Hydrogen separation and purification using crosslinkable PDMS/zeolite A nanoparticles mixed matrix membranes

The transport properties of gases in polydimethylsiloxane (PDMS)/zeolite A mixed matrix membranes (MMMs) were determined based on pure gas permeation experiments. MMMs were prepared by incorporating zeolite 4A nanoparticles into a PDMS matrix using a new procedure. The permeation rates of C₃H₈, CH₄, CO₂, and H₂ were evaluated through a dense homogeneous pure PDMS membrane and PDMS/4A MMMs to assess the viability of these membranes for natural gas sweetening and hydrogen purification. SEM investigations showed good adhesion of the polymer to the zeolite in MMMs. Permeation performance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of feed pressure, zeolite loading and pore size of zeolite on the gas separation performance of the MMMs were evaluated. The MMMs exhibited both higher selectivity of H₂/CH₄ and H₂ permeability as compared with the neat PDMS membrane, suggesting that these membranes are very promising for gas separations such as H₂/CH₄ separation.     

Fabrication and characterization of poly(phenylene oxide)/SBA-15/carbon molecule sieve multilayer mixed matrix membrane for gas separation

A novel multilayer mixed matrix membrane (MMM), consisting of poly(phenylene oxide) (PPO), large-pore mesoporous silica molecular sieve zeolite SBA-15, and a carbon molecular sieve (CMS)/Al₂O₃ substrate, was successfully fabricated using the procedure outlined in this paper. The membranes were cast by spin coating and exposed to different gases for the purpose of determining and comparing the permeability and selectivity of PPO/SBA-15 membranes to H₂, CO₂, N₂, and CH₄. PPO/SBA-15/CMS/Al₂O₃ MMMs with different loading weights of zeolite SBA-15 were also studied. This new class of PPO/SBA-15/CMS/Al₂O₃ multilayer MMMs showed higher levels of gas permeability compared to PPO/SBA-15 membranes. The permselectivity of H₂/N₂ and H₂/CH₄ combinations increased remarkably, with values at 38.9 and 50.9, respectively, at 10 wt% zeolite loading. Field emission scanning electron microscopy results showed that the interface between the polymer and the zeolite in MMMs was better at a 10 wt% loading than other loading levels. The increments of the glass transition temperature of MMMs with zeolite confirm that zeolite causes polymer chains to become rigid.     

Gas sorption in H2-selective mixed matrix membranes: Experimental and neural network modeling

Robust artificial neural network (ANN) was developed to forecast sorption of gases in membranes comprised of porous nanoparticles dispersed homogenously within polymer matrix. The main purpose of this study was to predict sorption of light gases (H₂, CH₄, CO₂) within mixed matrix membranes (MMMs) as function of critical temperature, nanoparticles loading and upstream pressure. Collected data were distributed into three portions of training (70%), validation (19%), and testing (11%). The optimum network structure was determined by trial-error method (4:6:2:1) and was applied for modeling the gas sorption. The prediction results were remarkably agreed with the experimental data with MSE of 0.00005 and correlation coefficient of 0.9994.     

Gas permeation through H2-selective mixed matrix membranes: Experimental and neural network modeling

Gas permeability through synthesized polydimethylsiloxane (PDMS)/zeolite 4A mixed matrix membranes (MMMs) were investigated with the aid of artificial neural network (ANN) approach. Kinetic diameter and critical temperature of permeating components (e.g. H₂, CH₄, CO₂ and C₃H₈), zeolite content and upstream pressure as input variables and gas permeability as output were inspected. Collected data of the experimental operation was used to ANN training and optimum numbers of hidden layers and neurons were obtained by trial-error method. The selected ANN architecture (4:10:1) was used to predict gas permeability for different inputs in the domain of training data. Based on the results, the predicted values demonstrate an excellent agreement with the experimental data, with high correlation (R² = 0.9944) and less error (RMSE = 1.33E−4). Furthermore, using sensitivity analysis, kinetic diameter and critical temperature were found as the most significant effective variables on gas permeability. As a result, ANN can be recommended for the modeling of gas transport through MMMs.     

