分离有机/有机混合物的PVA、CA系列膜及其渗透汽化性能研究(Ⅰ)膜材料与成膜工艺

依据溶度参数原则和分离甲基叔丁基醚(MTBE)/甲醇(MeOH)混合物的选择渗透性,选择了聚乙烯醇(PVA)为复合膜的分离层材料,聚丙烯腈(PAN)、醋酸纤维素(CA)系列为支撑层的膜材料.初步讨论了膜材料和复合膜结构对分离性能的影响,给出了用不同成膜工艺制备的膜性能,获得了可用于有机/有机体系分离的性能优良的PVA/PAN和PVA/CA复合膜,以及CTA中空纤维渗透汽化膜.     

Pervaporation separation of MTBE–methanol mixtures using cross‐linked PVA membranes

Poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) and PVA/sulfosuccinic acid (SSA) membrane performances have been studied for the pervaporation separation of methyl tert‐butyl ether (MTBE)/methanol (MeOH) mixtures with varying operating temperatures, amount of cross‐linking agents, and feed compositions. Typically, the separation factor, about 4000, and the permeation rate, 10.1 g/m²/h, were obtained with PVA/PAA = 85/15 membrane for MTBE/MeOH = 80/20 mixtures at 50°C. For PVA/PAA membranes, it could be considered that the flux is affected by the structural changes of the membranes due to the cross‐linking and the free carboxylic acid group also took an important role in the separation characteristics through the hydrogen bonding with PVA and the feed components leading to the increase of flux. The latter membrane of the 5% SSA membrane shows the highest separation factor of 2095 with the flux of 12.79 g/m²/h for MTBE/MeOH = 80/20 mixtures at 30°C. Besides the swelling measurements were carried out for pure MTBE and MeOH, and MTBE/MeOH = 90/10, 80/20 mixtures using PVA/SSA membranes with varying SSA compositions. It has been recognized that there are two factors, the membrane network and the hydrogen bonding in the swelling measurements of PVA/SSA membranes. These two factors act interdependently on the membrane swelling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1699–1707, 2000     

Solvent treatment of CTA hollow fiber membrane and its pervaporation performance for organic/organic mixture

Cellulose triacetate (CTA) hollow fiber membrane used to separate methanol/methyl tert-butyl ether (MTBE) by pervaporation (PV) has been prepared from CTA hollow fiber reverse osmosis (RO) membrane for desalination of brackish water with high salinity. Acetone was selected as a modification agent of CTA membrane. PV performance depended on the solvent concentration, the treatment time and modification temperature of CTA RO hollow fiber membrane soaked in the aqueous acetone. The results show that CTA hollow fiber membrane modified with the solvent has a superior performance both the separation factor and the permeate flux in the PV experiment conditions.     

Permeation behaviour in cellulose triacetate dense membrane during pervaporation separation of methanol/methyl tert-butyl ether mixture

The pervaporation separation of methanol/methyl tert-butyl ether through cellulose triacetate dense membranes has been carried out under different feed compositions, permeation temperatures and temperature cycles to investigate the permeation behaviour of the membrane during pervaporation process. The experimental data indicate that the plasticization effect has a decisive influence on pervaporation flux, permselectivity and permeation activation energy. The results show that the penetrants of different feeds are transported through the membrane by different pathways with the influence of plasticization effect at different temperatures. It has also been observed that plasticization had great effect on the membrane swelling and sorption selectivity. Furthermore, DSC results show that the membranes retain the influence of the plasticization effect after pervaporation separations are tested. © 2000 Society of Chemical Industry     

渗透汽化膜分离MeOH/MTBE混合物的传质分析——单组分在膜中的扩散

用石英晶体微平衡法测定了298.15 K、305.75 K、312.95 K下MeOH（甲醇）和MTBE（甲基叔丁基醚）在CA（醋酸纤维素）膜中的吸着平衡数据和吸着动力学数据.结果表明：MeOH和MTBE在CA膜中的传质过程属于Fick扩散类型;MeOH在CA膜中的平衡吸着量和扩散系数都比MTBE大,说明CA膜对MeOH/MTBE混合物有较好的分离性能;同一吸着温度下,吸着速度和平衡吸着量均随着吸着蒸气压的升高而升高;可用Eyring的扩散“空穴”理论解释MeOH和MTBE在膜中的扩散行为.     

