High temperature H2/CO2 separation using cobalt oxide silica membranes

In this work high quality cobalt oxide silica membranes were synthesized on alumina supports using a sol–gel, dip coating method. The membranes were subsequently connected into a steel module using a graphite based proprietary sealing method. The sealed membranes were tested for single gas permeance of He, H₂, N₂ and CO₂ at temperatures up to 600 °C and feed pressures up to 600 kPa. Pressure tests confirmed that the sealing system was effective as no gas leaks were observed during testing. A H₂ permeance of 1.9 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ was measured in conjunction with a H₂/CO₂ permselectivity of more than 1500, suggesting that the membranes had a very narrow pore size distribution and an average pore diameter of approximately 3 Å. The high temperature testing demonstrated that the incorporation of cobalt oxide into the silica matrix produced a structure with a higher thermal stability, able to resist thermally induced densification up to at least 600 °C. Furthermore, the membranes were tested for H₂/CO₂ binary feed mixtures between 400 and 600 °C. At these conditions, the reverse of the water gas shift reaction occurred, inadvertently generating CO and water which increased as a function of CO₂ feed concentration. The purity of H₂ in the permeate stream significantly decreased for CO₂ feed concentrations in excess of 50 vol%. However, the gas mixtures (H₂, CO₂, CO and water) had a more profound effect on the H₂ permeate flow rates which significantly decreased, almost exponentially as the CO₂ feed concentration increased.     

Repair of Pd-based composite membrane by polishing treatment

In this study, the effect of module configuration on the performance of Pd-based membrane devices was examined using a Pd-Au composite membrane deposited on a porous nickel support. Hydrogen permeation flux, recovery, and CO₂ enrichment were experimentally examined using two different modules. The module configuration that had a narrower space between the surface of the membrane and cover plate provided a large linear flow velocity of the gas mixture, which allowed for a reduction in the concentration polarization. The CO₂ enrichment capacity of the membrane module with a space distance of 0.4 mm was 4 times higher than the module with a space distance of 2.5 mm. In regards to the process design, the membrane with an effective area of 16.6 cm² could enrich 40% of the CO₂ at a flow rate of 2000 ml min⁻¹ up to 87% with a hydrogen recovery ratio of >90% at 673 K and a total feed pressure of 1600 kPa.     

Hydrogen permeation through a Pd-based membrane and RWGS conversion in H2/CO2, H2/N2/CO2 and H2/H2O/CO2 mixtures

This study investigated the effect of gases such as CO₂, N₂, H₂O on hydrogen permeation through a Pd-based membrane −0.012 m² – in a bench-scale reactor. Different mixtures were chosen of H₂/CO₂, H₂/N₂/CO₂ and H₂/H₂O/CO₂ at temperatures of 593–723 K and a hydrogen partial pressure of 150 kPa. Operating conditions were determined to minimize H₂ loss due to the reverse water gas shift (RWGS) reaction. It was found that the feed flow rate had an important effect on hydrogen recovery (HR). Furthermore, an identification of the inhibition factors to permeability was determined. Additionally, under the selected conditions, the maximum hydrogen permeation was determined in pure H₂ and the H₂/CO₂ mixtures. The best operating conditions to separate hydrogen from the mixtures were identified.     

Evaluation of two gas membrane modules for fermentative hydrogen separation

The ability of (dimethyl siloxane) (PDMS) and SAPO 34 membrane modules to separate a H₂/CO₂ gas mixture was investigated in a continuous permeation system in order to decide if they were suitable to be coupled to a biological hydrogen production process. Permeation studies were carried out at relatively low feed pressures ranging from 110 to 180 kPa. The separation ability of SAPO 34 membrane module appeared to be overestimated since the effect concentration polarization phenomena was not taken into consideration in the permeation parameter estimation. On the other hand, the PDMS membrane was the most suitable to separate the binary gas mixture. This membrane reached a maximum CO₂/H₂ separation selectivity of 6.1 at 120 kPa of feed pressure. The pressure dependence of CO₂ and H₂ permeability was not considerable and only an apparent slight decrease was observed for CO₂ and H₂. The mean values of permeability coefficients for CO₂ and H₂ were 3285 ± 160 and 569 ± 65 Barrer, respectively. The operational feed pressure found to be more adequate to operate initially the PDMS membrane module coupled to the fermentation system was 180 kPa, at 296 K. In these conditions it was possible to achieve an acceptable CO₂/H₂ separation selectivity of 5.8 and a sufficient recovery of the CO₂ in the permeate stream.     

