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Although carbon nanotubes possess unique characteristics to be used for separation purposes, one of the most challenging problems affecting the preparation of carbon nanotubes-incorporated-mixed matrix membranes has been ascribed to Van der Waals interactions among carbon nanotubes walls, which hinder the pristine nanotubes' ability to make good interfacial interactions within the polymer matrix. To overcome this challenge, herein, poly (styrene sulfonic acid)-grafted- multi-walled carbon nanotubes were prepared via in-situ radical polymerisation and then incorporated into poly (vinyl alcohol), resulting in enhanced pervaporation performance of poly (vinyl alcohol) membranes. The observed results indicated that poly (styrene sulfonic acid)-modified carbon nanotubes could effectively vanquish the Van der Waals forces between nanotube walls. In general, our experiments revealed that the attachment of a bulky polymer containing hydrophilic sulfonic groups could improve the pervaporation performance of a poly (vinyl alcohol) membrane. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effects of silica nanoparticles on the permeability of pure CO2, O2, and N2 gases in cellulose acetate (CA) membrane have been studied. Silica particles were prepared via the sol–gel method through the hydrolysis of tetraethyl orthosilicate (TEOS). CA and CA/silica nanocomposite membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier transfer infrared (FTIR) analyses were employed to characterize the CA and CA/silica nanocomposite membranes. Gas permeation experiments showed an increase in the permeability of CO2 from 6.32 to 7.3 barrer and a reduction in the permeability of N2 from 0.18 to 0.09 barrer with the increment in silica content of the prepared composite membranes up to 20 wt%. Therefore, CO2/N2 selectivity of the nanocomposite membranes increased by increasing the silica content in the polymer matrix from 30 to 80 for 20 wt% load of silica. [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]

Abstract: In this research, the effects of changing the polyol, disocyanate, and chain extender used in synthesized polyurethane membranes on gas permeability are investigated. The membranes are synthesized using PTMG, PPG, PCL as polyol; IPDI, HDI, TDI as diisocyanate; and BDO, BDA as chain extender in a 1/3/2 and 1/2/1M ratio of polyol/diisocyanate/chain extender. The results obtained from Fourier transfer infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed that changing the polyol type from PPG to PTMG and PCL leads to more phase interaction. Furthermore, changing the diisocyanate group from aromatic to aliphatic and from cyclic aliphatic to linear aliphatic leads to an increase in phase separation of hard and soft segments which cause the packing density of hard segment due to the enhancement of the hydrogen bonding. In addition, changing a chain extender from a diol one to a diamine leads to an increase in phase separation of hard and soft segments. Permeation experiments reveal that the larger, more condensable gases are more permeable than light ones in more rubbery polymers; and, the selectivity of polyurethane as a rubbery polymer is dominated by solubility. On the other hand, by enhancement of the microphase separation of hard and soft segments, the rubbery behavior and permeability of condensable gases increase along with their selectivity. Overall, polymers based on the PPG polyol show maximum permeability because of their higher rubbery property due to its higher phase separation. The results of permeability tests indicate high permeability, up to 200Barrer (1Barrer=1×10−10 [cm3 (STP) cm/cm2 scmHg]), and high selectivity for propane with respect to methane (C3H8/CH4: 5.47). [Copyright &y& Elsevier]

Abstract: The effect of silica nanoparticles on the gas permeation properties of polycaprolactone-based polyurethane membranes was investigated. Polyurethane and polyurethane-silica nanocomposite membranes were prepared by solution blending and casting-evaporation methods. Silica nanoparticles were prepared by sol–gel method using hydrolysis of tetraethoxysilane (TEOS). Polyurethane was synthesized by bulk two-step polymerization, including polycaprolactone 2000(PCL)/hexamethylene diisocyanate (HMDI)/1,4-butanediol (BDO). The homogeneity and nano scale distribution of the prepared polyurethane-silica membranes were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA). Gas permeation properties of these membranes with different silica contents, was studied for pure CO2, CH4, N2 and O2 gases. The results showed reduction in gas permeability, but enhancement in CO2/N2, CO2/CH4 and O2/N2 ideal selectivity. Also the effect of temperature and pressure on permeation properties of these membranes was investigated. The modified Higuchi model was applied to predict the permeability of polyurethane-silica nanocomposite membranes. Good agreement between the experimental data and the predicted gas permeability was obtained. [Copyright &y& Elsevier]