Pervaporation of methanol/methyl tert‐butyl ether mixtures through agarose/hydroxyethylcellulose blended membranes

In this study, we investigated methanol (MeOH)/methyl tert‐butyl ether (MTBE) separation with hydroxyethylcellulose (HEC)/agarose blended membranes by applying a pervaporation technique. The membranes permeated MeOH in preference to MTBE from MeOH/MTBE mixtures. From pervaporation and sorption data, the permselectivity of HEC/agarose blended membrane was dominantly due to solubility selectivity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3408–3411, 2002     

Copolyimide molecular brushes with poly(methacrylic acid) side chains as additive to polyphthalamide membrane: Organization,physical, and transport properties

Macromolecules of complex architecture find application as modifiers of commercial polymeric membrane materials. In this work, copolyimide molecular brushes (coPI) composed of polyimide backbone and poly(methacrylic acid) side chains were used to modify poly(m-phenylene iso-phthalamide) (PPA). Structure, physical, mechanical, and transport properties of dense nonporous PPA/coPI membranes containing up to 10 wt% coPI were studied. The effect of included coPI on the membrane structure was estimated using atomic force microscopy and mechanical tests. The coPI modifier contributes to the additional formation of free volume elements evenly distributed throughout the membrane. Transport properties of PPA/coPI membranes were investigated via sorption tests and pervaporation separation of methanol (MeOH) and methyl tert-butyl ether (MTBE) mixtures. The inclusion of coPI modifier in the PPA membrane leads to an increase in the total flux of the membrane. The highest separation factor was found for the PPA/coPI membrane containing 10 wt% coPI; transport properties of the best membrane were compared with the literature data on separation of the azeotropic MeOH–MTBE mixture.     

Plasticization of chitosan membrane for pervaporation of aqueous ethanol solution

The process of pervaporation in which two components diffuse through a nonporous polymer membrane was modelled when one of the penetrants can exert a plasticization action to the membrane material. Thereat a phenomenological model was employed for describing the plasticization effect on the diffusivities for penetrants in the membrane. The sorption equilibria and permeation fluxes for aqueous ethanol solutions in a chitosan membrane were measured, and the permeation fluxes for water were compared with those predicted by the proposed model. The concentration of sorbed water was linear with its weight fraction (x₄) in the feed solution, whereas the permeation flux of water was. affected by the plasticization action of sorbed water to the polymer. This plasticization effect on the diffusion process can be simulated in terms of the proposed phenomenological model.     

γ-(2,3环氧丙氧)丙基三甲氧基硅烷改性壳聚糖渗透蒸发杂化膜的制备及乙醇脱水性能研究

通过γ-缩水甘油醚氧丙基三甲氧基硅(KH-560)对壳聚糖进行交联改性制备乙醇脱水渗透蒸发杂化膜.实验结果表明偶联剂的加入能有效提高壳聚糖膜的分离效果,随着偶联剂含量的增加,杂化膜的对水的选择性先增加后下降,在2％(质量分数)时有最好的选择性.膜的分离因子随着进料温度的增大而降低,随着乙醇浓度的增大而增大;通量随着进料温度的增大而增大,随着乙醇浓度增大而减小.硅烷偶联剂/壳聚糖杂化膜呈现出良好的渗透蒸发分离性能,当进料乙醇浓度为95％(质量分数),温度为35℃时,通量和分离因子分别为134g/(h·m2)和97214.     

