Composite Pervaporation Membranes Research Articles

Preparation of PDMS/PVDF Composite Pervaporation Membrane Modified with Hydrophobic TiO2 Nanoparticles for Separating Formaldehyde Solution

In this paper, polydimethylsiloxane (PDMS) was blended with hydrophobic TiO2 nanoparticles and then coated on top of the polyvinylidene fluoride (PVDF) ultrafiltration membrane to form the (PDMS/TiO2)/PVDF composite membrane. The structure, morphology and physical property of the composite membrane were characterized by FTIR, SEM, contact angle measurement, and dry-wet swelling degree test. The TiO2 was uniformly distributed in the PDMS matrix, and the composite membrane showed higher affinity to formaldehyde than water. The membrane was used to separate the 1000 ppm formaldehyde water solution through a pervaporation (PV) process. The results showed that the membrane could selectively permeate formaldehyde over water and the best separation performance could be achieved at 50°C with a separation factor of 11.25, and a total flux of 187.72 g·m-2·h-1, which were better than the pristine PDMS/PVDF membrane with separation factor of 10.66 and total flux of 115.52 g·m-2·h-1. Hence, adding TiO2 not only increased the membrane flux, but also increased the separation factor of the composite membrane. This study showed that pervaporation technology had the potential for treating formaldehyde wastewater.

Impact of biopolymer purification on the structural characteristics and transport performance of composite polysaccharide membranes for pervaporation

This study discusses the impact of biopolymer purification – by dialysis and by dia-ultrafiltration – on the properties and transport performance of composite polysaccharide membranes for pervaporation. The composite membranes prepared, using as active layer polysaccharides purified by these two methods, were compared in terms of structure, resistance to solvents, mechanical and transport properties.Both composite membranes exhibited identical resistance to organic solvents, but presented significant differences in terms of swelling degree and transport selectivity. It was found that these differences may be caused by the shear stress imposed during purification by the dia-ultrafiltration method, which leads to a disintegration of polysaccharide aggregates. As a consequence denser membranes are obtained, due to smaller polysaccharide aggregates formed, which impact the transport selectivity.Membranes prepared with polysaccharides purified by dia-ultrafiltration revealed to be the best choice for ethanol dehydration by pervaporation, since a water/ethanol selectivity of 143 for 10.0wt% water in ethanol was achieved.

Effects of Dehydration Rate on the Yield of Ethyl Lactate in a Pervaporation-Assisted Esterification Process

Esterification of lactic acid and ethanol is typically a reversible reaction. The yield of ethyl lactate is low due to the limitation of chemical equilibrium. In this study, pervaporation composite membranes (glutaral crosslinked chitosan (GCCS)/carbomer (CP)/polyacrylonitrile (PAN), glutaral crosslinked gelatin (GCGE)/PAN, and glutaral crosslinked hyaluronic acid (GCHA)/hydrolysis modification (HM)-PAN) inspired by the bioadhesion phenomena were fabricated and used for the synthesis of ethyl lactate, which could promote the reaction by removing the water perferentially. The influence of dehydration rate on chemical equilibrium shift in different operating conditions was investigated. Pervaporation-assisted esterification results suggested that the yield of ethyl lactate was determined by the match between reaction rate and dehydration rate. The process is controlled by the reaction rate initially and the dehydration rate as time goes by. The incorporation of the pervaporation process could break the limi...

A Passive Vapor-Feed Direct Methanol Fuel Cell Based on a Composite Pervaporation Membrane

A passive micro direct methanol fuel cell (μDMFC) by using composite pervaporation membrane for vapor fuel supply without any extra power is presented. A simple and power free vaporizer, which consists of a polydimethylsiloxane (PDMS) active layer and a porous silicon support layer, is integrated with a μDMFC, converting the methanol from liquid phase to vapor phase. The novel anode vaporizer generates methanol vapor, which diffuses to and reacts with catalyst directly. The composite membranes with different parameters are prepared and tested to optimize the performance of the membrane vaporizer. The developed prototype exhibits a peak power density of 18.2 mW/cm 2 and a maximum fuel efficiency of 78.4% at room temperature. It is believed that the vapor-feed μDMFC will be more applicable for microsystems.

