Cellulose–poly(acrylamide or acrylic acid) interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures

A new type of interpenetrating polymer network (IPN) pervaporation membranes based on cellulose and synthetic polymers was developed. They were prepared by free-radical polymerization of acrylamide or acrylic acid in the presence (or absence) of the crosslinking agent (allyldextran or N,N′-methylenebisacrylamide) within cellophane films swollen in the reaction mixture. The swelling behavior of these membranes in water–ethanol solutions and their separation characteristics were investigated depending on the polyacrylamide (PAAm) or poly(acrylic acid) (PAA) content in the IPN (C_p) and for ionic cellulose–PAA membranes depending on the degree of neutralization of carboxylic groups and on the type of counterions. IPN membranes were selective over a wide range of ethanol concentration in the feed. The separation factor (α) and the permeation rate (P) significantly improved with increasing C_p in IPN membranes, especially for the cellulose–PAA(K⁺ form) membranes (for 86% EtOH feed at 50°C, and α and P values reached 1500 and 1.6 kg/m² h, respectively). The results for ionic and nonionic IPN membranes were compared. The separation characteristics of membranes were in good correlation with their swelling behavior. The α values of the membranes depended on the affinity of the IPN polymer chains functional groups for water. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 761–769, 1998     

Poly(acrylic acid)–poly(vinyl alcohol) semi- and interpenetrating polymer network pervaporation membranes

A series of poly(acrylic acid) (PAA)–poly(vinyl alcoho) (PVA) semiinterpenetrating (SIPN) and interpenetrating (IPN) polymer network membranes were prepared by crosslinking PVA alone or by crosslinking both PVA and PAA. Glutaraldeyde and ethylene glycol were used as crosslinking agents for the PVA and PAA networks, respectively. The presence of PAA increases the permeability of the membranes while the presence of PVA improves their mechanical and film-forming properties. The mechanical properties of the membranes were investigated via tensile testing. These hydrophilic membranes are permselective to water from ethanol–water mixture and to ethanol from ethanol–benzene mixtures. The IPN membranes were employed for the former mixtures and the SPIN membranes for the latter, because the IPN ones provided too low permeation rates. The permeation rates and seperation factors were determined as functions of the IPN or SIPN composition, feed composition, and temperature. For the azeotropic ethanol–water mixture (95 wt % ethanol), the separation factor and permeation rate at 50°C of the PAA-PVA IPN membrane, containing 50 wt % PAA, were 50 and 260 g/m²h, respectively. For the ethanol–benzene mixture, the PAA–PVA SIPN membranes had separation factors between 1.4 and 1200 and permeation rates between 6 and 550 g/m²h, respectively, depending on the feed composition and temperature. © 1996 John Wiley & Sons, Inc.     

Modified polydimethylsiloxane/polystyrene blended IPN pervaporation membrane for ethanol/water separation

In this article a modified polydimethylsiloxane (PDMS) blended polystyrene (PS) interpenetrating polymer network (IPN) membranes supported by Teflon (polytetrafluoroethylene) ultrafiltration membrane were prepared for the separation of ethanol in water by pervaporation application. The relationship between the surface characteristics of the surface‐modified PDMS membranes and their permselectivity for aqueous ethanol solutions by pervaporation are discussed. The IPN supported membranes were prepared by sequential IPN technique. The IPN supported membrane were tested for the separation performance on 10 wt % ethanol in water and were characterized by evaluating their mechanical properties, swelling behavior, density, and degree of crosslinking. The results indicated that separation performance, mechanical properties, density, and the percentage of swelling of IPN membranes were influenced by degree of crosslink density. Depending on the feed temperature, the supported membranes had separation factors between 2.03 and 6.00 and permeation rates between 81.66 and 144.03 g m^?2 h^?1. For the azeotropic water–ethanol mixture (10 wt % ethanol), the supported membrane had at 30°C a separation factor of 6.00 and a permeation rate of 85 g m^?2 h^?1. Compared to the PDMS supported membranes, the PDMS/PS IPN supported blend membrane ones had a higher selectivity but a somewhat lower permeability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Separation of water–ethanol by pervaporation through polyion complex composite membrane

