NaA分子筛膜的制备及其在醇类脱水中的应用

采用水热合成法在莫来石支撑体上制备NaA分子筛膜,并利用渗透汽化技术对甲醇、乙醇、异丙醇和叔丁醇等不同分子尺寸的醇水体系进行脱水性能的研究,同时考察操作温度和原料液中水含量对膜的分离性能的影响．研究表明：在优化条件下制备出致密无缺陷的NaA分子筛膜,所制备的膜对几种醇类体系脱水都具有良好的分离效果,膜的渗透水通量随温度的升高而增加,分离因予略有下降;随着醇类分子尺寸的增大,膜的分离因子和水通量都呈增大趋势．     

羧甲基壳聚糖-聚乙烯醇渗透汽化膜分离乙醇-水的性能

本文制备了羧甲基壳聚糖-聚乙烯醇渗透汽化膜,研究了羧甲基壳聚糖和聚乙烯醇配比、戊二醛交联时间以及操作温度和乙醇浓度等因素对膜分离乙醇-水性能的影响。实验结果表明,当乙醇含量较低（10（wt）%）时,该膜优先透醇,羧甲基壳聚糖与聚乙烯醇的比例1∶1时,膜的分离因子达到最大16.45（wt）%的乙醇溶液）;随着戊二醛交联时间的增加,膜的渗透通量减小而分离因子增大;操作温度升高,膜的渗透通量增大,而分离因子降低。     

CS/PVA-GA渗透蒸发膜分离偏二甲肼/水体系的实验研究

将壳聚糖(CS)和聚乙烯醇(PVA)按一定比例共混,再以戊二醛(GA)交联,制备CS/PVA-GA共混交联膜,研究了共混交联膜的结构、力学性能以及在偏二甲肼/水体系中的渗透蒸发脱水性能。结果表明,CS与PVA共混、GA交联,形成了致密的空间网状结构,随PVA含量增加,膜的抗张强度降低,而断裂伸长率增加。料液浓度、温度、膜厚度等因素对膜的渗透蒸发性能有较大影响,当料液中偏二甲肼的质量分数为50%,温度为20℃,渗透侧压力为100 Pa,膜厚约为25μm时,CS/PVA-GA共混交联膜的分离因子达到243,渗透通量可达167 g/(m2.h)。     

壳聚糖复合正渗透膜及其分离乳化油废水研究

研究以壳聚糖(CS)为正渗透(FO)膜成膜材料,以聚酯筛网为支撑材料,经过交联、碱液浸泡得到CS复合FO膜(CS-FO膜)。并将其用于石油醚乳化油废水的分离。结果表明,该CS-FO膜分离层为单一均质膜,具有良好的热稳定性和亲水性;该膜具有良好的渗透性能,以NaCl为驱动液时,其平均渗透水通量可达30 L/(m~2·h),截盐率可达到97%。分离乳化油废水时,膜面流速和乳化油废水含量均会影响膜的分离性能,膜面流速越大膜的渗透通量越大;废水乳化油含量越高,膜的通量越低。对质量浓度1.0 g/L的乳化油废水连续分离5 h后其水通量可维持在12L/(m~2·h),对乳化油的截留率可达到96.8%,这说明该FO膜在分离乳化油废水方面具有一定的应用前景。     

改性壳聚糖渗透蒸发膜用于酯化反应过程强化

壳聚糖(chitosan, CS)作为渗透蒸发膜材料来源广泛、亲水性好,但结构致密、渗透性较低。为改善CS膜的分离性能,将CS与聚醚-聚酰胺嵌段共聚物Pebax 1657共混,涂覆在NaOH水解处理的聚丙烯腈(polyacrylonitrile,PAN)超滤膜表面制备复合膜,用于渗透蒸发醇水分离过程,并进一步用渗透蒸发方法对乳酸-乙醇酯化反应进行强化。Pebax的聚酰胺与聚醚链段分别发挥调节膜结构与促进水跨膜传递的作用,有效地提高了膜分离性能。CS与Pebax质量比为2:1时,渗透蒸发醇水分离性能及对酯化反应强化的性能达到最优:渗透通量703 g·m^-2·h^-1、分离因子308,较未改性CS膜分别提高61%、65%;反应8 h后的乳酸乙酯产率由58%提高至73%。     

