Hydrogen Permselective Membrane Research Articles

Development of a hydrogen permselective silica membrane and its application to the thermochemical water splitting method

Abstract The thermochemical water splitting IS process is one of the hydrogen production method to use a heat directly. The temperature of the thermal decomposition of water (4000 K) can be reduced under 700 K by introducing I2 and SO2 as recycling catalysts. One of the problems in the IS process is that the conversion of the HI decomposition reaction is low at about 20%. If a membrane reactor with the H2 permselective membrane is applied to the HI decomposition reaction, the hydrogen can be extracted to improve the HI conversion. We focus on a counter diffusion CVD method for the preparation method of the membranes. Two reactants (e.g. silica precursor and oxidant) are provided at the opposite side of the porous substrates and hybrid silica is deposited inside the pore of the substrate. The pore sizes are controlled by introducing organic functional groups to silica precursor. In this study, the silica hybrid membrane with high H2 permeation performance and high H2/HI selectivity were developed by introducing organic functional groups. Effects of the organic functional groups were summarized by using a pore model. The HI gas and other inorganic gases permeation performance were tested through silica hybrid membranes.

Development of high hydrogen permselective membranes by using a vapor treatment method

Abstract In recent years, the depletion of energy resources and global warming have led to the promotion of new energy resources. Hydrogen is attracting attention as one of the energy sources for the carbon-neutral society by 2050. Membrane separation is a method for separating and purifying hydrogen. In this study, we focused on developing high hydrogen permselectivity of silica membranes. We investigated the conditions necessary for membrane production to obtain a thin, dense separation layer. The results exhibited that the hydrogen permeation selectivity was enhanced in the silica membrane through the utilization of a 2-step deposition technique, which involves the combination of alternative feed and counter-diffusion chemical vapor deposition (CVD). The H2 permeance achieved by the 2-step method is 1.4×10−6 [mol m−2 s−1 Pa−1], representing 1.4 times higher than that of counter-diffusion CVD. In addition, the permeance ratio, which represents hydrogen selectivity, was significantly enhanced with the 2-step method, with H2/C3H8 = 260, twice as high as with CVD. Elemental mapping analysis of the cross-sectional structure revealed a concentration gradient in the deposited silica within the intermediate layer. This indicates that the silica separation layer may become an asymmetric structure. The 2-step method is expected to yield a thinner dense layer, which could contribute to improved permeance of silica separation membranes by reducing permeation resistance.

Hydrogen permselective membrane prepared by plasma treatment of porous ceramic substrates

Abstract Demand for hydrogen is increasing as we move toward a decarbonized society. Membrane separation methods have attracted attention as a way to reduce the cost of hydrogen production. In this study, we focused on boron nitride (BN) as a chemically stable porous substrate material. CVD treatment at 250°C has been investigated for porous BN, but selectivity did not develop. Therefore, we focused on atmospheric pressure plasma as a treatment method. The objective of this study is to develop a membrane with high hydrogen selective permeance by immersion in silicon alkoxide after plasma treatment. After plasma treatment for 100 s, the H2 permeance was 3.52×10−6 [mol m−2 s−1 Pa−1] and the H2/N2 permeance ratio was 18.25. Since molecular hydrogen can pass between the BN crystal faces, it is considered that silica reacted with the hydroxy groups formed on BN by plasma treatment and blocked the space between crystals. Therefore, it is suggested that the performance of the separation membrane changes depending on the number and distribution of hydroxyl groups by plasma treatment, and further stabilization is needed.

