Pervaporation dehydration of ethylene glycol by NaA zeolite membranes

Home-made NaA zeolite membranes were used for pervaporation dehydration of ethylene glycol (EG)/water mixtures. Hydrothermal stability of the membranes in pervaporation was investigated for industrial application purpose. The membranes exhibited good stability for water content of less than 20 wt.% at 100 °C. The reduction of operating temperature was effective to improve membrane stability for operating at high feed water content (e.g. 30 wt.%). The influence of feed water content and operating temperature on dehydration of EG was extensively investigated. A permeation flux of 4.03 kg m⁻² h⁻¹ with separation factor of >5000 was achieved at 120 °C for the separation of the solution with 20 wt.% water content. A pilot-scale pervaporation facility with membrane area of 3 m² was built up for dehydration of EG with the water content of 20 wt.%, which showed technical feasibility for industrial application.     

Preparation and characterization of α-chitin whisker-reinforced poly(vinyl alcohol) nanocomposite films with or without heat treatment

α-Chitin whisker-reinforced poly(vinyl alcohol) (PVA) nanocomposite films were prepared by solution-casting technique. The α-chitin whiskers were prepared by acid hydrolysis of α-chitin from shrimp shells. The as-prepared whiskers exhibited the length in the range of 150-800 nm and the width in the range of 5-70 nm, with the average length and width being about 417 and 33 nm, respectively. Thermal stability of the as-cast nanocomposite films was improved from those of the pure PVA film with increasing whisker content. The presence of the whiskers did not have any effect on the crystallinity of the PVA matrix. The tensile strength of α-chitin whisker-reinforced PVA films increased, at the expense of the percentage of elongation at break, from that of the pure PVA film with initial increase in the whisker content and leveled off when the whisker content was greater than or equal to 2.96 wt%. Both the addition of α-chitin whiskers and heat treatment helped improve water resistance, leading to decreased percentage degree of swelling, of the nanocomposite films.     

Poly(vinyl alcohol)/Carboxyl Graphene Membranes for Ethanol Dehydration by Pervaporation

Carboxyl graphene (CG) with two functions of hybridization and crosslinking was incorporated into poly(vinyl alcohol) (PVA) matrix to form PVA/CG mixed-matrix membranes (MMMs). The membranes demonstrated excellent mechanical properties and thermal stability. The improved hydrophilicity and formed crosslinking structure led to moderate swelling. The membrane crystallinity decreased and the free volume was promoted with increasing CG loading amount. The pervaporation (PV) separation performance for ethanol dehydration indicated that both permeation flux and separation factor were enhanced simultaneously at the optimum CG loading. Subsequently, the permeation flux continued to increase while the separation factor declined at higher CG loadings.     

Dehydration of isopropanol by PVA-APTEOS/TEOS nanocomposite membranes

In the present work, dehydration of isopropanol was investigated by novel organic-inorganic nanocomposite membranes which were prepared through sol-gel reaction of polyvinyl alcohol (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) and tetraethoxysilane (TEOS). The PVA chains were crosslinked by mixing silane coupling agents. This reaction between polymer chains and silanols agents could control degree of swelling of the nanocomposite membranes in aqueous isopropanol (IPA) solutions. The membranes were characterized by SEM and ATIR. Effects of APTEOS content in the membranes, feed concentration and temperature on pervaporation (PV) performance were investigated. It was found out that separation factor and permeation flux increase with increasing APTEOS content in the membranes. Arrhenius-type relationship was used for describing the temperature dependence of permeation flux. It was also found out that separation factor decreases with increasing temperature.     

Synthesis and characterization of hydrophobically modified poly(vinyl alcohol) hydrogel membrane

Hydrophobically modified poly(vinyl alcohol), [PVA] was synthesized by graft copolymerization of N-tertiary butyl acrylamide [NTBA] onto PVA by free radical polymerization. The incorporation of NTBA onto PVA chains was confirmed by elemental analysis, FT-IR and NMR spectroscopy. A series of graft copolymers with different contents of NTBA were prepared and membranes were casted from these copolymer solutions in dimethyl sulfoxide. The increase in hydrophobicity with an increase in NTBA content was investigated by contact angle measurements. The swelling behaviour of membranes as a function of temperature, hydrophobic content, annealing temperature and period was studied. Permeability of solutes through these membranes was investigated as a function of solute size, membrane hydrophobicity and temperature. The swelling behaviour of the copolymer membranes showed that the lower content of NTBA gives discontinuous volume transition with respect to temperature whereas, the presence of higher amounts of NTBA showed decreased swelling ratios with very little influence of temperature on the swelling. The permeabilities of solutes through these membranes were strongly dependent on the size of the solute, solution temperature and hydrophobicity of the membrane. The copolymer membranes were further characterized using DSC, DMA and XRD. The peak becomes broader as the NTBA content increases.     

