Dehydration of 1,4-dioxane by pervaporation using filled and crosslinked polyvinyl alcohol membrane

Polyvinyl alcohol (PVOH) membrane, was modified both physically and chemically by incorporation of inorganic filler, sodium aluminosilicate and chemical crosslinking with maleic acid and glutaraldehyde. The change of morphology and crystallinity of PVOH by this physical and chemical modification was studied by FTIR, DSC, TGA, SEM and XRD. These membranes were evaluated in terms of its potential for dehydration of dioxane by preferential sorption and permeation using pervaporation (PV) technique. These membranes were cast in the laboratory by solution casting from the polymer and other additives. The performance of the unfilled (containing no filler) glutaraldehyde (GA) crosslinked PVOH-1 and maleic acid (MA) crosslinked PVOH-2 membranes were compared with filled (containing aluminosilicate filler) but GA crosslinked PVOH-3 and filled but MA crosslinked PVOH-4 membranes. The filled membranes were found to show higher flux and water selectivity. Among all the four used membranes, the MA crosslinked filled PVOH-4 membrane was found to show best results in terms of both water selectivity and flux.     

Dehydration of aqueous acetonitrile solution by pervaporation using PVA–iron oxide nanocomposite membrane

Pervaporative performances were investigated for dehydration of water–acetonitrile using nanocomposite metal oxide and Pervap^® 2202 membranes. Poly (vinyl alcohol) based nanocomposite metal oxide membranes were prepared through co-precipitation of different amounts of Fe (II) and Fe (III). The freestanding nanocomposite metal oxide membranes were characterized by Transmission electron microscopy and X-ray diffraction. Sorption studies evaluated the extent of interaction and degree of swelling of the membranes. Fe containing PVA polymer matrix showed improved flux and selectivity. In order to observe simultaneous effect of flux and selectivity, pervaporation separation index showed 10 wt.% iron oxide containing membrane is the most amongst all tested. The diffusion coefficients were calculated using pervaporation results and sorption kinetics data. An attempt was made to predict sorption selectivity thermodynamically. PV separation factor was observed to be governed by sorption and/or diffusion phenomena and sorption selectivity was found to be higher than PV separation factor. Prediction of concentration profile in the membrane was also attempted and the results showed that water concentration in the membrane drops down with increase in membrane thickness.     

In-situ complex membrane: Dehydration of pyridine aqueous solution by pervaporation

In this study, we proposed in-situ complex(ISC) membrane as a new type of PIC. We adapted simple acid/base reaction to invent the ISC membrane and applied to the dehydration of pyridine aqueous solution. ISC forms from the interaction of pyridine in feed and acid moiety in membrane and enhances the water transport through the membrane because of its hydrophilic nature. We compared the separation results by using ISC concept with those of non-ISC membranes and investigated the effect of the concentration of acid moiety in the membrane on the dehydration of pyridine/water mixture.     

Dehydration of acetic acid by pervaporation

Pervaporative dehydration of acetic acid over the entire concentration range of 0–100% is studied using four copolymer membranes of acrylonitrile and high performance Nafion and polyimide membranes. From each copolymer of acrylonitrile, three different membranes were produced with three different copolymer compositions. Polyimide showed high water selectivity but very low flux, while Nafion showed highest flux but lowest selectivity. Copolymers of acrylonitriles showed reasonable flux and selectivity behavior. Among the acrylonitrile copolymers, copolymers with hydroxyethyl methylacrylate yielded water selectivity comparable to that of polyimide with much higher flux.     