For the purpose of separating alcohol–water mixtures by the use of the pervaporation technique, new composite membranes composed of polyion complexes (PIC) as a separating layer were developed. The polyion complex structure, consisting of polyacrylic acid (PAA) and polycation, provided excellent permeation rate and selectivity. Among the polycations, ionenes, which have quaternary ammonium groups in the backbone chain, were effective in giving membranes of higher permselectivities. High selectivity of PIC membranes was observed at high ethanol concentration regions in the feed mixture. For the azeotropic mixture of water/ethanol (95 wt % EtOH) at 60°C, the PAA-based PIC membrane had the following separation properties: separation factor ～ 3,500 and permeation rate ～ 1.6 kg/m² h.     

Swelling behavior and pervaporation properties of new composite membrane systems: Porous polyethylene film‐poly(acrylic acid) hydrogel

A new type of composite membrane for pervaporation has been developed. These membranes were prepared by free‐radical copolymerization of acrylic acid with a macromolecular polyfunctional crosslinker (allylhydroxyethylcellulose) inside the porous polyethylene (PE) film. It was shown that the porous structure of the PE matrix is filled with poly(acrylic acid) (PAA), and a layer of acid is formed on the film surface. To investigate the effect of the porous matrix on the composite membrane properties, a hydrogel membrane of crosslinked PAA was also prepared without the matrix using the same procedure. PAA in both membranes was in the neutralized form (K⁺). Swelling behavior of the membranes and their separation characteristics for pervaporation were investigated in water–ethanol solutions depending on the ethanol concentration. All membranes exhibited a high degree of equilibrium swelling (Q = 20–50 g/g) in dilute ethanol solutions (0–30 vol %), and Q sharply dropped to 1.5–2 g/g at a EtOH concentration of 30–40 vol % due to collapse of the gel. All membranes under study were highly permeable and selective to water over a wide range of ethanol concentrations in the feed (50–96 vol %), but composite membranes had a higher separation factor due to the restriction effect of the matrix porous structure on swelling of PAA(K⁺) inside the pores. However, composite membranes were characterized by a lower permeation rate, compared to the crosslinked PAA membranes without a matrix, because of their lower effective surface for diffusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1461–1465, 2004     

Poly(ether sulfone) supported hybrid poly(vinyl alcohol)–maleic acid–silicone dioxide membranes for the pervaporation separation of ethanol–water mixtures

Microporous poly(ether sulfone) (PES) supported hybrid polymer–inorganic membranes were prepared by the crosslinking of poly(vinyl alcohol) (PVA), maleic acid (MA), and SiO₂ via an aqueous sol–gel route and a solution‐casting method. The membrane performance was tested for the pervaporation separation of ethanol–water mixtures from 20 to 60 °C with a feed ethanol concentration of 96 wt %. The membrane characterization results reveal that different SiO₂ loadings affected the crystallinity and roughness of the membranes. The PVA–MA–SiO₂ membrane containing 10 wt % SiO₂ showed that SiO₂ nanoparticles were well dispersed within the polymer matrix; this resulted in significant enhancements in both the flux and selectivity. The membrane achieved a high water permeability of 1202 g·μm·m^?2 h^?1 kPa^?1 and a selectivity of 1027 for the separation of a 96 wt % ethanol‐containing aqueous solution. This enhanced membrane performance might have been due to the dense crosslinking membrane network, increased free volume, and uniform distribution of SiO₂ nanoparticles. Both the water and ethanol fluxes increased with the feed water concentration and temperature. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44839.     

