Performance Of Membrane Reactor Research Articles

Solar membrane natural gas steam‐reforming process: evaluation of reactor performance

AbstractIn this work, the performance of an innovative plant for efficient hydrogen production using solar energy for the process heat duty requirements has been evaluated via a detailed 2D model. The steam‐reforming reactor consists of a bundle of coaxial double tubes assembled in a shell. The annular section of each tube is the reaction zone in which Ni‐based catalyst pellets are packed, whereas the inner tube is a dense Pd‐based selective membrane that is able to remove hydrogen from the reaction zone. By coupling reaction and hydrogen separation, equilibrium constrains inside the reactor are circumvented and high methane conversions at relatively low temperatures are achieved. The heat needed for the steam‐reforming reaction at this low operating temperature can be supplied by using a molten salt stream, heated up to 550 °C by a parabolic mirror solar plant, as heating fluid. The effects on membrane reactor performance of some operating conditions, as gas mixture residence time, reaction pressure and steam‐to‐carbon ratio, are assessed together with the enhancement of methane conversion with respect to the traditional process, evaluated in the range 40.5–130.9% at the same operating conditions. Moreover, owing to the use of a solar source for chemical process heat duty requirements, the greenhouse gases (GHG) reduction is estimated to be in the range 33–67%. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Theoretical study of a membrane reactor for the water gas shift reaction under nonisothermal conditions

AbstractA simulation of a membrane reactor for the water gas shift reaction is carried out by means of a 1D pseudo‐homogeneous nonisothermal mathematical model. The composite membrane consists of a dense layer of Pd (selective to H2) supported over a porous ceramic layer. The effect of temperature, overall heat‐transfer coefficient, and mode of operation on the membrane reactor performance and stability are analyzed, and the results obtained are compared with those corresponding to a reactor with no hydrogen permeation. © 2009 American Institute of Chemical Engineers AIChE J, 2009

The esterification of acetic acid with ethanol in a pervaporation membrane reactor

Pervaporation membrane reactors are the systems in which the separation and reaction are carried out simultaneously in order to increase conversions by removing one or more of the products formed during equilibrium reactions. In this study the esterification reaction of acetic acid and ethanol to produce ethyl acetate and water was investigated using a batch pervaporation membrane reactor. The experiments were carried out in the temperature range of 50–70°C. The ratios of ethanol concentration to acetic acid concentration were chosen as 1 and 1.5. Amberlyst 15 and sulfuric acid were used as the catalysts. Polydimethylsiloxane (PDMS) prepared in our labs was used as the membrane material, permselective to ethyl acetate formed by reaction. In this way, conversions were increased by continuous removal of ethyl acetate from the reaction media. Conversions are found to increase with an increase in both molar ratios of reactants and temperature. Temperature has a strong influence on the performance of the pervaporation membrane reactor because it acts on both the esterification kinetics and pervaporation.

Design of mixed conducting ceramic membranes/reactors for the partial oxidation of methane to syngas

AbstractThe performance of mixed conducting ceramic membrane reactors for the partial oxidation of methane (POM) to syngas has been analyzed through a two‐dimensional mathematical model, in which the material balance, the heat balance and the momentum balance for both the shell and the tube phase are taken into account. The modeling results indicate that the membrane reactors have many advantages over the conventional fixed bed reactors such as the higher CO selectivity and yield, the lower heating point and the lower pressure drop as well. When the methane feed is converted completely into product in the membrane reactors, temperature flying can take place, which may be restrained by increasing the feed flow rate or by lowering the operation temperature. The reaction capacity of the membrane reactor is mainly determined by the oxygen permeation rate rather than by the POM reaction rate on the catalyst. In order to improve the membrane reactor performance, reduction of mass transfer resistance in the catalyst bed is necessary. Using the smaller membrane tubes is an effective way to achieve a higher reaction capacity, but the pressure drop is a severe problem to be faced. The methane feed velocity for the operation of mixed conducting membrane reactors should be carefully regulated so as to obtain the maximum syngas yield, which can be estimated from their oxygen permeability. The mathematical model and the kinetic parameters have been validated by comparing modeling results with the experimental data for the La0.6Sr0.4Co0.2Fe0.8O3‐α (LSCF) membrane reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Simulation of Catalytic Dehydrogenation of Cyclohexane in Zeolite Membrane Reactor

