Separation of acid–water mixtures by pervaporation using nanoparticle filled mixed matrix copolymer membranes

BACKGROUND: Low energy and less expensive membrane based separation of acetic acid‐water mixtures would be a better alternative to conventional separation processes. However, suitable acid resistant membranes are still lacking. Thus, the objective of the present study was to develop mixed matrix membrane (MMM) which would allow high flux and water selectivity over a wide range of feed concentrations of acid in water. RESULTS: Three MMMs, namely PANBA0.5, PANBA1.5 and PANBA3 were made by emulsion copolymerization of acrylonitrile (AN) and butyl acrylate (BA) with 5.5:1 comonomer ratio and in situ incorporation of 0.5, 1.5 and 3 wt%, sodium montmorilonite (Na‐MMT) nanofillers, respectively. For a feed concentration of 99.5 wt% of acid in water the membranes show good permeation flux (2.61, 3.19, 3.97 kg m^?2 h^?1 µm^?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and very high separation factors for water (1473, 1370, 1292 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at 30 °C. Similarly for a dilute acid–water solution, i.e. for 71.6 wt% acid the membrane showed a very high thickness normalize flux (8.67, 9.44, 11.56 kg m^?2 h^?1 µm^?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and good water selectivity (101.7, 95.3, 79 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at the same feed temperature. The permeation ratio, permeability, diffusion coefficient and activation energy for permeation of the membranes were also estimated. CONCLUSION: Unlike most of the reported membranes, the present MMMs allowed high flux and selectivity over a wide range of feed concentrations. These membranes may also be effective for separating other similar organic‐water mixtures. Copyright © 2012 Society of Chemical Industry     

Dehydration of glycerin/water mixtures by pervaporation using homo and copolymer membranes

Separation characteristics of glycerol/water mixtures were studied using hydrophilic poly(acrylonitrile-comethacrylic acid) (PANMAC), poly(acrylonitrile-co-hydroxyethyl methacrylate) (PANHEMA), Poly(vinyl alcohol) GFT-1001, and poly(vinyl alcohol) (PVA) crosslinked with maleic anhydride (PVAManh) membranes. All membranes were found to be highly water selective. PVAManh membrane yielded the highest permeation flux for water over the entire range of water concentration studied. Homopolymers (PVAManh and GFT-1001) gave better permeation rates than copolymer membranes (PANHEMA and PANMAC). But the swelling of homopolymers is nuch greater than that of copolymers, which is why PVA membranes have poor longevity. No effect on selectivity of the membrane was observed with a change in operating parameters. No decomposition/polymerization of glycerin was observed, as there was no involvement of high temperatures as there is with distillation. A comparison of pervaporation with vapor-liquid equilibrium data showed that pervaporation of glycerin/water mixtures yielded better selectivity than vapor-liquid equilibrium, particularly for glycerol concentrations above 90 wt%.     

Characterization of permeation behaviors of ethanol–water mixtures through sodium alginate membrane with crosslinking gradient during pervaporation separation

Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique, which had different extents of crosslinking gradient structures. The SA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while blocking the other side by a polyester film to prevent the reaction solution from contacting it. The extent of the crosslinking gradient was controlled by the exposing time. When the swelling measurements were performed with uniformly crosslinked membranes in aqueous solutions of 70–90 wt % ethanol contents, it was observed that the crosslinking could reduce both the solubility of water in the membrane and the permselectivity of the membrane toward water. The pervaporation separation of the ethanol–water mixture of 90 wt % ethanol content was carried out with membranes with different extents of crosslinking gradients. As the crosslinking gradient was developed more across the membrane, the resulting flux as well as the separation factor to water was found to decrease while the membrane became stable against water. The pervaporation performances of the membranes with different membrane loadings in a membrane cell were also discussed using the schematic concentration and activity profiles of the permeant developed in them. The pervaporation separations of the ethanol/water mixtures through the membrane with an optimal crosslinking gradient were performed at different feed compositions and temperatures ranging from 40 to 80°C. The change in the membrane performance due to the relaxation process during pervaporation was observed with the operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis of the experimental data of the membrane performance measured by repeating the operation in a given temperature range. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1607–1619, 1998     