H2-selective mixed matrix membranes modeling using ANFIS,PSO-ANFIS,GA-ANFIS

The novel contribution of the current study is to employ adaptive neuro-fuzzy inference system (ANFIS) for evaluation of H₂-selective mixed matrix membranes (MMMs) performance in various operational conditions. Initially, MMMs were prepared by incorporating zeolite 4A nanoparticles into polydimethylsiloxane (PDMS) and applied in gas permeation measurement. The gas permeability of CH₄, CO₂, C₃H₈ and H₂ was used for ANFIS modeling. In this manner, the H₂/gas selectivity as the output of the model was modeled to the variations of feed pressure, nanofiller contents and the kind of gas, which were defined as input (design) variables. The proposed method is based on the improvement of ANFIS with genetic algorithm (GA) and particle swarm optimization (PSO). The PSO and GA were applied to improve the ANFIS performance. To determine the efficiency of PSO-ANFIS, GA-ANFIS and ANFIS models, a statistical analysis was performed. The results revealed that the PSO-ANFIS model yields better prediction in comparison to two other methods so that root mean square error (RMSE) and coefficient of determination (R²) were obtained as 0.0135 and 0.9938, respectively. The RMSE and R² values for GA-ANFIS were 0.0320 and 0.9653, respectively, and for ANFIS model were 0.0256 and 0.9787, respectively.     

GNs/MOF-based mixed matrix membranes for gas separations

NU-1000 and graphene nanosheet (GNs) with different loadings have been used as fillers to prepare mixed matrix membranes (MMMs) with polyethersulfone (PES). The high performance of the MMMs has been successfully fabricated for the evaluation of gas separation at 1 bar and various temperatures (20, 40, 60 °C). The successful fabrication of the MMMs were confirmed by using SEM, FTIR, AFM, and XRD. The crystalline nature of GNs and NU-1000 in the MMMs are evidenced by XRD, which confirms the successful fabrication of the MMMs. In addition, the thermal stability of the MMMs was enhanced with the increase of the GNs. Separation performance of H₂ was superior to CO₂, N₂ and CH₄ separation on the MMMs which is a critical for producing energy. The best gas separation results in terms of both permeability and selectivity were obtained with 0.03% GNs and 10% NU-1000. PG3N membrane presented maximum H₂/CO₂, H₂/N₂ and H₂/CH₄ selectivity of 5, 4.2, 3.3 at 20 C, respectively. With an increase in temperature, the permeability increased, while the selectivity of all the MMMs decreased. The MMMs exhibited excellent gas separation capability, which offers unique opportunities for potential large-scale practical applications.     

Accurate prediction of solubility of gases within H2-selective nanocomposite membranes using committee machine intelligent system

In-depth knowledge about the gas sorption within hydrogen (H₂) selective nanocomposite membranes at various conditions is crucial, particularly in petrochemical and separation processes. Hence, various artificial intelligence (AI) methods such as multilayer perceptron artificial neural network (MLP-ANN), adaptive neuro-fuzzy inference system (ANFIS), the adaptive neuro-fuzzy inference system optimized by genetic algorithm (GA-ANFIS), Genetic Programming (GP) and Committee Machine Intelligent System (CMIS) were applied to predict the sorption of gases in H₂-selective nanocomposite membranes consist of porous nanoparticles as the dispersed phase and polymer matrix as continuous phase. The momentous purpose of this paper was to estimate the sorption of C₃H₈, H₂, CH₄ and CO₂ within H₂-selective nanocomposite membranes considering the effect of nanoparticles loading, critical temperature (gas type characteristics) and upstream pressure. Obtained data were categorized into two parts including training and testing data set. The CMIS method showed more precise results rather than other intelligent models. Having developed different intelligent approaches rely on algorithms, a powerful successor for labor-intensive experimental processes of solubility was revealed. The prediction results and experimental data were significantly consistent in approach with a correlation coefficient (R²) of 0.9999, 0.9987, 0.9998, 0.9995, and 0.9997 for CMIS, GP, GA-ANFIS, ANFIS and ANN models respectively.     

