Pervaporation separation of binary and ternary mixtures with polydimethylsiloxane membranes

This study dealt with the separation of binary water–phenol and water–methanol mixtures and ternary water–phenol–methanol mixtures by pervaporation (PV) with polydimethylsiloxane (PDMS) membranes. The effects of the operating conditions (feed temperature, feed concentration, and feed flow rate) on the separation performance for binary mixtures were investigated. An increase in temperature or concentration increased the total permeation flux and decreased the organic separation factor. In other words, an increase in the temperature or feed organic concentration increased the water flux more significantly than the organic compound flux, which resulted in a separation factor reduction. Also, an increase in the feed flow rate increased the total flux and separation factor because the boundary layer effects diminished. The vapor–liquid equilibrium separation factor (α_VLE) and pervaporation separation factor (α_PV) values for the PDMS membrane were calculated, and this showed that α_PV for the water–phenol mixture was greater than α_VLE. This means that the membrane was highly efficient for the PV separation of phenol from dilute aqueous solutions relative to the separation of methanol. This was due to the fact that phenol has a higher solubility parameter than methanol in silicone membranes. To study the effect of a third component on membrane performance, PV experiments were also carried out with water–phenol–methanol mixtures. The results for total permeation flux and the phenol separation factor for PDMS membranes in contact with water–phenol–methanol ternary mixtures are similar to those in contact with water–phenol binary mixtures. The phenol separation factor of the membrane in contact with the ternary mixture was slightly lower than that in contact with the binary mixture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

二苯并-18-冠醚-6/聚醚嵌段酰胺膜富集水中苯酚性能研究

为提高聚醚嵌段酰胺 （PEBA）膜对水中苯酚的选择分离性能,采用二苯并-18-冠醚-6 (CE) 对PEBA膜进行改性制备了PEBA/CE渗透蒸发膜。通过FT-IR、SEM表征证实了CE与PEBA紧密结合且CE均匀分布在膜表面;AFM表征表明CE的修饰有效地提高了膜表面与苯酚的接触面积;水接触角测试表明CE的修饰极大地提高了PEBA/CE膜的疏水性。同时系统地研究了膜中CE含量、原料液苯酚浓度、进料温度对膜渗透汽化性能的影响,结果表明CE能显著提高PEBA膜对苯酚的选择性,在料液苯酚为0.8%（质量）及70℃操作温度条件下,当CE 的添加量为PEBA的6%（质量）时,PEBA/CE-6膜的分离因子和渗透通量分别为23.34和494.40 g/(m²·h),远超PEBA膜性能[分离因子8.46,总渗透通量547.48 g/(m²·h)]。长期性能稳定性测试表明所制备PEBA/CE-6膜具有良好稳定性,具有较好的工业运用潜力。     

β-环糊精/聚醚共聚乙酰胺填充膜的制备及渗透汽化分离水中微量苯酚

将β-环糊精（β-CD）添加到聚醚共聚乙酰胺（PEBA）中制备β-环糊精/聚醚共聚乙酰胺填充膜（β-CD-f-PEBA）,用于苯酚-水的渗透汽化分离研究。SEM、FTIR表明β-环糊精在膜中分散均匀且与膜结合紧密,与膜间只有氢键相互作用而未发生化学交联。拉伸实验表明膜的拉伸强度和断裂强度均随着β-CD添加量的增加先减小后增大。采用基团贡献法计算了PEBA、苯酚及水的溶解度参数,证明PEBA膜对苯酚具有较高的选择吸附性。通过溶胀验证膜对苯酚的选择吸附性能,膜对苯酚的吸附量度随着料液中苯酚浓度和膜中β-CD添加量的增加而增加。考察了PEBA和β-CD-f-PEBA膜的渗透汽化性能,当β-CD填充量为0.5%（质量）时,分离效果最佳,渗透通量和分离因子分别为3062.9 g·m^-2·h^-1和43.3。通过Arrhenius方程计算苯酚和水的渗透活化能分别为97.19和52.12 kJ·mol^-1。重复实验表明β-CD-f-PEBA膜的操作稳定性良好。     

