Comprehensive analysis on anomalous phenomenon of ethanol-soluble poly(vinyl butyral) membrane for ethanol recovery via pervaporation

Poly(vinyl butyral) (PVB) is selected as a promising ethanol-permselective membrane based on the solubility parameter theory; however, it exhibits anomalous water perm-selectivity in practical pervaporation (PV) process. Comprehensive analysis based on experimental and theoretical methods were carried out to explore the inherent mechanism of the anomalous performance. Firstly, sum frequency generation vibrational spectra and contact angle were developed to quantify the surface reconstruction of membrane in air and ethanol, which indicated that hydrophilic hydroxyl tended to expose on membrane surface with ethanol thus improving the membrane affinity to water. Meanwhile, swelling behaviors proved more water would accumulate in the ethanol swollen membrane. Furthermore, theoretical analysis in terms of sorption and diffusion process, based on the UNIFAC-FV model and Fujita free-volume theory, confirmed the mechanism of anomalous phenomenon of PVB membrane. The comprehensive investigation was expected to provide insights into the basic separation mechanism of PV process.     

Sodium alginate–poly(hydroxyethylmethacrylate) interpenetrating polymeric network membranes for the pervaporation dehydration of ethanol and tetrahydrofuran

Interpenetrating polymeric network (IPN) membranes of sodium alginate (NaAlg) and various amounts of poly(hydroxyethylmethacrylate) (PHEMA) have been prepared and tested for the pervaporation dehydration of ethanol and tetrahydrofuran (THF). The presence of hydrophilic PHEMA in the IPN matrix was found to be responsible for increase in membrane selectivity to water. NaAlg–PHEMA IPN membrane containing 20 wt % of PHEMA exhibited a selectivity of 571 to water for the water–ethanol mixture and 857 for water–THF mixture. These data are much better than those observed for the pristine NaAlg membrane. However, flux of the IPN membranes was smaller than that of pristine NaAlg membrane. Comparatively higher flux values were observed for water–THF mixture than for water–ethanol mixture. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3324–3329, 2006     

Keramische Membran zur Wasserabtrennung aus Lösungsmitteln

Novel hydrophilic SiO_x modified alumina membranes with high separation factors and flux rates have been prepared for the separation of water from organic solvents. The membranes are prepared by the deposition of SiO_x networks inside the γ‐Al₂O₃ layer of a commercial ultrafiltration membrane by hydrolysis of tetraethylorthosilicate in autoclaves at 250°C. The transport resistance of the individual membrane layers to the permeation flux are described by a model. The membranes are stable towards solvents up to at least 150°C. Pervaporation studies show that water can be separated from solvents like acetonitrile, tetrahydrofuran, 2‐isopropanol, ethanol, dimethylsulfoxide, dimethylformamide, phenol. The separation performance of the membranes allows their use in technical separation processes, especially for the remove of water.     

Characteristics of permeation and separation of aqueous alcoholic solutions with chitosan derivative membranes

Permeation and separation characteristics for the feed vapours from aqueous alcoholic solutions through chitosan derivative membranes such as chitosan acetate (GA-ChitoA), chitosan (GA-Chito), and carboxymethyl chitosan acetate (GA-CM-ChitoA) membrane crosslinked with glutaraldehyde were investigated by evapomeation. The GA-Chito and GA-CM-ChitoA membranes prepared from casting solutions containing an optimum amount of glutaraldehyde showed a high permeation rate and high water permselectivity for an azeotropic composition in an aqueous ethanol solution. The permselectivity for water through the GA-CM-ChitoA membrane in evapomeation was in the order of aqueous solutions of methanol < ethanol < 1-propanol. The effect of the chemical and physical structure of these hydrophilic membranes on the permeation and separation characteristics is discussed.     

Tuning the framework polarity in MFI membranes by deboronation: Effect on mass transport

The polarity of a zeolite is an important parameter determining the transport and separation properties in zeolite packed beds and membranes. This study focuses on the systematic variation of the zeolite polarity for membrane applications by varying the amount of silanol groups within the framework of the MFI zeolite by deboronation and consecutive heat treatment from 9 to 4 silanol groups per unit cell. The decrease in the number of silanol groups after heat treatment is confirmed by diffuse reflection infrared Fourier transform (DRIFT) and ²⁹Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The permeation of pure water through the modified silicalite membranes is insensitive to the number of silanol groups, attributed to a decreased adsorption compensated by an increased diffusivity. The ethanol selectivity in water/ethanol mixtures shows an increase with decreasing amount of silanol groups. Residual boron in the zeolite may react with ethanol and decrease its adsorption capacity. A reduction in flux through the debronated MFI membranes was not observed after ethanol/water permeation.     