Separation characteristics of acetic acid–water mixtures by using poly(vinyl alcohol‐g‐4‐vinyl pyridine) membranes by pervaporation and temperature difference evapomeation techniques

The separation of acetic acid–water mixtures was carried by using pervaporation (PV) and temperature difference evapomeation (TDEV) methods. For the separation process 4‐vinyl pyridine was grafted on poly(vinyl alcohol). Membranes were prepared from the graft‐copolymer by casting method and crosslinked by heat treatment. The effect of feed composition on the separation characteristics was studied and the performances of the separation methods were compared. Permeation rates obtained in PV were found to be high, whereas separation factors were high in TDEV method. Membranes gave permeation rates of 0.1–3.0 kg/(m² h) and separation factors of 2.0–61.0, depending on the composition of the feed mixture and the method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2030–2039, 2006     

Separation characteristics of acetic acid–water mixtures using poly(vinyl alcohol‐g‐4‐vinyl pyridine) membranes by pervaporation and temperature difference evapomeation techniques

The separation of acetic acid–water mixtures was carried out using pervaporation (PV) and temperature difference evapomeation (TDEV) methods. For the separation process, 4‐vinyl pyridine was grafted on poly(vinyl alcohol). Membranes were prepared from the graft‐copolymer by casting method and crosslinked by heat treatment. The effects of feed composition on the separation characteristics were studied and the performances of the separation methods were compared. Permeation rates were found to be high in PV whereas separation factors were high in TDEV method. Membranes gave permeation rates of 0.1–3.0 kg/m²h and separation factors of 2.0–61.0 depending on the composition of the feed mixture and the method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1385–1394, 2006     

Separation of phenol–water mixture by membrane pervaporation using polyimide membranes

Separation of components of aqueous waste streams containing organic pollutants is not only industrially very important but also is a challenging process. In this study, separation of a phenol–water mixture was carried out by using a membrane pervaporation technique with indigenously developed polyimide membranes. The membranes were found to permeate water selectively. The total flux as well as that of the individual components were measured. The effect of lithium chloride modification of polyimide film on total flux was investigated. The total flux obtained with 2% lithium chloride modification was about 3.6 times higher than that obtained with virgin membrane. The effects of different parameters such as feed composition and temperature on flux, and separation factor were determined. With modified membrane, a separation factor as high as 18.0 was obtained for water at 27°C and with 8.0 wt % phenol solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 822–829, 2002     

Performance of a rotating disc contactor using the system carbon tetrachloride–acetic acid–water

A typical rotating disc contactor of small scale was examined using the system carbon tetrachloride–acetic acid–water. The efficiency of extraction was established experimentally for a range of operating variables including rotational speed and phase flow rates and ratios. The results are compared with those of Russian authors for the same liquid system.     

Characterization and pervaporation of chlorinated hydrocarbon–water mixtures with fluoroalkyl methacrylate‐grafted PDMS membrane

It is desirable to enhance the selectivity of a polydimethylsiloxane (PDMS) membrane for chlorinated hydrocarbons. In this study, the PDMS membranes were improved by graft polymerization of 1H,1H,9H‐hexadecafluorononyl methacrylate (HDFNMA), which has the effect of increasing the selectivity for chlorinated hydrocarbons. The PDMS membrane and HDFNMA were irradiated simultaneously by a ⁶⁰Co source. The grafted membranes had a microphase‐separated structure, that is, a separated structure of PDMS and grafted HDFNMA. In the grafted PDMS membrane, a great separation performance for a TCE–water mixture was shown due to the introduction of the hydrophobic polymer, poly(HDFNMA). For the permeation of the grafted PDMS membrane, the permeability of molecules in the PDMS phase was significantly great, and that in the poly(HDFNMA) phase was too low to affect the whole permeation of the grafted PDMS membrane directly. However, the permeation of molecules at the interface of poly(HDFNMA) and PDMS played an important role because poly(HDFNMA) had a much stronger affinity for TCE than water. At a low feed concentration of the TCE solution, the diffusivity of TCE molecules must be much lower than that of water due to the larger molecular size of TCE. At a high concentration of TCE solution, TCE was sufficiently sorbed into the membrane so that the diffusion of water was prevented by TCE molecules; in turn, the permselectivity of TCE was increased significantly. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 273–287, 1999     

