Packed-bed Membrane Reactor Research Articles

Nanocomposite MFI–alumina membranes prepared via pore-pugging synthesis: Application as packed-bed membrane reactors for m-xylene isomerization over a Pt-HZSM-5 catalyst

In this paper, we present m-xylene isomerization in an extractor-type catalytic membrane reactor using nanocomposite MFI–alumina membrane tubes packed with a Pt-HZSM-5 catalyst. The catalytic performance of the membrane reactor was compared with that of a conventional fixed-bed reactor with similar dimensions and at comparable operation conditions. The influence of the reaction temperature, gas hourly space velocity, reaction time and reactor configuration on the performance of membrane reactor was explored. The membrane reactor displayed a maximum p-xylene yield of 5.1% at 523 K when computed at permeate-only mode, decreasing with temperature. At combined mode, the p-xylene yield was ca. 28%, showing an increase of about 18% compared to an equivalent fixed-bed reactor. The catalytic membrane reactor showed 100% selectivity towards p-xylene at permeate-only mode, displaying a maximum value of ca. 42% at 523 K at combined mode. Higher performance was obtained when the catalyst packing was close to the inner top layer of the membrane support. In this configuration, xylene permeate compositions higher than 95% could be achieved on the basis of the high p/o and p/m-xylene separation factors offered by the membrane.

Model-Based Analysis of Reactor Feeding Policies for Methane Oxidative Coupling

In this work, a new feeding policy structure for an alternative operation mode of the packed bed membrane reactor (PBMR) is proposed in order to increase the efficiency of the OCM—oxidative coupling of methane—process. This structure has a high potential to improve the process performance in comparison to fixed bed reactors (PFRs) and even to a conventional PBMR design structure. The main drawbacks in operating PFR or PBMR have been to find suitable operation policies toward the enhancement of both yield and selectivity at the same time. In this work, a model-based comparative study of the OCM process performance for these three reactors types is presented. For this purpose, the effect of oxygen accessibility in the different design structures is investigated. Basically, the new proposed feeding policy structure combines the advantages of PFR and the conventional PBMR so as to get a high yield amount by cofeeding methane and oxygen into the reactor entrance while guaranteeing an acceptable level of select...

Theoretical comparison of packed bed and fluidized bed membrane reactors for methane reforming

In this theoretical work the performance of different membrane reactor concepts, both fluidized bed and packed bed membrane reactors, has been compared for ultra-pure hydrogen production via methane reforming. Using detailed theoretical models, the required membrane area to reach a given conversion and the prevailing temperature profiles have been compared. The extent of mass and heat transfer limitations in the different reactors has been evaluated, and strategies to decrease (or avoid) these limitations have been proposed for the fluidized bed membrane reactor concept. The results show that the packed bed membrane reactor requires in some conditions double membrane area with respect to the fluidized bed membrane reactor.

Oxidative dehydrogenation of ethane to ethylene in a membrane reactor: A theoretical study

This contribution presents a theoretical study of a multitubular packed-bed membrane reactor for the ethane to ethylene oxidative dehydrogenation reaction over a highly active and selective Ni–Nb–O mixed oxide catalyst. This theoretical study takes into account the radial composition and temperature profiles using a two-dimensional pseudo-homogeneous model on the reaction side. The feasibility and convenience of using this novel design, as well as the influence of the main operating variables on the reactor performance, are analyzed. The introduction of the membrane leads to lower oxygen partial pressures inside the catalyst tubes, which results in an improved selectivity to ethylene (lower heat generation rates) and high effective heat transfer area per unit volume. The multitubular membrane reactor enables significant ethylene productions per tube and milder temperature profiles than a conventional wall-cooled fixed-bed reactor. Operating conditions have to be carefully adjusted to avoid undesired oxygen accumulation inside the tubes. The presence of small amounts of oxygen at the reactor inlet significantly improves the ethylene production rates.

A packed bed membrane reactor for the oxidative dehydrogenation of propane on a [formula omitted] based catalyst

Oxidative dehydrogenation of propane has been studied over a Ga 2 O 3 / MoO 3 based catalyst. Using a differentially operated packed bed reactor with premixed oxygen and propane feed, the kinetic parameters for the main reaction and the consecutive and parallel reactions were experimentally determined. It was concluded that the reaction order in oxygen is higher for side reactions than for the main reaction of propylene formation and that a major process improvement is possible by employing a packed bed membrane reactor with distributed oxygen feed. Detailed numerical model simulations have been performed to quantify the benefits of the packed bed membrane reactor for this system.