High performance graphene oxide/polyacrylonitrile composite pervaporation membranes for desalination applications

A GO/PAN pervaporation composite membrane was prepared and exhibited high desalination performance.

Pervaporation composite membranes for ethyl acetate production

This paper continues research on the physicochemical features of nanocomposites of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and fullerene C60 with the purpose of using them as a selective layer of composite membranes in pervaporation coupling esterification of acetic acid with ethanol to produce ethyl acetate. The C60–PPO/MFFC composite membranes containing up to 3wt%C60 were prepared in this work. SEM was employed in visualizing the internal morphology of the membranes. The nature of the interaction between PPO and C60 molecules in composite was studied by NMR. TG analysis reveals the fact of increasing thermal destruction point of the membrane due to certain structural changes of the PPO matrix upon incorporation of the C60 molecules. Transport properties of composite membranes with a selective layer containing up to 3wt%C60 were studied in the pervaporation of the quaternary mixture: ethanol, acetic acid, ethyl acetate, and water in order to identify the availability of their use in the hybrid process “esterification+pervaporation”. The strong permeability enhancement due to the introduction of C60 particles in the PPO network was observed whereas the selectivity was almost steady. The best complex of transport properties was obtained from the 2%C60–PPO/MFFC membrane.

PDMS/PVDF composite pervaporation membrane for the separation of dimethyl carbonate from a methanol solution

In this paper, polydimethylsiloxane (PDMS) composite membranes that were supported using polyvinylidene fluoride (PVDF) microfiltration membrane were developed for the pervaporation (PV) of dimethyl carbonate (DMC) from a methanol solution. Experimental studies on the solubility and the diffusivity of pure DMC and methanol in the membrane were first measured. Higher DMC uptake indicates that the sorption step is the rate-limiting step in the selective transport through the membrane. By controlling the fabricating parameters such as the concentration of the casting membrane solution, composite membranes with different thicknesses from 3 to 160μm were fabricated. When the composite membrane is defect-free, the separation factor is independent of its thickness. The composite membrane with a thickness of 6μm exhibited a separation factor of 3.95 and a normalized total flux of 0.4872kg/m2h in the pervaporation of 28wt% DMC–methanol mixture at 40°C. In addition, the membrane swelling effects, pervaporation performance, and stability were investigated. The results of the PDMS composite membrane exhibited higher and more stable performance in separating DMC from the methanol solution. The PDMS composite membrane can be a suitable PV membrane to separate DMC from a methanol solution.

High performance hydrophilic pervaporation composite membranes for water desalination

A three-layer thin film nanofibrous pervaporation composite (TFNPVC) membrane was prepared by sequential deposition using electrospraying/electrospinning. The poly(vinyl alcohol) (PVA) top barrier layer was first electrosprayed on aluminum foil and its thickness can be easily controlled by adjusting the collecting time. Next a polyacrylonitrile (PAN) nanofibrous scaffold was deposited by electrospinning as a mid-layer support. A nonwoven PET layer is used to complete the composite membrane. The pervaporation desalination performance of TFNPVC membranes was tested using NaCl solutions at 100Pa and at room temperature. The TFNPVC membranes show excellent desalination performance (high water flux and salt rejection >99.5%) for different salt concentrations with virtually no change in performance after 50h of operation.

Preparation and characterization of poly(dimethylsiloxane)-polytetrafluoroethylene (PDMS-PTFE) composite membrane for pervaporation of chloroform from aqueous solution

