微孔SiO_2膜在水蒸气条件下的稳定性能

以正硅酸乙酯为前驱体,通过聚合溶胶路线制备出稳定的SiO2溶胶和制膜液,采用浸浆法,经过一次涂膜,在平均孔径约为3nm的γ-Al2O3中孔膜上制备出完整无缺陷的SiO2微孔膜,考察了烧成温度对SiO2粉末和SiO2微孔膜气体渗透性能的影响.结果表明,在400～800℃焙烧温度下制备的SiO2膜在200℃及0.3MPa条件下对He的渗透通量为(7.29～12.7)×10-7mol/(m2·s·Pa),600℃下烧成的膜的理想分离因子分别为98(He/CO2),49(He/O2),64(He/N2),79(He/CH4)和91(He/SF6),具有分子筛分效应.微孔SiO2膜在水蒸气条件下的稳定性能取决于膜的烧成温度,400,600和800℃烧成的膜的水蒸气稳定压力分别为8,200和200kPa.     

镍掺杂SiO_2膜的制备及CH_4/CO_2气体分离性能

以正硅酸乙酯(TEOS)为前驱体,六水合硝酸镍(Ni(NO3)2·6H2O)为镍源,采用溶胶--凝胶法制备镍掺杂SiO2膜。研究了水用量及镍含量对镍掺杂SiO2膜的结构及形貌的影响,并对其进行CH4、CO2气体渗透性能测试。结果表明:水酯比为5.5时,制备的10%Ni掺杂SiO2膜具有良好的微孔结构,且孔径约为1.16nm,孔隙率为64.9%。一部分Ni元素以Ni和NiO晶体形式填充于SiO2孔道内,另一部分以Si—O—Ni形式进入SiO2骨架。Ni掺杂SiO2膜在84h内能够保持良好的气体渗透性能,表现出比纯SiO2膜更好的水热稳定性。CH4和CO2的气体渗透通量分别为1.56×10--7和0.64×10--7 mol/(m2·s·Pa),CH4/CO2气体分离因子达到2.43。     

SiO2气体分离膜的制备工艺优化

利用溶胶-凝胶法(sol-gel)进行了SiO2气体分离膜的实验研究,对制备过程中的主要影响因素--溶胶浓度、水解过程的pH值、干燥条件、热处理工艺和担载体的性质等进行了适当调整与分析,寻求制备担载SiO2无机膜的最佳条件,制得了孔径分布狭窄、分离效果良好的担载SiO2膜.     

膜蒸馏分离聚酯废水中微量乙醛的研究

本文采用膜蒸馏技术分离聚酯废水中的乙醛,通过实验比较了聚四氟乙烯微孔膜和聚偏氟乙烯微孔膜的分离性能,并考察了膜室温度、进料乙醛浓度和冷侧真空度列聚四氟乙烯微孔膜分离性能的影响。     

胶水粘合法制备非对称固液分离膜的探索

探索使用胶水粘合法制备非对称固液分离膜,即用胶水粘合法对聚丙烯微孔膜和聚丙烯针刺非织造布进行粘合获得非对称固液分离膜,聚丙烯微孔膜使非对称固液分离膜表面具有良好的孔径尺寸,探讨了热压温度和时间对非对称固液分离膜各项性能的影响.     

PTFE微孔薄膜在油水分离中的应用研究

研究了疏水性聚四氟乙烯(PTFE)微孔膜的结构、润湿性、可重复使用性以及在不同温度、pH下对煤油、汽油和柴油的分离速率的影响。结果表明,在常温下,PTFE微孔薄膜对含油废水中油的去除率可达90%以上;PTFE微孔薄膜油水分离速率不受含油废水中pH的影响,但随着温度的升高而加快;对不同的含油废水有着不同的分离速率,其中对汽油的分离速率最高,稳定后可达800 L/(m2.h),煤油次之,对柴油的分离效率最低,低至稳定后为650L/(m2.h)。另外,由于PTFE微孔膜采用的是表面过滤的方式,所以膜具有非常好的可重复使用性,是一种非常理想的油水分离膜。     

MFI型分子筛膜的修复

采用二次生长法制备完备的MFI型分子筛膜,在高温脱除模板剂后测试其CO2/N2分离性能,分离因子低,说明膜存在较大的缺陷。采用纳米SiO2对分子筛膜进行修复,SiO2修复后的分子筛膜对CO2/N2分离因子由1.6提高到5.0,且修复后的分子筛膜的性能很稳定。此外,该修复方法具有良好的重复性,用于多个具有低分离因子的膜都得到了比较好的效果。     