Improvement of Permeability of Poly(vinyl alcohol) Hydrogel by Using Poly(ethylene glycol) as Porogen

The porous structure of PVA hydrogel achieved with varying content and varying molecular weight of PEG was investigated. It was found that with increasing content or molecular weight of PEG, the diffusion coefficient D _e and UV transmission of ink solution increased, indicating that the permeability and mass transfer capability of the gel beads were enhanced. The swelling rate constant k and equilibrium swelling rate of the gel were significantly improved by addition of PEG, and many pores formed inside the gel to provide channels for microbial metabolites. With increasing molecular weight of PEG, the size of pores became increasingly large.     

Separation of Diacteone Alcohol‐Water Mixtures by Membrane Pervaporation

Abstract

A study was conducted to evaluate membrane pervaporation for the separation of diacetone alcohol‐water mixtures using commercially available membranes for organic enrichment and dehydration. Empirical correlations for the effect of the process parameters of feed concentration, feed temperature, permeate‐side pressure, and scale‐up were developed. The solvent‐water mixture was successfully separated with a poly(vinyl alcohol) based Sulzer PERVAP 2210 dehydration membrane. Various dehydration membranes were evaluated and a comparison of the flux and separation factor was made. The membrane performance in separating acetone‐water mixtures was also studied. An overall model to predict the membrane area needed for a scale‐up was developed based on the results.     

Transition of hydration states of poly(vinyl alcohol) in aqueous solution

A straightforward method for determination of the hydration number of polymer in aqueous solution based on ice-melting technique of DSC is proposed. The simple yet precise method has been applied to determine the hydration number of poly(vinyl alcohol) (PVA) in aqueous solution covering a wide range of concentrations, from 0.005 to 0.3 g(solute)/g(solution), for three samples with different molar masses. The hydration number of PVA maintains a constant lower value of 2.5 when the concentration exceeds 0.2 g(solute)/g(solution). It increases to a value of 7 when the concentration decreases to the overlap concentration C^∗ of the polymer, where C^∗ was estimated as the reciprocal of its intrinsic viscosity. For solutions of C < C^∗, the hydration number keeps constant again at the value of 7. This behavior evidently demonstrates that PVA has two hydration states, one occurs at the dilute regime and the other occurs at concentrated regime. The concentration dependent transition from one state to another is treated mathematically by a quantitative formula which involves two parameters: one denotes the transition concentration and the other denotes the width of the transition region. The transition concentration decreases linearly with increasing molar mass resembling the behavior of molar mass dependence of overlap concentration. The structural features for the two states of hydrated PVA are briefly discussed.     

Pervaporation characteristics and structure of poly(vinyl alcohol)/poly(ethylene glycol)/tetraethoxysilane hybrid membranes

Poly(vinyl alcohol) (PVA) blended with poly(ethylene glycol) (PEG) was crosslinked with tetraethoxysilane (TEOS) to prepare organic–inorganic PVA/PEG/TEOS hybrid membranes. The membranes were then used for the dehydration of ethanol by pervaporation (PV). The physicochemical structure of the hybrid membranes was studied with Fourier transform infrared spectra (FT‐IR), wide‐angle X‐ray diffraction WXRD, and scanning electron microscopy (SEM). PVA and PEG were crosslinked with TEOS, and the crosslinking density increased with increases in the TEOS content, annealing temperature, and time. The water permselectivity of the hybrid membranes increased with increasing annealing temperature or time; however, the permeation fluxes decreased at the same time. SEM pictures showed that phase separation took place in the hybrid membranes when the TEOS content was greater than 15 wt %. The water permselectivity increased with the addition of TEOS and reached the maximum at 10 wt % TEOS. The water permselectivity decreased, whereas the permeation flux increased, with an increase in the feed water content or feed temperature. The hybrid membrane that was annealed at 130°C for 12 h exhibited high permselectivity with a separation factor of 300 and a permeation flux of 0.046 kg m^?2 h^?1 in PV of 15 wt % water in ethanol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

PVA—Zr（IV）催化膜制备及其性能

１引言交联聚乙烯醇（ＰＶＡ）膜用于酯化反应脱水,膜性能随时间发生变化,膜表面红外光谱显示聚乙烯醇上部分ＯＨ被酸酯化了［１］。解决这个问题最好的办法是设计一种膜,既具有催化活性又具有分离功能,反应和分离合二为一。对某物系有催化活性的基团通过化学接枝,...     

