor are developed for FTS reactions. In other words, two different membrane layers are used. In order to investigate the performance of FMFMDR, a one-dimensional heterogeneous model is taken into consideration. The simulation results of three schemes named fluidized-bed membrane dual-type reactor (FMDR), FMFMDR and conventional fixed-bed reactor (CR) are presented. They have been compared in terms of temperature, gasoline and CO 2 yields, H 2 and CO conversions and the water permeation rate through the membrane layer. Results show that the gasoline yield in FMFMDR is higher than the one in FMDR. The FMFMDR configuration not only decreases the undesired product such as CO 2 but also produces more gasoline.

Dimethyl Ether Synthesis with in situ H2O Removal in Fixed-Bed Membrane Reactor: Model and Simulations

The potential and limits of in situ removal of water under dimethyl ether (DME) synthesis conditions in a fixed-bed membrane reactor were studied numerically. The motivation for in situ H2O removal during DME synthesis by means of hydrophilic membranes is to displace the water−gas shift equilibrium to enhance conversion of CO2 into methanol to improve DME productivity. In CO-rich feeds, methanol yield/selectivity increases/decreases slowly with increasing H2O permeance because only small amounts of water are removed from the system. Methanol dehydration is not inhibited by water, and DME selectivity is not improved significantly with increasing H2O permeance. When CO is gradually replaced with CO2, with the increase of H2O membrane permeance and H2O removal, methanol yield and DME selectivity are favored and the fraction of unconverted methanol is reduced as the dehydration reaction is accelerated due to reduced kinetic inhibition by H2O.

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.

A comparison of co-current and counter-current modes of operation for a novel hydrogen-permselective membrane dual-type FTS reactor in GTL technology

In this work, a comparison of co-current and counter-current modes of operation for a novel hydrogen-permselective membrane reactor for Fischer–Tropsch Synthesis (FTS) has been carried out. In both modes of operations, a system with two-catalyst bed instead of one single catalyst bed is developed for FTS reactions. In the first catalytic reactor, the synthesis gas is partly converted to products in a conventional water-cooled fixed-bed reactor, while in the second reactor which is a membrane fixed-bed reactor, the FTS reactions are completed and heat of reaction is used to preheat the feed synthesis gas to the first reactor. In the co-current mode, feed gas is entered into the tubes of the second reactor in the same direction with the reacting gas stream in shell side while in the counter-current mode the gas streams are in the opposite direction. Simulation results for both co-current and counter-current modes have been compared in terms of temperature, gasoline and CO 2 yields, H 2 and CO conversion, selectivity of components as well as permeation rate of hydrogen through the membrane. The results showed that the reactor in the co-current configuration operates with lower conversion and lower permeation rate of hydrogen, but it has more favorable profile of temperature. The counter-current mode of operation decreases undesired products such as CO 2 and CH 4 and also produces more gasoline.

High throughput multiscale modeling for design of experiments, catalysts, and reactors: Application to hydrogen production from ammonia

A novel approach for design of experiments (DOE) is outlined that combines high throughput multiscale modeling, sensitivity analysis, and information extraction from massive computational data using informatics tools. This approach is implemented by conducting experiments of ammonia decomposition on a Ru/γ-Al 2O 3 catalyst in a fixed bed reactor. It is shown that a relatively small number of experiments chosen from this new DOE approach can enable refinement of microkinetic models and render them predictive over the (large) experimentally important parameter space. Microkinetic models are subsequently used for process and product design. Specifically, a membrane fixed bed reactor is simulated and is shown to outperform the conventional fixed bed reactor at intermediate temperatures for hydrogen production. Also, the attributes of the best catalyst for ammonia decomposition are identified as a function of processing conditions. It is shown that for NH 3 decomposition, processing conditions do not significantly affect the best catalyst choice. In contrast, fundamental physicochemical phenomena, such as adsorbate–adsorbate interactions, can have a profound effect on catalyst discovery.

Design of a thermally balanced membrane reformer for hydrogen production

AbstractHydrogen production by autothermal methane steam reforming in a catalytic fixed bed membrane reactor has been analyzed and simulated. The two‐compartment reactor indirectly couples the endothermic steam reforming with methane oxidation, while hydrogen is separated by a permselective Pd membrane. Simulations of the reactor, using published kinetics, map the acceptable domain of operation and the optimal set of operating parameters. The simulations exhibit slow‐moving thermal fronts and the steady‐state operation domains bounded by stationary fronts, separating domains of upstream and downstream‐moving fronts. Front velocity depends on thermal coupling and hydrogen separation. An analytical approximation for the thermal front velocity in a thermally balanced reactor has been developed. © 2008 American Institute of Chemical Engineers AIChE J, 2008