Improvement of hydrogen-separating performance by on-stream catalytic cracking of silane over hollow fiber MFI zeolite membrane

MFI zeolite membranes were synthesized on porous α-alumina hollow fibers by in-situ hydrothermal synthesis. The membranes were further modified for H₂ separation by on-stream catalytic cracking deposition of methyldiethoxysilane (MDES) in the zeolitic pores. The separation performance of the modified membranes was characterized by separation of H₂/CO₂ gas mixture at 500 °C. Activation of MFI zeolite membranes by air at 500 °C was found to promote catalytic cracking deposition of silane in the zeolitic pores effectively, which resulted in significant improvement of H₂-separating performance. The H₂/CO₂ separation factor of 45.6 with H₂ permeance of 1.0 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ was obtained at 500 °C for a modified hollow fiber MFI zeolite membrane. The as-made membranes showed good thermochemical stability for the separation of H₂/CO₂ gas mixture containing H₂O and H₂S, respectively.     

Long-term CO2 capture tests of Pd-based composite membranes with module configuration

In this study, we investigate the configuration of a Pd–Au composite membrane on a porous nickel support and membrane modules for withstanding the capture of CO₂ from a coal gasifier for a long time. The hydrogen permeation flux, recovery and CO₂ capture were experimentally evaluated using two different modules and two conditions. As in our study, the CO₂ capturing and durability tests were performed with a 40% CO₂/60% H₂ feed gas mixture in stainless steel (SS) 316L and 310S membrane modules. As a result, it is achieved the durability tests for more than 1150, 1100 (SS 316L module) and 3150 h (SS 310S module) with pressure cycles from 100 to 2000 kPa at 673 K. The durability of the membranes and membrane modules was demonstrated under pressure cycles from 100 to 2000 kPa at 673 K and the SS 310S module was very stable after 3150 h. The durability test for more than 3000 h demonstrated that there was no significant intermetallic diffusion between the PNS and Pd–Au layer. The CO₂ capturing test performed using a 40% CO₂/60% H₂ mixture confirmed that the CO₂ capturing capacity of the membrane and membrane module was 2.0 L/min for a CO₂ concentration in the retentate stream of 92.3% and that the hydrogen recovery ratio increased with increasing pressure and reached 93.4%. Furthermore, we suggest that the SS 310S module configuration, CO₂ capturing test using Pd–Au/ZrO₂/PNS membrane and membrane module is very suitable for application as an Integrated Gasification Combined Cycle (IGCC) system due to very simple numbering-up stackable module design was successful.     

A mixed electronic and protonic conducting hydrogen separation membrane with asymmetric structure

In this work, highly doped ceria with lanthanum, La_0.5Ce_0.5O_2−δ (LDC), are developed as hydrogen separation membrane material. LDC presents a mixed electronic and protonic conductivity in reducing atmosphere and good stability in moist CO₂ environment. LDC separation membranes with asymmetrical structure are fabricated by a cost-saving co-pressing method, using NiO + LDC + corn starch mixture as substrate and LDC as top membrane layer. Hydrogen permeation properties are systemically studied, including the influence of operating temperature, hydrogen partial pressure in feed stream and water vapor in both sides of the membrane on hydrogen permeating fluxes. Hydrogen permeability increases as the increasing of temperature and hydrogen partial pressure in feed gas. Using 20% H₂/N₂ (with 3% of H₂O) as feed gas and dry high purity argon as sweep gas, an acceptable flux of 2.6 × 10⁻⁸ mol cm⁻² s⁻¹ is achieved at 900 °C. The existing of water in both sides of membrane has significant effect on hydrogen permeation and the corresponding reasons are analyzed and discussed.     