CNT/PDMS composite membranes for H2 and CH4 gas separation

Polydimethylsiloxane (PDMS) composites with different weight amounts of multi-walled carbon nanotubes (MWCNT) were synthesised as membranes to evaluate their gas separation properties. The selectivity of the membranes was investigated for the separation of H₂ from CH₄ gas species. Membranes with MWCNT concentrations of 1% increased the selectivity to H₂ gas by 94.8%. Furthermore, CH₄ permeation was almost totally blocked through membranes with MWCNT concentrations greater than 5%. Vibrational spectroscopy and X-ray photoelectron spectroscopy techniques revealed that upon the incorporation of MWCNT a decrease in the number of available Si–CH₃ and Si–O bonds as well as an increase in the formation of Si–C bonds occurred that initiated the reduction in CH₄ permeation. As a result, the developed membranes can be an efficient and low cost solution for separating H₂ from larger gas molecules such as CH₄.     

Development of hydrogen-selective CAU-1 MOF membranes for hydrogen purification by ‘dual-metal-source’ approach

Hydrogen provides reliable, sustainable, environmental and climatic friendly energy to meet world's energy requirement and it also has high energy density. Hydrogen is relevant to all of the energy sectors-transportation, buildings, utilities and industry. In all of these sectors, hydrogen-rich gas streams are needed. Thus, hydrogen-selective membrane technology with superior performances is highly demanded for separation and purification of hydrogen gas mixtures. In this study, novel [Al₄(OH)₂(OCH₃)₄(H₂N-BDC)₃]·xH₂O (CAU-1) MOF membranes with accessible pore size of 0.38 nm are evaluated for this goal of hydrogen purification. High-quality CAU-1 membranes have been successfully synthesized on α-Al₂O₃ hollow ceramic fibers (HCFs) by secondary growth assisted with the homogenously deposited CAU-1 nanocrystals with a size of 500 nm as seeds. The energy-dispersive X-ray spectroscopy study shows that the HCFs substrates play dual roles in the membrane preparation, namely aluminum source and as a support. The crystals in the membrane are intergrown together to form a continuous and crack-free layer with a thickness of 4 μm. The gas sorption ability of CAU-1 MOF materials is examined by gas adsorption measurement. The isosteric heats of adsorption with average values of 4.52 kJ/mol, 12.90 kJ/mol, 12.82 kJ/mol and 27.99 kJ/mol are observed for H₂, N₂, CH₄, and CO₂ respectively, indicating different interactions between CAU-1 framework and these gases. As-prepared HCF supported CAU-1 membranes are tested by single and binary gas permeation of H₂/CO₂, H₂/N₂ and H₂/CH₄ at different temperatures, feed pressures and testing time. The permeation results show preferential permeance of H₂ over CO₂, N₂, and CH₄ with high separation factors of 12.34, 10.33, and 10.42 for H₂/CO₂, H₂/N₂, H₂/CH₄, respectively. The temperature, pressure and test time dependent studies reveal that HCFs supported CAU-1 membranes possess high stability, resistance to cracking, temperature cycling, high reproducibility, these of which combined with high separation efficiency make this type of MOF membranes are promising for hydrogen recycling from industrial exhausts.     

Fabrication and characterization of highly efficient three component CuBTC/graphene oxide/PSF membrane for gas separation application

Metal organic frameworks (MOFs) with marvelous properties have aroused enormous attention for different application especially gas adsorption and separation. In this regard, fabrication of MOF hybrids with carbon based materials is new strategy to upgrade MOF performance. In this study CuBTC (Copper benzene-1,3,5-tricarboxylic acid)/graphene oxide (GO) composite was synthesized and characterized by BET, SEM, TGA, XRD and FT-IR techniques. Then CuBTC and CuBTC/GO composite were incorporated into polysulfone (PSF) polymer to construct mixed matrix membranes (MMMs). The obtained membranes were characterized by SEM, TGA, XRD and tensile tests and their gas permeability was measured. The results were compared to those of CuBTC/PSF MMMs. It was revealed that CuBTC/GO composite as filler showed superior performance relative to CuBTC. For instance, 15 wt% loading of CuBTC/GO in PSF represented outstanding gas separation behavior while the same loading of CuBTC in PSF deteriorated performance of MMM. Well particle dispersion and favorable polymer-filler interaction were responsible for such observed difference. A high H₂/CH₄ and H₂/N₂ selectivity of 80.03 and 70.46 were recorded for CuBTC/GO in PSF (15 wt%) compared to 44.56 and 40.92 for CuBTC in PSF (15 wt%).     