Separation Characteristics of Dimethylformamide/Water Mixtures through Alginate Membranes by Pervaporation,Vapor Permeation and Vapor Permeation with Temperature Difference Methods

Abstract

In this study permeation and separation characteristics of dimethylformamide (DMF)/water mixtures were investigated by pervaporation (PV), vapor permeation (VP), and vapor permeation with temperature difference (TDVP) methods using alginate membranes crosslinked with calcium chloride. The effects of membrane thickness (30–90 µm), feed composition (0–100 wt%), operating temperature (30–50°C) on the permeation rates and separation factors were investigated. The permeation rate was found to be inversely proportional to the membrane thickness whereas separation factor increased as the membrane thickness was increased. It was observed that the permeation rates in VP and TDVP were lower than in PV however the highest separation factors were obtained with TDVP method. Alginate membranes gave permeation rates of 0.97–1.2 kg/m² h and separation factors of 17–63 depending on the operation conditions and the method. In addition, sorption‐diffusion properties of the alginate membranes were investigated at the operating temperature and the feed composition. It was found that the sorption selectivity was dominant factor for the separating of DMF/water mixtures.     

Permeation and separation characteristics of acetic acid/water mixtures through poly(vinyl alcohol‐g‐itaconic acid) membranes by pervaporation,evapomeation, and temperature‐difference evapomeation

In this study, itaconic acid (IA) was grafted onto poly(vinyl alcohol) (PVA) with cerium(IV) ammonium nitrate as an initiator at 45°C. The grafted PVA was characterized with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. IA‐grafted PVA membranes were prepared with a casting method, and the permeation and separation characteristics of acetic acid/water mixtures were investigated with pervaporation (PV), evapomeation (EV) and temperature‐difference evapomeation (TDEV) methods. The effects of the feed composition, operating temperature, and temperature of the membrane surroundings on the permeation rate and separation factor for the acetic acid/water mixtures were studied. The permeation rates in EV were lower than those in PV, whereas the separation factors were higher. With the TDEV method, the permeation rates decreased and the separation factors increased as the temperature of the membrane surroundings decreased. The prepared membranes were also tested in PV, EV, and TDEV to separate the various compositions of the acetic acid/water mixtures (20–90 wt % acetic acid) at 40°C. The highest separation factor, 686, was obtained in TDEV with a 90 wt % acetic acid concentration in the feed. The activation energies of permeation in PV and EV were calculated to be 8.5 and 10.2 kcal/mol, respectively, for a 20 wt % acetic acid solution. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2322–2333, 2004     

Pervaporation separation of methyl tert-butyl ether/methanol mixtures using a high-performance blended membrane

For the separation of methyl tert-butyl ether (MTBE) and methanol mixtures, we investigated the pervaporation performance of a blend membrane made from cellulose acetate and cellulose acetate hydrogen phthalate. At first the influence of the blend composition was studied with a certain feed mixture. We found that all the tested membranes permeate methanol preferentially. The selectivity increases and the permeation rate decreases with increasing cellulose acetate content in the blend. Therefore, an optimal blend composition of 30 wt % in cellulose acetate was chosen to evaluate the influence of the feed composition and the experimental temperature on the pervaporation performance. When the feed temperature or the methanol content in the feed increases, the permeation rates are greatly enhanced and the selectivity decreases. However, the temperature effect is more significant at low methanol content in the feed and becomes negligible at high methanol content in the feed where plasticity effects prevail. A comparison, carried out with all the membranes until now used for the separation of MTBE/methanol mixtures, showed that the blended membrane studied in this present work presents good permselective properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 875–882, 1997     

Pervaporation separation of methanol/methyl tert‐butyl ether with poly(lactic acid) membranes

Poly(lactic acid), as a natural source polymer, was used to prepare pervaporation dense membranes. The performance of these membranes for the separation of the methanol (MeOH)/methyl tert‐butyl ether (MTBE) mixtures was investigated. The effects of different operating conditions, including the feed concentration of MeOH, temperature, and flow rate, were examined. Several characterization tests were performed as well. The swelling results, scanning electron microscopy images, contact angles, and mechanical strength measurements are presented. These membranes were found to be selective to MeOH, particularly for traces of MeOH in MTBE with a separation factor of more than 30. There was a small decrease in the separation factor when the feed temperature was increased; meanwhile, the total flux increased to some extent. This could be explained with respect to the thermal motions of the polymer chains and the permeating molecules. With an increase in the feed flow rate, both the selectivity and total flux increased because the concentration and temperature polarizations decreased. At higher flow rates, the feed components were homogeneously distributed over the membrane surface, whereas there may have been a concentration or temperature gradient at lower flow rates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thin film composite membranes with desirable support layer for MeOH/MTBE pervaporation

