Membrane Reactor Configuration Research Articles

Palladium based membranes and membrane reactors for hydrogen production and purification: An overview of research activities at Tecnalia and TU/e

In this paper, the main achievements of several European research projects on Pd based membranes and Pd membrane reactors for hydrogen production are reported. Pd-based membranes have received an increasing interest for separation and purification of hydrogen. In addition, the integration of such membranes in membrane reactors has been widely studied for enhancing the efficiency of several dehydrogenation reactions. The integration of reaction and separation in one multifunctional reactor allows obtaining higher conversion degrees, smaller reactor volumes and higher efficiencies compared with conventional systems. In the last decade, much thinner dense Pd-based membranes have been produced that can be used in membrane reactors. However, the thinner the membranes the higher the flux and the higher the effect of concentration polarization in packed bed membrane reactors. A reactor concept that can circumvent (or at least strongly reduce) concentration polarization is the fluidized bed membrane reactor configuration, which improves the heat transfer as well. Tecnalia and TU/e are involved in several European projects that are related to development of fluidized bed membrane reactors for hydrogen production using thin Pd-based (<5 μm) supported membranes for different application: In DEMCAMER project a water gas shift (WGS) membrane reactor was developed for high purity hydrogen production. ReforCELL aims at developing a high efficient heat and power micro-cogeneration system (m-CHP) using a methane reforming fluidized membrane reactor. The main objective of FERRET is the development of a flexible natural gas membrane reformer directly linked to the fuel processor of the micro-CHP system. FluidCELL aims the Proof-of-Concept of a m-CHP system for decentralized off-grid using a bioethanol reforming membrane reactor. BIONICO aims at applying membrane reactors for biogas conversion to hydrogen. The fluidized bed system allows operating at a virtually uniform temperature which is beneficial in terms of both membrane stability and durability and for the reaction selectivity and yield.

Impact of the fouling mechanism on enzymatic depolymerization of xylan in different configurations of membrane reactors

In order to maximize enzymatic xylan depolymerization while simultaneously purifying the resulting monosaccharide (xylose), different ultrafiltration (UF) membrane reactor configurations were evaluated. Initial results showed that the two hydrolytic enzymes required for complete depolymerization of xylan, endo-1,4-β-xylanase and β-xylosidase, promoted different types of fouling, which had a direct impact on the extent of xylan hydrolysis achieved during reaction. Endo-1,4-β-xylanase generated DP 1–6 xylo-oligomers. These products contributed to partial pore blocking of the 1 kDa polysulfone membrane and caused irreversible flux loss (∼20%). The presence of β-xylosidase could not prevent deposition of xylan and xylooligomers on the UF membrane surface. Mulder’s modelling of the filtration parameters affirmed that this xylan and xylooligosaccharide deposition formed a cake layer on the membrane which hindered enzymatic attack in addition to fouling. Reaction with both enzymes followed by UF was found to be the optimal configuration, providing at least 40% higher xylan hydrolysis than the cascade configuration (involving sequential reaction with each of the enzymes separately) and the simultaneous reaction-filtration with both enzymes, respectively. This study thus confirmed that the reactor configuration has a crucial impact on the performance of both the reaction and the separation process of xylose during enzymatic xylan degradation, and that the type of fouling mechanism varies in response to the type of enzyme treatment.

Development of Flow-Through Polymeric Membrane Reactor for Liquid Phase Reactions: Experimental Investigation and Mathematical Modeling

Incorporating metal nanoparticles into polymer membranes can endow the membranes with additional functions. This work explores the development of catalytic polymer membrane through synthesis of palladium nanoparticles based on the approaches of intermatrix synthesis (IMS) inside surface functionalized polyethersulfone (PES) membrane and its application to liquid phase reactions. Flat sheet PES membranes have been successfully modified via UV-induced graft polymerization of acrylic acid monomer. Palladium nanoparticles have been synthesized by chemical reduction of palladium precursor loaded on surface modified membranes, an approach to the design of membranes modified with nanomaterials. The catalytic performances of the nanoparticle incorporated membranes have been evaluated by the liquid phase reduction of p-nitrophenol using NaBH4 as a reductant in flow-through membrane reactor configuration. The nanocomposite membranes containing palladium nanoparticles were catalytically efficient in achieving a nearly 100% conversion and the conversion was found to be dependent on the flux, amount of catalyst, and initial concentration of nitrophenol. The proposed mathematical model equation represents satisfactorily the reaction and transport phenomena in flow-through catalytic membrane reactor.

