Polydimethylsiloxane Composite Membranes Research Articles

Pure and mixed gas permeation through a composite polydimethylsiloxane membrane

AbstractA thin polydimethylsiloxane (PDMS) layer on polyethersulfone (PES) support was synthesized and pure and mixed gas permeation of C3H8, CH4, and H2 through it was measured. At first, a macroporous PES support was prepared by using the phase inversion method and characterized. Then, a thin layer of PDMS was coated over the support. Finally, permeation behavior of the synthesized composite membrane was investigated by pure and mixed gas experiments under various operating conditions. The synthesized PDMS/PES membrane showed much better gas permeation performance than others reported in the literature. Pure gas experiments showed that increase in the transmembrane pressure increases the permeability coefficient of heavier gases, C3H8, while decreases those of lighter ones, CH4 and H2. Exactly opposite behavior was observed in mixed gas experiments due to the competitive sorption and diffusion in the plasticized polymer matrix. Temperature was realized to induce similar effects on the permeability of pure and mixed gases. As expected, in rubbery membranes such as PDMS, permeability values of more condensable gases decrease with increasing temperature, whereas those of permanent gases increase. In the case of mixed gas experiments, increase in the C3H8 concentration in feed led to increase in the permeabilities of all the components due to the C3H8‐induced swelling of the PDMS film. High C3H8/H2 and C3H8/CH4 ideal selectivities of 22.1 and 14.7, respectively, at a transmembrane pressure of 7 atm as well as reasonable C3H8 separation factor (SF) values for all mixed gas experiments (in the range of 8.1–16.8) demonstrated the ability of the synthesized PDMS/PES membrane for the separation of organic vapors from permanent gases. Copyright © 2009 John Wiley & Sons, Ltd.

Enhanced pervaporative desulfurization by polydimethylsiloxane membranes embedded with silver/silica core–shell microspheres

Pervaporative desulfurization based on membrane technology provides a promising alternative for removal of sulfur substances (as represented by thiophene) in fluid catalytic cracking (FCC) gasoline. The present study focused on the performance enhancement of polydimethylsiloxane (PDMS) membrane by incorporation of core–shell structured silver/silica microspheres. A silane coupling agent, N-[3-(trimethoxysily)propyl]-ethylenediamine (TSD), was used to chelate the Ag+ via its amino groups and attach the silver seeds onto the silica surface via condensation of its methoxyl groups. The resultant microspheres were characterized by Zeta-positron annihilation lifetime spectroscopy (ZetaPALS), inductively coupled plasmaoptical emission spectrophotometer (ICP), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Ag+/SiO2–PDMS composite membranes were prepared by blending PDMS with the as-synthesized silver/silica microspheres. PALS analysis was used to correlate the apparent fractional free volume with permeation flux. The sorption selectivity towards thiophene was enhanced after incorporation of silver/silica microspheres due to the π-complexation between the silver on the microsphere surface and the thiophene molecules. The pervaporative desulfurization performance of the composite membrane was investigated using thiophene/n-octane mixture as a model gasoline. The composite membrane exhibited an optimum desulfurization performance with a permeation flux of 7.76kg/(m2h) and an enrichment factor of 4.3 at the doping content of 5%.

Recovery of 2,3-butanediol from water by a solvent extraction and pervaporation separation scheme

An integrated separation scheme based on solvent extraction and pervaporation was proposed to recover 2,3-buthanediol from a synthetic fermentation broth. The selected extracting solvent 1-butanol was found to be more suitable than others. Polydimethylsiloxane membrane was employed to further enrich the 2,3-butanediol in the organic phase consisting of 2,3-butanediol, 1-butanol and water. Of the three species, water was found to be the most permeable in the membrane followed by 1-butanol, implying that concentration and purification of 2,3-butanediol as membrane retentate could be achieved by using the polydimethylsiloxane membrane alone. Two membrane batch operations, i.e., dehydration, and removal of 1-butanol using chitosan and polydimethylsiloxane composite membranes, respectively, were conducted to demonstrate the capability of the selected membranes for producing 2,3-butanediol with purities higher than 98 wt.%. And numerical simulation showed the viability of the membrane in continuous operation for the recovery of 2,3-buatendiol.