A thermodynamic comparison of membrane-assisted processes for hydrogen production with integrated CO2 capture

The energy efficiency of two novel process designs for the production of ultra-pure hydrogen with simultaneous capture of CO2 using CH4 as the feedstock, namely membrane-assisted chemical looping reforming (MA-CLR) and membrane-assisted sorption-enhanced reforming (MA-SER) has been compared. The modelling of the integrated network for mass and heat balances has been carried out using the ASPEN® Plus V10 process simulation tool to quantify the benefits and disadvantages of integrating hydrogen perm-selective membranes with either chemical looping or sorption-enhanced reforming. The evaluation of the MA-CLR process is carried out for a range of the following operating conditions: 10 < pR < 60 bar, 500 < TR < 900°C, and 1.5 < H2O/CH4 < 3.0. On the other hand, for the MA-SER process the operation ranges of 1.0 < pR < 10 bar, 400 < TR < 900°C, and 2.5 < H2O/CH4 < 4.0 were considered. Within the operation window of the MA-SER process, no carbon formation is observed, as any carbon present in the system reacts with CaO in the form of CO2. However, in the case of the MA-CLR process, carbon formation can occur during the pre-reforming stage, particularly at low H2O/CH4 ratios. In terms of hydrogen yield, energy utilization and carbon capture, the MA-CLR outperforms the MA-SER plant. However, the MA-SER plant offers certain advantages over the MA-CLR system, such as a pure CO2 product stream and lower reactor design temperatures. In the MA-CLR system, a carbon capture rate of 99.8% and a hydrogen product yield of 74.4% are achieved, whereas the MA-SER plant achieves a carbon capture rate of 98.5% and a hydrogen product yield of 69.7%.

A multi-criteria optimization and decision-making framework of green DME reactor configurations with a focus on high productivity and low CO2 emission rate

The combination of a conventional Dimethyl Ether (DME) reactor with hydrogen perm-selective membrane and effluent recycling creates innovative membrane reactor (MR) configurations that can efficiently improve thermodynamic limits plus low kinetic rates. In the present article, two eco-friendly configurations were applied to the DME conventional reactor (CR) to boost the DME production rate, yield, and selectivity. These configurations comprise two concentric pipes in which in the 1st configuration the fresh synthesis gas is fed to the inner tube side, hydrogen permeates through the reaction zone, and finally the effluent is recycled back to the outer tube, while in the 2nd one, the effluent of outer tube recycled to the inner pipe. The comprehensive 1-D heterogeneous model has an excellent agreement with industrial data. Also, the simulation results reveal that the higher temperature profile in the 2nd configuration is the consequence of more intensification in the reaction zone by H2 injection and proper heat removal which leads to around 9.5 %, 8.22 %, and 10 % increases in the DME production rate, selectivity, and yield compared to CR, respectively. Enjoying reaction output recycling and H2 permeation, the reaction rate of CO and CO2 hydrogenation plus methanol dehydration enhances significantly in the 2nd scheme.According to Euclidean Distance, the optimization results show that the MODE algorithm has a better performance compared to NSGA-II to obtain optimal Pareto Front and also more rapid respect to lower computational time. The LINMAP approach provides a minimum deviation index among all three decision-making algorithms. Employing optimal operation conditions leads to an enhancement of 17 %, 47 %, and 36 % in DME production rate, selectivity, and yield compared to CR. This eco-friendly configuration prevents the emission of 22000 tons of per year CO2 to the atmosphere.

Modeling and comprehensive analysis of hydrogen production in a newly designed steam methane reformer with membrane system

The use of a hydrogen perm-selective membrane in the conventional steam methane reformer (SMR) is a promising technology for producing ultra-pure hydrogen under moderate operating conditions. A detailed computational fluid dynamics (CFD) analysis is performed on a membrane SMR unit for an on-site hydrogen refueling station (HRS) to get the optimum operating conditions. The developed model was validated with experimental results. The obtained results predicted that the high temperature of the process gas inlet, the high operating pressure, and the low gas hourly space velocity (GHSV) were advantageous. However, these factors must be carefully adjusted to achieve optimal efficiency. Furthermore, the simulation with a counter-current sweep gas flow configuration gave better results than a co-current operation. The estimated optimal conditions for improved CH4 conversion and H2 recovery were 4500 h−1 GHSV, 500 K inlet temperature, and the 8.5 bar operating pressure, representing CH4 conversion and H2 recovery of approximately 94.7% and 95.8%, respectively.

