Pervaporation dehydration of ethylene glycol with chitosan–poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios

Chitosan–poly(vinyl alcohol), CS–PVA, blended membranes were prepared by solution casting of varying proportions of CS and PVA. The blend membranes were then crosslinked interfacially with trimesoyl chloride (TMC)/hexane. The physiochemical properties of the blend membranes were determined using Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), tensile test and contact angle measurements. Results from ATR-FTIR show that TMC has crosslinked the blend membranes successfully, and results of XRD and DSC show a corresponding decrease in crystallinity and increase in melting point, respectively. The crosslinked CS–PVA blend membranes also show improved mechanical strength but lower flexibility in tensile testing as compared to uncrosslinked membranes. Contact angle results show that crosslinking has decreased the surface hydrophilicity of the blend membranes. The blend membrane properties, including contact angle, melting point and tensile strength, change with a variation in the blending ratio. They appear to reach a maximum when the CS content is at 75 wt%. In general, the crosslinked blend membranes show excellent stability during the pervaporation (PV) dehydration of ethylene glycol–water mixtures (10–90 wt% EG) at different temperatures (25–70 °C). At 70 °C, for 90 wt% EG in the feed mixture, the crosslinked blend membrane with 75 wt% CS shows the highest total flux of 0.46 kg/(m² h) and best selectivity of 986. The blending ratio of 75 wt% CS is recommended as the optimized ratio in the preparation of CS–PVA blend membranes for pervaporation dehydration of ethylene glycol.     

Pervaporation separation of water + 1,4-dioxane and water + tetrahydrofuran mixtures using sodium alginate and its blend membranes with hydroxyethylcellulose—A comparative study

Sodium alginate and hydroxyethylcellulose blend membranes were prepared by solution casting, crosslinked with glutaraldehyde and urea–formaldehyde–sulfuric acid mixture. Crosslinking was confirmed by Fourier transform infrared spectroscopy, while the blend compatibility was studied by differential scanning calorimetry and scanning electron microscopy. Membranes were tested for pervaporation separation of feed mixtures ranging from 10 to 50 mass% water in water + 1,4-dioxane and water + tetrahydrofuran mixtures at 30 °C. For 10 mass% of the feed mixture, pervaporation experiments were also carried out at higher temperatures (40 and 50 °C). By increasing the temperature, a slight increase in flux with a considerable decrease in selectivity was observed for all the membranes and for both the mixtures. The blend membranes exhibited different pervaporation performance for both the binary mixtures investigated. For water + 1,4-dioxane mixture, the pervaporation performance did not improve much after blending, whereas for water + tetrahydrofuran mixture, the pervaporation performance has improved considerably over that of plain sodium alginate membrane.     

Pervaporation separation of aromatic/aliphatic hydrocarbons by crosslinked poly(methyl acrylate-co-acrylic acid) membranes

Copolymers of methyl acrylate and acrylic acid were synthesized to fabricate membranes ionically crosslinked using aluminum acetylacetonate for the separation of toluene/i-octane mixtures by pervaporation at high temperatures. The formation of the ionic crosslinking via bare aluminum cations was characterized by UV–VIS spectroscopy and solubility tests. Reproducibility and the reliability of the methodology for membrane formation and crosslinking were confirmed. The effects of acrylic acid content, crosslinking conditions, pervaporation temperature, and feed composition on the normalized flux and the selectivity for toluene/i-octane mixtures were determined. A typical crosslinked membrane showed a normalized flux of 26 kg μm m⁻² h⁻¹ and a selectivity of 13 for a 50/50 wt.% feed mixture at 100°C. The pervaporation properties including solubility selectivity and diffusivity selectivity are discussed in terms of swelling behavior. The performance of the current membranes were benchmarked against other membrane materials reported in the literature.     