A comprehensive study was performed on a new application of thin film composite membranes and selecting a stable sublayer for them as pervaporation membranes in organic solvent separation. For this purpose, four different polymeric sublayers of polyethersulfone (PES), cellulose acetate, polyacrylonitrile, and polyetherimide were prepared, and the interaction of methanol (MeOH) and methyl tert butyl ether (MTBE) with them was investigated. The contact angle results, scanning electron microscopy images, and swelling and mechanical strength measurements obviously displayed the effect of immersion in organic solvents on the sublayers. Finally, a polyamide active layer was subsequently deposited on the PES membrane surface as the stable sublayer via interfacial polymerization based on a multistep statistical optimization strategy involving fractional factorial design and a response surface method. The prepared TFC membranes were tested in the pervaporation of a MeOH/MTBE mixture and exhibited excellent performance compared with the current membranes in this context. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47519.     

Pervaporation characteristics of methyl methacrylate–methacrylic acid copolymer membranes ionically crosslinked with metal ions for a benzene/cyclohexane mixture

Methyl methacrylate–methacrylic acid copolymer (MMA–MAA) membranes ionically crosslinked with Fe³⁺ and Co²⁺ ions (MMA–MAA–Fe³⁺ and –Co²⁺) were prepared, and characteristics of permeation and separation for a benzene/cyclohexane mixture of 50 wt % benzene through these membranes in pervaporation (PV) were studied. Although the introduction of the metal ions to the MMA–MAA membrane enhanced both benzene permselectivity and permeability for a benzene/cyclohexane mixture, the PV characteristics between the MMA–MAA–Fe³⁺ and –Co²⁺ membranes were significantly different. The difference in the PV characteristics between these membranes was strongly governed by the difference of these membrane structures based on the glass transition temperature, contact angle to methylene iodide, degree of swelling, and mixture composition absorbed in the membrane, and so on. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 233–241, 1999     

A photocatalytic membrane reactor for gas-phase reactions using porous titanium oxide membranes

Photocatalytic membrane reactors using porous titanium oxide membranes having pore sizes of several nanometers were utilized for a gas-phase reaction of methanol. Air mixed with methanol (MeOH) vapor, the concentration of which was controlled in the range of 500–6000 ppm, was fed to the photocatalytic membrane reactor in the range of 50–500 cm³/min using several types of flow patterns. Photocatalysis with membrane permeation resulted in a large decomposition rate, compared to photocatalysis without membrane permeation. The characteristics of the reaction such as decomposition ratio of MeOH, the conversion of the decomposed MeOH to CO₂ and H₂O were found to be a function of the residence time in the reactor. The photocatalytic reaction was analyzed based on pseudo-first-order kinetics to ascertain its simplicity, and the fitted curves were found to be in a relatively good agreement with the experimental data. Apparent rate constants with and without membrane permeation were 2.5 and 1.5×10⁻⁶ m s⁻¹, respectively, indicating that the performance of the photocatalytic reaction system with membrane permeation was enhanced.     

An experimental study on the application of polymer membranes to the catalytic decomposition of MTBE (methyl tert.-butyl ether)

In this experimental study, the methyl tert.-butyl ether (MTBE) decomposition was carried out in various inert membrane reactors composed of H₃PW₂O₄₀ and a polymer membrane. Polycarbonate (PC), polyarylate (PA) and cellulose acetate (CA) membranes were used in the membrane reactor. It was revealed that all the tested polymer membranes showed larger permeability of methanol than that of either MTBE or isobutene, and the membrane reactor showed better performance than the corresponding fixed bed reactor. The perm-selectivity of methanol/MTBE was in the order of CA > PC > PA, and the permeation ratio of product/MTBE was in the order of CA > PA > PC. Among the membrane reactors tested CA membrane reactor showed the best performance. The enhanced performance of the membrane reactor was mainly due to the selective permeation of methanol that made a methanol-deficient phase suppressing MTBE synthesis reaction in the reversible reaction.     

