Flow-through Catalytic Membrane Research Articles

Modeling and numerical analysis for cylindrical flow-through catalytic membrane reactor with power-law reaction kinetics: Revealing dead-core phenomena

Cylindrical flow-through catalytic membrane reactors, employing porous membranes impregnated with catalysts, offer enhanced selectivity and yield in chemical reactions. This work focuses on the mathematical modeling and numerical analysis of a cylindrical flow-through catalytic membrane reactor. The proposed reactor model addresses a critical gap in research by incorporating realistic geometries of porous catalytic membranes. This model simulates a series of irreversible reactions following power-law kinetics under non-isothermal conditions within the reactor, formulated using a system of non-linear differential equations to account for mass and heat balances.The paper investigates the occurrence of dead zones within the membrane reactor as a result of rapid reactant depletion, a phenomenon that has not been extensively studied in prior literature for cylindrical membrane reactors. Problems with fractional reaction exponents require efficient numerical solvers since conventional iterative solvers encounter difficulties due to the fact that the power-law reaction term with fractional reaction exponent is not differentiable at the vanishing concentration. A novel time-marching scheme specifically designed for the cylindrical catalytic flow-through membrane reactor is developed and applied for simulations to get valuable insights into dead-core phenomena.The effects of dimensionless process parameters, including Thiele modulus, Peclet numbers, reaction exponent, Prater number, and a membrane geometrical parameter on the concentration and temperature profiles, as well as dead zone formation, are extensively investigated. The simulation results demonstrate that these parameters affect the occurrence of dead zones and their size. Finally, the effect of convective flow on the reactor performance indicators is presented.

Electro-driven multi-functional catalysis separation membrane reactor with switchable wettability for efficient water purification

A flow-through catalytic separation membrane reactor with adjustable wettability can achieve efficient and controllable on-demand separation and catalytic purification of wastewater.

A flow-through catalytic membrane micro-reactor for hydrogen production by methanol steam reforming

A flow-through catalytic membrane micro-reactor (CMR) with Cu/ZnO/Al2O3 nanoparticles immobilized in porous membrane pores has been developed for hydrogen production by methanol steam reforming (MSR). The characteristics for CMR demonstrated Cu/ZnO/Al2O3 nanoparticles with almost 200 nm were successfully in situ immobilized in membrane pores. During MSR for hydrogen production in CMR by flow-through mode, hydrogen yield of 500 mmol h−1 g−1 and selectivity of 100% can be achieved under the condition of temperature being 360℃, molar ratio of water to methanol of 8.8 and weight hourly space velocity (WHSV) of 9.28 h−1. Compared with the commercial fixed bed reactor, the hydrogen productivity in CMR is one order of magnitude higher, owing to MSR confined in the space of membrane pore with micro-scale. The methanol conversion rate of over 95% can be expected, if five sheets of CMR with thickness of 5 mm were assembled in series.

Flow-through catalytic nanofiber membrane assembly of hierarchically porous structure with Ag nanoparticles immobilized for enhanced catalysis

A hierarchically porous flow-through catalytic nanofiber membrane immobilized with Ag nanoparticles (Ag/HP-FCNM) has been developed by combining electrospinning and sacrificial template. The characterization results of Ag/HP-FCNM imply that mesopores with an average size of 50 nm are successfully fabricated on Polyacrylonitrile (PAN) nanofibers, and 6 nm of Ag nanoparticles are immobilized in the mesopores, effectively preventing the aggregation of Ag nanoparticles and increasing the surface area. The HP-FCNM with Ag nanoparticles content of 35.02% has a permeance of 18680 L·m−2·h−1·bar−1 can enhance the contact between catalyst and reactant. During the process of p-Nitrophenol (p-NP) reduction by Ag/HP-FCNM under the flow-through mode, the apparent reaction rate constant (Kapp) of 272.45 min−1, treatment capability of 200.34 mmol·m−2·h−1 and specific treatment capability of 14.27 mmol·g−1·h−1 can be achieved. Furthermore, good applicability of the Ag/HP-FCNM is also demonstrated with excellent conversions (both above 99%) when treating o-Nitrophenol (o-NP) and Rhodamine B (RhB) at a concentration of 0.25 mM and a membrane flux of 192 L·m−2·h−1. Good stability can be still performed after 160 min of continuous use, which implies the prospect of the Ag/HP-FCNM.

