Preparation and characterization of chitosan-boehmite nanocomposite membranes for pervaporative ethanol dehydration

Abstract

Pervaporative ethanol dehydration was studied using some chitosan-boehmite nanocomposite membranes. Nanocomposite membranes were prepared by incorporation of 1 and 2?Wt. % loading of the boehmite nanoparticles synthesized by the low temperature sol-gel process. The prepared samples were characterized by FTIR, FESEM and XRD analysis. The results showed the filler particles uniform distribution within the chitosan matrix. Pervaporation performance of the prepared pristine and the nanocomposite membranes were evaluated for ethanol dehydration. The 2?Wt. % loaded boehmite nanocomposite membrane exhibited highest ethanol dehydration performance for 20?Wt. % water content feed at 50?°C as 0.513?kg/m² h and 676 as permeation flux and separation factor revealed ～50% and 2 times increments, respectively.     

微波加热合成含有极少量非分子筛缺陷孔的LTA型分子筛膜

 以改进的原位合成路线,于管状氧化铝载体上合成了高性能的LTA型分子筛膜. 考察了常规加热和微波加热对合成的影响. 对于95%的异丙醇原料液,常规加热合成和微波加热合成的分子筛膜表现出了相似的优良性能. 但是,当原料液中的水含量低于2.0%时,常规加热合成的分子筛膜不再具有有效的脱水性能,这是由于其膜层中有相当数量的纳米级缺陷孔存在. 采用微波加热在很大程度上消除了合成过程中非分子筛缺陷孔的生成.     

Pervaporation separation of ethanol/water mixtures with chlorosilane modified silicalite-1/PDMS hybrid membranes

<正>Ultra-fine silicalite-1 particles were modified with four kinds of chlorosilanes(dodecyltrichlorosilane, octyltrichlorosilane,hexadecyltrichlorosilane and octadecyltrichlorosilane) and characterized by FI-IR,TGA,contact angle measurements and BET analysis.It was found that the surface hydrophobicity of silicalite-1 particles was improved significantly as the alkyl group was strongly bonded to the particle surface.Modified silicalite-1 particles were incorporated into PDMS(poly(dimethylsiloxanediol)) membranes,which were applied for the pervaporation separation of ethanol/water mixtures.The effect of surface properties,zeolite loading and operation conditions on pervaporation performance of the membranes was investigated.The separation factor of PDMS membranes filled with modified silicalite-1 increased considerably compared with that filled with unmodified ones,and the total flux decreased with increasing zeolite loading. The solution and diffusion selectivity of hybrid membranes were also measured to explain the pervaporation properties of silicalite-1 filled PDMS membranes.It was found that modification of silicalite-1 with dodecyltrichlorosilane effectively improved the solution and diffusion selectivity of silicalite-1 filled PDMS membranes with high zeolite loading.This may be attributed to the high surface hydrophobicity of modified silicalite-1 and its good integration with PDMS membranes.Both the high separation factor and solution selectivity indicated that modification of silicalite-1 with chlorosilanes was an effective method to improve the selectivity of silicalite-1/PDMS hybrid membranes for ethanol.     

Polyelectrolyte layer-by-layer self-assembly enhanced by electric field and their multilayer membranes for separating isopropanol–water mixtures

An electric field enhanced method is developed for fabricating layer-by-layer (LbL) self-assembly polyelectrolyte multilayer membranes. Three kinds of electric field enhanced polyelectrolyte multilayer membranes (EPEMs), poly(diallyl dimethylammonium chloride)/poly(styrenesulfonate sodium salt) (PDDA/PSS), poly(diallyldimethylammonium chloride)/poly(acrylic acid sodium salt) (PDDA/PAA) and polyethylenimine/poly(acrylic acid sodium salt) (PEI/PAA), were self-assembled on a reverse osmosis membrane (ROM). The pervaporation performances of EPEMs for separating isopropanol–water mixtures (90/10, w/w) are all superior to those of corresponding normal self-assembled polyelectrolytes membranes (PEMs), and the selectivity increases with PDDA/PSS, PDDA/PAA and PEI/PAA in order. For (PEI/PAA)₄PEI EPEM, the separation factor is 1075 and permeation flux is 4.05 kg m⁻² h⁻¹ at 70 °C. This novel method speeds up the LbL process, which makes it promising for the practical application of the LbL multilayer membrane.     