Pervaporation properties of oleyl alcohol-filled polydimethylsiloxane membranes for the recovery of phenol from wastewater

In the present work, the modified polydimethylsiloxane (PDMS) membranes incorporated by oleyl alcohol (OA) were prepared for the first time. The polymeric membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) before and after modification. These membranes were used for the pervaporative separation of phenol from wastewater. The effects of OA loading and feed temperature on the pervaporation performances have been investigated. The influence of ignoring the partial pressure at the permeate side was compared and discussed. The results showed that the OA presence increased phenol flux and separation factor, and decreased water flux greatly with less than 9 wt% OA loading. The highest pervaporation separation index was obtained with 5 wt% OA loading. The driving force of phenol across the membranes was much lower than that of water, and permeation of phenol was much higher than water in nature. It is necessary to discuss and compare the intrinsic properties of different membranes using permeation and selectivity, even though the membranes are tested under the same feed temperature and concentration. The partial pressure of phenol at the permeation side cannot be simply omitted for its great effect on the permeation. Increasing feed temperature will result in the increase of flux and separation factor, but decrease of permeation.     

渗透汽化-结晶耦合分离稀溶液中的香兰素

以聚醚嵌段共聚酰胺（PEBA2533）为膜材料,采用干法相转化法制备性能优异的高分子膜,用于渗透汽化-结晶耦合（PVCC）分离系统中回收稀水溶液中的香兰素。采用扫描电子显微镜（SEM）对PEBA2533膜的形貌进行表征。考察原料液浓度、温度对膜渗透汽化性能的影响。结果表明：随着溶液浓度的增加,PEBA2533膜溶胀性能增加,说明PEBA2533能够优先吸附香兰素;随原料液浓度增加,香兰素渗透通量增加,分离因子略微下降;原料液温度增加,香兰素渗透通量和分离因子都增加;并通过Arrhenius方程计算得到香兰素比水对温度更加敏感。PVCC系统中控制一级冷凝器温度为2℃时,一级冷凝器中结晶态香兰素通量为39.52 g·m^-2·h^-1,纯度在99%以上。     

PDMS/ZSM-5膜的制备及渗透汽化分离水中乙酸正丁酯和乙酸乙酯

为探究出适合分离水中的乙酸正丁酯和乙酸乙酯的新型渗透汽化膜材料,选用沸石ZSM-5 对聚二甲基硅氧烷(PDMS)材料进行填充改性,以聚偏氟乙烯(PVDF)为支撑层,采用刮涂法制备PDMS/ZSM-5/PVDF复合膜渗透汽化分离水中的乙酸正丁酯和乙酸乙酯。采用SEM、接触角测量仪、FTIR、TGA和XRD等对膜材料物理化学性能进行表征,考察了膜材料的溶胀行为及渗透汽化性能。结果表明,ZSM-5在 PDMS 膜中分散均匀,且没有发生化学作用,并提高了膜材料的疏水性和热稳定性。随着ZSM-5添加量的增加,膜在乙酸正丁酯和乙酸乙酯的溶胀度和待分离组分在膜材料中的扩散速率不断增加。随着进料浓度和温度的增加,渗透通量不断增大,分离因子先增大后减小。随着ZSM-5在PDMS/ZSM-5/PVDF复合膜中含量的增加,总渗透通量增加,而分离因子呈现先增加后减小的趋势。当添加量为10%（质量）时,分离因子达到最大值。对于乙酸正丁酯/水体系,渗透通量和分离因子最大值分别为319 g·m ^-2·h ^-1和131;而对于乙酸乙酯/水体系,渗透通量和分离因子最大值分别为1385 g·m ^-2·h ^-1和121。     

Pervaporation of organic solvents by poly[bis(2,2,2-trifluoroethoxy) phosphazene] membrane

