Separation of methanol from methanol/water mixtures with pervaporation hybrid membranes

A series of pervaporation (PV) hybrid membranes were prepared via the crosslinking of poly(vinyl alcohol) with formaldehyde solution with N‐3‐(trimethoxysilyl) propyl ethylenediamine (TMSPEDA) as a hybrid precursor of the sol–gel process. Both the thermal stability and separation performances of the prepared hybrid membranes were investigated. Thermogravimetric analysis showed that the thermal degradation temperature of the hybrid membranes was beyond 250°C. Differential scanning calorimetry indicated that both the glass‐transition temperature and the crystallization temperature increased with elevated TMSPEDA contents in the hybrid membranes. PV experiments demonstrated that for membranes A–D, both the permeation flux and separation factor indicated the same trade‐off effect. Moreover, it was found that for individual membranes, the permeation flux increased as the feed temperature was increased. Meanwhile, the separation factor revealed an change trend opposite to that of the permeation flux. Furthermore, proper addition of TMSPEDA in the hybrid membrane was found to reduce the permeation activation energy. On the basis of these findings, we deduced that these hybrid membranes have potential applications in the separation of methanol/water mixtures. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Separation of n-hexane/acetone mixtures by pervaporation using natural rubber membranes

Natural rubber (NR) membranes crosslinked by four different systems viz., conventional (CV), efficient (EV), dicumyl peroxide (DCP), and a mixture consisting of sulfur and peroxide (mixed), were employed for the separation of n-hexane/acetone mixtures of different compositions. The membranes exhibited preferential permeation toward n-hexane because of the closer solubility parameter values. The selectivity of the membranes depended on the nature and distribution of crosslinks between the macromolecular chains of the membrane but was independent on the thickness of the membrane. The effects of feed composition, cure time of the membranes, and the molecular size of the permeate on the permeation flux and selectivity were investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2597–2603, 1997     

Separation properties of alcohol–water mixture through silicalite-I-filled silicone rubber membranes by pervaporation

The structure and the adsorption–desorption properties of zeolite silicalite-I by different treatments after synthesis were studied. The pervaporation properties of the alcohol–water mixture through silicone rubber filled with zeolite silicalite-I by different treatments were also investigated. Treating silicalite-I by acid or/and under steam was found to eliminate the metallic impurities in the zeolite and to perfect the crystalline structure of the zeolite. After treatment, silicalite-I is more selective to alcohol and the desorption of the alcohol from the zeolite is also easier. The silicone rubber membrane filled with treated silicalite-I shows a high performance for alcohol extraction from the dilute aqueous solution by pervaporation. The separation factor of the poly(dimethyl siloxane) (PDMS) membrane filled with silicalite-I treated successively by acid and steam is about 30 when the ethanol content in the feed is 5 wt % at 50°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 629–636, 1998     

Dehydration of ethanol/water mixtures by pervaporation using soluble polyimide membranes

A series of soluble polyimides derived from 3,3′,4,4′‐benzhydrol tetracarboxylic dianhydride (BHTDA) with various diamines such as 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene (BATB), 1,4‐bis(4‐aminophenoxy)‐2,5‐di‐tert‐butylbenzene (BADTB), and 2,2′‐dimethyl‐4,4′‐ bis(4‐aminophenoxy)biphenyl (DBAPB) were investigated for pervaporation separation of ethanol/water mixtures. Diamine structure effect on the pervaporation of 90 wt% aqueous ethanol solution through the BHTDA‐based polyimide membranes was studied. The separation factor ranked in the following order: BHTDA–DBAPB > BHTDA–BATB > BHTDA–BADTB. The increase in molecular volume for the substituted group in the polymer backbone increased the permeation rate. As the feed ethanol concentration increased, the permeation rate increased, while the water concentration in the permeate decreased for all polyimide membranes. The optimum pervaporation performance was obtained by the BHTDA–DBAPB membrane with a 90 wt% aqueous ethanol solution, giving a separation factor of 141, permeation rate of 255 g m^?2 h^?1 and 36 000 pervaporation separation index (PSI) value. Copyright © 2006 Society of Chemical Industry     

Preparation of zeolite‐incorporated poly(dimethyl siloxane) membranes for the pervaporation separation of isopropyl alcohol/water mixtures

