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A series of mixed matrix membranes (MMMs) based on polyurethane (PU) and silica nanoparticles was fabricated. Three types of PU were synthesized with different polyethylene glycol (PEG)/polytetramethylene glycol ratios (PU0, PU75, and PU100, the corresponding numbers: PEG percent). The MMMs were characterized using FTIR, SEM, and gas permeation measurements (N2, O2, CH4, and CO2). The phase mixing of PU0 and PU75 membranes increased with silica content. This resulted in a decrease in gas permeability, while an increase in CO2/CH4 and CO2/N2 selectivities. The gas separation trend for PU100 membranes was the opposite. The molecular probing approach was served to study the interfacial structure of the MMMs. The existence of a rigidified polymer layer with 2.38 and 2.44 nm thicknesses around silica was revealed through PU0 and PU75 membranes, respectively. In contrary, silica was surrounded by a polymer chain dilution interphase with a thickness of 2.20 nm for PU100 MMMs. [ABSTRACT FROM AUTHOR]

A series of polysulfone (PSF) membranes were prepared using different solvents: dimethylformamide (DMF), tetrahydrofuran, dimethylacetamide, and n‐methyl‐2‐pyrrolidone (NMP). The PSF membrane prepared by NMP showed the highest gas permeability. The influence of propionic acid as a Lewis acid on gas separation properties of the PSF was explored. The PSF membrane prepared by the casting solution containing 25 wt% PSF, 35 wt% propionic acid, and 40 wt% NMP showed a superior gas separation performance. The gas permeation measurements indicated that incorporating 30 wt% γ‐alumina nanoparticles into the PSF matrix resulted in about the respective 43% and 41% increase in CO2 and O2 permeability together with a rise in CO2/CH4 and O2/N2 selectivities (13% and 7%, respectively). Furthermore, by rearranged modified Maxwell model, the role and nature of the interfacial layer in the PSF‐based mixed matrix membranes were mathematically analyzed considering a reduced permeability factor. [ABSTRACT FROM AUTHOR]

In this study, the effect of solvent type and nanoparticles of silica and zeolite 4A on the gas separation properties of polyimide (PI) membranes were investigated. Gas separation of the membranes based on pure solvents of dimethylformamide (DMF), n‐methyl‐2‐pirrolidone (NMP), dimethylacetamide (DMAc), and dimethylsulfoxide (DMSO) were studied. The prepared PI membranes using DMAc and DMSO showed the highest selectivity and permeability, respectively. In this regard, the influence of their mixing on transport properties of the PI was evaluated. The prepared membrane using the mixture of DMSO/DMAc with the volume ratio of 1:3 showed the best gas separation performance in comparison to the Robeson's upper bound. Incorporation of 20 wt% of silica and zeolite 4A nanoparticles into the PI membrane indicated that the selectivity of CO2/CH4 increased from 39.4 to 57.6 and 68.5, respectively. Besides, gas transport properties of the PI‐based mixed matrix membranes were satisfactory predicted by modified Maxwell model. Furthermore, characteristic parameters of the encapsulated particles by interfacial layer were determined. [ABSTRACT FROM AUTHOR]

Abstract A series of poly(urethane-urea) (PUU) membranes based on contributing hard segments in gas separation were prepared using two novel bulky chain extenders, polytetramethylene-glycol, isophorone and hexamethylene-diisocyanate. The chain extenders were synthesized by cyanuric chloride, aniline/naphthylamine and hydrazine. According to FTIR, AFM and DSC, bulkier PUU membranes showed more phase separation and lower glass transition temperature consistent with higher fractional free volume, which were correlated with single (CO 2 , CH 4 , O 2 and N 2) and mixed (CO 2 :N 2 and CO 2 :CH 4) gas permeation results. The main findings indicate these polyurethanes serve efficiently designed molecular structures favoring bulky hard segments contribution in gas separation. The bulky PUU membranes afford simultaneous increased permeability and selectivity, while maintaining high tensile properties. Enhanced O 2 /N 2 diffusivity selectivity by bulkier PUU and CO 2 sorption/desorption study by Ellipsometry confirmed hard segments' association, too. The bulkiest membrane provided 126% and 54% improvement for single CO 2 permeability and CO 2 /N 2 selectivity compared to linear one. Graphical abstract fx1 Highlights • A series of PUU membranes were prepared based on two novel bulky chain extenders. • The synthesized chain extenders and PUUs characterized completely. • The gas separation, physical and mechanical properties of bulky PUUs were evaluated. • Association of hard segments and enhancement on gas separation properties was shown. • High gas permeability/selectivity and high mechanical strength afforded in bulky PUUs. [ABSTRACT FROM AUTHOR]

