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1.
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.  相似文献   

2.
Hydrogen purification using palladium (Pd) membrane technology has been seen as a potential solution for producing pure hydrogen form hydrogen-rich gas. Compared to traditional practices of operating the permeate side of the membrane at atmospheric pressure, in this study, a vacuum is applied. The effects of various vacuum degrees applied to the permeate side of the Pd membrane are investigated and compared to the results under normal operation without a vacuum. The feed gas used for experiments consists of a mixture of hydrogen (70 vol%) and nitrogen (30 vol%). Three membrane operating temperatures (320, 350, and 380 °C), four pressure differences (2, 3, 4, and 5 atm) across the membrane, and four vacuum degrees (−15, −30, −45, and −53 kPa) applied to the permeate side are considered. For the three operating temperatures, the best improvements in the performance of hydrogen permeation are at 320 and 350 °C when a −53 kPa vacuum is applied, resulting in 79.4% and 79.1% improvements, respectively, compared to normal operations. Increasing temperatures leads to an increase in H2 permeation both with and without a vacuum; however, best performances of H2 permeation are observed in cases without a vacuum.  相似文献   

3.
Palladium (Pd) membranes are a crucial device for separating hydrogen and are usually operated at normal pressure on the permeate side with a single outlet. Instead of these common operating conditions, the difference between using a double outlet and a single outlet is studied. Four different vacuum degrees (15–60 kPa) are applied on the permeate side, and the results are compared with the non-vacuum operations. Situations under the vacuum and the effects of temperatures (300–400 °C) on H2 permeation are discussed. Finally, the influences of different feed gas mixtures (H2/N2, H2/CO2, and H2/CO) on the Pd membrane performance are investigated. The results show that there is no difference in H2 permeation impact the single outlet and the double outlet on the permeate side. When a vacuum is imposed on the permeate side, the H2 permeation rate and H2 recovery are efficiently intensified, that is, when the pressure difference is 9 atm, they increase from 73.21 to 84.51% and from 0.0035378 to 0.0040808 mol?s?1, respectively. Moreover, the H2 recovery can be improved to up to 68.44% under a vacuum degree of 60 kPa. At a given Reynolds number, an increase in temperature increases the H2 permeation rate but lowers its recovery, stemming from more H2 in the feed gas. This study also investigates the feed gas of H2/N2 under a vacuum to provide a useful insight into H2 production and separation from ammonia, and the results are compared with two different feed gases of H2/CO2 and H2/CO mixtures. The results suggest that the impurities (i.e., N2, CO2, and CO) have a negative influence on the Pd membrane, which causes the H2 permeation rate to decrease, and the effect of N2 is the least significant compared to the other two.  相似文献   

4.
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.  相似文献   

5.
A 2D axisymmetric model is developed for a H2-permeable membrane reactor for methane CO2 reforming. The effect of catalyst bed volume on CH4 conversion and H2 permeation rate is investigated. The simulation results indicate that catalyst bed volume with a shell radius of 9 mm is optimal for a tubular Vycor glass membrane with a diameter of 10 mm and H2 permeance of 2x10−6 mol/m2/Pa/s. The concentration polarization at the retentate side and the accumulation of H2 at permeate side make it hard to extract the H2 production at the zone far from the membrane surface. Though increasing pressure at the retentate side enhances H2 permeation, CH4 conversion is even decreased due to unfavorable thermodynamics. And increasing sweep gas flow rate at permeate side benefits to both CH4 conversion and H2 permeation. This work highlights the importance of determining the optimal catalyst bed volume to match the membrane in the design of membrane reactors.  相似文献   

6.
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.  相似文献   

7.
Herein, a methane steam reforming (MSR) reaction was carried out using a Pd composite membrane reactor packed with a commercial Ru/Al2O3 catalyst under mild operating conditions, to produce hydrogen with CO2 capture. The Pd composite membrane was fabricated on a tubular stainless steel support by the electroless plating (ELP) method. The membrane exhibited a hydrogen permeance of 2.26 × 10?3 mol m2 s?1 Pa?0.5, H2/N2 selectivity of 145 at 773 K, and pressure difference of 20.3 kPa. The MSR reaction, which was carried out at steam to carbon ratio (S/C) = 3.0, gas hourly space velocity (GHSV) = 1700 h?1, and 773 K, showed that methane conversion increased with the pressure difference and reached 79.5% at ΔP = 506 kPa. This value was ~1.9 time higher than the equilibrium value at 773 K and 101 kPa. Comparing with the previous studies which introduced sweeping gas for low hydrogen partial pressure in the permeate stream, very high pressure difference (2500–2900 kPa) for increase of hydrogen recovery and very low GHSV (<150) for increase hydraulic retention time (HRT), our result was worthy of notice. The gas composition monitored during the long-term stability test showed that the permeate side was composed of 97.8 vol% H2, and the retentate side contained 67.8 vol% CO2 with 22.2 vol% CH4. When energy was recovered by CH4 combustion in the retentate streams, pre-combustion carbon capture was accomplished using the Pd-based composite membrane reactor.  相似文献   

