Pervaporation dehydration of ethyl acetate aqueous solution using the doubly modified polyvinyl alcohol (PVA) composite membrane

Polyvinyl alcohol–tetraethoxysilane–perfluorosulfonic acid (PVA–TEOS–PFSA) hybrid membrane was prepared by sol–gel method through PVA being modified doubly by PFSA and TEOS. With polyacrylonitrile (PAN) ultrafiltration membrane as a substrate membrane, PVA–TEOS–PFSA/PAN composite membrane was fabricated by dip-coating method for pervaporation (PV) dehydration of ethyl acetate (EAc) aqueous solution. The hybrid membrane was characterized by swelling degree, static contact angle, Fourier transform infrared spectra and scanning electron microscope. Effects of PFSA and TEOS contents in coating solution on PV performance of composite membrane were investigated, respectively. With increasing PFSA content, the permeation flux of composite membrane increased, while the separation factor decreased. Just the opposite, the increase of TEOS content resulted in the decrease in permeation flux and the increase in separation factor. In addition, the PV performances of composite membranes were also investigated at different feed temperatures and water concentrations in feed, respectively. The PVA–TEOS–PFSA/PAN composite membrane, which was prepared from coating with PVA/PFSA mass ratio of 80/20 and TEOS content of 20 wt%, exhibited the permeation flux of 347.9 g m^?2 h^?1 and the separation factor of 2218 for PV dehydration of 2 wt% water of EAc solution at 40 °C.     

Preparation of mullite ceramic microfilter membranes using Response surface methodology based on central composite design

In this paper effect of free silica removal from mullite microfilter membranes using different sodium hydroxide (NaOH) concentrations at different temperatures and for different removal times was studied. The prepared membranes were subjected to XRD, SEM, porosity analysis, and mechanical strength measurement. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiments and analyze three operating parameters including; NaOH solution concentration, NaOH solution temperature and removal time. The optimum porosity of 49.4 was obtained with NaOH solution concentration of 35 wt% at temperature 75 °C and removal time equal to 8 h.Water flux and mechanical strength as important characteristics were measured for all the membranes. For the membrane with the optimum porosity, water flux, mechanical strength, and free silica removal percentage were 61.7 kg/m² h, 21.6 MPa, and 28.2%, respectively. The maximum rejection percentage was 97.2% and emulsion flux for this state was 15.6 kg/m² h at temperature 25 °C and cross flow velocity of 1.5 m/s.     

A novel membrane on pervaporation performance for dehydration of Caprolactam solution

Konjac glucomannan (KGM) is a kind of polysaccharide with wide applications, except in pervaporation (PV). This article focuses on the new function of KGM and simultaneously improving a new dehydration process for ?-Caprolactam (CPL). KGM was cross-linked with glutaraldehyde (GA) at proportions of 0.3, 0.5, and 0.7 wt%. Cross-linked membranes were characterized by scanning electron microscope, Fourier transform-infrared, and X-ray diffraction to assess the membranes of morphology, intermolecular interactions, and observe the effects of cross-linking on crystallinity, respectively. Cross-linked KGM as the active layer of the composite membranes has the net matrix structure, and many characteristics improved compared with pure KGM. Data showed that KGM cross-linked with GA displayed good swelling and PV performance, and the composite membranes had superior separation performances in dehydrating the CPL solution. The highest separation factor could reach 3531. The study provided a new way for both KGM application and CPL dehydration.     

New morphological Ba0.5Sr0.5Co0.8Fe0.2O3−α hollow fibre membranes with high oxygen permeation fluxes

Perovskite Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?α (BSCF) hollow fibre membranes were fabricated by a combined phase inversion and sintering technique. The membranes were characterised by XRD, SEM and tested for air separation. The membrane possesses a novel morphology consisting of one dense layer and one porous layer. Oxygen permeation fluxes through the obtained hollow fibre membranes were measured in the temperature range 650–950 °C using helium sweep gas rates from 50 to 200 mL min^?1. Experimental results indicated the oxygen permeation flux through the BSCF hollow fibre membrane sintered at 1050 °C was approximately 11.46 mL min^?1 cm^?2 at 950 °C when the helium sweep rate was kept at 200 mL min^?1. The BSCF hollow fibre membrane showed a stable oxygen permeation flux of 8.60 mL min^?1 cm^?2 over the investigated period of 120 h at 900 °C.     