Hydrogen separation and purification with poly (4-methyl-1-pentyne)/MIL 53 mixed matrix membrane based on reverse selectivity

The effect of MIL 53 (Al) metal organic framework on gas transport properties of poly (4-methyl-1-pentyne) (PMP) was determined based on reverse selectivity. Mixed matrix membranes (MMMs) were fabricated considering various weight percent of MIL 53 particles. The reverse MMMs permselectivities were evaluated through measurement of pure CO₂ and H₂ permeation together with calculation of CO₂/H₂ selectivity. The PMP/MIL 53 (Al) MMMs exhibited privileged CO₂/H₂ permselectivity in comparison with the neat PMP. In addition, CO₂ solubility coefficient was significantly increased with increasing the MIL 53 loading, while the H₂ solubility coefficient was almost remained unchanged. Moreover with increasing the feed pressure the permeability of CO₂ and CO₂/H₂ selectivity were dramatically enhanced, especially at higher filler loadings. Therefore, it was observed that the reverse selectivity of MMMs was enhanced so that the Robeson upper bound was overcome. The best yielding membranes (PMP/30 wt.% MIL 53) represented the CO₂ permeability and CO₂/H₂ selectivity of 377.24 barrer and 24.91 for pure gas experiments respectively.     

Structure-controlled mesoporous SBA-15-derived mixed matrix membranes for H2 purification and CO2 capture

The composite mixed matrix membranes (MMMs) were prepared by incorporating mesopore SBA-15 as a filler to discuss the effects of its particle shape, particle size, and loadings on the organic–inorganic interfacial morphology. The SBA-15 was synthesized by template method and it's particle shape and size was adjusted by adding electrolyte. The results indicated that the spherical SBA-15 can improve the dispersion and have better adhesion with organic phase, which showed better permselectivity than the rod-like one. The SBA-15 filler also could increase the diffusion selectivity of MMMs by the addition of different particle sizes. The permeabilities of H₂ and CO₂ were 1207.9 and 552.86 Barrer, respectively, with selectivities of H₂/CH₄ and CO₂/CH₄ reached 247.0 and 112.8, respectively, when 1.6 μm spherical SBA-15 was added at 3 wt. %. The dissimilarity occurring in the perm-selectivity values with changes made in the particle shape and size are much more pronounced at the lower SBA-15 loading, which exceeded the 2008 Robeson's upper bound limited.     

Preparation of PPO-silica mixed matrix membranes by in-situ sol–gel method for H2/CO2 separation

Poly(2,6-dimethyl-1,4-phenylene oxide)(PPO)-silica mixed matrix membranes (MMMs) were synthesized through the in-situ sol–gel method. The effects of the acid–base catalysis conditions and silica loading weight on the gas separation performance of the membranes were investigated. The functional groups, crystalline structure, thermal stability, and morphology of the MMMs were examined using Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and thermogravimetric analysis (TGA), respectively. The results indicate that using the in-situ sol–gel method to synthesize PPO-silica MMMs is beneficial for improving the adhesion between the silica and polymer and for the dispersion of the silica. The additives significantly enhanced the thermal stability of the membranes. Compared with pure PPO membranes, the PPO-silica MMMs prepared with 10 wt.% acid-silica loading exhibited the best H₂/CO₂ separation properties: H₂ permeability was enhanced from 82.1 to 548.7 Barrer, and an H₂/CO₂ separation ratio of approximately 3.56 was observed.     

