Characterization of permeation behaviors of ethanol–water mixtures through sodium alginate membrane with crosslinking gradient during pervaporation separation

Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique, which had different extents of crosslinking gradient structures. The SA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while blocking the other side by a polyester film to prevent the reaction solution from contacting it. The extent of the crosslinking gradient was controlled by the exposing time. When the swelling measurements were performed with uniformly crosslinked membranes in aqueous solutions of 70–90 wt % ethanol contents, it was observed that the crosslinking could reduce both the solubility of water in the membrane and the permselectivity of the membrane toward water. The pervaporation separation of the ethanol–water mixture of 90 wt % ethanol content was carried out with membranes with different extents of crosslinking gradients. As the crosslinking gradient was developed more across the membrane, the resulting flux as well as the separation factor to water was found to decrease while the membrane became stable against water. The pervaporation performances of the membranes with different membrane loadings in a membrane cell were also discussed using the schematic concentration and activity profiles of the permeant developed in them. The pervaporation separations of the ethanol/water mixtures through the membrane with an optimal crosslinking gradient were performed at different feed compositions and temperatures ranging from 40 to 80°C. The change in the membrane performance due to the relaxation process during pervaporation was observed with the operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis of the experimental data of the membrane performance measured by repeating the operation in a given temperature range. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1607–1619, 1998     

Modification of highly brittle polystyrene sulfonic acid-co-maleic acid crosslinked sodium alginate membrane into flexible membranes by the incorporation of dibutyl phthalate as a plasticizer for pervaporation separation

To convert highly brittle into flexible membrane, the polystyrene sulfonic acid-co-maleic acid crosslinked sodium alginate (PSSAMA/NaAlg) membrane was modified by incorporating the different weight% of dibutyl phthalate (DBP) as a plasticizer. The effect of DBP content on the physico-chemical properties of the membranes was thoroughly examined. The membranes exhibited lower glass transition temperatures with increasing the plasticizer content in the matrix of PSSAMA/NaAlg. The separation performance of the membranes for water/isopropanol and water/1,4-dioxane was studied at different temperatures. Among the modified membranes, the membrane containing 6 wt% of DBP exhibited the highest separation factors of 24,129 with a flux of 13.57 × 10⁻² kg/m² hr and 23,353 with a flux of 12.99 × 10⁻² kg/m² hr for water/isopropanol and water/1,4-dioxane at 30°C, respectively. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The estimated activation energy values for permeation of water (E_pw) and isopropanol (E_pIPA) were, respectively, ranged between 12.09 and 8.79, and 42.52 and 32.79 kJ/mol. A negative heat of sorption (ΔH_s) values was obtained for all the membranes, suggesting that Langmuir's mode of sorption was predominant. Based on the results, it is concluded that the modified membranes demonstrated excellent pervaporation performance for the separation of water/isopropanol and water/1,4-dioxane.     

Separation of toluene–methanol mixtures by pervaporation using crosslink IPN membranes

Polyvinyl alcohol (PVOH) has been chemically modified by crosslink copolymerization of acrylic acid (AA) and hydroxyethylmethacrylate (HEMA) in aqueous solution of PVOH and finally crosslinking PVOH to produce a full interpenetrating network (IPN) membrane termed as PVAH. Accordingly, three such full crosslink IPNs membranes, i.e. PVAHI, PVAHII and PVAHIII containing varied weight ratio of PVOH and copolymer have been synthesized and used for pervaporative separation of methanol from its mixtures with toluene. For comparison, a conventional PVOH membrane crosslinked with glutaraldehyde has also been used for the same pervaporation study. The flux and selectivity of these IPN membranes were found to be much higher than the conventional glutaraldehyde crosslinked PVOH membrane. Among the three membranes, PVAHII with 50 wt% polyAH incorporation showed optimum performance in terms of flux and methanol selectivity.     

