Pervaporation Zeolite-Based Composite Membranes for Solvent Separations

Thanks to their well-defined molecular sieving and stability, zeolites have been proposed in selective membrane separations, such as gas separation and pervaporation. For instance, the incorporation of zeolites into polymer phases to generate composite (or mixed matrix) membranes revealed important advances in pervaporation. Therefore, the goal of this review is to compile and elucidate the latest advances (over the last 2–3 years) of zeolite applications in pervaporation membranes either combining zeolites or polymers. Here, particular emphasis has been focused on relevant insights and findings in using zeolites in pervaporative azeotropic separations and specific aided applications, together with novel concepts of membranes. A brief background of the pervaporation process is also given. According to the findings of this review, we provide future perspectives and recommendations for new researchers in the field.     

含氟体系下高性能丝光沸石分子筛膜的制备及其性能

采用热涂-浸渍法在大孔α-Al2O3载体上形成薄且致密的晶种层,然后在不添加有机模板剂的含氟条件下二次水热生长法制备了高性能丝光沸石分子筛膜,考察了NaF含量、硅/铝比对丝光沸石分子筛膜形貌和性能的影响.将摩尔组成为6Na2O:1.2Al2O3:30SiO2:780H2O:1.5NaF条件下合成的丝光沸石分子筛膜用于渗透汽化分离91.5%乙醇/水体系,在渗透汽化温度70°C、真空度为400Pa条件下,分离因子和通量分别达到了6872和0.51kg/(m2·h);另外,在分离异丙醇/水、乙酸/水体系时,渗透侧水浓度达到了100%(在色谱检测极限范围内),该分离系数是目前报道的丝光沸石分子筛膜分离的最佳值,并在乙酸浓度为1mol/L的乙醇水溶液中表现出良好的耐酸性.该膜有望作为膜反应器在乙酸乙酯等酯类的生产中大大提高转化率.     

Pervaporation dehydration of isopropanol with chitosan membranes

Homogeneous and composite chitosan based membranes were prepared by the solution casting technique. The membranes were investigated for the pervaporation dehydration of isopropanol-water systems. The effects of feed concentration and temperature on the separation performance of the membranes were studied. In terms of the pervaporation separation index (PSI), the composite membrane was more productive than the homogeneous membrane for pervaporation of feed with high isopropanol content. It was observed that permeation increased and the separation factor decreased with the temperature. Modification of the homogeneous chitosan membrane by chemical crosslinking with hexamethylene diisocyanate improved the permselectivity but reduced the permeation rate of the membrane.     

‘Gate effect’ in templated polyacrylamide membranes influences the electrotransport of proteins and finds applications in proteome analysis

Templating is an effective way for the structural modifications of a material and hence for altering its functional properties. Here protein imprinting was exploited to alter polymeric polyacrylamide (PAA) membranes. The sieving properties and selection abilities of the material formed were evaluated by studying the electrically driven transport of various proteins across templated PAA membranes. The sieving properties correlated with the templating process and depended on the quantity of template used during the polymerisation. For 1 mg/mL protein-templated membranes a ‘gate effect’ was shown, which induced a preferential migration of the template and of similar-size proteins. Such template preferential electrotransport was exploited for the selective removal of certain proteins in biological fluids prior to proteome analysis (depletion of albumin from human serum); the efficiency of the removal was demonstrated by analysing the serum proteome by two-dimensional electrophoresis experiments. Figure PAA templeted membrane for the electroremoval of serum albumin before proteome analysis     

Preparation and characterizations of asymmetric sulfonated polysulfone membranes by wet phase inversion method

This paper presents an original approach to prepare the asymmetric sulfonated polysulfone membranes by using wet phase inversion method and their applications for dehydrating a water/ethanol mixture by pervaporation. The separation performances of sulfonated membranes were strongly affected by the degree of sulfonation and the degree of swelling of membranes. The substitution degree of sulfonic group enhanced the permselectivity of sulfonated polysulfone membranes by increasing the hydrophilicity of polymer backbone. Based on the observations of membrane morphology and light transmittance measurements, the degree of sulfonation of polysulfone presented less influence on the membrane formation pathway and the final structure of membrane in wet phase inversion process. It was also found that the sulfonated membranes showed well hydrophilic properties and facilitated water adsorption in the membranes. The sorption and permeation properties also showed that the permselectivity of asymmetric membrane was dominated by the permeate diffusion rather than the permeate sorption in the skin layer. The high separation performance of pervaporation membrane can be achieved by phase inverse method with sulfonated polysulfone.     

