Pervaporation Performance Research Articles

Poly(vinyl alcohol)/ZIF‐8‐NH2 mixed matrix membranes for ethanol dehydration via pervaporation

Ethanediamine‐modified zeolitic imidazolate framework (ZIF)‐8 particles (ZIF‐8‐NH2) is synthesized and incorporated in the poly(vinyl alcohol) (PVA) matrix to fabricate novel PVA/ZIF‐8‐NH2 mixed matrix membranes (MMMs) for pervaporation dehydration of ethanol. The PVA/ZIF‐8‐NH2 MMMs exhibit enhanced membrane homogeneity and separation performance because of the higher hydrophilicity and restricted agglomeration of the particles, as compared to corresponding MMMs loaded with unmodified particles. The effect of ZIF‐8‐NH2 loading in the MMMs is studied and the MMM with a 7.5 wt % ZIF‐8‐NH2 loading shows the best pervaporation performance for ethanol dehydration at 40°C. Various characterization techniques (Fourier transform infrared, scanning electron microscope, contact angle, sorption test, etc.) are used to investigate the MMMs loaded with ZIF‐8 and ZIF‐8‐NH2 particles. The impact of operation conditions on pervaporation performance is also performed. The performance benchmarking shows that the MMMs have superior separation factors and comparable flux to most other PVA hybrid membranes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1728–1739, 2016

Fabrication and characterization of graphene/graphene oxide based poly (vinyl alcohol) nanocomposite membranes for pervaporation dehydration of ethanol

Graphene (reduced graphene oxide-rgo) or graphene oxide (go)/poly(vinyl alcohol) (pva) nanocomposite membranes were fabricated by solution-casting method. The effects of additive content on the pervaporation (pv) performance of membranes were investigated. The membrane characterizations were performed by fourier-transform infrared spectroscopy, differential scanning calorimetry, x-ray diffraction, and transmission electron microscope. The characterized results indicated that thermal stability and pv performance of nanocomposite membranes were improved compared to the neat pva membrane. In comparison with neat pva, rgo/pva membrane showed a high selectivity of 51.2, but low permeate flux of 0.056 kg.m-2h-1); and go/pva exhibited an acceptable selectivity of 34.9, however equivalent permeate flux of 0.120 kg.m-2h-1

Submicrometer-thick b-oriented Fe–silicalite-1 membranes: microwave-assisted fabrication and pervaporation performances

The well-intergrown, purelyb-oriented andca.1 μm-thick Fe–silicalite-1 membranes on porous α-Al2O3supports possess superior pervaporation performances.

Development of composite anion-exchange membranes using poly(vinyl alcohol) and silica precursor for pervaporation separation of water–isopropanol mixtures

Composite anion-exchange membranes (AEMs) were prepared using sol–gel techniques with poly(vinyl alcohol) and anion-exchange silica precursor (AESP). Among the composite AEMs, the membrane containing 4 mass% of AESP (M-4) exhibited the excellent pervaporation performance.

Hydrophilic Nanocomposite Membranes for the Pervaporation Separation of Water - Ethanol Azeotropic Mixtures

Bentonite nanoclay reinforced Poly (vinyl alcohol) (PVA) nanocomposite membranes were used for the separation of azeotropic composition of water – ethanol mixtures by pervaporation process. Fourier – transform infrared (FTIR) spectroscopic studies revealed the interaction of bentonite nanoclay and the PVA matrix. The dispersion and distribution of nanoclay in the polymer matrix was demonstrated by transmission electron microscopic analysis (TEM). The intrinsic membrane properties with filler loading were also investigated. The results indicate that the hydrophilic nature of the nanoclay influenced the pervaporation to a greater extent. The hydrophilic nature and surface roughness of the nanocomposite membranes was analyzed by atomic force microscopic (AFM) analysis. The pervaporation process illustrates that the permeation flux increases and the separation factor decreases with nanoclay loading. The instrinsic selectivity, which reflects the membrane performance was maximum for 1 wt% clay loaded membranes. PVA with 1 wt% nanoclay loading showed better pervaporation performance. The separation factor of the 1 wt% nanoclay membranes increased to 13, i.e. nearly 4 times more than that of neat PVA membranes. Membrane selectivity also increased to 254% than that of pristine PVA membranes. Thus at lower filler loading, maximum separation was achieved. The increase in nanoclay loading is favorable to improve intrinsic permeance at the cost of decrease in selectivity