Pervaporation performance of PDMS-NiY zeolite hybrid membranes in the desulfurization of gasoline

PDMS-Ni²⁺Y zeolite hybrid membranes were fabricated and used for the pervaporation removal of thiophene from model gasoline system. The structural morphology, mechanical stability, crystallinity, and free volume characteristics of the hybrid membranes were systematically investigated. Molecular dynamics simulation was employed to calculate the diffusion coefficients of small penetrants in the polymer matrix and the zeolite. The effect of Ni²⁺Y zeolite content on pervaporation performance was evaluated experimentally. With the increase of Ni²⁺Y zeolite content, the permeation flux increased continuously, while the enrichment factor first increased and then decreased possibly due to the occurrence of defective voids within organic–inorganic interface region. The PDMS membrane containing 5.0 wt% Ni²⁺Y zeolite exhibited the highest enrichment factor (4.84) with a permeation flux of 3.26 kg/(m² h) for 500 ppm sulfur in feed at 30 °C. The effects of operating conditions on the pervaporation performance were investigated in detail. It has been found that the interfacial morphology strongly influenced the separation performance of the hybrid membrane, and it was of great significance to rationally modify the interfacial region in order to improve the organic–inorganic compatibility.     

以微孔β沸石为硅铝源合成强酸性介孔分子筛

以微孔β沸石为硅铝源,通过碱处理和以十六烷基三甲基溴化铵为模板剂,合成了具有较强酸性的六方结构介孔分子筛材料B-MCM-41,并采用XRD、N₂吸附脱附、FT-IR、²7Al MAS NMR、HRTEM和水热处理等手段对其进行了结构表征,采用NH₃-TPD对其进行了酸性表征。实验结果表明,B-MCM-41具有明显强于常规介孔分子筛的酸性,且在C⁺₁0混合芳烃加氢脱烷基化反应中表现出了良好的催化性能。这主要是由于碱溶液将β沸石降解为沸石结构单元,在表面活性剂作用下五元环次级结构单元被引入了介孔铝硅酸盐B-MCM-41的结构。     

Blended chitosan and polyvinyl alcohol membranes for the pervaporation dehydration of isopropanol

Homogeneous membranes were prepared by casting the solution of blended chitosan and polyvinyl alcohol (PVA) on a glass plate. The percent weight of chitosan in the membrane was varied from 0 to 100%. The membrane thickness was in the range of 15–30 μm. The membranes were heat treated at 150 °C for an hour. After that the membranes were crosslinked by glutaraldehyde and sulfuric acid in acetone aqueous solution. The membranes were tested at 30–60 °C for dehydration performance of 50–95% isopropanol aqueous solutions. At around 90% of isopropanol in the feed mixture, permeate flux increased whereas the percent of water in permeate tended to decrease when the feed temperature increased for all membranes, except that the water content in permeate from the membrane containing 75 wt.% chitosan remained constant. The swelling degree in water and the total flux increased with increasing chitosan content in membranes. The effect of temperature on permeate flux followed the Arrhenius relationship. The permeate flux decreased when isopropanol in the feed increased for all membranes. However, water content in permeate and isopropanol concentration in the feed formed complex relationship for different chitosan content membranes. Sorption did not appear to have significant effects on separation. The membrane containing chitosan 75% performed the best. For a feed solution containing 90% isopropanol at 60 °C, the permeate flux was 644 g/m² h with water content of nearly 100% in the permeate. At 55% isopropanol in the feed at 60 °C, the permeate flux was 3812 g/m² h. In the range of 55–95% of isopropanol in the feed, the water content in permeate was more than 99.5%. This membrane showed very excellent performance with good mechanical strength. It is promising to develop this membrane for industrial uses.     