A LDH Template Triggers the Formation of a Highly Compact MIL-53 Metal-Organic Framework Membrane for Acid Upgrading

Highly compact metal–organic framework (MOF) membranes offer hope for the ambition to cope with challenging separation scenarios with industrial implications. A continuous layer of layered double hydroxide (LDH) nanoflakes on an alumina support as a template triggered a chemical self-conversion to a MIL-53 membrane, with approximately 8 hexagonal lattices (LDH) traded for 1 orthorhombic lattice (MIL-53). With the sacrifice of the template, the availability of Al nutrients from the alumina support was dynamically regulated, which resulted in synergy for producing membranes with highly compact architecture. The membrane can realize nearly complete dewatering from formic acid and acetic acid solutions, respectively, and maintain stability in a continuous pervaporation over 200 h. This is the first success in directly applying a pure MOF membrane to such a corrosive chemical environment (lowest pH value of 0.81). The energy consumption is saved by up to 77 % when compared with the traditional distillation.     

Deep desalination of water by evaporation through polymeric membranes

Transport properties and structural features of a number of already known and new types of polymeric membranes in desalination of aqueous salt solutions by membrane distillation and pervaporation were studied. The possibility of obtaining distilled water in a single stage by pervaporation from dilute or concentrated aqueous salt solutions was examined for the example of membranes fabricated from celluloses of varied origin (wood, cotton, bacterial).     

Separation of aqueous organic mixtures by pervaporation and analysis by mass spectrometry or a coupled gas chromatograph—mass spectrometer

A method of analysis has been developed based on the use of selective membranes which gives the possibility of enriching, identifying and quickly analysing organic volatile compounds in dilute aqueous solution. The process used to separate water from organic products is pervaporation. p]One side of the selective membrane is in contact with the liquid mixture. The other side of the membrane, under vacuum, is directly connected with the ionization source of a mass spectrometer which analyses quantitatively and qualitatively the organic compounds in proportion as they pass through the membrane. p]A number of different pervaporation membranes were studied and the selectivity of the membranes to different aqueous mixtures has been measured. Four types of analytical applications are described.     

Comparison between the pervaporation and vapor permeation performances of polycarbonate membranes

The pervaporation and vapor permeation performance of symmetrical and asymmetrical polycarbonate membranes, prepared via a dry-phase inversion and wet-phase inversion methods, respectively, were studied by measuring the permeation rate and separation factor. It was found that the polymer concentration effect on the pervaporation performance for the symmetrical polycarbonate membrane was lower than that for the asymmetrical polycarbonate membrane. Compared with pervaporation, vapor permeation has a significantly increased separation factor with a decreased permeation rate for the symmetrical polycarbonate membrane. Water molecules preferentially dissolve into the symmetrical polycarbonate membrane and diffuse easily through the membrane.     

Dehydration of water-alcohol mixtures by pervaporation and vapor permeation through surface resintering expanded poly(tetrafluoroethylene) membranes

For the purpose of separating aqueous alcohol mixtures by the use of the pervaporation and vapor permeation techniques, a surface resintering expanded poly(tetrafluoroethylene) (e-PTFE), membrane was investigated. The surface properties of the modified e-PTFE membranes were characterized by atomic force microscopy, scanning electron microscopy, and contact angle meter. The X-ray diffraction measurements show that the crystallinity of the e-PTFE membrane decreases with increasing the surface resintering temperature. The surface roughness decreases with the surface resintering temperature increases. The membrane exhibited water selectivity during all process runs. The effects of feed composition, surface resintering temperature, and molar volume of the alcohols on pervaporation and vapor permeation were investigated. Compared with the e-PTFE membrane without surface modified, the e-PTFE membrane with surface resintering treatment effectively improve the separation factor for pervaporation of aqueous alcohol mixtures. The separation performances of e-PTFE membranes in vapor permeation are higher than that in pervaporation.     

