Comparative study on the numerical simulation of hydrogen separation through palladium and palladium–copper membranes

The hydrogen (H₂) diffusion through palladium (Pd) and Pd–copper (Cu) membranes was numerically investigated by developing a two-dimensional computational fluid dynamics model for predicting the performance of H₂ separation. The momentum and mass transport phenomena in the laminar flow conditions were solved at different operating conditions in a vertical cylindrical-type reactor. The effect of feed-gap distance, H₂ concentration, and reactor heating temperature on the H₂ permeation processes were simulated and compared for both Pd-based membranes. The concentration, velocity, and convective and diffusion mass transfer flux distributions were analyzed using the designed model. The H₂ concentration was proportional to the feed-gap distance/cross-sectional area. The smaller the feed-gap distance, the greater the probability of a H₂ molecule being adsorbed by the membrane surface and the ionization energy increasing, leading to further H₂ dissociation through the Pd-based membranes. It was found that the diffusion flux of all feed concentrations was substantially decreased 50 s after the start of the permeation process. Moreover, the diffusion flux of the Pd–Cu40% membrane was relatively larger than that of the pure Pd membrane under the same operating conditions. The distributions of the convective flux, diffusion mass transfer flux, and concentration of the Pd–Cu40% membrane were substantially increased up to 350 °C, then fell to a lower value at higher temperatures. The simulation results were validated with the experimental results, with analysis indicating a good agreement with the experimental results under the same operating conditions. It can be concluded that the simulation modeling for Pd-based membranes was able to predict the optimum operating conditions at high H₂ diffusion rates.     

Hydrogen separation from synthesis gas using silica membrane: CFD simulation

In the present article, an axisymmetric two-dimensional (2D) computational fluid dynamic (CFD) model was adapted to predict the efficiency of the silica membrane for hydrogen (H₂) separation as a renewable energy source. In this model, continuum flows on the shell and tube sides are defined through the Navier-Stokes and transport of chemical species equations. Components transfer through the silica membrane is characterized by introducing source-sink terms based on activating transport mechanisms. To validate the presented model results related to H₂ molar fraction at the retentate and permeate sides were compared with experimental data. The CFD model prognosticates the local information of velocity distribution and the molar fraction of the components. Finally, considering the effects of temperature, pressure difference, gas flow rate, and inner radius of the module on the H₂ molar fraction, silica membrane performance was investigated. Moreover, it has been shown that with increasing working temperature from 323 to 473 K, H₂ molar fraction at the shell side decreases from 59% to 28.4%, and in the tube side, it rises from 78.8% to 82.8%. On the shell side, it could be seen that H₂ permeates better for a low gas flow rate. At the tube side, this parameter has a positive effect on H₂ purification. The result of the impact of pressure differences at shell and tube sides was used to indicate the variation in the H₂ molar fraction. An increase in pressure difference causes a decrease of H₂ molar fraction at the tube side. At the shell side, H₂ molar fraction would be decreased with an addition in pressure difference from 1 to 3 bar. Any further pressure difference rise from 3 to 4 bar, make this trend ascending. Likewise, at the shell and tube sides, by enhancing the inner radius of the module, the molar fraction of H₂ increases.     

Influences of geometry and flow pattern on hydrogen separation in a Pd-based membrane tube

The abatement of concentration polarization in a membrane tube is of the utmost importance for improving the efficiency of hydrogen separation. In order to enhance the performance of hydrogen separation, the characteristics of hydrogen permeation in a Pd-based membrane system under various operating conditions and geometric designs are studied numerically. The effects of Reynolds numbers, shell size, baffle, and pressure difference on hydrogen mass transfer across the membrane are evaluated. The predictions suggest that a larger shell deteriorates concentration polarization, stemming from a larger H₂ concentration boundary layer. Baffles equipped in the shell are conducive to disturbing H₂ concentration boundary layer and reducing concentration polarization at the retentate side, thereby intensifying H₂ permeation. The more the number of baffles, the less the increment of improvement in H₂ permeation is. The installation of one baffle is recommended for enhancing H₂ separation and it is especially obvious under the environments of high pressure difference. Within the investigated ranges of Reynolds number at the permeate side and the retentate side, the feasible operating conditions are suggested in this study.     