Characterization of sodium alginate membrane crosslinked with glutaraldehyde in pervaporation separation

Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde (GA) have been prepared by the solution method, wherein a nonsolvent of SA (acetone) was used in a reaction solution instead of an aqueous salt solution. Through infrared radation, X-ray diffractometry, and the swelling measurement, the crosslinking reaction between the hydroxyl groups of SA and the aldehyde groups of GA was characterized. To investigate the selective sorption behavior of the crosslinked SA membranes, swelling measurements of the membranes in ethanol-water mixtures of 70–90 wt % ethanol contents were conducted by equipment that was able to measure precisely the concentration and amount of the liquid absorbed in the membranes. It was observed that the crosslinking could reduce both the solubility of water in the resulting membrane and the permselectivity of the membrane toward water at the expense of membrane stability against water. The pervaporation separation of a ethanol-water mixture was conducted with the membranes prepared at different GA contents in the reaction solution. When the membrane was prepared at a higher GA content, both flux and separation factor to water were found to be reduced, thus resulting from the more crosslinking structure in it. The pervaporation separations of ethanol-water mixtures were also performed at different feed compositions and temperatures ranging from 40 to 80°C. A decline in the pervaporative performance was observed due to the relaxation of polymeric chains taking place during pervaporation, depending on operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis on experimental data of the membrane performance measured by repeating the operation in the given temperature range. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 209–219, 1998     

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     

Tunable physicochemical properties of PVA nanocomposite membranes for enhanced pervaporation performance

This study reveals the effect of hydrophilic bentonite nanoclay on the pervaporation separation of azeotropic composition of water and 1,4‐dioxane. The permselectivity of the membrane increased with filler concentration and was selective toward water at minimum filler loading. The intrinsic properties such as membrane permeance and selectivity increased with the concentration of hydrophilic bentonite nanoclay and crosslinked poly(vinyl alcohol) (PVA) with 2 wt% nanoclay membranes showed intrinsic selectivity 443 (532% increment than that of pristine membranes) with water permeance 4,675 gas permeation unit which is significantly higher compared to earlier literature. X‐ray diffraction and Transmission electron microscopy showed the well exfoliated and distributed nanoclay structure in the crosslinked PVA matrix. Interaction of PVA with nanoclay and the hydrophilic character of the membranes were characterized by Fourier transform infrared spectra and contact angle analysis, respectively. Interestingly, in this work the membranes exhibited simultaneous increment in both permeation flux and selectivity with filler loading, rather than the usual inverse trend of flux and selectivity. A predictive model of pervaporation was used to explain the pervaporation behavior and it showed good agreement with experimental results for overall pervaporation performance, preferential sorption of water, and hydrophilic‐hydrophobic nature of the membranes. POLYM. ENG. SCI., 58:849–858, 2018. © 2017 Society of Plastics Engineers     

Characterization of sodium alginate and poly(vinyl alcohol) blend membranes in pervaporation separation

By blending a rigid polymer, sodium alginate (SA), and a flexible polymer, poly(vinyl alcohol) (PVA), SA/PVA blend membranes were prepared for the pervaporation separation of ethanol–water mixtures. The rigid SA membrane showed a serious decline in flux and a increase in separation factor due to the relaxation of polymeric chains, whereas the flexible PVA membrane kept consistent membrane performance during pervaporation. Compared with the nascent SA membrane, all of the blend membranes prepared could have an enhanced membrane mobility by which the relaxation during pervaporation operation could be reduced. From the pervaporation separation of the ethanol–water mixtures along with the temperature range of 50–80°C, the effects of operating temperature and PVA content in membrane were investigated on membrane performance, as well as the extent of the relaxation. The morphology of the blend membrane was observed with PVA content by a scanning electron microscopy. The relaxational phenomena during pervaporation were also elucidated through an analysis on experimental data of membrane performance measured by repeating the operation in the given temperature range. SA/PVA blend membrane with 10 wt % of PVA content was crosslinked with glutaraldehyde to enhance membrane stability in water, and the result of pervaporation separation of an ethanol–water mixture through the membrane was discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:949–959, 1998     

