Membrane Reactor Concept Research Articles

Simultaneous overcome of the equilibrium limitations in BSCF oxygen-permeable membrane reactors: Water splitting and methane coupling

The equilibrium limitations of water splitting and the coupling of methane to C2 hydrocarbons (ethane+ethylene) were simultaneously overcome by using a perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) oxygen-permeable membrane reactor. Oxygen produced from thermal water splitting was transported through the BSCF membrane and consumed in the coupling of methane. The BSCF membrane consists of an about 70μm thick dense BSCF layer on an about 0.8mm thick porous BSCF layer as support. By applying the membrane reactor concept instead of a fixed bed reactor without oxygen supply, the methane conversion and C2 yield increased from 3.7% to 26% and 3.1% to 6.5% at 950°C, respectively. In both experiments, the supported 2wt.% Mn–5wt.% Na2WO4 catalyst was used at 950°C. Simultaneously, about 9% of the H2O injected was converted to hydrogen with a production rate of about 3.3cm3min−1cm−2 at 950°C which is higher than 1 m3 (STP) H2 m−2h−1.

REMOVED: A Model Based on Maxwel Stefan to Evaluate Membrane Reactor Concepts

REMOVED: A Model Based on Maxwel Stefan to Evaluate Membrane Reactor Concepts

A dynamic membrane reactor concept for naphtha reforming, considering radial-flow patterns for both sweeping gas and reacting materials

Hydrogen will become an essential energy source in the near future. In this regard, refineries can be considered as alternative sources of hydrogen production. In the present study, a tubular membrane reactor with radial-flow patterns of the sweeping gas and the naphtha feed named RF-TMR is proposed as a novel configuration for radial-flow naphtha reformers. Radial-flow reactors are used in refineries as a remedy for high pressure drop through the catalytic packed-bed reactors which disturbs the reactor operation. The cross section area of the tubular membrane reactor is divided into some subsections. The walls of the gaps are coated by a Pd–Ag membrane layer to separate hydrogen from reaction side and enhance the hydrogen and aromatic production rates by 0.33 ton/day and 5.5 ton/day, respectively (compared with the AF-TR). The performance of this novel configuration is investigated and compared with the axial-flow conventional tubular reactor (AF-TR) and axial-flow tubular membrane reactor (AF-TMR). Set of coupled partial differential–algebraic equations are solved by the orthogonal collocation method. Owing to a slight pressure drop in the tube side of RF-TMR, smaller catalysts’ particles with a negligible internal mass transfer resistance can be used to increase aromatics and hydrogen yields. This novel approach has the feasibility to be applied in the radial-flow moving bed reformers which are widely installed in refineries by licensors.

A novel slurry bubble column membrane reactor concept for Fischer–Tropsch synthesis in GTL technology

Fischer–Tropsch synthesis (FTS) plays an important role in the production of ultra-clean transportation fuels, chemicals, and other hydrocarbon products. In this work, a novel combination of fixed-bed and slurry bubble column membrane reactor for Fischer–Tropsch synthesis has been proposed. In the first catalyst bed, the synthesis gas is partially converted to hydrocarbons in a water-cooled reactor which is fixed bed. In the second bed which is a membrane assisted slurry bubble column reactor, the heat of reaction is used to preheat the feed synthesis gas to the first reactor. Due to the decrease of H2/CO to values far from optimum reactants ratio, the membrane concept is suggested to control hydrogen addition. A one-dimensional packed-bed model has been used for modeling of fixed-bed reactor. Also a one-dimensional model with plug flow pattern for gas phase and an axial dispersion pattern for liquid-solid suspension have been developed for modeling of slurry bubble column reactor. Proficiency of a membrane FTS reactor (MR) and a conventional FTS reactor (CR) at identical process conditions has been used as a basis for comparison in terms of temperature, gasoline yield, H2 and CO conversion as well as selectivity. Results show a favorable temperature profile along the proposed concept, an enhancement in the gasoline yield and, thus a main decrease in undesirable product formation. The results suggest that utilizing this type of reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the proposed reactor.

