Modification of poly(vinyl alcohol) using maleic acid and its application to the separation of acetic acid-water mixtures by the pervaporation technique

The ‘solution technique’ modification of poly(vinyl alcohol) (PVA) using maleic acid was carried out with the help of triethanolamine/water catalysts. The resulting PVA membranes were characterized by differential scanning calorimetry, infrared spectroscopy, and tensile studies to investigate the reaction between PVA polymer and maleic acid. It was found that the resulting PVA membranes had two portions, branched and crosslinked, and there were no more branched than cross-linked portions. For the pervaporation separation of the acetic acid-water system, two reaction densities (X_cr = mole maleic acid per mole monomeric unit of PVA) of 0.05 and 0.1 were studied for the separation of the entire range of mixture compositions at 25° C. The separation factors of the X_cr = 0.05 modified PVA membranes were higher than those of the X_cr 0.1 modified ones and the highest separation factor of 7.80 was obtained at 70wt% water in the feed with the X_cr = 0.05 modified PVA membrane.     

Synthesis of sulfoxide-modified ethylene—vinyl alcohol copolymers for the permselective membrane of sulfur dioxide

The Michael-type addition reaction of ethylene-vinyl alcohol copolymer (EVAL) with a series of vinyl sulfoxides namely methyl, ethyl, t-butyl and phenyl vinyl sulfoxides, was performed with NaOH as a catalyst in DMSO solution to produce 2-(alkyl or phenyl sulfinyl)ethyl EVAL derivatives. The high perm-selectivity of sulfur dioxide against nitrogen was achieved through these sulfoxide-modified EVAL membranes.     

亚砜基改性纤维素膜的SO2气体渗透性能研究

分别使用二甲基亚砜浸泡的物理方法及苯基乙烯基亚砜加成的化学方法对纤维素膜进行了改性,并对改性膜的性能进行了测试.结果表明改性后纤维素膜仍为致密结构,SO2的渗透性能及其对N2的分离性能明显提高,其中改性液中添加二甲基亚砜的均相化学加成反应所得的改性膜具有较好的SO2渗透稳定性.     

Dialdehyde polyethylene glycol cross-linked poly(vinyl alcohol) membranes with enhanced CO2/N2 separation performance

The development of carbon dioxide (CO₂) separation technology is crucial for mitigating global climate change and promoting sustainable development. In this study, we successfully synthesized an array of cross-linked poly(vinyl alcohol) (PVA) membranes, xALD-PEG-ALD-c-PVA, with enhanced CO₂/N₂ separation performance by employing dialdehyde polyethylene glycol (ALD-PEG-ALD) as a cross-linker. The formation of the cross-linked network structure not only inhibits the crystallization of PVA but also disrupts hydrogen bonding and thus increases fractional free volume of PVA chains. Under the synergistic effect of these multiple factors, the cross-linked PVA membranes exhibit a significantly improved CO₂ permeability. Moreover, they maintain high CO₂/N₂ selectivity, attributing to the CO₂-philic characteristic of ethylene oxide groups in the cross-linked structure. At the ALD-PEG-ALD content of 1.6 mmol g⁻¹, the xALD-PEG-ALD-c-PVA membrane demonstrates a CO₂ permeability of 41.4 barrer and a CO₂/N₂ selectivity of 57.4 at 2 bar and 25°C. Furthermore, compared with the pristine PVA membrane, xALD-PEG-ALD-c-PVA membranes manifest superior mechanical properties and outstanding separation performance for a CO₂/N₂ (15/85, vol%) gas mixture. The excellent combination of permeability and selectivity makes xALD-PEG-ALD-c-PVA membranes highly promising for various CO₂ separation applications.     