Hydrogen production from partial oxidation of methane in a membrane reactor

Partial oxidation of methane was performed in a packed-bed reactor (PBR), packed-bed membrane reactor with a porous membrane distributor (PBMR#1), packed-bed membrane reactor with a Pd membrane separator (PBMR#2) and a dual membrane reactor equipped with membrane distributor and separator (DMR). Product with H 2/CO = 6 was obtained from the PBR operating within flammable region with a feed mixture of CH 4/O 2 = 1. Safer operation was obtained using the PBMR#1 by partitioning and adding the oxygen reactant through the membrane distributor. Continuous and selective permeation of H 2 by Pd membrane in the PBMR#2 allow the production of 97% pure H 2 stream, while simultaneously suppressing CO production. Carbon monoxide was absent in both the retentate and permeate streams of the PBMR#2. However, the Pd membrane in the PBMR#2 suffered from severe coking leading to membrane failure. The DMR showed that partitioning oxygen through the membrane distributor could ameliorate coking on the Pd membrane and improve hydrogen selectivity ( i.e., PBR = 45%, PBMR#1 = 60%, PBMR#2 = 60% and DMR = 75%). A 100-h monitoring showed that a stable hydrogen permeance rate and purity could be obtained from the DMR.

Oxidative coupling of methane (OCM) in a catalytic membrane reactor and comparison of its performance with other catalytic reactors

The oxidative coupling of methane (OCM) was studied in a catalytic membrane reactor (CMR), catalyst packed bed reactor (PBR) and catalyst packed bed membrane reactor (PBMR) respectively. The CMR consists of a mixed ionic-electronic conducting membrane (MIECM) Ba0.5Ce0.4Gd0.1Co0.8Fe0.2O3−δ (BCGCF) coating on the outer surface of ceramic tubular support using sol–gel method. The inner surface of the membrane tube was coated with 3 components (Na-W-Mn) catalyst using mixture slurry dip coating method. Prior to the OCM reaction, separation of oxygen from the mixture of nitrogen and oxygen similar to air composition was performed in the membrane reactor. In the absence of chemical reaction, the oxygen permeation flux was 0.6 cm3/min cm2 at 900 °C with sweep gas flow rate 100 cm3/min. The oxygen permeation flux increased significantly during the oxidative coupling of methane reaction. 67.4% of C2+ selectivity and methane conversion of 51.6% with oxygen permeation flux 1.4 cm3/min cm2 was obtained at 850 °C with sweep gas flow rate of 100 cm3/min. The performances of PBR and PBMR using Na-W-Mn/SiO2 were compared with the performance of CMR. The catalytic membrane reactor performed best among three reactors with C2+ yield of 34.7%. The deterioration of the catalytic membrane performance after reaction was investigated by SEM and XRD analyses.

Oxidative dehydrogenation of ethane in an electrochemical packed-bed membrane reactor: Model and experimental validation

Abstract A model was developed for the electrochemical oxidative dehydrogenation of ethane to ethylene in a solid electrolyte membrane reactor. Experimental data from the process with oxygen being supplied either electrochemically or gaseously were used in the model validation. In the model description, the converse axial distribution of the oxygen concentration in the reactor operated in the co-feed modus as well as in the electrochemical membrane modus was taken into account. The conversion of ethane and the selectivity to the desired product ethylene were well predicted with the model that included the kinetic equations based upon the Mars-van-Krevelen or the Langmuir-Hinshelwood mechanisms for investigations in the co-feed modus with gaseous dioxygen. This model was not directly applicable for the conditions of an electrochemical membrane reactor. The kinetics of the oxygen reduction on the cathode, the transfer of oxygen ions from the cathode to the anode, as well as the formation of the gaseous dioxygen on the anode, were therefore included in the model. Furthermore, the model for the electrochemical operation was extended by two additional side reactions that describe the electrochemically induced oxidation of the intermediate ethylene. After this, the experimental data measured in the temperature range of 540–620 °C agreed well with the predictions of the extended model.