ZSM‐5 zeolite‐incorporated poly(dimethyl siloxane) membranes were prepared, and the molecular dispersion of the zeolite in the membrane matrix was confirmed with scanning electron microscopy. After the swelling of the membranes was studied at 30°C, the membranes were subjected to the pervaporation separation of isopropyl alcohol/water mixtures at 30, 40, and 50°C. The effects of the zeolite loading and feed composition on the pervaporation performances of the membranes were analyzed. Both the permeation flux and selectivity increased simultaneously with increasing zeolite content in the membrane matrix. This was examined on the basis of the enhancement of hydrophobicity, selective adsorption, and the establishment of molecular sieving action. The membrane containing the highest zeolite loading (30 mass %) had the highest separation selectivity (80.84) and flux (6.78 × 10^?2 kg m^?2 h^?1) at 30°C with 5 mass % isopropyl alcohol in the feed. From the temperature dependence of the diffusion and permeation values, the Arrhenius activation parameters were estimated. A pure membrane exhibited higher activation energy values for permeability (E_p) and diffusivity (E_D) than zeolite‐incorporated membranes, and signified that permeation and diffusion required more energy for transport through the pure membrane because of its dense nature. Obviously, the zeolite‐incorporated membranes required less energy because of their molecular sieving action, which was attributed to the presence of straight and sinusoidal channels in the framework of the zeolite. For the zeolite‐incorporated membranes, the activation energy values obtained for isopropyl alcohol permeation were significantly lower than the water permeation values, and this suggested that the zeolite‐incorporated membranes had higher selectivity toward isopropyl alcohol. The E_p and E_D values ranged between 21.81 and 31.12 kJ/mol and between 15.27 and 41.49 kJ/mol, respectively. All the zeolite‐incorporated membranes exhibited positive values of the heat of sorption, and this suggested that the heat of sorption was dominated by Henry's mode of sorption. sorption. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1377–1387, 2005     

Dehydration of glycerin/water mixtures by pervaporation using homo and copolymer membranes

Separation characteristics of glycerol/water mixtures were studied using hydrophilic poly(acrylonitrile-comethacrylic acid) (PANMAC), poly(acrylonitrile-co-hydroxyethyl methacrylate) (PANHEMA), Poly(vinyl alcohol) GFT-1001, and poly(vinyl alcohol) (PVA) crosslinked with maleic anhydride (PVAManh) membranes. All membranes were found to be highly water selective. PVAManh membrane yielded the highest permeation flux for water over the entire range of water concentration studied. Homopolymers (PVAManh and GFT-1001) gave better permeation rates than copolymer membranes (PANHEMA and PANMAC). But the swelling of homopolymers is nuch greater than that of copolymers, which is why PVA membranes have poor longevity. No effect on selectivity of the membrane was observed with a change in operating parameters. No decomposition/polymerization of glycerin was observed, as there was no involvement of high temperatures as there is with distillation. A comparison of pervaporation with vapor-liquid equilibrium data showed that pervaporation of glycerin/water mixtures yielded better selectivity than vapor-liquid equilibrium, particularly for glycerol concentrations above 90 wt%.     

Separation of acid–water mixtures by pervaporation using nanoparticle filled mixed matrix copolymer membranes

BACKGROUND: Low energy and less expensive membrane based separation of acetic acid‐water mixtures would be a better alternative to conventional separation processes. However, suitable acid resistant membranes are still lacking. Thus, the objective of the present study was to develop mixed matrix membrane (MMM) which would allow high flux and water selectivity over a wide range of feed concentrations of acid in water. RESULTS: Three MMMs, namely PANBA0.5, PANBA1.5 and PANBA3 were made by emulsion copolymerization of acrylonitrile (AN) and butyl acrylate (BA) with 5.5:1 comonomer ratio and in situ incorporation of 0.5, 1.5 and 3 wt%, sodium montmorilonite (Na‐MMT) nanofillers, respectively. For a feed concentration of 99.5 wt% of acid in water the membranes show good permeation flux (2.61, 3.19, 3.97 kg m^?2 h^?1 µm^?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and very high separation factors for water (1473, 1370, 1292 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at 30 °C. Similarly for a dilute acid–water solution, i.e. for 71.6 wt% acid the membrane showed a very high thickness normalize flux (8.67, 9.44, 11.56 kg m^?2 h^?1 µm^?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and good water selectivity (101.7, 95.3, 79 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at the same feed temperature. The permeation ratio, permeability, diffusion coefficient and activation energy for permeation of the membranes were also estimated. CONCLUSION: Unlike most of the reported membranes, the present MMMs allowed high flux and selectivity over a wide range of feed concentrations. These membranes may also be effective for separating other similar organic‐water mixtures. Copyright © 2012 Society of Chemical Industry     