A novel dynamic membrane reactor concept with radial‐flow pattern for reacting material and axial‐flow pattern for sweeping gas in catalytic naphtha reformers

AbstractNaphtha reforming units are of high interest for hydrogen production in refineries. In this regard, the application of membrane concept in radial‐flow tubular naphtha reactors for hydrogen production is proposed. Because of the importance of the pressure drop problem in catalytic naphtha reforming units, the radial‐flow reactors are proposed. A radial‐flow tubular membrane reactor (RF‐TMR) with the radial‐flow pattern of the naphtha feed and the axial‐flow pattern of the sweeping gas is proposed as an alternative configuration for conventional axial‐flow tubular reactors (AF‐TR). The cross‐sectional area of the tubular reactor is divided into some subsections in which walls of the gaps between subsections are coated with the Pd‐Ag membrane layer. A dynamic mathematical model considering radial and axial coordinates ((r, z)‐coordinates) has been developed to investigate the performance of the new configuration. Results show ∼300 and 11 kg/h increase in aromatic and hydrogen production rates in RF‐TMR compared with AF‐TR, respectively. Furthermore, smaller catalyst particles with higher efficiency can be used in RF‐TMR due to a slight pressure drop. The enhancement in aromatics (octane number) and hydrogen productions owing to applying simultaneously the membrane concept and radial‐flow pattern in naphtha reactors motivates the application of RF‐TMR in refineries. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Application of a flow-through catalytic membrane reactor (FTCMR) for the destruction of a chemical warfare simulant

In this study the flow-through catalytic membrane reactor (FTCMR) concept is applied in the thermal oxidation of a chemical warfare simulant, namely dimethyl methylphosphonate (DMMP), in air. Preliminary experiments under different DMMP feed concentrations and reactor temperatures (373–573 K) have demonstrated the potential advantage of the FTCMR concept in the catalytic oxidation of DMMP. Complete destruction of various concentrations of DMMP in air was achieved at lower temperatures, with the FTCMR showing superior performance when compared to a wall-coated, plug-flow reactor (monolith) containing the same amount of catalytic metal. A mathematical model has also been developed in order to provide a better understanding of the fundamental transport phenomena underpinning the FTCMR operation. The model makes use of the Dusty-Gas formulation of transport, and incorporates continuum and Knudsen diffusion, as well as viscous flow as the mechanisms for gas transport through the porous membrane. The model is used for identifying the advantages of the FTCMR concept in comparison with the wall-coated catalytic monolith, and also for investigating some of the limitations, which may exist in applying this concept for the complete oxidation of chemical warfare simulants. The results of the model support the superiority of the FTCMR concept over the more conventional plug-flow monolith reactor.

The aromatic enhancement in the axial‐flow spherical packed‐bed membrane naphtha reformers in the presence of catalyst deactivation

AbstractBecause of some disadvantages of conventional tubular reactors (CTRs), the concept of spherical membrane reactors is proposed as an alternative. In this study, it is suggested to apply hydrogen perm‐selective membrane in the axial‐flow spherical packed‐bed naphtha reformers. The axial flow spherical packed‐bed membrane reactor (AF‐SPBMR) consists of two concentric spheres. The inner sphere is supposed to be a composite wall coated by a thin Pd‐Ag membrane layer. Set of coupled partial differential equations are developed for the AF‐SPBMR model considering the catalyst deactivation, which are solved by using orthogonal collocation method. Differential evolution optimization technique identifies some decision variables which can manipulate the input parameters to obtain the desired results. In addition to lower pressure drop, the enhancement of aromatics yield by the membrane layer in AF‐SPBMR adds additional superiority to the spherical reactor performance in comparison with CTR. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Continuous membrane-based screening system for biocatalysis.

