Preparation of PVA membranes containing β-cyclodextrin oligomer (PVA/CD membrane) and their pervaporation characteristics for ethanol/water mixtures

Poly(vinyl alcohol) (PVA) membranes were modified by introducing β-cyclodextrin (β-CD) oligomer, which has an inclusion ability sensitive to size, structure, and hydrophilicity of the guest molecule. The modified membranes (PVA/CD membrane) were prepared by casting of the aqueous solutions of PVA and β-CD oligomer. The CD oligomer was immobilized in the membranes by cross-linking with glutaraldehyde. The cross-linking times were 1 and 8 h. The content of CD in the membranes was 33 wt %. The effects of CD on the pervaporation characteristics for water/ethanol were investigated by comparisons with those of the cross-linked PVA membranes. For the 1 h cross-linked membranes, CD increased both the water permeation rate and selectivity at lower ethanol concentrations in the feed. At higher ethanol concentrations, CD increased the water selectivity, but it decreased the water permeation rate. For the 8 h cross-linked membranes, at lower ethanol concentrations, CD increased the water permeation rate, but the water selectivity through the PVA/CD membrane was almost equal to that of the PVA membrane. At higher ethanol concentrations, CD increased the water selectivity and decreased the water permeation rate. These effects of CD can be interpreted in terms of the inclusion strength in the cavity and the reduction of the cross-linking density of the PVA phase in the membranes. © 1994 John Wiley & Sons, Inc.     

Pervaporation separation of water/alcohol mixtures through hydroxypropylated chitosan membranes

The present study investigated the pervaporation performance of novel hydroxypropylated chitosan (HPCS) membranes to separate water from an aqueous alcohol solution. Hydroxypropylated chitosan was prepared from the reaction of chitosan and propylene oxide. The results show that the separation factor decreases and the flux increases with increasing of the substitution degree of the hydroxypropylated chitosan membrane. Crosslinking with glutaraldehyde or treatment with Cu²⁺ can improve the pervaporation performance of modified chitosan membrane grately. The performance data indicate that the crosslinking hydroxypropylated chitosan membrane treated with Cu²⁺ is an excellent pervaporation membrane for the separation of alcohol–water mixtures, and one-stage separation is attainable for some alcohol–water mixtures such as an n-propanol–water and an isopropanol–water system, which has a good separation factor of 220 for the n-PrOH/water system and 240 for the i-PrOH/water system using 85 wt % alcohol concentration at 60°C. The flux for both cases is around 0.5 kg m⁻² h⁻¹. At the same time, the structure of the chemically modified chitosan membranes and their separation characteristics for aqueous alcohol solutions are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2035–2041, 1998     

Pervaporation of MTBE/methanol mixtures through PVA membranes

Sorption and pervaporation experiments were carried outwith PVA/PAA cross-linked membranes for the separation of azeotropic methyl tert-butyl ether and methanol mixtures. The influence of the PVA/PAA ratio and liquid mixture composition were investigated. With increasing PAA content in the membranes, solubilities and fluxes decreased and selectivities increased. Total sorption and fluxes increased with increasing concentration of McOH. Increasing the concentration of McOH resulted in decreasing selectivities. Because of polarity, McOH permeated selectively through the membranes. Sorption results showed the same tendency with pervaporation results.     

Sorption equilibria and diffusion coefficients of ethanol and water in the PVA membranes containing cyclodextrin

Effects of cyclodextrin (CD) on the pervaporation characteristics for water/ethanol through the PVA/CD membranes (PVA membranes containing β-CD oligomer) have been investigated in terms of sorption equilibria and diffusion coefficients based on the sorption–diffusion theory. The increase in water selectivity through the pervaporation by CD was due mainly to the changes in the diffusion coefficients by CD, which depended on the feed composition and the cross-linking time. The water selectivity through the sorption equilibria was not increased by the addition of CD, and the ethanol-sorption amount was increased by CD. These effects of CD were interpreted by the inclusion strength in the CD cavity and the cross-linking density of the PVA phase. © 1994 John Wiley & Sons, Inc.     