疏水SiO_2/PTFPMS杂化复合膜的制备及其气体分离性能

为了提高气体分离膜的耐溶胀特性,以多孔聚醚酰亚胺(PEI)为支撑层,采用溶液共混法制备了疏水SiO2/PTFPMS杂化复合膜,研究了疏水SiO2质量共混比对膜形态、耐溶胀性以及不同操作压差下的纯气渗透分离性能的影响。光学显微照片显示,当共混比不超过0.018时,杂化膜的透明度较高,表明疏水SiO2与PTFPMS具有较好的相容性;当SiO2与PTFPMS的共混比超过0.018时,SiO2团聚明显。SEM表征结果显示,杂化膜表面光洁,断面杂化涂层紧密贴合支撑层。疏水SiO2/PTFPMS杂化膜在异辛烷中的溶胀度为0,在乙酸乙酯中的溶胀度比PTFPMS均质膜的下降了11.9%,显示了其优异的耐溶胀性能。在操作压力为1.0 MPa,操作温度为25℃下,SiO2共混比为0.012时,疏水SiO2/PTFPMS杂化复合膜的CO2渗透通量达到最高156.1GPU,CO2/N2选择性为15.86。     

纳米SiO2改性聚乙烯醇渗透汽化膜

将纳米Si0：添加到聚乙烯醇(PVA)渗透汽化膜中，通过X—射线衍射、TCA分析、强度测试和渗透汽化分离实验研究了改性PVA膜的性能。与纯PVA膜相比，改性膜的结晶度浅小，拉伸强度明显增大，断裂伸长率有所减少，热稳定性增加。且随着纳米SiO2的增加，改性膜的结晶度和断裂伸长率逐渐浅小，热稳定性逐渐增大，拉伸强度增大的幅度逐渐浅小。改性膜用于分离质量分数40％。95％的乙醇水溶液，分离性能随料液乙醇浓度的变化规律与纯PVA膜相似。随着纳米Si02的增加，分离选择性先增大后下降，透过速率单调增加，添加1％(与PVA质量比)以内的纳米SiO2能得到综合性能较好的PVA渗透汽化膜。     

疏水微孔膜的制备与改性

膜蒸馏是一种新兴高效的膜分离技术,具有重要的应用前景。膜蒸馏中所用的膜是多孔的和不被料液润湿的疏水膜。分离膜的制备是应用这一技术的关键。文章对膜蒸馏过程及疏水性微孔膜做了介绍。进一步综述了疏水性微孔膜的制备,成膜方法和膜的改性,最后对膜蒸馏在不同领域中的应用趋势作了分析。     

Fabrication of inorganic/polymer nanocomposite membranes containing very high silica content via in situ surface grafting reaction and reactive dispersion of silica nanoparticles: Proton conduction,water uptake,and oxidative stability

In this study, we present a new fabrication process for proton exchange membranes based on inorganic/organic nanocomposite using in situ surface grafting reaction and reactive dispersion of silica nanoparticles in the presence of reactive dispersant, urethane acrylate nonionomer (UAN). Through in situ surface grafting reaction of silica nanoparticles, urethane acrylates were chemically introduced on the surface of silica nanoparticles, which were dispersed in DMSO solutions containing UAN and sodium styrene sulfonate (NaSS). After urethane linkage and copolymerization of NaSS, UAN and urethane acrylate moieties of silica nanoparticles, the solutions were converted to silica nanoparticle‐dispersed proton exchange membranes where silica particles were chemically connected with organic polymer chains. 5.89–29.45 wt % of silica nanoparticles could be dispersed and incorporated in polymer membranes, which were confirmed by transmittance electron microscopy (TEM) measurement. On varying weight % of silica nanoparticles dispersed within the membranes, water uptake and oxidative stability of nanocomposite membranes were largely changed, but membranes showed almost the same proton conductivity (greater than 10⁻² S cm⁻¹). At 5.89 wt % of silica nanoparticles, nanocomposite membranes showed the lowest water uptake and excellent oxidative stability compared to the sulfonated polyimide membranes fabricated by us. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and pervaporation performances of fumed‐silica‐filled polydimethylsiloxane–polyamide (PA) composite membranes