Effect of organo clay content on proton conductivity and methanol transport through crosslinked PVA hybrid membrane for direct methanol fuel cell

In the present study, crosslinked poly(vinyl alcohol) (PVA) membranes were prepared using poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA) (PVA:PSSA_MA = 1:7). The PSSA_MA was used both as a crosslinking agent and as a donor of the hydrophilic group (–SO₃H and/or –COOH). The hybrid membranes were prepared by modified clay such as Clay Na⁺, Clay 30B, and Clay 15A. The thermal, water uptake, proton and methanol transport properties of the hybrid membrane were found to be sensitive to the clay type and content. The hybrid membrane with Clay 30B shows higher proton conductivity than other hybrid membranes due to hydroxyethyl group. The membrane with Clay 15A showed the lowest methanol permeability due to lower specific gravity than other clay. Compared to the membrane without modified, the PVA/PSSA_MA/Clay 15A containing 4 wt% of Clay 15A showed both high proton conductivity (0.023 S/cm) and low methanol permeability (2.19 × 10^?7 cm²/s).     

Effects of hypochlorite exposure on flux through polyethersulphone ultrafiltration membranes

Polyethersulphone ultrafiltration membranes with a nominal molecular weight cut off of 10 kDa were degraded in solutions of sodium hypochlorite over a range of pH values at 55 °C to achieve exposure measured in ppm-days of chlorine exposure. The degraded membranes were tested, using an ÄKTAcrossflow? system, for clean water flux, demineralised whey flux and protein rejection. The water fluxes for three membranes (new, 10,000 ppm-day pH 12, and 10,000 ppm-day pH 9) were found to be about 100, 200 and 400 L m^?2 h^?1, respectively with cross flow at 1 bar transmembrane pressure. However whey fluxes were about 23, 5, and 6 L m^?2 h^?1 for the same three membranes. Size exclusion chromatography of the permeates showed significant permeation of α-lactalbumin and β-lactoglobulin through membranes degraded at pH 9 for 20,000 ppm-days, while almost no permeation was found for degradation at pH 12.These results show that hypochlorite degradation affected fluxes by at least two mechanisms. It was likely that membrane pitting increased the pore size causing increased water flux and reduced protein rejection. However hypochlorite also seemed to alter the membrane surface properties, causing the protein to form a less permeable layer that reduced the flux of whey.     

Synthesis and characterization of PVA/PES thin film composite nanofiltration membrane modified with TiO2 nanoparticles for better performance and surface properties

Novel polyethersulfone (PES)/poly (vinyl alcohol) (PVA)/titanium dioxide (TiO₂) composite nanofiltration membranes were prepared by dip-coating of PES membrane in PVA and TiO₂ nanoparticles aqueous solution. Glutaraldehyde (GA) was used as a cross-linker for the composite polymer membrane in order to enhance the chemical, thermal as well as mechanical stabilities. TiO₂ nanoparticles with different concentrations (0, 0.05, 0.1, 0.5 wt.%) were coated on the surface of PVA/PES composite membrane. The morphological study was investigated by atomic force microscopy (AFM), scanning surface microscopy (SEM) and along with X-ray diffraction (XRD). In addition, the membranes performances, in terms of permeate flux, ion rejection and swelling factor were also investigated. It was found that the increase in TiO₂ solution concentration can highly affect the surface morphology and filtration performance of coated membranes. The contact angle measurement and XRD studies indicated that the TiO₂ nanoparticles successfully were coated on the surface of PVA/PES composite membranes. However, rougher surface was obtained for membranes by TiO₂ coating. The filtration performance data showed that the 0.1 wt.% TiO₂-modified membrane presents higher performance in terms of flux and NaCl salt rejection. Finally, TiO₂ modified membranes demonstrated the lower degree of swelling.     

Studies on structural,morphological, electrical and electrochemical properties of activated carbon prepared from sugarcane bagasse

Activated carbon composite was prepared from sugarcane bagasse. The X-ray diffraction revealed the evolution of crystallites of carbon and silica during activation at higher temperature. FTIR spectrum shows the presence of functional groups and silica in the carbon composite. The morphology of the carbon sample was determined by SEM. The surface area, pore volume and pore size distribution of carbon composites were measured. The dc conductivity was determined and conductivity at room temperature was found to increase from 10.22 × 10^?3 to 25.131 × 10^?3 S cm^?1. The samples show good electrochemical property and the specific capacitance in the range of 92–340 F g^?1.     