Hydrophobic polydimethylsiloxane — polytetrafluoroethylene (PDMS-PTFE) flat-sheet membranes for pervaporation (PV) of chloroform from aqueous solution were successfully fabricated by solution casting method. The structures and the performance of the membranes was characterized by X-ray diffraction (XRD), scanning electron microscope combined with energy dispersive X-ray spectroscopy (SEM-EDXS), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and the tests of contact angle and mechanical properties. The adding of PTFE particles (<4 μm) in the PDMS matrix enhanced the crystallinity, hydrophobicity, mechanical strength and thermal stability of the membranes. The examinations showed that the PTFE filled PDMS membranes exhibited striking advantages in flux and separation factor as compared with unfilled PDMS membranes. All the filled PDMS membranes with different PTFE content showed excellent PV properties for the separation of chloroform from water. When the content of the PTFE additive in PDMS composite membrane was 30 wt%, membrane performance was the best at feed temperature 50 °C and permeate-side vacuum 0.101MPa. For the 30% PTFE-PDMS membrane, with the increase of the feed temperature from 30 to 60 °C, the total, water and chloroform fluxes as well as the separation factor increased, the apparent activation energy (ΔEa) of total, chloroform and water were 21.08, 66.65 and 11.49 KJ/mol, respectively, with an increase of chloroform concentration in the feed from 50 to 950 ppm, total, water and chloroform fluxes increased but the separation factor decreased.

Pervaporation performance enhancement through the incorporation of mesoporous silica spheres into PVA membranes

Spherical, discreet, size-monodisperse mesoporous silica particles of 1.8–2μm diameter, with pore diameters of ∼1.8nm were incorporated into a poly (vinyl alcohol) [PVA] polymer to produce composite pervaporation membranes. The selective membrane layers were cast on polyacrylonitrile [PAN]/non-woven fabric supports. The inclusion of particulate silica had beneficial effects on pervaporation performance for the dehydration of ethanol, improving flux throughout the composition range studied, as well as increasing selectivity in all but the highest silica content samples. The unique pervaporation in mesoporous membranes is discussed in terms of polarity and solubility data.

Multiple sprayed composite membranes with high flux for alcohol permselective pervaporation

Alcohol permselective pervaporation is a promising technology for bio-alcohol production. In this study, a multiple spray technique has been developed to prepare hydrophobic composite membranes for alcohol permselective pervaporation. A defect-free permselective layer was successfully obtained by repeated alternate spraying of dihydroxypolydimethylsiloxane (PDMS) and tetraethylorthosilicate with the addition of dibutyltin dilaurate on to a polysulfone ultrafiltration membrane using an automatic spray system. The effects of PDMS molecular weight and concentration, number of spraying cycles, spraying time and standing interval on the membrane performance were intensively investigated. Experiments proved that, compared with the dip-coated membrane, the membrane flux obtained in this way showed a dramatically increase while the selectivity remained at a comparable level. It was found that the multiple spray technique can ensure that there are no defects in the separation layer, by repeated adjustment of the number of spraying cycles, and can also greatly reduce the thickness of a selective layer. In addition, the automatic spray technology removes the inherent unreliability of manual techniques, so is beneficial for large-scale rapid preparation of composite membranes.

Pervaporative recovery of ABE during continuous cultivation: Enhancement of performance

Acetone, butanol and ethanol were produced in a continuous two-stage fermentation integrated with pervaporation using freely suspended cells of C. acetobutylicum ATCC 824. PDMS composite pervaporation membranes were directly coupled to the second fermentor which lead to decreased solvent titers. Overall productivity was increased from 0.45gL−1h−1 to 0.88gL−1h−1 when increasing the carbohydrate concentration in the feed from 60 to 120gL−1. The highest overall productivity of 1.13gL−1h−1 was achieved when increasing the carbohydrate concentration further to 150gL−1 even though productivity decreased significantly in the first fermentor due to substrate inhibition. In this phase that lasted 200h, the average flux reached 0.621kgm−2h−1 and the total solvent concentration in the permeate was 202gL−1. High solvent titers in the second fermentor were beneficial for the performance of the pervaporation unit leading to higher fluxes and total solvent concentrations in the permeate.

Polymeric nanofibrous composite membranes for energy efficient ethanol dehydration

Ethanol derived from the fermentation process (e.g., from corn) is widely used as a blend to improve the air quality and to decrease the demand for gasoline. During the production process, ethanol dehydration is usually carried out by azeotropic distillation, which consumes about twice amount of energy than the “pervaporation” method. The purpose of this study is to demonstrate an energy-efficient nanofibrous composite pervaporation membrane system for production of dehydrated ethanol. The nanofibrous membrane system consists of a cross-linked polyvinyl alcohol hydrophilic barrier layer, an buffer layer based on ultra-fine cellulose nanofibers (diameter about 5 nm), and an electrospun nanofibrous scaffold layer with high porosity (e.g., 80%) and fully interconnected pore structures. The performance between the conventional pervaporation membranes and nanofibrous composite membranes was compared under the same pervaporation conditions.