Abstract: In this study, the effect of the structure of polyether-based polyurethane (PU) membranes on their gas separation properties has been investigated. In this regard, a series of polyurethanes based on hexamethylene diisocyanate (HDI) and 1,4-butanediol as hard segments and different soft segments such as poly(tetramethylene glycol) (PTMG, 2000g/mol), poly(ethylene glycol) (PEG, 2000g/mol) and PTMG/PEG mixture were synthesized. PU membranes were prepared by thermal phase inversion method and their physical properties were analyzed by FT-IR, XRD and DSC analyses. The obtained results from FT-IR and DSC analyses indicated that the phase separation of hard and soft segments decreased and chain mobility was restricted, resulting in the increase in glass-transition temperature of the soft segment, by content of the PEG in the PU structure. The permeability of pure N2, O2, CH4 and CO2 gases were determined using constant pressure method at different feed pressures and temperatures. The results of gas permeation experiments showed that by increasing the ether group content in the polymer structure, permeability of the pure gases decreased, while CO2/N2 ideal selectivity increased. The obtained results also indicated that the permeability of CO2 decrease from 132.52 barrer in PU0 (PU containing 100wt% of PTMG in soft segment) to 20 barrer in PU100 (the PU containing 100wt% of PEG in soft segment), respectively. CO2/N2 selectivity increased from 28 to 90. Trade-off evaluation also showed that the potential of studied membranes for commercialization in CO2/N2 and even CO2/CH4 separations increase by PEG content in polymer and the PU membrane which contains 75/25wt% ratio of PEG/PTMG had the highest. [Copyright &y& Elsevier]

Abstract: This work presents the structural properties of gas permeation of a group of polyurethane membranes. All polymers were synthesized using a 1:3:2 molar ratio of polyol:diisocyanate:chain extender. The obtained results from Fourier transform infrared spectrometer (FT-IR) of polymers indicate that by changing the diisocyanate from aromatic to linear aliphatic, the microphase separation of hard and soft segments increases. Study of the differential scanning calorimetery (DSC) and X-ray diffraction (WAXD) patterns confirmed that PTMG and PCL polyols can be arranged in small crystalline structures. Furthermore, a hard ordered segment in crystal phase could be obtained, owing to the high phase separation of the polymer based on HDI. Permeation measurements of polymers revealed that the permeability of gases increases with microphase separation in polymer and selectivity of gases drops down. Polymers based on PPG showed the highest phase separation and permeability. The obtained results revealed more phase mixing of the polymer based on DMPA chain extender in comparison to BDO, which lead to lower permeability and higher selectivity. The solubility and diffusivity of gases indicate solubility domination of gas transport in these membranes. The observed solubility domination increases by phase separation. The results of permeability tests indicate high permeability, up to 186Barrer (1Barrer=1×10−10 [cm3 (STP) cm/cm2 scmHg]), and high selectivity for carbon dioxide with respect to nitrogen (CO2/N2: 45). Our data sheds light on gas permeation properties of polyurethane membranes. [Copyright &y& Elsevier]

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: The effect of urethane and urea contents on gas separation properties of the groups of polyurethane–urea membranes is studied. The membranes used in this study were prepared by polytetramethylene-glycol (PTMG) and isophorone diisocyanate (IPDI) prepolymers. The prepolymers were converted to final polymer using the designed proportion of 1,4-butane diol (BDO) and 1,4-butane diamine (BDA) as a chain extender. Five different BDO/BDA ratios were chosen in order to synthesize poly(urethane-urea)s with different urethane/urea linkage content. The prepared polymers were characterized and the permeability of gases through them was investigated. Results obtained by Fourier transform infrared spectrometer (FT-IR) and differential scanning calorimetery (DSC) indicate that by increasing the urea linkage in the polymers, the microphase separation of hard and soft segments increase. Study of the X-ray diffraction (WAXD) patterns confirmed that polyols may be arranged in small crystalline structures. Permeation measurements of polymers revealed that the permeability of gases decreases with increasing urethane content in the polymers and selectivity of gases decreases with increasing urea content. The solubility and diffusivity of gases indicate solubility domination of gas transport in these membranes. The results of permeability also show high amounts up to 128Barrer (1Barrer=1×10−10 [cm3 (STP) cm/cm2 scmHg]), and high selectivity for carbon dioxide with respect to nitrogen (CO2/N2: 27). [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]

Abstract: The effect of silica nanoparticles on the gas separation properties of ethylene vinyl acetate (EVA) copolymer containing 28% vinyl acetate has been investigated. The EVA and hybrid EVA–silica membranes were prepared via thermal phase inversion method. Silica nanoparticles prepared by hydrolysis of tetraethylorthosilicate (TEOS), through the sol–gel mechanism. The prepared membranes were characterized using FT-IR, SEM, DSC and XRD methods. FT-IR and SEM results indicated the nanoscale dispersion of silica particles in polymer matrix. As confirmed by XRD and DSC analyses, increasing the silica content enhances the amorphous regions significantly. Gas permeation of EVA–silica nanocomposite membranes with silica contents of 5, 6 and 10wt.% was studied for N2, O2, CO2 and CH4 single gases at pressures of 4, 6 and 8bar. The obtained results suggest a significant increase in permeability of all gases and an increase in CO2/N2 and CO2/CH4 gases selectivities upon increasing the silica content. The possible reasons for such behavior were stated and discussed. The pressure dependence of the gas permeabilities of the membranes was also investigated. [Copyright &y& Elsevier]

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]