Homogeneous polyimide/cyclodextrin composite membranes for pervaporation dehydration of isopropanol

Composite membranes with a sub-nanoscale homogeneous distribution of CD toroids in the Matrimid matrix were developed for dehydration of aqueous isopropanol. The composite membranes demonstrated separation factor far surpassing that of the neat Matrimid dense membrane. The heart of this innovation is the utilization of a CD derivative, ethylenediamine-β-cyclodextrin (EDA-β-CD), where the amine of CD could react with the imide of Matrimid and efficiently immobilize the CD rings during membrane formation. The superior separation properties for membranes embedded with 2–5% EDA-β-CD were attributed to the additional water channels created by the hydrophilic outer surface of CD and its interactions with the polymer matrix. FT-IR, density measurements and XRD have confirmed these hypotheses. Nevertheless, the separation factor exhibited an increasing then decreasing trend as a function of CD content and the opposite trend was observed with permeation flux. Investigation on the effect of feed water concentration showed that the neat Matrimid membrane possessed almost constant performance, but the Matrimid/EDA-β-CD (0.05) composite membrane exhibited an obvious increase in permeability and a decrease in selectivity at high water content. Even though the composite membrane swelled more at higher water content due to the intensified hydrophilicity ascribed to the introduction of CD structure, it always had much better separation factor. In addition, the Matrimid mixed matrix membranes embedded with 2–5% EDA-β-CD held reasonably tensile strength and modulus. The newly developed mixed matrix membrane approach may open up a new way to prepare next-generation high-performance asymmetric pervaporation membranes for isopropanol separation.     

Removal of organics from produced water by reverse osmosis using MFI-type zeolite membranes

Separation of an organics/water mixture was carried out by reverse osmosis using an α-alumina-supported MFI-type zeolite membrane. The organic rejection performance is strongly dependent on the ionic species and dynamic size of dissolved organics. The membrane showed high rejection efficiency for electrolytes such as pentanoic acid. An organic rejection of 96.5% with a water flux of 0.33 kg m⁻² h⁻¹ was obtained for 100 ppm pentanoic acid solution at an operation pressure of 2.76 MPa. For non-electrolyte organics, separation efficiency is governed by the molecular dynamic size; the organics with larger molecular dynamic size show higher separation efficiency. The zeolite membrane gives an organic rejection of 99.5% and 17% for 100 ppm toluene and 100 ppm ethanol, respectively, with a water flux of 0.03 kg m⁻² h⁻¹, 0.31 kg m⁻² h⁻¹ at an operation pressure of 2.76 MPa. It was observed that organic rejection and water flux were affected by the organic concentration. As pentanoic acid concentration increased from 100 ppm to 500 ppm, both organic rejection and water flux decreased slightly.     

Evaluation of PTMSP membranes in achieving enhanced ethanol removal from fermentations by pervaporation

The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years. Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne] (PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance in operation with cell-containing fermentation broths.     