Fumed‐silica‐filled polydimethylsiloxane (PDMS)–polyamide (PA) composite membranes were prepared by the introduction of hydrophobic fumed silica into a PDMS skin layer. The cross‐sectional morphology of these filled composite membranes was observed with scanning electron microscopy. Their pervaporation performances were tested with aqueous ethanol solutions at 30, 35, and 40°C. Increasing the amount of the fumed silica resulted in significantly enhanced ethanol permeability of the membranes. When the content of the fumed silica in the PDMS skin layer was 20 wt %, the ethanol permeability increased to nearly twice that of the unfilled PDMS–PA composite membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Filled poly(2,6-dimethyl-1,4-phenylene oxide) dense membranes by silica and silane modified silica nanoparticles: characterization and application in pervaporation

The effects of silica and silane modified silica fillers on the pervaporation properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) dense membranes have been studied. Crystallinity, thermal and mechanical properties of unfilled and filled PPO membranes with silica and silane modified silica nanoparticles were investigated. The surface energy together with the solubility parameters of the membranes and the nanoparticles were determined. Pervaporation separation of methanol/methyl tert butyl ether (MTBE) mixtures over the entire range of concentration were carried out using both filled and unfilled membranes. The results are discussed in terms of the solubility and the diffusivity of each liquid component in the membranes. Flory-Huggins theory was used to predict the sorption methanol selectivity. Compared to the unfilled PPO membrane, the filled PPO membranes exhibit higher methanol selectivity and lower permeability. For methanol concentration in liquid feed mixture lower than 50 wt%, methanol selectivity of the filled PPO membranes with silane modified silica is better than that of the silica filled and unfilled PPO membranes.     

Hybrid sol–gel membranes of polyacrylonitrile–tetraethoxysilane composites for gas permselectivity

Sol–gel reaction of tetraethoxysilane (TEOS) with fumed silica–polyacrylonitrile (PAN) membrane was carried out to prepare hybrid gas permeable membranes for oxygen and nitrogen separation. Various amounts of fumed silica microparticles with a few μm diameters were compounded in PAN–dimethylsulfoxide (DMSO) solution. After casting of the viscous compound solution on a flat sheet with 100 μm thickness, DMSO was evacuated under vacuum at 80°C. Then, the silica–PAN composite membranes were treated with TEOS for 1 day at 40°C in methanol. Air permeation was examined and compared in silica–PAN composite membranes with and without TEOS treatment. The latter hybrid membranes showed selective oxygen permeability, which depended on amounts of fumed silica in the membrane. The TEOS hybrid PAN membranes have a high ability of oxygen permselectivity for O₂/N₂ gas mixture with α(O₂/N₂) = 13–17, when the silica content was in the range of 13–20 wt %. This is attributed to siloxane network formation in hybrid silica–PAN composite membranes. Favorable siloxane network formation resulted in high oxygen permeability of the hybrid composite membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1752–1759, 2003     

Recovery of alcohols from water using polydimethylsiloxane–silica nanocomposite membranes: Characterization and pervaporation performance

Different polydimethylsiloxane (PDMS) nanocomposite membranes were synthesized by incorporating various contents of nanosized silica particles to improve the PDMS pervaporation (PV) performance. A uniform dispersion of silica nanoparticles in the PDMS membranes was obtained. The nanocomposite membranes were characterized morphologically by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that surface roughness increases by incorporating silica, and this decreases absorption of penetrants on the membrane. Swelling studies showed that the presence of silica nanoparticles into the PDMS membranes decreases degree of swelling, which can be attributed to rigidification of the PDMS matrix. Additionally, the results revealed that helium permeability decreases through the nanocomposite membranes, due to the more polymer chains packing. Effects of silica on recovery of isopropanol (IPA) from water mixtures were also investigated. Based on the results, incorporating silica nanoparticles promotes significantly the PDMS membrane selectivity because the polymer chains are rigidified and also the polymer free volume decreases. However, permeation flux decreases as diffusion of the penetrants reduces in the presence of silica nanoparticles within the PDMS membranes. As PV performance depends on operating conditions, effects of feed composition, and temperature were also studied. Moreover, recoveries of IPA, ethanol, and methanol from water mixtures were compared using the PDMS‐silica nanocomposite membranes. The results demonstrated that polarity and solubility of alcohols affect permeation flux and selectivity resulting in the higher permeation flux and selectivity for IPA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Facile synthesis of hydrophobic microporous silica membranes and their resistance to humid atmosphere

The ethylene-modified silica membranes were prepared by the acid-catalyzed co-hydrolysis and condensation reaction of tetraethylorthosilicate (TEOS) and ethylenetriethoxysilane (TEVS) in ethanol and the final materials were characterized by scanning electron microscope (SEM), water contact angle measurement, solid-state ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR), and N₂ adsorption. The modification leads to a transform from superhydrophilicity for the unmodified silica membranes to hydrophobicity for the modified materials. The ethylene-modified silica membranes are much less water sensitive than the unmodified materials because the hydrophobic ethylene groups replace a portion of the hydrophilic hydroxyl groups on the pore surface. The modified materials process a microporous structure with a narrow pore size distribution centered at 1.1 nm. Such a microporous structure can be stabilized after exposured to humid atmosphere for 450 h, in intense contrast to the collapse of the micropores in the unmodified silica membranes.     