有机硅烷改性ZSM-5/BPPO非对称膜制备及其渗透汽化性能

以硅烷改性ZSM-5分子筛为填充剂,采用沉浸凝胶相转化法制备了ZSM-5/BPPO非对称膜. 结果表明,分子筛在BPPO膜中分散均匀,填充分子筛后膜表面粗糙度增大、疏水性增强. 以低浓度乙醇-水体系为研究对象,考察了分子筛填充量、进料液浓度及进料液温度对ZSM-5/BPPO膜渗透汽化分离性能的影响. 结果表明,随乙醇浓度增大,ZSM-5/BPPO膜的分离因子减小,渗透通量增大;随进料液温度升高,ZSM-5/BPPO膜的分离因子及渗透通量均增大;在60℃、分子筛填充量为0.3%(w)时,ZSM-5/BPPO膜对5%(w)乙醇-水体系的分离因子高达18.49,渗透通量为529.69 g/(m2×h). ZSM-5/BPPO膜对不同醇-水体系的分离结果表明,醇类分子量越大,膜分离性能越好.     

响应面优化法在PDMS/PVDF膜制膜条件优化中的应用

用响应面优化法优化了乙烯基封端PDMS/PVDF渗透汽化透醇膜的制膜条件,研究了硅橡胶浓度、B/A质量比、交联温度和交联时间对膜性能的影响,拟合了分离因子、渗透通量与四因素之间的回归方程,并用方差分析法考察了四因素的主效应、二次效应以及相互作用效应对复合膜的分离因子与渗透通量的影响。研究发现,硅橡胶浓度对膜的分离因子与渗透通量的影响最为显著,交联时间对分离因子几乎没有影响。通过对回归方程的优化分析得知,在料液乙醇浓度为10%(wt),操作温度40℃条件下,当硅橡胶浓度为93%(wt),B/A质量比为0.08,交联温度为100℃,交联时间为13.83 h时,膜的综合分离性能达到最佳,此时分离因子与渗透通量预测值分别为9.47、77.57 g(m2 h)1,渗透侧乙醇浓度达到51.3%(wt)。回归方程的验证实验结果表明,回归方程的估计值与实验值较为吻合,可用于乙烯基封端的PDMS/PVDF复合膜的渗透汽化性能的预测与优化。     

CS/GO复合分离膜的制备及非对称渗透行为研究

以壳聚糖/氧化石墨烯(CS/GO)为功能层，以PVDF多孔膜为基膜，采用层层自组装技术制备了CS/GO复合分离膜。基于插入到GO片层中交联CS分子的柔韧性，GO片层间距(膜孔)能够随着不同方向的水压而改变，从而使得所制备的复合分离膜具有独特的非对称渗透性能。研究发现，随着组装层数的增加，表面结构更为完善，反向/正向通量比从3.79倍增加到了27.39倍。当组装层数为两层时，膜具有更优异的综合性能。此外，复合分离膜还显示出比基膜更好的截污性、抗污性和亲水性。     

新型渗透蒸发膜聚甲基双苯基硅氧烷膜的制备和分离

采用2种不同配方制备出苯基含量不同的聚甲基双苯基硅氧烷(PMPhS)膜并用于分离苯-水体系。接触角测定结果表明2种膜比PDMS膜亲苯疏水性增强。以渗透通量和分离因子为评价指标,研究了原料液温度、流动状况、质量分数、膜下游侧压力对渗透蒸发分离性能的影响,结果表明,随着原料液温度、流速以及料液浓度的提高,通量和分离因子都增加,随着下游侧压力的升高,通量和分离因子均降低。     