An application of a Pd-based membrane in a multistage spherical styrene monomer production process for hydrogen extraction

One of the main processes in the petrochemical industry is the dehydrogenation of ethylbenzene (EBDH). The process suffers from some practical deficiencies, the most important of which is limitation of conversion progress due to the reversible main reaction. Therefore, the use of spherical membrane reactors (SMR) to carry out the EBDH process is proposed. This paper presented a metal-based hydrogen permselective membrane layer that could mitigate the limitations associated with conventional tubular reactors (CTRs). In the new configuration, pure hydrogen was produced and ethylbenzene conversion was improved, resulting in a reduction in separation and purification costs. In addition, co-current and countercurrent flows were compared to evaluate the performance of the system. Based on the proposed structure, EB conversion, and SM yield were improved by approximately 23% and 15.9%, respectively, over CTRs. As a result of the spherical membrane EBDH, at least 60% of the produced hydrogen gases could be separated from the catalytic bed, resulting in a hydrogen-rich stream.

High hydrogen permselective carbon molecular sieve membrane and its structural formation mechanism

A novel hydroxyl-containing polyetherimide (named BAHPPF-ODPA) with highly aromatic backbone and contorted chain conformation was designed and synthesized as the precursor to fabricate carbon molecular sieve membranes (CMSMs) for H2/N2 separation. The structural evolution from polymeric precursor to carbon during pyrolysis was investigated using characterization techniques combined with pyrolysis simulation. And the relationship between membrane structure formation and their separation performance was explored here. Results indicate that the generation and evolution of pyrolysis products including formed fragments and gases, which depend on the precursor chemistry and pyrolysis conditions, exhibited a significant influence on microstructure and performance of derived CMSMs. Designing precursors with an aromatic backbone and contorted structure and precisely tuning pyrolysis temperature allows the fabrication of CMSMs with controllable micropore structure and excellent H2 separation performance. The BAHPPF-ODPA derived CMSM pyrolyzed at 600 °C exhibited the high H2 permeability of about 3500 Barrer and the superior H2/N2 selectivity of more than 400 were obtained after 750 h of long-term mixed gas (75:25 mixture of H2/N2) testing, showing promising application prospects. The experimental and simulation results obtained here would be beneficial to understand the CMS formation and reasonable to design the precursor molecular structure for fabrication of high-performance CMSMs.

Development of a Trireforming Fluidized‐Bed Reactor with a Hydrogen Permselective Membrane

AbstractThree models were developed for a conventional fluidized‐bed reactor and a cocurrent and a countercurrent membrane fluidized‐bed reactor for methane trireforming. Firstly, the effects of the operating parameters on the reactor performance were assessed. Then, a single‐objective optimization was established. Finally, a membrane was added to the reactor to improve the reactor performance. The simulated results illustrate that the reaction rates are highest near the reactor entrance due to the high volume fraction of the dispersed phase and the existence of a hot zone. Moreover, the optimization process indicates that the maximum H2 yield in the conventional fluidized‐bed reactor is obtained when the inlet temperature, inlet flow rate, and H2O/CH4 ratio, are 804 °C, 3.6 × 105 L h−1, and 2.5, respectively.

Development of Hydrogen Permselective Membranes for Propylene Production

Development of Hydrogen Permselective Membranes for Propylene Production

Development of Hydrogen-Permselective Porous Membranes Using Radiation-Induced Graft Polymerization

Hydrogen-permselective membranes were developed using a radiation-induced grafting method. Styrene (St) and acrylic acid (AAc) monomers were introduced into porous polyvinylidene fluoride (PVDF) membranes to obtain St- and AAc-grafted PVDF membranes with grafting degrees of 82% and 92%, respectively. The porosities of the grafted membranes were controlled in the range 30–40% by hot-press compression at 159 °C and 4 MPa. The hydrogen permeability was found to be of the order of 10−7 mol/m2∙s∙Pa, which was higher than the permeability for water vapor and nitrogen (oxygen model). The St- and AAc-grafted membranes exhibited 9.0 and 34 times higher permeability for H2 than for H2O and N2, respectively.

