Synthesis and characterization of hybrid membranes using poly(vinyl alcohol) and tetraethylorthosilicate for the pervaporation separation of water–isopropanol mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis and cocondensation reaction for the pervaporation separation of water‐isopropanol mixtures. The resulting membranes were characterized by Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and differential scanning calorimetry. The glass transition temperature of these membranes varied from 100 to 120°C with increasing TEOS content. Effects of crosslinking density and feed compositions on the pervaporation performances of the membranes were studied. The membrane containing 1.5:1 mass ratio of TEOS to PVA gave the highest separation selectivity of 900 at 30°C for 10 mass % of water in the feed mixture. It was found that the separation selectivity and permeation flux data are strongly dependent on the water composition of the feed and operating temperature. However, the membrane with the highest crosslinking density showed unusual pervaporation properties. The overall activation energy values were calculated using the Arrhenius‐type equation. The activation energy values for the permeation and diffusion varied from 49.18 to 64.96 and 55.13 to 67.31 kJ/mol, respectively. Pervaporation data have also been explained on the basis of thermodynamic quantities. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1304–1315, 2004     

Permeation and Separation Characteristics of Acetic Acid‐Water Mixtures by Pervaporation through Acrylonitrile and Hydroxy Ethyl Methacrylate Grafted Poly(vinyl alcohol) Membrane

Abstract

In this study, acrylonitrile (AN) and hydroxyl ethyl methacrylate (HEMA) were grafted onto poly(vinyl alcohol) (PVA) using cerium (IV) ammonium nitrate as initiator at 30°C. The graft copolymer was characterized using the Fourier transform infrared spectroscopy (FTIR) and elemental analysis. The grafted PVA membranes (PVA‐g‐AN/HEMA) were prepared by a casting method, and used in the separation of acetic acid‐water mixtures by pervaporation. The effects of the membrane thickness, operating temperature, and feed composition on the permeation rate and separation factor for acetic acid‐water mixtures were studied. Depending on the membrane thickness, the temperature and feed composition PVA‐g‐AN/HEMA membranes gave separation factors 2.26–14.60 and permeation rates of 0.18–2.07 kg/m²h. It was also determined that grafted membranes gave lower permeation rates and greater separation factors than PVA membranes. Diffusion coefficients of acetic acid‐water mixtures were calculated from permeation rate values. The Arrhenius activation parameters were calculated for the 20 wt.% acetic acid content in the feed using the permeation rate and the diffusion data obtained at between 25–50°C.     

Pervaporative permeations of homologous series of alcohol aqueous mixtures through a hydrophilic membrane

The permeation behaviors of permeants were investigated in the pervaporation of a homologous series of alcohol aqueous mixtures through a hydrophilic poly(vinyl alcohol) (PVA). The PVA membrane was crosslinked with glutaraldehyde. A homologous series of alcohols used in this study were methanol, ethanol, 1‐propanol, and 1‐butanol. The pervaporation experiments were carried out with feed having 70–97 wt % of alcohol contents and at various feed temperatures. In a high alcohol content above 92 wt %, the permeation rate was increased in the order of the interaction strength between alcohol and water in the feed. However, in a low alcohol content below 90 wt %, the tendency of the permeation rate was found to be the opposite, indicating that the interactions between permeant constituents play an important role in determining the permeation and separation of the mixtures. These observations were discussed in terms of changes in the interaction between the permeant/permeant or the permeant/membrane in varying feed compositions and feed temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 703–713, 2001     

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%.     

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     

Crosslinked blended poly(vinyl alcohol)/N-methylol nylon-6 membranes for the pervaporation separation of ethanol–water mixtures

Crosslinked blended membranes of poly(vinyl alcohol) (PVA) and N-methylol nylon-6 were prepared either by thermal crosslinking at 180°C or by chemical crosslinking with maleic acid. The pervaporation performance for the separation of ethanol–water mixtures of these membranes was investigated in terms of feed concentration, PVA content, and crosslinking agent content. The pervaporation performance of two differently crosslinked membranes was strongly influenced by the nature of the crosslinkage. Significant improvement in the pervaporation separation index can be achieved for chemically crosslinked membranes. From the comparison between the pervaporation and sorption tests, it is suggested that, for hydrophilic membranes, sorption properties dominate the pervaporation performance at feed solutions of higher water content, while diffusion properties govern at feed solutions of higher ethanol content. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 317–327, 1998     

Pervaporation separation and swelling measurement of acetic acid-water mixtures using crosslinked PVA membranes