Different viscosity grade sodium alginate and modified sodium alginate membranes in pervaporation separation of water + acetic acid and water + isopropanol mixtures

Different viscosity grade sodium alginate (NaAlg) membranes and modified sodium alginate membranes prepared by solution casting method and crosslinked with glutaraldehyde in methanol:water (75:25) mixture were used in pervaporation (PV) separation of water+acetic acid (HAc) and water+isopropanol mixtures at 30 °C for feed mixtures containing 10–50 mass% of water. Equilibrium swelling experiments were performed at 30 °C in order to study the stability of membrane in the fluid environment. Membranes prepared from low viscosity grade sodium alginate showed the highest separation selectivity of 15.7 for 10 mass% of water in the feed mixture, whereas membranes prepared with high viscosity grade sodium alginate exhibited a selectivity of 14.4 with a slightly higher flux than that observed for the low viscosity grade sodium alginate membrane. In an effort to increase the PV performance, low viscosity grade sodium alginate was modified by adding 10 mass% of polyethylene glycol (PEG) with varying amounts of poly(vinyl alcohol) (PVA) from 5 to 20 mass%. The modified membranes containing 10 mass% PEG and 5 mass% PVA showed an increase in selectivity up to 40.3 with almost no change in flux. By increasing the amount of PVA from 10 to 20 mass% and keeping 10 mass% of PEG, separation selectivity decreased systematically, but flux increased with increasing PVA content. The modified sodium alginate membrane with 5% PVA was further studied for the PV separation of water+isopropanol mixture for which highest selectivity of 3591 was observed. Temperature effect on pervaporation separation was studied for all the membranes; with increasing temperature, flux increased while selectivity decreased. Calculated Arrhenius parameters for permeation and diffusion processes varied depending upon the nature of the membrane.     

Composite poly(vinyl alcohol)–poly(sulfone) membranes crosslinked by trimesoyl chloride: Characterization and dehydration of ethylene glycol–water mixtures

Composite membranes prepared from poly(vinyl alcohol) and poly(sulfone) were crosslinked with trimesoyl chloride (TMC) solutions. The degree of crosslinking, crystallinity, surface roughness and hydrophobicity of the crosslinked PVA–PSf membranes were determined from attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM) and contact angle measurements, respectively. Results showed a consistent trend of changes in the physicochemical properties: the degree of crosslinking, crystallinity, surface roughness, hydrophobicity and swelling degree all decrease with increasing crosslinking agent (TMC) concentration and reaction time. The crosslinked membrane performance was assessed with pervaporation dehydration of ethylene glycol solutions at a range of concentrations (30–90 wt% EG) in the feed mixtures. The total flux of permeation was found to decrease, while the selectivity to increase, with increasing TMC concentration and reaction time. The decrease in flux was most prominent at low EG concentrations in the feed mixtures. In addition, the temperature effect on the pervaporation dehydration was investigated in relation to solution–diffusion mechanisms.     

Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol)

Homogeneous membranes were prepared by blending poly(acrylic acid) with poly(vinyl alcohol). These blend membranes were evaluated for the selective separation of alcohols from toluene by pervaporation. The flux and selectivity of the membranes were determined both as a function of the blend composition and of the feed mixture composition. The results showed that a polymer blending method could be very useful to develop new membranes with improved permselectivity. The pervaporation properties could be optimized by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing poly(vinyl alcohol) content for both methanol—toluene and ethanol—toluene liquid mixtures. The alcohols permeated preferentially through all tested blend membranes, and the selectivity values increased with increasing poly(vinyl alcohol) content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The fluxes increased exponentially with increasing alcohol concentration in the feed mixtures, whereas the selectivities decreased for both liquid mixtures.     

