Performance Of Membrane Reactor Research Articles

Packed-Bed Reactor Performance Enhancement by Membrane Distributed Feed: The Case of Methanol Oxidative Dehydrogenation

ABSTRACTFor methanol oxidative dehydrogenation to formaldehyde, the performance of the packed-bed membrane reactor (PBMR) is compared with that of the conventional fixed-bed reactor (FBR) over a wide range of operating conditions. The reaction was studied in three reactor configurations: the conventional FBR and the packed-bed membrane reactor, with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined and incorporated in a PBMR model. Both experimental data and model considerations demonstrate that the PBMR enhances reactant conversion and selectivity.Small oscillations in CO production were observed experimentally. Their amplitude was taken as a basis for comparison of packed-bed operation instability. The likely source of oscillatory behavior is the non-uniformity in reaction conditions along the reactor. It was found that membrane distributed feed, by providing a more uniform reactor operation, is an effective remedy from these instabilities.It is found, both by simulations and experimental observations, that relative reactor performance depends strongly on the operating conditions. Using formaldehyde yield as the basis for optimization, optimal reactor performances are determined to be in the order: PBMR-O > FBR > PBMR-M. Further PBMR productivity enhancement is possible by optimizing the membrane feed distribution pattern.

Oxidative dehydrogenation of butane using inert membrane reactor with a non-uniform permeation pattern

Inert ceramic membrane reactors have been investigated for the oxidative dehydrogenation of butane to butadiene and butene. The partially coated porous ceramic membranes have been used as an air distributor to a fixed-bed of V–Mg–O catalyst. The catalyst characterization was carried out by BET, X-ray diffraction (XRD). The performance of inert membrane reactors (IMRs) has been compared to that obtained in a conventional fixed-bed reactor (FBR). The IMRs are more efficient than the FBR. The moderate non-uniform inert membrane reactor (NIMR1) slightly outperforms the uniform inert membrane reactor (UIMR) in most operation conditions investigated. A feeding mode with 10% of air mixing with butane in the NIMR1 (10NIMR1) was found to be more efficient than the feeding mode with all air permeating through ceramic membrane. Selectivity of up to 61.1% and a yield of 42.2% were obtained in the 10NIMR1.

Dynamics of penicillin G hydrolysis in an electro‐membrane reactor

AbstractAnalysis of penicillin G hydrolysis in a membrane reactor with membrane‐entrapped penicillin G acylase is performed using a mathematical model of the reactor system. An electric field imposed to the reactor is considered to enhance transport rates of reaction components and reaction rate. Diffusion, electrophoretic migration and electro‐osmotic flux across the membrane are considered. The analysis focuses on possible effects of the principal operational parameters (electric field intensity, inlet substrate concentration, membrane thickness) on reactor performance. Multiplicities of steady states are frequently encountered. The membrane reactor performance can be easily targeted towards the required reaction regime by applying a constant or periodically varying electric field to the system. The periodic alternation of the polarity of the electric field substantially increases the effectiveness factor of penicillin hydrolysis compared with the steady state operation. Proper adjustments of electric field intensity may also compensate for the decay in enzyme activity.© 2001 Society of Chemical Industry

Continuous Application of Chemzymes in a Membrane Reactor: Asymmetric Transfer Hydrogenation of Acetophenone

The application of homogeneously soluble catalysts is limited by the recovery in cases where the price of the catalyst is high. Biological catalysts, enzymes, can be efficiently recycled by means of an ultrafiltration membrane due to their high molecular weight, for example, in the continuously operated membrane reactor. In order to transfer this principle to chemical catalysis, we have attached a transfer hydrogenation catalyst, first invented by Gao and Noyori, to a polymer. The resulting homogeneously soluble, polymer-bound catalyst (chemzyme) can now be retained by ultrafiltration membranes like enzymes. On applying this catalyst in continuously operated membrane reactors, a continuous isopropoxide dosage is necessary in order to compensate deactivation caused by water residues in the feed stream. Thus, high space-time yields up to 578 g L −1 d −1 and enantioselectivities up to 94% can be achieved. These results were compared to an enzyme catalyzed system consisting of a carbonyl reductase that also utilizes 2-propanol as a hydrogen source for the cofactor regeneration of NADH.