Dehydration of acetic acid by pervaporation using SPEK-C/PVA blend membranes

Sulfonated cardo polyetherketone (SPEK-C) and poly(vinyl alcohol) (PVA) blend membranes were prepared by solution casting method and used in pervaporation (PV) dehydration of acetic acid. The membranes were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle meter. The results show that thermal crosslinking occurred to the membrane under high temperature annealing. The effective d-spacing (inter-segmental spacing) decreased with PVA content decreasing. The hydrophilicity of the blend membrane increased with SPEK-C content increasing. Swelling and sorption experiments show that the swelling degree of the blend membrane increased, however both the sorption and diffusion selectivities decreased with increasing PVA content. The diffusion selectivity is higher than the sorption selectivity. This suggests that PV dehydration of acetic acid is dominated by the diffusion process. The pervaporation separation index (PSI) of the membrane increases with increasing PVA content and arrives at a maximum when the SPEK-C/PVA ratio is 3/2, then decreases with further addition of PVA. The membrane has an encouraging separation performance with a flux of 492 g m⁻² h⁻¹ and separation factor of 59.3 at 50 °C at the feed water content 10 wt%.     

Continuous ethanol extraction by pervaporation from a membrane bioreactor

In order to obtain a high productivity of ethanol, a membrane bioreactor consisting of a fermentor and a pervaporation system was applied to the continuous alcoholic fermentation process. A microporous hydrophobic polytetrafluoroethylene membrane was used for pervaporation. Glucose medium and baker's yeast were used for the fermentation. Three types of continuous fermentation experiment were carried out: conventional free-cell fermentation as the standard process; a fermentation in which product ethanol was extracted continuously by pervaporation from the membrane bioreactor; and a fermentation in which ethanol was extracted by pervaporation and part of the culture broth was simultaneously removed from the fermentation system.

The fermented ethanol was continuously extracted, and simultaneously concentrated by pervaporation, from the membrane bioreactor, and the extracted ethanol concentration was 6 to 8 times higher than in the broth. A high concentration of microorganisms was realized by immobilizing cells in the membrane bioreactor. When the ethanol concentration in the broth was kept low by pervaporation, the specific rate of ethanol production increased. However, the fraction of viable cells decreased because of the accumulation of inorganic salts fed as a nutrient, of nonvolatile by-products and of aged cells, which were not extracted by pervaporation from the fermentation solution. In order to achieve a high ethanol productivity, part of the fermentation broth must be removed from the membrane bioreactor.     

Polymeric membrane pervaporation

Pervaporation is an efficient membrane process for liquid separation. The past decades had witnessed substantial progress and exciting breakthroughs in both the fundamental and application aspect of pervaporation. This review provided an analytical overview on the potential of pervaporation for separating liquid mixtures in terms of the solubility parameter and the kinetic parameter of solvents. Focus of the review was given to the fundamental understanding of the membrane. Research progress, challenges and opportunities, and the prospect of pervaporation were also discussed. The thermodynamic approach of pervaporation, featuring emphasizing membrane/species interactions, though gained great successes in the past decades, is now facing its toughest challenge in the org–org separation. A kinetic era of pervaporation, featuring emphasizing diffusion selectivity, as well as the synergy between the selective diffusion and sorption, is in the making, and this approach will eventually find solutions to the challenging org–org separation.     

Preparation and pervaporation performance of surface crosslinked PVA/PES composite membrane

This study describes the facile preparation of poly(vinyl alcohol) (PVA)/polyethersulfone (PES) composite membranes by interfacial reaction technique, aiming at acquiring the improved structural and operational stability of the resulting membranes. The effect of interfacial crosslinking agent and hydrophilicity of support layer on the interfacial adhesive strength and pervaporation performance of composite membranes were investigated. The optimal recipe for PVA/PES composite membrane preparation was as follows: PES support layer was treated with 0.1 wt.% borax aqueous solution, fully dried and then immersed into 2 wt.% PVA aqueous solution. The resulting PVA active layer was 1–1.5 μm thick after twice dip-coating. The as-prepared PVA/PES composite membrane exhibited high separation factor of over 438, high permeation flux of 427 g m⁻² h⁻¹ for 80 wt.% EG in the feed at 70 °C and desirable structural stability. It could be derived that adoption of interfacial reaction would be an effective method for preparing the composite membranes suitable for large-scale dehydration of ethylene glycol/water mixture.     

