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Graphical abstract Highlights • New mixed matrix membranes (MMMs) were fabricated. • Dispersion of nanoparticles was controlled by adjusting nanoparticles chemistry. • The gas-separation performance of the MMMs is higher than that of the pristine membrane. Abstract This paper presents a study on control of nanoparticles dispersion in the hard and soft segments of a polyurethane (PU) membrane, via adjusting surface groups of the nanoparticles. The dispersion control allows for tailoring physical and transport properties of the membrane. PU-based mixed-matrix membranes (MMMs) embedded with cyanuric chloride and its derivatives, melamine, and 2,4,6-trihydazino-1,3,5-triazine (THDT) nanoparticles, are prepared. The MMMs are characterized using FTIR, XRD, TGA, DSC, and SEM analyses, and tensile strength tests. Peak assignment of the bonded carbonyl, crystallinity change, mechanical properties of the membranes, possible hydrogen-bonding of the PU backbone and the nanoparticles, and permeation tests indicate that cyanuric chloride nanoparticles are dispersed in the hard segments, whereas melamine and the THDT nanoparticles are distributed in the soft domains. As the cyanuric chloride nanoparticle concentration of the MMMs increases, the gas permeabilities and O 2 /N 2 , CO 2 /CH 4 and CO 2 /N 2 selectivities of the membranes increase. In the case of THDT and melamine, as the filler loading increases, the permeabilities of the gases decrease, whereas O 2 /N 2 , CO 2 /CH 4 and CO 2 /N 2 selectivities increase. A 10 wt% incorporation of THDT into the PU increases CO 2 /N 2 and CO 2 /CH 4 selectivities by 92% and 75%, respectively. These results point to the potential of cyanuric chloride nanoparticles for simultaneous improvement of gas permeability and selectivity, and the potential of melamine and THDT nanoparticles for preparation of highly selective nanocomposite membranes for CO 2 removal. [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]

Mixed matrix membranes (MMMs) composed of polyethersulfone (PES) and MCM-41 mesoporous silicas were fabricated by solution casting method. To investigate the effect of silane coupling agents on gas separation properties, 3-aminopropyltrimethoxysilane (APTMS) and trimethylchlorosilane (TMCS) were separately used for modifying the surface of particles. The prepared membranes were characterized by FT-IR, SEM-EDX, XRD, TGA and stress-strain tests. Moreover, ideal permeabilities of CH 4 , N 2 , O 2 and CO 2 through the MMMs were precisely measured. Regardless of the type of particles, the incorporation of MCM-41 into polymer matrix increased the gas permeability of the MMMs compared to neat PES. Adding unmodified particles into a rigid PES matrix led to non-ideal effects such as formation of interfacial nonselective voids. These voids caused a decrease in thermal stability, Young's modulus and gas selectivity, especially at high loadings. On the contrary, the APTMS-modified MCM-41 with polar N-H groups and long side chains had a good compatibility with PES matrix which facilitated the fabrication of defect free membranes with higher thermal and mechanical strength and unique gas separation performance by 250% and 40% increment in CO 2 permeability and CO 2 /CH 4 selectivity respectively. However, the TMCS nonpolar groups did not interact with the PES as strong as APTMS while the TMCS silylation could hamper the particle-particle attraction by replacing hydroxyl groups. [ABSTRACT FROM AUTHOR]

In this research, the effects of Zeolite 4Å and ZSM-5 on the separation of C 2 H 6 and C 3 H 8 from CH 4 through polyurethane/zeolite mixed matrix membranes (MMM) are evaluated. Physical properties of synthesized polyurethane and polyurethane/zeolite MMM were investigated by FTIR, XRD, TGA and SEM analyses. Results indicate that phase separation of hard and soft segments in polyurethane would be increased by adding butanediamine (BDA) chain extender in polymer due to the generation of more hydrogen bonds between hard segment domains. The obtained SEM micrographs confirm that the Zeolite is distributed in the polymer matrix homogenously. The results of gas permeation represent that permeability and selectivity of Hydrocarbons are increased by increasing the urea groups in the polymer structure. Moreover, the obtained results of gas permeation of polyurethane–zeolite (4Å) membranes indicate an increase in the permeability of Methane, with the reduction in C 2 H 6 /CH 4 and C 3 H 8 /CH 4 selectivity by increasing the Zeolite 4Å up to 10 wt%. In addition, the results of the gas permeation of polyurethane–zeolite (ZSM-5) MMM indicate a significant increment in permeability and selectivity of all Hydrocarbons. The permeability of Propane and its selectivity over Methane is increased from 64.8 Barrer and 2.6 into 117.2 Barrer and 3.64 in with 20 wt% filled PU–ZSM 5 MMM, respectively. [ABSTRACT FROM AUTHOR]