Design of polymer membrane with permselectivity for water–ethanol mixture. II. Preparation of crosslinked poly(methyl acrylate) membrane with diethylene triamine and its permselectivity

In order to permeate water from a water–ethanol mixture by pervaporation on the basis of the difference in solubility between two components toward a polymer membrane, polymer membrane having polar group, poly(methyl acrylate) (PMA) membrane crosslinked with diethylene triamine (DETA) was prepared. The permselectivity of the membrane was investigated with attention to the feed composition of water–ethanol mixture and the effect of introduction of DETA into the membrane. It is found that water was permeated through PMA–DETA crosslinked membrane preferentially in all ranges of feed composition, the highest permselectivity being observed at 25% ethanol aqueous solution. Moreover, the pervaporation rate of water was found to depend on the ratio of DETA introduction into the membrane. When the ratio of introduction into the membrane was 0.144, water was permeated through the membrane from 25% ethanol aqueous solution at a rate of 1.26 × 10^?1 g m/m² h. These results can be explained by high diffusivity of the membrane due to the low glass transition temperature of PMA and permeation of water through polar DETA moiety in the membrane.     

Molecular dynamics studies of a model polymer-catalyst-carbon interface

Classical molecular dynamics simulations are performed to obtain insights into structural and dynamical behavior of water and O₂ transport through a model polymer membrane, and at the interface of such hydrated polymer with graphite-supported nanocatalyst platinum particles. Water clustering is observed near the membrane hydrophilic sites constituted by sulfonic groups, which due to their affinity with platinum, are located near the metallic surface. It is found that the diffusion of water through the model hydrated polymer membrane depends strongly on the level of membrane hydration due to contribution from various mechanisms whose relative weights change with the degree of hydration. Possible scenarios for O₂ diffusion are also analyzed.     

Solute transport in non‐aqueous nanofiltration: effect of membrane material

Nanofiltration experiments in methanol and ethanol were carried out for six reference components with different molecular weights (MW 228–880) and polarities (logP 0–12). The contribution of diffusion to solute transport, calculations based on results from cell diffusion experiments, was found to be only 1–7%; solute transport occurs mainly by convection. Furthermore, it was found that solute transport is influenced by solute–solvent–membrane interactions. Solvent–solute interactions (solvation) cause a different effective solute diameter in each solvent: it is smaller in ethanol than in methanol, resulting in lower rejections in ethanol than in methanol. Solute rejection increases with increasing molecular size (for components with similar polarity). Solute–membrane interactions were expressed in polarity terms and charge effects. A decrease of the rejection with decreasing solute polarity (for components with similar MW) was observed. Since non‐polar components (high logP) are exposed to smaller repulsion forces from the polymeric membrane material, the resistance against solute permeation is lower for these components. The solvent–membrane interactions were found to result in solvation of the pore wall; the degree of membrane solvation is different for each solvent. It is determined by the affinity between the solvent and the membrane, and by the molecular size of the solvent. In ethanol, hydrophilic membranes show a larger drop in solute rejection than hydrophobic membranes. The differences in solvent–membrane affinity (measured by contact angle) are much smaller for the first membranes, and therefore pore wall solvation decreases with increasing solvent size. Hydrophobic membranes have a much larger affinity for ethanol than for methanol, leading to stronger interactions, but undergo competitive forces due to the larger solvent size. Therefore, the difference in degree of solvation and effective pore diameter is less pronounced. Based on these three observed or postulated interactions, rejections of all six reference solutes in methanol and ethanol could be explained. Copyright © 2005 Society of Chemical Industry     

Improvement of the properties of plasma‐modified ground tire rubber‐filled cement paste