Pore flow-through catalytic membrane reactor for steam methane reforming: characterization and performance

A new reactor configuration with low Pd loadings allows good methane conversion results at low temperatures.

Numerical simulations of dead zone formation in the catalytic flow-through membrane reactor

The use of catalytic membranes in chemical reactor engineering has significantly improved the reactor performance. Therefore, mathematical modelling and numerical simulations of catalytic membrane reactors are important for optimal parameter design increasing the selectivity and yield of certain products in chemical reactions. In this paper, the mathematical model of the flow-through catalytic membrane reactor is based on coupled nonlinear convection-diffusion-reaction equations with temperature-dependent reaction rate constants. The series reactions in the reactor are characterized by the power-law kinetics of fractional order which until now has been rarely investigated in the literature. Under specific reaction and process conditions the reactant can be depleted and a dead-zone can be formed in the membrane reactor. The numerical simulation of this phenomenon requires special solvers. The key idea of this work is to construct an appropriate time-marching scheme for solving the steady-state model equations. The effects of parameters such as reaction order, Peclet number, and Thiele modulus on solution profiles and formation of dead-zones are studied numerically. The simulation results show how these parameters influence the appearance and size of the dead zone for the non-isothermal multi-reaction systems.

Polydopamine modified Au/FAU catalytic membrane for CO preferential oxidation

A hollow-fiber-supported stable Au/FAU catalytic membrane was successfully synthesized through a polydopamine coating modification-removal strategy and used as a flow-through catalytic membrane reactor for preferential oxidation of CO. Small Au nanoparticles can be efficiently isolated by dopamine and the dopamine-derived carbon shells. The interactions between Au nanoparticles and zeolite layer support are enhanced during annealing at high temperature under an inert atmosphere. A zeolite membrane supported Au nanoparticle catalyst was obtained after the removal of carbon shells, which showed high catalytic activity and stability for the removal of CO from hydrogen.

Pd nanoparticles immobilized on TiO2 nanotubes-functionalized ceramic membranes for flow-through catalysis

A high performance catalytic membrane was fabricated with Pd nanoparticles supported by TiO2 nanotubes, where the TiO2 nanotubes were synthesized on the ceramic membrane via a simple hydrothermal etching. A flow-through catalytic membrane reactor was developed for testing the catalytic properties in the p-nitrophenol reduction. The effect of etching time was investigated in detail and an optimal etching time was determined to be 16 h. The characterization results highlighted that the as-prepared bouquet-like TiO2 nanotubes could significantly improve the loading amount and dispersity of Pd nanoparticles. The fabricated catalytic membrane exhibited considerably improved catalytic activity and stability, with a 100% conversion of p-nitrophenol and no loss in catalytic activity during five reaction cycles. The obtained activation energy was much lower than the values in literatures, implying that the p-nitrophenol reduction could take place more easily on our catalytic membranes compared to other catalysts.

Development and characterization of a catalytic membrane for volatile organic compound combustion

Platinum-alumina (Pt/γ-Al 2 O 3 )catalytic membranes were obtained using the reservoir technique for the combustion of volatile organic compounds (VOCs). The membranes were characterized by scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDXA) observation, Brunauer-Emmett-Teller (BET) measurement and gas permeation. Propane (C 3 H 8 ) and n-butane (C 4 H 10 ) combustion was obtained. Maximum VOC conversion for p ropane and n-butane of 93 and 48 (%) was achieved on 3.52wt% Pt catalyst at a temperature of 427 and 259 ( 0 C) and flow rates of between 185-222 and 295-379 (ml/min) without any changes in conversion . The combustion results of C 3 H 8 and C 4 H 10 corroborate with literature on Pt/γ-Al 2 O 3 catalysts. The conversion was achieved using flow-through catalytic membrane reactor operating in the Knudsen flow regime. http://dx.doi.org/10.4314/njt.v37i4.18

Comparison of membrane and conventional reactors under dry methane reforming conditions

A flow-through catalytic membrane reactor has been experimentally compared with a conventional fixed bed catalytic reactor by matching the specific rate constants in the reaction of dry reforming of methane. Crushed membrane and powdered catalysts with tungsten carbide as the active ingredient have been used as a reference in the conventional reactor. An increase in the reaction rate in the membrane reactor has been explained in terms of emerging Knudsen transport and also by the features of the membrane catalyst, which make it possible to force transport in the pore space of the catalytically active substance. It has been assumed that the “rarefaction” of the gases in the catalyst pores can be accompanied by a change in the equilibrium and a shift in the process toward the products of the direct reaction.