The pervaporation separation and the swelling behavior of acetic acid-water mixtures were investigated at 30, 40, and 50°C using the crosslinked poly(vinyl alcohol) (PVA) membranes with varying the poly(acrylic acid) (PAA) contents and the acetic acid concentration in the feed mixture. Typically, for the pervaporation separation of 90 wt % acetic acid in the feed, the PVA/PAA = 75/25 membrane gives the separation factor of 795 and the flux of 5.6 g/m² h at 30°C, respectively. The swelling degree decreases as the PAA content in the membrane decreases to 20 wt % of PAA due to the increase of the crosslinking portion in the membrane and increases beyond this PAA content. The swelling degrees show fairly high at the operating temperatures and the total range of the liquid mixtures in question. The overall activation energy of permeation was also calculated using an Arrhenius type relationship. From this study, it could be concluded that the diffusion step is dominant over the sorption step. © 1997 John Wiley & Sons, Inc.     

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     

Dehydration of light oil by pervaporation using poly(vinyl alcohol)–poly(acrylic acid‐co‐maleic acid) membranes

A new blended membrane was prepared and tested by pervaporation of light oil, a mixture of five alcohols plus water. The blended membrane was synthesized by blending poly(vinyl alcohol) and poly(acrylic acid‐co‐maleic acid) sodium salt in the presence of sulfuric acid to dope the reaction. We tested several membranes in order to choose the adequate composition to have the best permselectivity. The PVA(60)–PAA‐co‐maleic acid(40) membrane was selected as it was found to be highly selective. Sorption experiments were performed using binary and ternary water–alcohol solutions. The influence of temperature and feed composition on the selectivity and flux in pervaporation was investigated for two different binary mixtures (water/ethanol, water/isobutanol) and one ternary system (water/ethanol/isobutanol). This membrane presents good permselective properties, high water flux, and good selectivity and can even be used for high‐water activities The performances of this new membrane were compared to those obtained with the PVA(90)–PAA(10) membrane synthesized recently: The fluxes observed for the water–ethanol separation were of the same order of magnitude but the selectivity was found to be much higher. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1709–1716, 2002     

Zeolite 4A-Incorporated Polymeric Membranes for Pervaporation Separation of Methanol–Methyl Acetate Mixtures

Zeolite 4A-incorporated poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) membranes were prepared for pervaporation separation of methanol/methyl acetate mixtures. These membranes were characterized by Infrared spectroscopy, X-ray diffraction and Scanning electron microscopy. The results showed that crystallinity of the membrane decreased with the increase of zeolite 4A content. The effect of zeolite loading, feed composition and temperature on the membrane separation performance were discussed in detail. With the increase of zeolite 4A content, permeation flux increased continuously, but separation factor first increased and then decreased. The addition of 2.5 wt% zeolite 4A in the polymer membrane improved the separation factor from 12.9 (for PVA/PVP membrane) to the maximum value of 34.4 for 20 wt% methanol in feed at 45 °C. The separation factor decreased with increasing feed temperature, however, the flux increased with increasing feed temperature. Zeolite 4A-incorporated PVA/PVP membranes provide an effective method for the separation of methanol/methyl acetate azeotropic mixtures.     

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.     

A study on permeation behavior of a liquid mixture through PVA membranes having a crosslinking gradient structure in pervaporation

Two types of dense poly(vinyl alcohol) (PVA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique: membranes with uniform crosslinking structure and with crosslinking gradient structure. From the permeation of pure water through a membrane having a uniform crosslinking structure, the effect of crosslinking density in the membrane on the permeation activation energy, plasticizing coefficient, and diffusivity of the permeant was investigated. The concentration and activity profiles of the permeant in the membrane in the pervaporation process were determined using the diffusion equation and Flory–Huggins thermodynamics. PVA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while the other side was blocked by a polyester film to prevent the reaction solution from contacting it. The extent of the gradient was controlled by the exposing time. The pervaporation separation of the water–acetic acid mixture was carried out on the membrane having a crosslinking gradient structure, and the pervaporation performance with different membrane loading in the membrane cell was discussed using a schematic concentration and activity profiles of the permeant which was made based on the results from the permeation of a pure component through the membrane with a uniform crosslinking structure. © 1996 John Wiley & Sons, Inc.     