Macrovoid-free high performance polybenzimidazole hollow fiber membranes for elevated temperature H2/CO2 separations

Thermally robust membranes are required for H₂ production and carbon capture from hydrocarbon fuel derived synthesis (syn) gas. Polybenzimidaole (PBI) materials have exceptional thermal, chemical and mechanical characteristics and high H₂ perm-selectivity for efficient syngas separations at process relevant conditions. The large gas volumes processed mandate the use of a high-throughput, small footprint hollow fiber membrane (HFM) platform. In this work, an industrially attractive spinning protocol is developed to fabricate PBI HFMs with unprecedented H₂/CO₂ separation performance. A unique dope composition incorporating an acetonitrile diluent is discovered enabling asymmetric macro-void free PBI HFM fabrication using a water coagulant. The influences of dope viscosity, coagulant chemistry, and air gap on HFM morphology are evaluated. Elevated temperature (up to 350 °C) H₂ permeances of 400 GPU with H₂/CO₂ selectivities > 20 are achieved. This unprecedented separation performance is a ground breaking achievement at temperatures traditionally considered out-of-reach for polymeric membranes.     

Characteristic of a multi-pass membrane separator for hydrogen separation through self-supported PdAg membranes

Dense PdAg membranes have shown immense potential to achieve high hydrogen purity required for proton exchange membrane (PEM) fuel cell. However, high hydrogen recovery and flux at lower transmembrane partial pressure is still a concern. In current study self-supported dense PdAg membranes were used to study the hydrogen recovery in a multi-pass membrane separator. Performance of a single and four collective membranes are tested in a single (without baffle) and multi-pass (with longitudinal baffles) membrane separator. Further, array of membrane configurations were tested experimentally by using longitudinal baffles and placing membranes at different locations. The hydrogen recovery for each configuration was measured experimentally. Experiments were performed using binary gas mixture 50H₂:50N₂ (v/v) at 3 bar pressure, 673 K temperature and gas-hourly space velocity (GHSV) 43 h^?1. The best assembly was further tested with typical methanol reformate gas composition by using simulated gas mixture of 50H₂:30N₂:18CO₂:2CO (v/v) at same operating condition. Numerical simulations were performed by using commercial software ANSYS 14.5 to understand the flow dynamics inside the separator with and without baffle. The results demonstrate that a multi-pass membrane separator enables to control hydrogen partial pressure radially along the length of reactor. This resulted in 33% enhancement in hydrogen recovery with multi-pass in comparison to single pass membrane separator.     

A multi-scale flow analysis in hydrogen separation membranes using a coupled DSMC-SPH method

The membrane separation process has been developed as an effective and efficient method for obtaining ultra-high purity hydrogen from impure feed streams. A typical membrane gas flow possesses multi-scale flow characteristics, comprising a macroscopic flow regime on both sides of the membrane and a microscopic flow regime in the pores within the membrane. A better understanding of the fundamentals of such flow behaviors and mass transfer at a multi-scale level is therefore crucial for a better membrane architecture design, which could lead to better membrane separation efficiency and reliability for hydrogen productions in fuel cells. In this paper, a novel numerical analysis method combining the direct simulation Monte Carlo (DSMC) method with the smoothed particle hydrodynamics (SPH) method is presented for the multi-scale flow prediction in a membrane. Using the coupled method, the rarefied flow behaviors within a micro-orifice pore can be predicted by the DSMC method, while the continuum flow behaviors on both sides of the membrane can be simulated by the SPH method simultaneously. To investigate the various flow behaviors and mass transfer between different components, such as H₂ and CO in the membrane, the pressure, velocity, molar concentration, mass flowrate and rarefaction of the H₂ and CO components are compared in details. The influences to the multi-scale flow from the orifice feature and size are discussed. Some unique phenomena are observed to be quite different from that observed in either a solely macroscopic or microscopic flow. The results can be greatly beneficial for the understanding of the mechanism of membrane separation, and the designing of the membranes for hydrogen productions in fuel cell applications.     