Pervaporation with chitosan membranes II. Blend membranes of chitosan and polyacrylic acid and comparison of homogeneous and composite membrane based on polyelectrolyte complexes of chitosan and polyacrylic acid for the separation of ethanol-water mixtures

Three different types of blend membranes based on chitosan and polyacrylic acid were prepared from homogeneous polymer solution and their performance on the pervaporation separation of water-ethanol mixtures was investigated. It was found that all membranes are highly water-selective. The temperature dependence of membrane permselectivity for the feed solutions of higher water content (>30 wt%) was unusual in that both permeability and separation factor increased with increase in temperature. This phenomenon might be explained from the aspect of activation energy and suggested that the sorption contribution to activation energy of permeation should not always be ignored when strong interaction occurs in the pervaporation membrane system.A comparison of pervaporation performance between composite and homogeneous membranes was also studied. Typical pervaporation results at 30°C for a 95 wt% ethanol aqueous solution were: for the homogeneous membrane, permeation flux = 33 g/m² h, separation factor = 2216; and for the composite membrane, permeation flux = 132 g/m² h, separation factor = 1008. A transport model consisting of dense layer and porous substrate in series was developed to describe the effect of porous substrate on pervaporation performance.     

Recent advances in sodium alginate-based membranes for dehydration of aqueous ethanol through pervaporation

Sodium alginate (SA) is a progressive material for membrane fabrication. The technological development of SA-based membranes has made a significant contribution to the separation techniques, especially in aqueous organic solutions. The outstanding performance of SA is attributed to its outstanding structural flexibility and hydrophilicity. In view of structural characteristics, SA membranes have immense utilization in the pervaporation separation of organics. Among various organics, dehydration of aqueous ethanol is employed as a standard to check the success of pervaporation (PV) membrane. Because ethanol and water have comparable molecular sizes, thus difficult to extract water from aqueous ethanol mixtures than it is for other organics. A literature survey shows that wide-ranging data are available on the PV performance of SA and its modified membranes. In this context, the present review addresses the recent advances made in SA membranes for enhanced ethanol dehydration performance during the last decade. Available data since 2010 has been compiled for grafted, crosslinked, blend, mixed matrix, and composite hybrid sodium alginate membranes in terms of separation factor, permeation flux, and pervaporation separation index PSI. The data are assessed with reference to the effect of feed composition, membrane selectivity, flux, and swelling behavior.     

Poly(vinyl alcohol)/poly(methyl methacrylate) blend membranes for pervaporation separation of water + isopropanol and water + 1,4-dioxane mixtures

Pervaporation (PV) separation of water + isopropanol and water + 1,4-dioxane mixtures has been attempted using the blend membranes of poly(vinyl alcohol) (PVA) with 5 wt.% of poly(methyl methacrylate) (PMMA). These results have been compared with the plain PVA membrane. Both plain PVA and PVA/PMMA blend membranes have been crosslinked with glutaraldehyde in an acidic medium. The membranes were characterized by differential scanning calorimetry and universal testing machine. Pervaporation separation experiments have been performed at 30 °C for 10, 15, 20, 30 and 40 wt.% of feed water mixtures containing isopropanol as well as 1,4-dioxane. PVA/PMMA blend membrane has shown a selectivity of 400 for 10 wt.% of water in water + isopropanol feed, while for water + 1,4-dioxane feed mixture, membrane selectivity to water was 104 at 30 °C. For both the feed mixtures, selectivity for the blend membrane was higher than that observed for plain PVA membrane, but flux of the blend membrane was lower than that observed for the plain PVA membrane. Membranes of this study are able to remove as much as 98 wt.% of water from the feed mixtures of water + isopropanol, while 92 wt.% of water was removed from water + 1,4-dioxane feed mixtures at 30 °C. Flux of water increased for both the feed mixtures, while the selectivity decreased at higher feed water concentrations. The same trends were observed at 40 and 50 °C for 10, 15 and 20 wt.% of water mixtures containing isopropanol as well as 1,4-dioxane feed mixtures, which also covered their azeotropic composition ranges. Membrane performance was studied by calculating flux (J_p), selectivity (), pervaporation separation index (PSI) and enrichment factor (β). Permeation flux followed the Arrhenius trend over the range of temperatures investigated. It was found that by introducing a hydrophobic PMMA polymer into a hydrophilic PVA, the selectivity increased dramatically, while flux decreased compared to plain PVA, due to a loss in PVA chain relaxation.     