Partial Oxidation of Methane to Syngas in a Packed Bed Catalyst Membrane Reactor

The planar membrane reactor configuration was explored for partial oxidation of methane (POM) to syngas. A supported membrane composed of yttria‐stabilized zirconia and La0.8Sr0.2Cr0.5Fe0.5O3‐δ was sealed to a stainless holder, and a Ni/Al2O3 catalyst bed was placed under the membrane plane with a small slit between them. This reactor configuration would facilitate the POM reaction via oxidation‐reforming mechanism: the oxidation reaction occurring at the membrane surface and the reforming reaction taking place in the catalyst bed. At 800°C and a methane feed rate of 32 mL min−1, the reactor attained methane throughput conversion over 90%, CO and H2 selectivity both over 95%, and an equivalent oxygen permeation rate 1.4 mL cm−2 min−1. The membrane and catalyst remained intact after the POM testing. The planar membrane reactor configuration explored in this study may lead to the development of a compact reactor for syngas production. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2170–2176, 2016

Simulation study of the effect of water removal from Fischer–Tropsch products on the process performance using a hydrophilic membrane reactor

In this study, a mathematical model describing Fischer–Tropsch synthesis over an iron catalyst carried out in two configurations of membrane reactors was developed to predict the process performance. For this purpose, the impact of water removal from the reaction side on syngas conversion and on hydrocarbons selectivity was theoretically analyzed and quantified under different operating conditions. The obtained main results reveal that the process can be intensified when the catalyst was packed in a single region, whereas the produced water was continuously removed from the reaction side to the permeate side, which is constituted of two identical and parallel regions. This configuration design is characterized by a sufficient large area, which can enable fast water removal by an adequate sweep-fluid flow rate. As a result, the conversion and product selectivity could be enhanced obviously at the suitable conditions.

Gas permeation effect on the Two-Section Two-Zone Fluidized Bed Membrane Reactor (TS-TZFBMR) fluid dynamics: A CFD simulation study

Two-Fluid Model simulations were conducted using the commercial software Ansys CFX and Fluent to study the effect of the gas extraction on the fluid dynamic behavior of a membrane-assisted Two-Section Two-Zone Fluidized Bed Membrane Reactor (TS-TZFBMR). Simulated bubble properties and bed dynamics were analyzed and compared among different membrane reactor configurations, including reactor-wall (RWM) and immersed tubular (ITM) membranes, for their future use in catalytic reactions, e.g., alkane dehydrogenation or methane steam reforming. According to the solids hold-up distribution at different fluidization regimes and permeation fluxes, the ITM configuration is the most suitable to enhance the gas-particle contact and to favor the solids axial mixing for in-situ catalyst regeneration purposes. However, the RWM configuration provides a greater permeation area for selective gas removal and is preferred to enhance purification. It was found that relative permeation fluxes above 20% of the total feed gas have a significant impact on the fluid dynamic regime within the TS-TZFBMR, concerning the appearance of local defluidized regions, gas channeling and solids axial mixing.