Processing of alumina-coated clay–diatomite composite membranes for oily wastewater treatment

Crack-free alumina-coated clay–diatomite composite membranes were successfully prepared by a simple pressing and dip-coating route using inexpensive raw materials at a temperature as low as 1000 °C in air. The changes of porosity, flexural strength, pore size, flux, and oil rejection rate of the membranes were investigated while changing the diatomite content. A simple burn-out process subjected to the used membranes in air completely recovered the specific surface area, steady state flux, and oil rejection rate of the virgin membranes. The recycled membranes showed an exceptionally high oil rejection rate (99.9%) with a feed oil concentration of 600 mg/L at an applied pressure of 101 kPa. The typical porosity, pore size, flexural strength, oil rejection rate, and steady state flux of the recycled alumina-coated clay–diatomite composite membrane were 36.5%, 0.12 μm, 32 MPa, 99.9%, and 6.91×10⁻⁶ m³ m⁻² s⁻¹, respectively, at an applied pressure of 101 kPa.     

Development of novel grafted hybrid PVA membranes using glycidyltrimethylammonium chloride for pervaporation separation of water–isopropanol mixtures

Tetraethylorthosilicate incorporated hybrid poly(vinyl alcohol) membranes were grafted with glycidyltrimethylammonium chloride (GTMAC) in different mass%. The resulting membranes were subjected to physico-chemical investigations using Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA) and scanning electron microscopy (SEM). The effects of grafting and feed composition on pervaporation performance of the membranes were systematically investigated. The membrane containing 30 mass% of GTMAC exhibited the highest separation selectivity of 1570 with a flux of 1.92 × 10^?2 kg/m² h at 30 °C for 10 mass% of water in the feed. The total flux and flux of water are almost overlapping each other, manifesting that these membranes could be used effectively to break the azeotropic point of water–isopropanol mixtures. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (E_pw) are two to three times lower than those of isopropanol permeation (E_pIPA), suggesting that the developed membranes have higher separation ability for water–isopropanol system. The E_p and E_D values ranged between 63.73 and 33.07, and 62.78 and 32.75 kJ/mol, respectively. The positive heat of sorption (ΔH_s) values was obtained for all the membranes, suggesting that Henry's mode of sorption is predominant in the process.     

Effect of additives on the properties and performance of cellulose acetate derivative membranes in the separation of isopropanol/water mixtures

In this work, various cellulose acetate (CA) membranes for pervaporation were prepared by the incorporation of different additives, i.e. polyethylene glycol-600 (PEG-600), propylene glycol (PG), and ethylene glycol (EG) to enhance the separation of isopropanol (IPA)/water mixtures. These membranes were characterized by FTIR, DSC, TGA, SEM and UTM. Each additive was responsible for its characteristic effect on the membrane morphology, mechanical strength, permeation flux and separation factor. The SEM micrograph showed that the additives were evenly dispersed in the membrane matrix with the formation of dense membranes. The UTM tests for the membrane reveled that both the Young's Modulus and tensile strength increased with the increase in additive contents. TGA studies for the CA/PEG blend membrane exhibited the highest thermal stability as compared to the CA/PG and CA/EG blends. For each of these synthesized membranes, the separation factor decreased while the permeation flux increased with the increase in additive contents, while the CA/PG membrane with 20 wt.% additive content showed highest permeation flux of 452.27 g/m²h.     

SrCo0.9Sc0.1O3−δ perovskite hollow fibre membranes for air separation at intermediate temperatures

SrCo_0.9Sc_0.1O₃ (SCSc) perovskite powders with sub-micron particle size were synthesized by a modified Pechini method combined with a post-treatment of sintering and ball-milling. From the prepared powders, the SCSc hollow fibre membranes with asymmetric structure and gas-tight property were fabricated by spinning a polymer solution containing 58.4 wt% SCSc followed by sintering at 1200 °C for 5 h. The oxygen permeation properties of the obtained SCSc fibres were measured under air/He gradients at 500–800 °C. This showed the oxygen flux of 1 mL cm^?2 min^?1 at 750 °C and 4.41 mL cm^?2 min^?1 at 900 °C. Modeling analysis reveals that the oxygen permeation process is predominated by oxygen surface exchange kinetics with an activation energy of 95.0 kJ mol^?1. The SCSc membranes showed excellent oxygen permeation performance while exhibiting high structural and permeating stability at intermediate temperatures (500–800 °C).     