二丙酮丙烯酰胺共聚物膜用于渗透汽化法分离乙醇—水混合物

为将稀薄的乙醇水溶液浓缩,传统的蒸馏方法不能避免乙醇-水的共沸,能耗也很大。渗透汽化法克服了蒸馏法的这两个缺点,有希望成为分离乙醇水溶液的较为理想的方法。 作为水优先透过膜材料,有聚乙烯醇、磺化聚苯乙烯、聚丙烯腈、醋酸纤维素、聚乙烯亚胺、阴、阳离子交换膜阴、阳离子性多糖类、聚丙烯酸等及各种共聚物和共混     

Prediction of separating characteristics of pervaporation membranes by inverse gas chromatography

The potentiality of inverse gas chromatography to predict separating properties of pervaporation membranes is studied for the example of a membrane composed of a mixture of polyvinyl alcohol and polyacrylic acid. Correlation relationships between the retention time of substances and relative rate of their mass transfer across the membrane were derived. A comparative method for assessment of the membrane selectivity was suggested proposed, and its consistency was checked for pervaporation separation of methanol-methyl acetate-water-acetic acid, methanol-toluene, and ethanol-ethyl acetate mixtures, including those with an azeotropic composition.     

渗透气化法分离液体混合物

渗透气化法是一种用来分离液体混合物的膜分离方法。本综述简要地讨论了渗透气化法的机理。本法用于乙醇-水混合物的分离,对于从生物源生产乙醇具有重要意义。乙醇-水混合物的分离膜可以分成二类:亲水性膜和亲乙醇膜。使用若干物理方法可改进渗透气化过程。最后,作者认为渗透气化膜的发展趋势是从均质膜,不对称膜向复合膜过渡。     

Electric field-enhanced assembly of polyelectrolyte composite membranes

In this paper, a novel method was developed to enhance the assembly of polyelectrolyte composite membranes by inducing an electric field during electrostatic adsorption process. The hydrolyzed polyacrylonitrile (PAN) ultrafiltration (UF) membrane was placed in between a capacitor setup. The polyethyleneimine (PEI) was compulsorily assembled on the PAN support under the action of external electric force. Subsequently, the polyelectrolyte composite membranes were evaluated by pervaporation separation of water and alcohol mixture. The membrane obtained with only one PEI layer had a separation factor of 304 and a permeate flux of 512 g/m² h (75 °C) for pervaporation of 95 wt% ethanol–water mixture. An atomic force microscopy was also used to observe the microtopographical changes. The regularity of the membranes assembled by the new method was also improved in comparison with the membrane assembled by a dynamic layer-by-layer adsorption.     

氧化石墨烯-Ag纳米粒子/聚酰亚胺混合基质膜及其渗透汽化性能

以聚乙二醇（PEG-400）为还原剂,AgNO₃为前驱体,采用浸渍-还原法合成氧化石墨烯-Ag纳米粒子（GO-AgNP）复合物,再通过共混法制备氧化石墨烯-Ag纳米粒子/聚酰亚胺（GO-AgNP/PI）混合基质膜,用于苯/环己烷混合物的渗透汽化分离。使用透射电子显微镜、红外吸收光谱、拉曼光谱、热失重以及X射线光电子能谱等分析表征GO-AgNP复合物、GO-AgNP/PI混合基质膜的形貌和结构;探讨了Ag掺杂量对GO-AgNP复合物的结构以及GO-AgNP/PI混合基质膜的结构和渗透汽化性能的影响。结果发现,Ag⁺被还原形成AgNP的同时,GO失去了部分含氧官能团;Ag掺杂破坏了GO的结构,使其无序度增加,但改善了GO-AgNP复合物在混合基质膜中的分散性,提升了GO-AgNP/PI混合基质膜的苯/环己烷渗透汽化性能。然而过量的Ag掺杂将使GO片层上产生Ag粒子团聚,从而降低混合基质膜的渗透汽化性能。当Ag掺杂量为15%时,GO-AgNP/PI混合基质膜渗透汽化性能最佳,渗透通量为1 404 g·m^-2·h^-1,分离因子可达36.2。     

Pervaporation separation of water-acetic acid mixtures through poly(vinyl alcohol) membranes crosslinked with glutaraldehyde

Poly(vinyl alcohol) (PVA) membranes crosslinked with glutaraldehyde (GA) were prepared by a solution method for the pervaporation separation of acetic acid-water mixtures. In the solution method, dry PVA films were crosslinked by immersion for 2 days at 40°C in reaction solutions which contained different contents of GA, acetone and a catalyst, HCl. In order to fabricate the crosslinked PVA membranes which were stable in aqueous solutions, acetone was used as reaction medium in stead of aqueous inorganic salt solutions which have been commonly used in reaction solution for PVA crosslinking reaction. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of GA was characterized by IR spectroscopy. Swelling measurements were carried out in both water and acetic acid to investigate the swelling behavior of the membranes. The swelling behaviour of a membrane fabricated at different GA content in a reaction solution was dependent on crosslinking density and chemical functional groups created as a result of the reaction between PVA and GA, such as the acetal group, ether linkage and unreacted pendent aldehydes in PVA. The pervaporation separation of acetic acid-water mixtures was performed over a range of 70–90 wt% acetic acid in the feed at temperatures varying from 35 to 50°C to examine the separation performances of the PVA membranes. Permeation behaviour through the membranes was analyzed by using pervaporation activation energies which had been calculated from the Arrhenius plots of permeation rates.     