Pure hydrogen production in a Pd-Ag multi-membranes module by methane steam reforming

An experimental test campaign has been carried out in order to investigate the performances in terms of pure hydrogen production of a multi-membrane module coupled with a methane reforming fixed bed reactor. The effect of operating parameters such as the temperature, the pressure, the water/methane feed flow rates and the feed molar ratio has been studied. The hydrogen produced into the traditional reformer has been recovered in the shell side of the membrane module by vacuum pumping. The membrane module consists of 19 Pd/Ag permeator tubes of wall thickness 150 μm, diameter 10 mm and length 250 mm: these dense permeators permitted to separate ultra-pure hydrogen.The experiments have been carried out with the reaction pressure of 100-490 kPa, the temperature of the reformer of 570-720 °C and the temperature of the Pd/Ag membranes module of 300-400 °C. A water/methane stream of molar ratio of 4/1 and 5/1 has been fed into the methane reformer at GSHV of 1547.6 and 1796.1 L_(STP) kg⁻¹ h⁻¹. Hydrogen yield value of about 3 has been measured at reaction pressure of 350 kPa, temperature reformer of 720 °C and methane feed flow rate of 6.445 × 10⁻⁴ mol s⁻¹.     

PdCu membrane integration and lifetime in the production of hydrogen from methane

PdCu membranes prepared by sequential electroless plating were integrated into a hydrogen production and purification process. Hydrogen was produced from methane through catalytic partial oxidation and wet catalytic partial oxidation with Ni-based catalysts. Membrane permeance was measured with thermal cycles in an inert and hydrogen atmosphere at 673 and 773 K. Permeability was 1.98·10⁻³ mol/(smPa^0.5) at 673 K and 2.62·10⁻³ mol/(smPa^0.5) at 773 K. The optimum sweep gas flow required in the membrane module when operating with hydrogen-containing mixtures was selected. Peak hydrogen recovery was obtained using 15–20% of the feed to the module as sweep gas flow. Membranes were then placed downstream of the hydrogen production reactor. The CO and H₂O percentages fed to the membrane module did not have a major impact on membrane behavior. Around 60–67% of the hydrogen fed to the membrane module was separated, regardless of its composition.     

Synthesis of thin amine-functionalized MIL-53 membrane with high hydrogen permeability

A thin amine-functionalized MIL-53 membrane with high permeability of hydrogen was successfully prepared on a porous α-Al₂O₃ support by using the secondary growth method. Seeded α-Al₂O₃ supports were prepared by a dip-coating technique. In contrast, a discontinuous membrane was obtained by using unseeded support under the same synthesis conditions, implying that the seeds play the key role in the formation of compact membranes. The resulting compact membranes were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation testing. Results showed that the thickness of the as-prepared membrane was around 2 ∼ 4 μm. Hydrogen permeance of the as-prepared membrane reached a remarkable value of 1.5 × 10⁻⁵ mol m⁻² s⁻¹·Pa⁻¹ at room temperature under a 0.1 MPa pressure drop. The ideal H₂/CO₂ selectivity was found to be 4.4. In addition, the influence of seeding solution on the membrane performance was investigated. We found that the membrane permeance decreased and the ideal selectivity increased when the seeding solution content was increased.     

Highly selective high-silica SSZ-13 zeolite membranes for H2 production from syngas

A highly CO₂-selective high-silica SSZ-13 zeolite membrane was used for H₂ production by separating CO₂ from syngas (CO₂/H₂ mixture). High-silica SSZ-13 zeolite membranes were fabricated using outside asymmetric alumina tubes by secondary growth of ball-milled SSZ-13 seeds. The composition of membrane gel and synthesis time were modified. The Si/Al ratio in framework of the membrane was as high as 42 when SiO₂/Al₂O₃ ratio of the gel increased to 140. The effects of test parameters such as pressure drop, temperature, feed flow rate and concentration on membrane performance were investigated. The test pressure drop was up to 2 MPa. The ultra-high CO₂/H₂ selectivity of 161 with excellent CO₂ permeances of ~6.3 × 10⁻⁷ mol/(m² s Pa) (=3760 GPU) were observed for the best membrane at 243 K and pressure drop of 0.2 MPa. Carbon dioxide permeance through high-silica SSZ-13 zeolite membrane was 4.2 × 10⁻⁷ mol/(m² s Pa) (=2500 GPU) at 298 K and pressure drop of 2.0 MPa, and the CO₂/H₂ selectivity was 17.4. The current high-silica SSZ-13 zeolite membranes exceeded the upper bound of polymeric membranes and other inorganic membranes in CO₂/H₂ plots and owned great potentials for H₂ production from syngas.     