Effect of Silica Nanoparticles on the Performance of Polysulfone Membranes for Olefin‐Paraffin Separation

The separations of ethylene/ethane and propylene/propane using polysulfone‐silica nanocomposite membranes were studied. Silica nanoparticles were prepared via sol‐gel method and the membranes by phase inversion. Characterization by Fourier transform spectroscopy and scanning electron microscopy indicated a good distribution of silica nanoparticles in the polymer matrix and also a good compatibility between the two phases. The performances of the prepared membranes in ethylene‐ethane and propylene‐propane separation were evaluated. The results showed the increments in gas permeability and selectivity by silica. Higher silica contents increased the solubility coefficient and reduced the diffusion coefficient of gases. The plasticization pressure of polysulfone was increased by incorporating the silica nanoparticles in polymer.     

Growing well-defined monodispersed silica in polyimide host membranes using a surfactant assisted sol-gel process

Polyimide-silica membranes are interesting hybrid architectures that possess excellent mechanical, thermal and chemical properties. However, the dispersion of inorganic domains in the polymer matrix and the compatibility between the organic and inorganic phases are critical factors in these hybrid systems, due to the lack of favorable interactions between the hydrophobic polymer and hydrophilic silica. In this study, a new approach to forming hybrid membranes by the in situ generation of silica and functionalized silica in the polyimide matrix is presented. The new surfactant assisted sol-gel process improves the particle dispersion and the compatibility between the organic and inorganic phases. Moreover, this synthetic strategy allows the sol-gel process to proceed in the presence of a fully imidized, high molecular weight polyimide to generate a chemically well-defined silica phase. The importance of the polymer-silica and silica-surfactantfaffinities and the influence of functionalization of silica in guiding the construction of the hybrid network are also examined here.     

Pore Size Reduction and Performance Upgrade of Silica Membranes with an Ambient Temperature C-ALD Post-Treatment Method

An ambient temperature C-ALD (with NH₃ as catalyst) method was employed to modify sol-gel silica membranes, in order to reduce their pore size and upgrade their gas separation performance. Membranes were characterized before and after modification in terms of permeance and permselectivity with the use of He and N₂, as gas separation indicators. The application of the proposed method significantly improved the permselectivity of the membranes accompanied with a minor permeance reduction. The process temperature renders it ideal for application in commercial membrane modules which utilize economic, current available, sealing technologies. The performance of the C-ALD modified silica membranes in various gas separation applications was further examined, indicating that they are potential candidates for H₂ separation in various chemical processes. Finally, the stability of the C-ALD modified silica membranes in H₂O was studied, indicating some performance loss during the first hours of the membrane's exposure to a H₂O atmosphere, which nevertheless remained high and steady then on.     

Influence of solvent and nanoparticles on the morphology and gas separation properties of copolyimide membranes

In this study, the effect of solvent type and nanoparticles of silica and zeolite 4A on the gas separation properties of polyimide (PI) membranes were investigated. Gas separation of the membranes based on pure solvents of dimethylformamide (DMF), n-methyl-2-pirrolidone (NMP), dimethylacetamide (DMAc), and dimethylsulfoxide (DMSO) were studied. The prepared PI membranes using DMAc and DMSO showed the highest selectivity and permeability, respectively. In this regard, the influence of their mixing on transport properties of the PI was evaluated. The prepared membrane using the mixture of DMSO/DMAc with the volume ratio of 1:3 showed the best gas separation performance in comparison to the Robeson's upper bound. Incorporation of 20 wt% of silica and zeolite 4A nanoparticles into the PI membrane indicated that the selectivity of CO₂/CH₄ increased from 39.4 to 57.6 and 68.5, respectively. Besides, gas transport properties of the PI-based mixed matrix membranes were satisfactory predicted by modified Maxwell model. Furthermore, characteristic parameters of the encapsulated particles by interfacial layer were determined.