Recovery of pyridine from water by pervaporation using filled and crosslinked EPDM membranes

Organoselective membrane was prepared from ethylene propylene diene monomer (EPDM) rubber. Crosslinked EPDM rubber was filled with 2, 4 and 6 wt% N330 carbon black filler to produce three different filled membranes designated as EPDMCV2, EPDMCV4 and EPDMCV6, respectively. These filled rubber membranes were used for pervaporative recovery of low concentration of pyridine from water. These filled membranes were characterized by crosslink density, SEM, XRD and mechanical properties. Sorption thermodynamics were discussed. Partial permeability, intrinsic membrane selectivity and diffusion coefficients of solvents were also determined. The filled membranes showed much higher pyridine selectivity than most of the membranes reported for similar system.     

Polysiloxaneimide membranes for removal of VOCs from water by pervaporation

For the separation of volatile organic compounds (VOCs) from water by pervaporation, three polysiloxaneimide (PSI) membranes were prepared by polycondensation of three aromatic dianhydrides of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic dianhydride (PMDA) with a siloxane‐containing diamine. The PSI membranes were characterized using ¹H‐NMR, ATR/IR, DSC, XRD, and a Rame‐Hart goniometer for contact angles. The degrees of sorption and sorption selectivity of the PSI membranes for pure organic compounds and organic aqueous solutions were investigated. The pervaporation properties of the PSI membrane were investigated in connection with the nature of organic aqueous solutions. The effects of feed concentration, feed temperature, permeate pressure, and membrane thickness on pervaporation performance were also investigated. The PSI membranes prepared have high pervaporation selectivity and permeation flux towards hydrophobic organic compounds. The PSI membranes with 150‐μm thickness exhibit a high pervaporation selectivity of 6000–9000 and a high permeation flux of 0.031–0.047 kg/m² h for 0.05 wt % of the toluene/water mixture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2691–2702, 2000     

Wettability switchable metal-organic framework membranes for pervaporation of water/ethanol mixtures

To evaluate the effect of MOF surface wettability for the purification of ethanol from water/ethanol mixtures, the hydrophilic Ni₂(l-asp)₂bipy membrane is switched to hydrophobic Ni₂(l-asp)₂bipy@PDMS membrane via vapor deposition of PDMS. The PDMS coating can improve the hydrothermal stability of MOF membranes. The stable Ni₂(l-asp)₂bipy membrane exhibits a high flux of H₂O and acceptable separation factor. The pervaporation studies based on the both two membranes provide insight into the effect of surface wettability on the bio-ethanol purification performance.     

聚乙烯醇-二氧化硅/聚丙烯腈杂化复合膜渗透蒸发分离己内酰胺/水溶液

制备了以聚乙烯醇(PVA)填充纳米SiO2改性膜为活性层,聚丙烯腈(PAN)超滤膜为底膜的PVA-SiO2/PAN杂化复合膜,并用于己内酰胺(CPL)脱水。用FTIR,SEM,XRD,TGA分别对膜进行了表征,并考察了膜中纳米SiO2粒子的质量分数、进料组分质量分数和温度对复合膜分离性能的影响。结果表明,引入纳米SiO2后,杂化膜的热稳定性明显提高。当膜中纳米SiO2质量分数为1.0%时,复合膜渗透蒸发分离性能最佳。60℃下此复合膜用于分离质量分数为40%的CPL溶液时,其总通量和分离因子分别达到2 177 g/(m2.h)和349。     

Sorption,diffusion and pervaporation of water/ethanol mixtures in polyetherimide membranes

Homogeneous and composite aromatic polyetherimide membranes were prepared by casting from N-methylpyrrolidinone (NMP) solutions and by electrodeposition of polymer at the cathode, respectively. The membranes were evaluated for their sorption, diffusion and pervaporation separation of water from ethanol with emphasis on the breaking of azeotropic composition. The membrane performance was shown to be dependent on the feed concentration, but still selective towards water over the whole composition range of the feed mixture. By looking at the surface energy parameters, the determination of degree of swelling and the calculation of deviation coefficients (ε), an interesting insight was gained into the coupling effect in this solvent/membrane system. From the sorption, diffusion and temperature-dependent permeation behaviour, it could be concluded that in this system the diffusivity of permeant plays a major role in determining the pervaporation performance, rather than the solubility. © 1999 Society of Chemical Industry     