The use of membrane reactors for enzymatic and co-factor regenerating reactions offers versatile advantages such as higher conversion rates and space-time-yields and is therefore often applied in industry. However, currently available screening and kinetics characterization systems are based on batch and fed-batch operated reactors and were developed for whole cell biotransformations rather than for enzymatic catalysis. Therefore, the data obtained from such systems has only limited transferability for continuous membrane reactors. The aim of this study is to evaluate and to improve a novel screening and characterization system based on the membrane reactor concept using the enzymatic hydrolysis of cellulose as a model reaction. Important aspects for the applicability of the developed system such as long-term stability and reproducibility of continuous experiments were very high. The concept used for flow control and fouling suppression allowed control of the residence time with a high degree of precision (±1% accuracy) in a long-term study (>100 h).

Impact of ceramic membranes for CO2 separation on IGCC power plant performance

The potential of carbon capture from coal gasification power plants by H2 selective ceramic membranes is investigated. Detailed models of a reference power plant and three different carbon capture concepts were setup with Aspen Plus and Ebsilon. Parameter variations were performed to investigate the influence of membrane characteristics and power plant specific boundary conditions on the performance of the capture concepts. For ceramic membranes with a selectivity of H2 versus N2 and CO2 of 500 the results showed that for a sour CO-shift and sweet CO-shift efficiency losses of 9.07 and 9.43% points are feasible, respectively, while separating about 97% of the CO2 with a purity of 95%. A ceramic membrane reactor concept with simultaneous CO2 separation and CO-shift was the third carbon capture concept investigated. This concept achieves separation degrees of 96.6% and purities above 95% with an efficiency loss of 6.7% points.

A novel cascade membrane reactor concept for methanol synthesis in the presence of long-term catalyst deactivation

In this study, a dynamic model for a novel cascade membrane methanol reactor (CMMR) in the presence of long term catalyst deactivation was developed. In the first catalyst bed the synthesis gas partially convert to methanol. In the second reactor the reaction heat is used to preheat the feed gas to the first bed. The wall of the tubes in the both of reactors is covered with a palladium–silver membrane. The simulation results represent 4.7% and 3.92% enhancement in the yield of methanol production during 1400 days of operation in the CMMR in comparison with conventional dual type methanol reactor (CDMR) and membrane dual type methanol reactor (MDMR), respectively and a favorable profile of temperature and activity along the CMMR relative to MDMR and CDMR. Copyright © 2010 John Wiley & Sons, Ltd.

Continuous screening system for inhibited enzyme catalysis: A membrane reactor approach

The screening of catalysts, substrates or conditions in the early stages of bioprocess development requires an enormous number of experiments and is a tedious, expensive and time-consuming task. Currently available screening systems can only be operated in batch or fed-batch mode, which can lead to severe misinterpretations of screening results. For example, catalysts that are inhibited by substrates or accumulating products will be excluded from further investigations in the early stages of process development despite the fact that they might be superior to other candidates in a different operational mode. Important and advantageous properties such as turnover stability can also be overshadowed by product inhibition. The aim of this study was to develop a novel screening system that enables continuous feeding of substrates and continuous removal of products. A prototype based on the membrane reactor concept was designed and operated for a model reaction, the hydrolysis of cellulose.