ABSTRACT: The effect of zeolite 3A, 4A, and ZSM‐5 on the gas separation performance of polyurethane (PU)–zeolite mixed matrix membranes (MMMs) has been investigated in this study. Permeation of pure CO2, CH4, N2, and O2 gases through PU–zeolite MMMs with zeolite content of 6, 12, 18, and 24 wt% was studied. The prepared hybrid membranes were characterized using Fourier transform infrared spectroscopy and scanning electron microscope. Membrane characterization confirmed the homogeneous distribution of zeolite particles at low zeolite loadings in the prepared membranes. The obtained results confirmed a significant enhancement in the permeability of all gases and the CO2/N2, CO2/CH4, and O2/N2 selectivities by increasing the content of zeolite particles in PU–zeolite MMMs. The PU–zeolite 4A with 12 wt% zeolite loading showed the best performance in terms of gas permeability and selectivity for CO2/N2, CO2/CH4 and O2/N2 gas pairs. [ABSTRACT FROM AUTHOR]

Interfacial properties play an important role in determining characteristics and performance of composite materials, especially in membrane gas separation applications. Formation of any undesirable defect at polymer-particle interface can directly influence on membrane permeability and selectivity in addition to unwanted effects on the other mechanical/physical properties. For achieving a quick insight about the role and nature of interfacial morphologies in mixed matrix membranes (MMMs) and their effects on gas transport properties, a new technique mainly in terms of mathematical modeling was developed. Based on the proposed approach, although ideal models often failed in predicting MMMs performance, these models can provide guidelines for discernment of the types of formed interfacial morphology, like current methods in characterization. [ABSTRACT FROM AUTHOR]

This study involves the preparation and characterization of polyurethane (PU) and polyurethane/poly(ether-block-amide) (PU/PEBA) blend membranes for gas separation. Polyurethane was synthesized by two-step polymerization based on isophorone diisocyanate (IPDI), polytetramethylene glycol (PTMG2000), 1,4-butanediamine (BDA) and 1,4-butanediol (BDO) in mole ratios of 3:1:2. Two kinds of PEBA, MV3000 and MH1657, were chosen to prepare PU/PEBA blend membranes. The effects of the blend composition on the permeability of N 2 , O 2 , CO 2 and CH 4 were investigated. All membranes were prepared by thermal phase inversion. Physical properties of synthesized polyurethane and prepared blend membranes were investigated by FT-IR, XRD and SEM analyses. FT-IR results indicate that phase separation of hard and soft segments decreased as the amount of PEBA in blend membranes increased. XRD results demonstrate that crystallinity rose by increasing the amount of PEBA in the blends. According to the SEM micrographs of the prepared samples, PU/PEBA blend membranes are miscible systems. The results of gas permeation experiments demonstrate that by increasing the amount of PEBA in PU/PEBA blend membranes, the permeability of all gases decreased while selectivity increased. [ABSTRACT FROM AUTHOR]

In the present study, two seriess of poly (urethane urea)s (PUUs) membranes containing aromatic and aliphatic side chains with different sizes were used for separation of higher hydrocarbons from methane. Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetery (DSC), fractional free volume (FFV) estimation, and gas permeation measurements (CH 4 , C 2 H 6 , C 3 H 8) were done to characterize the membranes. Bulkier or longer side chains in aromatic and aliphatic substituted PUUs provided enhanced phase separation, lower glass transition temperature and higher gas permeability. Fractional free volume (FFV) as a significant factor controlling gas separation had a reverse trend in both series by increasing the size of side chains. The main findings confirmed the capability of higher phase separated PUUs for hydrocarbon separation. The highest permeability and selectivity was obtained by the longest side chain based PUU with propane permeability of 186 barrer and propane/methane selectivity of 6.51. [Display omitted] • Two series of poly (urethane-urea)s (PUU)s with various structures were synthesized. • The separations of C 2 H 6 /CH 4 and C 3 H 8 /CH 4 were carried through the PUU membranes. • Higher phase separation was obtained by bulkier and longer side chain-based PUUs. • Efficient separation of more condensable hydrocarbons was obtained. • The longest aliphatic side chain based PUU provide the best hydrocarbon separation. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of silica nanoparticles on the gas permeation properties of polyether-based polyurethane membrane was investigated. Polyether-based polyurethane was synthesized by bulk two-step polymerization of polypropylene glycol/hexamethylenediisocyanate (HMDI)/1,4-butanediol (BDO) in mole ratios of 1:3:2. Silica nanoparticles were prepared through the sol–gel method by hydrolysis of tetraethoxysilane (TEOS). Polyurethane and polyurethane–silica nanocomposite membranes were prepared by solution blending and casting method. The prepared polyurethane–silica membranes were characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), thermal gravimetery analysis (TGA) and differential scanning calorimetry (DSC) analyses. These methods confirmed the homogenous and nano scale distribution of silica nanoparticles in prepared polymers. Gas permeation properties of polyurethane–silica nanocomposite membranes with silica content of 2.5, 5, 10 and 20wt.% was studied for pure CO2, CH4, N2 and O2 gases. The obtained results indicated the reduction in permeability of all gases, but enhancement in CO2/N2, CO2/CH4 and O2/N2 selectivities was observed by increasing the content of non-permeable silica nanoparticles in polyurethane–silica membranes. In the case of polyurethane–silica (20wt.%) nanocomposite membrane, the obtained CO2/N2 selectivity was 1.65 times of pure polyurethane, while the CO2 permeability reduction of polyurethane–silica membranes was 35.6% in comparison with pure polyurethane. Finally, the modified Higuchi model was applied to predict the permeability of polyurethane–silica membranes and fairly good agreement was observed between experimental and predicted gas permeabilities of these membranes. [Copyright &y& Elsevier]