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

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

Poly(vinyl alcohol)/ZIF‐8‐NH2 mixed matrix membranes for ethanol dehydration via pervaporation

Ethanediamine‐modified zeolitic imidazolate framework (ZIF)‐8 particles (ZIF‐8‐NH₂) is synthesized and incorporated in the poly(vinyl alcohol) (PVA) matrix to fabricate novel PVA/ZIF‐8‐NH₂ mixed matrix membranes (MMMs) for pervaporation dehydration of ethanol. The PVA/ZIF‐8‐NH₂ MMMs exhibit enhanced membrane homogeneity and separation performance because of the higher hydrophilicity and restricted agglomeration of the particles, as compared to corresponding MMMs loaded with unmodified particles. The effect of ZIF‐8‐NH₂ loading in the MMMs is studied and the MMM with a 7.5 wt % ZIF‐8‐NH₂ loading shows the best pervaporation performance for ethanol dehydration at 40°C. Various characterization techniques (Fourier transform infrared, scanning electron microscope, contact angle, sorption test, etc.) are used to investigate the MMMs loaded with ZIF‐8 and ZIF‐8‐NH₂ particles. The impact of operation conditions on pervaporation performance is also performed. The performance benchmarking shows that the MMMs have superior separation factors and comparable flux to most other PVA hybrid membranes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1728–1739, 2016     

Changes in free volume and gas permeation properties of poly(vinyl alcohol) nanocomposite membranes modified using cage-structured polyhedral oligomeric silsesquioxane

The present work reports the effect of various organically functionalized polyhedral oligomeric silsesquioxane (POSS) particles on the gas transport properties (N₂, O₂, and CO₂ molecules) in poly(vinyl alcohol) (PVA) membranes. The incorporation of polyethylene glycol-POSS (PEG-POSS), octa-tetramethylammonium-POSS (Octa-TMA-POSS) and m-POSS (Octa-TMA-POSS molecule was modified using cetyltrimethyl ammonium bromide) led to the enhancement in CO₂ separation performance of PVA, among which, PEG-POSS exhibited highest CO₂ separation due to the dipole-quadrupolar interaction of CO₂ with ethylene oxide group in POSS. Octa-TMA-POSS and m-POSS reduced the O₂ and N₂ permeability of the PVA membrane due to the reduction in the number of permeating pathways as compared to pure PVA. Free volume of the membranes was evaluated by positron annihilation lifetime spectroscopic (PALS) and coincidence Doppler broadening measurements. PALS confirms the increase in polymer free volume in PVA/POSS system due to the presence of rigid and spherical POSS molecule, which could enter in the polymer chain and provide viable pathway for molecular transport. Maxwel–Wagner–Sillar and Higuchi models were applied for the theoretical prediction of permeability of the fabricated membranes.     

A thin film composite membrane supported by a hydrophilic poly(vinyl alcohol‐co‐ethylene) nanofiber membrane: Preparation,characterization, and application in nanofiltration

In this study, a fabricated hydrophilic poly(vinyl alcohol‐co‐ethylene) (PVA‐co‐PE) nanofiber membrane was used as the middle support layer to prepare thin film composite (TFC) membranes for nanofiltration. The effects of the supporting nonwoven layer, grams per square meter (GSM) of nanofiber, reaction time, heat treatment, monomer concentration, operating pressure, and pH value on the separation performance of the TFC membranes were analyzed. These results show that the TFC membranes prepared with the PVA‐co‐PE nanofiber membrane can be used to filtrate different metal ions. For NaCl, Na₂SO₄, CaCl₂, CuCl₂, CuSO₄, and methyl orange solutions, the rejection rates of the TFC membrane with nonwoven polyester as the supporting layer and a nanofiber GSM of 12.8 g/m² are 87.9%, 93.4%, 92.0%, 93.1%, 95.8%, and 100%, respectively. This indicates the potential application of the PVA‐co‐PE nanofiber membrane in the preparation of nanofiltration and reverse‐osmosis TFC membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46261.     

Preparation and performance evaluation of composite hollow fiber membrane for SO2 separation

Emission of sulfur dioxide (SO₂) from coal power plants has to be controlled and minimized to reduce environmental risk. This study aimed to investigate the hollow fiber composite membrane was used for the removal of SO₂ from a SO₂/CO₂/N₂ mixed gas. Moreover, for the improvement of SO₂ removal efficiency, the polyetherimide (PEI) membrane was coated with poly(vinyl chloride)‐graft‐poly(oxyethylene methacrylate) (PVC‐g‐POEM). The PVC‐g‐POEM/PEI composite hollow fiber membrane was extensively characterized by various techniques including scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy. Experiments with permeation of SO₂, CO₂, N₂, and a ternary gas mixture were carried out to observe membrane behavior in response to different operating conditions. As a result, permeance of SO₂ was 105–2705 GPU and selectivity of SO₂/CO₂ was 3.9–175.6. From the mixed gas separation experiment, the maximum SO₂ removal efficiency reached up to 84.5%. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2298–2306, 2014     