In the current study, the effect of operating conditions including pH value, feed flow and applied pressure on heavy metal removal of a nanofiltration membrane for drinking water production was investigated. A polyamide nanofiltration membrane with a net negative surface charge was used for the experiments. In the first series of experiments, single salt solutions containing 1 ppm lead in the form of lead (II) nitrate and 1 ppm nickel in the form of nickel (II) sulfate were used as feed. According to the results, recovery rate, rejection rate and saturation factor were all increased with increasing applied pressure. After that, optimization of operating conditions for maximizing the membrane's heavy metal rejection performance was performed. According to the results, 93% of nickel and 86% of lead ions were eliminated in the optimum condition. In the next series of experiments, the effect of heavy metal ion concentration on the performance of nanofiltration membrane was studied and finally, the effect of mixed salt solutions on the performance of the membrane was discussed. Results showed that, nickel rejection in the mixed salt solution was lower than its value in the single salt solution; but for the lead ion, rejection performance was improved due to the mixing. [ABSTRACT FROM AUTHOR]

A new model for prediction of the effective permeability of gases in mixed matrix membranes (MMMs), considering the effects of particle shape and the interfacial layer, is presented. The proposed model treats core filler particles and interfacial shell layers as complex particles. Moreover, the Bruggman mathematical procedure is used to improve the accuracy of the presented model for high concentrations of fillers in MMMs. Also, an appropriate uniform criterion is established to make efficient use of the new model for various experimental data to avoid the need for curve-fitting procedures. Finally, the proposed model is examined for several sets of experimental data. [ABSTRACT FROM AUTHOR]

In this study, the effects of various solvents on the structure and permeation properties of polysulfone-silica nanocomposite membranes were investigated. Silica nanoparticles were prepared by the sol-gel method through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Polysulfone-silica nanocomposite membranes were prepared by the thermal phase inversion method. N-methyl pyrrolidone (NMP), N, N-dimethyl acetamide (DMAc) and tetrahydrofuran (THF) were used as solvents. Based on the experimental results, it was observed that the CO/N and O/N selectivities increased in the presence of silica nanoparticles in all cases. However, the permeabilities of the applied gases decreased, except for CO. Based on the obtained selectivity data, permeability data, and favorable dispersion of silica nanoparticles in the polymer matrix, the results indicate that NMP is the best solvent for polysulfone-silica membrane preparation. The obtained CO permeability and CO/N selectivity of the polysulfone-silica (5 wt%) membrane prepared using NMP as the solvent were 7 barrers and 35, respectively. [ABSTRACT FROM AUTHOR]

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]

The diffusion and permeation of sulfuric, perchloric, and phosphoric acids through the polybenzimidazole (PBI) membrane were evaluated by using the time-lag method. The results showed that the permeation of these acids in the polymeric film is due to normal Fickian diffusion. Increasing the acidity and concentration of each inorganic acid upstream increased the diffusion coefficients. Permeation results confirmed that the dual-mobility model was applicable. The dual-mobility model constants were found by using a least square program via fitting experimental data to dual-mobility equation. The results have indicated that the partial immobilization of Langmuir sorption coefficient, F, decreases with molecular size of acids. Besides, the diffusion coefficient of acid molecules in Henry's law, D, increases with increasing acidity of the acids studied. Comparison of permeability coefficients of acids in PBI membrane indicates that permeability increases with acidity. Therefore, diffusion is considered the dominant factor in this transport mechanism. [ABSTRACT FROM AUTHOR]

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]

The sorption behaviors of sulfuric, perchloric, and phosphoric acids in polybenzimidazole membranes have been investigated. The results of sorption isotherms are consistent with the general form of a dual-mode sorption isotherm. The dual-mode sorption parameters were found using a least-squares program by fitting experimental data to a dual-mode equation. Results indicate a correlation between permeant properties like acidity, size, and the affinity constant in Langmuir-mode sorption species. Moreover, the results show that the size of the permeants has the dominant effect on Henry's constant. The obtained results for [image omitted], site saturation constant, in Langmuir-mode sorption in the case of perchloric and phosphoric acids, reveals that the two acid molecules interact with two N-H basic groups in the polybenzimidazole repeat units. But in the case of sulfuric acid, it is shown that sulfuric acid neutralizes some of the basic groups in the polymer by its strong second hydrogen and the obtained value for [image omitted] was 1.25. [ABSTRACT FROM AUTHOR]

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]

Poly(ether sulfone) (PES), because of its low chain mobility and high gas selectivity, was selected as a gas‐separation membrane. Because poly(ethylene glycol) (PEG) contains polar ether groups favorable for carbon dioxide (CO2) capture, we investigated the effects of PEG on the CO2/CH4 and CO2/N2 separation properties of PES–PEG blend membranes. PEG with different molecular weights (4000, 6000, and 10,000) and concentrations of up 30 wt % was added to PES. Scanning electron microscopy and wide‐angle X‐ray diffraction analyses on the blends confirmed the uniformity and dense surfaces of the membranes and no changes in the crystallinity, respectively. Fourier transform infrared spectra indicated good interactions between the PEG and PES segments. Gas permeation tests showed that with increasing PEG molecular weight, its weight fraction permeability of CH4 and CO2 increased, whereas the permeability of O2 and N2 decreased. The best composition of PES–PEG was a 70/30 ratio; with this composition, the selectivities of CO2/N2 and CO2/CH4 were enhanced by 64 and 14%, respectively, compared to that of the pure membrane. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46845. [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]