Water Permselectivity Research Articles

Pervaporation and membrane reactor performance of polyimide based mixed matrix membranes containing MOF HKUST-1

Mixed matrix membranes (MMM) containing MOF Cu3(BTC)2 (HKUST-1) at 20–40wt% loading have been prepared using commercial polyimide (PI) Matrimid® 5218 as polymer matrix. With the addition of this hydrophilic MOF, the water/ethanol separation via pervaporation was improved by increasing the water flux from 0.24kgm−2h−1 for bare PI up to 0.43kgm−2h−1 with 40wt% Cu3(BTC)2 MMM without significant changes in the separation factor (>200). Due to their selective water permeation, these MMMs have been used to displace equilibrium in the esterification of acetic acid with ethanol. By coupling separation by membrane and the reaction in the same device, the conversion obtained at the same feed rate and catalyst loading was higher than that achieved without any membrane. At 70°C the membrane reactor reached a conversion of 70%, higher than the equilibrium value (66%).

Enhanced water permeation through sodium alginate membranes by incorporating graphene oxides

Pristine graphene oxide (pGO) and reduced graphene oxide (rGO) nanosheets with different physical and chemical structures were prepared, and blended into sodium alginate matrix to fabricate two types of hybrid membranes. Compared with pGO, rGO possessed smaller nanosheet size, more structural defects, less negative charges, less oxygen-containing groups, and more non-oxide regions. The hybrid membranes exhibited brick-and-mortar morphology, unusual crystallinity change, and increased free volume. Swelling resistance and mechanical stability of the hybrid membranes were both enhanced. Pervaporation dehydration was conducted utilizing ethanol/water mixture as model to explore the selective water permeation through hybrid membranes. Due to synergy between permselectivity of water channels and crystallinity of polymer matrix, the hybrid membranes, particularly for rGO-filled membranes, exhibited improved separation performance with increased separation factor and an unusual change of permeation flux. When the rGO content was 1.6wt%, optimum separation performance with a separation factor of 1566 and a permeation flux of 1699g/(m2h) was achieved. The transport mechanism was investigated based on transport property comparison of the two types of membranes, revealing that more water channels with higher selectivity could be constructed and controlled by graphene oxide structure. Moreover, the hybrid membrane displayed a good long-term operation stability.

A graphene oxide membrane with highly selective molecular separation of aqueous organic solution.

A graphene oxide (GO) membrane is supported on a ceramic hollow fiber prepared by a vacuum suction method. This GO membrane exhibited excellent water permeation for dimethyl carbonate/water mixtures through a pervaporation process. At 25 °C and 2.6 wt % feed water content, the permeate water content reached 95.2 wt% with a high permeation flux (1702 g m(-2) h(-1)).

<b>Separation of Ethanol-Water Mixtures by the Membranes Prepared from Liquid Silk</b>

Silk-based membranes with the thickness of around 6 micrometers were prepared from the silk glands of fully grown larvae of domestic Bombyx mori silkworm instead of its fibers, and the fundamental vapor permeation as well as pervaporation experiments of ethanol-water mixtures were performed. The permselectivity of water for the membranes developed was almost comparable to that for chitosan and a little superior to PVA. The observed ATR-FTIR spectra bands in the range of amide I and II frequencies for the silk-based membranes were unchanged after the treatments with ethanol. The membranes produced from liquid silk seem to be fairly stable against ethanol.

Fabrication of Ultrathin Membrane via Layer-by-Layer Self-assembly Driven by Hydrophobic Interaction Towards High Separation Performance

A novel and facile layer-by-layer (LbL) self-assembly process driven by hydrophobic interaction and then reinforced by hydrogen bond was developed to prepare ultrathin membranes. Gelatin (GE) and tannic acid (TA) were alternately deposited on polyacrylonitrile (PAN) ultrafiltration membranes to obtain GE/TA membranes. The required number of deposition cycles for acceptable permselectivity of membrane was greatly reduced compared with that of the traditional LbL self-assembly process and could be ascribed to the rapid growth of membrane thickness and the integrity of the innermost gelatin layer. Higher surface hydrophilicity and more appropriate free volume characteristics were obtained for GE/TA multilayer membranes compared with pristine gelatin membrane. Moreover, the GE/TA multilayer membrane exhibited improved stability even at high water content of 30 wt %. The membrane separation experiments with pervaporation dehydration of ethanol aqueous solution as a model system demonstrated the GE/TA multilayer membrane achieved higher water permselectivity than the pristine gelatin membrane. High operation stability was acquired in the long-term membrane separation test.