Abstract: In the present work, the effect of silica nano particles on the permeability of CO2, CH4 and N2 gases in polybenzimidazole (PBI) membranes has been studied. Silica particles were prepared via the sol–gel method through the hydrolysis of tetraethoxysilane (TEOS). PBI and PBI–silica hybrid membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), X-ray diffraction and FTIR analyses were employed in order to characterize the PBI and PBI–silica composite membranes. The obtained SEM micrographs confirmed the nano-scale distribution of silica particles in the polymer matrix. Gas permeation experiments showed an increase in the solubility and a corresponding reduction in the diffusivity of the gases through the membranes by increasing the silica content in the polymer matrix; consequently, the permeability of the condensable CO2 and CH4 gases were enhanced whereas that of non-condensable N2 gas significantly decreased upon increasing the silica content of the nano-composite membranes. The permeability of CO2 and its selectivity over N2 was increased from 0.025Barrer and 3.5 in pure PBI to 0.11Barrer and 71.3 in the nano-composite containing 20wt% of the silica particles. There was a strong correlation between the solubility coefficients and condensability of the gases, as well as the diffusion coefficient of the penetrants and their kinetic diameter. Higuchi model fitted fairly well with the experimental results concerning the permeability of nitrogen gas in nanocomposite membranes, supposing the K H =3.8. [Copyright &y& Elsevier]

Abstract: The gas separation properties of ethylene vinyl acetate (EVA) membranes containing 18 and 28wt% of vinyl acetate (VA) were investigated in this study. The effects of membrane preparation conditions, such as thermal and thermal/wet phase inversion, and the type of solvent on the gas separation properties of EVA membranes were investigated. The permeation of pure O2, N2, CH4, and CO2 gases at different feed pressures ranging from 2 to 11 bar were examined. The results indicated that the CO2 permeability was evidently higher than those of the other gases. Furthermore, the solubility mechanism was found to be the dominant mechanism for permeation of gases through EVA membranes. Moreover, the membranes prepared using tetrahydrofuran (THF) as solvent showed higher gas permeabilities than those prepared using chloroform (CHCl3) as solvent. The results indicated that the gas permeabilities through membranes prepared using wet phase inversion technique were higher. Also, the membranes prepared by thermal/wet phase inversion method at higher temperatures showed improved gas separation properties. In addition, the membrane with higher VA content prepared using THF as solvent presents higher gas separation properties. Trade-off evaluation also showed that certain types of the prepared EVA membranes in this study have potential for commercialization. [Copyright &y& Elsevier]