Characteristics of sodium alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures

Alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures were prepared and tested. The sodium alginate membrane was water soluble and mechanically weak but it showed promising performance for the pervaporation dehydration. To control the water solubility the sodium alginate membrane was crosslinked ionically using various divalent and trivalent ions. Among them the alginate membrane crosslinked with Ca²⁺ ion showed the highest pervaporation performance in terms of the flux and separation factors.     

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 1,4-dioxane through blend membranes of poly(vinyl alcohol) and chitosan by pervaporation

Blend membranes prepared from poly(vinyl alcohol) (PVA) and chitosan (CS) were crosslinked with glutaraldehyde and used in the pervaporation dehydration of 1,4-dioxane. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (X-RD) to assess, respectively, the intermolecular interactions, thermal stability and crystallinity. Equilibrium sorption studies were carried out in pure liquids and binary mixtures of different compositions of water + 1,4-dioxane mixtures to assess the polymer–liquid interactions. The crosslinked membrane showed a good potential in breaking the azeotrope of 82 wt.% aqueous 1,4-dioxane giving a selectivity of 117 with a reasonable water flux of 0.37 kg/m² h. The effect of operating parameters such as feed composition, membrane thickness and permeate pressure was evaluated.     

Performance of Commercial and Laboratory Membranes for Recovering Bioethanol from Fermentation Broth by Thermopervaporation

A poly[1-(trimethylsilyl)-1-propyne] membrane was studied in a thermopervaporation process for ethanol recovery from fermentation media. Four commercial composite membranes based on polysiloxanes (Pervap 4060, Pervatech PDMS, PolyAn, and MDK-3) were studied for comparison. The dependences of the permeate flux, permeate concentration, separation factor, and pervaporation separation index on the temperature of the feed mixture (5 wt % ethanol in water) were obtained. The maximal values of the ethanol concentration in the permeate (35 wt %) and separation factor (10.2) were obtained for the poly[1-(trimethylsilyl)-1-propyne] membrane, whereas the PolyAn membrane provided the highest permeate flux (5.4 kg m^–2 h^–1). The ethanol/ water separation factor for the systems studied has a maximum at 60°С; this temperature of the feed mixture is optimum for recovering ethanol from aqueous media by thermopervaporation. The existing membranes based on polysiloxanes show low ethanol–water selectivity (less than 1). Poly[1-(trimethylsilyl)-1-propyne] membranes are the most promising for recovering bioethanol from fermentation mixtures by thermopervaporation, because they showed the highest selectivity to ethanol.     

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.     

Novel nanocomposite pervaporation membranes composed of poly(vinyl alcohol) and chitosan-wrapped carbon nanotube

Novel nanocomposite membranes (PVA–CNT(CS)) were prepared by incorporating chitosan-wrapped multiwalled carbon nanotube (MWNT) into poly(vinyl alcohol) (PVA). To further explore the intrinsic correlation between pervaporation performance and free volume characteristics, molecular dynamics simulation was first introduced to qualitatively analyze the contribution of carbon nanotube incorporation on improving free volume characteristics of the nanocomposite membranes. Secondly, the pervaporation performance of PVA–CNT(CS) nanocomposite membranes was investigated using permeation flux and separation factor as evaluating parameters. For benzene/cyclohexane (50/50, w/w) mixtures at 323 K, permeation flux and separation factor of pure PVA membrane are only 20.3 g/(m² h) and 9.6, respectively, while the corresponding values of PVA–CNT(CS) (CNT content: 1%) nanocomposite membrane are 65.9 g/(m² h) and 53.4. In order to explain the simultaneous increase of permeation flux and separation factor, as well as to check the calculation reliability of molecular dynamics simulation, positron annihilation lifetime spectroscopy (PALS) analysis was employed.     