Analysis of single and multi-stage membrane reactors for the oxidation of short-chain alkanes—Simulation study and pilot scale experiments

This contribution intends to provide insight into various aspects of multi-stage dosing concepts based on an experimental and model based analysis. For this aim the oxidative dehydrogenation (ODH) of ethane to ethylene on a VO x /Al 2O 3 catalyst was considered as a model reaction. Additionally, first results of the industrially more important ODH of propane will be given as an outlook. For the experimental study, a pilot scale set-up has been constructed realising a single-stage packed-bed membrane reactor as well as a three-stage membrane reactor cascade. The inner/outer diameter of the asymmetric alumina membranes used was 21/35 mm. A comparison with a conventional fixed-bed reactor as a reference concept was feasible using totally vitrified membranes operating in the same equipment in a co-feed mode. Reduced simple 1D and more detailed 2D models have been developed to identify optimal operation parameters and to describe the concentration and temperature profiles, respectively. Based on a preliminary theoretical analysis, a large set of experimental studies was carried out in a temperature range between 520/630 °C (ethane) and 350/500 °C (propane). The molar O 2/C n H m ratio was varied between 0.5 and 8. In the three-stage membrane reactor cascade different dosing profiles could be realised, e.g. increasing, uniform and decreasing profiles. Due to the separated and distributed feeding of the reactants, the resulting concentration and residence time profiles and the corresponding product spectra are different in membrane reactors compared to fixed-bed reactors. The analysis performed reveals for the investigated operation range a higher ethylene/propylene selectivity and a simultaneously higher conversion in membrane reactors. In case of low oxygen concentrations the selectivity of the desired product ethylene can be increased significantly compared to the conventional fixed-bed reactor. The developed detailed 2D models allowed a good mathematical description of the exothermal reactions taking place in the membrane reactor exploiting a distributed oxygen dosing over the porous wall.

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

“Pd nanopore” composite membranes are a novel class of H 2 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 H 2 from the catalytic decomposition of anhydrous NH 3. An effective 4 μm thick Pd nanopore membrane and 13 μm thick Pd top-layer membrane were synthesized on 2 mm O.D. α-Al 2O 3 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 NH 3 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 NH 3 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 H 2, 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 m 3 (at 85% H 2 utilization) to 7 mol/s m 3 (at 50% H 2 utilization) were obtained. The permeate stream purity exceeded 99.2% H 2. 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.

Catalytic decomposition of H2S in a double-pipe packed bed membrane reactor: Numerical simulation studies

Abstract H2 recovery from large quantities of toxic H2S, the by-product of various minerals, coal and petroleum processing operations is an attractive proposition for efficient resource and energy utilization. This study has examined the analysis of a double-pipe membrane reactor internally packed with a Ru-Mo catalyst for the catalytic desulfurization of H2S and H2 generation. Due to the endothermic nature of the reaction, a non-isothermal model was employed. The effect of tube and shell-side residence times, sweep gas (argon) flow direction within the annular space between shell and inner membrane tube (relative to the H2S feed) and the shell-to-tube side pressure ratio on H2S conversion were investigated. The counter-current mode of reactor operation generally gave better H2S conversions than the co-current mode (40–60%). Irrespective of shell-to-tube side pressure ratio, conversion in both modes of operation exceeded the thermodynamically-imposed ceiling by between two- and five-fold increase. The niobium membrane proposed was internally-coated with platinum to improve resistance to H2S attack. The analysis showed that an optimum Pt thickness of about 1 μm is attainable although the possible formation of hairline cracks may necessitate the use of a higher coating. The model also accounted for the temperature-dependency of the membrane H2 permeability in order to have a more realistic assessment of the reactor performance.

Dehydroalkylation of toluene with ethane in a packed-bed membrane reactor with a bifunctional catalyst and a hydrogen-selective membrane

The dehydroalkylation of toluene with ethane to form isomeric ethyltoluenes has been carried out in a packed-bed membrane reactor under mild conditions of 350 degrees C, where it is shown that ethyltoluene yields significantly increase with increasing sweep gas flow rate and pressure.

Simulation study of water gas shift reaction in a membrane reactor

The water gas shift (WGS) reaction is an important step of hydrogen production in industrial cycles for upgrading H 2 rich streams by CO conversion present in syngas mixtures. WGS was studied in a Pd-alloy membrane reactor (MR) by means of a non-isothermal mathematical model using, as main parameter, Damköhler's number ( Da), the ratio of characteristic times of flow rate and reaction, in a temperature range of 220–320 °C. Two different reactant equimolecular feed streams were considered: one containing only CO and H 2O, the other containing also H 2 and CO 2 of higher industrial interest. The permeation driving force was generated by feed pressure ranging 200–1500 kPa which allows a good H 2 recovery index (up to 95%) and a retentate stream rich (up to 80%) in CO 2. No sweep gas was used; therefore, a pure H 2 stream is obtained as permeate. CO conversion, H 2 recovery index and its partial pressure are the main variables used for analysing the MR performance and showing its advantages with respect to a TR in the large feed pressure range. In addition, the volume index and conversion index are introduced for the first time and proposed as simple tools analysing the volume reduction or improved conversion shown by MRs; both lead to the catalyst amount and reactor size being reduced. The two new indexes proposed by membrane engineering open a window on the analysis of MRs for H 2 production and CO 2 separation for the process intensification strategy. This paper describes a modelling analysis of a packed-bed membrane reactor involving dense Pd–Ag commercial permselective membrane.