Performance of batch membrane reactor: Glycerol-3-phosphate synthesis coupled with adenosine triphosphate regeneration.

Glycerol-3-phosphate (G3P) was synthesized from glycerol using glycerol kinase (GK). This reaction requires adenosine triphosphate (ATP) and was coupled with the ATP regeneration reaction using acetate kinase (AK) in a batch-operated ultrafiltration hollow-fiber reactor. By taking into consideration the dynamic nature of the bioreactor performance under non-steady-state conditions, a model for the performance of a batch membrane reactor for G3P synthesis coupled with ATP regeneration was developed and studied. The simulation results showed good agreement with the experimental results. The simulation studies have provided some insight into the process dynamics of the coupled reactions in the reactor system studied. For the reactor operational model used, in which the enzymes are retained in the shell side and the substrates are also initially placed in the shell side, it was found that the substrate concentration in the lumen side increased to a level higher than that in the shell side, and a backdiffusion occurred from the lumen side to the shell side during reactor operation. The ratio of the reaction rate to diffusion rate goes through a sharp peak during the time that the direction of diffusion is reversed. For another reactor operational model, in which the substrates were initially placed in the lumen side and enzymes were retained in the shell side, it was found that the rate-controlling step between the reaction and diffusion was switched during the reactor operation. Initially, the reaction rate increased while the diffusion rate was high and the substrate concentrations increased in the shell side. The ratio of reaction rate to diffusion rate increased to a maximum and remained at a constant level as the diffusion rate decreased to a low level due to the nonlinear characteristics of mass transfer process. This study provides information that is useful for optimization of batch membrane enzyme reactor operation and for a fed-batch-type process with an intermittent feeding strategy for efficient use of substrates.

On the importance of non-ideal flow effects in the operation of industrial-scale adiabatic membrane reactors

A mathematical model taking into account mass dispersion is presented for the simulation of the performance of an adiabatic full-scale membrane reactor. Results are presented from the application of this model to a membrane reactor, that is introduced in an integrated gasification combined cycle plant, to control carbon dioxide emissions. The performance of this reactor equipped with highly selective membranes is studied in detail. The extent of the impact of the non-ideal flow effects on the membrane reactor operation is discussed. It is shown that dispersion effects have a negative influence on the performance of industrial-scale membrane reactors and they must be considered as a basic parameter to their design.

A study on the performance of a dense polymeric catalytic membrane reactor

A theoretical study on a catalytic polymeric dense membrane reactor (CPDMR) is performed. The conversion enhancement over the thermodynamic equilibrium value is studied for an equilibrium gas-phase reaction of the type aA+ bB⇔ cC+ dD for three different conditions: Δ n>0, Δ n=0 and Δ n<0, where Δ n=( c+ d)−( a+ b). For each of these cases, it is studied the influence of the reaction product sorption and diffusion coefficients. The model used considers perfectly mixed flow patterns and isothermal operation in the retentate and permeate sides. It is concluded that the conversion of a reversible reaction can be significantly enhanced when the diffusion coefficients of the products are higher than the reactants’ and/or the sorption coefficients are lower. The extension of this enhancement depends on the reaction stoichiometry, global concentration inside the membrane, Thiele modulus and contact time values. It was also observed that it would be preferable to have a conversion enhancement based on higher product diffusion than on lower product sorption coefficients, since this leads to smaller reactor size. Since the performance of a dense membrane reactor depends on both the sorption and diffusion coefficients in a different way, a study of such a system cannot be based only on the permeabilities of the reaction components.