The permeation and pervaporation behaviour of water and several organic solvents through poly[bis(2,2,2-trifluoroethoxy)phosphazene] (PBFP) membrane have been investigated in the temperature range from 42 to 80°C. The steady-state permeation fluxes of the solvents increased in the following order: methanol > ethanol > benzene > water > cyclohexane. An Arrhenius plot of permeation flux of water suddenly changed in its gradient at about 66–70°C, which corresponds closely to the T(1) transition temperature (75°C) of PBFP studied. Interestingly, in the pervaporation of water-methanol mixtures, methanol permeated more rapidly through the membrane than did water; however, the pervaporation of water-ethanol mixtures showed poor permselectivties. In the case of an athermal mixture of methanol and ethanol, the fluxes of methanol and ethanol indicated convex and concave curves, respectively, to the axis of methanol concentration; thus the separation characteristics of this system were slightly better than those of a simple distillation technique. The pervaporation of benzene-cyclohexane mixtures showed excellent permselectivty enrichment in benzene resulting in a separation factor of 12.     

蒙脱石填充改性PDMS膜对稀溶液中苯的渗透分离性能

研究了CTAB柱撑改性蒙脱石填充聚二甲基硅氧烷(PDMS)膜对稀溶液中苯的渗透分离性能,考察了操作温度、有机蒙脱石填充量及料液中苯浓度对填充膜分离性能的影响. 结果表明,蒙脱石的填充不但能增强膜的机械性能,而且能明显改善膜的分离性能,随着蒙脱石填充量的增加,渗透通量增大,而分离因子先增大后减小;随着操作温度的提高,渗透通量明显增大,分离因子却减小;当料液中苯浓度增大时,苯通量增大,水通量保持不变,而分离因子减小. 用填充量为9.09%的填充膜对苯浓度为1000 kg/kg的料液进行渗透汽化实验,得到膜的渗透通量为115 g/(m2×h),分离因子达到798,比纯PDMS膜通量增大了12%,分离因子增大了32%.     

A characterization of pdms pervaporation membranes for the removal of trace organic from water

A new silicone pervaporation membrane for the removal of one of trace organies, 1,2-dichloroethane from water has been developed using polydimethylsiloxane (PDMS) and oligomeric silylstyrene as a crosslinking agent of PDMS. Optimal conditions for fabricating the best membrane were determined from swelling measurements ard pervaporation experiments and then the membrane was characterized at different membrane thickness and operating conditions. In the pervaporation separation of 55–70 ppm of l,2-dichlorocthanc aqueous mixtures, the developed membrane has flux of 2.5–330 g/(m².h) and selectivity of 230–1750 depending on membrane thickness, permeate pressure and operating Temperature. Water permeation through thin membrane was found to be subjected to significant desorption resistance, while the desorption resistance and thermodynamic factors as well as the concentration polarization of the organic at the boundary layer in feed can affect the organic permeation, depending on membrane thickness. Selectivity change with permcaic pressure depends on membrane thickness: at small membrane thickness range, selectivity increases with permeate pressure and at large thickness region it decreases. From the Arrhenius plots of each component fluxes, the permeation activation energies were determined. Through an analysis of the permeation activation energies of each components, the desorption resistance as well as the effects of the thermodynamic factors on permeation was qualitatively characterized.     

Pervaporation of esters with hydrophobic membrane

Surface-modified alumina membrane (A1₂O₃) was used for ester flavor recovery by pervaporation. This study focused on the permeation characteristics of ester compounds (ethyl acetate, EA; ethyl propionate, EP; ethyl butyrate, EB) through tube-type hydrophobic membrane. Experiments were performed to evaluate the effects of the feed concentration (0.15-0.60 wt%) and temperature (30-50 ‡C) on separation of EA, EP, and EB from aqueous solutions. It was found that the permeation flux increased with increasing feed ester concentration and operating temperature. The fluxes of EA, EP, and EB at 0.60wt% feed concentration and 40 ‡C were 254, 343, and 377 g/m² hr, which was much higher than those of polymer membranes. It was reported that the permeate flux of EA with PDMS was 1.1-58 g/m²Phr at feed concentration of 90-4,800 ppm and 45 ‡C. The separation factors for the 0.15-0.60 wt% feed solution of EA, EP, and EB at 40 ‡C were in the range of 66.9-78.9, 106.5-97.3, and 120.5-122.8, respectively. Due to the high separation factor, phase separation occurred in permeate stream because the ester concentration in permeate was much above the saturation limit.     