Material properties and operating configurations of membrane reactors for propane dehydrogenation

A modeling‐based approach is presented to understand physically realistic and technologically interesting material properties and operating configurations of packed‐bed membrane reactors (PBMRs) for propane dehydrogenation (PDH). PBMRs composed of microporous or mesoporous membranes combined with a PDH catalyst are considered. The influence of reaction and membrane transport parameters, as well as operating parameters such as sweep flow and catalyst placement, are investigated to determine desired “operating windows” for isothermal and nonisothermal operation. Higher Damköhler (Da) and lower Péclet (Pe) numbers are generally helpful, but are much more beneficial with highly H2‐selective membranes rather than higher‐flux, lower‐selectivity membranes. H2‐selective membranes show a plateau region of conversion that can be overcome by a large sweep flow or countercurrent operation. The latter shows a complex trade‐off between kinetics and permeation, and is effective only in a limited window. H2‐selective PBMRs will greatly benefit from the fabrication of thin (∼1 µm or less) membranes. © 2014 American Institute of Chemical Engineers AIChE J, 61: 922–935, 2015

DME production in multi-stage radial flow spherical membrane reactors: Reactor design and modeling

In this paper, the modeling of simulation of Dimethyl ether (DME) production through methanol dehydration in radial flow spherical membrane reactors has been focused. The spherical reactor has two concentric spheres that the space between spheres has been filled with catalyst. In this research, the performance of one and two-stage spherical reactors is investigated through a mathematical model. To verify the accuracy of the considered model, the simulation results of a conventional reactor are compared with the plant data. Then, the efficacy of the radial flow water vapor-permselective membrane reactor configurations is compared against the conventional process. The advantages of radial flow membrane reactors are the higher DME production, shifting thermodynamic equilibrium limitation, lower pressure drop and decreasing purification cost in the next stage. The simulation results showed that DME production is improved about 2.8% and 3.7% in the one and two-stage membrane configurations against conventional tubular reactor.

Investigation on the reforming reactions of coke-oven-gas to H2 and CO in oxygen-permeable membrane reactor

The reaction mechanisms for the reforming of coke oven gas (COG) and partial oxidation of methane (POM) to H2 and CO in Ba1.0Co0.7Fe0.2Nb0.1O3−δ (BCFNO) membrane reactor packed with NiO/MgO catalyst were investigated through designing experiments and test of oxygen permeation. The results indicated the direct partial oxidation mechanism was the dominant mechanism of POM process in BCFNO membrane reactor. The H2 in COG was proven to have an important effect on the oxygen permeation. The packing amount of catalysts in catalyst bed has little effect on oxygen permeation, while it has obvious effects on CO and H2 selectivity. Then the reaction mechanism was proposed. The H2 in COG adsorbs and reacts with the permeated oxygen to form H2O. Simultaneously the CH4 dissociates over Ni0 sites to form hydrogen and surface active carbon. The formed hydrogen reacts with oxygen to give H2O again. The remained CH4 was converted to H2 and CO by reforming with produced H2O in catalyst bed. Based on the reaction mechanism, the author had given a permeation-reforming tubular membrane reactor configuration for the COG conversion to hydrogen. The permeation-reforming reactor shows promise for scale-up of the reforming of COG.

Gas back-mixing study in a membrane-assisted micro-structured fluidized bed

Membrane-assisted micro-structured fluidized beds have been proposed as efficient membrane reactors and in particular for hydrogen production. However, very little information is available on the effects of gas permeation through the membrane on the gas back-mixing and mass transfer rates in this type of reactors. This study carefully investigates the gas back-mixing characteristics in a micro-fluidized bed and the influence of gas permeation (both addition and extraction) through flat membranes installed in the left and right walls confining the fluidized bed. The tracer gas injection (stimulus-response) method has been used combined with Particle Image Velocimetry and Digital Image Analysis techniques for additional insightful information on the solids flux profiles that strongly influence the gas back-mixing. The results of this study demonstrate that micro-structuring of the fluidized bed results in reduced gas back-mixing and thus in a more efficient membrane reactor configuration for hydrogen production because of the increased driving force for gas permeation. The results also provide some guidelines for the design of micro-structured fluidized bed membrane reactors in terms of preferred specific membrane area and particle size.