Pervaporation separation of water/dimethylformamide mixtures using poly(vinyl alcohol)‐g‐polyacrylamide copolymeric membranes

Grafted copolymeric membranes of poly(vinyl alcohol) with acrylamide (PVA‐g‐AAm) were developed and used in the pervaporation separation of water–dimethylformamide mixtures by varying the amount of water in the feed from 0 to 100%. From these data, the permeation flux, pervaporation separation index, diffusion coefficient, swelling index, and separation selectivity were calculated at 25, 35, and 45°C. The Arrhenius activation parameters for permeation flux ranged between 22 and 63 kJ/mol, while the activation energy for diffusion ranged between 23 and 67 kJ/mol. Separation selectivity was between 15 and 22. The highest permeation flux of 0.459 kg m^?2 h^?1 was obtained for the 93% grafted membrane at 90% of water in the feed mixture. The results are discussed using the principles of the solution–diffusion model. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 273–282, 2002     

Pervaporation separation of water–isopropanol mixture using carboxymethylated poly(vinyl alcohol) composite membranes

The pervaporation separation of water–isopropanol mixtures was carried out using carboxymethylated poly(vinyl alcohol) (CMPVA) composite membranes. Carboxymethylated PVA (CMPVA) was synthesized by reacting PVA with various concentrations of monochloroacetic acid. Substitution efficiency of the CMPVA ranged from 12–32%. The cross‐sectional structure of the composite membrane for pervaporation was confirmed by scanning electron microscopy (SEM) exhibiting a 20‐μm active skin layer. Glass transition temperature of the CMPVA was in the range of 74–84°C, and decreased with increasing substitution efficiency. Degree of swelling and permeation flux for water–isopropanol in pervaporation increased with the substitution degree of carboxymethylation. CMPVA composite membrane, having 16% substitution efficiency, showed the following pervaporation performance; permeation flux of 831 g/m² h and separation factor of 362 measured at 80°C and 85 wt % feed isopropanol concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 241–249, 1999     

Preparation of PFSA‐PVA/PSf hollow fiber membrane for IPA/H2O pervaporation process

Using Na⁺ form of perfluorosulfonic acid (PFSA) and poly(vinyl alcohol) (PVA) as coating materials, polysulfone (PSf) hollow fiber ultrafiltration membrane as a substrate membrane, PFSA‐PVA/PSf hollow fiber composite membrane was fabricated by dip‐coating method. The membranes were post‐treated by two methods of heat treatment and by both heat treatment and chemical crosslinking. Maleic anhydride (MAC) aqueous solution was used as chemical crosslinking agent using 0.5 wt % H₂SO₄ as a catalyst. PFSA‐PVA/PSf hollow fiber composite membranes were used for the pervaporation (PV) separation of isopropanol (IPA)/H₂O mixture. Based on the experimental results, PFSA‐PVA/PSf hollow fiber composite membrane is suitable for the PV dehydration of IPA/H₂O solution. With the increment of heat treatment temperature, the separation factor increased and the total permeation flux decreased. The addition of PVA in PFSA‐PVA coating solution was favorable for the improvement of the separation factor of the composite membranes post‐treated by heat treatment. Compared with the membranes by heat treatment, the separation factors of the composite membranes post‐treated by both heat treatment and chemical crosslinking were evidently improved and reached to be about 520 for 95/5 IPA/water. The membranes post‐treated by heat had some cracks which disappeared after chemical crosslinking for a proper time. Effects of feed temperature on PV performance had some differences for the membranes with different composition of coating layer. The composite membranes with the higher mass fraction of PVA in PFSA‐PVA coating solution were more sensitive to temperature. It was concluded that the proper preparation conditions for the composite membranes were as follows: firstly, heated at 160°C for 1 h, then chemical crosslinking at 40°C for 3 h in 4% MAC aqueous solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Separation of aqueous salt solution by pervaporation through hybrid organic–inorganic membrane: Effect of operating conditions

Hybrid polymer-inorganic membranes were prepared by crosslinking poly(vinyl alcohol) (PVA), maleic acid (MA) and silica via an aqueous sol–gel route. Membrane characterisation results revealed silica nanoparticles (< 10 nm) were well dispersed in the polymer matrix and significantly reduced swelling of the membrane. The membranes were tested for pervaporation separation of aqueous salt solution with NaCl concentrations of 0.2–5.0 wt% at temperatures 20–65 °C, feed flowrates 30–150 mL/min and permeate pressures 2–40 Torr. The salt rejection remained high (up to 99.9%) under all operating conditions. A high water flux of 11.7 kg/m² h could be achieved at a feed temperature of 65 °C and a vacuum of 6 Torr. The effect of operating conditions on water flux is discussed in relation to diffusion coefficients of water and fundamental transport mechanism through the membrane. The activation energy for water permeation was found to vary from 23.8 to 20.1 kJ/kmol when the salt concentration in the feed was increased from 0.2 to 5.0 wt%.     