Separation of water–alcohol mixtures by pervaporation through asymmetric nylon 4 membrane

The dehydration of aqueous alcohol solutions through asymmetric nylon 4 membranes were investigated using pervaporation processes. The formation of asymmetric pervaporation membranes are discussed in terms of the content of the nonsolvent in the casting solution, polymer concentration, and compositions of the coagulation medium. The effects of the feed composition, feed temperature, and molar volume of the alcohols on the pervaporation performances of the asymmetric membranes are discussed. A separation factor of 4.72 and a permeation rate of 0.78 kg/m² h for the asymmetric membrane were obtained. Compared to the conventional homogeneous nylon 4 membrane, the asymmetric membrane can effectively overcome the pervaporation performances of the nylon 4 membrane for separation of water–alcohol mixtures. © 1994 John Wiley & Sons, Inc.     

Swelling behavior of pervaporation membranes in ethanol–water mixtures

Novel hydrophobic composite membranes made of crosslinked poly(dimethylsiloxane) and poly(methyl hydrogen siloxane) (PDMS–PMHS) with various amounts of catalyst were prepared. Pervaporation experiments with water–ethanol mixtures revealed that an optimum ratio of catalyst to polymer base existed. Both swelling behavior and dynamic–mechanical properties of these silicone films were studied. The swelling experiments in different mixtures of ethanol and water determined that ethanol is preferentially sorbed and that the membranes are only capable to absorb a limited quantity of solvent. Equilibrium swelling data were also used in combination with the analysis of the viscoelastic relaxation of the swollen samples to obtain the dependence of the dynamic–mechanical properties of the silicone films on the quantity of permeants sorbed into the membrane. It was observed that the permselective parameters were related with the mobility of the chains and the free volume. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1424–1433, 2000     

Permeation and separation characteristics of alcohol–water mixtures through poly(dimethyl siloxane) membrane by pervaporation and evapomeation

Permeation and separation characteristics for aqueous alcoholic solutions such as methanol/water, ethanol/water and 1-propanol/water were studied using a poly(dimethyl siloxane) membrane by pervaporation and evapomeation. Poly(dimethyl siloxane) membrane preferentially permeated alcohol from aqueous alcoholic solutions in both methods. The concentration of alcohol in the permeate by evapomeation was higher than that by pervaporation. However, the permeation rate for the former method was smaller than that for the latter method. In evapomeation with a temperature difference between the feed solution and the membrane surroundings, when the temperature of the membrane surroundings was kept constant and the temperature of the feed solution was raised, both the permeation rate and the permselectivity for ethanol increased with increasing temperature of the feed solution. On the other hand, as the temperature of the feed solution was kept constant and the temperature of the membrane surroundings was changed, the permeation rate decreased, but the permselectivity for ethanol increased remarkably with dropping temperature in the membrane surrounding. Under permeation conditions of a feed solution of 40°C and a membrane surrounding temperature of ?30°C in evapomeation, an aqueous solution of 10 wt % ethanol in the feed was concentrated to about 90 wt % in the permeate. The permselectivity for alcohol was in the order of methanol <ethanol <1-propanol. The above permeation and separation characteristics are discussed from the viewpoint of the physicochemical properties of the poly(dimethyl siloxane) membrane and the permeating molecules.     

Characterization of relaxation phenomena and permeation behaviors in sodium alginate membrane during pervaporation separation of ethanol–water mixture