Fe-Beta分子筛催化剂在选择催化还原氮氧化物反应中的活性:Fe含量的影响

NOx是主要的大气污染物之一,对环境和人体健康具有极大的危害.其主要来源之一是柴油机尾气排放,V2O5-WO3/TiO2催化剂是现阶段大规模商用的SCR催化剂,但V2O5-WO3/TiO2催化剂相对较窄的温度窗口和V2O5的生物毒性使得迫切需要新型的环境友好的高效SCR催化剂,其中分子筛因其特殊的孔道结构和催化性能受到广泛的关注.用于SCR过程的分子筛主要包括ZSM-5,Beta,MOR,SAPO-34和SSZ-13等,通常采用Cu,Fe,Mn和Co等过渡金属对其进行改性,通过调变分子筛的表面酸性和氧化还原性能,提高催化剂的SCR活性.Beta分子筛具有三维12元环孔道结构,相对其它分子筛具有较好的水热稳定性,而且制备工艺成熟,价格低廉,因此该类分子筛催化剂在SCR过程中具有很好的应用前景.我们采用离子交换法制备了系列Fe-Beta催化剂,发现将相同质量硝酸铁溶解在不同体积去离子水中,配制成不同浓度的硝酸铁溶液后与分子筛进行离子交换反应,制备得到的Fe-Beta催化剂中Fe的含量和NH3-SCR催化活性均存在显著差别.在此基础上,我们固定硝酸铁溶液浓度(0.02mol/L),通过增加溶液的体积,分别制备了Fe含量为(2.6,6.3和9)wt%的Fe-Beta分子筛.结果表明,Fe负载量为6.3 wt%时,Fe-Beta催化剂表现出最好的催化活性,NOx转化率大于80%的温度窗口为202-616℃.虽然三个催化剂在比表面积,孔径和Fe的价态上没有明显的差别,但Fe含量为6.3 wt%的催化剂在保持相对较高的Fe负载量的同时具有更多的孤立Fe3+物种,同时具有较好的NH3和NO吸附性能以及NO氧化能力,这些特性使得该催化剂相对于其它两个催化剂表现出更高的NH3-SCR催化活性.当Fe含量增加到9 wt%时,催化剂中FexOy纳米颗粒的含量大幅增加,使得NH3非选择性氧化能力加强,从而导致高温NH3-SCR反应活性大幅下降.     

In situ polymerization: A novel route for thermally stable proton-conductive membranes

In this paper, a new solvent-free route for preparing proton-conductive membranes is proposed. Flexible and fiber-supported polymer electrolyte membranes, as potential proton exchange membranes, were readily obtained by in situ polymerization of a homogenous solution that consisted of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO, polymer)–monomer mixtures of styrene (ST) and divinylbenzene (DVB), which was pre-cast onto SEFAR PETEX fibers. Factors such as the components of the casting solution and the sulfonation time, were fully investigated. The membrane structure and components were confirmed by FTIR-ATR spectra and SEM-EDXA images, and the thermal stability was examined via TGA and DrTGA. The membrane exhibited a proton conductivity of about 0.07 S/cm at 100% humidity and at room temperature, which is close to that of Nafion 117 at identical conditions (around 0.08 S/cm), whereas its thickness (about 120 μm) was less than that of Nafion 117. The tensile strength and the elongation at the break of the membrane were 31.2 MPa and 71%, respectively, which are several times higher than those of Nafion (about 6.16 MPa tensile strength and 36% elongation ratio). The dimensional change ratio of the membrane between the wet and dry states was below 3%, which is much lower than that of Nafion 117. The membrane showed a high thermal stability up to 400 °C. The method can be applied to other compatible systems of (aromatic) polymers and (aromatic) monomers.     

薄片状MFI晶体无凝胶蒸汽辅助晶化制备b轴取向沸石膜

采用新型薄片状MFI沸石晶体作为晶种,通过无凝胶蒸汽辅助晶化法(gel-less steam-assisted crystallization,GLSAC)在烧结氧化硅多孔载体上制备了致密平整、b轴取向的MFI沸石膜。考察了GLSAC中模板剂浓度、釜底水量、生长温度及时间对MFI沸石膜的影响。扫描电子显微镜和X射线衍射结果显示,适量的模板剂和釡底水量能抑制晶种的面外生长。成功制备了厚度750 nm、致密平整的MFI沸石膜。制备的对丁烷异构体气体分离测试表明,25℃时,等物质的量的丁烷异构体的分离因子(SF_A/B)可达36,对正丁烷的渗透速率为1.5×10^-7mol·m^-2·s^-1·Pa^-1。     