Separation of aqueous phenol through polyurethane membranes by pervaporation

The separation of a phenol-water mixture using a polyurethane membrane by a pervaporation method was investigated. Polyurethane was selected as a membrane material because its affinity for phenol was considered to be high. Polyurethane was prepared by the polyaddition of 1,6-diisocyanatohexane and polytetramethyleneglycol. The polyurethane layer was sandwiched with a porous polypropylene membrane (Celgard® 2500). Pervaporation measurement was carried out under vacuum on the permeate side, and the permeate vapor was collected with a liquid nitrogen trap. The phenol concentration in the permeate solution increased from 0 to 65 wt % with increasing feed concentration of phenol from 0 to 7 wt %. The total flux also increased up to 930 g m^-2 h^-1 with increasing phenol partial flux. In the sorption measurement at 60°C, the concentration of phenol in the membrane was 68 wt %, which was higher than that of the permeate solution. Therefore, it was considered that the phenol selectivity was based on high solubility in the polyurethane membranes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:469–479, 1997     

Synthesis of graft copolymeric membranes of poly(vinyl alcohol) and polyacrylamide for the pervaporation separation of water/acetic acid mixtures

Graft copolymers of poly(vinyl alcohol) (PVA) with polyacrylamide were prepared and membranes were fabricated at 48 and 93% grafting of acrylamide onto PVA. These membranes were used in the pervaporation separation of water/acetic acid mixtures at 25, 35, and 45°C. The permeation flux, separation selectivity, diffusion coefficient, and permeate concentration were determined. The highest separation selectivity of 23 for neat PVA at 25°C and the lowest value of 2.2 for 93% acrylamide‐grafted PVA membranes were observed. A permeation flux of 1.94 kg m^?2 h^?1 was found for the 93% grafted membrane at 90 mass % of water in the feed mixture. The diffusion coefficients in a water/acetic acid mixture had an effect on the membrane permselectivity. The Arrhenius equation was used to calculate the activation parameters for permeation as well as for the diffusion of water and of acetic acid. The activation energy values for the permeation flux varied from 97 to 28 kJ/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 244–258, 2002     

Incorporation of multiwalled carbon nanotubes into poly(vinyl alcohol) membranes for use in the pervaporation of water/ethanol mixtures

Multiwalled carbon nanotube (MWNT)/poly (vinyl alcohol) (PVA) blend membranes were prepared by the solution‐casting method to determine the effect of MWNTs with nanoscale empty inner space along the tube length on the pervaporation performance of a PVA membrane in the separation of alcohol/water mixtures. The blend membranes were then characterized with several analytical methods such as transmission electron microscopy, differential scanning calorimetry, and X‐ray diffractometry: Transmission electron microscopy showed that the MWNTs were homogeneously distributed through the PVA matrix. The glass‐transition temperature of the PVA membrane was increased from 69.21 to 78.53°C via blending with MWNTs. The crystallinity of the PVA matrix decreased with increasing MWNTs up to 5 wt % from 41 to 36%. The pervaporation properties of the blend membranes were completely different from those of the pure PVA membrane in the separation of water/ethanol mixtures. The flux of the membrane was increased with the amount of MWNTs, whereas the separation factor was maintained up to 1.0 wt % MWNTs. However, beyond that, it was reduced. These results suggested that two factors, the crystallinity of the membrane and the diameters of the MWNTs, affected the performance of the membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polyacrylonitrile‐g‐poly(vinyl alcohol) membranes for the pervaporation separation of dimethyl formamide and water mixtures

Poly(vinyl alcohol) as well as its grafted copolymer membranes with polyacrylonitrile (PAN‐g‐PVA) were prepared and used to separate water and dimethyl formamide mixtures by the pervaporation technique. The three following membranes were prepared: (1) pure PVA; (2) 46% grafted PAN‐g‐PVA; and (3) 93% grafted PAN‐g‐PVA. Pervaporation separation experiments were carried out at 25°C for the feed mixture containing 10 to 90% water. By use of the transport data, permeation flux, separation selectivity, swelling index, and diffusion coefficients have been calculated. By increasing the grafting of the membrane, flux decreased, whereas separation selectivity increased slightly over that of pure PVA membrane. Arrhenius activation parameters for transport processes were calculated for 10 mass % water containing feed mixture by using flux and diffusion data obtained at 25, 35, and 45°C. Transport parameters were discussed in terms of sorption‐diffusion principles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4091–4097, 2004     