High-performance Ni–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) membranes for hydrogen separation

Cermet membranes composited of Ni and doped barium cerate have been widely studied for hydrogen separation; however, their practical application is limited primarily by the relatively low permeation rate and instability of doped barium cerate in H₂O and CO₂ containing gases. Here we report our findings on the development of a thin-film cermet membrane consisting of Ni and BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb), supported on a porous Ni–BZCYYb substrate. High fluxes of 1.12 and 0.49 ml min⁻¹ cm⁻² have been demonstrated at 900 °C and 700 °C, respectively, when hydrogen was used as the feed gas on one side and N₂ as the sweep gas on the other side. Most importantly, the high-performance membrane can be easily fabricated by a cost-effective particle-suspension coating/co-firing process, offering great promise for large scale hydrogen separation applications.     

In-situ repair of composite palladium membranes with macro defects: A case study

A new method was developed for repairing Pd/Al₂O₃ membranes with macro defects without the need of disassembling the membrane from the module. In order to target and fill the membrane defect automatically with solid particles, a TiO₂ powder was firstly tested by flowing high-pressure nitrogen as a carrier gas, followed by a heat treatment. A filter cake was found on the membrane defect but still porous. A glass powder was selected instead of TiO₂, and the membrane defect was successfully sealed by glazing. The in-situ repair of a waste commercial Pd/Al₂O₃ membrane separator was carried out with the glass powder, and the hydrogen flux and H₂/N₂ selectivity of the membrane separator at 450 °C under 100 kPa reached 12.6 m³m⁻²h⁻¹ and 1600, respectively.     

Pd–Cu alloy membrane deposited on CeO2 modified porous nickel support for hydrogen separation

In this study, the hydrogen permeation behavior of a Pd₉₃–Cu₇ alloy membrane deposited on ceria-modified porous nickel support (PNS) was evaluated. PNS, which has an average pore size of 600 nm, was modified by alumina sol. Alumina sol was prepared using precursors that had a mean particle size of 300 nm. Alumina-modified PNS was further treated with ceria sol modification to produce a smoother surface morphology and narrow surface pores. A 7 μm thick Pd₉₃–Cu₇ alloy membrane was made on an alumina-modified PNS and a ceria-finished membrane was fabricated by magnetron sputtering followed by Cu-reflow at 700 °C for 2 h. SEM analysis showed that the membrane deposited on a ceria-finished PNS contained more clear grain boundaries than the membrane deposited on the alumina-modified PNS. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Permeation tests were then conducted using pure hydrogen and helium at temperatures ranging from 673 to 773 K and feed side pressures ranging from 100 to 400 kPa. These tests showed that the membrane had a hydrogen permeation flux of 2.8 × 10⁻¹ mol m⁻² s⁻¹ with H₂/He selectivity of >50,000 at a temperature of 773 K and pressure difference of 400 kPa.     

Optimization analysis of hydrogen separation from an H2/CO2 gas mixture via a palladium membrane with a vacuum using response surface methodology

This study uses a palladium membrane to separate hydrogen from an H₂/CO₂ (90/10 vol%) gas mixture. Three different operating parameters of temperature (320–380 °C), total pressure difference (2–3.5 atm), and vacuum degree (15–49 kPa) on hydrogen are taken into account, and the experiments are designed utilizing a central composite design (CCD). Analysis of variance (ANOVA) is also used to analyze the importance and suitability of the operating factors. Both the H₂ flux and CO₂ (impurity) concentration on the permeate side are the targets in this study. The ANOVA results indicate that the influences of the three factors on the H₂ flux follow the order of vacuum degree, temperature, and total pressure difference. However, for CO₂ transport across the membrane, the parameters rank as total pressure difference > vacuum degree > temperature. The predictions of the maximum H₂ flux and minimum CO₂ concentration by the response surface methodology are close to those by experiments. The maximum H₂ flux is 0.2163 mol s^?1 m^?2, occurring at 380 °C, 3.5 atm total pressure difference, and 49 kPa vacuum degree. Meanwhile, the minimum CO₂ concentration in the permeate stream is t 643.58 ppm with the operations of 320 °C, 2 atm total pressure difference, and 15 kPa vacuum degree. The operation with a vacuum can significantly intensify H₂ permeation, but it also facilitates CO₂ diffusion across the Pd membrane. Therefore, a compromise between the H₂ flux and the impurity in the treated gas should be taken into account, depending on the requirement of the gas product.     