Hydrogen and/or syngas production through combined dry and steam reforming of biogas in a membrane reactor: A thermodynamic study

The possibility of valorizing biogas by producing pure H2 and/or syngas while minimizing the net CO2 emissions was analyzed, combining both dry and steam reforming of biogas. For this purpose, a multifunctional membrane reactor (MR) with a hydrogen permselective membrane was used. The MR, which allows obtaining ultra-pure hydrogen in the permeate side, is compared with a conventional reactor (CR). All analyses were performed from thermodynamic equilibrium calculations based on the Gibbs free energy minimization method. The temperature was varied up to 800 °C and 550 °C for the CR and the MR, respectively. The influence of water addition in the feed on the productivity of hydrogen and CO2 reduction was assessed as well. Results showed that the CR is more suitable to obtain syngas with high purity (only CO and H2) because it allows operating at very high temperatures. The syngas H2/CO ratio can be adjusted for further applications depending on the co-fed amount of water. However, in the permeate side of the MR high-purity hydrogen with a productivity of 73 mol per 100 mol of biogas fed can be obtained. This productivity is equivalent to an H2 production of 131 kg/h, assuming the biogas generation capacity of an existing landfill plant; still, by CO2 recycling, net CO2 emission can be reduced up to 50%.

Synthesis of nano-sheets seeds for secondary growth of highly hydrogen permselective ZIF-95 membranes

Recently, more and more attentions have been focused on the preparation of metal-organic framework (MOF) membranes for gas or liquid separations. However, it is rather difficult to prepare a dense MOF membrane by a direct solvothermal synthesis route because of poor heterogeneous nucleation of MOF on the native ceramic support surface. Chemical modifications or seeds coating are usually carried out to promote nucleation and growth of MOF membranes. In this work, we report the synthesis of ZIF-95 nano-sheets as seeds for secondary growth of highly hydrogen permselective ZIF-95 membranes. Under the action of the vacuum force, the ZIF-95 seeds in the colloidal suspensions are attracted and transported onto the whole area of the support surface continuously and uniformly, thus forming a continuous and uniform ZIF-95 seeding layer, which is helpful to promote the nucleation and growth of ZIF-95 membranes. After solvothermal synthesis at 120 °C for 48 h, a well-intergrown ZIF-95 membrane was formed on the seeding support surface. Attributing to a preferentially affinity to CO2 and a narrow pore size of ~0.37 nm, the developed ZIF-95 membrane shows high hydrogen permselectivity for the separation H2 from other large molecules. At 200 °C and 1 bar, the mixture separation factors of H2/CO2, H2/N2, and H2/CH4 are 41.6, 36.8, and 40.3, respectively, with H2 permeances over 1.7 × 10−7 mol m−2 s−1·Pa−1.

Development of CVD Silica Membranes Having High Hydrogen Permeance and Steam Durability and a Membrane Reactor for a Water Gas Shift Reaction.

Water gas shift reaction of carbon monoxide (CO) with membrane reactors should be a promising method for hydrogen mass-production because of its high CO conversion, high hydrogen purity and low carbon dioxide emission. For developing such membrane reactors, we need hydrogen permselective membranes with high hydrogen permeance with order of 10−6 mol m−2 s−1 Pa−1 at 573 K and high steam durability. In this study, we have optimized the kind of substrates, precursors, vapor concentration, and chemical vapor deposition (CVD) time using the counter-diffusion CVD method for developing such membranes. The developed membrane prepared from hexamethyldisiloxane has a hydrogen permeance of 1.29 × 10−6 mol m−2 s−1 Pa−1 at 573 K and high steam durability. We also conducted water gas shift reactions with membrane reactors installed the developed silica membranes. The results indicated that reactions proceed efficiently with the conversion around 95–97%, hydrogen purity around 94%, and hydrogen recovery around 60% at space velocity (SV) 7000.