Factors affecting phenol transfer through polydimethylsiloxane composite membrane

Polydimethylsiloxane composite membrane was employed for the separation of phenol and sodium chloride in synthetic wastewater. The major operational parameters affecting phenol transfer through this composite membrane were screened by the orthogonal array and range analysis. The results showed that the significance of parameters on the permeate flux followed the order of phenol concentration, membrane skin layer thickness, recirculation rate, and sodium chloride concentration after 6 and 48 h operations. Optimal operation range was determined by the response surface methodology coupled with central composite design. The higher was the phenol concentration in the influent or the thicker was the membrane skin layer thickness, the higher was the permeate flux throughmembrane. Also, the higher was the recirculation rate, the higher was the permeate flux through membrane.

Mass transfer characteristics for VOC permeation through flat sheet porous and composite membranes: The impact of the different membrane layers on the overall membrane resistance

In this paper, the mass transfer coefficients for trichloroethylene (TCE), toluene (TOL) and dimethyl sulfide (DMS) are experimentally determined for different porous and composite membranes. For polypropylene/polyvinylidenedifluoride porous layer/thin film polydimethylsiloxane dense layer composite membranes, membrane mass transfer coefficients are 2.55E−03, 2.82E−03 and 2.90E−03 m/s for TCE, TOL and DMS in N 2 at 30.0 ± 0.1 °C, respectively. For polyester/polyacrylonitrile porous layer/thin film polydimethylsiloxane dense layer composite membranes, they are higher, namely 4.28E−03, 4.55E−03 and 4.81E−03 m/s for TCE, TOL and DMS in N 2 at 30.0 ± 0.1 °C, respectively. Analysis of the contribution of the dense layer of both composite membranes to the total membrane resistance for mass transfer, showed that this contribution was small for both composite membranes. The higher mass transfer coefficients of the thin film polydimethylsiloxane composite membranes from this study in comparison to others from the literature are primarily due to improvement of the mass transfer characteristics of the porous layer. Analysis of the mass transfer characteristics of the different porous layers of which the total porous layer is composed, showed that the contribution of the porous “backing” layer for mechanical support can be substantial in comparison to the porous layer in contact with the dense layer.

Influence of binding interface between active and support layers in composite PDMS membranes on permeation performance

AbstractEffect of the binding interfaces of composite polydimethylsiloxane (PDMS) membranes on their pervaporation performance was studied. The membranes were made up of PDMS as active skin layer and polysulfone (PSF) or polyamide (PA) as supporting layer. PDMS‐PSF membrane was numbered 1, and PDMS‐PA membrane numbered 2. The pervaporation experiments were carried out by using the composite membranes and dilute ethanol–water mixture. The experimental measurements for the permeation performance under various operating conditions (e.g., feed concentration and temperature) showed that the specific permeation rate of membrane 2 was over membrane 1 by seven times at least. A resistance‐in‐series model was applied to formularize the transport of the permeants. Influence of the binding interfaces between the active skin layer and support layers in these membranes on pervaporation performance was analyzed. The cross section morphology of the membranes and chemical element distribution along membrane thickness were examined by using SEM and EDS. It was found that, although the PDMS intrusion layer into PSF near the interface was only about 2 μm, it gave significant effect on the permeation performance. It implied that the resistance produced by the intrusion layer into PSF was apparently larger than that of PDMS intruding PA and over intrinsic PDMS resistance. These should be probably attributed to structures and formation of the binding interfaces. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2468–2477, 2007

Removal of 1,2‐dichloroethane from aqueous solutions with novel composite polydimethylsiloxane pervaporation membranes

AbstractComposite pervaporation membranes were prepared by the crosslinking of H‐terminated oligosilylstyrene (oligo‐SiH3) and vinyl‐terminated polydimethylsiloxane (vinyl‐PDMS) on the surface of polysulfone ultrafiltration membranes. The morphology of the composite pervaporation membranes were investigated through changes in the mass ratio of oligo‐SiH3 to vinyl‐PDMS. The pervaporation of crosslinked polydimethylsiloxane composite membranes was evaluated by the removal of 1,2‐dichloroethane (1,2‐DCE) from dilute aqueous solutions with different downstream pressures, feed temperatures, feed concentrations, and top layer thicknesses. A low feed flow rate, corresponding to a Reynolds number of 97, was maintained during the entire process. The separation factor of 1,2‐DCE was 600–4300, and the permeation rate of 1,2‐DCE was 0.4–15 g/m2 h; they depended on the operating conditions and the compositions of the membranes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1477–1491, 2005