Pervaporation of benzene/cyclohexane and benzene/n-hexane mixtures through PVA membranes

Poly(vinyl alcohol) (PVA) membranes (both homogeneous and asymmetric) were studied for the pervaporation separation of benzene/n-hexane and benzene/cyclohexane mixtures. The asymmetric PVA membrane with skin and porous layers was prepared through the phase inversion technique. Both asymmetric and homogeneous membranes were benzene-selective for all the feed compositions. The benzene separation factor of homogeneous PVA membrane was smaller than three, and the total permeation flux was several g/m²/h. The benzene selectivity of the asymmetric PVA membrane was much higher than that of the homogeneous membrane; weight fraction of benzene in the permeate side was larger than 90% for all the feed compositions. On the other hand, the total flux was almost unchanged compared with that of the homogeneous membrane. These results indicate that the density of the skin layer of the asymmetric membrane should be much higher than that of the homogeneous membrane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1061–1065, 1997     

Pervaporation of water/alcohol mixtures through chitosan/cellulose acetate composite hollow‐fiber membranes

For the purpose of separating aqueous alcohol by the use of pervaporation technique, a composite membrane of chitosan (CT) dip‐coated cellulose acetate (CA) hollow‐fiber membranes, CT‐d‐CA, was investigated. The effects of air‐gap distance in the spinning of CA hollow‐fiber membranes, chitosan concentration, and sorts of aqueous alcohol solutions on the pervaporation performances were studied. Compared with unmodified CA hollow‐fiber membrane, the CT‐d‐CA composite hollow‐fiber membrane effectively increases the permselectivity of water. The thickness of coating layer increases with an increase in chitosan concentration. As the concentration of chitosan solution increased, the permeation rate decreased and the concentration of water in the permeate increased. In addition, the effects of feed composition and feed solution temperature on the pervaporation performances were also investigated. The permeation rate and water content in permeate at 25°C for a 90 wt % aqueous isopropanol solution through the CT‐d‐CA composite hollow‐fiber membrane with a 5‐cm air‐gap distance spun, 2 wt % chitosan dip‐coated system were 169.5 g/m² h and 98.9 wt %, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1562–1568, 2004     

Characteristics of permeation and separation for propanol isomers through poly(vinyl alcohol) membranes containing cyclodextrin

Poly(vinyl alcohol) membranes containing cyclodextrin (CD–PVA membrane) were prepared and characteristics of permeation and separation for propanol (PrOH) isomers through the CD–PVA membranes were investigated by pervaporation and evapomeation. Evapomeation was more effective for the separation of PrOH isomers through the CD–PVA membrane than was pervaporation. The CD–PVA membrane more preferentially permeated n-PrOH than i-PrOH from their mixtures. In particular, the mixture of 10 wt % n-PrOH concentration was concentrated to about 45 wt % through the CD–PVA membrane. Both permeability and selectivity for n-PrOH were improved with an increase of CD content in the membrane. The results were supported by the fact that the affinity of CD for n-PrOH was stronger than that for i-PrOH. The permeation mechanism of PrOH isomers through the CD–PVA membrane is discussed based on the solution–diffusion theory. © 1994 John Wiley & Sons, Inc.     

Modified free-volume model for pervaporation of water/ethanol mixtures through membranes containing hydrophilic groups or ions

The free-volume model for pervaporation has been modified by considering the polar path, in order to apply the model to membranes containing hydrophilic groups. The free-volume parameters were determined by inverse gas chromatography. For the polyacrylonitrile (PAN) membrane, the transport mechanism could be analyzed only by the free-volume model; however, for a membrane containing a hydrophilic moiety, the transport properties could be interpreted by the modified model. In water/ethanol mixtures, ethanol transports through the membrane matrix, while water permeates through the polar pathways consisting of polar groups or ions and water molecules as well as through the membrane matrix. © 1995 John Wiley & Sons, Inc.     

Dehydration of water–alcohol mixtures by vapor permeation through PVA/clay nanocomposite membrane

An organic/inorganic hybrid nanocomposite membrane, poly(vinyl alcohol)/clay (PVAC), was prepared. The morphology of PVAC nanocomposite membranes were characterized using transmission electron microscopy (TEM), X‐ray diffraction (XRD), and atomic force microscopy (AFM). The crystallinity and surface roughness increases with an increasing clay content in the PVAC nanocomposite membrane. Compared with the pure poly(vinyl alcohol) (PVA) membrane, the hybrid nanocomposite membrane (PVAC) shows an improvement in the thermal stability and the prevention of the water‐soluble property. The oxygen permeability and the water‐vapor permeation rate decreases with an increasing clay content (1–3 wt %) in the PVAC nanocomposite membranes. In addition, the effects of the clay content on the vapor‐permeation performance of an aqueous ethanol solution through the PVAC nanocomposite membranes was also investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3632–3638, 2003     