• PUU membranes were designed by different length-side chains based chain extenders. • Shielding hard segment by side chains increased phase separation and reduced FFV. • Dominant plasticizing effect increased permeability by longer side chain based PUU. • The molecular designing of the PUUs allowed a further tuning of gas permeation. Novel poly(urethane-urea) (PUU) membranes were developed as the aim of a structure-property relationship study to enhance gas permeation. Designing the PUUs was followed by three synthesized chain extenders with different length-alkyl side chains, polytetramethylene glycol, and isophorone and hexamethylene diisocyanates. The longest substituted PUU indicated higher phase separation and lower glass transition temperature. Pure and mixed gas permeabilities of prepared membranes grew as phase separation of PUU material increased, while fractional free volume decreased by lengthening the side chain of the PUUs. The reasons for this event were the migration of the side chains to the surface of hard domain, thereby shielding it and filling the soft/hard interface. Enhanced permeability of materials with l onger side chains is attributed to its plasticizing effect. The highest CO 2 permeability (287 barrer) was obtained for the longest substituted PUU. The findings revealed an increase in gas permeation without a significant reduction of selectivity by longer substituted PUUs. [ABSTRACT FROM AUTHOR]

Polymer blending and mixed-matrix membranes are well-known modification techniques for tuning the gas separation properties of polymer membranes. Here, we studied the gas separation performance of mixed-matrix membranes (MMMs) based on the polyurethane/poly(vinyl alcohol) (PU/PVA) blend containing silica nanoparticles. Pure (CO2, CH4, N2, O2) and mixed-gas (CO2/N2 and CO2/CH4) permeability experiments were carried out at 10 bar and 35 °C. Poly(vinyl alcohol) (PVA) with a molecular weight of 200 kDa (PVA200) was blended with polyurethane (PU) to increase the CO2 solubility, while the addition of silica particles to the PU/PVA blend membranes augmented the CO2 separation performance. The SEM images of the membranes showed that the miscibility of the blend improved by increasing the PVA contents. The membrane containing 10 wt % of PVA200 (PU/PVA200–10) exhibited the highest CO2/N2~32.6 and CO2/CH4~9.5 selectivities among other blend compositions, which increased to 45.1 and 15.2 by incorporating 20 wt % nano-silica particles. [ABSTRACT FROM AUTHOR]

Polyurethanes (PUs) and polyurethane-ureas (PUUs), with good mechanical stability and the possibility of tuning the gas transport properties are promising materials for selective gas separation membranes. Here, we synthesized various types of PUs and PUUs with polytetramethylene glycol (PTMG), isophorone diisocyanate (IPDI) and different ethereal chain extenders (1:3:2 M ratio). FTIR and DSC results showed that the phase separation would vary in PUs and PUUs structures by changing the length and functionality of the chain extenders. More mixing was inferred for PUs and PUUs with high ethereal content. In contrast, phase separation was more likely with increases in the chain extender length. Pure (CO 2 , CH 4 , O 2 and N 2 ) and mixed gas (CO 2 :N 2 (50:50 vol%) and CO 2 :CH 4 (50:50 vol%)) permeation measurements correlated well with the phase separation in the polymer structure. The octanediamine-based PUU with the highest amount of phase separation showed the highest permeability (160 barrer for CO 2 and CO 2 /N 2 selectivity of 30). On the other hand, the 3,6-dioxa- 1,8-octanediol- based PU, despite having the same chain extender length as octanediamine-based PUU, presented the lowest phase separation and gas permeability (62 barrer for CO 2 and CO 2 /N 2 selectivity of 29). [ABSTRACT FROM AUTHOR]

• Surface modified silica nanoparticles with hyperbranched structure were prepared. • The mixed matrix membranes were prepared based on two types of poly(urethane-urea)s. • The silica impressed the phase segregation and chain mobility of the membranes. • CO 2 permeability and all selectivities of membranes increased up to 5 wt% loading. • 5 wt% loaded membranes provided the highest CO 2 capture and mechanical properties. Two types of poly(urethane-urea)-based mixed matrix membranes containing hyperbranched structures of surface-modified silica nanoparticles were fabricated. The stepwise surface modification of nanoparticles was done based on aminopropyltriethoxysilane, cyanuric chloride, and ethylenediamine. FTIR, TGA, elemental analysis, and SEM-EDX were served to characterize the modified particles. The incorporation of the nanoparticles into poly(urethane-urea)s (PUUs) altered the phase separation degree of soft and hard segments, elevated the glass transition of soft segments and reduced the chain order. MMM containing the optimal distribution of 5 wt% modified silica showed improved mechanical and gas separation properties with 20–25% and 30–36% enhancement in CO 2 permeability and CO 2 /N 2 selectivity, respectively. The presence of long adsorbent chains with NH moieties on the particles improves the particle distribution in the matrix, thereby enhanced CO 2 permeability up to 5 wt% particle content. At higher loadings, the agglomeration of the particles led to the formation of non-selective channels for gas diffusion and reduced gas separation performance and mechanical properties. [ABSTRACT FROM AUTHOR]