Poly(ethylene oxide)/clay nanocomposite: Thermomechanical properties and morphology

Poly(ethylene oxide) (PEO)/clay nanocomposites were prepared by a solution intercalation method using chloroform as a solvent. The nanocomposites were characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), hot-stage polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FT-IR), tensile analysis, dynamic mechanical analysis (DMA) characterisation techniques. Formation of nanocomposite was confirmed by X-ray diffraction (XRD) analysis. A decrease in PEO crystallinity in case of nanocomposite, was confirmed by a decrease in the heat of melting and spherulite size as indicated by DSC and POM studies, respectively. Improvement in tensile properties in all respect was observed for nanocomposites with optimum clay content (12.5 wt%). DMA studies indicate an increase in loss peak temperature and broadening of loss peak as a result of clay intercalation.     

Mixed matrix membranes prepared from natural rubber/poly(vinyl alcohol) semi-interpenetrating polymer network (NR/PVA semi-IPN) incorporating with zeolite 4A for the pervaporation dehydration of water-ethanol mixtures

The pervaporation dehydration of water-ethanol mixtures was investigated using the mixed matrix (MM) membranes prepared from natural rubber (NR) and crosslinked poly(vinyl alcohol) (PVA) semi-IPN embedded with the zeolite 4A. With the presence of NR as well as zeolite, the swelling of MM membranes in water was effectively suppressed. Examined by DSC, the non-freezing bound water in the MM membranes was found decreasing with more zeolite loading because the water-polymer interaction is diminishing. The sorption study of MM membranes revealed a preferential sorption to water with improved water sorption selectivity as increasing the zeolite loading. For pervaporation at 5 vol% water in feed, the reversed trade-off with respect to the zeolite loading was encountered such that the total permeation flux increased along with an enhancement of the water separation factor. For higher feed water concentration, despite the greater total permeation flux, the separation factor was reduced owing to the extensive swelling of the polymer matrix. The temperature dependency of the partial water and ethanol fluxes followed the Arrhenius relationship and the estimated activation energies for water flux were lower than those of the ethanol flux, suggesting that the developed MM membranes are highly water selective.     

Intermolecular interaction in aqueous solution of binary blends of poly(acrylamide) and poly(ethylene glycol)

The interaction between poly(acrylamide) (PAM) and poly(ethylene glycol) (PEG) in their solid mixture was studied by Fourier transform infrared spectroscopy (FTIR); and their interaction in aqueous solution was investigated by nuclear magnetic resonance spectroscopy (NMR). For the solid PAM/PEG mixtures, an induced shift of the >C?O and >N? H in amide group was found by FTIR. These results could demonstrate the formation of intermolecular hydrogen bonding between the amide group of PAM and the ether group of PEG. In the aqueous PAM/PEG solution system, the PAM and PEG associating with each other in water, i.e., the amide group of PAM interacting with the ether group of PEG through hydrogen bonding was also found by ¹H NMR. Furthermore, the effects of different molecular weight of PAM on the strength of hydrogen bonding between PAM and PEG in water were investigated systemically. It was found that the hydrogen bonding interaction between PAM and PEG in water did not increase with the enlargement of the PAM molecular weight as expected. This finding together with the viscosity reduction of aqueous PAM/PEG solution with the PAM molecular weight increasing strongly indicated that PAM molecular chain, especially having high molecular weights preferred to form spherical clews in aqueous PEG solution. Therefore, fewer amide groups in PAM could interact with the ether groups in PEG. Based on these results, a mechanism sketch of the interaction between PAM and PEG in relatively concentrated aqueous solution was proposed. The fact that the phase separation of aqueous PAM/PEG solution occurs while raising the temperature indicates that this kind of hydrogen bonding between PAM and PEG in water is weak and could be broken by controlling the temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(vinyl alcohol) hydrogel fixation on poly(ethylene terephthalate) surface for biomedical application