Grand canonical Monte Carlo and molecular dynamics simulations of the structural properties,diffusion and adsorption of hydrogen molecules through poly(benzimidazoles)/nanoparticle oxides composites

Comprehensive structural/molecular simulations have been undertaken to study the poly(benzimidazoles) (PBI) membrane combined with four different nano-oxide materials (ZnO, Al₂O₃, SiO₂ and TiO₂) for purification and production of hydrogen from natural gases. Composite membranes were built with different amounts of nano-oxide materials to investigate the influence of nano-oxide content on the PBI membrane performance. Several structural characterizations such as FFV, WAXD and also a thermal one (glass transition temperature) were done to study the structural properties of all simulated membrane cells. Moreover, MSD and adsorption isotherms tasks were used to estimate the diffusivity and solubility of hydrogen molecules through the latter mixed matrix membranes (MMMs), respectively. Permeability and permselectivity of H₂ penetrate molecules were also carefully calculated using the aforementioned penetrating factors (diffusivity and solubility). Results show a significant improvement in structural and transport properties by increasing the nanomaterials content, which could be due to the growth of penetration pathways through the membranes. Furthermore, membranes with SiO₂ yield the best results compared to other three nano-oxide fillers. H₂ gas yields the best results that help the storage and separation of this precious gas from other gas molecules, which present in natural gases. Compared to the previous studies and literature results, the current results are accurate and reliable to describe the structural and transport properties of PBI/nano-oxides composites.     

Preparation,characterization and gas permeation properties of PDMS/PEI composite asymmetric membrane for effective separation of hydrogen from H2/CH4 mixed gas

In this work, PDMS/PEI membranes were synthesized and sorption and permeation of H₂/CH₄ mixture were studied. The influence of pressure, temperature and feed composition were investigated. It was shown that permeances increased and selectivity decreased with an increment in the feed temperature. Increasing feed pressure caused a decline in gas permeance and increased selectivity. Higher concentrations of hydrogen in the feed declined the selectivity. The effect of different non-solvents was explained by their effect on precipitation time and it was concluded that water made the membrane denser while isopropanol forms a sponge-like structure. Coagulation bath temperature made the membrane denser. Film casting and dip-coating techniques were used to prepare selective membranes. Obtained selectivity results introduced dip-coating as a better method than film casting. Sequential coating improved selectivity of the prepared membrane. Finally, sequential coating with different concentrations was applied and enhanced selectivity significantly from about 22 to more than 70.     

Development of hybrid models for prediction of gas permeation through FS/POSS/PDMS nanocomposite membranes

The present paper aims to use intelligent methods for prediction of gas permeation in binary-filler nanocomposite membranes containing fumed silica (FS) and octatrimethylsiloxy polyhedral oligomeric silsesquioxane (POSS) nanoparticles incorporated within a polymer matrix of polydimethylsiloxane (PDMS). Two reliable and rigorous hybrid models, i.e., differential evolution-adaptive neuro-fuzzy inference system (DE-ANFIS) and coupled simulated annealing-least square support vector machine (CSA-LSSVM) were developed in order to predict pure gas permeability of including H₂, CH₄, CO_2, and C₃H₈ through the nanocomposite membranes. The coupled simulated annealing (CSA) optimization algorithm was also used for tuning of the model parameters. The impacts of several key parameters such as pressure, FS nanoparticles loading as well as the kinetic diameter of gases on permeation were investigated. The experimental data were randomly divided into two main groups, namely training (70%) and testing (30%) sets. The results of the study suggested that DE-ANFIS model is a more robust and accurate model than the CSA-LSSVM with the R² values of 0.9981 and 0.9689, respectively.     

Molecular-level mixed matrix membranes comprising Pebax and POSS for hydrogen purification via preferential CO2 removal

The molecular-level mixed matrix membranes (MMMs) comprising Pebax^® and POSS have been developed by tuning the membrane preparation process in this work. They exhibit a simultaneous enhancement in CO₂ permeability and CO₂/H₂ selectivity by optimizing the POSS content at extremely low loadings. This is mainly attributed to the large cavity of POSS itself and its effect on the segmental-level polymeric chain packing. More interestingly, the Pebax^®/POSS MMMs reveal a much higher separation performance in the mixed gas test than that in the pure gas test. The highest CO₂/H₂ selectivity reaches 52.3 accompanied by CO₂ permeability of 136 Barrer at 8 atm and 35 °C. This is due to the CO₂-induced plasticization that improves the free volume and polymer chain mobility, hence benefiting the interaction between the polymer matrix and penetrant CO₂. These features may ensure the superiority of Pebax^®/POSS molecular-level MMMs as CO₂-selective membranes in the industrial application of hydrogen purification.     