Study on hydrogen permeation of Ni‐BaZr0.1Ce0.7Y0.2O3−δ asymmetric cermet membrane

Early on, we had reported the preparation process of Ni‐BaZr_0.1Ce_0.7Y_0.2O_3?δ asymmetric cermet membrane (Ni‐BZCY ACM). In this work, we further optimized the sintering procedure and investigated the effect of water vapor in feed gas, operating time, H₂ concentration difference across the membrane, and dense layer thickness of Ni‐BZCY ACM on hydrogen permeation behaviors. Adding the water vapor into feed gas can effectively improve the hydrogen permeability due to the appearance of a new proton hydration path. An almost unchanged hydrogen permeation output during 100‐hour testing confirms the membrane stability under operating condition. More important, the rate‐limiting step for hydrogen permeation process was elucidated according to the relationship between dense membrane thicknesses and hydrogen permeation fluxes. The surface exchange kinetics predominated permeation performance when the thickness is down to 50 μm, especially at a lower temperature, which was found for the first time for Ni‐BZCY cermet membrane. This result indicated that enhancing exchange kinetics of membrane surface became significant and indispensable for higher hydrogen separation efficiency.     

Conjugate heat and mass transfer in a hollow fiber membrane module for liquid desiccant air dehumidification: A free surface model approach

Conjugate heat and mass transfer in a hollow fiber membrane module used for liquid desiccant air dehumidification is investigated. The module is like a shell-and-tube heat exchanger where the liquid desiccant stream flows in the tube side, while the air stream flows in the shell side in a counter flow arrangement. Due to the numerous fibers in the shell, a direct modeling of the whole module is difficult. This research takes a new approach. A representative cell comprising of a single fiber, the liquid desiccant flowing inside the fiber and the air stream flowing outside the fiber, is considered. The air stream outside the fiber has an outer free surface (Happel’s free surface model). Further, the equations governing the fluid flow and heat and mass transfer in the two streams are combined together with the heat and mass diffusion equations in membranes. The conjugate problem is then solved to obtain the velocity, temperature and concentration distributions in the two fluids and in the membrane. The local and mean Nusselt and Sherwood numbers in the cell are then obtained and experimentally validated.     

Impact of vacuum operation on hydrogen permeation through a palladium membrane tube

Palladium (Pd) membranes are characterized by their high permselectivity to hydrogen and easy operation, and are promising devises for separating hydrogen from hydrogen-rich gases. The membranes are normally operated with atmospheric pressure at the permeate side. Instead of this common operation, hydrogen permeation through a Pd membrane under vacuum operation at the permeate side is investigated and compared with that under normal operation. In this study, two membrane operating temperatures (320 and 380 °C), four H₂ partial pressure differences (2, 3, 4, and 5 atm) across the membrane, and four feed gases are considered. The results suggest that the vacuum operation can efficiently intensify the H₂ permeation rate. The improvement in H₂ permeation rate due to the vacuum operation can be increased up to 136%. The positive effect of the vacuum operation is especially pronounced when the gas mixtures are used as the feed gases, stemming from the effective attenuation of the concentration polarization. An increase in membrane temperature raises the H₂ permeation rate, but its influence in enhancing the H₂ permeation rate with the vacuum operation is not as significant as that without the vacuum one. It is found that the retardation effect of impurities on the mass transfer is always ranked as CO > CO₂ > N₂, regardless of with/without vacuum operation.     

Air and H2 feed systems optimization for open-cathode proton exchange membrane fuel cells

In this study, air and H₂ feed systems optimization for open-cathode proton exchange membrane fuel cells (PEMFCs) has been evaluated. For air feed system, a spoiler was introduced. The air velocity distribution, polarization curve, single-cell voltage distribution, and temperature distribution of the 11-cell open-cathode fuel cell stack with blowing, blowing-spoiler, and drawing air feed system were assessed. On this basis, the influences of the distance between the fan and stack with different air feed systems were investigated. The results show that the application of the spoiler could solve the problem of low air velocity in the middle of the stack and increase stack performance by 7.3%. And drawing air feed system could enhance the heat dissipation capacity of the stack and the uniformity of temperature distribution, resulting in the 7.9% stack performance increase. Optimization of the distance between the fan and stack enhances the full development of turbulence and the rate of heat transfer. In addition, the effects of four different H₂ feed systems and the flow direction between air and hydrogen on the fuel cell performance were also investigated. It is beneficial for open-cathode PEMFC to be operated with the location of the H₂ inlet and outlet staggered in two different endplates for better stack performance and single-cell voltage uniformity. Evidence also shows that the higher performance also could be obtained when the flow direction of air and hydrogen is vertical with lower ohmic resistance, charge and mass transfer resistance. The study contributes to the design of the open-cathode fuel cell stack to get better performance and reliability.     