Nonequilibrium nanoblend membranes for the pervaporation of benzene/cyclohexane mixtures

Immiscible blends of polymers were cast from solution, and the rate of evaporation was controlled relative to the rate of phase separation to produce different morphologies; upon crosslinking, stable nonequilibrium nanoblends were realized. This process of forced assembly produced useful membrane materials that could be designed for solubility selectivity with the group contribution methodology. Crosslinked ternary blends of nitrile butadiene rubber (NBR), poly(methyl methacrylate) (PMMA), and a tercopolymer of ethylene oxide/epichlorohydrin/allyl glycidyl ether (Hydrin) were examined for use in the separation of benzene from cyclohexane by pervaporation. For a 50 : 50 wt % benzene/cyclohexane feed, blend 811 (containing 80 wt % NBR, 10 wt % Hydrin, and 10 wt % PMMA) gave a separation factor of 7.3 and a normalized flux of 28 kg μm/m² h; such a performance is unmatched in the literature, with the flux being very high for the reported separation factor. Among the samples tested, the flux of the membrane increased as the amount of NBR in the ternary blend decreased; however, the separation factor was not largely affected. Blended samples showed no sign of deformation after 48 h at the operating temperature as compared to pure NBR, which did show evidence of creep. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Separation of phenol–water mixture by membrane pervaporation using polyimide membranes

Separation of components of aqueous waste streams containing organic pollutants is not only industrially very important but also is a challenging process. In this study, separation of a phenol–water mixture was carried out by using a membrane pervaporation technique with indigenously developed polyimide membranes. The membranes were found to permeate water selectively. The total flux as well as that of the individual components were measured. The effect of lithium chloride modification of polyimide film on total flux was investigated. The total flux obtained with 2% lithium chloride modification was about 3.6 times higher than that obtained with virgin membrane. The effects of different parameters such as feed composition and temperature on flux, and separation factor were determined. With modified membrane, a separation factor as high as 18.0 was obtained for water at 27°C and with 8.0 wt % phenol solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 822–829, 2002     

Synthesis of highly selective copolymer membranes and their application for the dehydration of tetrahydrofuran by pervaporation

Acrylonitrile was copolymerized with 2‐hydroxyethyl methacrylate (HEMA) at three different copolymer compositions by emulsion polymerization to produce polyacrylonitrile–2‐hydroxyethyl methacrylate (PANHEMA) copolymer membranes containing increasing amounts of HEMA from PANHEMA‐1 to PANHEMA‐3. The dehydration of tetrahydrofuran (THF) over a concentration range of 0–14 wt % water in the feed was studied by pervaporation with these three copolymer membranes. The permeate water flux and separation factor for water was measured over the same concentration range at 30, 40, and 50°C. Among the copolymer membranes, PANHEMA‐1 exhibited a reasonable water flux (34.9 g m^?2 h^?1) with a very high water selectivity (264), whereas PANHEMA‐3 showed a higher water flux (52 g m^?2 h^?1) but a lower water selectivity (176.5) for highly concentrated THF (0.56 wt % water in the feed) at 30°C. The permeation factors of water for all of the membranes were much greater than unity, which signified a strong positive coupling effect of THF on water permeation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 728–737, 2007     

Effect of crosslinking on the conductivity of conductive silicone rubber

We investigated the effect of polyvinylsilicone oil (C gum) as a crosslinker and 2,5‐bis(tert‐butyl peroxy)‐2,5‐dimethyl hexane (DBPMH) as a curing agent on the conductivity of conductive silicone rubber with two different kinds of conducting mechanisms. The experimental results show that the volume resistivity of conductive silicone rubber changed with its degree of crosslinking. When the carbon black loading was 25 parts per hundred rubber (phr) and a completely continuous conducting network had not formed, the volume resistivity of the vulcanizates decreased with increasing crosslink density. The volume resistivity of the vulcanizate with a suitable amount of C gum decreased to 53%, and the tensile strength increased by 0.8 MPa compared to the vulcanizate without C gum. When the carbon black loading was 40 phr and a completely continuous conducting network had formed, the crosslink density of vulcanizates changed as the amount of DBPMH changed. The volume resistivity of vulcanizates first decreased and then increased with increasing crosslink density. There was a valley value in the resistivity–crosslink density curve. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3471–3475, 2003