Composite PDMS membrane with high flux for the separation of organics from water by pervaporation

The composite polydimethylsiloxane (PDMS) membranes supported by Cellulose acetate (CA) were prepared by pre-wetting method for the separation of methanol, ethanol, n-propanol and acetone from water. The experiments were carried out to investigate the effects of operating parameters on the pervaporation performance and the results showed that the membranes exhibited high total permeation flux. A resistance-in-series model was applied to analyze the transport of the permeants. It was found that boundary-layer mass transfer coefficient was proportional to Re 0.5 and increased exponentially with temperature. The membrane mass transfer coefficient conformed to Arrhenius correlation and was independent of flow status. The estimated diffusivities of alcohols in membrane had a magnitude order of 10 −10 m 2·s −1 under a wider range of temperature, which was identical with those reported in the literature.

Mass transfer in pervaporation of active fermentation broth with a composite PDMS membrane

The pervaporation behavior and mass transfer coefficients of active fermentation broth as well as concerned ethanol mixtures were experimentally investigated. Ethanol was produced by Saccharomyces cerevisiae and recovered by pervaporation using a composite polydimethylsiloxane (PDMS) membrane prepared in the laboratory. The overall transfer coefficients across the membrane were nearly invariable when recovering ethanol from fermentation broth under the constant operating condition, which was 1.93 × 10 −6 m/s on average for flow rate of 100 L/h, downstream pressure of 5 mmHg and cell concentration of 5 g/L at 35 °C in contrast with 1.34 × 10 −6 m/s for an aqueous ethanol solution under similar conditions. Ethanol fluxes and selectivities for fermentation broth were all higher than those for aqueous ethanol solution at the same feed concentration. According to the resistance-in-series model, the boundary layer transfer coefficient of fermentation broth was nearly three times as much as the value with the model solution on the assumption that diffusive transfer coefficients in the same membrane remained invariable at a constant temperature. Overall transfer coefficient increased slightly with active cell concentration for fermentation broth but decreased with solid concentration for inactive cell suspension. Active fermentation broth gave the highest transfer coefficients among the feeds involved during pervaporation using the composite PDMS membrane.

Effect of low flow rate on pervaporation of 1,2-dichloroethane with novel polydimethylsiloxane composite membranes

Crosslinked oligosilylstyrene–polydimethylsiloxane composite membranes were used to separate trace 1,2-dichloroethane (1,2-DCE) from the mixtures of 1,2-DCE and water by pervaporation. The performances of pervaporation were evaluated by low feed flow rates (0.35–1.0 l/min), corresponding to Reynolds number from 79 to 220. The resistance-in-series model and semi-empirical Sherwood correlations were employed to study the transfer characteristics. For the given hydrodynamic conditions, both mass transfer resistances of the boundary layer and the membrane were found to be important to the overall mass transfer. The transfer resistance of 1,2-DCE through the boundary layer and the membrane decreased as the decrease of thickness of boundary layer. The permeation rate and the separation factor of 1,2-dichloroethane increased, but the permeation rate of water kept unchanged as the feed flow rate increased. The theoretical data from resistance-in-series model were compared with experimental data. The good correlation between the theoretical and experimental data can work as the predication of pervaporation performance and the management of pervaporation process.

Preparation and characterization of thin-film zeolite–PDMS composite membranes

Thin-film zeolite filled PDMS composite membranes, as thin as 3μm, have been prepared. Two criteria are essential for the successful preparation of these membranes: (a) application of ultrafine silicalite crystallites (0.2–0.5 μm) and (b) prepolymerization of the suspension comprising silicalite, two-component polydimethylsiloxane (PDMS) polymer, and isooctane. The separation properties of the composite membrane were characterized by pervaporation and gas permeation. High flux and high selectivity were observed in the pervaporation of aqueous ethanol solution. Composite membranes, having a silicalite to PDMS ratio ( w s/ w p) of 3.3, give a selectivity of 34 for separating ethanol from water, while the flux remains 150 g/m 2-hr, at 22°C. The composite membranes also show improved performance in gas permeation, e.g. for separating O 2 from N 2. Optimization experiments provide suitable conditions and compositions for the preparation of the membranes. Employing PDMS concentrations in the 3.5–4.0 wt.% range and silicalite to PDMS ratios from 1.5 to 3.3, highly-selective composite membranes can be fabricated with high reproducibility.