A mathematical model is presented to investigate the performance of tubular catalytic membrane reactor for dehydrogenation of cyclohexane using a FAU type zeolite membrane. The empirical correlations for the permeance of cyclohexane, benzene and hydrogen through FAU type zeolite membrane as a function of temperature have been developed. Three reactor configurations have been considered: conventional fixed bed, full length membrane reactor and hybrid reactor. The reactor performance has been studied in terms of conversion of cyclohexane to produce hydrogen. The observed conversions are ranked in the order: full length membrane reactor > hybrid reactor > fixed bed reactor. The simulation studies have been carried out for two feed conditions: one with hydrogen and another without hydrogen. The effect of cofeeding of hydrogen, sweep gas flow rate variation, and dilution ratio on the conversion of cyclohexane has been investigated in detail. The maximum percent increase in conversion of cyclohexane has been obtained at 473 K in hybrid as well as in membrane reactor. This temperature is also found to be optimum for sweep gas flow rate of 4.5 x 10-5 mol s-1. The conversion is observed to be suppressed by cofeeding of hydrogen and percent reduction is lowest at high temperature of 490 K in membrane reactor. The enhancement in the conversion is observed as a consequence of dilution of the feed with inert gas. The results reveal that hybrid reactor is not necessarily a better choice than the full length membrane reactor. However, at the expense of loss of reactant, hybrid reactor is better than full length membrane reactor.

Simulation of a membrane reactor for the WGS reaction: Pressure and thermal effects

A simulation study of a membrane reactor for the water-gas shift reaction is presented. A pseudohomogenous 1D mathematical model is considered to describe the performance of the membrane reactor under steady-state operation. The membrane consists on a dense Pd layer (selective to H 2) deposited on a porous ceramic support. The influence of operating pressure and thermal effects on the membrane reactor performance is analyzed and the results are compared with those corresponding to a reactor with no hydrogen permeation.

Ammonia oxidation in Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ membrane reactor

Selective oxidation of ammonia to NO was studied in a dense mixed ion electron conducting Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ membrane reactor, which integrates the separation and catalytic reaction process in a single reactive separation unit. The influence of the temperature and feed concentration on the membrane reaction performance were investigated in detail. Under reaction conditions, the oxygen permeation flux through the dense membrane increases with increasing temperature and ammonia flow rate. The lower temperature and ammonia concentration can favor the formation of NO, in which higher catalytic performance is obtained, suggesting that the membrane reactor operation is much beneficial for selective oxidation of ammonia.

An operability level coefficient ( OLC) as a useful tool for correlating the performance of membrane reactors

An operability level coefficient ( OLC), defined as the ratio of product permeation and product formation rates, and related to the inverse combination of the Damköhler number and the Peclet number (1/ DaPe), is suggested as a useful tool for estimating performances of membrane reactors (MRs) operating as separators in equilibrium-limited reactions. The OLCs for product hydrogen formation in previously reported MRs for methane dry-reforming (MDR), methane steam-reforming (MSR), methanol steam-reforming (MeOHSR), and ethanol steam-reforming (EtOHSR) were correlated with conversion and yield enhancements. For values of OLCs ranging from 0.03 to 0.78, a clear universal trend for increasing conversions and hydrogen yields with increasing OLC was observed for these different types of reforming reactions. The OLC curve calculated from a numerical simulation without adjustable parameters was found to closely approximate experimental data obtained from the MRs, and was shown not to depend on the assumed kinetics. This study confirms that hydrogen selectivity (from the ratio of single-gas permeances) has a substantial influence on conversion and hydrogen yield enhancements in a MR, and demonstrates that a hydrogen selectivity of 100 is sufficient to achieve high performance in a MR.