Pervaporation of flavors with hydrophobic membrane

Using a pervaporation process, a surface-modified hydrophobic membrane was used for recovery of esters which are volatile organic flavor compounds; ethyl acetate (EA), propyl acetate (PA), and butyl acetate (BA). A surface-modified tube-type membrane was used to evaluate the effects of the feed concentration (0.15–0.60 wt%) and feed temperature (30–50 °C) on the separation of EA, PA, and BA from dilute aqueous solutions. The permeation flux increased with the increasing feed ester concentration and operating temperature. EA, PA, and BA in the permeate were concentrated up to 9.13–32.26, 11.44–34.95, and 14.96–36.37 wt%, respectively. The enrichment factors for the 0.15–0.60 wt% feed solution of EA and BA were in the range of 48.5-62.8 and 97.7-101.5, respectively. Phase separation occurred in the permeate stream because the ester concentration in the permeate was above the saturation limit. This meant that selectivity of the membrane was high enough for the recovery of esters from dilute aqueous solution, even though the enrichment factor of the membrane was lower than that of non-porous PDMS membrane. The fluxes of EA, PA, and BA at 0.60 wt% (6,000 ppm) feed concentration and 40 °C were 254, 296, and 318 g/m².hr, which are much higher than those obtained with polymer membranes. In the case of non-porous PDMS at feed concentrations of 90-4,800 ppm and at 45 °C, it was reported that the permeate flux of EA was 1.1–5.8 g/m^2.h. Compared to non-porous PDMS, the surface-modified membrane investigated in this study showed a much higher flux and enough selectivity of esters.     

Preparation and characterization of Silicalite‐1/PDMS surface sieving pervaporation membrane for separation of ethanol/water mixture

To improve the pervaporation performance of Silicalite‐1/PDMS composite membrane by adding a small amount of Silicalite‐1 zeolite, novel Silicalite‐1/PDMS surface sieving membranes (SSMs) were prepared by attaching Silicalite‐1 particles on the PDMS membrane surface. The obtained membranes and traditional mixed‐matrix membranes (MMMs) were characterized by SEM, XRD, TGA, FT‐IR, and pervaporation separation of ethanol–water mixture. Effects of Silicalite‐1 particles content, feed temperatures, and feed compositions on the separation performance were discussed. From the cross‐section view SEM images of SSMs, a two‐layer structure was observed. The thickness of the Silicalite‐1 layer was about 300 nm to 2 μm. The TGA analysis indicates that the zeolite concentration in 3 wt % SSM is lower than 10 wt % MMMs. In the ethanol/water pervaporation experiment, the separation factor of Silicalite‐1/PDMS SSMs increased considerably compared with pure PDMS membrane. When the suspensions concentrations of Silicalite‐1 particles reached 3 wt %, the separation factor was about 217% increase over pure PDMS membrane and 52.9% increase over 10 wt % Silicalite‐1/PDMS MMMs. As the ethanol concentration in the feed increases, the separation factor of SSMs increases, whereas permeation flux decreases. At the same time, with increasing operating temperature, the permeation flux of SSMs increased. The stability of SSMs at high temperature is better than the traditional MMMs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42460.     

Preparation and Characterization of Silicone Rubber Membrane

Pervaporation membrane with preferential permeation for organic compounds over water was prepared and characterized. Selection of membrane material and the effects of polydimethylsiloxane (PDMS), cross-linker, and catalyst concentrations on performances of pervaporation membrane at room temperature were discussed. In addition, the time of cross-linking, and the kinds of basic plate in the process of preparation were tested. The formulation of pervaporation membrane material was determined. Through the characterization of membrane by infrared spectrometry(IR), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffraction(XRD), it is proved that the structures and characters are suitable for the pervaporation process. Experiments also demonstrate that the permeate flux and separation factor are suitable for the process.     