Optimization of microstructure and geometry of hydrophobic ceramic membrane for SO2 absorption from ship exhaust

Membrane gas absorption (MGA) is of great interest for SO₂ capture from ship exhaust, as it has high separation efficiency and, more importantly, is comprised of a separator that can be flexibly installed and operated on ships. Here, we report a class of hydrophobic tubular asymmetric ceramic membranes for SO₂ absorption. To find the membranes with reasonable microstructure and geometry, we used a numerical 2D model to simulate SO₂ absorption process and verified the model by comparing its results with experimental data. Simulations showed that most of the SO₂ mass transfer resistance existed in membrane phase, indicating that the optimization of membrane parameters, rather than operational conditions, should be the primary consideration to enhance the overall SO₂ mass transfer performance. Furthermore, simulations indicated that the SO₂ separation performance depended negligibly on membrane pore sizes, but can be significantly improved by optimizing the thickness and inner diameter of membrane tubes. © 2018 American Institute of Chemical Engineers AIChE J, 65: 409–420, 2019     

Evaluating the chemical stability of metal oxides in SO3 and applications of SiO2-based membranes to O2/SO3 separation

The decomposition of sulfur trioxide to produce sulfur dioxide and oxygen using a catalytic membrane reactor is technology that promises to improve the economic viability of the thermochemical water-splitting Iodine-Sulfur (IS) process for large-scale CO₂-free hydrogen production. The chemical stability of membrane materials under SO₃, however, is a significant challenge for this strategy. In this study, microporous membranes with a layered structure that consisted of a membrane support prepared from α-Al₂O₃, an intermediate layer prepared from silica-zirconia, and a top layer prepared from bis (triethoxysilyl)ethane-derived organosilica sols, were examined for stability under SO₃ and for use in SO₃/O₂ separation. An α-Al₂O₃ support that features SiO₂–ZrO₂ intermediate layers with large pore sizes and a high Si/Zr molar ratio showed excellent resistance to SO₃, which was confirmed by N₂ adsorption, Energy Dispersive X-ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). These membranes also demonstrated a negligible change in gas permeance before and after SO₃ exposure. Subsequently, in binary-component gas separation at 550°C, microporous organosilica-derived membranes achieved an O₂/SO₃ selectivity of 10 (much higher than the Knudsen selectivity of 1.6) while maintaining a high O₂ permeance of 2.5 × 10⁻⁸ mol m^–2 s^–1 Pa^–1.     

Proton‐conducting blend membranes of crosslinked poly(vinyl alcohol)–sulfosuccinic acid ester and poly(1‐vinyl‐1,2,4‐triazole) for high temperature fuel cells

New type of composite membranes were synthesized by crosslinking of poly(vinyl alcohol) (PVA) with sulfosuccinic acid (SSA) and intercalating poly(1‐vinyl‐1,2,4‐triazole) (PVTri) into the resulting matrix. The complexed structure of the membranes was confirmed by Fourier transform infrared (FTIR) spectroscopy. The resulting hybrid membranes were transparent, flexible, and showed good thermal stability up to ～200°C. The proton conductivities of the membranes were investigated as a function of PVTri and SSA and operating temperature. The water/methanol uptake was measured and the results showed that solvent absorption of the materials increased with increasing PVTri content in the matrix. The proton conductivity of the membranes continuously increased with increasing SO₃H content, PVTri content, and the temperature. In the anhydrous state, the maximum proton conductivity is 7.7 × 10^?5 S/cm for PVA–SSA–PVTri‐1 and for PVA–SSA–PVTri‐3 is 1.6 × 10^?5 S/cm at 150°C. After humidification (RH = 100%), PVA–SSA–PVTri‐4 showed a maximum proton conductivity of 0.0028 S/cm at 60°C. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Low viscous aminoalkyl-phenyl-silane with π–π interaction and its optimal SO2 capture condition