Effect of ethanol–water mixture as gelation medium during formation of cellulose acetate reverse osmosis membranes

By using ethanol–water mixtures in a wide range of alcohol concentrations and temperatures, cellulose acetate membranes with a wide range of surface porosities can be obtained. Two different casting solution compositions were used, involving cellulose acetate, acetone, and aqueous magnesium perchlorate (composition I) or formamide (composition II). All reverse osmosis experiments were carried out at 250 psig using a 3500 ppm NaCl–H₂O feed solution at laboratory temperature. The effective area of film surface was 12 cm² in all cases. With composition I, with pure water gelation medium at 0°C, the resulting membrane gave a solute separation of 5% and product rate of 220 g/hr, whereas with 95% alcohol as gelation medium, the resulting membrane gave a solute separation of ～1% and product rate of 1240 g/hr under otherwise identical experimental conditions. With composition II membranes, the maximum product rate of 360 g/hr with the corresponding minimum solute separation of ～1% was obtained with 71.2% alcohol–water gelation medium at 0°C. Increase in the temperature of the gelation medium in the range 12° ?25°C tends to increase the average size of pores on the membrane surface. These results offer a basis for the development of cellulose acetate ultrafiltration membranes.     

Pervaporation separation of binary organic–aqueous liquid mixtures using crosslinked PVA membranes. III. Ethanol–water mixtures

The application of the pervaporation process in biotechnology is rapidly growing. A two stage pervaporation process could be applied to the downstream processing of ethanol fermentation. In this paper, the second stage process—a water-selective process—was investigated in detail using the crosslinked poly(vinyl alcohol) membranes with the low molecular weight of poly(acrylic acid) as the crosslinking agent. The ratio of poly(vinyl alcohol) and poly(acrylic acid) in the membrane was 90/10, 85/15, and 80/20 by weight. The prepared membranes were tested to separate the various compositions of the water–ethanol mixtures, specially 50/50 solution at 60°C and 30/70, 20/80, 10/90, and 4.4/95.6 solutions at 60, 70, and 75°C. For water: ethanol = 50 : 50 solution, the separation factor α_w/e = 260 at 75°C was obtained by using a PVA/PAA = 80/20 membrane. The permeation rate and the separation factor at the azeotropic point of a water–ethanol mixture showed 30 g/m²/h and 5800 at 75°C, respectively, when a PVA/PAA = 80/20 membranes was used. © 1995 John Wiley & Sons, Inc.     

Pervaporation separation of water–ethanol mixtures using metal‐ion‐exchanged poly(vinyl alcohol) (PVA)/sulfosuccinic acid (SSA) membranes

Poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) membranes in the hydrogen form were converted to monovalent metal ion forms Li⁺, Na⁺, and K⁺. The effect of exchange with metal ions was investigated by measuring the swelling of water–ethanol (10/90) mixtures at 30 °C and by the pervaporative dehydration performance test for aqueous ethanol solutions with various ethanol concentrations at 30, 40, and 50 °C. In addition, electron spectroscopy for chemical analysis (ESCA) analysis was carried out to study the quantity of metal ions in membranes. From the ESCA analysis, the lithium ion quantity in the resulting membranes is greater than that of any other metal ions in question because of the easy diffusion of a smaller metal ion into the membrane matrix. The swelling ratio was in the following order: PVA/SSA‐Li⁺ > PVA/SSA‐Na⁺ > PVA/SSA‐K⁺ membranes. For pervaporation, the PVA/SSA‐Na⁺ membrane showed the lowest flux and highest separation factor for all aqueous ethanol solutions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1867–1873, 2002     

Water–alcohol separation by pervaporation through poly(amide-sulfonamide)s (PASAs) membranes

Pervaporation membranes derived from seven homopolymers of poly(amide-sulfonamide)s (PASAs) were prepared by casting 10–17% polymer solutions of N,N-dimethylacetamide. The membranes were characterized by sorption experiments, scanning electron microscope, and wide-angle X-ray diffraction. During the pervaporation of 90 wt % aqueous solution of methanol, ethanol, 1-propanol, and 2-propanol, all membranes were preferentially permeable to water, and their separation factors were mainly dependent on the molecular weight of the solvent. The exact structure of the PASAs had a profound effect on their pervaporation characteristics. Polymeric membrane based on N,N′-bis(4-aminophenylsulfonyl)-1,3-diaminopropane and isophthaloyl chloride exhibited the best selectivity factor of 1984 for a 10 : 90 (by weight) mixture of water/ethanol at 20°C. However, the permeation rates of all materials for dehydration of 90 wt % ethanol were slow in a range of 6.6–34.4 g m⁻² h⁻¹. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1113–1119, 1997     