Active block copolymer layer on carboxyl-functionalized PET film for hydrogen separation

To rationalize the energy requirements and environmental complications of the world, supply of pure hydrogen is the most promising as well best possible approach of such issues. Purified hydrogen gas is the necessity factor for the hydrogen-based economy. Hydrogen perm-selective membrane plays a crucial role for producing a large amount of hydrogen. Palladium is one of the best materials because of its excellent affinity to absorb hydrogen. In present work, our aim to improve selectivity as well permeability of the H2 gas compare to N2 and CO2 gases of the block copolymer coated functionalized porous PET membrane. Porous polyethylene terephthalate (PET) membranes having pore size 0.2 μm, functionalized with a carboxyl group. The supramolecular assembly was prepared from PS (35500)-b- P4VP (4400) and 2-(4- Hydroxyphenylazo) benzoic acid (HABA) in 1, 4-dioxane. Chemically synthesized palladium nanoparticles were deposited on carboxylated block copolymer (BC) coated porous PET membrane. It is an appropriate way to use H2 sensitive materials with block copolymer coated functionalized membranes to enhance the selectivity of H2. It has been found that such membranes gain better permeability and selectivity towards H2 as compared with N2 and CO2. Increment with the dipping time of these membranes in the palladium nanoparticle solution, permeability as well selectivity of H2 over N2, CO2 increases as the more attachment of Palladium nanoparticles. A fine active layer of block copolymer on the carboxyl functionalized PET membrane play a crucial role for hydrogen based gas separation. The magnitude of the permeability of such membranes for different gases shows dependency on the pore size of the upper layer (BC coated) of the membrane in addition to the molecule size of the permeating gas. Block copolymer coating of the membranes established an effective responsibility for the selectivity of H2 over CO2 gas as well over N2 gas.

Supporting the propane dehydrogenation reactors by hydrogen permselective membrane modules to produce ultra-pure hydrogen and increasing propane conversion: Process modeling and optimization

The main aim of this research is supporting the moving bed radial flow reactors in the propane dehydrogenation unit by membrane modules to produce ultra-pure hydrogen and increasing equilibrium conversion. The propane dehydrogenation is a thermodynamically limited and endothermic reaction, which decreasing hydrogen concentration and increasing operating temperature in the system could increase equilibrium conversion. In the first step, the conventional and membrane supported reactors are heterogeneously modeled based on the mass and energy conservation laws considering catalyst decay. To verify the precision of developed model, the results of simulation are compared with the available plant data. Then, the performance of designed membrane configuration is compared with the conventional process at the same feed condition. It appears that the activity of catalyst decreases along the reactors due to coke build up on the catalyst surface, and it results in the lower propane conversion. The results show that supporting the conventional reactors by hydrogen permselective membrane module increases propane conversion up to 3.09%.

A numerical study on concentration polarization in 3D cylindrical fluidized beds with vertically immersed membranes

Concentration polarization is a serious issue for systems in which high-flux, palladium-based, hydrogen perm-selective membranes are used to extract hydrogen, not only for packed-bed reactor systems, but also for fluidized bed membrane reactors. Two-Fluid Model simulations of 3D cylindrical lab-scale fluidized beds with single and multiple vertically immersed cylindrical membranes with state-of-the-art hydrogen permeability were performed to quantify concentration polarization, to study the interaction between concentration polarization zones of multiple vertically immersed membranes and to link these findings to the bed hydrodynamics. Simulations of a fluidized bed consisting of 500 μm particles using a H2/N2 mixture as fluidization gas with a single immersed membrane, show that reduced hydrogen concentrations prevail mostly within 1 cm from the membrane surface, and have disappeared beyond about 2 cm distance from the membrane surface. A 3D simulation was compared to a Cartesian 2D simulation that represents a slice of the 3D system, to assess the accuracy of 2D simulations. The 2D simulation did not fully capture the hydrodynamics and radial mass transfer effects of 3D cylindrical fluidized bed membrane reactors and overestimated the severity of concentration polarization and the formation of densified zones near the membrane surface. In particular, the hydrogen fluxes were determined at 0.217 mol/(m2 s Pa0.5) for the 3D case, and 0.133 mol/(m2 s Pa0.5) for the 2D case. The severity of densified zones is also affected by the particle size, because for smaller particles (250 μm) the emulsion phase density near the membrane surface is higher than for systems with larger particles (500 μm), which results in increased concentration polarization and a reduced extractive hydrogen flux. Therefore, employing relatively large particles of at least 500 μm in fluidized beds with modern high-flux membranes is advised. In fluidized beds with multiple membranes, interaction between concentration polarization zones of each membrane was observed. The interaction becomes more significant at smaller inter-membrane distances, especially below 2 cm, and decreasing the bed diameter decreases the system performance even more due to hydrogen depletion. Vertically immersed membranes also affect the fluidized bed hydrodynamics by reducing bubble size and increasing the number of small bubbles.