The high viscosity of ionic liquids (ILs) limits their practical application in SO₂ capture. In this work, the low viscous aminoalkyl-phenyl-silanes were synthesized to capture SO₂. The π–π interaction between phenyl groups reduced the volatility of aminoalkyl-phenyl-silanes greatly, but it did not increase their viscosity significantly. Among them, N-[(dimethylphenylsilyl)methyl]-N-methylbenzenemethanamine (DPSA) containing two phenyl groups exhibited the strongest π–π interaction. Therefore, the thermal decomposition temperature reached 150°C, while its viscosity was only 8.45 mPa·s at 25°C, which is much lower than that of ILs. The absorption enthalpy and entropy change of DPSA absorption reaction were −79.284 kJ/mol and −224 J/mol/K, respectively. These values are more negative than those of SO₂ capture reaction with ILs. An objective function was proposed to obtain the optimal absorption and desorption temperature. Furthermore, five cycles of regeneration experiments indicated that DPSA possessed good regeneration ability.     

Rheological properties of high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (PVA)/HMW atactic PVA blend solutions

To identify the effect of blend ratios of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA)/atactic PVA (a‐PVA) having similar number‐average degrees of polymerization (P_n)s of 4000 and degrees of saponification (DS)s of 99.9% on the rheological properties of s‐PVA/a‐PVA/water solutions, water‐soluble s‐PVA and a‐PVA with different syndiotactic diad contents of 58.5 and 54.0%, respectively, were prepared by bulk copolymerization of vinyl pivalate and vinyl acetate (VAc) and solution polymerization of VAc, followed by saponifying the corresponding copoly(vinyl pivalate/vinyl acetate) and poly(vinyl acetate). The blend ratios played a significant role in rheological behavior. Over the frequency range of 10^?1–10² rad/s, s‐PVA/a‐PVA blend solutions with larger s‐PVA content show more shear thinning at similar (P_n)s and (DS)s of polymer, suggesting that PVA molecules are more readily oriented as s‐PVA content increases. Yield stress is higher for s‐PVA/a‐PVA blend solutions with larger s‐PVA content at similar (P_n)s and (DS)s of polymer. This indicates that more domains with internal order are produced at larger s‐PVA content in s‐PVA/a‐PVA blend solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3934–3939, 2006     

Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

Crosslinked blended poly(vinyl alcohol)/N-methylol nylon-6 membranes for the pervaporation separation of ethanol–water mixtures

Crosslinked blended membranes of poly(vinyl alcohol) (PVA) and N-methylol nylon-6 were prepared either by thermal crosslinking at 180°C or by chemical crosslinking with maleic acid. The pervaporation performance for the separation of ethanol–water mixtures of these membranes was investigated in terms of feed concentration, PVA content, and crosslinking agent content. The pervaporation performance of two differently crosslinked membranes was strongly influenced by the nature of the crosslinkage. Significant improvement in the pervaporation separation index can be achieved for chemically crosslinked membranes. From the comparison between the pervaporation and sorption tests, it is suggested that, for hydrophilic membranes, sorption properties dominate the pervaporation performance at feed solutions of higher water content, while diffusion properties govern at feed solutions of higher ethanol content. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 317–327, 1998     

Poly(vinyl alcohol) modified by KE reactive dyes as a novel proton‐exchange membrane for potential fuel‐cell applications

A new type of proton‐exchange membrane based on poly(vinyl alcohol) (PVA) modified KE reactive dyes (KE‐4BD) was prepared and evaluated as H⁺‐conducting polymer electrolytes. The effects of the content of KE‐4BD on the membrane H⁺ conductivity and water uptake were studied with an alternating‐current impedance technique and the method of weighing, respectively. Fourier transform infrared and scanning electron microscopy were used for the chemical and structural characterization of these membranes. With all of these properties, the optimal mass ratio between PVA and KE‐4BD was 1:0.5, and the resulting membrane exhibited a high proton conductivity (0.109 S/cm) at room temperature; this afforded a power density of 83.9 mW/cm² at 210.4 mA/cm² and an open‐circuit voltage of 810.8 mV. The PVA/KE‐4BD membranes showed a high oxidative stability in Fenton's reagent (3% H₂O₂ v/v, 2 ppm FeSO₄). Thermal analysis also showed that the membranes exhibited a significant improvement in thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43019.     

