Sorption behavior and preliminary pervaporation results of cross-linked polyvinylalcohol and polydimethylsiloxane membranes prepared for the separation of water-ethylacetate mixtures

Since pervaporation process is the coupling of solution and diffusion mechanisms, a sorption study was carried out with membranes prepared by cross-linking polyvinylalcohol (PVA) and polidimethylsiloxane (PDMS). Tartaric acid (Tac) was used as the cross-linking agent for PVA, and a commercial cross-linking agent was used for PDMS. Sorption experiments were carried out at 30-50°C temperature range in pure water and ethyl acetate using the films prepared. The PVA and PDMS films prepared preferentially sorb water and ethylacetate, respectively. A pervaporation study at 30°C was carried out for pure ethylacetate and pure water, and mixtures of ethylacetate containing 2 and 2.5 wt% water using 100 w m thick PVA membrane. The results indicate that the PVA membrane prepared is extremely selective for water.     

Tubular composite PVA ceramic supported membrane for bio-ethanol production

Thin polyvinyl alcohol (PVA) layers loaded with fumed silica were coated on porous ceramic supports. Scanning electron microscope (SEM) was used to characterize the ceramic-supported thin PVA active layers and the effects of coating gel PVA concentration on thickness and density of the active layers were investigated. Pervaporation (PV) dehydration of 90 wt.% ethanol was performed at temperatures of 30, 45 and 60 °C. The values of water flux (0.05–2.92 kg/m² h) and selectivity (3–180) exceed typical values obtained for pure PVA membranes. Besides the pervaporation separation index (PSI) varies from 5.84 to 82.81. Compared to pure PVA membrane with maximum PSI of 47.2, the pervaporation performance was significantly improved. The best separation performance was obtained using the membrane prepared from 5 wt.% PVA solution containing 6 wt.% fumed silica and at pervaporation temperature of 45 °C with permeation flux of 1.69 kg/m² h, and selectivity of 50. The highest permeation flux, selectivity and PSI was 2.92 kg/m² h, 180 and 82.81, obtained at 60, 30 and 45 °C, respectively, while using membranes loaded with 8, zero and 6 wt.% of fumed silica in PVA membrane prepared from 5, 10 and 5 wt.% PVA solutions, respectively. The novel ceramic support increased mechanical strength of the membrane and protected the ultrathin polymeric top active layer under aggressive operating conditions, especially high pressure gradient across the membrane. Incorporation of fumed silica also resulted in higher water permeation flux. Due to these results, the synthesized membranes are suitable for ethanol purification in industrial scales.     

DESORPTION OF ETHYL ACETATE-WATER MIXTURE BY USING CROSS-LINKED POLY(VINYLALCOHOL) MEMBRANE AND COMPARISON OF RESULTS WITH PERVAPORATION

In this study using poly(vinylalcohol) (PVOH) membranes cross-linked with tartaric acid (Tac) desorption experiments were performed for selected concentrations of binary ethyl acetate (EtAc)-water mixture at temperatures of 30°, 40°, and 50°C to determine sorption of components. Sorption values measured were compared with those estimated by the Flory-Huggins approach. Additionally, desorption results were compared with pervaporation results of another study in terms of solution-diffusion theory, and the effect of thermodynamic interactions on selective transport of the binary mixture and membrane system was investigated. The results obtained show that selective transport of EtAc-water mixture was influenced by increasing temperature and water content in the feed. It is shown that preferential sorption is more effective for pervaporation selectivity than diffusion selectivity.     