The pervaporation separation of a concentrated ethanol–water mixture with 90 wt % of ethanol content through a sodium alginate (SA) membrane was carried out to investigate both the relaxation process and permeation behavior of the membrane in pervaporation. From the swelling measurement of the membrane in 90 wt % of ethanol content of the aqueous solution, it was observed that SA has an excellent permselectivity toward water and a high solubility of water: about 1000 of sorption selectivity and 21 wt % of water content in the swollen membrane at 40°C. Its excellent sorption properties could result in the outstanding pervaporation performance for the aqueous solution; higher than 10,000 of separation factors and 120–290 g/(m²h) of fluxes, depending on the operating temperature. However, a serious flux decline took place with operating time due to the occurrence of a significant relaxation process in SA. The flux decline was remarkable at the beginning stage and then mitigated with operating time. The fluxes were reduced by about 40–50% because of the relaxation process during the measurement. To analyze these phenomena in more detail, the hysteresis behavior of membrane performance along with an operation temperature cycle was investigated. During the heating process in the cycle, the relaxation process was important to affect membrane performance while the formation of excess stress in the membrane might be a crucial factor during the cooling process. It was postulated from the experimental observations that in the heating process an increase in flux with temperature is restricted by a more rapid relaxation process at a higher operation temperature, while in the cooling process, the excess stresses in the membrane are formed and accumulated in and near the transition zone and near the area in the membrane because of slower relaxational consolidation in unequilibrium cooling than in relaxational dilation in the heating process, resulting in flux more sensitive to temperature than in the heating process. These phenomena were found diminished as the relaxation time increased with aging time. The relaxation phenomena were discussed through an analysis on permeation activation energy data obtained from the pervaporation experiments. A qualitative model was established to describe the relaxation phenomena in the membrane material during the pervaporation process by using the basic principles of polymeric relaxation and the experimental observations obtained in this study. © 1996 John Wiley & Sons, Inc.     

Dehydration of acetic acid/water mixtures by pervaporation with a modified poly(4-methyl-1-pentene) membrane

The dehydration of acetic acid/water mixtures by pervaporation with a EVA/TPX membrane has been studied. The membrane exhibited water selectivity during all process runs. Investigations were focused on the effects of heat treatment temperature on membrane formation, membrane thickness, feed solution concentration, EVA content, and feed solution temperature. Compared with pure TPX membrane, the EVA/TPX blend membrane effectively improved the pervaporation performances. The permeation rate decreases with increasing heat treatment temperature during the membrane formation. Optimum pervaporation results were obtained by EVA/TPX membrane with 12.5 wt % EVA content, giving a separation factor of 606 and permeation rate of 215 g/m²h.     

Sorption,diffusion and pervaporation of water/ethanol mixtures in polyetherimide membranes

Homogeneous and composite aromatic polyetherimide membranes were prepared by casting from N-methylpyrrolidinone (NMP) solutions and by electrodeposition of polymer at the cathode, respectively. The membranes were evaluated for their sorption, diffusion and pervaporation separation of water from ethanol with emphasis on the breaking of azeotropic composition. The membrane performance was shown to be dependent on the feed concentration, but still selective towards water over the whole composition range of the feed mixture. By looking at the surface energy parameters, the determination of degree of swelling and the calculation of deviation coefficients (ε), an interesting insight was gained into the coupling effect in this solvent/membrane system. From the sorption, diffusion and temperature-dependent permeation behaviour, it could be concluded that in this system the diffusivity of permeant plays a major role in determining the pervaporation performance, rather than the solubility. © 1999 Society of Chemical Industry     

Swelling behavior of PDMS–PMHS pervaporation membranes in ethyl acetate–water mixtures

Pervaporation composite membranes were prepared with a three‐layer structure: a PP support, a PEI microporous structure, and a PDMS–PMHS selective layer. Swelling tests were performed in water, ethyl acetate, and four different ethyl acetate–water mixtures, to calculate the diffusional and swelling parameters. Moreover, the dynamic–mechanical properties of the membranes were obtained before and after the swelling experiments, and their relaxation spectra were characterized with the Fuoss–Kirkwood equation and analyzed in terms of the free volume parameter. It was found that the ethyl acetate possesses high affinity with the composite membranes and that the absorption of these small molecules substantially modifies the viscoelastic behavior and structure of the active layer. The combination of swelling experiments and the study of the mechanical relaxations proved to be an appropriate technique to investigate the behavior of pervaporation membranes immersed in different mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1384–1393, 2004     

Sorption and pervaporation separation of ethyl tert—butyl ether and ethanol mixtures through a blended membrane