Hydrogen permeation properties of Pd-coated V89.8Cr10Y0.2 alloy membrane using WGS reaction gases

The influence of co-existing gases on the hydrogen permeation was studied through a Pd-coated V_89.8Cr₁₀Y_0.2 alloy membrane. Preliminary hydrogen permeation experiments have been confirmed that hydrogen flux was 6.26 ml/min/cm² for a Pd-coated V_89.8Cr₁₀Y_0.2 alloy membrane (thick: 0.5 mm) using pure hydrogen as feed gas. Also, the hydrogen permeation flux decreased with decrease of hydrogen partial pressure at constant pressure when H₂/CO₂ and H₂/CO₂/H₂S mixture applied as feed gas respectively and permeation fluxes were satisfied with Sievert's law in different feed conditions. It was found from XRD and SEM results after permeation test that the Pd-coated V_89.8Cr₁₀Y_0.2 alloy membrane had good stability and durability for various mixture feeding conditions.     

Effect of sweep gas on hydrogen permeation of supported Pd membranes: Experimental and modeling

Membrane reactor processes are being increasingly proposed as an attractive solution for pure hydrogen production due to the possibility to integrate production and separation inside a single reactor vessel. High hydrogen purity can be obtained through dense metallic membranes, especially palladium and its alloys, which are highly selective to hydrogen. The use of thin membranes seems to be a good industrial solution in order to increase the hydrogen flux while reducing the cost of materials. Typically, the diffusion through the membrane layer is the rate-limiting step and the hydrogen permeation through the membrane can be described by the Sieverts’ law but, when the membrane becomes thinner, the diffusion through the membrane bulk becomes less determinant and other mass transfer limitations might limit the permeation rate. Another way to increase the hydrogen flux at a given feed pressure, is to increase the driving force of the process by feeding a sweep gas in the permeate side. This effect can however be significantly reduced if mass transfer limitations in the permeate side exist. The aim of this work is to study the mass transfer limitation that occurs in the permeate side in presence of sweep gas. A complete model for the hydrogen permeation through PdAg membranes has been developed, adding the effects of concentration polarization in retentate and permeate side and the presence of the porous support using the dusty gas model equation, which combines Knudsen diffusion, viscous flow and binary diffusion. By studying the influence of the sweep gas it has been observed that the reduction of the driving force is due to the stagnant sweep gas in the support pores while the concentration polarization in the permeate is negligible.     

Gas-liquid mass transfer in a cross-flow hollow fiber module: Analytical model and experimental validation

The cross-flow operation of hollow fiber membrane contactors offers many advantages and is preferred over the parallel-flow contactors for gas-liquid mass transfer operations. However, the analysis of such a cross-flow membrane gas-liquid contactor is complicated due to the change in concentrations of both phases in the direction of flow as well as in the direction perpendicular to flow. In addition, changes in the volumetric flow rate of compressible fluid can also occur over the volume of membrane contactor. These hollow fiber membrane contactors resemble to the more conventional shell and tube cross-flow heat exchanges where a similar variation in the local driving force within the module occurs. Hence heat transfer analogy can be applied to predict the performance of these contactors.Analytical expressions are derived in this work to describe the mass transfer in these hollow fiber cross-flow contactors analogously to heat transfer in cross-flow shell and tube heat exchangers. CO₂ absorption experiments were carried out in a commercial as well as in the lab-made single-pass cross-flow hollow fiber membrane contactors to check the applicability of this heat transfer analogy under different conditions. Experimental results show that the derived analytical expressions can be applied to the cross-flow membrane gas-liquid contactor under the asymptotic conditions of negligible or small volumetric flow changes. However, in the case of significant changes in the flow rate of compressible fluid, the application of heat transfer analogy results into slight under predictions of the module performance. A more rigorous model is then required for an accurate prediction of the performance.     