In this issue: Biotechnology Journal 8/2010

AbstractBiocatalyst microemulsionsPavlidis et al., Biotechnol. J. 2010, 5, 805–812Enzymes maintain their catalytic activity when hosted in aqueous nanodroplets like reverse micelles. Researchers from Ioannina, Greece, propose the use of water‐in‐ionic liquid microemulsionbased organogels (w/IL MBGs) as novel supports for the immobilization of lipase B from Candida antarctica and lipase from Chromobacterium viscosum. These novel lipase‐containing w/IL MBGs can be effectively used as solid phase biocatalysts in various polar and non‐polar organic solvents or ILs, exhibiting up to 4.4‐fold higher esterification activity compared to water‐in‐oil microemulsion‐based organogels. The immobilized lipases retain their activity for several hours at 70°C, while their half life time is up to 25‐fold higher compared to that observed in w/IL microemulsionsBiocatalyst cryogelationBieler et al., Biotechnol. J. 2010, 5, 881–885Entrapment of biocatalysts in hydrogel beads allows stable operation in otherwise deteriorating solvents. Doing this by cryogelation is a gentle method to extend the scope of biocatalysis. To foster the use of this versatile method, researchers from Aachen, Germany, devised an automated injector for the production of PVA/PEG‐enzyme immobilisates. The device consists of a thermostated reservoir connected to a programmable injector nozzle and an agitated receiving bath for the droplets. This lab‐scale production unit yields up to 1500 beads with immobilized enzyme per minute with a narrow size distribution and good roundness.Biocatalyst membrane reactorLyagin et al., Biotechnol. J. 2010, 5, 813–821Screening of biocatalysts, substrates or conditions in the early stages of bioprocess development requires an enormous number of experiments and is a tedious, expensive and time‐consuming task. Currently available screening systems can only be operated in batch or fed‐batch mode, which can lead to severe misinterpretations of screening results. Researchers from Berlin, Germany, now developed a novel screening system that enables continuous feeding of substrates and continuous removal of products. A prototype based on the membrane reactor concept was designed and operated for a model reaction, the hydrolysis of cellulose.

Reaction integrated separation of homogenous catalysts in the hydroformylation of higher olefins by means of organophilic nanofiltration

Discovered in 1938, hydroformylation is one of the most important reactions using homogeneous precious metal catalysts. In the process, olefins react to aldehydes using hydrogen and carbon monoxide (synthesis gas). The main problem for the sensitive and expensive catalyst system, however, is the downstream processing of the reaction products, typically done by thermal separation, by which the catalyst system deactivates and is lost by clustering. In contrast, organophilic nanofiltration allows the catalyst to be separated under stabilizing conditions in a gentle and also energy saving way. As a first step to an integrated membrane reactor concept for homogeneous catalysis, two different membranes and the influence of CO on the separation were investigated for the Rh catalysed hydroformylation of octene and dodecene as examples. Catalyst rejections in excess of 99% in a single stage membrane separation combined with a high CO partial pressure that prevents the catalyst from deactivation and losses through the formation of clusters during the separation shows that organophilic nanofiltration can be a benchmark setting separation technology in homogeneous catalysis.

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.

Biocatalytic membrane reactor and membrane emulsification concepts combined in a single unit to assist production and separation of water unstable reaction products

The aim of the present work was to develop and proof the concept of an integrated and intensified membrane system able to carry out in a single operation unit, bioconversion (in water phase), and simultaneous separation of reaction products (having different solubility and stability in water), by creating water in oil emulsion. To achieve this aim, the concepts of biocatalytic membrane reactor and membrane emulsification have been integrated. This resulted in a combined membrane operation system where hydrolysis occurred within the microporous membrane structure (that contained immobilized enzyme) and extraction occurred at the membrane interface. Here, the permeating water reaction phase was collected as droplets into the organic phase circulated along the lumen membrane surface. The oleuropein hydrolysis into glucose and isomer of oleuropein aglycon (3,4-DHPEA-EA) by means of β-glucosidase immobilized in porous polymeric membrane has been used as a model reaction system.

On the Membrane Reactor Concept for One-Step Hydroxylation of Benzene to Phenol with Oxygen and Hydrogen

The one-step hydroxylation of benzene to phenol with oxygen and hydrogen is a promising process, but there are severe challenges associated with the low phenol production. It was reported that the reaction can be greatly promoted by the simultaneous use of a dense palladium membrane as a catalyst and as a hydrogen distributor. We also carried out this reaction concept with palladium membranes under different reaction conditions, but found that the palladium membranes were almost inert for both the target reaction and the benzene combustion. This work summarized and compared among the literature results as well as ours, investigating the effects of the membrane preparation method and the combustion of hydrogen and benzene. The arguments on the mechanism and feasibility of the membrane concept were given in detail.