A new kind of membrane was prepared by blending poly(acrylic acid) with cellulose acetate propionate for the separation of ethyl tert—butyl ether and ethanol mixtures. The properties of the membranes were evaluated by the pervaporation separation of mixtures of ethyl tert—butyl ether/ethanol and the sorption experiments. The experimental results showed that the selectivity and the fluxes of this membrane depend on the blend composition and on that of processed feed mixtures. With respect to temperature, the ethanol fluxes obey the Arrhenius equation. The fluxes increase with the increase of the poly(acrylic acid) content in the blended membrane, the ethanol concentration in the feed, and the experimental temperature. But the selectivity decreases as the poly(acrylic acid) content and the experimental temperature are raised up. When the feed composition is varied, this membrane shows the special characteristics at the azeotropic composition. In the vicinity of the azeotropic point, the minimum values of ethanol concentration in the permeate and in sorption solution are obtained. The swelling ratios increase with an increase in the temperature and the ethanol concentration. The ethanol concentration in the sorption solution is also influenced by the temperature and composition of the mixtures. When the temperature increases, the sorption selectivity of the membrane decreases. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1631–1638, 1997     

Separation of alcohol–water mixture by pervaporation through a reinforced polyvinylpyridine membrane

A membrane consisted of cross-linked poly(4-vinylpyridine) and reinforced by a nonwoven cloth made of poly(ethylene terephthalate) was prepared by copolymerization of 4-vinylpyridine with divinylbenzene in the presence of the nonwoven cloth. Pervaporation performance of this polyvinylpyridine membrane was examined at several feed alcohol concentrations and temperatures. The membrane showed water selectivity, and the permselectivity, α_W/_A, for the alcohol–water mixture was in the order isopropyl > propyl > tert-butyl > ethyl > methyl. The membrane showed a large permeability, and the pervaporation flux, ?, for the ethanol–water mixture was 7–13 kg/h per square meter of the membrane in pervaporation with sweeping of carbon dioxide under atmospheric pressure and at 40°C. The membrane was durable and long lasting for a prolonged-period, and permselectivity and permeability of the membrane did not fall off even after repeated use for 1000 h. © 1993 John Wiley & Sons, Inc.     

Sorption,diffusion, and pervaporation separation of water–acetic acid mixtures through the blend membranes of sodium alginate and guar gum‐grafted‐polyacrylamide

Nonporous homogeneous dense membranes were prepared from the blends of sodium alginate (Na–Alg) with guar gum‐grafted polyacrylamide (GG‐g‐PAAm) in the ratios of 3 : 1 and 1 : 1 and these were tested for the pervaporation separation of water–acetic acid mixtures at 30°C. Blend compatibility was studied in solution by measuring the viscosity and the speed of sound. Membranes were crosslinked by glutaraldehyde. The GG‐g‐PAAm polymer and the crosslinked blend membranes were characterized by Fourier transform infrared spectra. High separation selectivity was exhibited by the pure Na–Alg membrane for water–acetic acid (HAc) mixtures containing 20 mass % of water. The permeation flux increased with increasing mass percent of water in the feed as well as with an increase in the amount of GG‐g‐PAAm in the blend, but separation selectivity decreased. Sorption selectivity was higher for the Na–Alg membrane than for the blend membranes, but it decreased with increasing mass percent of GG‐g‐PAAm in the blends. Diffusion selectivity values vary systematically with the blend composition, but not with the amount of water in the feed. Diffusion coefficients of the water–HAc mixtures were calculated from Fick's equation using sorption data and compared with those calculated from flux values obtained in pervaporation experiments. The Arrhenius activation parameters were calculated for the 20 mass % of water in the feed using flux and diffusion data obtained at 30, 40, and 50°C. The diffusion and pervaporation results are explained in terms of solution–diffusion concepts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 259–272, 2002     

Separation of liquid mixtures by using polymer membranes. III. Water–alcohol separation by pervaporation through modified PAN membrane

The modification of polyacrylonitrile membrane with ethanolamine was carried out, and the permeation characteristics in pervaporation were examined using the aqueous alcohol solutions. In pervaporation of a water/alcohol solution, preferential permeation of water was observed for all these membranes because of the hydrogen-bonding interaction. The selectivity of the modified polyacrylonitrile (PAN) membrane depended on operating temperature, but was independent on the thickness of the membrane. Furthermore, it was found that the membrane with more ethanolamine content had a higher affinity to water. The effect of feed concentration and the molecular size of the permeating species on the separation factor and permeation flux was also investigated.