RECOVERY OF ACETIC ACID OVER WATER BY PERVAPORATION WITH A COMBINATION OF HYDROPHOBIC IONIC LIQUIDS

The present work considers the application of an integrated pervaporation process to improve the pervaporation performance of acetic acid over water. This integrated pervaporation process was based on a plain PDMS membrane with a hydrophobic ionic liquid composed of a heterocyclic cation and [PF₆]^? anions. The hydrophobic ionic liquid was introduced as the third phase between the aqueous phase and the plain PDMS membrane for improving mass-transfer of acetic acid from its aqueous matrix to the PDMS membrane. The primary results indicated that the ionic liquid as an extractant prior to pervaporation was favorable for improving the permeate selectivity and the permeate flux of acetic acid compared with using only a plain PDMS membrane. This performance could be attributed to the acetic acid concentrated and the water molecules rejected by ionic liquid prior to pervaporation. Extraction of a real effluent containing acetic acid from an antibiotic pharmaceutical plant was carried out using the above integrated pervaporation, and the results imply that this integrated pervaporation process could be scaled up for recovering acetic acids over its water-rich effluents.     

RECOVERY OF ACETIC ACID OVER WATER BY PERVAPORATION WITH A COMBINATION OF HYDROPHOBIC IONIC LIQUIDS

The present work considers the application of an integrated pervaporation process to improve the pervaporation performance of acetic acid over water. This integrated pervaporation process was based on a plain PDMS membrane with a hydrophobic ionic liquid composed of a heterocyclic cation and [PF₆]^- anions. The hydrophobic ionic liquid was introduced as the third phase between the aqueous phase and the plain PDMS membrane for improving mass-transfer of acetic acid from its aqueous matrix to the PDMS membrane. The primary results indicated that the ionic liquid as an extractant prior to pervaporation was favorable for improving the permeate selectivity and the permeate flux of acetic acid compared with using only a plain PDMS membrane. This performance could be attributed to the acetic acid concentrated and the water molecules rejected by ionic liquid prior to pervaporation. Extraction of a real effluent containing acetic acid from an antibiotic pharmaceutical plant was carried out using the above integrated pervaporation, and the results imply that this integrated pervaporation process could be scaled up for recovering acetic acids over its water-rich effluents.     

Polyacrylonitrile‐g‐poly(vinyl alcohol) membranes for the pervaporation separation of dimethyl formamide and water mixtures

Poly(vinyl alcohol) as well as its grafted copolymer membranes with polyacrylonitrile (PAN‐g‐PVA) were prepared and used to separate water and dimethyl formamide mixtures by the pervaporation technique. The three following membranes were prepared: (1) pure PVA; (2) 46% grafted PAN‐g‐PVA; and (3) 93% grafted PAN‐g‐PVA. Pervaporation separation experiments were carried out at 25°C for the feed mixture containing 10 to 90% water. By use of the transport data, permeation flux, separation selectivity, swelling index, and diffusion coefficients have been calculated. By increasing the grafting of the membrane, flux decreased, whereas separation selectivity increased slightly over that of pure PVA membrane. Arrhenius activation parameters for transport processes were calculated for 10 mass % water containing feed mixture by using flux and diffusion data obtained at 25, 35, and 45°C. Transport parameters were discussed in terms of sorption‐diffusion principles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4091–4097, 2004     

A study on permeation behavior of a liquid mixture through PVA membranes having a crosslinking gradient structure in pervaporation

Two types of dense poly(vinyl alcohol) (PVA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique: membranes with uniform crosslinking structure and with crosslinking gradient structure. From the permeation of pure water through a membrane having a uniform crosslinking structure, the effect of crosslinking density in the membrane on the permeation activation energy, plasticizing coefficient, and diffusivity of the permeant was investigated. The concentration and activity profiles of the permeant in the membrane in the pervaporation process were determined using the diffusion equation and Flory–Huggins thermodynamics. PVA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while the other side was blocked by a polyester film to prevent the reaction solution from contacting it. The extent of the gradient was controlled by the exposing time. The pervaporation separation of the water–acetic acid mixture was carried out on the membrane having a crosslinking gradient structure, and the pervaporation performance with different membrane loading in the membrane cell was discussed using a schematic concentration and activity profiles of the permeant which was made based on the results from the permeation of a pure component through the membrane with a uniform crosslinking structure. © 1996 John Wiley & Sons, Inc.     