Synthetic membranes containing schardinger cyclodextrin additives

The permeation characteristics of the isomers of such aromatics as dichlorobenzenes, nitrochlorobenzenes, xylenes, etc., through a Methocel HG membrane containing various amounts of Schardinger α-cyclodextrin and β-cyclodextrin additives were measured in liquid/liquid dialysis and pervaporation experiments. The results showed that the cyclodextrins are able to selectively mediate molecular transport through the Methocel HG membranes. In general, increased membrane selectivity and a decrease in permeation rates were observed. Permeation rates for some aromatic compounds were decreased several hundred times with only 25% amounts of additive cyclodextrins in the Methocel HG membranes. Concentration electrical potential and bi-ionic electrical potential in membranes containing the Schardinger cyclodextrin have been measured and also show that the cyclodextrins are able to induce ion transport selectively through nonionic membranes. Dynamic mechanical properties of Methocel HG membranes containing cyclodextrins suggest these additives to be antiplasticizing agents. A mechanism for the modification of the intrinsic membrane permeation properties by cyclodextrin additive involving antiplasticizing action by the additives plus induced tortuous diffusion, where the latter is a result of specific interactions between the cyclodextrin additive and the permeating molecules, is proposed.     

Pervaporation performance and Transport phenomenon of PVA blend membranes for the separation of THF/water azeotropic mixtures

Summary Dense polymer membranes were made by mixing aqueous solutions of hydrophilic polymers poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the separation of Tetrahydrofuran (THF)/water azeotropic mixtures by pervaporation (PV). In order to gain a more detailed picture of the molecular transport phenomenon, we have performed sorption gravimetric experiments at 30 °C to compute diffusion, swelling, sorption and permeability coefficients of PVA/PEI membranes in the presence of THF and water. The membranes were found to have good potential for breaking the azeotrope of THF at 6% concentration of water. An increase in PVA content in the blend caused a reduction in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest separation factor of 181.5, exhibited a flux of 1.28 kg/m²h for THF respectively at azeotropic feed composition.     

Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes for pervaporation separation of ethanol/water solution

Polysulfone (PSF) hollow fiber membranes were spun by phase‐inversion method from 29 wt % solids of 29 : 65 : 6 PSF/NMP/glycerol and 29 : 64 : 7 PSF/DMAc/glycol using 93.5 : 6.5 NMP/water and 94.5 : 5.5 DMAc/water as bore fluids, respectively, while the external coagulant was water. Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes were prepared after PSF hollow fiber membranes were coated using different PVA aqueous solutions, which were composed of PVA, fatty alcohol polyoxyethylene ether (AEO₉), maleic acid (MAC), and water. Two coating methods (dip coating and vacuum coating) and different heat treatments were discussed. The effects of hollow fiber membrane treatment methods, membrane structures, ethanol solution temperatures, and MAC/PVA ratios on the pervaporation performance of 95 wt % ethanol/water solution were studied. Using the vacuum‐coating method, the suitable MAC/PVA ratio was 0.3 for the preparation of PVA/PSF hollow fiber composite membrane with the sponge‐like membrane structure. Its pervaporation performance was as follows: separation factor (α) was 185 while permeation flux (J) was 30g/m²·h at 50°C. Based on the experimental results, it was found that separation factor (α) of PVA/PSF composite membrane with single finger‐void membrane structure was higher than that with the sponge‐like membrane structure. Therefore, single finger‐void membrane structure as the supported membrane was more suitable than sponge‐like membrane structure for the preparation of PVA/PSF hollow fiber composite membrane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 247–254, 2005     

Separation of liquid mixtures by using polymer membranes. II. Water-alcohol separation by pervaporation through porous PVA membranes

The permeation and separation characteristics of alcohol/water systems through porous PVA membranes were investigated. Porous PVA membranes with different pore size and number were prepared by solution blending of PVA with several synthesized polymers or copolymers, such as polyacrylic acid, polyacrylamide, polyacrylonitrile, and methylmethacrylate-co-maleic anhydride, etc. Then casting, and finally extracting the blended polymers or copolymers by solvent from the membranes. The dependency of both permeation and separation on the molecular size and shape of the permeating species was dicussed qualitatively. Moreover, the permselectivity was investigated with attention to the feed composition of alcohol/water mixture and the effect of pore size and number. The selectivity was found to depend on the weight ratio and the molecular weight of polymer introduced to the membrane. When the weight ratio of polymer introduced into the membrane was larger than 0.1, methanol was permeated through membrane preferentially in methanol/water system, and the separation factor increased with increasing the methanol feed concentration. On the other hand, membrane had a selective permeability for water in the other alcohol/water systems. The influence of operating conditions was also studied.     