Polymer/Ceramic Composite Membranes and Their Application in Pervaporation Process

Pervaporation (PV), as an environmental friendly and energy-saving separation technology, has been received increasing attention in recent years. This article reviews the preparation and application of macroporous ceramic-supported polymer composite pervaporation membranes. The separation materials of polymer/ceramic composite membranes presented here include hydrophobic polydimethylsiloxane (PDMS) and hydrophilic poly(vinyl alcohol) (PVA), chitosan (CS) and polyelectrolytes. The effects of ceramic support treatment, polymer solution properties, interfacial adhesion and incorporating or blending modification on the membrane structure and PV performance are discussed. Two in-situ characterization methods developed for polymer/ceramic composite membranes are also covered in the discussion. The applications of these composite membranes in pervaporation process are summarized as well, which contain the bio-fuels recovery, gasoline desulfuration and PV coupled process using PDMS/ceramic composite membrane, and dehydration of alcohols and esters using ceramic-supported PVA or PVA-CS composite membrane. Finally, a brief conclusion remark on polymer/ceramic composite membranes is given and possible future research is outlined.

Optimization of Preparation Conditions for PDMS-Silica Composite Pervaporation Membranes Using Response Surface Methodology

In this article, response surface methodology was used to optimize the preparation conditions of fumed silica filled polydimethylsiloxane/cellulose acetate composite membranes. The silica loading, polydimethylsiloxane concentration, and NH2-C3H6-Si(OC2H5)3/silica weight ratio were considered as factors. Two regression equations, which described the effects of the three factors on the permeation flux and selectivity of the membranes, were derived from the results of 20 experiments by using a statistical software Design-Expert 7.1.4. The results revealed that the three factors had important effects on the permeation flux and the selectivity. The obtained regression equations were confirmed with another four groups of experiments. According to the regression equations, for the separation of an ethanol aqueous solution with the concentration of 10 wt%, the maximum selectivity of the membrane, 11.5 could be obtained at the feed temperature of 40°C, and the corresponding permeation flux was 197.3 g · m−2 · h−1. The preparation conditions for making the composite membrane with the above separation performances were: the silica loading was 5.21 wt%, the polydimethylsiloxane concentration was 13.36 wt%, and the NH2-C3H6-Si(OC2H5)3/silica weight ratio was 0.59.

Improved performance of PDMS/ceramic composite pervaporation membranes by ZSM-5 homogeneously dispersed in PDMS via a surface graft/coating approach

A homogeneous dispersion of inorganic fillers in polymer matrix is a primary challenge for the advancement of mixed matrix membranes (MMMs) in pervaporation and gas separation. In this work, a surface graft/coating approach was developed for homogeneously dispersing ZSM-5 zeolite in polydimethylsiloxane (PDMS) for preparing ZSM-5 filled PDMS mixed matrix/ceramic composite membranes. Molecular dynamics simulations were carried out to calculate the interaction energy between zeolite and PDMS. It was found that surface modification of zeolite particles could highly improve their interaction with PDMS matrix. The SEM images confirmed the uniform dispersions of surface-modified ZSM-5 particles in PDMS matrix even at highest zeolite loading of 40 wt.%. As revealed in the FT-IR analysis and contact angle measurements, the prepared ZSM-5 filled PDMS membranes exhibited less hydroxyl groups and became more hydrophobic with increasing zeolite loading. The pervaporation experiment in 5 wt.% ethanol–water solution indicated that the homogeneously incorporated ZSM-5 particles improved the selectivity of PDMS membrane, and the separation factor of surface-modified ZSM-5 filled PDMS membrane increased gradually with zeolite loading. This effective dispersion method could be instructive for the fabrication of organic–inorganic composite materials.