Eco-friendly fabrication of hydrophilic ZSM-5 membranes for alcohol upgrading

The synthesis of continuous and low-siliceous ZSM-5 membranes was achieved without organic templates under mild conditions (a low temperature of 100 °C and ambient pressure). The resultant high-quality membranes with good water perm-selectivity were further applied in water-alcohol separation, exhibiting an extraordinarily high separation factor of above 10,000 and an improved water flux (3.43-6.88 kg m(-2) h(-1)) for ethanol and isopropanol aqueous azeotropes.

Preparation and characterization of high water perm-selectivity ZSM-5 membrane without organic template

Abstract Well water perm-selectivity ZSM-5 membranes were rapidly prepared from an aluminum-rich and organic template-free precursor gel by the static secondary hydrothermal synthesis. Influences of synthesis parameters (i. e., crystallization time, support type, silica source, fluoride source, fluoride and alkalinity) on the growth and morphology of ZSM-5 membranes were investigated based on the results of XRD, SEM, TEM characterization and pervaporation (PV). The colloidal silica and nanometer silicalite-1 crystals were found to accelerate the preparation of the well-intergrowth and aluminum-rich ZSM-5 membrane. Without organic template, appropriate ratios of NaF/SiO 2 and Na 2 O/SiO 2 in the precursor gel were crucial to prepare a continuous and compact ZSM-5 membrane. Besides, the perm-selectivity of as-synthesized membranes was significantly dependent on the nature of supports. Under the optimum synthesis conditions, the ZSM-5 membrane Z9 was prepared and applied to dehydration of different H 2 O/organic mixtures by PV. For dehydration of 50 wt% H 2 O/IPA mixture at 75 °C, the total flux and separation factor of Z9 membrane were achieved to 6.25 kg m −2 h −1 and 1000, respectively. Furthermore, Z9 also exhibited a great hydrophilic property for dehydration of other organic aqueous, and the dehydration perm-selectivity performance was as follows: H 2 O/Acetone>H 2 O/IPA>H 2 O/EtOH>H 2 O/MeOH.

Pervaporation dehydration of water/ethanol/ethyl acetate mixtures using poly(vinyl alcohol)–silica hybrid membranes

AbstractThe novel organic–inorganic hybrid membranes were prepared from poly(vinyl alcohol) (PVA) and vinyltriethoxysilane (VTES). They were characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and contact angle metering. The as‐prepared membranes are formed at a molecular scale at a low VTES content. Aggregations in the surface of the as‐prepared membranes were clearly evident above 18.43 wt % VTES loading. The introduction of VTES into the PVA matrix resulted in a decrease in the crystalline and an increase in compactness and thermal stability of the as‐prepared membranes. Silica hybridization reduced the swelling of the as‐prepared membranes in water/ethanol/ethyl acetate mixtures, decreased the permeation flux, and remarkably enhanced water permselectivity in pervaporation dehydration of ethanol/ethyl acetate aqueous solution. The hybrid membrane with 24.04 wt % VTES has the highest separation factor of 1079 and permeation flux of 540 g m−2h−1. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Amino-functionalized poly(vinyl alcohol) membranes for enhanced water permselectivity

The surfaces of poly(vinyl alcohol) (PVA) membranes are treated using γ-aminopropyl triethoxysilane (APTEOS) to prepare PVA/APTEOS hybrid membranes. The as-prepared membranes are characterized by wide-angle X-ray diffraction (WXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), contact angle meter and X-ray photoelectron (XPS). The performance of the membranes is investigated for pervaporation separation of ethanol/water (85/15) mixtures. The effect of surface treating time and feed temperature is studied. The surface-treated membranes exhibit good water permselectivity. The separation factor increases with increasing the APTEOS content, and first increases with increasing treating time below 120 min then slightly decreases afterwards. However, the separation factor is found to demonstrate a unique temperature dependence in a range 50–70 °C.