Aliphatic–aromatic polyimide blends for H2 separation

In this work the synthesis of a semi aliphatic BTDA-DAH polyimide and their blends with BTDA-ODA and BTDA-DDS polyimides was carried out in order to improve the H₂ permselective properties of polyimides. The syntheses were made using the well-known two steps method and the silylation method. The prepared films were characterized by FTIR, DSC, thermal stability and fluorescence spectroscopy. Intercatenary distances (d-spacing) and gas separation properties were also investigated. PI blend membranes presented only one glass transition temperature (Tg) intermediate between those of the neat polyimides. Fluorescence spectra were a useful tool to recognize electron-donor and electron-acceptor interactions indicating intermolecular charge-transfer complex (CTC) formation which were confirmed by UV–Vis absorptions. As a result, a decrease in the intercatenary distances and a shift for both IR and fluorescence bands of polyimide blends were measured. PI blend membranes showed a permeability decrease with respect to the neat ones, while the selectivity increased according to X-ray diffraction results. To analyze the polyimide blend permselectivities, H₂/CH₄, H₂/CO₂, H₂/O₂ and H₂/N₂ systems were chosen. As a result, H₂/CH₄ separation factor of PI blends was among the highest reported by other authors using traditional membrane materials.     

Preparation and characterization of PPSU/PBNPI blend membrane for hydrogen separation

Novel polymer blend membranes of poly(bisphenol A-co-4-nitrophthalic anhydride-co-1,3-phenylenediamine) (PBNPI) and polyphenylsulfone (PPSU) in different weight ratios were prepared by a solution casting technique with N-methyl-2-pyrrolidone (NMP) as solvent. The effects of blend polymer composition on the membrane structure and the H₂, CO₂ and CH₄ separation performance were investigated. The membranes appear macroscopically miscible but microscopically immiscible based on thin-film X-ray diffraction investigations. A remarkably and continuously enhanced permeability has been achieved for these gases with increasing PPSU content from 0 to 50%. The highest pure H₂, CO₂ and CH₄ permeability are, respectively, equal to 40.4, 34.1 and 8.0 barrer.     

Co-based zeolitic imidazolate framework ZIF-9 membranes prepared on α-Al2O3 tubes through covalent modification for hydrogen separation

Hydrogen has been regarded as the most promising clean and renewable energy. Beside the production of the hydrogen, the separation of hydrogen is also an import issue before it can be used in fuel cells. Membrane-based separation technologies have gained considerable attentions due to its high efficiency and low energy consumption. Zeolite imidazolate framework (ZIF) membranes have drawn intense interest due to their zeolite-like properties such as permanent porosity, uniform pore size and exceptional thermal and chemical stability. It is rather challenged to prepare well-intergrown Co-based zeolitic imidazolate frameworks (ZIFs) membranes on porous α-Al₂O₃ tubes since Co-based ZIFs prefer to form crystals in the synthesis solution rather than grow as membrane layer on the support surface. In this work, we report the preparation of high-quality ZIF-9 membrane with high H₂/CO₂ selectivity and excellent thermal stability by using 3-aminopropyltriethoxysilane (APTES) as a covalent linker to modify the α-Al₂O₃ tube. Due to the formation of covalent bonds between APTES and ZIF-9, ZIF-9 nutrients are bound to the support surface, thus promoting the growth of dense and phase-pure ZIF-9 membrane with a thin thickness of about 4.0 μm. The gas separation performances of the ZIF-9 membrane were evaluated by single gas permeation and mixture gas separation of H₂/CO₂, H₂/N₂ and H₂/CH₄, respectively. The mixture separation factors of H₂/CO₂, H₂/CH₄, and H₂/N₂ of the ZIF-9 membrane are 21.5, 8.2 and 14.7, respectively, which by far exceeds corresponding Knudsen coefficients. Moreover, the as-prepared ZIF-9 membrane exhibits excellent stability at a relatively broad range of operating temperature, which is beneficial for the industrial application of hydrogen separation or further membrane reactor.