高分子致密膜内渗透现象的同一性研究

在渗透汽化（PV）和蒸汽渗透（VP）膜分离过程,利用高分子膜材料对原料中不同组分的溶解度与扩散系数不同实现混合物分离.由于两种过程原料状态分别呈现液态和蒸汽形式,长期以来作为两种膜分离过程展开研究,其传质推动力都是组分在膜中的化学位梯度.为了从热力学和传质角度研究PV和VP膜分离过程,本文设计了特殊的渗透池,可以在同一渗透池中同时进行渗透汽化和蒸汽渗透膜分离过程,保持气液界面为热力学平衡状态.使用PVA/PAN复合膜进行水/乙醇混合物以及水/异丙醇混合物的PV和VP渗透实验,对两个过程中渗透通量随浓度变化情况进行了分析和比较.实验结果和理论分析表明：溶液的PV过程和与之呈相平衡的蒸汽相的VP过程在一定温度范围内,当原料中水含量较低的情况下具有相同的渗透通量,其传质遵从溶解扩散机理;当原料溶液中水含量较高时,PV过程中膜溶胀现象较为严重,渗透通量存在一定差别.     

Pervaporation dehydration of ethyl acetate aqueous solution using the doubly modified polyvinyl alcohol (PVA) composite membrane

Polyvinyl alcohol–tetraethoxysilane–perfluorosulfonic acid (PVA–TEOS–PFSA) hybrid membrane was prepared by sol–gel method through PVA being modified doubly by PFSA and TEOS. With polyacrylonitrile (PAN) ultrafiltration membrane as a substrate membrane, PVA–TEOS–PFSA/PAN composite membrane was fabricated by dip-coating method for pervaporation (PV) dehydration of ethyl acetate (EAc) aqueous solution. The hybrid membrane was characterized by swelling degree, static contact angle, Fourier transform infrared spectra and scanning electron microscope. Effects of PFSA and TEOS contents in coating solution on PV performance of composite membrane were investigated, respectively. With increasing PFSA content, the permeation flux of composite membrane increased, while the separation factor decreased. Just the opposite, the increase of TEOS content resulted in the decrease in permeation flux and the increase in separation factor. In addition, the PV performances of composite membranes were also investigated at different feed temperatures and water concentrations in feed, respectively. The PVA–TEOS–PFSA/PAN composite membrane, which was prepared from coating with PVA/PFSA mass ratio of 80/20 and TEOS content of 20 wt%, exhibited the permeation flux of 347.9 g m^?2 h^?1 and the separation factor of 2218 for PV dehydration of 2 wt% water of EAc solution at 40 °C.     

Vulcanized paper for separation of alcohol aqueous solutions by pervaporation

Paper membranes made from vulcanized cellulose were used for the pervaporation (PV) of aqueous solutions containing methanol, ethanol, and isopropanol. It was noted that the vulcanized cellulose paper membranes (VCPM) could effectively separate alcohol and water from the mixture solutions. To observe the effect of the separation of alcohol aqueous mixtures, the permeation behavior of water and alcohol was examined by means of the separation factor and the permeation flux. The values of the permeation flux in the ethanol/water mixtures were found to vary from 6.2 kg/m²h to 2.1 kg/m²h, as the concentration of ethanol increased from 8 to 87 wt %, and the separation factor (α) changed from α = 2.6 to 6.6, respectively. This showed that the VCPM enhanced the separation of water and alcohol. The highest value observed for the permeation flux was 11 kg/m²h at 87 wt % of methanol concentration and the separation factor at this condition was 4.1. It was shown also that an efficient separation was obtained in the isopropanol/water mixture with a separation factor of 16.6. The contact angles of alcohol/water droplets on the VCPM were measured as well as the wettability of the membrane. There was a tendency of decrease for the contact angle, as the alcohol concentration decreased. This suggested that the solvent wettability decreased in high alcohol concentrations. It was concluded that a high permeabilitty of water through the VCPM resulted in the separation of alcohols and water in the PV process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011