Sago/PVA blend membranes for the recovery of ethyl acetate from water

Sago starch is a relatively new polymeric material for development of a hydrophilic membrane for dehydration of alcohol/water. In this study sago based membranes were developed through casting technique for the dehydration of ethyl acetate at azeotropic conditions via pervaporation. Sago was blended with polyvinyl alcohol (PVA) to produce blended sago–PVA membranes with improved physical and chemical properties. The membranes were cross-linked using three different approaches; firstly, using glutaraldehyde, secondly using thermal treatment (80 °C) and thirdly by using both glutaraldehyde and thermal treatment. The effects of various cross-linking methods on the intrinsic properties of hydrophilic polymer membrane were investigated. The membranes were characterized using Fourier transform infrared (FTIR), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The effect of operating conditions such as feed temperature and concentration on the separation factor and flux was discussed. Sago starch polymer shows very high performance and very good stability after polymer blending and cross-linking, which is promising for use in industrial applications.     

Recent advances in sodium alginate-based membranes for dehydration of aqueous ethanol through pervaporation

Sodium alginate (SA) is a progressive material for membrane fabrication. The technological development of SA-based membranes has made a significant contribution to the separation techniques, especially in aqueous organic solutions. The outstanding performance of SA is attributed to its outstanding structural flexibility and hydrophilicity. In view of structural characteristics, SA membranes have immense utilization in the pervaporation separation of organics. Among various organics, dehydration of aqueous ethanol is employed as a standard to check the success of pervaporation (PV) membrane. Because ethanol and water have comparable molecular sizes, thus difficult to extract water from aqueous ethanol mixtures than it is for other organics. A literature survey shows that wide-ranging data are available on the PV performance of SA and its modified membranes. In this context, the present review addresses the recent advances made in SA membranes for enhanced ethanol dehydration performance during the last decade. Available data since 2010 has been compiled for grafted, crosslinked, blend, mixed matrix, and composite hybrid sodium alginate membranes in terms of separation factor, permeation flux, and pervaporation separation index PSI. The data are assessed with reference to the effect of feed composition, membrane selectivity, flux, and swelling behavior.     

Composite polymer electrolyte membranes comprising P(VDF‐co‐CTFE)‐g‐PSSA graft copolymer and zeolite for fuel cell applications

Hybrid organic/inorganic composite polymer electrolyte membranes based on a poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) grafted membrane and varying concentrations of zeolite were investigated for application in proton exchange membrane fuel cells (PEMFC). A proton conducting comb copolymer consisting of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) (PSSA) side chains, i.e. P(VDF‐co‐CTFE)‐g‐PSSA (graft copolymer) with 47 wt% of PSSA was synthesized using atom transfer radical polymerization (ATRP) and solution blended with zeolite. Upon incorporation of zeolite, the symmetric stretching band of both SO group (1169 cm^?1) and the ? OH group (3426 cm^?1) shifted to lower wavenumbers. The shift in these FT‐IR spectra suggests that the zeolite particles strongly interact with the sulfonic acid groups of PSSA chains. When the weight percent of zeolite 5A is above 7%, the proton conductivity at room temperature was reduced to 0.011 S/cm. The water uptake of the composite membranes decreased from 234 to 125% with an increase of the zeolite 5A weight percent to 10 wt%. The decrease in water uptake is likely a result of the decrease in the number of available water absorption sites because of the hydrogen bonding interactions between the zeolite particles and the graft copolymer matrix. This behavior is successfully investigated by scanning electron microscopy (SEM). The results of thermal gravimetric analysis (TGA) also showed that all the membranes were stable up to 300°C. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of mordenite composite membranes with seeding