Preparation of PFSA‐PVA/PSf hollow fiber membrane for IPA/H2O pervaporation process

Using Na⁺ form of perfluorosulfonic acid (PFSA) and poly(vinyl alcohol) (PVA) as coating materials, polysulfone (PSf) hollow fiber ultrafiltration membrane as a substrate membrane, PFSA‐PVA/PSf hollow fiber composite membrane was fabricated by dip‐coating method. The membranes were post‐treated by two methods of heat treatment and by both heat treatment and chemical crosslinking. Maleic anhydride (MAC) aqueous solution was used as chemical crosslinking agent using 0.5 wt % H₂SO₄ as a catalyst. PFSA‐PVA/PSf hollow fiber composite membranes were used for the pervaporation (PV) separation of isopropanol (IPA)/H₂O mixture. Based on the experimental results, PFSA‐PVA/PSf hollow fiber composite membrane is suitable for the PV dehydration of IPA/H₂O solution. With the increment of heat treatment temperature, the separation factor increased and the total permeation flux decreased. The addition of PVA in PFSA‐PVA coating solution was favorable for the improvement of the separation factor of the composite membranes post‐treated by heat treatment. Compared with the membranes by heat treatment, the separation factors of the composite membranes post‐treated by both heat treatment and chemical crosslinking were evidently improved and reached to be about 520 for 95/5 IPA/water. The membranes post‐treated by heat had some cracks which disappeared after chemical crosslinking for a proper time. Effects of feed temperature on PV performance had some differences for the membranes with different composition of coating layer. The composite membranes with the higher mass fraction of PVA in PFSA‐PVA coating solution were more sensitive to temperature. It was concluded that the proper preparation conditions for the composite membranes were as follows: firstly, heated at 160°C for 1 h, then chemical crosslinking at 40°C for 3 h in 4% MAC aqueous solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Transport properties of cross-linked fullerenol–PVA membranes

Polyhydroxy fullerenes such as fullerenol C₆₀(OH)_22–24 have helped to bridge the gap between fullerenes and their innate solubility issues, where fullerenol solubility in water is 50 mg/ml whereas C₆₀ solubility is 1.3 × 10⁻¹¹ mg/ml. The improved solubility of these fullerene derivatives allows them to be better integrated into composite materials. Here we investigated the transport properties of cross-linked fullerenol–polyvinyl alcohol membranes with the addition of maleic acid for increased stability. High humidity causes the mechanical properties of polyvinyl alcohol to decrease. Using fullerenol as a cross-linker, we were able to decrease the sorption of water with these PVA membranes.     

Mass transfer modeling of equilibrium and dynamic periods during osmotic dehydration of radish in NaCl solutions

Equilibrium and dynamic mass transfer properties of water and solute were investigated during osmotic dehydration (OD) of radish slices in sodium chloride (NaCl) solutions. OD experiments were performed in 0.05, 0.15 and 0.25 g/g solutions at different temperatures (25, 40, 55 and 70 °C) using a brine-to-vegetable mass ratio of 15:1. An analytical solution for unsteady-state mass transfer based on Fick's second law of diffusion was used to mathematically describe water loss and solute gain curves and for the simultaneous estimation of diffusion coefficients and final dehydration–impregnation levels in product. Under such experimental conditions, effective water diffusivity was in the range of 1.85–2.74 × 10^?9 m²/s, whereas solute diffusivity values were between 0.74 × 10^?9 and 2.88 × 10^?9 m²/s. Corresponding dehydration and impregnation levels of radish at equilibrium were estimated between 0.25 and 0.81 g water/g fresh product and 0.01–0.11 g solute/g fresh product, respectively. As demonstrated, current results may be applied to determine the set of conditions (process time, brine concentration and process temperature) yielding an osmodehydrated radish product within given specifications.     

Effect of supercritical CO2 flux,temperature and processing time on physicochemical and morphological properties of commercial reverse osmosis membranes

Coupling supercritical CO₂ (SC-CO₂) extraction with membrane separation leads to energy savings by recycling CO₂ at supercritical state while separating extract components. However, high pressure operating conditions may cause physicochemical and morphological changes in polymer membranes, which in turn can adversely affect membrane performance. In this study, the effect of different flux (50 and 200 kg/m² h), temperature (40 and 80 °C) and time (0–8 h) levels were investigated at 120 bar on two commercial reverse osmosis membranes, AK and SG using contact angle, ATR-FTIR and FE-SEM measurements. Contact angle of AK increased substantially with high flux and high temperature processing unlike SG. The peaks assigned to N–H and carbonyl groups at 1541, 1609 and 1663 cm⁻¹ showed the highest decrease in absorbance with high flux processing while high temperature was more effective on O–H groups between 2700 and 3700 cm⁻¹. AK membrane exhibited the formation of bead-like structures at different processing times and conditions. The effect of SC-CO₂ processing on the membranes varied depending on their chemical structure, which is important to understand for further process development.     