APTES改性ZIF-L/PEBA混合基质膜强化渗透汽化分离苯酚研究

渗透汽化(PV)膜分离是一种高效节能、无污染的化工分离技术,在有机废水处理领域的应用潜力巨大。以3-氨丙基三乙氧基硅烷(APTES)改性二维ZIF-L(AZLs),将其引入聚醚嵌段酰胺(PEBA)内制备AZLs/PEBA混合基质膜,用于分离水溶液中的苯酚。系统表征了所制膜的微结构与物化特性,考察了APTES添加量、AZLs填充量、操作温度、料液浓度等对膜分离性能的影响。结果表明：AZLs均匀分散在PEBA基质中,表明两者具有良好的界面相容性。AZLs的加入使得膜疏水性增强而表面自由能降低,从而提高了PEBA膜的选择性。当分离80℃、1000 mg/kg苯酚水溶液时,AZLs/PEBA膜总通量可达2046 g/(m²·h),分离因子为25.4,并且具有一定的稳定性。所制AZLs/PEBA混合基质膜在含酚废水处理方面具有应用前景。     

Pervaporation of Organic Liquids from Binary Aqueous Mixtures using Poly(trifluoropropylmethylsiloxane) and Poly(dimethylsiloxane) Dense Membranes

In this work we have compared and contrasted the pervaporation behaviour (separation factor and flux) of fluorosilicone dense membranes based on poly(trifluoropropylmethylsiloxane) (PTFPMS) with poly(dimethylsiloxane) (PDMS) dense membranes. In particular, pervaporation experiments were carried out at 298 K using lab-made PTFPMS, lab-made PDMS and commercial PDMS membranes in order to remove three different organic liquids pyridine (PY), isopropanol (IPA) and methylethylketone (MEK) from dilute (<10 wt.%) binary aqueous mixtures. All of the silicone membranes studied were found to be successful for the desired separations. The permeation flux of pyridine–water liquid mixtures for the PTFPMS membranes was found to increase with the pyridine concentration in the feed mixtures. The separation factor for PDMS membranes for the removal of pyridine, IPA and MEK from aqueous binary mixtures (1 wt.%) was found to be higher than that of PTFPMS membranes while the normalized flux was higher for PTFPMS membranes under identical test conditions. The effect of crosslink density of the PTFPMS membranes on the separation of pyridine–water mixtures was also studied. For a 1 wt.% feed solution the total flux increased with the molar mass between crosslinks, whereas the separation factor for pyridine–water was highest for a molar mass between crosslinks of 15,320 g mol⁻¹.     

Comparative Study of Separation of Acetonitrile from Aqueous Solutions by Pervaporation using Different Membranes

Pervaporation of acetonitrile-water mixtures was carried out using three commercial membranes, viz: polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). The effects of feed concentration and feed temperature on the pervaporation performance, total and partial permeate fluxes, as well as acetonitrile selectivity, were investigated. It was found that increase in temperature yields higher total fluxes and lower selectivity for acetonitrile-water system. Changing concentration of acetonitrile in the range concerned leads to significant effect on total flux and selectivity. PDMS membrane was found to be most selective for acetonitrile separation. The total flux through the membranes was found to be in the order of PTFE > PVDF > PDMS, and the acetonitrile selectivity was found to be in the order of PDMS > PVDF > PTFE. The activation energies of water and acetonitrile associated with the permeation process for the PDMS, PTFE, and PVDF membranes were calculated to be in the ranges of 0.29–0.99, 0.6–0.87, 0.45–2.73 kJ/mol for acetonitrile and 1.23–1.95, 1.37–1.71, 1.16–3.37 kJ/mol for water at different concentrations, respectively.     