Mordenite composite membranes were prepared by means of coating a porous α-alumina support with nanosized mordenite seeds followed by hydrothermal crystallization. A systematic investigation was performed on the influence of several factors such as ageing of the reaction mixture, alkalinity, salt addition and temperature on the formation of a mordenite membrane on the seeded support. The ageing of the reaction mixture reduces the growth rate of mordenite crystal along a-axis and b-axis but hardly influences the growth rate along c-axis. As a result, the boundaries between the surface crystals become a little larger with prolonging the period of ageing time. The growth rate of the mordenite crystal along individual axes increases first and then decreases with increasing concentration of sodium hydroxide. A higher alkalinity is unfavorable for the formation of a continuous mordenite membrane. The addition of salt in the reaction mixture has different effect on the growth rate of the mordenite crystal along each axis. With increasing the amount of salt, there was hardly influence on the growth rate along c-axis, whereas an obvious decline was observed in the growth rate along either a-axis or b-axis, which enlarges the boundaries between the surface crystals. The growth rate of the mordenite crystal increases more along c-axis than that along a-axis or b-axis with increasing temperature for hydrothermal crystallization. The use of a temperature as high as 473 K produces a membrane composed of bar-like crystals with larger boundaries. __________ Translated from Journal of Zhejiang University (Science Edition), 2005, 32(4) (in Chinese)     

Electrochemical properties of PP membranes with plasma polymer coatings of acrylic acid

Commercial polypropylene (PP) membranes were modified by plasma polymerization coating of acrylic acid, in combination with oxygen flow or oxygen plasma etching. First, conditions for plasma polymerization coating were optimized in terms of the chemical resistance of the coatings and their ion exchange capacity as a function of plasma power, internal pressure and treatment time. Next, the plasma polymerization coating of acrylic acid was combined with oxygen flow or oxygen plasma etching, and their conditions were also optimized by measuring the ion exchange capacity. Finally, the modified membranes were subjected to electrical resistance and transport number measurements and characterized by -step, FT-IR/ATR and SEM. Among the modification methods, oxygen plasma etching followed by the plasma polymerization coating of acrylic acid provided the best electrochemical properties with 1.75 meq/g (IEC) and 112 Ω cm² (ER), 0.88 (TN).     

Preparation and application of zeolite/ceramic microfiltration membranes for treatment of oil contaminated water

NaA zeolite microfiltration (MF) membranes were prepared on α-Al₂O₃ tube by in situ hydrothermal synthesis method and investigated for water separation and recovery from oily water. NaA/α-Al₂O₃ MF membranes with average inter-particle pore sizes of 1.2 μm, 0.4 μm and 0.2 μm were prepared. The membranes were characterized by scanning electron microscope (SEM) and the inter-particle pore size distribution (PSD) was determined by gas bubble pressure method. Membranes with pore sizes of 1.2 μm (NaA1) and 0.4 μm (NaA2) were used to treat an oil-in-water emulsion containing 100 mg/L oil. Better than 99% oil rejection was obtained and water containing less than 1 mg/L oil was produced at 85 L m⁻² h⁻¹ by NaA1 at a membrane pressure of 50 kPa. Consistent membrane performance was maintained by a regeneration regime consisting of frequent backwash with hot water and alkali solution.     

Polysulfone ionomers for proton-conducting fuel cell membranes: sulfoalkylated polysulfones

Polysulfones (PSUs) carrying short pendant alkyl side-chains with terminal sulfonic acid units have been prepared and studied as proton-conducting membrane materials. The first step in the preparation involved quenching of lithiated PSU with SO₂ gas, resulting in sulfinated PSU. In the second step, the lithium sulfinate units on the polymer were reacted with sodium 2-bromoethanesulfonate, sodium 3-bromopropanesulfonate, or 1,4-butane sultone to produce sulfoethylated, sulfopropylated, or sulfobutylated PSUs, respectively. Analysis by thermogravimetry showed that membranes based on the sulfoalkylated polymers were stable up to approximately 300 °C under N₂ atmosphere. Calorimetry measurements revealed that the modified polymers absorbed large amounts of non-freezing water, corresponding to 11–14 mol H₂O/mol SO₃H under immersed conditions. The proton conductivity of a membrane based on a PSU carrying 0.9 sulfopropyl chains per repeating unit was measured to be 77 mS/cm at 70 °C under humidifying conditions.