Performance of shell and tube-type membrane reactors equipped with heteropolyacid-polymer composite catalytic membranes

Experimental studies on the performance of shell and tube-type membrane reactors equipped with heteropolyacid-polymer composite catalytic membranes were carried out for the vapor-phase decomposition of MTBE (methyl tert-butyl ether). Three types of catalytic membranes comprised of 12-tungstophosphoricacid (H 3PW 12O 40, PW) and polyphenylene oxide (PPO) were designed in this work. The PW-PPO/Al 2O 3 (type-1), PW-PPO/PPO/Al 2O 3 (type-2) and PW/PPO/Al 2O 3 (type-3) catalytic membranes not only showed catalytic reactivity for the reaction, but also were perm-selective for the reaction species. The selective removal of methanol through the catalytic membrane led to an equilibrium shift in a direction favorable to MTBE decomposition. Among three types of catalytic membrane reactor, the PW-PPO/PPO/Al 2O 3 (type-2) catalytic membrane reactor showed the best performance. The enhanced performance of the PW-PPO/PPO/Al 2O 3 (type-2) catalytic membrane reactor can be attributed to the intrinsic perm-selective capabilities of the PW-PPO catalytic membrane and the sub-layered PPO membrane.

Isobutane dehydrogenation in a membrane reactor: Influence of the operating conditions on the performance

Isobutane dehydrogenation has been investigated in a membrane reactor combining a bimetallic PtIn/zeolite fixed-bed catalyst and a microporous MFI-alumina tubular membrane. The membrane reactor performance has been studied as a function of the feed and sweep flow rates and of the sweep (co- or counter-current sweep modes). Isobutene yields up to four times higher than that observed in a conventional reactor have been obtained. Depending on the conditions, it is shown that the performance of the membrane reactor is controlled either by the membrane or by the catalyst.

Analysis of intermediate product yield in distributed-feed nonisothermal tubular membrane reactors

A comparative study of yield to intermediate products obtained from the distributed-feed membrane reactor (MR) and the conventional cooled-tube plug-flow reactor (PFR) is presented. The nonisothermal, nonadiabatic one-dimensional pseudo-homogeneous reactor model was used. The analysis is presented in terms of the usual dimensionless groups (Damköhler number ( Da), heat of reaction parameter, Stanton number ( St), etc.) and delineates regions of parameter space where the membrane reactor gives improved yield with no higher maximum temperature. Optimal conditions for the PFR usually lie on or close to the boundaries between either pseudo-adiabatic operation (PAO) or hot-spot operation (HSO), and runaway operation. Results show that when compared under optimal operating conditions and at the same catalyst volume, reactant feed rate, temperature and pressure, the membrane reactor performance is better than that of the PFR only over restricted regions of parameter space. In general, distributed feed is preferred at higher Da, and under conditions of high heat release or lower cooling rates. The distributed-feed reactor performance can be enhanced by a mixed-feed strategy, or by slightly increased inlet temperature.

Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C 2 selectivity up to 40–70% was achieved, albeit that conversion rate were low, typically 0.5–3.5% at 800–900°C with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/γ-Al 2O 3 with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH 4 conversion, 93.0% CO selectivity and 10.45 ml/cm 2 min oxygen permeation flux were achieved under steady state at 850°C. Methane conversion and oxygen permeation flux increased with increasing temperature. No fracture of the membrane reactor was observed during syngas production. However, H 2-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875°C for more than 500 h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm 2 min.

Modeling a catalytic polymeric non-porous membrane reactor

A theoretical study on a catalytic polymeric non-porous membrane reactor is performed. The conversion enhancement over the thermodynamic equilibrium is studied when conducting an equilibrium gas-phase reaction of the type A+B⇔C+D. The model used considers perfectly mixed flow patterns and isothermal operation for the retentate and permeate. It is concluded that the conversion of a reversible reaction can be significantly enhanced when the reactants’ diffusion coefficients are lower and/or sorption coefficients are higher than the products’. This happens for Thiele modulus and contact time over certain threshold values. It was also observed that it is preferable to enhance conversion through an increase in the reactants’ sorption coefficients, since this leads to lower reactor dimensions. Since the performance of a non-porous membrane reactor depends on both the sorption and diffusion coefficients, a study of such system cannot be based exclusively on the permeabilities of the components. Favorable combinations of diffusion and sorption coefficients can provide a coupled effect over the reactor’s conversion.