Development of polyion complex membranes for the separation of water–alcohol mixtures. III. Preparation of polyion complex membranes based on the k-carrageenan for the pervaporation separation of water–ethanol

Pervaporation separation of water–ethanol was carried out with polyion complex membranes based on k-carrageenan. The polyion complex membranes were prepared by the ion complex formation between k-carrageenan (anionic polymer) and poly{1,3-bis[4-alkylpyridi-nium]propane bromide}s (cationic polymers) with different numbers of methylene units between two ionic sites within a repeating unit, respectively. The ion complex membranes were characterized with FT-IR, X-ray diffractometry. Dehydration of 90 wt % aqueous ethanol solution was carried out at different temperatures (30, 40, 50, and 60°C). The selectivity and permeability through them were very good over a wide temperature range; in the case of the polyion complex membrane consisting of k-carrageenan and poly{1,3-bis[4-ethylpyridinium]propane bromide}, the permselectivity was 45,000 and permeability was 150 g/m² h at 30°C. With increasing operating temperature, the permeability was increased highly but the selectivity decreased slightly. © 1996 John Wiley & Sons, Inc.     

Pervaporation membranes for ethanol–water mixture prepared by plasma polymerization. III. Perfluorocarbon membranes

Pervaporation membranes for the ethanol–water mixture were prepared by plasma polymerization of tetrafluoroethylene, perfluoropropane, and perfluoropropylene onto porous substrates. The influence of the monomers on the elemental ratio (F/C) of the polymer depositions by X-ray photoelectron spectroscopy was rather small compared with that of the W/FM parameter (W = wattage for plasma excitation, FM = mass flow rate of a monomer). The optical emission spectroscopy indicated the similarity of gaseous species formed in the plasmas. The membranes were found ethanol-permselective, showing separation coefficients (α_EtOH) around 4–7 and a wide range of permeation rates (J), 10–10^?2 kg/m² h, for the 4.8 wt % ethanol solution at 40°C. The α_EtOH of the membranes with thicker depositions could be correlated to the F/C ratios as a measure of membrane hydrophobicity. It was thought that, by making a plot α_EtOH against J values for the perfluorocarbon membranes, they could be classified into three groups on thickness of deposition. The ethanol-separation mechanisms for each group, which may contain four kinds of mass transfer schemes, i.e., distillation through larger pores, flow of sorption layer at the liquid–membrane interface, and diffusions through deposition or substrate, were also discussed.     

Pervaporation separation of water–acetic acid mixtures through NaY zeolite‐incorporated sodium alginate membranes

The pervaporation (PV) separation and swelling behavior of water–acetic acid mixtures were investigated at 30, 40, and 50°C using pure sodium alginate and its zeolite‐incorporated membranes. The effects of zeolite loading and feed composition on the pervaporation performance of the membranes were analyzed. Both the permeation flux and selectivity increased simultaneously with increasing zeolite content in the polymer matrix. This was discussed on the basis of a significant enhancement of hydrophilicity, selective adsorption, and molecular sieving action, including a reduction of pore size of the membrane matrix. The membrane containing 30 mass % of zeolite showed the highest separation selectivity of 42.29 with a flux of 3.80 × 10^?2 kg m^?2 h^?1 at 30°C for 5 mass % of water in the feed. From the temperature dependency of diffusion and permeation data, the Arrhenius activation parameters were estimated. The E_p and E_D values ranged between 72.28 and 78.16, and 70.95 and 77.38 kJ/mol, respectively. The almost equal magnitude obtained in E_p and E_D values signified that both permeation and diffusion contribute equally to the PV process. All the membranes exhibited positive ΔH_s values, suggesting that the heat of sorption is dominated by Henry's mode of sorption. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2101–2109, 2004     