Characterization of sodium alginate and poly(vinyl alcohol) blend membranes in pervaporation separation

By blending a rigid polymer, sodium alginate (SA), and a flexible polymer, poly(vinyl alcohol) (PVA), SA/PVA blend membranes were prepared for the pervaporation separation of ethanol–water mixtures. The rigid SA membrane showed a serious decline in flux and a increase in separation factor due to the relaxation of polymeric chains, whereas the flexible PVA membrane kept consistent membrane performance during pervaporation. Compared with the nascent SA membrane, all of the blend membranes prepared could have an enhanced membrane mobility by which the relaxation during pervaporation operation could be reduced. From the pervaporation separation of the ethanol–water mixtures along with the temperature range of 50–80°C, the effects of operating temperature and PVA content in membrane were investigated on membrane performance, as well as the extent of the relaxation. The morphology of the blend membrane was observed with PVA content by a scanning electron microscopy. The relaxational phenomena during pervaporation were also elucidated through an analysis on experimental data of membrane performance measured by repeating the operation in the given temperature range. SA/PVA blend membrane with 10 wt % of PVA content was crosslinked with glutaraldehyde to enhance membrane stability in water, and the result of pervaporation separation of an ethanol–water mixture through the membrane was discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:949–959, 1998     

Acetic acid/water separation by pervaporation with silica filled PDMS membrane

Silica‐filled polydimethylsiloxane (PDMS) composite membranes are prepared on a polytetrafluoroethylene support structure. The structure and the performance of the membranes are characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X‐ray diffraction, and thermogravimetry. The pervaporation process for acetic/water separation is performed within the PDMS membranes. The vulcanization temperature was found to have a great influence on the separation performance of the membrane. The addition of silica can significantly improve the pervaporation flux and enhance the thermal stability of the membrane. With an increase in the feed temperature, selectivity decreases and permeation flux increases. Performed with a pure PDMS membrane vulcanized at 30°C, the separation factor at first will increase, then decrease when the feed flow rate was increased from 14 to 38 L · h^?1. The maximum separation factor is achieved when the feed flow rate is 26 L · h^?1. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Preparation and Characterization of Silicone Rubber Membrane

Pervaporation membrane with preferential permeation for organic compounds over water was prepared and characterized. Selection of membrane material and the effects of polydimethylsiloxane (PDMS), cross-linker, and catalyst concentrations on performances of pervaporation membrane at room temperature were discussed. In addition, the time of cross-linking, and the kinds of basic plate in the process of preparation were tested. The formulation of pervaporation membrane material was determined. Through the characterization of membrane by infrared spectrometry(IR), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffraction(XRD), it is proved that the structures and characters are suitable for the pervaporation process. Experiments also demonstrate that the permeate flux and separation factor are suitable for the process.     

全氟磺酸改性聚乙烯醇渗透汽化膜分离乙酸乙酯-水溶液

以聚乙烯醇(PVA)为原材料,全氟磺酸(PFSA)为共混改性材料,以聚丙烯腈(PAN)中空纤维超滤膜为底膜制备了PVAfPAN、PVA-PFSA/PAN复合膜,并用于乙酸乙酯脱水.考察了共混涂膜液中PVA、PFSA配比,交联剂酒石酸(Tat)用量以及原料液温度与浓度对PVA、PAN、PVA-PFSA、PAN复合膜分离件能的影响.实验结果表明,Tac交联的PVA,PAN、PVA-PFSA/PAN复合膜均对水具有较好的分离选择性.共混涂膜液中PVA/PFSA质量比为1/1、Tac/PVA质量比为l/5时所制备的PVA-PFSA/PAN复合膜渗透汽化分离性能最佳.40下℃此复合膜用于分离98%(wt)的乙酸乙酯水溶液时,其渗透通量和分离因予分别为81.1 g·m-2·h-1和1890.同样条件下,与交联PVA/PAN复合膜相比,交联PVA-PFSA/PAN复合膜的渗透通量显著提高.     