丙炔醇-丁炔二醇-水溶液的渗透汽化分离研究

用PDMS复合膜从实际的丙炔醇-丁炔二醇-水溶液中渗透汽化分离丙炔醇。实验证明,膜渗透汽化可以实现丙炔醇的选择性分离,对水的分离因子可达3.78;丁炔二醇被膜完全截留;丙炔醇通量对温度具有敏感性,通量随着温度的增加上升得很快,丙炔醇通量在25℃时为45.28g/(m2.h),在60℃时为243.24g/(m2.h),显示了PDMS膜从这个体系中分离丙炔醇具有某种优势;对实验数据进行线性回归,证明丙炔醇通量和温度的关系可以用Arrhenius公式表征。为工业上用PDMS膜渗透汽化分离提纯丙炔醇提供参考。     

Synthesis of graft copolymeric membranes of poly(vinyl alcohol) and polyacrylamide for the pervaporation separation of water/acetic acid mixtures

Graft copolymers of poly(vinyl alcohol) (PVA) with polyacrylamide were prepared and membranes were fabricated at 48 and 93% grafting of acrylamide onto PVA. These membranes were used in the pervaporation separation of water/acetic acid mixtures at 25, 35, and 45°C. The permeation flux, separation selectivity, diffusion coefficient, and permeate concentration were determined. The highest separation selectivity of 23 for neat PVA at 25°C and the lowest value of 2.2 for 93% acrylamide‐grafted PVA membranes were observed. A permeation flux of 1.94 kg m^?2 h^?1 was found for the 93% grafted membrane at 90 mass % of water in the feed mixture. The diffusion coefficients in a water/acetic acid mixture had an effect on the membrane permselectivity. The Arrhenius equation was used to calculate the activation parameters for permeation as well as for the diffusion of water and of acetic acid. The activation energy values for the permeation flux varied from 97 to 28 kJ/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 244–258, 2002     

Formation of multilayer poly(acrylic acid)/poly(vinylidene fluoride) composite membranes for pervaporation

Dual‐ and multilayer composite membranes, consisting of poly(acrylic acid) (PAA) and poly(vinylidene fluoride) (PVDF), were synthesized by the plasma‐induced polymerization technique. The dual‐layer membrane had a dense PAA layer grafted onto a microporous PVDF substrate, whereas in the multilayer membranes, the grafted PAA and the PVDF layers were arranged in an alternating sequence (e.g., PAA/PVDF/PAA and PAA/PVDF/PAA/PVDF/PAA). These membranes were used in a pervaporation process to separate ethanol–water solutions. For the dual‐layer membranes, the results indicated that the separation factor increased and the permeation flux decreased with increasing amounts of grafted PAA. For the case of grafting yield < 0.6 mg/cm², the composite membrane demonstrated poor separation. As the grafting yield reached 0.85 mg/cm², a sharp increase of the separation factor was observed. For the multilayer membranes, the pervaporation performances were very good, with high separation factors (on the order of 100) and reasonable permeation fluxes over a wide ethanol concentration range. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2266–2274, 2004     

聚环糊精填充PDMS渗透蒸发膜分离苯酚水溶液

以聚二甲基硅烷为预聚体,正硅酸乙酯为交联剂,二丁基二月桂酸锡为催化剂,三氯甲烷或正庚烷为溶剂,通过相转化法制备得到了空白聚二甲基硅氧烷（PDMS）膜和聚环糊精（CDP）填充PDMS（CDP-f-PDMS）膜.考察了空白PDMS膜和CDP-f-PDMS膜对苯酚水溶液的渗透蒸发分离性能,证明填充膜优于空白膜.还分别考察了溶剂类型、填充剂用量等制膜因素和操作温度、原料液流量、原料液浓度等操作因素对PDMS膜的渗透蒸发分离性能的影响.当温度为60℃,CDP填充量为1%（质量）时,CDP-f-PDMS膜的渗透通量和分离因子分别可达32.0 g&#8226;m-²&#8226;h^-1和7.2.