Pervaporation behavior of PVA membrane containing β‐cyclodextrin for separating xylene isomeric mixtures

To evaluate molecular recognition function of β‐cyclodextrin to xylene isomers, β‐CD polymer of branching chain extension (β‐CD‐EGDE) was synthesized by crosslinking β‐CD with ethylene glycol diglycidyl ether (EGDE). The pervaporation blend membranes of β‐CD‐EGDE/PVA were prepared by casting an aqueous solution of PVA and β‐CD polymer mixture, and the membranes were used for separation of p‐/m‐ and p‐/o‐xylene mixtures. It was observed that the pristine PVA membrane almost had no selectivity for xylene isomer mixtures. The PVA membrane incorporating β‐CD polymer had molecular recognition function, which selectively facilitated the transport of the xylene isomers. To ascertain pervaporation behavior, the sorption and desorption processes of the membrane in xylenes were investigated. The sorption result showed that the complex formation constant between β‐CDs and xylenes played a key role in swelling behavior. There was a significant difference between diffusion coefficients D and D⁰, calculated from the sorption and desorption measurements, respectively, indicating that the diffusivity selectivity in desorption stage may have remarkable effect on the total selectivity during pervaporation process. © 2012 American Institute of Chemical Engineers AIChE J, 59: 604–612, 2013     

Pervaporation of ethanol–water mixtures through styrene-substituted N-phenylmaleimide copolymer membranes

A number of copolymers of styrene with substituted N-phenylmaleimides were synthesized and their solutions in chloroform were used in the casting of homogeneous membranes. The latter were applied in the separation of variously concentrated ethanol—water mixtures by pervaporation at 35°C. The membranes were characterized by the separation factor related to preferentially transported water and by the flux of the permeate. In contrast to membranes made from copolymers of styrene with N-phenylmaleimide, the separation factor of membranes containing substituted N-phenylmaleimides increased with increasing amount of ethanol in the feed solution. The effect of incorporated imide units on the properties of the membranes under investigation is discussed. © 1992 John Wiley & Sons, Inc.     

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 binary organic–aqueous liquid mixtures using cross-linked PVA membranes. II. Phenol–water mixtures

The pervaporation separation of water-phenol mixtures was carried out using poly(vinyl alcohol) (PVA) cross-linked membranes with low molecular weight poly(acrylic acid) (PAA) at 30, 40, and 50°C. The separation was concentrated on the second stage of the water-selective process at which the phenol concentration could be 80 wt % of phenol. The high separation factor of α_w/p, = 3580 for the PVA/PAA = 80/20 membrane was obtained for the phenol : water = 80 : 20 solution at 30°C. © 1994 John Wiley & Sons, Inc.     

Pervaporation of tertiary butanol/water mixtures through chitosan membranes cross‐linked with toluylene diisocyanate

Membranes made from 84% deacetylated chitosan biopolymer were cross‐linked by a novel method using 2,4‐toluylene diisocyanate (TDI) and tested for the separation of t‐butanol/water mixtures by pervaporation. The unmodified and cross‐linked membranes were characterized by Fourier transform infra red (FTIR) spectroscopy, X‐ray diffraction (XRD) studies and sorption studies in order to understand the polymer–liquid interactions and separation mechanisms. Thermal stability was analyzed by differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) while tensile strength measurement was carried out to assess mechanical strength. The membrane appears to have good potential for breaking the aqueous azeotrope of 88.2 wt% t‐butanol by giving a high selectivity of 620 and substantial water flux (0.38 kg m^?2 hr^?1). The effects of operating parameters such as feed composition, membrane thickness and permeate pressure on membrane performance were evaluated. Copyright © 2005 Society of Chemical Industry     

Pervaporation separation of water/isopropanol mixtures through crosslinked carboxymethyl chitosan/polysulfone hollow‐fiber composite membranes

Carboxymethyl chitosan (CMCS)/polysulfone (PS) hollow‐fiber composite membranes were prepared through glutaraldehyde (GA) as the crosslinking agent and PS hollow‐fiber ultrafiltration membrane as the support. The permeation and separation characteristics for dehydration of isopropanol were investigated by the pervaporation method. Pure chitosan, carboxymethyl chitosan, and crosslinked carboxymethyl chitosan membranes were characterized by Fourier transform infrared (FT‐IR) spectroscopy and X‐ray diffraction (XRD) to study the crosslinking reaction mechanism and degree of crystallinity, respectively. The effects of feed composition, crosslinking agent, membrane thickness, and feed temperature on membrane performance were investigated. The results show that the crosslinked CMCS/PS hollow‐fiber composite membranes possess high selectivity and promising permeability. The permeation flux and separation factor for isopropanol/water is 38.6 g/m²h and 3238.5, using 87.5 wt % isopropanol concentration at 45°C, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1959–1965, 2007