PVA/PVP共混交联膜的渗透蒸发分离性质(Ⅰ)

研究了4,4'-双叠氮芪-2,2'-二磺酸钠和戊二醛对聚乙烯吡咯烷酮(PVP)、聚乙烯醇(PVA)共混膜的交联及交联对共混膜分离恒沸点附近的乙醇/水混合物的影响.结果表明,膜的分离性质随着膜中PVP含量的增加而改变;采用混合型交联剂对PVA/PVP共混膜交联能明显改善膜的选择性.     

A Uniformly Oriented MFI Membrane for Improved CO2 Separation

Membrane separation of CO₂ from natural gas, biogas, synthesis gas, and flu gas is a simple and energy‐efficient alternative to other separation techniques. But results for CO₂‐selective permeance have always been achieved by randomly oriented and thick zeolite membranes. Thin, oriented membranes have great potential to realize high‐flux and high‐selectivity separation of mixtures at low energy cost. We now report a facile method for preparing silica MFI membranes in fluoride media on a graded alumina support. In the resulting membrane straight channels are uniformly vertically aligned and the membrane has a thickness of 0.5 μm. The membrane showed a separation selectivity of 109 for CO₂/H₂ mixtures and a CO₂ permeance of 51×10^?7 mol m^?2 s^?1 Pa^?1 at ?35 °C, making it promising for practical CO₂ separation from mixtures.     

Preparation and Pervaporation Performances of PEA‐based Polyurethaneurea and Polyurethaneimide Membranes to Benzene/Cyclohexane Mixture

Pervaporation is promising in the separation of benzene/cyclohexane mixture for the petrochemical industry. Two kinds of pervaporation membrane materials, including PEA‐based polyurethaneurea (PUU) and polyurethaneimide (PUI), were successfully synthesized from the same soft segment of poly(ethylene adipate)diol (PEA) and different hard segments via a two‐step method. The hard segment of PUU was prepared from toluene diisocyanate (TDI) and 4,4′‐diaminodiphenyl methane (MDA), while that of PUI was from 4,4′‐methylene‐bis(phenylisocyanate) (MDI) and pyromellitic dianhydride (PMDA). The structures and properties of PUU and PUI were characterized by means of FT‐IR, DSC and TGA. During the pervaporation experiment, the PUI membranes had a flux of 12.13 kg µm m^?2 h^?1 and separation factor of 8.25, while the PUU membranes had a flux of 26.35 kg µm m^?2 h^?1 and separation factor of 6.29 for 50 wt% benzene in the benzene/cyclohexane mixture at 40°C. The effects of the structures of hard segments on pervaporation performances were discussed. The investigation of the relationship in molecular structure and PV performances will be helpful for the choice and design of membrane materials in the separation of benzene/cyclohexane mixture.     

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.     

Poly (caprolactone)/poly (ethylene glycol) pervaporation blend membranes: Synthesis,characterization, and performance

Poly (caprolactone) membranes with addition of different poly (ethylene glycol) concentrations were prepared for separation of water/isopropanol azeotropic mixture by pervaporation process. Different characterization tests including Fourier transform infrared, scanning electron microscopy, water contact angle, and thermogravimetric analysis were carried out on the prepared membranes. In addition, the effect of poly (ethylene glycol) PEG content on the swelling degree and the performance of the prepared membranes in pervaporation process were investigated. According to the obtained results, all the membranes were water selective and the blend membrane containing 3 wt% PEG exhibited the best pervaporation performance with a water flux of 0.517 kg/m² hour and separation factor of 1642 at the ambient temperature. Hydrophilicity improvement of the blend membranes was confirmed by constant decrease in water contact angle of the membranes as PEG content increased in the casting solution. Scanning electron microscopy cross‐sectional images indicated that the blend membranes containing PEG had a closed cellular structure. Furthermore, mechanical and thermal properties of the membranes decreased by adding PEG.