Preparation and characterization of BaCe0.95Tb0.05O3−α hollow fibre membranes for hydrogen permeation

BaCe_0.95Tb_0.05O_3?α (BCTb) perovskite hollow fibre membranes were fabricated by spinning the slurry mixture containing 66.67 wt% BCTb powder, 6.67 wt% polyethersulphone (PESf) and 26.67 wt% N-methyl-2-pyrrolidone (NMP) followed by sintering at elevated temperatures. The influence of sintering temperature on the membrane properties was investigated in terms of crystal phase, morphology, porosity and mechanical strength. In order to obtain gas-tight hollow fibres with sufficient mechanical strength, the sintering temperature should be controlled between 1350 and 1450 °C. Hydrogen permeation through the BCTb hollow fibre membranes was carried out between 700 and 1000 °C using 50% H₂–He mixture as feed on the shell side and N₂ as sweep gas in the fibre lumen. The measured hydrogen permeation flux through the BCTb hollow fibre membranes reached up to 0.422 μmol cm^?2 s^?1 at 1000 °C when the flow rates of the H₂–He feed and the nitrogen sweep were 40 mL min^?1 and 30 mL min^?1, respectively.     

Pervaporation separation of benzene/cyclohexane through AAOM-ionic liquids/polyurethane membranes

Supported ionic liquids/polyurethane (PU) membranes were prepared by immobilizing ionic liquids on a porous anodic aluminum oxide membrane (AAOM) support that was coated on one side with polyurethane (PU). The microstructure of all membranes was characterized using scanning electron microscopy (SEM). The pervaporation separation performance of the supported ionic liquids/polyurethane membranes was investigated for benzene/cyclohexane (Bz/Cy) mixtures. The SEM results demonstrated that the porous surface of the AAOM support was sealed by the dense polyurethane membrane and the pores of the AAOM support were impregnate with ionic liquids. The ionic liquids filling in the AAOM support enhanced the separation selectivity of Bz/Cy. The separation factor of Bz to Cy increased from 5 to 34.4 and the largest PSI of AAOM-[C₄mim]PF₆/PU membrane reached 452.54 g m⁻² h⁻¹ at 55 °C for a 50 wt.% Bz/Cy mixture. Because the polyurethane prevented the leakage of ionic liquids filled in the AAOM support, the supported ionic liquids/polyurethane membranes exhibited excellent stability.     

Preparation and characterization of CMCS/PVA blend membranes and its sorption and pervaporation performance (I)

Novel pervaporation (PV) membranes for ethanol dehydration were prepared by blend poly(vinyl alcohol) (PVA) and carboxymethyl chitosan (CMCS), followed by the crosslinking reaction with glutaraldehyde; the structure and miscibility of the blend membranes were characterized by Fourier transform infrared, X‐ray diffraction, and differential scanning calorimetry; the results indicated that the blends were miscible. The effect of feed concentration, operation temperature, crosslinking agent content, etc. on sorption performance and PV performance of the blend membrane is investigated. The membrane of CMCS/PVA blend ratio of 8 : 2 exhibited a high separation factor of 2959 with a reasonably high water flux value of 0.14 kg m^?2h^?1 at the azeotropic feed composition (95 wt % of ethanol) at a temperature of 45°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A hydrogen-permselective amorphous silica membrane derived from polysilazane

A microporous amorphous silica membrane has been synthesized by thermal conversion in air of polysilazane on a silicon nitride (Si₃N₄) porous substrate. The porous substrate near the surface layer was penetrated by polysilazane, and converted into mesoporous amorphous silica/Si₃N₄ composite layer. Then, an active molecular sieving microporous amorphous silica thin layer was synthesized on the surface of the mesoporous composite layer. The polysilazane-derived amorphous silica membrane exhibited H₂ permeance of 1.3 × 10⁻⁸ mol/m² s Pa at 573 K, and the permeability ratio of H₂/N₂ was measured to be 141. The effects of heat treatment condition on the meso/microporous structure development of the polysilazane-derived amorphous silica within the Si₃N₄ porous substrate are discussed from a viewpoint of fabricating hydrogen-permselective amorphous silica membranes through polymeric precursor route.