Reduction of concentration polarization in pervaporation using vibrating membrane module

A vibrating membrane module currently marketed for filtration applications was evaluated for the separation of volatile organic compounds (VOCs) from aqueous solutions by pervaporation. Preliminary screening experiments with three VOCs, three silicone membranes, and in the presence and absence of a surfactant were performed to determine if further consideration of the vibrating module for a field demonstration project was warranted. The primary process variables studied were vibrational amplitude and liquid flow rate. The vibrations greatly reduced concentration polarization in the system as inferred from an order of magnitude increase in the overall mass transport coefficient. Mass transfer coefficients for the vibrating module compared favorably with those for traditional spiral wound modules.     

Effect of separating layer in pervaporation composite membrane for MTBE/MeOH separation

The composite membranes with polyvinylalcohol (PVA) as separating layer material and polyacrylonitrile (PAN) or cellulose acetate (CA) as supporting layer material were prepared for separating methyl tert-butyl ether (MTBE)/MeOH mixture by pervaporation (PV). The results showed that PV performance of the composite membrane with PVA membrane as separating layer was superior to that with CA membrane as separating layer, and the PV performance of PVA/CA composite membrane with CA membrane as supporting layer was better. The parameters to prepare the composite membrane remarkably affected PV performance of the composite membrane. The permeate flux of both composite membranes of PVA/PAN and PVA/CA was over 400 g/m² h, and the concentration of MeOH in the permeate reached over 99.9 wt.% for separating MTBE/MeOH mixture.     

Continuous process for singlet oxygenation of hydrophobic substrates in microemulsion using a pervaporation membrane

Chemically generated singlet oxygen (1O2, 1Deltag) is able to oxidize a great deal of hydrophobic substrates from molybdate-catalyzed hydrogen peroxide decomposition, provided a suitable reaction medium such as a microemulsion system is used. However, high substrate concentrations or poorly reactive organics require large amounts of H2O2 that generate high amounts of water and thus destabilize the system. We report results obtained on combining dark singlet oxygenation of hydrophobic substrates in microemulsions with a pervaporation membrane process. To avoid composition alterations after addition of H2O2 during the peroxidation, the reaction mixture circulates through a ceramic membrane module that enables a partial and selective dewatering of the microemulsion. Optimization phase diagrams of sodium molybdate/water/alcohol/anionic surfactant/organic solvent have been elaborated to maximize the catalyst concentration and therefore the reaction rate. The membrane selectivity towards the mixture constituents has been investigated showing that a high retention is observed for the catalyst, for organic solvents and hydrophobic substrates, but not for n-propanol (cosurfactant) and water. The efficiency of such a process is illustrated with the peroxidation of a poorly reactive substrate, viz., beta-pinene.     

Recovery of pyridine from aqueous solution by membrane pervaporation

Three different membranes, based on poly(dimethylsiloxane) (PDMS), cation-exchange material and poly(vinyl alcohol) (PVA) respectively, were tudied for the separation of pyridine-water mixtures by pervaporation. The PDMS membrane was preferentially permeable to pyridine and the other two were selective towards water. Three membranes showed different permeation performance, allowing the application of the technique to the separation of feeds of different composition. The temperature profile of the permeability suggests that it is possible to carry out the operation at an elevated temperature in order to achieve high productivity. A combination of the three types of membranes was designed for the production of anhydrous pyridine from dilute pyridine aqueous solution by pervaporation.     

EPDM as a selective membrane material in pervaporation

Various types of ethylene–propylene-diene terpolymers (EPDM) and crosslinking procedures have been investigated with pervaporation, vapor sorption, liquid sorption and gas permeation experiments. The EPDM parameters that have been changed are ethylene content, molecular weight, choice of third monomer, type of branching and various crosslinking procedures.The permeability coefficients were determined from pervaporation experiments and were about 40,000 Barrer for toluene and 700 Barrer for water. However, from vapor sorption measurements, a value of 22,000 Barrer for toluene was obtained which is somewhat lower. It should be realized that these data can only be compared qualitatively; the permeabilities obtained from sorption isotherms are derived data while in case of the pervaporation experiments it is experimentally measured.There is an indication that toluene behaves independently from water but the presence of toluene does influence the water flux during pervaporation. Gas permeation experiments resulted in permeabilities for CO₂, O₂ and N₂ of 120, 24 and 11 Barrer, respectively. No clear differences were found for both EPDM-variation and different crosslinking procedures.     