Pervaporation performance of quaternized poly(vinyl alcohol) and its crosslinked membranes for the dehydration of ethanol

Quaternized poly(vinyl alcohol) (q-PVA) was synthesized, and crosslinked by glutaraldehyde to reduce the swelling of the q-PVA in an aqueous solution. The structure of the q-PVA and its crosslinked membranes was characterized by scanning electron microscopy, X-ray powder diffraction, and water contact angle measurements. Pervaporation performance of the membranes was studied by the dehydration of 85 wt% ethanol solution at 50 °C. The introduction of quaternary ammonium groups enhanced the hydrophilicity and water permselectivity. The water permeability and permselectivity of the q-PVA membranes increased simultaneously with increasing degree of quaternization (DQ). The crosslinking caused a decrease in swelling and an increase in water permselectivity of the q-PVA membranes. The q-PVA membrane with DQ of 4.035% has a highest water permeability of 12.628 g μm m −2 h −1 kPa −1, and the crosslinked q-PVA membrane with degree of crosslinking of 3.92% has a highest water permselectivity of 75.

Dehydration of ethylene glycol by pervaporation using poly( N, N-dimethylaminoethyl methacrylate)/polysulfone composite membranes

Dehydration of ethylene glycol by pervaporation was carried out using poly( N, N-dimethylaminoethyl methacrylate)/polysulfone (PDMAEMA/PSF) composite membranes prepared by solid/liquid interfacial crosslinking. The effects of feed water concentration and operating temperature on the pervaporation performance were investigated. The membrane performance compared favorably with other membranes reported in literature. At a feed water concentration of 1 mol%, a permeation flux of ∼1 mol/(m 2 h) and a permeate water concentration of 99.7 mol% were achieved at 30 °C. The permeation flux was shown to increase with an increase in temperature, while the membrane selectivity was essentially the same. The increase in permeation flux with temperature was primarily due to the increased driving force for permeation, and the membrane permeability was shown to decrease as the temperature increased. The sorption uptake of the permeant in the PDMAEMA membrane was also studied, and it was revealed that the selective permeation of water through the membranes was derived from the diffusion selectivity.

Pervaporation performance of polystyrene membrane surface with perfluoroalkyl groups

AbstractResearch on the effect of various chemical groups on the pervaporation performance of membranes was very important for understanding the separation phenomenon. In this article, a polystyrene membrane with CF3 groups on its surface was prepared by casting normal polystyrene (PS‐H) solution with small‐molecular‐weight α,ω‐fluoroalkyl‐terminated polystyrene (S‐PS‐(CF3)2) on a glass plate. The amount of CF3 groups on the surface was adjusted by changing S‐PS‐(CF3)2 content, which was documented by X‐ray photoelectron spectroscopy analysis, surface energy, and contact angle measurements. The effect of S‐PS‐(CF3)2 content on separation performance of S‐PS‐(CF3)2/PS‐H blend membranes for ethanol/water mixture was investigated. The results showed that water concentration in the permeate decreased with increasing S‐PS‐(CF3)2 content; however, the permeation rate did not change until the S‐PS‐(CF3)2 content was increased to 1 wt %. The reason for this was attributed to the fact that a small amount of S‐PS‐(CF3)2 enables a simple surface modification of the membrane keeping its inner structure relatively unchanged. This was confirmed by swelling degree measurements and other experiments. Comparison with our previous work showed that the CF3 groups on the surface lowers the water permselectivity of the polystyrene membranes, whereas the COOH groups enhance the water permselectivity. However, neither hydrophobic CF3 nor hydrophilic groups on the membrane surface appeared to have any influence on flux. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Structure optimization of water-permselective membrane surfaces by reconstruction

The pervaporation performance with operating time through poly(vinyl alcohol) (PVA) membrane for the separation of various alcohol/water (methanol–water, ethanol–water, isopropanol–water) mixtures was investigated. The water selectivity through the air-side surface of a PVA membrane increased and finally reached an equilibrium value, which was lower than that through the glass-side surface, implying the structure on the glass-side surface of PVA membrane is favorable towards the enhancement of the water permselectivity compared to that on the air-side surface. This phenomenon was attributed to the reconstruction occurred at the air-side surface of the membrane, hence a more hydrophilic membrane surface was formed when it was in contact with the feed mixtures. In order to optimize the water permselective structure on the air-side surface of PVA membrane, the membrane was pre-treated in 80% methanol/water mixtures. For dehydration ethanol and isopropanol, the separation factor through the air-side surface of the pre-treated PVA membrane was improved greatly, approaching that through the glass-side surface. Our results indicate that a desirable structure at the air-side surface can be optimized by surface reconstruction in various environments, which is very useful for the industrial applications of pervaporation membranes because their air-side surfaces are usually in contact with the feed.