Effect of Mass-Transport Limitations on the Performance of a Packed Bed Membrane Reactor for Partial Oxidations. Intraparticle Mass Transport

For partial oxidation systems, where the reaction order in oxygen of the formation rate of the target product is smaller than the reaction order in oxygen of the consecutive reaction rate toward the waste product, a packed bed membrane reactor can be applied to distributively dose oxygen along the reactor in order to improve the selectivity toward the desired intermediate product. In this paper, how the performance of a PBMR for partial oxidations is influenced by the extent of intraparticle diffusion limitations has been investigated. First, the intrinsic effects for a single catalyst particle are discussed, and subsequently the integral effects over the entire reactor on the conversion and selectivity are studied with numerical models (considering different sets of reaction orders, different ratios of reaction rates of the primary and secondary reaction, and different stoichiometric coefficients). In Part 2, the effects of radial oxygen concentration gradients from the membrane wall to the center of the packed bed are investigated. The main objective of this work is to provide guidelines to assess whether mass-transfer limitations inside the particles (Part 1) and/or from the membrane wall to the center of the catalyst bed (Part 2) affect the reactor performance and to quantify these effects.

Effect of Mass-Transport Limitations on the Performance of a Packed Bed Membrane Reactor for Partial Oxidations. Transport from the Membrane to the Packed Bed

With a packed bed membrane reactor, the product yield can be significantly enhanced for partial oxidation systems, via distributive addition of oxygen to the reaction mixture along the axial coordinate of the reactor, provided that the reaction order in oxygen of the formation rate of the target product is smaller than the reaction order in oxygen of the consecutive reaction toward the waste product. In Part 1, the intrinsic and integral effects of intraparticle diffusion limitations on the performance of the packed bed membrane reactor have been investigated. In this paper, the study is extended by studying the effects of mass-transfer limitations from the membrane wall to the center of the packed bed. Again, first the intrinsic effects are examined, followed by a study of the integral effects over the entire reactor using a two-dimensional reactor model. A modified Thiele modulus Φ‘‘ was defined and it was found that only for Φ‘‘> 1 radial concentration profiles inside the packed bed does the integral reactor performance deteriorate and that for values <1, a one-dimensional reactor model suffices. Asymptotic solutions for high values of the modified Thiele modulus for the relative conversion rate of the main reaction and the relative product selectivity have been derived, which allows a quick (conservative) estimate of the influence of the mass-transfer limitations from the membrane wall to the center of the packed bed.

Feasibility Study of the Oxidative Dehydrogenation of Ethane in an Electrochemical Packed-Bed Membrane Reactor

The feasibility of the oxidative dehydrogenation of ethane to ethylene with alumina-supported vanadium oxide catalyst (VOx/γ-Al2O3) in an electrochemical packed-bed membrane reactor was investigated at temperatures between 500 and 620 °C with molar ratios of oxygen to ethane of 0.06−3.10. An oxygen-ion-conducting yttria-stabilized zirconia (YSZ) membrane was employed in a reactor of Au|YSZ|Pt, and the oxygen flux transferred across the membrane was controlled over the faradic coupling of oxygen-ion conduction and the external current between the electrodes. The oxidative dehydrogenation of ethane with electrochemically supplied oxygen in the membrane reactor was compared to that obtained with gaseous dioxygen in a conventional packed-bed reactor. The selectivity to ethylene was found to decrease as a function of supplied oxygen in both investigated operating modes. For all investigated oxygen/ethane molar ratios, the selectivity ratio, SCO2/SCO, was found to be clearly higher in the electrochemical than in the packed-bed reactor mode. The electrochemical oxygen supply significantly promoted CO2 formation, whereas the ethane conversion and ethylene selectivity were almost equal in the two investigated reactors. The experimental results indicate that, in the electrochemical operation, additional oxygen species exist in the system and are especially reactive in the total oxidation reactions.

New membrane for use as hydrogen distributor for hydrocarbon selective hydrogenation

Catalytic selective hydrogenation is a reaction widely used in petrochemical industry, particularly to produce intermediate olefins for polymer production. The main drawback of these industrial conversion processes, carried out in fixed beds, is their low selectivity at high conversion levels: injection of the whole hydrogen stream along with the hydrocarbon feed at the inlet of the reactor does not allow an efficient control of the reaction selectivity. The use of a packed bed membrane reactor (PBMR) in order to improve the distribution of hydrogen throughout the length of the reactor has been suggested as a possible solution to this problem. Consequently a new method to improve the hydrogen distribution properties of MFI zeolite membranes, which are potential candidates for a PBMR, is presented in this paper. The chemical composition of these new membranes were analysed and their performances were assessed before and after a chemical modification. After the modification treatment, the membranes were able to distribute hydrogen with a very low loss of hydrocarbon by counter diffusion.