Bench-scale WGS membrane reactor for CO2 capture with co-production of H2

This study investigated the water-gas shift reaction in a bench-scale membrane reactor (M-WGS), where three supported Pd membranes of 44 cm in length and ca. 6 μm in thickness were used, reaching a total membrane surface area of 580.6 cm². The WGS reaction was studied with the syngas mixture: 4.0% CO, 19.2% CO₂, 15.4% H₂O, 1.2% CH₄ and 60.1% H₂, under high temperature/pressure conditions: T = 673 K, p_feed = 20–35 bar(a), p_perm = 15 bar(a), mimicking CO₂ capture with co-production of H₂ in a natural gas fired power plant. High reaction pressure and high permeation of Pd membranes allowed for near complete CO conversion and H₂ recovery. Both the membranes and the membrane reactor demonstrated a long-term stability under the investigated conditions, indicating the potential of M-WGS to substitute conventional systems.     

Preparation of thin Pd membrane on porous stainless steel tubes modified by a two-step method

Thin Pd membranes for hydrogen filtration were deposited on modified porous stainless steel (PSS) tubes using an electroless plating technique. Alumina oxide (Al₂O₃) particles of two different sizes were subsequently used to modify the non-uniform pore distribution and the surface roughness of the PSS tubes. The principle of the modification was to use large Al₂O₃ particles (∼10 μm) to fill larger pores on the surface, and leave the smaller pores intact. Small Al₂O₃ particles (∼1 μm) were then used to further decrease the surface roughness. The detailed manufacturing steps of the Al₂O₃ modification were investigated and optimized to achieve a continuous dense Pd membrane with a minimum thickness of 4.4 μm on the modified PSS tubes. The highest hydrogen permeance of the membrane was 2.94 × 10⁻³ mol/m²-s-kPa^0.5 at 773 K, with a selectivity coefficient (H₂/He) of 1124 under a pressure difference of 800 kPa. In comparison, the thickness and hydrogen permeance of a dense Pd membrane on unmodified PSS tubes were 31.5 μm and 5.97 × 10⁻⁴ mol/m²-s-kPa^0.5, respectively, at 773 K under an 800 kPa pressure difference. The stability of the membranes at high temperatures was also investigated. The hydrogen permeation flux at 773 K was stable during a test period of 500 h. These results demonstrate that the two-step method modifies the surface of PSS tubes in a relatively simple way and results in thin, dense Pd membranes with high hydrogen permeance and good thermal stability.     

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H₂ production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H₂ and N₂) and mixtures (H₂ with N_2, CO or CO₂) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5, while it decreases until 0.66–1.35·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H₂–18%CO–12%CO₂) and a stoichiometric H₂O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h⁻¹. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.     

Thermal stability and effect of typical water gas shift reactant composition on H2 permeability through a Pd-YSZ-PSS composite membrane

This work comprises a study of hydrogen separation with a composite Pd-YSZ-PSS membrane from mixtures of H₂, N₂, CO and CO₂, typical of a water gas shift reactor. The Pd layer is extended over a tubular porous stainless steel support (PSS) with an intermediate layer of yttria-stabilized-zirconia (YSZ). YSZ and Pd layers were incorporated over the PSS using Atmospheric Plasma Spraying and Electroless Plating techniques, respectively. The Pd and YSZ thickness values are 13.8 and 100 μm, respectively, and the Pd layer is fully dense. Permeation measurements with pure, binary and ternary gases at different temperatures (350–450 °C), trans-membrane pressures (0–2.5 bar) and gas composition have been carried out. Moreover, thermal stability of the membrane was also checked by repeating permeation measurements after several cycles of heating and cooling the system. Membrane hydrogen permeances were calculated using Sieverts' law, obtaining values in the range of 4·10⁻⁵–4·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5. The activation energy of the permeance was also calculated using Arrhenius' equation, obtaining a value of 16.4 kJ/mol. In spite of hydrogen selectivity being 100% for all experiments, the hydrogen permeability was affected by the composition of feed gas. Thus, a significant depletion in H₂ permeate flux was observed when other gases were in the mixture, especially CO, being also more or less significant depending on gas composition.     

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.