Effects of Catalyst Amount, Membrane Tube Diameter and Permeation Rate on the Performance of Porous Membrane Reactors.

Effects of catalyst amount, membrane tube diameter, and permeation rate on porous membrane reactor performance were investigated through experiments and simulations. Porous Vycor glass membrane reactors were used in the experiment. To study the effect of catalyst amount, permeation side of a membrane reactor was filled with the same catalyst as that used in the feed side, i.e. 0.5 wt% Pt/Al2O3. The Ω, that is, a volume fraction of a catalyst in the permeation side was varied from 0% to 100%. It was observed that overall conversion increases with the Ω value. To study the effect of membrane tube diameter on the performance of a modified porous membrane reactor (MPMR), experiment and simulation using different membrane tube diameters were conducted. The results show that there are optimum membrane tube diameter to achieve maximum conversion. It also reveals that in an MPMR, membrane surface area and ratio of VT/VS are more important than membrane thickness. In order to study the effect of permeation rate, some simulations were conducted. The results show that permeation rate significantly affects the performance of porous membrane reactors. By designing appropriate parameters, it is possible to achieve high purity organic product in the permeation side of MPMR.

Method for Improving the Performance of Porous Membrane Reactor.

Experiments and simulations have been carried out to study the possibility of a new proposed method (MPMR) for improving the performance of a conventional porous membrane reactor system (CPMR), by which the sweep side is filled the same dehydrogenation catalyst as used in the feed side. By experiment and simulation, it is proved that MPMR can improve CPMR not only with pure feed but also with diluted feed. The reason for the improvement is because the sweep side can effectively convert reactant that permeates through the membrane. However, Vycor glass-based MPMR cannot exceed the performance of GFBR, which is a fixed bed reactor where all inert gas dilutes the reaction system. Simulation results show that partial pressures of products in the sweep side of the MPMR are much smaller than those in the feed side. Therefore permeation of reactive species from the feed side to the sweep side still occurs as observed for CPMR.

Synthesis and Characterization of Heteropolyacid Nanoporous Carbon Membranes

Heteropolyacid nanoporous carbon membranes were synthesized by re-precipitation of 12-tungstophosphoric acid on a prefabricated nanoporous carbon film. The Keggin structure is maintained on and within the 8 μm film as inferred from FTIR spectroscopy and XRD. Gas permeation reveals that separation performance of the carbon membrane is maintained after deposition although total membrane flux decreases by nearly 40% for N2 permeation. Semi-batch membrane reactor performance in the decomposition of methyl tert-butyl ether at 55°C shows significant enhancement of the conversion with 96.5% compared with 64.1% for a non-selective membrane analog under the same conditions.

Modeling and simulation of non-isothermal catalytic packed bed membrane reactor for H 2S decomposition

The recovery of H 2 from H 2S is an economical alternative to the Claus process in petroleum and minerals processing industries. Previous studies [React. Kinet. Catal. Lett. 62 (1997) 55; Catal. Lett. 37 (1996) 167] have demonstrated that catalytic decomposition of H 2S over bimetallic sulfide can proceed at relatively higher rates than over mono-metallic systems due to chemical synergism although conversions are still thermodynamically limited. In the present study, the performance of a catalytic membrane reactor containing a packed bed of Ru–Mo sulfide catalyst has been investigated with a view to improving H 2 yield beyond the equilibrium ceiling. A system of differential equations describing the non-isothermal reactor model has been solved to examine the effect of important hydrodynamic and transport properties on conversion. The results were obtained using a Pt-coated Nb membrane tube as the catalytic reactor enclosed in a quartz shell cylinder. Reynolds number for shell and tube side ( Re s and Re t) as well as the modified wall Peclet number, Pe m, dramatically affect H 2S conversions. Membrane reactor conversion rose monotonically with axial distance exceeding the equilibrium conversion by as much as eight times under some conditions.