A new conception of enzymatic membrane reactor for the production of whey hydrolysates with low contents of phenylalanine

A novel concept of enzymatic membrane reactor (EMR) is presented, aiming at the production of cheese whey protein hydrolysates with low contents of phenylalanine (Phe) for the diet of phenylketonuria patients. Whey proteins were first hydrolyzed by chimotrypsin, followed by the action of carboxypeptidase A (CPA), immobilized on agarose gel particles, which were retained inside the reactor using a filter. The liquid medium passes through hollow fiber ultrafiltration unit (1 kDa cut-off), and the retentate is recycled to the reactor. The innovation here is that the membrane is not used to retain the enzyme neither physically nor as an immobilization support. The EMR provided a higher performance than the classical, sequential approach: batch reaction followed by ultrafiltration. It was confirmed that the removal of products promoted by the EMR enhances reaction rates, due to the reduction of inhibition effects. A mathematical model of the EMR is also presented and validated.

Autothermal Reforming of Methane with Integrated CO2 Capture in a Novel Fluidized Bed Membrane Reactor. Part 1: Experimental Demonstration

Two fluidized bed membrane reactor concepts for hydrogen production via autothermal reforming of methane with integrated CO2 capture are proposed. Ultra-pure hydrogen is obtained via hydrogen perm-selective Pd-based membranes, while the required reaction energy is supplied by oxidizing part of the CH4 in situ in the methane combustion configuration or by combusting part of the permeated H2 in the hydrogen combustion configuration (oxidative sweeping). In this first part, the technical feasibility of the two concepts has been studied experimentally, investigating the reactor performance (CH4 conversion, CO selectivity, H2 production and H2 yield) at different operating conditions. A more detailed comparison of the performance of the two proposed reactor concepts is carried out with a simulation study and is presented in the second part of this work.

Reactors for Fischer‐Tropsch Synthesis

AbstractThe Fischer‐Tropsch synthesis was discovered in Germany in the 1920s and has since been developed to industrial scale within a relatively short period of time. In the 21st century, the process is undergoing a renaissance, because an increasing fraction of liquid fuels will have to be produced from alternative raw materials like natural gas, coal or biomass in the future. On industrial scale, multitubular and bubble column reactors are used for this highly exothermic reaction. Due to several disadvantages of both reactor systems, new concepts are presently investigated. For intensification of mass transfer properties of multiphase reactors, alternative catalyst geometries like honeycombs, structured packings or foams are discussed. High catalyst utilization and isothermal operating conditions can be achieved in microstructured reactors. Furthermore, several membrane reactor concepts are under investigation. After an introduction to historical development and state of the art of Fischer‐Tropsch reactors, chances and challenges of new reactor technologies will be discussed.

Fischer–Tropsch synthesis with in situ H2O removal – Directions of membrane development

H2O is the main by-product of the Fischer–Tropsch (FT) reaction. The motivation for in situ H2O removal by means of hydrophilic membranes is threefold: (a) to reduce H2O promoted catalyst deactivation, (b) to boost the reactor productivity, and (c) to displace the water gas shift (WGS) equilibrium to enhance the conversion of CO2 to hydrocarbons. The selective removal of H2O from a complex mixture of H2, CO, CO2 and hydrocarbons under FT conditions is a challenging task for membranes and membrane preparation.The potential of the FT membrane reactor concept is illustrated by mathematical case studies. The results of the experimental demonstration of in situ H2O removal under reactive FT conditions with an amorphous silica membrane and a ceramic supported polymer membrane prove the concept but confirm the high demands on membrane permeance, permselectivity and stability. Based on mathematical case studies, experimental results and a literature study on hydrophilic membranes, the following critical membrane specifications are formulated: (a) permeance QH2O>1×10−7mol/(sm2Pa) and (b) permselectivities SH2O/H2, SH2O/CO, SH2O/CO2>75.With regard to the literature on hydrophilic membranes, microporous zeolite membranes outperform amorphous microporous membranes and polymer membranes. A new type of membrane prepared by direct hydrothermal synthesis on α-Al2O3 supports is a thin defect free hydroxy sodalite (H-SOD) film with a layer thickness of 2μm. This type of membrane offers high permselectivities and high H2O fluxes at temperatures up to 200°C and is therefore, a promising candidate for in situ H2O removal during FT synthesis.