Membrane assisted fluidized bed reactors: Potentials and hurdles

Recent advances in the development of more stable membranes with increased permeance have significantly enhanced the possibilities for integrating membranes into catalytic reactors in order to achieve a major increase in reactor performance by process integration and process intensification. Several reviews and even special issues of catalysis related journals illustrate the significant progress in the field of inorganic membrane reactors within the last two decades. Chemical engineers and material scientists have joined forces and addressed this topic from various view-points. In spite of their considerable efforts in these directions, the application of the membrane reactors, especially packed bed membrane reactors, in commercial processes has been very limited because of technical as well as economical drawbacks. The most recent trend in membrane reactor technology has been in the direction of incorporating inorganic membranes into fluidized beds to combine the perm-selective and controlled dosing capabilities of membranes with excellent gas–solid contact and heat transfer capabilities of fluidized beds, thereby overcoming the limitations often prevailing in packed bed membrane reactors. The opportunities for this novel fluidized bed membrane reactor compared to conventional reactors and packed bed membrane reactors have never been systematically reviewed before. This paper seeks to review literature and new developments in the area of membrane assisted fluidized bed reactors, with special emphasis on possible applications, integration of different membranes in the fluidized beds, reactor modelling studies, experimental demonstration of various reactor concepts and future prospects and hurdles for commercialization. Finally, an assessment of the state of the art has been given and directions for future research are indicated.

The use of OCM reactors for ignition enhancement of natural gas combustion for practical applications: Reactor design aspects

The major goal of the study is the improvement of the ignition characteristics of lean, premixed natural gas (NG) combustion under engine-like conditions. A new process is investigated involving the oxidative coupling of methane reaction (OCM) for the in situ production of C 2 hydrocarbons to be used as ignition enhancers during lean combustion of methane in internal combustion (IC) engines. Addition of the OCM product mixture enhances the ignition characteristics of lean methane/air mixtures, the beneficial effect resulting from the C 2H 4/C 2H 6 components. OCM in both conventional plug flow and packed-bed membrane reactors is modelled and optimised with respect to reactor conditions and ignition characteristics. An additional ignition technique that includes flowing a jet of a fuel/air stream against a hot inert surface has been implemented for quantifying the effect of the proposed ignition enhancers.

Hydrogen generation in a Pd membrane fuel processor: Productivity effects during methanol steam reforming

Performance analyses are carried out for the palladium membrane fuel processor for catalytic generation of high purity hydrogen. The reactor model includes detailed particle-scale multi-component diffusion, multiple reversible reactions, flow, and membrane transport. Using methanol steam reforming on Cu / ZnO / Al 2 O 3 catalyst as the test reaction, a systematic examination of the effects of operating and reactor design parameters on key performance metrics is presented. Single particle simulations reveal a complex interplay between nonisobaric transport and the reversible reactions (methanol reforming and decomposition, and water–gas shift), which impact overall reactor performance. An analysis of characteristic times helps to identify four different productivity controlling regimes: (i) permeation control, encountered with thick membranes and/or insufficient membrane area; (ii) catalyst pore diffusion control encountered with diffusion of reacting species in larger particles; (iii) reaction control, encountered when intrinsic catalytic rates are too low because of inadequate activity or catalyst loading; and (iv) feed control, encountered when the limiting reactant feed rate is inadequate. The simulations reveal that a maximum in the hydrogen productivity occurs at an intermediate space velocity, while the hydrogen utilization is a decreasing function of space velocity, implying a trade-off between productivity and hydrogen utilization. The locus of productivity maxima itself exhibits a maximum at an intermediate membrane surface to volume ratio, the specific value of which is dependent on the particle size, membrane thickness and reaction conditions. At moderate temperature and total pressure ( 260 ∘ C , 10 bar), particles smaller than 2 mm diameter, Pd membranes with thickness less than 10 μ m , and membrane surface to volume ratio exceeding 500 m 2 / m 3 are needed to achieve viable productivity ( > 50 mol H 2 / m 3 s ) . A comparison between the packed-bed membrane reactor and conventional packed-bed reactor indicates a modest improvement in the conversion and productivity due to in situ hydrogen removal.