Ethanol/water mixture pervaporation performance of b‐oriented silicalite‐1 membranes made by gel‐free secondary growth

b‐oriented silicalite‐1 membranes on porous silica supports were synthesized using gel‐free secondary growth. The porous silica supports were made by pressing crushed quartz fibers followed by sintering and polishing, and further modified by slip‐coating three layers of Stöber silica particles (1000, 350, and 50 nm). The b‐oriented seed layers were prepared by rubbing silicalite‐1 particles (2 μm × 0.8 μm × 3 μm along a‐, b‐, and c‐axis, respectively) after depositing a polymeric layer on the support. After silicalite‐1 seed deposition, a final coating of spherical silica particles was applied. Well‐intergrown, μm‐thick, b‐oriented membranes were obtained, which, after calcination, exhibited ethanol permselectivity in ethanol/water mixture pervaporation. At 60°C and for ～5 wt % ethanol/water mixtures, the best membrane exhibited overall pervaporation separation factor of 85 (corresponding to membrane intrinsic selectivity of 7.7) and total flux of 2.1 kg/(m²·h). This performance is comparable to the best performing MFI membranes reported in the literature. © 2015 American Institute of Chemical Engineers AIChE J, 62: 556–563, 2016     

Pervaporation separation of MTBE–methanol mixtures using cross‐linked PVA membranes

Poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) and PVA/sulfosuccinic acid (SSA) membrane performances have been studied for the pervaporation separation of methyl tert‐butyl ether (MTBE)/methanol (MeOH) mixtures with varying operating temperatures, amount of cross‐linking agents, and feed compositions. Typically, the separation factor, about 4000, and the permeation rate, 10.1 g/m²/h, were obtained with PVA/PAA = 85/15 membrane for MTBE/MeOH = 80/20 mixtures at 50°C. For PVA/PAA membranes, it could be considered that the flux is affected by the structural changes of the membranes due to the cross‐linking and the free carboxylic acid group also took an important role in the separation characteristics through the hydrogen bonding with PVA and the feed components leading to the increase of flux. The latter membrane of the 5% SSA membrane shows the highest separation factor of 2095 with the flux of 12.79 g/m²/h for MTBE/MeOH = 80/20 mixtures at 30°C. Besides the swelling measurements were carried out for pure MTBE and MeOH, and MTBE/MeOH = 90/10, 80/20 mixtures using PVA/SSA membranes with varying SSA compositions. It has been recognized that there are two factors, the membrane network and the hydrogen bonding in the swelling measurements of PVA/SSA membranes. These two factors act interdependently on the membrane swelling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1699–1707, 2000     

Pervaporation separation of ethanol/water mixture using modified zeolite filled PDMS membranes

In this article, the composite polydimethylsiloxane (PDMS) membranes supported by cellulose acetate (CA) microfiltration membrane were successfully prepared by adding modified zeolite particles with a silane coupling agent, NH₃–C₃H₆–Si(OC₂H₅)₃. The sorption and diffusion behaviors of ethanol and water in the films were studied. The results showed that with the increase in the modified zeolite content, the solubility selectivity increased, but the diffusion selectivity first increased, then decreased. The effects of modified zeolite content and feed temperature on the pervaporation performance of the composite membranes in 10 wt % ethanol/water mixture were also investigated. When modified zeolite loading was 20 wt %, for 10 wt % ethanol/water mixture at 40°C, the permeate flux was 348.7 g·m^?2·h^?1, the separation factor was 14.1, and the permeate separate index was 4568, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41897.     

Preparation of polymer of intrinsic microporosity composite membranes and their applications for butanol recovery

We fabricated novel composite membranes composed of a polymer of intrinsic microporosity (PIM-1) and carbon black (CB) nanoparticles functionalized with the silane coupling agent aminopropyl triethoxysilane to recover butanol from aqueous solutions by pervaporation (PV). Scanning electron microscopy showed that the composite membranes were dense and defect free and had good adhesion with substrates. Compared with the those of pristine PIM-1 membranes, the water contact angles of the composite membranes increased from around 86° to more than 90°; this confirmed the improvement of the hydrophobicity. The swelling degree of the 6 wt % CB-filled PIM-1 membranes dropped 23%; this indicated an increase in the swelling resistance. Furthermore, the PV results show experimentally that the incorporation of the functionalized CBs into the PIM-1 matrix considerably improved both the permeability and selectivity to butanol. At a 4 wt % CB content, the optimum separation performance, with a separation factor of 19.7 and a permeation flux of 1116 g m⁻² h⁻¹, was achieved in an aqueous solution containing 5 wt % butanol at 30°C. It was noteworthy that the as-fabricated membranes exhibited a good separation stability. This is a step forward in terms of continuous butanol production with hybrid membranes in fermentation processes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46912.     