Pd-membrane Integration in a Propane Dehydrogenation Process for Highly Selective Propylene Production

The forecasts in the industrial chemistry field evidenced the growing demand of propylene, and the necessity to develop effective processes able to sustain the market. Selective propane dehydrogenation is emerging as the most competitive technology for the production of propylene, on the other hand, the well-known drawback closely linked to the high temperature required to reach a sustainable propane conversion and the coke formation that suppress the catalytic stability still requires appropriate solutions. In this sense, the process intensification through the combination of hydrogen permselective membranes and the reduction of operating temperature could strike the targets of very high propylene selectivity and a quite high conversion value. Since the integration of membrane units in a process required a revision of the operating conditions, the effect of feed composition and temperature was investigated, in order to determine the optimal operating parameters window to operate the system, and assess the overall concept performance. A commercial membrane was characterized, in order to understand the suitability in the propane dehydrogenation process that may cause a severe membrane deactivation due to coke deposition. Finally, specific tests on a simulated process configuration, obtained in an open architecture, confirmed that the smart combination of PDH catalytic reactors and Pd-based membranes was able to allow a reduced operating temperature, so increasing propylene selectivity, and to overcome typical thermodynamic limitations related to a traditional configuration.

Pd-membrane Integration in a Propane Dehydrogenation Process for Highly Selective Propylene Production

The forecasts in the industrial chemistry field evidenced the growing demand of propylene, and the necessity to develop effective processes able to sustain the market. Selective propane dehydrogenation is emerging as the most competitive technology for the production of propylene, on the other hand, the well-known drawback closely linked to the high temperature required to reach a sustainable propane conversion and the coke formation that suppress the catalytic stability still requires appropriate solutions. In this sense, the process intensification through the combination of hydrogen permselective membranes and the reduction of operating temperature could strike the targets of very high propylene selectivity and a quite high conversion value. Since the integration of membrane units in a process required a revision of the operating conditions, the effect of feed composition and temperature was investigated, in order to determine the optimal operating parameters window to operate the system, and assess the overall concept performance. A commercial membrane was characterized, in order to understand the suitability in the propane dehydrogenation process that may cause a severe membrane deactivation due to coke deposition. Finally, specific tests on a simulated process configuration, obtained in an open architecture, confirmed that the smart combination of PDH catalytic reactors and Pd-based membranes was able to allow a reduced operating temperature, so increasing propylene selectivity, and to overcome typical thermodynamic limitations related to a traditional configuration.

Mass transfer phenomena in fluidized beds with horizontally immersed membranes: A numerical investigation

Mass transfer phenomena in gas-solid fluidized beds with horizontally immersed membrane tube banks in different configurations were investigated using a Two-Fluid Model, considering the case of a binary hydrogen/nitrogen gas mixture fed to a 2D fluidized bed where hydrogen was extracted via hydrogen perm-selective membranes. The simulations showed that the hydrogen flux is strongly non-uniform over the radius of the membranes. The hydrogen flux is lowest on top of the membranes and highest at the bottom of the membranes, which is caused by the formation of densified zones on top of the membranes and the fact that the membranes shield their own top side from hydrogen replenishment. Also, in systems with membrane tube banks, the performance of individual membranes differs significantly. The membranes located near the bed walls perform considerably worse, because of downwards solids flow near the walls, resulting in more densified zones and gas back-mixing. The average hydrogen recovery per membrane is highest for the cases with a staggered tube bank configuration and without membranes positioned close to the bed walls. In-line tube bank configurations suffer from gas channeling, reducing the hydrogen recovery per membrane. The membrane tube banks also significantly improve the bed hydrodynamics by enhanced bubble-breakage, decreasing the bubble size to approximately the membrane pitch.