Plasma graft polymerization of acrylamide onto crosslinked HTPB based PU membrane for pervaporation

Pervaporation of water-ethanol mixtures through plasma graft polymerization of acrylamide onto crosslinked hydroxyl terminated poly-butadiene (HTPB) based PU membranes, plasma graft polymerization of acrylamide onto crosslinked PU membrane (AAm-p-CPU), were investigated. The grafting was dependent on the discharge power and pretreatment period. The effects of crosslinking, plasma treatment conditions, feed compositions, and feed temperature on the performance of these membranes were studied. The physical properties of crosslinked membrane were better than those of the uncrosslinked membrane. In addition, compared with crosslinked PU membranes (CPU), the plasma modified crosslinked PU membranes effectively improve the pervaporation separation performances.     

交联壳聚糖膜对各种醇水体系分离特性的研究

壳聚糖（CS）膜对不同醇水混合物的分离性能与醇分子的体积相关,随醇分子体积的增加,膜的分离因子增加,而渗透通量下降。然而经戊二醛交联后的CS膜,在分离丙醇水体系时不但具有高的分离因子,还具有比乙醇水体系同的渗透通量。本文研究了在分离不同醇水体系时交联剂量对交联CS膜分离性能的影响,并就交联前后CS膜对醇水体系的分离性能发生变化的原因进行了探讨。     

Effect of Deacetylation Degree in Chitosan Composite Membranes on Pervaporation Performance

ABSTRACT

The effect of the degree of deacetylation in chitosan composite membranes on their pervaporation performance for ethanol dehydration was investigated. The degree of deacetylation of chitosans was measured by using an infrared spectroscopic method and elemental analysis. The chitosan composite membranes were prepared by coating a chitosan solution onto a microporous polyethersulfone membrane with 3–7 nm pore sizes. Then the surface of the top layer (chitosan) of well-dried membranes was crosslinked with sulfuric acid, and pervaporation experiments for binary mixtures (water—ethanol) were carried out at various conditions. In the case of a chitosan membrane with a high degree of deacetylation, the flux increases while the separation factor decreases compared with membranes with a low degree of deacetylation.     

Novel PVA-silica nanocomposite membrane for pervaporative dehydration of ethylene glycol aqueous solution

To effectively suppress the swelling of poly(vinyl alcohol) (PVA) membrane, polymer-inorganic nanocomposite membranes composed of PVA and γ-mercaptopropyltrimethoxysilane (MPTMS) were prepared by in situ sol-gel technique for pervaporative separation of water-ethylene glycol (EG) mixtures. Effects of the types of catalyst for sol-gel process and MPTMS content on the physical and chemical structure of PVA-silica nanocomposite membranes (designated as PVA-MPTMS hereafter) were investigated by ²⁹Si NMR, FTIR, SEM, XRD and TGA-DTA. Due to the formation of more compact crosslinked structure, nanocomposite membranes exhibited enhanced thermal stability. It was found that when 50 wt% of MPTMS was incorporated into PVA, the nanocomposite membranes possessed optimum pervaporation performance for 80 wt% EG aqueous solution at 70 °C. Unexpectedly, there was no improvement in the pervaporation performance of PVA-MPTMS nanocomposite membranes after mercapto group was oxidized into sulfonic group.     

Pervaporation separation of acetic acid-water mixtures using modified membranes. I. Blended polyacrylic acid (PAA)-nylon 6 membranes

Membranes consisting of ionically crosslinked polyacrylic acid (PAA) and Nylon 6 were prepared and tested for the pervaporation separation of acetic acid-water mixtures. The polyacrylic acid (PAA) membranes were crosslinked in aluminum nitrate aqueous solution while the polyacrylic acid (PAA)-Nylon 6 blends were cast from homogeneous PAA-Nylon 6 mixtures to appropriate thicknesses and then crosslinked in aqueous aluminum nitrate solutions. Optimum pervaporation results were obtained from blends of Nylon 6 and PAA in the weight ratio of 60–75 wt% Nylon 6 and 25–40 wt% PAA which have separation factors (water/acetic acid) of over 60 and flux rates higher than 100 g/m² h at 15°C for the separation of acetic acid-water mixtures. The flux rates and separation factors could be altered by changing the blend composition of the membrane. The effects of the feed composition on the separation factors were investigated.     