Progress in Reactors for High-Temperature Fischer–Tropsch Process: Determination Place of Intensifier Reactor Perspective

Abstract High-temperature Fischer–Tropsch (HTFT) process aims to produce lighter cuts such as gasoline and diesel. For many years there have been studies and improvements on HTFT process to make the existing reactors more efficient. Recent studies proposed new configurations such as dual-type membrane reactor and coupling configurations reactor, which improved the performances of this process. This achievement persuades us to update the existing knowledge about the available reactors for HTFT process. In this article, features and performances overview of two classes of reactors are reviewed. The first class consists of the reactors which are based on older studies, and the second one includes recent studies which are called product intensifier reactors. Finally, it is shown that the product intensifier reactors have higher CO conversions and lower selectivity of undesired by-products which results in higher production yield of gasoline. Furthermore, the place of product intensifier reactor among common reactors with regard to the influence of the process parameters on the product distribution has been estimated.

Comparison between fixed bed and fluidized bed membrane reactor configurations for PEM based micro-cogeneration systems

This simulation work analyzes different membrane reactor configurations applied to a 2 kW micro-cogeneration system based on Proton Exchange Membrane Fuel Cell. The adoption of membrane reactor technology achieves an overall electrical and 2nd law efficiency of about 43% and 48% respectively, in comparison to 34% and 38% with conventional fuel processor. The comparison between packed bed and fluidized bed membrane reactor shows an increase of about 25% in membrane area required for the packed bed configuration (without pre-reforming section); this difference decreases when a pre-reformer is used for the packed bed option. Furthermore, a parametric study on the effect of reactor pressure and temperature has been carried out along with an exergy analysis, showing that fuel processor and steam generator exergy losses with conventional fuel processing systems accounts for 33.6%, while membrane reformer reduces to 20.4%. Finally, the performance of a membrane reactor configuration offering the capability of CO 2 capture, integrated within the fuel cell cogeneration system, is presented and discussed.

Applicability of membrane reactor for WGS coal derived gas processing: Simulation-based analysis

Gas from coal gasification contains less hydrogen than from other syngas production methods. An attractive option is its further hydrogen enrichment for pure hydrogen production in a membrane reactor (MR) by water gas shift (WGS). The goal of the present study was to analyse MR fed with coal derived gas. Simulations for feasible membrane permeation parameters revealed that to get high conversion above 90% a relatively high S/C should be applied. Moreover, hydrogen recovery is in this case low (below 30%) so for hydrogen production an additional H 2 separation after the MR should have been applied. The paper also shows that a clear advantage of counter- over co-current flow configuration in MR appears only for low pressure in the reaction zone. The realistic feasible Pd–Cu–Ni membrane parameters result in a rather large membrane area, thus possible heat exchange between the reaction and permeation zone can have important influences on temperature profiles in the MR. This cooling effect could lessen excessive temperature increase in the reaction zone. Results for other than single step MR configurations are also presented in the paper. It is stated in conclusion that future successful application of MRs for coal-derived gas depends on development of not only new catalysts with adequately wide operational temperature range, but also membranes with a high enough permeability.

Membrane Reactor Microstructure for Polymer Grade Olefin Production and Hydrogen Cogeneration

The current communication describes research work on effective membrane reactor nanostructures and nanoreaction-nanoseparation technology for polymer grade olefin production via catalytic paraffin dehydrogenation reactions. Emphasis is given in systems of permreactors and permeators to perform the described reactive and separative operations. We elaborate on new membrane microstructure designs for paraffin dehydrogenations including the design of experiments, operation, and best parameter selection and optimization of such systems. The described processes are of current significance in the area of new microreactor design and operation including hydrocarbon processing and conversion to valuable fuels and chemicals such as hydrogen, olefins, and polyolefins. These improved results are because of the unique design characteristics of the examined microreactor systems to perform accurate multiphase and heterogeneous functions into one unit operation. A number of membrane reactor configurations were made and tested on stream for the catalytic propane dehydrogenation reaction to propylene with successful results. Some of the results are discussed below which show the better performance of nanostructured membrane reactors for the specific dehydrogenation.