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

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

PDMS mixed matrix membranes containing hollow silicalite sphere for ethanol / water separation by pervaporation

Separation of ethanol/water mixtures through classical separation methods, like distillation, are very energy consuming. Pervaporation is an alternative membrane separation process with much lower energy demand, but still lacking high performance membranes with sufficient flux-selectivity properties. In this study, polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) were developed and their pervaporation performance investigated. The fillers consist of hollow spheres (HS) covered with a shell of silicalite-1 crystals. These HS were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption and X-ray diffraction (XRD). The spheres were approximately 1μm in size with a shell thickness of 30nm. Nitrogen physisorption revealed the micro- and mesoporous nature of the spherical shells, with a BET surface area of over 800m2/g. The hollow silicalite spheres were then uniformly distributed in the PDMS membrane to increase the membrane permeability since the hollow core of the HS allows very fast flow of the permeating compound. Furthermore, the zeolitic shell improves the ethanol selectivity through its specific pore structure and hydrophobicity, while additional crosslinking of the HS with the PDMS matrix further increases the selectivity of the polymer matrix, thus reaching a separation factor and flux value of 16 and 3.8×10−6g.m/m2.s respectively for a 6% aqueous ethanol solution at 40°C.

Dehydration Pervaporation of Ethyl Acetate-Water Mixture via Sago/PVA Composite Membranes Using Surface Methodology

In the present study hydrophilic sago/polyvinyl alcohol (PVA) blend membranes were used for pervaporation of ethyl acetate-water mixture. The effects of feed concentration, temperature and permeate pressure on the separation factor and permeation flux were studied by using response surface methodology (RSM). The central composite design (CCD) was used to design the experiment and analyze pervaporation performance of homogenous sago/PVA membranes and also to obtain process optimum conditions. It was observed that the permeation flux and selectivity were changed by feed temperature and concentration more than the permeate pressure. The validity of the model was confirmed by the experiments.

Mechanics and Pervaporation Performance of Ionic Liquid Modified CNT Based SBR Membranes - A Case Study for the Separation of Toluene/Heptane Mixtures

Mechanics and Pervaporation Performance of Ionic Liquid Modified CNT Based SBR Membranes - A Case Study for the Separation of Toluene/Heptane Mixtures

Mechanics and Pervaporation Performance of Ionic Liquid Modified CNT Based SBR Membranes - A Case Study for the Separation of Toluene/Heptane Mixtures

SBR/ionic liquid modified CNT Nanocomposites were prepared using different concentration of CNT. Nano scale dispersion of CNT affected the properties of SBR. The results have been compared with the unfilled SBR films. Cure characteristics and mechanical properties such as tensile strength, modulus, abrasion resistance and hardness were measured for different composites. Morphological behaviour and structural characteristics of the composites were investigated by AFM, TEM, FTIR and Raman spectroscopy. Microstructural development in presence of filler and interfacial interaction between modified CNT and polymer matrix led to enhanced properties. The pervaporation performances of membranes were analysed using a toluene/heptane mixture. Membranes displayed high selectivity towards heptane. The influence of feed composition on pervaporation was also analysed. The 5 phr CNT loaded membrane showed enhanced membrane permeance and selectivity value, an improvement of 18% over the neat polymer. A drop in selectivity and an increase in permeation rate were observed at higher CNT loadings.