Permeation and separation characteristics of acetic acid/water mixtures through poly(vinyl alcohol‐g‐itaconic acid) membranes by pervaporation,evapomeation, and temperature‐difference evapomeation

In this study, itaconic acid (IA) was grafted onto poly(vinyl alcohol) (PVA) with cerium(IV) ammonium nitrate as an initiator at 45°C. The grafted PVA was characterized with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. IA‐grafted PVA membranes were prepared with a casting method, and the permeation and separation characteristics of acetic acid/water mixtures were investigated with pervaporation (PV), evapomeation (EV) and temperature‐difference evapomeation (TDEV) methods. The effects of the feed composition, operating temperature, and temperature of the membrane surroundings on the permeation rate and separation factor for the acetic acid/water mixtures were studied. The permeation rates in EV were lower than those in PV, whereas the separation factors were higher. With the TDEV method, the permeation rates decreased and the separation factors increased as the temperature of the membrane surroundings decreased. The prepared membranes were also tested in PV, EV, and TDEV to separate the various compositions of the acetic acid/water mixtures (20–90 wt % acetic acid) at 40°C. The highest separation factor, 686, was obtained in TDEV with a 90 wt % acetic acid concentration in the feed. The activation energies of permeation in PV and EV were calculated to be 8.5 and 10.2 kcal/mol, respectively, for a 20 wt % acetic acid solution. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2322–2333, 2004     

Separation of ethylene glycol–water mixtures with composite poly(vinyl alcohol)–polypropylene membranes

Composite membranes consisting of a crosslinked poly(vinyl alcohol)(PVA) active layer on top of a porous polypropylene (PP) support were prepared with glutaraldehyde as a crosslinking reagent. The degree of crosslinking and the thickness of the active layer were determined with attenuated total reflection–Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The membranes were used in the pervaporation dehydration of ethylene glycol (EG)–water mixtures. The effects of the crosslinker content and operational conditions, including feed EG concentration and operating temperature, on the permeation flux and selectivity of the PVA–PP composite membranes were investigated. We observed that the dehydration of a 80 wt % EG mixture at temperature of 60°C, a feed flow rate of 1.5 L/min, and a vacuum pressure of 10 mmHg could be effectively performed, and a moderate permeation flux and a high separation factor were obtained, that is, 0.91 kg m⁻² h⁻¹ and 1021, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Blend membranes of chitosan and poly(vinyl alcohol) in pervaporation dehydration of isopropanol and tetrahydrofuran

Blend membranes of a natural polymer, chitosan, with a synthetic polymer, poly(vinyl alcohol) (PVA), were prepared by solution casting and crosslinked with a urea formaldehyde/sulfuric acid (UFS) mixture. Chitosan was used as the base component in the blend system, whereas PVA concentration was varied from 20 to 60 wt %. Blend compatibility was studied by differential scanning calorimetry, and Fourier transform infrared spectroscopy was used to study membrane crosslinking. Membranes were tested for pervaporation dehydration of isopropanol and tetrahydrofuran (THF) at 30°C in close proximity to their azeotropic compositions. Membrane performance was assessed by calculating flux and selectivity. Swelling experiments performed in water + organic mixtures at 30°C were used to explain the pervaporation results. The blend membrane containing 20 wt % PVA when tested for 5 and 10 wt % water–containing THF and isopropanol feeds exhibited selectivity of 4203 and 17,991, respectively. Flux increased with increasing concentration of water in the feed. Selectivity was highest for the 20 wt % PVA‐containing blend membrane. The results of this study are unique in the sense that the crosslinking agent used—the UFS mixture—was novel. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1918–1926, 2007     

Separation of MTBE-Methanol Mixtures by Pervaporation

Abstract

Membranes made of a polymer blend of poly(acrylic acid) and poly(vinyl alcohol) were evaluated for the separation of methanol from methyl tert-butyl ether (MTBE) by pervaporation. The influence of the blend composition and the feed composition on the pervaporation performance were investigated. Methanol permeates preferentially through all tested blend membranes, and the selectivity increases with increasing poly(vinyl alcohol) content in the blends. However, a flux decrease is observed with increasing poly(vinyl alcohol) content. With increasing feed temperature the flux increases, and the selectivity remains constant. In addition, the influence of crosslinking on the permselectivity was investigated. The pervaporation flux decreases with increasing crosslinking density, but the selectivity is enhanced. This is due to a more rapid decrease in the component flux of MTBE compared to that of methanol.