Stability, oxygen permeability and chemical expansion of Sr(Fe,Al)O 3 − δ- and Sr(Co,Fe)O 3 − δ-based membranes

Perovskite-type SrFe 0.7Al 0.3O 3 − δ and SrCo 0.8Fe 0.2O 3 − δ , and two related dual-phase composites with nominal compositions (SrFeO 3 − δ ) 0.7(SrAl 2O 4) 0.3 and (SrCo 0.8Fe 0.2O 3 − δ ) 0.7(SrAl 2O 4) 0.3, were comparatively studied employing controlled-atmosphere dilatometry, thermogravimetry, Mössbauer spectroscopy, and measurements of steady-state oxygen permeation fluxes through dense ceramic membranes. The composite materials display lower thermal and chemical expansion compared to the parent single-phase perovskites. The thermal expansion coefficients at 1023–1223 K are however still high, (20–23) × 10 − 6 K − 1 at atmospheric oxygen pressure and (17–18) × 10 − 6 K − 1 at p(O 2) = 10 Pa, thus limiting the range of possible membrane reactor configurations. Sr(Co,Fe)O 3 − δ -based materials exhibit extensive vacancy-ordering processes in inert atmospheres, resulting in a slow relaxation of the oxygen nonstoichiometry, chemical expansion and oxygen permeation fluxes. In comparison to Sr(Fe,Al)O 3 − δ , the stability of cobalt-containing ceramics in CO 2 is also poor, which leads to a partial blocking of the membrane surface by decomposition products and degradation of the oxygen transport. Thermogravimetric analysis showed that the interaction with carbon dioxide occurs even at elevated temperatures, up to 1223 K. Under high oxygen chemical potential gradients such as air/(H 2–H 2O), the composite membranes showed kinetically stable operation without bulk decomposition at 1073 K. The kinetic stabilization associated with surface-limited oxygen permeation was confirmed by the conversion-electron Mössbauer spectroscopy analysis of one (SrFeO 3 − δ ) 0.7(SrAl 2O 4) 0.3 membrane exposed to dry CH 4 at 1173 K, where no traces of Fe 2+ and metallic iron were detected in the reduced surface layer.

Integrated analysis of a membrane-based process for hydrogen production from ethanol steam reforming

The aim of this work is to investigate the performance and energy efficiency achieved by an integrated system based on two different ethanol fuel processor configurations: a Conventional Reactor (CR) and a Membrane Reactor (MR). The CR-based configuration system consists of an ethanol reformer followed by two water-gas shift reactors operating at high and low temperatures. The final hydrogen purification is carried out by a preferential oxidizer in order to reduce the CO concentration before feeding the polymer electrolyte membrane fuel cell (PEMFC). A multi-tubular MR process using thin Pd–Ag tubes has also been considered, where the water-gas shift reaction and the hydrogen separation take place simultaneously. The analysis showed that the MR process configuration possesses a simpler system design with a minor advantage in terms of energy efficiency (30%) compared with the conventional system (27%). Moreover, a detailed parametric analysis concerning the effects of water-to-ethanol molar ratio, reaction pressure, reformer and MR temperature, sweep-gas molar ratio and MR configuration on the achieved performance (hydrogen yield) and energy efficiency of the system has also been done. The importance of optimizing integrated systems is shown since the optimal operating conditions from a global efficiency analysis point of view are in general distinct when compared with those obtained when focusing on the reformer reactor or individual process units alone.

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.