A surface modification technique was developed for the covalent immobilization of poly(vinyl alcohol) (PVA) hydrogel onto poly(ethylene terephthalate) (PET) to improve the biocompatibility of the film. The PET film was first graft copolymerized with poly(ethylene glycol) monomethacrylate (PEGMA) in the presence of ethylene glycol dimethacrylate (EGDMA) as crosslinker, and then oxidized with a mixture of acetic anhydride (Ac₂O) and dimethyl sulfoxide (DMSO) to produce aldehyde groups on the PET surface. Finally, the prepared PVA solution was cast onto the film and covalently immobilized on the film through the reaction between the aldehyde groups on the PET film and the hydroxyl groups of PVA. The good attachment of the PVA layer to the PET film was confirmed by observing the cross-section of the PET-PVA film using scanning electron microscopy (SEM). Heparin was immobilized on the PVA layered PET using two different methods, physical entrapment and covalent bonding, to further improve the biocompatibility of the film. Attenuated total reflectance (ATR) FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the chemical composition of the surface modified films. The biocompatibility of the various surface modified PET films was evaluated using plasma recalcification time (PRT) and platelet adhesion.     

Novel ternary poly(vinyl pyrrolidone)/poly(amide-imide)/ZnO nanocomposite: Synthesis,characterization, thermal and optical performance

The present work describes the synthesis and properties of polymer composites based on poly(vinyl pyrrolidone) (PVP) as polymer shell and poly(amide-imide)(PAI)/ZnO nanocomposite (ZNC) as efficient filler. At first, the alanine amino acid containing dicarboxylic acid was grafted on the surface of ZnO NPs. Then, modified ZnO (12 wt%) was incorporated into the PAI matrix under ultrasonic irradiations. The obtained hybrid ZNC showed high thermal stability and the size of the NPs in the TEM image of ZNC was about 31 nm. Secondly, PVP NCs with different ZNC loadings such as 2, 4 and 6 wt% were prepared via ultrasonication. Transmission electron microscopy (TEM) observations showed that the ZnO NPs were uniformly and highly dispersed in the PVP matrix. The UV–vis results exposed that the high UV-shielding efficiency of the obtained composites. Thermal analysis represented that the onset decomposition temperatures of the obtained PVPNCs had remarkable increasing in compared to the neat PVP due to the presence of both ZnO NPs and PAI.     

Chitosan/TiO2 nanocomposite pervaporation membranes for ethanol dehydration

Novel chitosan/titanium dioxide (CS/TiO₂) nanocomposite membranes were prepared using tetrabutyl titanate (TBT) as precursor and acetyl acetone as chelating agent by in situ sol-gel process, and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetry (TG). The characterization results demonstrated that nano-sized TiO₂ particles dispersed homogeneously within the CS matrix, which could be assigned to the hydrogen and titanoxane bonds formed between CS and TiO₂. Moreover, the pervaporation performance of these membranes was investigated using the separation of ethanol-water mixture as model system. Compared with CS/TiO₂ hybrid membranes prepared by blending method, most of CS/TiO₂ nanocomposite membranes prepared by in situ sol-gel process exhibited higher permeation flux and separation factor under the identical conditions. Among all the prepared membranes, CS/TiO₂ nanocomposite membrane containing 6 wt% TiO₂ exhibited the best pervaporation performance, whose averaged permeation flux and separation factor were 0.340 kg m⁻² h⁻¹ and 196 for 90 wt% aqueous solution of ethanol at 80 °C, respectively.     

The effect of microwave irradiation on poly(vinyl alcohol) dissolved in ethylene glycol

Poly(vinyl alcohol) (PVA) dissolved in ethylene glycol is subjected to microwave (MW) irradiation for 1 h to determine possible degradation. Fourier transform infrared spectroscopy results show that MW treatment produces a minor effect on the solutions. Ultraviolet–visible spectroscopy suggests that PVA could undergoes loss of hydroxyl groups followed by formation of unsaturated conjugated bonds although the extent of degradation is limited, whereas size exclusion chromatography indicates that MW irradiation do not cause significant changes in PVA molar mass and neither chain cleavage nor crosslinking reactions are observed. Hence, polymer degradation induced by MWs in solution can be considered as negligible for prospective applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of PSSA/PVA catalytic membrane for biodiesel production