Effects of annealing on the physico-chemical structure and permeation performance of novel hybrid membranes of poly(vinyl alcohol)/γ-aminopropyl-triethoxysilane

Novel organic–inorganic hybrid membranes of poly(vinyl alcohol) (PVA)/γ-aminopropyl-triethoxysilane (APTEOS) were prepared through a sol–gel approach in this study. The PVA/APTEOS hybrid membranes were characterized by a wide angle X-ray diffractometer (WXRD), scanning electronic microscope (SEM), themogravimetric analysis (TGA) and a contact angle meter to elucidate the effect of annealing temperature and time on the structure of the hybrid membranes. The swelling of the annealed hybrid membranes in an aqueous ethanol solution was investigated, and permeation performance of the annealed hybrid membranes was studied by pervaporation (PV) of 85 wt% ethanol aqueous solution. With annealing temperature or time increasing, both the swelling degree and the permeation flux of the hybrid membranes decreased, while water permselectivity increased. The interaction parameter of water with the membrane χ 13, and ethanol with the membrane χ 23 increased with annealing temperature and time increasing. The relation of the free volume with the permeation properties of the annealed hybrid membranes was studied by positron annihilation lifetime spectroscopy (PALS). And the diffusion behavior of water and ethanol in an aqueous ethanol solution through the hybrid membranes was analyzed by Maxwell–Stefan equation.

Pervaporation characteristics and structure of poly(vinyl alcohol)/poly(ethylene glycol)/tetraethoxysilane hybrid membranes

AbstractPoly(vinyl alcohol) (PVA) blended with poly(ethylene glycol) (PEG) was crosslinked with tetraethoxysilane (TEOS) to prepare organic–inorganic PVA/PEG/TEOS hybrid membranes. The membranes were then used for the dehydration of ethanol by pervaporation (PV). The physicochemical structure of the hybrid membranes was studied with Fourier transform infrared spectra (FT‐IR), wide‐angle X‐ray diffraction WXRD, and scanning electron microscopy (SEM). PVA and PEG were crosslinked with TEOS, and the crosslinking density increased with increases in the TEOS content, annealing temperature, and time. The water permselectivity of the hybrid membranes increased with increasing annealing temperature or time; however, the permeation fluxes decreased at the same time. SEM pictures showed that phase separation took place in the hybrid membranes when the TEOS content was greater than 15 wt %. The water permselectivity increased with the addition of TEOS and reached the maximum at 10 wt % TEOS. The water permselectivity decreased, whereas the permeation flux increased, with an increase in the feed water content or feed temperature. The hybrid membrane that was annealed at 130°C for 12 h exhibited high permselectivity with a separation factor of 300 and a permeation flux of 0.046 kg m−2 h−1 in PV of 15 wt % water in ethanol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Stoichiometric Ester Condensation Reaction Processes by Pervaporative Water Removal via Acid-Tolerant Zeolite Membranes

We successfully developed a pervaporation-aided (PV-aided) dehydration reaction process that enabled ester condensation reactions stoichiometrically at nearly room temperature. The reactions were conducted at nearly room temperature, lower than 323 K, by the help of effective water removal by PV at that temperature. Zeolite membranes we developed consist of acid-tolerant hydrophilic zeolites, which have excellent permselectivity of water, even with coexistence of methanol. The acid-tolerant nature of membranes enabled stable and continuous dehydration via PV during the reaction. The advantage of the PV-aided dehydration reaction became apparent in ester condensation reactions with alcohols, in which the ester yields exceeded by >20% from equilibrium conversion without distillation. Also, compared with the conventional reactive distillation process (Eastman Process), our reaction process does not alter the volatility of the product, because water is removed from the reaction system in any combination of substrates. We regard that the reaction process will show advantages for the dehydration reaction dealing with lower alcohols (methanol, ethanol, etc.), such as free acid treatment in biodiesel fuel (BDF) production processes or perfume synthesis.