The thesis investigated that the adhesion of ground tire rubber (GTR) to cement can be improved by applying surface plasma modification. The hydrophobic surface of GTR powder has been transformed to a hydrophilic one through plasma treatment. Attenuated total reflectance Fourier transform infrared spectral studies showed the increase in peak intensity at the range of 1400–1600 cm^?1, indicating the generation of carbon–carbon double bond after plasma treatment on the surface of the GTR powder. The X‐ray photoelectron spectroscopic analysis further confirmed the presence of oxygen‐containing polar functional groups on the surface of the GTR powder after atmospheric plasma treatment. The improvements in plastic deformation and elastic deformation that attributed to the enhanced interfacial interaction between modified GTR powder and cement matrix were observed for the modified GTR‐filled cement paste via triaxial test. The pore size distribution testing manifested a better compactness of plasma GTR‐filled cement paste. Besides, scanning electron microscope illustrated that adhesion of modified GTR powder with cement matrix increased. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Peculiar transition observed on the temperature dependence of water permeability of a novel hydrophilic polyamide membrane

Summary The relationship between the logarithmic hydraulic permeability and the reciprocal absolute temperature for a novel hydrophilic polyamide membrane peculiarly refracted at about 27°C, which was inferred to be some kind of transition point of the poly(BOL) in water. Some participation mode of water molecules in polar sites, including inter- and intramolecular hydrogen bonds through amide and ether groups, along poly(BOL) chains may vary discontinuously at the temperature.     

Water and methanol crossover in direct methanol fuel cells—Effect of anode diffusion media

Various anode diffusion media have been experimentally studied to reduce water crossover in a direct methanol fuel cell (DMFC). A two-phase water transport model was also employed to theoretically study their effects on water transport and saturation level in a DMFC anode. It is found that wettability of the anode microporous layer (MPL) has a dramatic effect on water crossover or the water transport coefficient (α) through the membrane. Under different current densities, the MEA with a hydrophobic anode MPL has consistently low α, several times smaller than those with a hydrophilic MPL or without an anode MPL. Methanol transport in the anode is found to be not influenced by a hydrophobic anode MPL but inhibited by a hydrophilic one. Constant-current discharge shows that the MEA with hydrophobic anode MPL displays much smaller voltage fluctuation than that with the hydrophilic one. A modeling study of anode water transport reveals that the liquid saturation in the anode is lowered significantly with the increase of anode MPL contact angle, which is thus identified as a key parameter to minimize water crossover in a DMFC.     

CO2, N2 gas sorption and permeation behavior of chitosan membrane

The sorption equilibria for CO₂ and N₂ in dry chitosan membrane at 20 and 30 ‡C were measured by a pressure decay method. The steady-state permeation rates for CO₂ and N₂ in dry and wet (swollen with water vapor) chitosan membranes at 20 and 30 ‡C were measured by a variable volume method. The sorption equilibrium for N₂ obeyed Henry’s law, whereas that for CO₂ was described apparently by a dual-mode sorption model. This non-linear sorption equilibrium for CO₂ could be interpreted by the interaction of sorbed CO₂ with the chitosan matrix expressed as a reversible reaction. The logarithm of the mean permeability coefficient for CO₂ in dry chitosan membrane increased linearly with upstream gas pressure. A linear increase of the logarithmic mean permeability coefficient for CO₂ with the pressure could be interpreted in terms of a modified free-volume model. The mean per-meability coefficient for N₂ in dry chitosan membrane only slightly increased with upstream gas pressure. The per-meabilities for CO₂ and N₂ in wet chitosan membrane increased by 15 to 17 times and 11 to 15 times, respectively, as compared to those in the dry membrane.     

Preferential separation of ethanol from aqueous solution through hydrophilic polymer membranes

The pervaporation behaviors of aqueous ethanol mixtures through the poly(ethylene oxide) (PEO)/chitosan (CS) blend membrane were investigated. The results show that both CS and PEO/CS membrane preferentially permeate ethanol at a lower alcohol concentration in feed, and the selectivity of CS membrane toward alcohol can be greatly improved by introducing hydrophilic polymer PEO into CS. The PEO/CS blend membrane gave a separation factor of 4.4 and a flux of 0.9 kg m⁻² h for 8 wt % of ethanol in the feed at 20°C. At the same time, the reason introducing PEO can improve alcohol-permselectivity of CS membrane is explained on the basis of experimental data. Blending with PEO made the structure of CS chain looser, which resulted in ethanol molecules passing through easily, on the other hand, strengthened the ability of forming water clusters that inhibit the permeation of water molecules. From the experimental results, although the PEO/CS blend membrane was not a usable membrane with high selectivity to alcohol, a new method to prepare alcohol-permselective membranes appears to be developed by modifying hydrophilic polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1145–1151, 1999     