Coupling membrane pervaporation with a fixed-bed reactor for enhanced esterification of oleic acid with ethanol

Process intensification through membrane pervaporation (PV) integrated with a fixed-bed reactor could be successfully applied to the esterification of oleic acid and ethanol, which is a crucial step in the biodiesel synthesis using waste oil and grease as resource. The properties of the NaA zeolite membrane such as structure, formulation and separation were investigated by scanning electronic microscopy–energy dispersive spectrometry (SEM–EDS), X-ray diffractometry (XRD) and PV dehydration. Results showed that the NaA zeolite membrane had good separating property for removing water from the organics mixture. The operating conditions were optimized as the ethanol to oleic acid molar ratio of 15:1, feedstock flow rate of 1.0ml/min, reaction temperature of 80.0°C and catalyst bed height of 132mm. The final conversion of oleic acid increased from 84.23% to 87.18% by PV using the NaA zeolite membrane at 24.0h of operation. The membrane showed good PV performance after used for eight successive runs in the PV-assisted esterification. The resin exhibited a much high catalytic activity and operation stability after used for 100h in the consecutive single pass fixed-bed esterification.

Pervaporation removal of volatile organic compounds from aqueous solutions using the highly permeable PIM‐1 membrane

Wastewater containing volatile organic compounds (VOCs) is generated in various industrial processes and is seriously harmful to the natural environment and human health. Its treatment has become extremely important due to increasing environment concerns. Here, a high permeable membrane for fast and high‐efficient VOCs removal from aqueous solutions by pervaporation is reported. The as‐prepared PIM‐1 membrane allows ultrafast permeation of VOCs and exhibits excellent VOCs selectivity, particularly for ethyl acetate, dimethyl ether, and acetonitrile. Typically, the PIM‐1 membrane exhibits an ultrahigh flux and separation factor of 39.5 kg μm m−2 h−1 and 189, respectively, in the pervaporation of 1.0 mol% aqueous ethyl acetate solution. Furthermore, the solubility‐diffusion mechanism is revealed in the pervaporation of 10 kinds of 1.0 mol% VOCs solutions. It is found that the pervaporation performance is affected directly by physicochemical properties of VOCs. Moreover, effects of feed composition and temperature on the pervaporation are studied in details. © 2015 American Institute of Chemical Engineers AIChE J, 62: 842–851, 2016

Surface modification of silicalite-1 with alkoxysilanes to improve the performance of PDMS/silicalite-1 pervaporation membranes: Preparation, characterization and modeling

The objective of this work was to study the effect of silane coupling agent on the performance of mixed matrix membranes (MMMs) and to develop a mathematical model to analyze the performance of the MMMs. The silicalite-1 modified by various alkoxysilanes was incorporated into polydimethysiloxane (PDMS) to prepare dense MMMs. The modified silicalite-1 and corresponding MMMs were characterized by FT-IR, CA, TGA, DSC and SEM. These results confirmed that the silicalite-1 was successfully modified by various alkoxysilanes. The effects of alkoxysilane chain length and chemical structure on the pervaporation (PV) performance of MMMs were discussed in detail. All the silane modification did not change the framework of silicalite-1. Better dispersion of silicalite-1 in PDMS was attained after modification and all the modified membranes could eliminate the nonselective voids inside the membranes. Moreover, the silane coupling agent had a contradictory effect on the PV performance of the membranes. On the one hand, the silane coupling agent improved the compatibility between silicalite-1 and PDMS. On the other hand, the silane coupling agent introduced a silane phase around the silicalite-1, which depressed the selectivity of the pristine silicalite-1. Silicalite-1 grafted with vinyl group showed the best compatibility with PDMS, and the resulting MMMs had the highest separation factor to ethanol because strong chemical bonds between vinyl-silicalite-1 and PDMS were formed with the thinnest silane film. For the separation of ethanol from a dilute solution, a separation factor of 34.3 was obtained with the vinyl-MMMs, which was 49% higher than that of unmodified membrane. As the silicalite-1 content increased, the separation factor increased. Furthermore, a mathematical model was proposed to predict the performance of MMMs. And both the permeability and selectivity obtained by the proposed model were in good agreement with the experiment data.