8.
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.  相似文献   

9.
This study presents numerical studies of hydrogen production performance via water gas shift reaction in membrane reactor. The pre-exponential factor in describing the hydrogen permeation flux is used as the main parameter to account for the membrane permeance variation. The operating pressure, temperature and H2O/CO molar ratio are chosen in the 1–20 atm, 400–600 °C and 1–3 ranges, respectively. Based on the numerical simulation results three distinct CO conversion regimes exist based on the pre-exponential factor value. For low pre-exponential factors corresponding to low membrane permeance, the CO conversion approaches to that obtained from a conventional reactor without hydrogen removal. For high pre-exponential factor, high CO conversion and H2 recovery with constant values can be obtained. For intermediate pre-exponential factor range both CO conversion and H2 recovery vary linearly with the pre-exponential factor. In the high membrane permeation case CO conversion and H2 recovery approach limiting values as the operating pressure increases. Increasing the H2O/CO molar ratio results in an increase in CO conversion but decrease in H2 recovery due to hydrogen permeation driving force reduction. As the feed rate increases in the reaction side both the CO conversion and hydrogen recovery decrease because of decreased reactant residence time. The sweep gas flow rate has a significant effect on hydrogen recovery. Low sweep gas flow rate results in low CO conversion H2 recovery while limiting CO conversion and hydrogen recovery can be reached for the high membrane permeance and high sweep gas flow rate cases.  相似文献   

10.
The influence of co-existing gases on the hydrogen permeation was studied through a Pd-coated V89.8Cr10Y0.2 alloy membrane. Preliminary hydrogen permeation experiments have been confirmed that hydrogen flux was 6.26 ml/min/cm2 for a Pd-coated V89.8Cr10Y0.2 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 V89.8Cr10Y0.2 alloy membrane had good stability and durability for various mixture feeding conditions.  相似文献   

11.
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.  相似文献   

12.
In this experimental work, methane steam reforming (MSR) reaction is performed in a dense Pd-Ag membrane reactor and the influence of pressure on methane conversion, COx-free hydrogen recovery and COx-free hydrogen production is investigated. The reaction is conducted at 450 °C by supplying nitrogen as a sweep gas in co-current flow configuration with respect to the reactants. Three experimental campaigns are realized in the MR packed with Ni-ZrO catalyst, which showed better performances than Ni-Al2O3 used in a previous paper dealing with the same MR system. The first one is directed to keep constant the total pressure in both retentate and permeate sides of the membrane reactor. In the second case study, the total retentate pressure is kept constant at 9.0 bar, while the total permeate pressure is varied between 5.0 and 9.0 bar. As the best result of this work, at 450 °C and 4.0 bar of total pressure difference between retentate and permeate sides, around 65% methane conversion and 1.2 l/h of COx-free hydrogen are reached, further recovering 80% COx-free hydrogen over the total hydrogen produced during the reaction. Moreover, a study on the influence of hydrogen-rich gas mixtures on the hydrogen permeation through the Pd-Ag membrane is also performed and discussed.  相似文献   

13.
This work presents the use of doped CeO2 particles with palladium as intermediate barrier for the preparation of fully dense Pd films by Electroless Pore-Plating. The use of doped ceria particles instead of non-doped ones clearly helps to reduce the final palladium thickness required to prepare a fully dense membrane over porous stainless steel supports from 15 to 9 μm (average values by gravimetric analyses), thus saving around 40% of total palladium required in the process. Pure hydrogen permeation tests reveal a consequent increase in the H2 flux in the range 15–30%, depending on the operation mode. Thus, a H2 permeance of 6.26·10−4 mol m−2 s−1 Pa−0.5 at 400 °C and ΔP = 1 bar is reached, maintaining a really high H2/N2 ideal separation factor (≥10,000) and an activation energy within the typical range for these type of membranes, Ea = 13.1 kJ mol−1. Permeation of binary H2/N2 gas mixtures and the effect of feeding the mixture from the inner or the outer side of the membrane have been also studied. A significant concentration-polarization effect was observed, being higher when the gas is fed from the inner to the outer side of the membrane. This effect becomes more relevant for the membrane prepared with doped CeO2, instead of raw CeO2, due to its lower Pd thickness and higher relative influence of the surface processes. However, it should be emphasized that higher H2 permeance values were obtained for the entire set of experiments when using the Pd-membranes containing doped ceria. Finally, long-term permeation tests for more than 850 h with pure gases at T = 400 °C and ΔP = 1 bar were also carried out, demonstrating a suitable mechanical stability of membranes at these operating conditions.  相似文献   