Reduction of methylene blue with Ag nanoparticle-modified microporous polypropylene membranes in a flow-through reactor

Methylene blue was reduced by the flow-through catalytic membrane reactor in real time with the flow rate larger than 210 L m−2 h−1.

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.

Biodiesel Production by Quaternized Polysulfone Membrane: Experimental and Kinetics Model

Abstract The quaternized polysulfone catalytic membrane as a heterogeneous catalyst was used for producing biodiesel from continuous transesterification of soybean oil and methanol in flow-through catalytic membrane reactor. A kinetic model of transesterification for describing the transesterification was established. The conversions obtained from established model are in good agreement with the experimental data. The kinetics model of membrane can well predict the transesterificaton conversion.

VOC oxidation in excess of oxygen using flow-through catalytic membrane reactor

Platinum gamma-alumina (Pt/γ-Al2O3) impregnated membrane was prepared through the evaporative-crystallization deposition method for volatile organic compounds (VOCs) conversion to carbon dioxide (CO2) and water (H2O). The catalytic oxidation of VOCs (propane, n-butane and propylene), fed alone with oxygen were obtained after characterization (SEM-EDXA observation, BET measurement, permeability assessment). VOC conversion of 95%, 52% and 82% for propane, n-butane and propylene was achieved at 378 °C, 245 °C and 420 °C respectively, by varying the reaction temperature using the contactor flow-through catalytic membrane reactor operating in the Knudsen flow regime. The BET surface area and the pore diameter of the 3.52 wt% Pt membrane are 0.426 m2/g and 3.70 nm respectively. The results are comparable with the literature.

CO preferential oxidation in a novel Au@ZrO2 flow-through catalytic membrane reactor with high stability and efficiency

CO preferential oxidation (CO-PROX) achieves much interest as a strategy to remove trace CO in reformed gases for hydrogen utilization. Herein, we reported a novel Au@ZrO2 catalytic membrane reactor by embedding gold nano-particles in ZrO2 hollow fiber membrane for CO-PROX. The flow-through catalytic membrane exhibited high catalytic activity and oxygen selectivity, which gave a turnover frequency of 4.73 s−1 at 60 °C, 2–3 times higher than conventional catalyst pellets. CO conversion of >95% was achieved over the catalytic membrane, which maintained great operational stability during 500-h operation even CO2 and H2O were added in the feed stream. The excellent catalytic performance of the flow-through catalytic membrane makes gold catalyst possible for practical application in the removal of CO from hydrogen.

Flow-through catalytic membrane reactors for the destruction of a chemical warfare simulant: Dynamic performance aspects

A model was developed to describe the dynamic performance of a flow-through catalytic membrane reactor (FTCMR) used for the destruction of a chemical warfare agent (CWA) simulant, specifically dimethyl methylphosphonate (DMMP). For such a reactor, after a certain time period during which it provides full protection, its performance begins to decline, as manifested by a gradual decline in the thermocatalytic destruction rate of the DMMP and discernible changes in the membrane's throughput. The model ascribes these phenomena to changes in the catalytically active membrane surface area and in the accessible membrane pore volume, which are brought upon by the deposition of phosphorous-containing by-products of the DMMP's thermocatalytic decomposition reaction. Such a hypothesis is supported by experimental data for both fresh and aged membranes that substantiate significant losses in surface area and pore volume, and indicate the presence of phosphorous in the aged membranes. The model was used to fit the experimental data from a FTCMR operating under a total flow-through (100% stage-cut) mode of operation, and was shown to describe well the experimental data. In addition, the model was utilized in a predictive mode to describe the performance of a FTCMR employing another membrane from the same batch and catalytically activated under the same procedure, but operating under different operating conditions (0% stage-cut). The model was shown to provide an adequate fit to the experimental data. Following such validation, the model has been used to gain further insight into the impact of the various reactor parameters on FTCMR performance. Its use has, subsequently, led to the development of a novel reactor configuration that significantly expands the operating performance window of the FTCMR for the thermocatalytic CWA destruction.