ZIF-8 Filled Polydimethylsiloxane Membranes for Pervaporative Separation of n-Butanol from Aqueous Solution

ZIF-8-filled polydimethylsiloxane (PDMS) membranes, PDMS/ZIF-8, were prepared by a two-step polymerization process and were used to recover n-butanol from an aqueous solution by pervaporation (PV). Compared with pure PDMS membrane, PDMS/ZIF-8 membranes demonstrated an obviously higher n-butanol permselectivity. As an increase of ZIF-8 content, n-butanol/water selectivity increased initially and then decreased, while the n-butanol and water permeability decreased monotonously. PDMS/ZIF-8 membrane containing 2 wt% ZIF-8, that is, PDMS/ZIF-8-2 showed the highest selectivity. On the other hand, selectivity and permeability for n-butanol and water of PDMS/ZIF-8-2 membrane decreased with the increase of operating temperature. The selectivity and permeability for n-butanol reached 7.1 and 3.28 × 10⁵ barrer, respectively, at 30°C when the feed concentration of n-butanol was 0.96 wt%.     

渗透汽化分离DMF/水混合物的PVA-g-AAm膜的制备和表征

使用聚乙烯醇及丙烯酰胺这两种材料,合成了不同枝度的共聚物(PVA-g-AAm),并对两种渗透汽化复合膜(PVA-g-AAm)进行制备。黏均分子量是运用用黏度法测定的,而表征则分别由接触角,红外光谱(FT-IR)和热重(TGA)等方法进行测定。而DMF/水混合体系的渗透汽化分离主要是复合膜的运用,并对膜分离的影响因素进行分析。实验结果显示,分离性能最好的是接枝度为90%的PVA。而PVA的渗透量随着DMF质量分数的增加而减少,PVA的通量最小时是在0.25~0.65 kg/(m~2·h)之间,在0.2~而膜的分离因子达到最大时DMF质量分数为33%。而温度的增加可是渗透量增大,分离因子减小。     

热处理条件对PVA/PAN和PPVA/PAN渗透汽化复合膜分离性能的影响

制备了以聚乙烯醇（PVA）、磷酸酯化聚乙烯醇（PPVA）和活性分离层的PVA／PAN、PPVA／PAN渗透汽化复合膜并用于乙醇－水恒沸混合物的分离。考察了热处理条件对复合膜分离性能及吸附性能的影响。结果表明,复合膜的分离性能主要是由热处理温度决定的,并且,PPVA／PAN复合膜比PVA／PAN复合膜具有更好的分离性能。确定了最佳的热处理条件,对于PVA／PAN复合膜：在403K下,热处理时间不小于4h,对于PPAV／PAN复合膜：在423K下,热处理时间不小于2h。     

Pervaporation separation of binary organic–aqueous liquid mixtures using cross-linked PVA membranes. II. Phenol–water mixtures

The pervaporation separation of water-phenol mixtures was carried out using poly(vinyl alcohol) (PVA) cross-linked membranes with low molecular weight poly(acrylic acid) (PAA) at 30, 40, and 50°C. The separation was concentrated on the second stage of the water-selective process at which the phenol concentration could be 80 wt % of phenol. The high separation factor of α_w/p, = 3580 for the PVA/PAA = 80/20 membrane was obtained for the phenol : water = 80 : 20 solution at 30°C. © 1994 John Wiley & Sons, Inc.     

Blend membranes of chitosan and poly(vinyl alcohol) in pervaporation dehydration of isopropanol and tetrahydrofuran

Blend membranes of a natural polymer, chitosan, with a synthetic polymer, poly(vinyl alcohol) (PVA), were prepared by solution casting and crosslinked with a urea formaldehyde/sulfuric acid (UFS) mixture. Chitosan was used as the base component in the blend system, whereas PVA concentration was varied from 20 to 60 wt %. Blend compatibility was studied by differential scanning calorimetry, and Fourier transform infrared spectroscopy was used to study membrane crosslinking. Membranes were tested for pervaporation dehydration of isopropanol and tetrahydrofuran (THF) at 30°C in close proximity to their azeotropic compositions. Membrane performance was assessed by calculating flux and selectivity. Swelling experiments performed in water + organic mixtures at 30°C were used to explain the pervaporation results. The blend membrane containing 20 wt % PVA when tested for 5 and 10 wt % water–containing THF and isopropanol feeds exhibited selectivity of 4203 and 17,991, respectively. Flux increased with increasing concentration of water in the feed. Selectivity was highest for the 20 wt % PVA‐containing blend membrane. The results of this study are unique in the sense that the crosslinking agent used—the UFS mixture—was novel. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1918–1926, 2007     