Poly(styrene sulfonic acid) (PSSA)/Poly(vinyl alcohol) (PVA) blend membranes prepared by the solution casting were employed as heterogeneous acid catalysts for biodiesel production from acidic oil obtained from waste cooking oil (WCO). The membranes were annealed at different temperature in order to enhance their stability. The structure and properties of the membranes were investigated by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), X-ray diffraction (XRD). It is found that the crosslinking structure among PVA and PSSA chains formed when the thermal treatment temperature was higher than 80 °C. The retention of PSSA in the blend membranes in the methanol/water solvent was markedly increased from 50% to 85% with the increase of the annealing temperature from room temperature (for the untreated membrane) to 150 °C due to the formation of the crosslinking structure. The results of esterification of acidic oil show that the conversion was slightly improve with the PVA content in the membrane at a fixed PSSA content. The thickness of the catalytic membrane had no significant effect on the conversion in the end. The membrane annealed at 120 °C exhibited the best catalytic performance among the membranes, with a stable conversion of 80% with the runs.     

Mixed matrix membranes of sodium alginate and poly(vinyl alcohol) for pervaporation dehydration of isopropanol at different temperatures

Mixed matrix membranes of sodium alginate (NaAlg) and poly(vinyl alcohol) (PVA) containing 5 and 10 wt.% silicalite-1 particles were fabricated by solution casting method and the cured membranes were crosslinked with glutaraldehyde. These membranes were used in pervaporation (PV) dehydration of isopropanol at 30, 40, 50 and 60 °C. Membrane morphology was studied by scanning electron microscopy and universal testing machine to assess their mechanical strengths. Swelling results of the pristine and mixed matrix membranes were correlated with their PV performances. Selectivities of the mixed matrix membranes of NaAlg were 11,241 and 17,991 with the fluxes of 0.039 and 0.027 kg/m² h, respectively, for 5 and 10 wt.% silicalite-1 loadings. Corresponding values for mixed matrix membranes of PVA were 1295 and 2241, and 0.084 and 0.069 kg/m² h, respectively, for 10 wt.% water-containing feed at 30 °C. Pristine membranes of NaAlg and PVA exhibited lower selectivities of 653 and 77 with increased fluxes of 0.067 and 0.095 kg/m² h, respectively. From the temperature dependence of flux and diffusivity data with 10 wt.% water-containing feed, Arrhenius plots were constructed to compute heat of sorption, ΔH_s values. Mixed matrix membranes of NaAlg were better than PVA mixed matrix membranes at all compositions (10-40 wt.%) of water. Molecular dynamics (MD) simulation was employed to compute the interfacial interaction energies of NaAlg and PVA polymers with silicalite-1 filler; also sorption of liquid molecules was computed. Simulated diffusivities compared well with the experimental data. Thermodynamic treatment of sorption, diffusion and permeation processes was attempted based on the Flory-Huggins theory to explain the PV performances of the membranes.     

Glycerol-modified poly(vinyl alcohol)/poly(ethylene glycol) self-healing hydrogel for artificial cartilage

Poly(vinyl alcohol) (PVA) hydrogels have shown potential applications in bionic articular cartilage due to their tissue-like viscoelasticity, good biocompatibility and low friction. However, their lack of adequate mechanical properties is a key obstacle for PVA hydrogels to replace natural cartilage. In this study, poly(ethylene glycol) (PEG) and glycerol were introduced into PVA, and a PVA/PEG–glycerol composite hydrogel was synthesized using a mixing physical crosslinking method. The mechanical properties, hydrophilicity and tribological behavior of the PVA/PEG–glycerol hydrogel were investigated by changing the concentration of glycerol in PEG. The results showed that the tensile strength of the hydrogel reached 26.6 MPa at 270% elongation at break with 20 wt% of glycerol plasticizer, which satisfied the demand of natural cartilage. In addition, the excellent hydrophilicity of glycerol provides good lubricating properties for the composite gel under dry friction. Meanwhile, self-healing and cellular immunity assays demonstrated that the composite gel could have good self-healing ability and excellent biocompatibility even in the absence of external stimuli. This study provides a new candidate material for the design of articular cartilage, which has the potential to facilitate advances in artificial joint cartilage repair. © 2022 Society of Industrial Chemistry.