Ionic salt permeability through phase‐separated membranes composed of amphoteric polymers

Amphoteric copolymers composed of hydrophilic poly(dimethyl acrylamide) and hydrophobic poly(dimethyl siloxane) formed phase‐separated membranes. The hydrophilic and hydrophobic components formed continuous phase‐separated domains in the membranes. The hydrated poly(dimethyl acrylamide) domains formed membrane‐spanning pathways, which permitted an ionic salt to permeate the membranes. The permeability of the ionic salt through the amphoteric copolymer membranes was studied. On the basis of the results, the mechanism of salt transport could be explained by the free‐volume theory, which was used for the analysis of diffusive transport in the hydrated, homogeneous membranes. The diffusion coefficient of the ionic salt increased exponentially as the volume ratio of the hydrophilic polymer to water [(1 − H)/H, where H is the degree of hydration] decreased in the membrane. It was possible to postulate that the diffusion of the ionic salt through the membranes was dependent on the free‐volume fractions of water and hydrophilic poly(dimethyl acrylamide) domains in the membranes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Sorption and transport of methanol and ethanol in H+-nafion

Methanol and ethanol sorption and transport in 1100 equivalent weight H+Nafion were compared to water sorption and transport. Sorption isotherms for methanol and ethanol were fit to a solvation shell model, with four molecules in the first solvation shell. The larger molar volume of alcohols resulted in greater swelling from sorption. Proton conductivity is five times greater for water saturated Nafion than alcohol saturated Nafion. Alcohol pervaporation and alcohol vapor permeation is slower than water pervaporation and water vapor permeation. The Nafion/vapor interfacial transport coefficients for alcohols and water scale with vapor pressure. The diffusivity of water is 3–4 times greater than the diffusivity of methanol and ethanol. The results indicate that alcohols sorb by solvating the sulfonic acid groups, similar to the interaction of water with Nafion. Larger alcohol molecules diffuse slower in the hydrophilic channels of Nafion than the smaller water molecules.     

Mixed Matrix Silicone and Fluorosilicone/Zeolite 4A Membranes for Ethanol Dehydration by Pervaporation

The ability of homogeneous and mixed matrix membranes prepared using standard silicone rubber, poly(dimethylsiloxane) (PDMS), and fluorosilicone rubber, poly(trifluoropropylmethylsiloxane) (PTFPMS), to dehydrate ethanol by pervaporation was evaluated. Although PDMS is generally considered to be the benchmark hydrophobic membrane material in pervaporation, water/ethanol molar permselectivity of a pure PDMS membrane was found to be 0.89 for a feed containing 80/20 w/w ethanol/water at 50°C, indicating a slight selectivity for water. Fluorinated groups in PTFPMS improved the water-ethanol permselectivity to 1.85, but decreased the water permeability from 9.7 × 10^?12 kmol · m/m² · s · kPa in PDMS to 5.1 × 10^?12 kmol · m/m² · s · kPa (29,000 and 15,200 Barrer, respectively). These water permeabilities are attractive, particularly since the rubbery materials should not experience the steep declines in water permeability observed with most standard dehydration membranes as water concentration in the feed decreases. However, the water selectivity is lower than desired for most applications. Particles of hydrophilic zeolite 4A were loaded into both PDMS and PTFPMS matrices in an effort to boost water selectivity and further improve water permeability. Water-ethanol permselectivities as high as 11.5 and water permeabilities as high as 23.2 × 10^?12 kmol · m/m² · s · kPa were observed for the PTFPMS/zeolite 4A mixed matrix membranes?6 times higher than for the unfilled PTFPMS membrane.     