Pervaporation and solute separation through semi-interpenetrating and interpenetrating polymer network membranes prepared from poly(4-vinylpyridine) and poly(glycidyl methacrylate)

Semi-interpenetrating (SPN) and interpenetrating polymer network (IPN) membranes were prepared from a mixture system of poly(4-vinylpyridine) (P4VP) and poly(glycidyl methacrylate) (PGMA) by quaternizing crosslinking of P4VP with 1,4-dibromobutane (DBB) and by simultaneous crosslinking of P4VP with DBB and PGMA with tetraethylenepentamine (TEPA), respectively. The difference between SPN and IPN was demonstrated by IR, tensile strength, and dimension stability. The membrane performance in pervaporation (PV) for ethanol–water mixtures and reverse osmosis (RO) was investigated. The polymer mixture of 1 : 1 on a monomer base with 30 mol % DBB on the 4VP unit and 5.6–7.5 mol % (8–10 wt %) TEPA on the GMA unit gave an optimum membrane performance. Those crosslinked membranes were stronger than was the cellulose acetate membrane, mostly owing to the PGMA chains, and exhibited a high separation factor for the azeotropic feed in PV. IPN membranes generally showed a performance higher than that of the SPN ones. An attempt to improve the product rate was made by the addition of a water-soluble polymer to the membrane on casting. The separation factor for solubility in the membrane at the feed side dominated the overall separation factor, particularly for feeds of higher ethanol concentrations. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 1953–1963, 1998     

Crosslinked chitosan membranes: characterization and study of dimethylhydrazine dehydration by pervaporation

Crosslinked chitosan membranes were synthesized using glutaraldehyde and characterized by infra‐red (IR) and wide‐angle X‐ray diffraction (WAXD) spectroscopic methods. The membranes were applied for the pervaporation‐based dehydration of the highly hazardous and hypergolic unsymmetrical dimethylhydrazine liquid propellant. The characterization techniques were an efficient tool in identifying polymer–liquid interaction sites and the separation mechanisms involved. The crosslinked polymer was found to have good potential for the separation of the aqueous azeotrope of the propellant (20 wt%) and its enrichment to >90% purity. An equilibrium sorption study examined the preferential affinity of the membrane amongst the two penetrating liquids. The pervaporation performance of the membrane was evaluated by varying the experimental parameters of feed composition, membrane thickness and permeate pressure, and found to be promising. © 2001 Society of Chemical Industry     

Pervaporation of chlorinated hydrocarbon-acetone mixtures through poly(ethylene-co-vinyl acetate) membranes

Crosslinked and uncrosslinked ethylene-vinyl acetate copolymer membranes were prepared. The permeation characteristics in the pervaporation process were examined using carbon tetrachloride-acetone mixtures. Modified membranes exhibit carbon tetrachloride permselectivity, but unmodified membranes did not display the permselectivity of crosslinked polymer. Furthermore, membranes modified with dicumyl peroxide (DCP) showed a higher flux and selectivity than those of benzoyl peroxide (BP) modified ones. The effects of feed concentration, molecular size, and polarity of the permeating species on pervaporation were analyzed. The influence of crosslinking density of the membranes on pervaporation was also analyzed. The maximum separation and flux were found to be associated with an optimum amount of crosslinking agent in the membrane. A mixture of chloroform and acetone having a composition near the azeotropic region was also separated by the pervaporation technique. © 1996 John Wiley & Sons, Inc.     