Continuous enzymatic transformation in an enzyme membrane reactor with simultaneous NAD(H) regeneration. Reprinted from Biotechnology and Bioengineering, Vol. XXIII, No. 12, Pages 2789-2802 (1981).

Multienzyme reaction systems with simultaneous coenzyme regeneration have been investigated in a continuously operated membrane reactor at bench scale. NAD(H) covalently bound to polyethylene glycol with a molecular weight of 10(4) [PEG-10,000-NAD(H)] was used as coenzyme. It could be retained in the membrane reactor together with the enzymes. L-leucine dehydrogenase (LEUDH) was used as catalyst for the reductive amination of alpha-ketoisocaproate (2-oxo-4-methylpentanoic acid) to L-leucine. Formate dehydrogenase (FDH) was used for the regeneration of NADH. Kinetic experiments were carried out to obtain data which could be used in a kinetic model in order to predict the performance of an enzyme membrane reactor for the continuous production of L-leucine. The kinetic constants V(max) and k(m) of the enzymes are all in the same range regardless of whether native NAD(H) or PEG-10,000-NAD(H) is used as coenzyme. L-leucine was produced continuously out of alpha-ketoisocaproate for 48 days; a maximal conversion of 99.7% was reached. The space-time yield was 324 mmol/L day (or 42.5 g/L day).

The effect of enzyme concentration and space time on the performance of a continuous recycle membrane reactor for one-step starch hydrolysis

In spite of minor limitations due to membrane fouling and catalyst inactivation, one-step hydrolysis of starch with termamyl enzyme in a continuous recycle membrane reactor appears to be a promising way to produce high DE sugar syrups. In addition to the main advantage over batch process to correctly integrating reaction and separation, this type of system opens up to process engineer tunable performance in terms of conversion, capacity and productivity. In this paper the effects of enzyme concentration and space time have been examined. As a whole it appears that by increasing these two parameters the conversion is improved; but the capacity and productivity are reduced leading to higher processing costs. Optimisation of enzyme concentration and space time needs that economic criteria are very carefully taken into account.

Performance of double-pipe membrane reactor comprising heteropolyacid catalyst and polymer membrane for the MTBE (methyl tert-butyl ether) decomposition

Simulation and experimental studies on the double pipe (shell and tube) polymer membrane reactors were examined for the vapor-phase methyl tert-butyl ether (MTBE) decomposition. H 3PW 12O 40 catalyst supported on silica was used as an active catalyst for the reaction. Polyphenylene oxide (PPO), polysulfone (PSF) or cellulose acetate (CA) membrane coated on the double-layered alumina tube was used as a constituent membrane. It was observed that permeabilities of methanol through each polymer membrane were higher than those of isobutene and MTBE regardless of the kind of polymer material used. The selective removal of methanol through polymer membrane shifted the chemical equilibrium toward a favorable direction in the model reaction. The MTBE conversions in the membrane reactors were much enhanced compared to the equilibrium conversions. The PPO membrane reactor showed the best performance under the experimental conditions. The simulation results on the performance of the membrane reactors were in good agreement with the experimental results within the error of ±5%. It was revealed from the simulation that the CA membrane reactor showed the best performance at high contact time whereas the PPO membrane reactor showed the best performance at low contact time in terms of MTBE conversion, isobutene yield and isobutene selectivity. It was also observed that the performance of membrane reactor was much improved with the decrease of coating amount of polymer membrane and reaction temperature, but with the increase of partial pressure of MTBE. It was concluded that the simulation program developed in this work described the performance of the membrane reactor very well for the vapor-phase MTBE decomposition.

A carbon membrane reactor

A carbon membrane reactor as one of the applications of carbon membranes was newly developed and examined using dehydrogenation of cyclohexane as a test reaction. Permeation of hydrogen, argon, cyclohexane and benzene through carbon membranes showed the so-called molecular-sieving like diffusion behavior. The performance of the carbon membrane reactor for the dehydrogenation was found to exceed that of a normal reactor, i.e., equilibrium conversion.