无机盐对聚二甲基硅氧烷/陶瓷复合膜渗透汽化性能的影响

将渗透汽化应用于醇/水体系的分离,具有诸多显著的优势。然而,目前的研究大都基于二元体系,而实际的应用体系是多元的,还包含少量无机盐和糖类等,它们的存在对膜的性能具有一定的影响。本文研究了NaCl、KCl和MgCl2 3种无机盐的加入对聚二甲基硅氧烷 （PDMS）/陶瓷复合膜渗透汽化性能的影响。结果表明,在313 K,无机盐的加入使复合膜的分离因子和通量均有所提高。其中二价盐MgCl2对渗透汽化性能的影响最为显著,分离因子最大提高到醇/水体系的2.8倍。而一价盐NaCl和KCl的加入,使分离因子分别提高为醇/水体系的2.5倍和2.4倍。同时借助于Setschenow扩展方程计算了乙醇活度,对实验结果进行了初步的解释。     

Pervaporative Dehydration of Organic Solvents

Abstract

Pervaporative separation of acetone/water and isopropanol (IPA)/water systems has been studied in the water-lean range of composition of the feed mixtures. Poly(vinyl alcohol) (PVA) membranes crosslinked with citric acid, adipic acid, maleic acid, glutaraldehyde, and glyoxal were used for this purpose. The sorption characteristics of all the membranes indicate that these membranes have a good sorption selectivity for water in view of the hydrophilic nature of PVA. The type of crosslinker used for crosslinking has been shown to have an important bearing on the permeation characteristics of the membranes. Thus, the trifunctional citric acid yields the highest selectivity but lowest flux. A comparison of the productive capacities of the various membranes indicates that the glutaraldehyde crosslinked membrane has the maximum productive capacity for IPA dehydration whereas maleic acid crosslinked membrane yields the highest productive capacity for acetone dehydration.     

Separation of Acetic Acid/Water Mixtures by Pervaporation through Poly(Vinyl Alcohol)–Sodium Alginate Blend Membranes

Abstract

Dense pervaporation (PV) membranes were prepared by blending hydrophilic polymers, poly(vinyl alcohol) (PVA), and sodium alginate (SA), which were then crosslinked with glutaraldehyde (GA) for the separation of acetic acid/water mixtures. These membranes (PVA‐SA) were characterized for morphology, intermolecular interactions, thermal stability, and physico‐mechanical properties using XRD, FTIR, TGA and tensile testing respectively. The effect of experimental parameters such as feed composition and permeate pressure on separation performance of the crosslinked membranes was determined. Sorption studies and porosity measurement were carried out to evaluate the extent of interaction and degree of swelling of the polyion membranes, in acetic acid and water as well as in mixtures of acetic acid and water. Further the results were compared with the commercial membrane (Sulzer pervap 2205). The membrane appears to have a good potential for dehydrating 90 wt% acetic acid with a reasonably high selectivity of 21.5 and a substantial water flux of 0.24 kg/m²/h/10 µm. Separation factor was found to improve with decreasing feed water concentration whereas the corresponding flux decreased. Higher permeate pressures caused a reduction in both flux and selectivity.     

Separation of Water/Ethanol Vapor Mixtures through Chitosan and Crosslinked Chitosan Membranes

Abstract

The separation of water/ethanol vapor mixtures through chitosan membranes and crosslinked chitosan membranes was studied by means of the vapor permeation technique. The permeation performance was discussed in terms of separation factor and permeation flux. Crosslinking the chitosan membrane by glutaraldehyde enhanced the selectivity. The highest separation factor obtained was 6000 for a crosslinked chitosan membrane with a degree of deacetylation of 100%.     