Influence of water vapor on hydrogen permeation through 2.5 μm Pd-Ag membranes

Hydrogen permeation experiments were performed to evaluate the influence of water vapor on hydrogen permeability in 80-20% by weight Pd-Ag membranes of 2.5 μm thickness. In particular, hydrogen flux was measured in pure hydrogen permeation tests as well as in experiments with binary mixtures containing also nitrogen or water vapor, that were performed at temperatures ranging from 473 to 723 K and at a transmembrane pressure differences up to about 3 bar. The membranes, supplied by NGK Insulator Ltd., Japan, showed a very high hydrogen permeance and lifetime, as well as virtually infinite selectivity (exceeding 10000 for H₂-N₂ mixtures). The experiments in hydrogen-nitrogen mixtures were carried out at different temperatures, hydrogen concentrations and feed flow rates and confirmed the existence of a non-negligible concentration polarization phenomenon in the experimental module. The gas phase mass transport and the module fluid dynamics were thus analyzed and the dimensionless numbers characterizing these processes were evaluated at the different operative conditions; a linear correlation was found to hold between Sherwood and Péclet numbers. Interestingly, the hydrogen permeate fluxes measured with feeds containing H₂-H₂O mixtures resulted always lower than those obtained for the nitrogen-hydrogen mixtures performed at the same hydrogen mole fraction and operative conditions: in particular, the hydrogen flux depletion increased with decreasing temperature and/or increasing the concentration of water vapor. All the experimental evidences suggest a clear interaction between water vapor and metallic layer, causing a lower hydrogen adsorption capacity of the membrane surface. That phenomenon is reversible, since the original permeance of the membrane was restored once the water vapor was removed from the feed, and is apparently due to a competitive H₂-H₂O adsorption on the Pd-Ag surface. The hydrogen flux depletion was then modeled by considering the simultaneous effects of gas phase resistance and competitive adsorption on the surface, obtaining a rather good agreement between experimental data and calculated results.     

Enhanced H2 production by using La5.5WO11.25-δ-La0.8Sr0.2FeO3-δ mixed oxygen ion-proton-electron triple-conducting membrane

Although lanthanum tungstates (Ln_nWO_12-δ) show superior CO₂-tolerance compared to the traditional perovskite-type oxides, their hydrogen permeation fluxes are not competitive. Herein, a mixed oxygen ion-proton-electron triple-conducting membrane with a nominal composition of La_5.5WO_11.25-δ-La_0.8Sr_0.2FeO_3-δ (LWO-LSF) was developed for H₂ production. The triple-conducting membrane is composed of a LWO phase with proton conductivity and a LSF phase with mixed oxygen ion-electron conductivities. In the LWO-LSF membrane, proton (H⁺) permeation and oxygen ion (O²⁻) counter-permeation property was simultaneously displayed. The improved H₂ production can be ascribed to (1) hydrogen permeated as H⁺ through LWO phase, and (2) hydrogen produced from water splitting that is enhanced by O²⁻ counter-permeation through LSF phase. A higher H₂ flux of 0.15 mL min⁻¹ cm⁻² was achieved at 900 °C using LWO-LSF triple-conducting membrane, compared with the conventional proton-electron conducting membranes LWO or La_5.5WO_11.25-δ-La_0.8Sr_0.2CrO_3-δ (LWO-LSC). Furthermore, the constant H₂ fluxes in various atmospheres indicated the good stability of LWO-LSF membrane in simulated raw hydrogen.     

Optimization of hydrogen enrichment via palladium membrane in vacuum environments using Taguchi method and normalized regression analysis

In this study, the separation of hydrogen from gas mixtures using a palladium membrane coupled with a vacuum environment on the permeate side was studied experimentally. The gas mixtures composed of H₂, N₂, and CO₂ were used as the feed. Hydrogen permeation fluxes were measured with membrane operating temperature in the range of 320–380 °C, pressures on the retentate side in the range of 2–5 atm, and vacuum pressures on the permeate side in the range of 15–51 kPa. The Taguchi method was used to design the operating conditions for the experiments based on an orthogonal array. Using the measured H₂ permeation fluxes from the Taguchi approach, the stepwise regression analysis was also employed for establishing the prediction models of H₂ permeation flux, followed by the analysis of variance (ANOVA) to identify the significance and suitability of operating conditions. Based on both the Taguchi approach and ANOVA, the H₂ permeation flux was mostly affected by the gas mixture composition, followed by the retentate side pressure, the vacuum degree, and the membrane temperature. The predicted optimal operating conditions were the gas mixture with 75% H₂ and 25% N₂, the membrane temperature of 320 °C, the retentate side pressure of 5 atm, and the vacuum degree of 51 kPa. Under these conditions, the H₂ permeation flux was 0.185 mol s^?1 m^?2. A second-order normalized regression model with a relative error of less than 7% was obtained based on the measured H₂ permeation flux.     