Esterification of ethyl hexanoic acid using flow-through catalytic membrane reactor

Catalytic membrane reactors, as a promising novel technology, are widely recommended for carrying out heterogeneous reactions. If the reactant feed is forced to flow through the pores of a membrane, which has been impregnated with a convenient catalyst, the intense contact provides high catalytic activity with negligible resistance to diffusive mass transport. The synthesis of a fatty ester (ethylhexanoic ester) by esterification was developed by the Factorial Design and Response Surface Methodology (FDRSM). Selection of factors was based on the operating conditions that have a significant influence on the esterification process, namely temperature, molar ratio of ethanol to fatty acid, and internal surface area of membrane pores. Experimental results indicated that the optimum conditions (under which the conversion achieved 99.7%) were as follows: temperature of 30°C, molar ratio of 5: 1, and internal membrane area of 252450 cm2. It can be concluded that the factorial design is an important tool to reduce time and to facilitate reaching optimum reaction conditions.

Thermocatalytic decomposition of dimethyl methylphosphonate (DMMP) in a multi-tubular, flow-through catalytic membrane reactor

The potential for the use of chemical weapons has increased in recent times. The successful use of a flow-through catalytic membrane reactor (FTCMR) as a protection system against a chemical warfare agent (CWA) was recently reported by this group. This FTCMR, employing a single catalytically active mesoporous membrane, was applied for the destruction of dimethyl methylphosphonate (DMMP), which is known as a chemical precursor (and used to simulate its characteristics) for Sarin (GB), a toxic CWA. In this paper, results are reported of efforts to scale-up this lab-scale FTCMR towards practical individual protection (IP) and collective protection (CP) applications. A multi-tubular FTCMR (MFTCMR) has been developed and tested towards the destruction of DMMP. The MFTCMR has been shown quite effective, providing extended protection periods against this CWA simulant. A key part of the research effort focused on improving the preparation of the catalytically active membranes to prepare membrane bundles with reproducible transport characteristics and reactivity. A key challenge for the large-scale production of such devices, furthermore, remains the development of a simple non-destructive test that assures that the produced parts are appropriate for the proposed application and that they continue to remain active during their shelf-life prior to their use. As part of this effort a simple propane-in-air light-off test was studied, which was shown capable to track the reactivity and performance of the MFTCMR.

A hybrid catalytic membrane reactor for destruction of a chemical warfare simulant

The possibility of use of chemical weapons has increased in recent years, both as a result of potential terrorist attacks as well as of ongoing international conflicts. The successful application of a flow-through catalytic membrane reactor (FTCMR) as an individual protection system for the destruction of dimethyl methylphosphonate (DMMP), which is known as a chemical precursor (and used to simulate its characteristics) for Sarin (GB), a toxic chemical warfare agent (CWA) was previously investigated and reported by this group. As part of the study, the effect of the DMMP concentration in the feed on its complete combustion in the FTCMR was investigated. The studies indicate that the protection (complete conversion) time is a function of the DMMP concentration, with longer times observed for the lower concentrations, and shorter protection times associated with the higher concentrations. In this study a novel hybrid system is being developed that combines the FTCMR with a surface-flow membrane system (SFMS). Preliminary experimental results presented here manifest the main advantage of this hybrid system, combining the SFMS, capable of the physical removal of a large fraction of the CWA from contaminated air streams, and the FTCMR which completely oxidizes the remaining amount, which is the continuous CWA destruction for extended time periods which are appropriate for both individual and collective protection applications. The study investigates the impact on performance of the membrane characteristics, the transmembrane pressure gradient and the sweep ratio. Hybrid system performance is also compared with that of a sole FTCMR showing the superiority of the hybrid system in terms of offering higher destruction rates for DMMP and prolonged protection times.

Biodiesel production from waste chicken fat with low free fatty acids by an integrated catalytic process of composite membrane and sodium methoxide

An integrated process of catalytic composite membranes (CCMs) and sodium methoxide was developed to produce biodiesel from waste chicken fat. The free fatty acids (FFAs) in the chicken oil were converted to methyl esters by esterification with methanol using a novel sulfonated polyethersulfone (SPES)/PES/non-woven fabric (NWF) CCMs in a flow-through catalytic membrane reactor. The CCM is that the NWF fibers were fully embedded in SPES/PES with a homogeneous and microporous structure. The oil obtained after esterification was carried out by transesterification of sodium methoxide. The results showed that the FFAs conversion obtained by CCMs with the acid capacity of 25.28 mmol (H(+)) was 92.8% at the residence time 258s. The CCMs present a good stability during the continuous running of 500 h. The conversion of transesterification was 98.1% under the optimum conditions. The quality of the biodiesel met the international standards.