Separation of acetic acid-water mixtures by pervaporation through silicalite membrane

Polycrystalline silicalite membranes were prepared on two kinds of porous supports by hydrothermal synthesis. The pervaporation performance of the silicalite membrane obtained was investigated using an acetic acid-water mixture as a feed. The silicalite membrane on the sintered stainless steel support selectively permeates acetic acid in the concentration of the feed acetic acid in the region of 5 to 40 vol%. However, the membrane on the porous alumina support showed no separation for the aqueous acetic acid solution. From the fact that the top layer of the membrane on the alumina support was not composed of pure silicalite but ZSM-5 zeolite crystals, which contained Brønsted acidic sites (Si(OH)Al) in the framework, it was suggested that the acidic sites associated with the framework aluminums play an important role in the separation of the acetic acid-water mixture. A long-term test of the pervaporation was also carried out to clarify the stability of the membrane.     

Chitosan/poly(tetrafluoroethylene) composite membranes using in pervaporation dehydration processes

Chitosan/PTFE composite membranes were prepared from casting a γ-(glycidyloxypropyl)trimethoxysilane (GPTMS)-containing chitosan solution on poly(styrene sulfuric acid) grafted expended poly(tetrafluoroethylene) film surface. The adhesion between the chitosan skin layer and the PTFE substrate was pretty good to warrant the high performance of chitosan/PTFE composite membranes using in pervaporation dehydration processes on isopropanol. The chitosan/PTFE membrane exhibited a permeation flux of 1730 g/m² h and a separation factor of 775 at 70 °C on pervaporation dehydration of a 70 wt% isopropanol aqueous solution. The membrane also survived after a long-term operation test in 45 days.     

Novel crosslinked chitosan/poly(vinylpyrrolidone) blend membranes for dehydrating tetrahydrofuran by the pervaporation technique

Pervaporation separation has been attempted for dehydrating tetrahydrofuran (THF) from its aqueous mixtures using the novel blend membranes of poly(vinylpyrrolidone) (PVP) and chitosan (CS). Membranes were physically blended and crosslinked with glutaraldehyde as well as with sulfuric acid in methanol/sulfuric acid mixture bath to enhance their selectivity and mechanical strength properties. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA) and X-ray diffractometer (X-RD) to assess their intermolecular interactions, thermal stability and crystallinity. Sorption studies were carried out in pure as well as in different compositions of THF + water mixtures to assess polymer–liquid interactions. The membrane exhibited a high selectivity of 1025 with a reasonably high water flux value of 0.0995 kg/m² h at the azeotropic feed composition (94.31 wt.% of THF). Effect of operating parameters such as feed composition, membrane thickness and permeate pressure were evaluated.     

Transport mechanism in ion-exchange pervaporation membranes: Dehydration of water-ethanol mixture by sodium polyethylene sulphonate membranes

Pervaporation of a water-ethanol mixture with sulphonated polyethylene membranes of various capacities at various temperatures and for various feed compositions was studied both theoretically and experimentally. A model is proposed that accounts both for the effects of partial immobilization of water in the membrane due to adsorption by the groups and for the obstruction effect of the polymer matrix on the basis of percolation arguments. Analysis of the pervaporation data against the results of previous sorption experiments showed that the model is in fair agreement with the experiment. A number of peculiarities not predicted by the model and not observed for ethanol transport, such as enhanced diffusivity and selectivity and reduced apparent activation energy, were observed concerning the transport of water. These deviations are explained by assuming the existence of a selective facilitated mechanism of water transport. Other possible mechanisms are also discussed.