In-situ crosslinked PVA/organosilica hybrid membranes for pervaporation separations

In this work, two novel poly(vinyl alcohol) (PVA)/organosilica hybrid membranes are developed via the sol–gel process, with phenyltriethoxysilane (PTES) and diethoxydiphenylsilane (DEDPS) as crosslinkers and organosilica precursors, and employed for ethanol dehydration via pervaporation. Effects of organosilane type on the membrane morphology, physicochemical properties and pervaporation performance of the as-fabricated membranes are studied. In addition, the effects of the organosilane loading and the thermal treatment temperature on the physicochemical properties and pervaporation performance of the membrane are explored systematically. Various characterization techniques (FT-IR, TGA, SEM, etc) are employed to illuminate physicochemical changes of membranes. The optimal pervaporation performance of PVA–PTES hybrid membrane with 0.4mmol/g PTES loading and thermally treated at 80°C has a flux of 145g/m2h and a separation factor of 1026 for the pervaporation dehydration of 85% ethanol aqueous solution at 40°C.

The influence of nanoseeds on the pervaporation performance of MFI-type zeolite membranes on hollow fibers

Thin MFI-type zeolite membranes are prepared on α-Al2O3 hollow fibers by secondary growth. Nanoseeds with different gel amounts have been prepared and the influences of silicalite-1 nanoseeds on membrane formation and separation performance of the membrane are investigated. Both the as-synthesized zeolite seeds and membranes are characterized by X-ray diffraction (XRD), dynamic light scattering (DLS) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX). The separation properties of as-synthesized membranes are evaluated by pervaporation of 5 wt% ethanol aqueous solution at 60 °C. It is found that the gel amount in the nanoseeds is critical in obtaining continuous membranes with high separation performance. Membranes prepared via nanoseeds from ball-milled crystals show higher hydrophobicity and denser microstructure, and thus exhibit higher pervaporation performance than those prepared from as-synthesized nanoseeds.

Structure and performance characterization of PDMS/PES-based pervaporation membranes for ethanol/water separation

Composite membranes, with a supporting layer of polyethersulfone (PES) and different active layers based on poly(dimethylsiloxane) (PDMS), were prepared to perform pervaporative separation of ethanol from water. Two approaches were adopted to enhance the ethanol selectivity of PDMS by: (1) evaluation of the effects of PDMS viscosity of two different grades and (2) the incorporation of new hydrophobic silica in the active layer. First, the structural morphology of support and active layers of the composite membranes was characterized. AFM images were evidence of the nodular structure of the membrane surfaces. Mean pore size and pore size distribution of PES layer, mean nodular size of PDMS layer, and their surface roughness and water contact angle were determined. The relationship between these structural properties and the pervaporation performance of composite membranes has then investigated. The effects of operating parameters, feed concentration and temperature on the membrane performance indicated that increasing the feed temperature improved PDMS/PES membranes pervaporative efficiency. Based on the results obtained, it was found that PDMS viscosity influenced the pervaporation performance; low-viscosity PDMS had a greater separation factor and greater permeation fluxes than high-viscosity PDMS. Moreover, silica-filled membranes improved the separation factor and enhanced the ethanol flux relatively.

Microstructure manipulation of MFI-type zeolite membranes on hollow fibers for ethanol–water separation

MFI-type zeolite membranes on hollow fibers are fabricated by a facile secondary growth method. The microstructure of the membranes is systematically manipulated by tuning the seed size, seed morphology and the structure-directing agent content. The as-synthesized MFI-type zeolite membranes are thoroughly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, water contact angle, pervaporation and gas permeation tests. High quality thin membranes (~3μm) can be obtained on alumina hollow fibers by using appropriate seed size and morphology (e.g., 500nm coffin-shaped crystals), and certain low TPA+ content (e.g., TPA+/Si=0.05), achieving a separation factor as high as 58 with a high flux of 9.8kgm−2h−1 for pervaporation of a 5wt% ethanol aqueous solution at 60°C. A linear decrease relationship between the total flux and the separation factor is obtained. The high pervaporation performance of the membranes can be ascribed to their dense membrane layer and low concentration polarization effect owing to their particular microstructures.