Chemical and transport behaviors in a microfluidic reformer with catalytic-support membrane for efficient hydrogen production and purification

Microchannel reformer integrated with H₂ selective membrane offers an efficient, compact and portable way to produce hydrogen. The performance of a membrane-based microfluidic reformer is restricted by species diffusion limitation within the porous support of the membrane. Recent development in novel catalytic-supported membranes has the potential to enhance H₂ production by decimating the diffusion limitation. Loading a Pd-Ag layer on to a Ni-catalytic porous support, the membrane achieves both H₂ separation and production functions. In this study, a two-dimensional CFD model combined with chemical kinetics has been developed to simulate a microchannel autothermal reformer fed by methane. The species conversion and transport behaviors have been studied. The results show that the permeation process enhances the mass transport within the catalytic layer, and as a result, the reactions are intensified. Most notably, the effectiveness factor of the water-gas shift reaction as high as 6 is obtained. In addition, the effects of gaseous hourly space velocity (GHSV) on methane conversion and H₂ flux through the membrane are also discussed, and an optimal value of GHSV is suggested.     

H2 permeation and its influence on gases through a SAPO-34 zeolite membrane

This work analysed the permeation of binary and ternary H₂-containing mixtures through a SAPO-34 membrane, aiming at investigating how hydrogen influences and its permeation is influenced by the presence of the other gaseous species, such as CO₂ and CH₄. We considered the behaviour of various gas mixtures in terms of permeability and selectivity at various temperatures (25–300 °C), feed pressures (400–1000 kPa) and compositions by means of an already validated mass transport model, which is based on surface and gas translation diffusion. We found that the presence of CO₂ and CH₄ in the H₂-containing mixtures influences in a similar way the H₂ permeation, reducing its permeability of about 80% compared to the single-gas value because of their stronger adsorption. On the other hand, H₂ promotes the permeation of CO₂ and CH₄, causing an increment of their permeability with respect to those as single gases. These combined effects reflected in interesting selectivity values in binary mixture (e.g., CO₂/H₂ about 11 at 25 °C, H₂/CH₄ about 9 at 180 °C), which showed the potential of SAPO-34 membranes in treating of H₂-containing mixtures.     

Methanol steam reforming over PdZn/ZnAl2O4/Al2O3 in a catalytic membrane reactor: An experimental and modelling study

A catalytic membrane reactor equipped with Pd–Ag metallic membranes and loaded with PdZn/ZnAl₂O₄/Al₂O₃ catalytic pellets was tested for the methanol steam reforming reaction (S/C = 1) aimed at producing a pure hydrogen stream for PEM fuel cell feeding. The catalyst was prepared in two steps. First, commercial γ-Al₂O₃ pellets were impregnated with ZnCl₂ and calcined at 700 °C to obtain a ZnAl₂O₄ shell, and subsequently impregnated with PdCl₂ and reduced at 600 °C to obtain PdZn alloy nanoparticles. The catalyst was tested both in a conventional packed bed reactor and in a catalytic membrane reactor. A 3D CFD non-isothermal model with mass transfer limitations was developed and validated with experimental data. The reactions of methanol steam reforming, reverse water-gas shift and methanation were modeled under different pressure, temperature and feed load values. The model was used to study and simulate the CMR under different operation conditions.     

CFD modeling of two-stage H2 recovery process from ammonia purge stream by industrial hollow fiber membrane modules

This research introduces an unabridged two-dimensional mathematical model for H₂ recovery from an ammonia plant's purge stream through two-stage industrial polyimide hollow fiber (PIHF) membrane modules. According to validated results, the effect of operational and geometrical parameters beside flow patterns was investigated on H₂ recovery potential at first and second stages of PIHF membrane modules. H₂ recovery at first and second separation stages decreased from 5.887% to 4.82% and from 99.57% to 99.05%, respectively when the feed mass flow rate increased from 0.3847 to 0.5014 kg/s at constant pressure of 97.5 barg. However, a reverse trend between H₂ cumulation and feed pressure was observed at constant feed mass flow rate for each separation steps. As fiber length increased from 2 m to 3.06 m, the H₂ recovery percentage grew up at each of those separation stages at fixed operational conditions. Counter-current flow pattern showed higher H₂ recovery in comparison with co-current flow arrangement at the same operation conditions due to the higher partial pressure difference. Moreover, a concentration polarization index (CPI) was also described to demonstrate the scope of polarization. Evaluations depicted that CPI enhanced with increasing the feed pressure and serious concentration polarization arose at higher feed pressures.