Fabrication of multilayer ceramic membranes

AbstractThe development of multilayer mixed conducting oxide membranes on macroporous dead‐end tubular composite glass/ceramic substrates is presented. Sol modification of glass/ceramic substrate enhances the performance of catalytic membrane reactor (CMR) with reduced thickness of ceramic layers. The shrinkage misfit between support and ceramic layers can be regulated by different processing steps including sol modification of substrate and preliminary annealing of ceramic powders. Nanopowders of compatible complex perovskites as membrane materials were obtained by mechanochemical synthesis. Porous and dense ceramic layers were supported onto the internal wall of substrate by slip casting of slurries comprised of the narrow fractions of agglomerated powders dispersed in organic media with addition of surfactants. For SrFeO3‐based dense perovskite ceramics, both dynamics of oxygen loss at high temperatures and mechanical properties were found to be affected by the presence of SrSO4 surface inclusions formed due to sulfur admixture in starting reactants. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Water–gas shift reaction in a Pd membrane reactor over Pt/Ce0.6Zr0.4O2 catalyst

A water–gas shift (WGS) Pt/Ce 0.6 Zr 0.4 O 2 catalyst has been prepared, which exhibits much faster kinetics than conventional high-temperature ferrochrome catalysts in the temperature range most suitable for operation of WGS Pd membrane reactors, i.e. above 623 K. The performance of the Pt catalyst was tested in a reactor furnished with a supported, 1.4 μm thick high-flux Pd membrane using feeds obtained by autothermal reforming of natural gas. CO conversion remained above thermodynamic equilibrium up to feed space velocities of 9100 l kg −1 h −1 at 623 K, P total = 1.2 MPa and steam-to-carbon ratio S/C = 3, but H 2 recovery decreased from 84.8% at GHSV = 4050 l kg −1 h −1 to 48.7% at the highest space velocity. This rapid decline of separation performance is attributed to slow H 2 diffusion through the catalyst bed, suggesting that external mass flow resistance has a significant impact on the H 2 permeation rate in such membrane reactors. This could be minimized by the development of WGS catalysts with even faster kinetics which would allow further reduction of the catalyst bed height.

Elaboration of La 0.8Sr 0.2Fe 0.7Ga 0.3O 3− δ/La 0.8M 0.2FeO 3− δ (M = Ca, Sr and Ba) asymmetric membranes by tape-casting and co-firing

The performance of a catalytic membrane reactor (CMR), for partial oxidation of methane, mainly depends on the oxygen semi-permeation properties of the membrane and on its architecture. This paper presents the elaboration, by tape-casting lamination and co-firing process, of a membrane consisting of a crack free La 0.8Sr 0.2Fe 0.7Ga 0.3O 3− δ (LSFG8273) dense thin film supported by a porous layer. In the porous layer, gallium must be eliminated due to its cost. In order to avoid membrane cracking during the sintering and under working conditions, the material of the porous support was chosen and adapted to have the same shrinkage during the co-firing and a thermal expansion coefficient similar to the dense membrane material. Two materials fulfil these conditions: La 0.8Sr 0.2FeO 3− δ (LSF821) and La 0.8Ba 0.2FeO 3− δ (LBF821). Asymmetric membranes lead to an enhancement of the oxygen semi-permeation flux compared to self-supported membranes, with suitable mechanical properties in working conditions. The porous layer has a beneficial influence on oxygen semi-permeation of the membrane. At working temperature, the limiting mechanism of oxygen transport through the membrane is the oxygen surface exchanges.

Polyurethane‐ and Polystyrene‐Supported 2,2,6,6‐Tetramethyl‐ piperidine‐1‐oxyl (TEMPO); Facile Preparation, Catalytic Oxidation and Application in a Membrane Reactor

AbstractIn this contribution, the facile synthesis of two new polymer‐supported 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) catalysts and their application in the catalytic oxidation of alcohols to carbonyl compounds are described. For attachment of the TEMPO group to the polymer an isocyanate functionalized polymer is chosen. This new approach facilitates the synthesis in comparison with previously existing methods which generally require deprotonation of TEMPO prior to reaction with the polymer. Following this approach, polyurethane (PU)‐ and polystyrene (PS)‐based TEMPO catalysts are prepared in a one‐step reaction from commercially available compounds. Both polymer‐supported catalysts showed promising yields for a variety of substrates using inorganic and/or organic co‐oxidants in biphasic and/or monophasic systems. The recyclability of the corresponding catalysts was studied in repetitive batch experiments using filtration or distillation depending on the support type. Furthermore, application of the homogeneous polyurethane‐supported TEMPO for the selective oxidation of benzyl alcohol in a continously operated membrane reactor is demonstrated.