Three‐component mixed matrix organic/inorganic hybrid membranes for pervaporation separation of ethanol–water mixture

Mixed matrix membranes (MMMs) were made by incorporating vinyltrimethoxysilane (VTMS)‐modified Silicalite‐1 zeolite nanoparticles (V‐Silicalite‐1 NPs) into fluorinated polybenzoxazine (F‐PBZ) modified polydimethylsiloxane (PDMS) polymer through in situ polymerization method. The membrane morphology, surface wettability, and pervaporation performance were systematically investigated. The addition of F‐PBZ into PDMS membranes resulted in substantially improved flux and marginal increase of separation factor, which is the result of higher free volume and higher hydrophobicity caused by the addition of F‐PBZ. The modification of Silicalite‐1 NPs improved the interfacial contact between zeolite crystals and polymer phase. The incorporation of hydrophobic V‐Silicalite‐1 zeolite NPs into the PDMS membranes led to much higher separation factor but reduced flux, which is the result of increased hydrophobicity and reduced free volume. The three‐component MMMs with V‐Silicalite‐1 zeolite NPs in the F‐PBZ fluorinated PDMS exhibited separation factor of 28.7 and flux of 0.207 kg m^?2 h^?1 for 5 wt % ethanol aqueous solution at 50 °C, while the pure PDMS membranes only had separation factor of 4.8 and flux of 0.088 kg m^?2 h^?1. The substantial increase of both flux and separation factor were attributed to the higher hydrophobicity and free volume caused by the incorporation of both hydrophobic zeolite crystals and F‐PBZ polymer into the PDMS membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44753.     

Properties of modified polyacrylonitrile membranes prepared by copolymerization with hydrophilic monomers for water–ethanol mixture separation

A new kind of terpolymer membrane was employed to separate a permselective water–alcohol mixture. This membrane was prepared via the copolymerization of acrylonitrile, sodium salt styrene sulfonic acid (SStSA), and hydroxyethyl methacrylate in dimethylsulfoxide with azobisisobutyronitrile as an initiator. The reaction mechanism, resultant structure, and polymer composition were confirmed by IR and elemental analysis. The effects of the feed composition on the polymer composition, mechanical properties, thermal properties, and degree of swelling were investigated. It was found that water permeated through the membrane preferentially in a water/alcohol system. The flux increased with the increase of SStSA, but the separation factor decreased drastically with higher SStSA. For a 50 wt % water–ethanol mixture, a flux of 0.65 kg/m² h and a separation factor of 212 were obtained at 30°C when the membrane containing the highest SStSA content was used. The capacities of the metal ions absorbed by the membranes were investigated in the study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 244–250, 2003     

Synthesis and Characterization of ETS-10/Chitosan Nanocomposite Membranes for Pervaporation

Chitosan (CS) and microporous titanosilicate ETS-10/CS mixed matrix membranes (MMMs) were prepared. The pervaporation performance was tested on the water-ethanol mixtures in the range 85–96 wt.% ethanol. The permeate flux increased from 0.45 to 0.55 kg m^?2 h^?1 at 50°C for the ETS-10/CS MMM with respect to the pure CS membranes. Characterization by SEM and TEM, XRD, DSC, and TGA allowed inferring an intimate contact between the dispersed ETS-10 and the continuous chitosan phase. The 5 wt.% loading of titanosilicate scarcely decreased the hydrophilic character of the mixed matrix membrane but increased the molecular sieving effect on the transport and separation properties, thus affecting the membrane behavior on pervaporation.