Development of bacterial cellulose/alginate nanocomposite membrane for separation of ethanol–water mixtures

A bacterial cellulose (BC) hydrogel was modified via impregnation by diffusion of sodium alginate and cross-linking with calcium chloride solution. BC/alginate (BCA) membranes were configured, characterized, and used for pervaporation of mixtures of ethanol–water. BCA membranes were more hydrophilic with a more dense structure and showed improved affinity toward water and considerable enhancement of pervaporation performance. At a permeate pressure of 10mmHg, the BCA membrane impregnated with 3% (w/v) alginate solution separated water from ethanol in the feed solution (95%, w/w) with 429.9 selectivity, and a total permeate flux of 33g/(m2h).

Effect of silica nanoparticles in mixed matrix membranes for pervaporation dehydration of acetic acid aqueous solution: plant-inspired dewatering systems

Clean technology in dehydration of acetic acid using pervaporative separations inspired by plant dewatering systems is studied in this work. The novel polyphenylsulfone-based membranes, modified with silica nanoparticles, were used to dehydrate a binary mixture of acetic acid and water. The Stöber process was applied for the synthesis of monodispersed silica colloids by hydrolysis of alkyl silicates and condensation of silicic acid in alcoholic solution. The surface free energy of the synthesized silica particles was altered through a silanization treatment with hexamethyldisilazane to convert the surface hydroxyl groups to trimethylsilyl[–Si(CH3)3] groups. The synthesized particles and the modified polyphenylsulfone based membranes were characterized using dynamic light scattering, scanning electron microscopy, atomic force microscopy, Fourier-transform infrared and macroscopic contact angle measurements. Pervaporation was used for the dehydration of 70 wt% acetic acid at 70 °C using nine different membrane variations. Inspired by the natural dewatering in plants containing silica, the performance of the synthetic silica nanoparticles filled-membranes was investigated. Similar to plants, the incorporation of silica nanoparticles in these membranes significantly affected the dewatering process. It was found that at higher concentrations of silica, an improvement of membrane properties was observed, particularly in terms of selectivity. Besides that, the hydrophilicity and surface roughness increases when sufficient amounts of silanols groups were present on the membrane surface. It was concluded that more hydrophilic silica should be first produced and incorporated into the membranes for efficient removal of water from acetic acid. This can be achieved by controlling the composition ratio of ammonium hydroxide, water and ethanol for the nanoparticle fabrication. The effect of different nanoparticle types on membrane morphology and pervaporation performance is also discussed in detail in this work.

A study on the separation performance of zeolite filled thin film composite poly(dimethyl siloxane) membrane

In this study, ethanol/water was separated by means of pervaporation using a zeolite filled poly(dimethyl siloxane) (PDMS) non-porous membrane. Pristine and ZSM-5 type zeolite loaded membranes were prepared by means of solvent-free twin-screw compounding and subsequent compressing molding method. Effects of zeolite loading-level, feed temperature and concentration during separation were evaluated as experimental parameters. Hydrophobicity of the membranes was investigated by means of water contact angle. Mechanical properties were obtained through tensile tests. Morphologies of membranes were characterized by means of scanning electron microscopy (SEM). Pervaporation performance was evaluated in terms of flux, separation factor, and pervaporation separation index. Optimum zeolite loading level was determined as 30%by weight in terms of pervaporation and mechanical performance. At optimum concentration, separation factor and flux were determined as 4.95 and 0.246kg/m2h, respectively. It was demonstrated that flux drastically reduced from 0.246 to 0.03kg/m2h above 30wt.% ZSM-5.