Pervaporation and characterization of chitosan membranes cross-linked by 3-aminopropyltriethoxysilane

Chitosan (CS) was cross-linked with 3-aminopropyl-triethoxysilane (APTEOS) to prepare chitosan–silica hybrid membranes (CSHMs). The CSHMs were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results show that there are strong hydrogen bond and covalent bonds formed in the CSHMs matrix, the crystallinity of the CSHMs is lower than that of CS, and silica is well distributed in the CSHMs matrix. The CSHMs exhibited a low degree of swelling (DS) in ethanol/water mixture. Both the solubility and diffusion selectivity increase with increasing ethanol content in the range of 55–95 wt%. The rate of increase in the solubility selectivity is faster than the rate of decrease in the diffusion selectivity with increasing the feed temperature. These caused the permeate ethanol content to decrease with increasing either the feed ethanol content or the feed temperature. Both the permeation flux and water permselectivity increased remarkably with increasing APTEOS content, CSHM-10 containing 10 wt% APTEOS has the highest separation factor of 597 with a flux of 0.887 kg/(m 2 h) in PV of 85 wt% feed ethanol at 323 K.

The relationship between proton conductivity and water permeability in composite carboxylate/sulfonate perfluorinated ionomer membranes

Composite carboxylate/sulfonate Nafion ® films were prepared with different ratios of anion equivalents as a test of the relationship between proton conductivity and water permeability in perfluorinated ionomers. Substitution of carboxylate groups for sulfonate groups dramatically reduced water permeability and modestly reduced proton conductivity in the films. Small angle X-ray scattering (SAXS) was used to probe the polymer microstructure and showed that with up to 20% carboxylate equivalents, the size of hydrated ionic domains within the ionomer remains constant. Water sorption measurements showed little decrease in water uptake with increased carboxylate functionality, supporting the SAXS data. Methanol/water permeability experiments showed that the carboxylate moieties slow the diffusion of both water and methanol, with no permselectivity of water. Results indicate that the proton transport mechanism is altered by addition of carboxylic acid. As such, the composites may show interesting behavior in H 2/O 2 and direct methanol fuel cells. It is proposed that permeability and conductivity measurements may provide an inexpensive and simple screening tool for early evaluation of new experimental proton exchange membranes.

Anti-trade-off in dehydration of ethanol by novel PVA/APTEOS hybrid membranes

Novel organic–inorganic hybrid membranes were prepared through sol–gel reaction of poly(vinyl alcohol) (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) for pervaporation (PV) separation of ethanol/water mixtures. The membranes were characterized by FTIR, EDX, WXRD and PALS. The amorphous region of the hybrid membranes increased with increasing APTEOS content, and both the free volume and the hydrophilicity of the hybrid membranes increased when APTEOS content was less than 5 wt%. The swelling degree of the hybrid membranes has been restrained in an aqueous solution owing to the formation of hydrogen and covalent bonds in the membrane matrix. Permeation flux increased remarkably with APTEOS content increasing, and water permselectivity increased at the same time, the trade-off between the permeation flux and water permselectivity of the hybrid membranes was broken. The sorption selectivity increased with increasing temperature, and decreased with increasing water content. In addition, the diffusion selectivity and diffusion coefficient of the permeants through the hybrid membranes were investigated. The hybrid membrane containing 5 wt% APTEOS has highest separation factor of 536.7 at 50 °C and permeation flux of 0.0355 kg m −2 h −1 in PV separation of 5 wt% water in the feed.

Study of the separation properties of chitosan/polysulfone composite hollow-fiber membranes

The separation performances of an aqueous ethanol solution through chitosan dip-coated chitosan/polysulfone (PSf) composite hollow-fiber membranes with the vapor permeation operating process were investigated. The effects of chitosan concentration and dip-coated temperature on the separation performances were studied. Compared with unmodified PSf hollow-fiber membranes, chitosan dip-coated polysulfone (PSf) composite hollow-fiber membranes can effectively increase the permselectivity of water. By increasing the concentration of chitosan solution, the permeation rate as well as ethanol content in permeate decrease. In addition, the effect on the vapor permeation performances of the feed composition and feed solution temperature were also investigated. The permeation rate decreases while the separation factor toward water increases with increasing ethanol concentration in the feed. Moreover, the permeation rate increases while the separation factor toward water decreases with increasing feed temperature. The permeation rate, separation factor and PSI at 25°C for a 90 wt% aqueous ethanol solution through the chitosan/PSf composite hollow-fiber membrane with a 3 wt% chitosan dip-coated system were 63 g/m 2 h, 2440, and 153,700, respectively.