氧化石墨烯-Ag纳米粒子/聚酰亚胺混合基质膜及其渗透汽化性能

以聚乙二醇(PEG-400)为还原剂,Ag NO3为前驱体,采用浸渍-还原法合成氧化石墨烯-Ag纳米粒子(GO-Ag NP)复合物,再通过共混法制备氧化石墨烯-Ag纳米粒子/聚酰亚胺(GO-Ag NP/PI)混合基质膜,用于苯/环己烷混合物的渗透汽化分离。使用透射电子显微镜、红外吸收光谱、拉曼光谱、热失重以及X射线光电子能谱等分析表征GO-Ag NP复合物、GO-Ag NP/PI混合基质膜的形貌和结构;探讨了Ag掺杂量对GO-Ag NP复合物的结构以及GO-Ag NP/PI混合基质膜的结构和渗透汽化性能的影响。结果发现,Ag+被还原形成Ag NP的同时,GO失去了部分含氧官能团;Ag掺杂破坏了GO的结构,使其无序度增加,但改善了GO-Ag NP复合物在混合基质膜中的分散性,提升了GO-Ag NP/PI混合基质膜的苯/环己烷渗透汽化性能。然而过量的Ag掺杂将使GO片层上产生Ag粒子团聚,从而降低混合基质膜的渗透汽化性能。当Ag掺杂量为15%时,GO-Ag NP/PI混合基质膜渗透汽化性能最佳,渗透通量为1 404 g·m-2·h-1,分离因子可达36.2。     

Studies on Pervaporation Separation of Ethanol/Water Mixtures with Membranes of Polypropylene Sulfonate Salts

Sulfonated polypropylene membranes loaded with different kinds of counter-ions were prepared by heterogeneous chiorosulfonation reaction of polypropylene membrane followed by hydrolysis and ion-exchange reaction. The membranes obtained were used for selective separation of ethanol/water mixtures by pervaporation. The effects of counter-ion species, ion-exchange capacity, solution composition, thickness of membrane and temperature on the separation behavior of the membranes were investigated. Microstructure and morphology of the membranes were examined by X-ray and SEM as well.     

Chitosan/polyvinyl alcohol/amino functionalized multiwalled carbon nanotube pervaporation membranes: Synthesis,characterization, and performance

In the present study, novel biodegradable nanocomposite membranes were prepared by adding the amino functionalized multiwalled carbon nanotube (NH₂‐MWCNT) to the chitosan/polyvinyl alcohol blend polymers, and the obtained membranes were used for dehydration of isopropyl alcohol through pervaporation process. For this purpose, the membranes were prepared with chitosan/polyvinyl alcohol ratio of 4:1 on the basis of “solution casting” method and then crosslinked using glutaraldehyde, after addition of different amounts of NH₂‐MWCNT. The prepared membranes were characterized using scanning electron microscopy, contact angle, mechanical strength, degree of swelling (DS), and biodegradability. Also, the ability of the prepared membranes in dehydration of isopropyl alcohol was determined using pervaporation experiments. Results indicated that contact angle, mechanical resistance, separation factor (α), and pervaporation separation index were increased with the addition of NH₂‐MWCNT up to 10 wt% (relative to the total amount of polymer) and then decreased in the higher presence of nanotubes (15 wt%). Furthermore, the DS and permeate flux were first decreased and then increased for the same mentioned amounts of additive. In this study, optimized membrane was obtained by the addition of 10 wt% NH₂‐MWCNT. This membrane showed the maximum α (99.5), pervaporation separation index parameter (78.29 kg m⁻² h⁻¹), biodegradability, and mechanical stability as well as minimum DS.     

离子交换膜的渗透汽化

本文介绍了离子交换膜的渗透汽化研究工作。从离子交换膜的吸附溶解性、离子特性等几个方面论述了渗透汽化过程的分高性能及可能的传递机理。