Preferential separation of ethanol from aqueous solution through hydrophilic polymer membranes

The pervaporation behaviors of aqueous ethanol mixtures through the poly(ethylene oxide) (PEO)/chitosan (CS) blend membrane were investigated. The results show that both CS and PEO/CS membrane preferentially permeate ethanol at a lower alcohol concentration in feed, and the selectivity of CS membrane toward alcohol can be greatly improved by introducing hydrophilic polymer PEO into CS. The PEO/CS blend membrane gave a separation factor of 4.4 and a flux of 0.9 kg m⁻² h for 8 wt % of ethanol in the feed at 20°C. At the same time, the reason introducing PEO can improve alcohol-permselectivity of CS membrane is explained on the basis of experimental data. Blending with PEO made the structure of CS chain looser, which resulted in ethanol molecules passing through easily, on the other hand, strengthened the ability of forming water clusters that inhibit the permeation of water molecules. From the experimental results, although the PEO/CS blend membrane was not a usable membrane with high selectivity to alcohol, a new method to prepare alcohol-permselective membranes appears to be developed by modifying hydrophilic polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1145–1151, 1999     

Pervaporation properties of a three‐layer structure composite membrane

A novel composite membrane with a three‐layer structure has been prepared. The top layer is a thin dense film of chitosan crosslinked with glutaraldehyde, and the support layer is made of microporous polyacrylonitrile (PAN). Between the dense and the microporous layer, there is an intermolecular crosslinking layer. The performance data show that this is an excellent pervaporation membrane for alcohol dehydration and one‐stage separation is attainable for some alcohol/water mixtures such as ethanol/water and isopropanol/water systems, which has a good separation factor of 1410 and a good flux of 0.33 kg m⁻² h⁻¹ for the EtOH/H₂O mixture, and 5000 and 0.43 kg m⁻² h⁻¹ for the i‐PrOH/H₂O mixture using 90 wt % alcohol concentration at 70°C.Using 90 wt % methanol aqueous solution at 60°C, a flux of 0.17 kg m⁻² h⁻¹ and selectivity of 123 are also obtained. The structure and performance of the novel composite membrane varies with conditions of membrane preparation, such as hydrolysis degree of PAN membrane, content of crosslinking agent, and heat‐curing temperature. The results indicate that the separation factor and the permeation rate of this novel composite membrane increase with the increase of operating temperature. At the same time, the pervaporation properties can be adjusted by changing the structure of the top layer and the middle layer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 740–745, 2000     

Modification of poly(vinyl alcohol) membranes using sulfur-succinic acid and its application to pervaporation separation of water–alcohol mixtures

For the purposes of the water-selective membrane material development for pervaporation separation, we crosslinked poly(vinyl alcohol) (PVA) with sulfur-succinic acid (SSA), which contains —SO₃OH, by heat treatment and investigated the effect of the crosslinking density on the separation of water–alcohol mixtures by pervaporation technique. The crosslinking reaction between PVA and SSA was characterized through Fourier transform infrared spectroscopy and differential scanning calorimetry tests by varying the amount of the crosslinking agent, the reaction temperature, and the swelling measurements of each pure component. The separation performance of the water–methanol mixture is not good due to the existence of sulfonic acid, hydrophilic group, in the crosslinking agent. However, for the water–ethanol mixture, the flux of 0.291 kg/m²h and the separation factor of 171 were obtained at 70°C when PVA-crosslinked membrane containing 7 wt % SSA was used. The same membrane also showed flux of 0.206 kg/m²h and a separation factor of 1969 at the same operating temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1717–1723, 1998     

Dehydration of 1,4-dioxane by pervaporation using crosslinked calcium alginate-chitosan blend membranes

Summary  Sodium alginate (SA) and chitosan (CS) blended membranes were crosslinked with maleic anhydride (MA) for the separation of 1,4-dioxane/water mixtures at 30 °C by pervaporation (PV). The membranes were characterized by Fourier transform infrared (FTIR) analysis and Ion Exchange Capacity (IEC) to verify the crosslinking. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) pattern were used to observe the thermal degradation and crystalline nature of the membrane respectively. The membrane performance was studied by calculating flux, selectivity, and pervaporation separation index. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the membranes in pure liquids as well as in binary mixtures. The effects of experimental parameters such as feed composition, membrane thickness, and permeate pressure on separation performance of the crosslinked membranes were determined. The experimental result suggested that the membrane has a good potential for breaking the aqueous azeotrope 1,4-dioxane.     