Pervaporation separation of ethanol–water mixtures using ionically crosslinked blended polyacrylic acid (PAA)–nylon 6 membranes

The pervaporation separation of ethanol–water mixtures was carried out through a series of ionically crosslinked polyacrylic acid (PAA)–Nylon 6-blended membranes crosslinked to varying degrees in aluminum nitrate solution. The polyacrylic acid (PAA)–Nylon 6 membranes were cast from homogeneous PAA–Nylon 6 mixtures to various thicknesses and then crosslinked. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt% Nylon 6 and 25 wt% PAA. These membranes have separation factors (water/ethanol) of 35–40 at flux rates of 120–160 g/m² h. The optimum crosslinking time was found to be approximately 35 h to yield membranes with the best separation and flux rates at 25 wt% PAA content.     

A selective organosilica membrane for ethyl acetate dehydration by pervaporation

Organosilica bis(triethoxysilyl) ethane (BTESE) membranes were explored for pervaporation dehydration of binary and ternary mixtures of ethyl acetate (EA) by undiluted sol coating combined with flash firing. Three BTESE membranes (M1, M2, and M3) were fabricated on macroporous supports by varying BTESE concentrations (0.5, 2.5, and 5 wt% BTESE, respectively) in polymer sols. The membranes were characterized by DLS, SEM, FTIR, XRD, contact angle, AFM, and pervaporation performance to discuss the effect of the BTESE contents in the polymer sol on the formation and dehydration performance of resulting organosilica membranes. It was found that 5 wt% loading of BTESE led to a highly selective membrane for dehydration of EA/H₂O mixture. Among the synthesized membranes, M3 delivered flux of 0.84 ± 0.05 kg.m⁻².h⁻¹ with a selectivity of >10,000 for EA/H₂O mixture (98/2 wt%) at 60°C. The time course of pervaporation dehydration for the EA/H₂O mixture (95/5 wt%) confirms the stability of BTESE membrane in the investigated time period of 120 h. Further, the membrane exhibited excellent selectivity larger than 10,000 for separation of ternary mixtures (90/2/8 wt%) of ethyl acetate/ethanol/water and n-propyl acetate/isopropanol/water respectively, the composition of which is similar to the top product of the distillation column used in the industrial esterification process. The best separation performance and excellent acid stability of BTESE membranes in this study suggest that the simple synthesis protocol of undiluted sol coating and flash firing will provide a cost-effective, quick, and efficient synthesis route for practical membrane based applications.     

Separation of Acetic Acid/Water Mixtures by Pervaporation through Poly(Vinyl Alcohol)–Sodium Alginate Blend Membranes

Abstract

Dense pervaporation (PV) membranes were prepared by blending hydrophilic polymers, poly(vinyl alcohol) (PVA), and sodium alginate (SA), which were then crosslinked with glutaraldehyde (GA) for the separation of acetic acid/water mixtures. These membranes (PVA‐SA) were characterized for morphology, intermolecular interactions, thermal stability, and physico‐mechanical properties using XRD, FTIR, TGA and tensile testing respectively. The effect of experimental parameters such as feed composition and permeate pressure on separation performance of the crosslinked membranes was determined. Sorption studies and porosity measurement were carried out to evaluate the extent of interaction and degree of swelling of the polyion membranes, in acetic acid and water as well as in mixtures of acetic acid and water. Further the results were compared with the commercial membrane (Sulzer pervap 2205). The membrane appears to have a good potential for dehydrating 90 wt% acetic acid with a reasonably high selectivity of 21.5 and a substantial water flux of 0.24 kg/m²/h/10 µm. Separation factor was found to improve with decreasing feed water concentration whereas the corresponding flux decreased. Higher permeate pressures caused a reduction in both flux and selectivity.     

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     

Dehydration of aqueous pyridine solution through crosslinked chitosan membrane

Summary The present study investigates the pervaporation performance of crosslinked chitosan membrane for the dehydration of aqueous pyridine solution. The control of the degree of crosslinking contributes to an improved pervaporation performance of chitosan membranes. The chitosan membrane crosslinked with 4.515x15^-4 (mol/g polymer) glutaraldehyde solution shows the separation factor of 510 and the flux of 140g/m²hr measured with 93wt% aqueous pyridine solution at 25°C.