Electrochemical properties of polypropylene membranes modified by the plasma polymerization coating of SO2/acetylene

Polypropylene membranes were modified by the plasma etching of SO₂, SO₂? O₂, or SO₂? H₂O, followed by the plasma polymerization coating of SO₂/acetylene. The conditions for SO₂ plasma etching were optimized by the measurement of the ion‐exchange capacity (IEC) as a function of the plasma‐etching power (10–30 W), gas pressure (40–60 mTorr), and treatment time (15–120 s). For the plasma etching of SO₂? O₂ and SO₂? H₂O, only the pressure ratio (SO₂/O₂ and SO₂/H₂O) was optimized under the optimized conditions determined from SO₂ plasma etching. Plasma etching was then combined with the plasma polymerization coating of SO₂/acetylene, for which the conditions were again optimized by the measurement of the IEC as a function of the plasma power (10–40 W), chamber pressure (50–200 mTorr), SO₂/acetylene ratio (15/135–60/90), and treatment time (0–10 min). Next, the electrical resistance and water uptake were evaluated. The modified membranes were also analyzed with scanning electron microscopy, whereas plasma polymer coatings were characterized with Fourier transform infrared/attenuated total reflection. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3692–3699, 2006     

Synthesis,antimicrobial activity,and release of tetracycline hydrochloride loaded poly(vinyl alcohol)/soybean protein isolate/zirconium dioxide nanofibrous membranes

Tetracycline hydrochloride loaded poly(vinyl alcohol)/soybean protein isolate/zirconium (Tet–PVA/SPI/ZrO₂) nanofibrous membranes were fabricated via an electrospinning technique. The average diameter of the PVA/soybean protein isolate (SPI)/ZrO₂ nanofibers used as drug carriers increased with increasing ZrO₂ content, and the nanofibers were uneven and tended to stick together when the ZrO₂ content was above 15 wt %. The Tet–PVA/SPI/ZrO₂ nanofibers were similar in morphology when the loading dosage of the model drug tetracycline hydrochloride was below 6 wt %. The PVA, SPI, and ZrO₂ units were linked by hydrogen bonds in the hybrid networks, and the addition of ZrO₂ improved the thermostability of the polymer matrix. The Tet–PVA/SPI/ZrO₂ nanofibrous membranes exhibited good controlled drug‐release properties and antimicrobial activity against Staphylococcus aureus. The results of this study suggest that those nanofibrous membranes were suitable for drug delivery and wound dressing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40903.     

Modified poly(vinyl alcohol)/chitosan blended membranes for isopropanol dehydration via pervaporation: Synthesis optimization and modeling by response surface methodology

Box–Behnken (BB) design of response surface methodology (RSM) was effectively applied to optimize fabrication conditions of modified poly(vinyl alcohol) (PVA) and chitosan (CS) blended pervaporation (PV) membranes. The PVA/CS membranes were crosslinked either by chemical reaction with glutaraldehyde (GA) or by heat‐treating at different temperatures. The main objectives were to determine the optimal levels of fabricating parameters and also to investigate interactions among the variables. CS content in the blended membranes, concentration of crosslinking agent and heat‐treating temperature were the fabrication parameters, the main effects and interaction effects of which on membrane structure and PV performance toward isopropanol (IPA)/water dehydration were investigated, and for which regression models were established. The modified PVA/CS blended membranes were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) as well as X‐ray diffraction (XRD). It was found that the CS content is the most significant factor influencing flux and separation factor among the three studied variables and the experimental results are in excellent accordance with predicted values from the developed RSM regression models. The RSM results indicated that under preparation conditions of 80 wt % CS in the blended membrane, 0.58 wt % GA concentration, and 77 °C heat‐treating temperature, the maximum separation factor of 5222.8 and the normalized flux of 9.407 kg µm/m²h can be acquired with feed content of 85 wt % IPA at 25 °C, showing that the prepared membrane is highly efficient for PV dehydration of IPA. The models were satisfactorily validated against experimental data. Furthermore, the optimum membrane presents excellent separation performance at different feed compositions and temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44587.