Production of Hydrogen by Dehydrogenation of Cyclohexane in High-Pressure (1−8 atm) Membrane Reactors Using Amorphous Silica Membranes with Controlled Pore Sizes

We have developed membrane reactors to dehydrogenate cyclohexane, using amorphous silica membranes with controlled pore sizes, and successfully operated them under pressures ranging from 1 to 8 atm. The membranes were prepared by chemical vapor deposition (CVD) using tetramethoxysilane (TMOS) or dimethoxydiphenylsilane (DMDPS). Both membranes had hydrogen-permselective properties. At 473−573 K, the TMOS-derived membranes showed hydrogen permeances on the order of 10−8 mol m−2 s−1 Pa−1, whereas the DMDPS-derived membranes showed permeances on the order of 10−6 mol m−2 s−1 Pa−1. Both membrane reactors produced hydrogen with conversions greater than equilibrium, and the DMDPS-derived membrane achieved higher conversion than the TMOS-derived membrane because of the greater hydrogen extraction effect of the DMDPS-derived membrane. In addition, it should be noted that this is the first report of successful operation of membrane reactors with highly hydrogen-permselective silica membranes under pressure.

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation—Experimental studies

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. Continuous separation of product hydrogen from the reforming gas mixture is expected to increase the yield of hydrogen significantly as predicted by model simulations. In the laboratory-scale experimental studies reported here steam reforming of liquid hydrocarbon fuels, butane, methanol and Clearlite ® was conducted to produce pure hydrogen in a single step membrane reformer using commercially available Pd–Ag foil membranes and reforming/WGS catalysts. All of the experimental results demonstrated increase in hydrocarbon conversion due to hydrogen separation when compared with the hydrocarbon conversion without any hydrogen separation. Increase in hydrogen recovery was also shown to result in corresponding increase in hydrocarbon conversion in these studies demonstrating the basic concept. The experiments also provided insight into the effect of individual variables such as pressure, temperature, gas space velocity, and steam to carbon ratio. Steam reforming of butane was found to be limited by reaction kinetics for the experimental conditions used: catalysts used, average gas space velocity, and the reactor characteristics of surface area to volume ratio. Steam reforming of methanol in the presence of only WGS catalyst on the other hand indicated that the membrane reactor performance was limited by membrane permeation, especially at lower temperatures and lower feed pressures due to slower reconstitution of CO and H 2 into methane thus maintaining high hydrogen partial pressures in the reacting gas mixture. The limited amount of data collected with steam reforming of Clearlite ® indicated very good match between theoretical predictions and experimental results indicating that the underlying assumption of the simple model of conversion of hydrocarbons to CO and H 2 followed by equilibrium reconstitution to methane appears to be reasonable one.

Methanol steam reforming in a dense Pd–Ag membrane reactor: The pressure and WHSV effects on CO-free H 2 production

In this experimental work, a dense tubular Pd–Ag membrane reactor is used for carrying out the methanol steam reforming reaction for producing a CO-free hydrogen stream. A non-commercial Cu/Zn/Mg-based catalyst is used in the lumen side of the membrane reactor and the experimental tests are performed at a reaction temperature of 300 °C and H 2O/CH 3OH feed molar ratio of 3/1. In both co-current and counter-current flow configurations, the effect of the weight hourly space velocity (WHSV) as well as the reaction pressure on the membrane reactor performances in terms of CO-free hydrogen recovery, hydrogen yield and hydrogen selectivity are proposed and discussed.

Non-isothermal simulation of cyclohexane dehydrogenation in an inert membrane reactor with catalytic pellets in the feed-side chamber

A mathematical model is presented to simulate the performance of a non-isothermal inert membrane reactor with catalytic pellets in the feed-side chamber (IMRCF). The simulation takes into account the various heat exchanges that take place inside the reactor. The model consists of the full set of partial difference equations that describe the conservation of mass, momentum, energy and chemical species, coupled with chemical kinetics and appropriate boundary conditions for the physical problem. The set of equations is solved by finite difference method. The model is applied to investigate the endothermic dehydrogenation of cyclohexane in the IMRCF, where a permselective Vycor glass membrane is used. The simulation results show that the conversion of cyclohexane for non-isothermal IMRCF at the temperature of 550 K and below is higher than the equilibrium conversion. On the contrary, when the temperature is 570 K and above, the conversion will be lower than the equilibrium conversion. The heat effects have a greater influence on the IMRCF.