Incorporation of multiwalled carbon nanotubes into poly(vinyl alcohol) membranes for use in the pervaporation of water/ethanol mixtures

Multiwalled carbon nanotube (MWNT)/poly (vinyl alcohol) (PVA) blend membranes were prepared by the solution‐casting method to determine the effect of MWNTs with nanoscale empty inner space along the tube length on the pervaporation performance of a PVA membrane in the separation of alcohol/water mixtures. The blend membranes were then characterized with several analytical methods such as transmission electron microscopy, differential scanning calorimetry, and X‐ray diffractometry: Transmission electron microscopy showed that the MWNTs were homogeneously distributed through the PVA matrix. The glass‐transition temperature of the PVA membrane was increased from 69.21 to 78.53°C via blending with MWNTs. The crystallinity of the PVA matrix decreased with increasing MWNTs up to 5 wt % from 41 to 36%. The pervaporation properties of the blend membranes were completely different from those of the pure PVA membrane in the separation of water/ethanol mixtures. The flux of the membrane was increased with the amount of MWNTs, whereas the separation factor was maintained up to 1.0 wt % MWNTs. However, beyond that, it was reduced. These results suggested that two factors, the crystallinity of the membrane and the diameters of the MWNTs, affected the performance of the membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pervaporation separation of binary organic-aqueous liquid mixtures using crosslinked poly(vinyl alcohol) membranes. IV. Methanol–water mixtures

The pervaporation separation of methanol–water (M/W) mixtures was carried out using crosslinked poly(vinyl alcohol) (PVA) membranes with the low molecular weight of poly(acrylic acid) (PAA) as the crossinking agent. The PVA/PAA ratio in the crosslinked membrane was 90/10, 85/15, and 80/20 by weight. The operating temperatures were 50, 60, and 70°C, and the compositions of methanol–water mixtures to be separated were 70/30, 80/20, 90/10, and 95/5 (M/W) solutions. In all cases, the PVA/PAA = 80/20 membrane showed the best results. For M/W = 90/10 solution, the separation factor, α_w/m = 465, and the permeation rate, 0.109 kg/m²h, at 70°C were obtained using the PVA/PAA = 80/20 menbrane. The permeation rate and the separation factor for M/W = 95/5 solution showed 0.033 kg/m²h and α_w/m = 2650, respectively, when PVA/PAA = 80/20 membrane was used. © 1996 John Wiley & Sons, Inc.     

Pervaporation membrane reactor study for the esterification of acetic acid and isobutanol using polydimethylsiloxane membrane

In this study, isobutyl acetate, a valuable solvent in cosmetics, aroma and paint industries, is produced by pervaporation–esterification equilibrium reaction in a batch pervaporation membrane reactor (PVMR) using homogeneous (sulphuric acid) and heterogeneous (Dowex 50W-X8) catalysts. The effects of catalyst loading, catalyst type, reaction time, membrane thickness, temperature and initial molar ratio of reactants were investigated. A cross-linked polydimethylsiloxane (PDMS) membrane selective to esters was prepared and used in PVMR. Batch reactions were carried out also in a simple batch reactor (SBR) without pervaporation under the same conditions to compare the conversions for the reactions with and without pervaporation. In conclusion, PVMR experiments showed that the PDMS membrane can be used to remove the isobutyl acetate formed selectively with acceptable conversions and pervaporation fluxes.     

VISCOSITY AND SURFACE TENSION OF TOLUENE-ETHYLACETATE LIQUID MIXTURE

The viscosity and surface tension of aromatic hydrocarbon (toluene) and ester (ethylacetate) liquid mixture is reported at 20,25 and 30°C, over the entire compositional range.