Pervaporation dehydration of isopropyl alcohol with NaY zeolite incorporated hybrid membranes

With a solution technique, NaY zeolite incorporated, tetraethylorthosilicate‐crosslinked poly(vinyl alcohol) membranes were prepared. The resulting membranes were tested for their ability to separate isopropyl alcohol/water mixtures by pervaporation in the temperature range of 30–50°C. The effects of the zeolite content and feed composition on the pervaporation performance of the membranes were investigated. The experimental results demonstrated that both flux and selectivity increased simultaneously with increasing zeolite content in the membranes. This was explained on the basis of the enhancement of hydrophilicity, selective adsorption, and establishment of a molecular sieving action attributed to the creation of pores in the membrane matrix. The membrane containing 15 mass % zeolite exhibited the highest separation selectivity of 3991 with a flux of 5.39 × 10^?2 kg/m² h with 10 mass % water in the feed at 30°C. The total flux and flux of water were close to each other for almost all the studied membranes, and this suggested that the membranes could be used effectively to break the azeotropic point of water/isopropyl alcohol mixtures to remove a small amount of water from isopropyl alcohol. From the temperature‐dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water were significantly lower than those for isopropyl alcohol, and this suggested that the developed membranes had a higher separation efficiency for water/isopropyl alcohol systems. The activation energy values for total permeation and water permeation were found to be almost the same for all the membranes, and this signified that coupled transport was minimal because of the highly selective nature of the membranes. Positive heat of sorption values were observed in all the membranes, and this suggested that Henry's mode of sorption was predominant. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pervaporation separation of ethanol–water mixtures using ionically crosslinked blended polyacrylic acid (PAA)–nylon 6 membranes

The pervaporation separation of ethanol–water mixtures was carried out through a series of ionically crosslinked polyacrylic acid (PAA)–Nylon 6-blended membranes crosslinked to varying degrees in aluminum nitrate solution. The polyacrylic acid (PAA)–Nylon 6 membranes were cast from homogeneous PAA–Nylon 6 mixtures to various thicknesses and then crosslinked. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt% Nylon 6 and 25 wt% PAA. These membranes have separation factors (water/ethanol) of 35–40 at flux rates of 120–160 g/m² h. The optimum crosslinking time was found to be approximately 35 h to yield membranes with the best separation and flux rates at 25 wt% PAA content.     

Pervaporation separation of water/alcohol mixtures through hydroxypropylated chitosan membranes

The present study investigated the pervaporation performance of novel hydroxypropylated chitosan (HPCS) membranes to separate water from an aqueous alcohol solution. Hydroxypropylated chitosan was prepared from the reaction of chitosan and propylene oxide. The results show that the separation factor decreases and the flux increases with increasing of the substitution degree of the hydroxypropylated chitosan membrane. Crosslinking with glutaraldehyde or treatment with Cu²⁺ can improve the pervaporation performance of modified chitosan membrane grately. The performance data indicate that the crosslinking hydroxypropylated chitosan membrane treated with Cu²⁺ is an excellent pervaporation membrane for the separation of alcohol–water mixtures, and one-stage separation is attainable for some alcohol–water mixtures such as an n-propanol–water and an isopropanol–water system, which has a good separation factor of 220 for the n-PrOH/water system and 240 for the i-PrOH/water system using 85 wt % alcohol concentration at 60°C. The flux for both cases is around 0.5 kg m⁻² h⁻¹. At the same time, the structure of the chemically modified chitosan membranes and their separation characteristics for aqueous alcohol solutions are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2035–2041, 1998