Exclusive and fast water channels in zwitterionic graphene oxide membrane for efficient water–ethanol separation

Graphene oxide (GO) membranes have shown great prospects as the next-generation membranes to tackle many challenging separation issues. However, the employment of GO membranes remains difficult for the precise separation of molecules with strong coupling effect and small size discrepancy such as water–ethanol. Herein, a new strategy of constructing exclusive and fast water channels in GO membrane was proposed to achieve high-performance water–ethanol separation via the synergy between zwitterion-functionalized GO and hydrophilic polyelectrolyte. The as-formed ordered and stable channels possess high-density ionic hydrophilic groups, which benefit from inhibiting the strong coupling between water and ethanol, facilitating the fast permeation of water molecules while suppressing ethanol molecules. As a result, the ultrathin GO-based membrane acquires exceptionally high separation performance with a flux of 3.23 kg/m² h and water–ethanol separation factor of 2,248 when separating water–ethanol (10 wt%/90 wt%) mixture at 343 K. This work paves a feasible way to construct 2D channels for the high-efficiency separation of strong-coupling mixtures.     

Titanate nanotubes-embedded chitosan nanocomposite membranes with high isopropanol dehydration performance

Titanate nanotubes (TNTs) are prepared by a hydrothermal method, and then modified with poly(aspartic acid). Subsequently, they are incorporated into chitosan (CS) to fabricate the modified TNTs (MTNTs)-embedded chitosan hybrid membranes supported by the polyacrylonitrile (PAN) membrane (CS-MTNTs/PAN) and utilized for isopropanol dehydration. The physicochemical properties including physical morphology, chemical interaction, hydrophilicity, crystallinity, thermal stability and free-volume of CS-MTNTs hybrid separation layers are characterized by SEM, FTIR, water contact angle, XRD, TG and PALS analysis, respectively. It is found that the modification of poly(aspartic acid) can apparently improve the interfacial morphology and compatibility between TNTs and membrane matrix. Moreover, the superior isopropanol dehydration performance of CS-MTNTs/PAN composite membranes compared to pure CS membrane is verified via pervaporation experiments, which can be ascribed to the strong hydrophilicity and tubular structure of TNTs. For 90 wt% aqueous solution of isopropanol, the CS-MTNTs/PAN composite membrane containing 6 wt% MTNTs acquires the highest permeation flux and separation factor of 1498 g/m² h and 6237 at 80 °C, respectively. These results indicate the promising application potential of nanotube-filled membranes in the pervaporative dehydration of alcohols.     

Improvement of the properties of ground tire rubber (GTR)‐filled nitrile rubber vulcanizates through plasma surface modification of GTR powder

The surface modification of ground tire rubber (GTR) powder to enhance its adhesion to nitrile rubber (NBR) vulcanizates was investigated. The hydrophobic surface of GTR powder has been transformed to a hydrophilic one through atmospheric pressure dielectric barrier discharge (DBD). The water contact angle dropped markedly from 116 to 0° after being treated for more than 10 s. Attenuated total reflectance Fourier transform infrared spectral (ATR‐FTIR) studies revealed the increase in peak intensity at 3298 and 1640 cm^?1 that correspond to O? H and C?C, respectively, on the surface of the GTR powder. The X‐ray photoelectron spectroscopic (XPS) analysis further confirmed the presence of oxygen containing polar functional groups on the surface of the GTR powder after atmospheric plasma treatment. The improvement in tensile strength and tear strength was observed for the modified GTR‐filled NBR vulcanizates, which is attributed to the enhanced interfacial interaction between modified GTR and NBR matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microstructure dependent diffusion of water-ethanol in swollen poly(vinyl alcohol): A molecular dynamics simulation study

Molecular dynamics (MD) simulation was used to study the swelling properties of poly(vinyl alcohol) (PVA) in ethanol solutions containing 15, 30 and 45 wt% water. The characteristics of the swollen PVA, intrinsic relation between the microstructure of the swollen PVA and the diffusion of water and ethanol in the PVA matrix were analyzed. It was found that the free volume of the swollen PVA reduced with reductions in the degree of crystallinity was accompanied by an increase in the mobility of PVA chains. Water located mostly in the hydrophilic region of the hydroxyl groups of PVA chains; and hydrogen bonding formed between water and PVA. It was also noted water clusters form in the swollen PVA, whose size increased with increasing degree of swelling, whereas ethanol molecules disperse almost individually in the PVA matrix. The diffusion coefficients of water and ethanol in the swollen PVA are predicted to increase linearly with increasing swelling.