Economic feasibility of silica and palladium composite membranes for industrial dehydrogenation reactions

This article addresses the economic feasibility of silica and palladium composite membranes for gaseous dehydrogenation reaction schemes. Unlike other methodologies addressed so far, this work presents the economic assessment of dehydrogenation reaction schemes using a conceptual design based simulation methodology for the comparative economic assessment of membrane reactors with conventional reactors. The suggested methodology is applied to two industrially prominent reaction schemes namely styrene (from ethylbenzene) and propylene (from propane) production using silica and palladium composite membrane reactors. Various sub-cases studied in this work include the influence of membrane area per reaction zone volume, reaction zone temperature, reaction and permeation zone pressure, membrane thickness and sweep gas flow rate on process economics. Based on this work, the propylene production scheme is evaluated to provide 60–70% excess profits using membrane reactors when compared with the conventional reactor based technology. However, the gross profit profiles for both conventional reactor and membrane reactor configurations have been found to be similar for styrene production case. For all cases, the cost contribution of membranes and other auxiliary equipment is estimated not to exceed 20% of the total costs. In addition, similar economic performance has been observed for both silica and palladium membranes. Based on these studies, it has been concluded that the industrial applicability of membrane reactors is economically suitable for those dehydrogenation reactions that enable significant conversion enhancement with respect to the conventional reactor technologies.

Feasibility of Coupling Dehydrogenation of Ethylbenzene with Hydrogenation of Nitrobenzene in an Autothermal Catalytic Membrane Reactor: Modeling Study

The coupling of reactions in catalytic membrane reactors provides novel reactor configurations that allow shifting the thermodynamic equilibrium and yields of thermodynamically limited reactions and enhancing significantly the rate of production. An interesting pair to couple is the dehydrogenation of ethylbenzene to styrene and the hydrogenation of nitrobenzene to aniline. Hydrogen produced in the dehydrogenation side diffuses through the membrane and assists in shifting the equilibrium conversion of ethylbenzene and the yield of styrene while the large heat of reaction released from the hydrogenation side is utilized to provide the heat needed on the dehydrogenation side. The feasibility and performance of the co-current integrated catalytic membrane reactor configuration is investigated by means of models based on both homogeneous and heterogeneous fixed bed concepts. The ethylbenzene conversion and styrene yield obtained from the proposed reactor are then compared with those for simple fixed bed reactors without membranes. In the homogeneous modeling, the conversion of ethylbenzene is predicted to be ~39% in the simple fixed bed (without any membrane) compared to ~85% in the proposed catalytic membrane reactor. When intraparticle diffusion resistance is taken into consideration, the integrated reactor is predicted to have an ethylbenzene conversion of ~72% when catalyst pellets are isothermal and ~65% for non-isothermal catalyst pellets. The yields of styrene predicted by the homogeneous modeling are ~35% and ~80% for the simple fixed bed and the catalytic integrated reactor, respectively. The heterogeneous model of the integrated reactor, however, predicts less substantial, though still major gains, than the homogenous model, i.e. a styrene yield of ~70% for the isothermal catalyst pellets compared to ~65% for the non-isothermal catalyst pellets.

Computational study of staged membrane reactor configurations for methane steam reforming. I. Optimization of stage lengths

AbstractThis article and Part II report a computational study carried out to analyze the performance achievable using a staged membrane reactor in the methane steam reforming process to produce high purity hydrogen. A reaction/separation unit in which reactive stages are laid out in series to permeative stages already proposed in literature (Caravella et al., J Memb Sci. 2008;321:209–221) is modified here to increase its flexibility. The improvement includes the consideration of the Pd‐based membrane along the entire length. Two‐ and ten‐staged reactors are examined in terms of methane conversion, hydrogen recovery factor and hydrogen recovery yield, considering co‐ and counter‐current flow configurations. Individual stage lengths are obtained by maximizing either methane conversion or hydrogen recovery yield, comparing the results to the ones of an equivalent traditional reactor and a conventional membrane reactor. The analysis allows demonstrating that the counter‐current configuration leads to significant improvements in the hydrogen recovery, but proves almost irrelevant with respect to methane conversion. The influence of the number of stages and the amount of catalyst is quantified in the accompanying part II article. © 2009 American Institute of Chemical Engineers AIChE J, 2010