Effects of system parameters on the performance of CO 2-selective WGS membrane reactor for fuel cells

Performing water gas shift (WGS) reaction efficiently is critical to hydrogen purification for fuel cells. In our earlier work, we proposed a CO 2-selective WGS membrane reactor, developed a one-dimensional non-isothermal model to simulate the simultaneous reaction and transport process and verified the model experimentally under an isothermal condition. Further modeling investigations were made on the effects of several important system parameters, including inlet feed temperature, inlet sweep temperature, feed-side pressure, feed inlet CO concentration, and catalyst activity, on membrane reactor performance. The synthesis gases from both autothermal reforming and steam reforming were used as the feed gas. As the inlet feed temperature increased, the required membrane area reduced because of the higher WGS reaction rate. Increasing the inlet sweep temperature decreased the required membrane area more significantly, even though the required membrane area increased slightly when the inlet sweep temperature exceeded about 160 °C. Higher feed-side pressure decreased the required membrane area as a result of the higher permeation driving force and reaction rate. A potentially more active catalyst could make the membrane reactor more compact because of the enhanced reaction rate. The modeling results have shown that a CO concentration of less than 10 ppm is achievable from syngases containing up to 10% CO.

Performance of an emulsion enzyme membrane reactor combined with premix membrane emulsification for lipase-catalyzed resolution of enantiomers

Enzyme membrane reactors combined with the large interfacial area of a fine emulsion, called emulsion enzyme membrane reactors (E-EMRs), were investigated for the optical resolution of ( R, S)-naproxen methyl esters to produce ( S)-naproxen. Preparation of a fine emulsion by continuous premix membrane emulsification (ME) was studied and compared to direct ME. By continuous ME, an emulsion with 1.32 μm of average droplet size and 46.5% (v/v) of organic phase content was obtained using a Shirasu porous glass (SPG) membrane of 5 μm pore size under 0.12 MPa pressure. The performance of the E-EMR, including mass transfer, reaction rate, enzyme activity, productivity, enantiomeric excess and enantioselectivity, were studied with different loads of lipase on the membrane or with different substrate concentrations in the emulsion. The immobilized enzyme layer caused the main mass transfer resistance in E-EMRs. An increase of the amount of lipase in the membrane did not result in a production increase but an increase in substrate concentration led to an increase in reaction rate. Up to 100% of enantiomeric excess and more than 100 of enantioselectivity was obtained in E-EMR.

Study of the influence of the hydrodynamic parameters on the performance of an enzymatic membrane reactor

Active membranes prepared by covalent attachment of Candida antarctica lipase B (CALB) onto a ceramic support previously coated by polymers (gelatine/polyethyleneimine PEI) were tested in a membrane reactor under different hydrodynamic conditions (Reynolds number and transmembrane pressure) for the synthesis of butyl laurate in hexane. The ester production was found to be directly related to the permeation flux across the membrane. However, the permeate flux unexpectedly decreased when the Reynolds number values increased. Scanning electron microscopy (SEM) and mercury porosimetry showed that this phenomenon is related to morphological changes which occurred in the polymer layer when the tangential velocity varied.

A fundamental analysis of continuous flow bioreactor models and membrane reactor models to process industrial wastewaters

We analyse the steady-state treatment of industrial wastewaters in a continuous flow bioreactor and in an idealised continuous flow membrane reactor. The reaction is assumed to be governed by Contois growth kinetics, which is often used to model the growth of biomass in wastewaters containing biodegradable organic materials. We show that a flow reactor with idealised recycle has the same performance as an idealised membrane reactor and that the performance of a non-idealised membrane reactor is identical to an appropriately defined continuous flow bioreactor with non-idealised recycle. The performance of all three reactor types can therefore be obtained by analysing a flow reactor with recycle. The steady-states of the model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained. In the limit as the residence time becomes very large, all three reactor configurations have identical performances. Thus the main advantage of using a membrane reactor, or a flow reactor with recycle, for the treatment of industrial wastewaters and slurries is to improve the performance at low residence times.