14.
Ethanol steam reforming in membrane reactors is a promising route for decentralized H2 production from biomass because H2 yield can be greatly enhanced due to the equilibrium shift triggered by instantaneous H2 extraction. Here a highly active Ir/CeO2 catalyst has been combined with ca. 4 μm thin Pd membranes employing a 6:1 steam/ethanol feed between 673 K and 873 K at reforming pressures up to 1.8 MPa. The H2 yield reached 94.5% at 873 K and 1300 kPa due to the separation of 91.8% H2 whereas H2 yield was limited to 28.9% without membrane. At lower temperatures and pressures sweep gas was needed at the membranes' permeate side for efficient H2 generation since the H2 partial pressure remains equilibrium-limited on the reaction side. Furthermore, the H2 yield improved from 63.0% to 84.7% at 773 K, 1500 kPa and sweep-to-feed flow ratio 0.5 when the distance between membrane and reactor wall was shortened by ca. 30%. Thus, external H2 diffusion towards the membrane has a large impact on membrane reactor performance pointing towards microstructured membrane reactors as optimum devices for sustainable H2 production from biomass.  相似文献   

15.
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.  相似文献   

16.
In this work, highly doped ceria with lanthanum, La0.5Ce0.5O2−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.  相似文献   

17.
A palladium selective tubular membrane has been prepared to separate and purify hydrogen. The membrane consists of a composite material, formed by different layers: a stainless steel support (thickness of 1.9 mm), an yttria-stabilized zirconia interphase (thickness of 50 μm) prepared by Atmospheric Plasma Spraying and a palladium layer (thickness of 27.7 μm) prepared by Electroless Plating. The permeation properties of the membrane have been tested at different operating conditions: retentate pressure (1-5 bar), temperature (350-450 °C) and hydrogen molar fraction of feed gas (0.7-1). At 400 °C, a permeability of 1.1 × 10−8 mol/(s m Pa0.5) and a complete selectivity to hydrogen were obtained. The complete retention of nitrogen was maintained for all tested experiment conditions, with both single and mixtures of gases, ensuring 100% purity in the hydrogen permeate flux.A rigorous model considering all the resistances involved in the hydrogen transport has been applied for evaluating the relative importance of the different resistances, concluding that the transport through the palladium layer is the controlling one. In the same way, a model considering the axial variations of hydrogen concentration because of the cylindrical geometry of the experimental device has been applied to the fitting of the experimental data. The best fitting results have been obtained considering Sieverts’-law dependences of the permeation on the hydrogen partial pressure.  相似文献   

18.
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.  相似文献   

19.
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.  相似文献   

20.
A new high temperature tube-shell membrane reactor (MR) design for separation and utilization of CO2 from the flue gas and for simultaneous production of syngas through carbon dioxide reforming of methane (CRM) is reported. The MR is based on a dual-phase CO2 permeation membrane consisting of mixed-conducting oxide and molten carbonate phases. High temperature CO2-containing flue gas and CH4 are respectively fed into the shell and tube sides of the reactor packed with a reforming catalyst. Under performance conditions, CO2 permeates selectively through the membrane from the shell side to the tube side and reacts with CH4 to produce syngas. Additionally, the heat from the flue gas can transfer directly through the membrane to provide energy for the endothermic CRM reaction. An isothermal steady-state model was developed to simulate and analyze CRM in the MR in this work. The effect of the design and operational parameters, such as inlet CH4 flow rate, shell side CO2 partial pressure and the flue gas composition, i.e., containing O2 or not, as well as the membrane thickness on the reactor performance with respect to the CH4 conversion and the CO2 permeation flux were investigated and discussed. The results show that the MR has a high efficiency in separating and utilizing CO2 from the flue gas. For a CH4 space velocity of 3265.31 h−1, with a membrane thickness of 0.075 mm and the shell side CO2 partial pressure of 1 atm, a CH4 conversion of 48.06% and an average CO2 permeation flux of 1.52 mL(STP) cm−2 min−1 through the membrane tube at 800 °C are obtained. Further improvement of the MR performance can be achieved by involving O2 in the permeation process.  相似文献   

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