Pervaporation Separation of Butanol-Water Mixtures Using Polydimethylsiloxane/Ceramic Composite Membrane

Pervaporation has attracted considerable interest owing to its potential application in recovering biobutanol from biomass acetone-butanol-ethanol (ABE) fermentation broth. In this study, butanol was recovered from its aqueous solution using a polydimethylsiloxane (PDMS)/ceramic composite pervaporation membrane. The effects of operating temperature, feed concentration, feed flow rate and operating time on the membrane pervaporation performance were investigated. It was found that with the increase of temperature or butanol concentration in the feed, the total flux through the membrane increased while the separation factor decreased slightly. As the feed flow rate increased, the total flux increased gradually while the separation factor changed little. At 40°C and 1% (by mass) butanol in the feed, the total flux and separation factor of the membrane reached 457.4 g·m −2·h −1 and 26.1, respectively. The membrane with high flux is suitable for recovering butanol from ABE fermentation broth.

A novel atmospheric dielectric barrier discharge (DBD) plasma graft-filling technique to fabricate the composite membranes for pervaporation of aromatic/aliphatic hydrocarbons

A double-plasma grafting strategy for the fabrication of the “pore-filling” composite membranes was proposed herein. By means of atmospheric dielectric barrier discharge (DBD) plasma, the graft copolymer was covalently anchored in the sublayer pores and onto the surface of the asymmetric polyacrylonitrile (PAN) ultrafiltration (UF) membrane through the combination of syn-irradiation grafting and postirradiation grafting of macromonomer poly(ethylene glycol) methacrylate (PEO526OHMA), consequently, a “pore-filling” composite membrane for pervaporation of aromatic/aliphatic hydrocarbons was obtained. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), water contact angle measurements (WCA), and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) were utilized to characterize the composite membrane. The effects of DBD irradiation time, DBD input voltage, macromonomer concentration on the degree of grafting and pervaporation performance of composite membrane for the toluene/n-heptane mixtures (1:4 in mass) at 80°C were investigated. Separation factor αtoluene/n-heptane up to 7.8 and permeate flux up to 1.62kg/m2h were achieved.

Dehydration of ethyl acetate–water mixtures using PVA/ceramic composite pervaporation membrane

Dehydration of ethyl acetate (EAC)–water mixtures by pervaporation (PV) was studied using a ceramic-supported polyvinyl alcohol (PVA) composite membrane. The effects of feed temperature, feed water content and feed flow rate on the PV performance of the membrane were systematically investigated. In addition, swelling experiments were performed to evaluate the sorption characteristic of the membrane. Flory-Huggins and NRTL (non-random two liquid) theories were applied to analyze the interactions of the membrane and penetrants and the mutual interaction between the penetrants. The membrane exhibited high PV performance, the water permeance and selectivity of water to EAC were 1.45 × 10 −5 kg m −2 s −1 kPa −1 and 129, respectively, at 60 °C with the feed water content of 5.1 wt% and the feed flow rate of 252 mL min −1.

Studies on the PVA/P(AA-Co-AN/SiO2)/ PVA Composite Membranes for Pervaporation Dehydration of Methanol

Acrylic acid (AA) and acrylonitrile (AN) were synthesized by solution polymerization with nanometer SiO2. The copolymer solution was made into main body of the membranes, then composited with the polyvinyl alcohol (PVA) acetal membranes, to make the three-layer sandwich composite pervaporation membranes. The adsorption and the preferential sorption characteristics of the membranes were analyzed by studying swelling degree in different concentrations of methanol solution. Furthermore, the structure unit ratios of the P(AA-Co-AN/SiO2) membranes were analyzed by X-ray Photoelectron Spectroscopy (XPS). Pervaporation experiments were carried out using these membranes to separate methanol/water mixture, and results showed that selectivity of the membranes has increased with increasing the ratio of AN, but ?ux decreased. When the comonomer ratio AA/AN was 1/1, for the 98wt% mixtures at 60?, the separate factor was up to 1534, and the permeation ?ux was 583 g/(m2·h). Moreover, the composite membranes also showed good stability by a long-term test of the pervaporation experiments.