Polydimethylsiloxane Pervaporation Membranes Research Articles

Effect of butanol, ethanol and acetone feed composition through activated carbon-containing polydimethylsiloxane pervaporation membrane

The ABE route, whose products are acetone, butanol and ethanol, is an industrial process that has been investigated by the possibility of incorporating renewable resources as inputs of chemical compounds and fuels. In view of the toxicity of 1-butanol to the cells of the fermentation broth, pervaporation by means of a polydimethylsiloxane mixed matrix membrane containing 1 wt% activated carbon was used as an alternative to recover this alcohol simultaneously to its production. Synthetic aqueous solution of acetone, 1-butanol and ethanol was investigated with total organic content varied from 1.5 to 2.7 wt%. Permeate flux and selectivity (separation and enrichment factors) were reported. Regarding the organics transport through the membrane, there was not a linear relation of their content in feed stream and flux. Besides, the permeation sequence did not follow a single transport mechanism. High separation and enrichment factors for acetone and butanol were observed.

Pollution and Cleaning of PDMS Pervaporation Membranes after Recovering Ethyl Acetate from Aqueous Saline Solutions

The removal of volatile organic compounds (VOCs) from wastewater containing nonvolatile salts has become an important and interesting case of the application of the pervaporation (PV) process. The aim of this study was to evaluate the influence of salts on the PV removal of ethyl acetate from wastewater using a polydimethylsiloxane (PDMS) membrane. The fouled membrane was then characterized via scanning electron microscopy–energy-dispersive X-ray analysis (SEM–EDX) to investigate salt permeation. The membrane backflushing process was carried out by periodically flushing the permeate side of the tubular membrane. The results demonstrated that salts (NaCl and CaCl2) could permeate through the PDMS membrane and were deposited on the permeate side. The presence of salts in the feed solution caused a slight increase in the membrane selectivity and a decrease in the permeate flux. The flux decreased with increasing salt concentration, and a notable effect occurred at higher feed-salt concentrations. A permeate flux of up to 98.3% of the original flux was recovered when the permeation time and backflushing duration were 30 and 5 min, respectively, indicating that the effect of salt deposition on flux reduction could be mitigated. Real, organic, saline wastewater was treated in a pilot plant, which further verified the feasibility of wastewater PV treatment.

Determination of sorption and diffusion for ethanol through superhydrophobic ZIF/PDMS mixed matrix membrane

The hydrophobicity-hydrophilicity properties of the surface play decisive roles in the resultant separation performance of the membrane, especially the hydrophobicity of mixed matrix membranes (MMMs) for pervaporation recovery of various organic systems from aqueous solution. Herein, superhydrophobic Zeolitic Imidazolate Framework-90 (S-ZIF-90) was employed as filler to incorporate into Polydimethylsiloxane (PDMS) to prepare superhydrophobic S-ZIF-90/PDMS MMMs for ethanol permselective pervaporation. The chemical structures and superhydrophobicity properties of the surface of S-ZIF-90 and S-ZIF-90/PDMS MMMs were demonstrated by various characterization techniques. The results showed that S-ZIF-90 particles and S-ZIF-90/PDMS composite membranes were successfully prepared and S-ZIF-90/PDMS MMMs have higher hydrophobicity property as compared to ZIF-90/PDMS MMMs or pure PDMS. Therefore, S-ZIF-90/PDMS MMMs showed more excellent separation performance than ZIF-90/PDMS MMMs or pure PDMS. In particular, S-ZIF-90/PDMS MMMs with 15 wt% S-ZIF-90 loading have a total flux of 1064 g/(m 2 h) with a maximum separation factor of 14.9 at 40 °C for 5 wt% dilute ethanol solution. The diffusion coefficients, permeation coefficients, adsorption heat (△H S ) and adsorption entropy (△S) of ethanol and water were also calculated by sorption tests, which might provide a method to further determinate the mass transfer mechanism of MMMs in pervaporation process. • The superhydrophobic S-ZIF-90/PDMS pervaporation membranes were fabricated successfully. • Thermodynamic and kinetic parameters were obtained by sorption tests. • Separation factor and total flux of ethanol/water were improved by 175.9% and 116.3% then pure PDMS membrane, respectively. • S-ZIF-90/PDMS membrane exhibited excellent separation performance to most other PDMS-based MMMs.

High performance and thermally stable PDMS pervaporation membranes prepared using a phenyl-containing tri-functional crosslinker for n-butanol recovery

Polydimethylsiloxane (PDMS) pervaporation membranes for n-butanol recovery were fabricated using various crosslinkers: a conventional tetra-functional crosslinker and tri-functional crosslinkers containing different organic (hexyl, cyclohexyl and phenyl) groups. Irrespective of the feed solution conditions, the membranes prepared using tri-functional crosslinkers exhibited a higher permeate flux than the membrane prepared using the tetra-functional crosslinker because their less crosslinked structures increased the free volume. Importantly, among the fabricated membranes, the membrane prepared using the phenyl-containing tri-functional crosslinker exhibited the highest separation factor with a remarkably high permeate flux even under high alcohol concentration and elevated temperature conditions. Its superior pervaporation performance was attributed to its highest hydrophobicity and excellent thermal stability, which are imparted by the phenyl group in the crosslinker, combined with the tri-functional structure of the crosslinker. Our proposed strategy provides an effective and facile method to fabricate high performance pervaporation membranes for alcohol recovery.

PIM-1/PDMS hybrid pervaporation membrane for high-efficiency separation of n-butanol-water mixture under low concentration

Mixed matrix membranes (MMMs) prepared by blending nanocomposites and organic polymers are attractive for producing new materials with improved characteristics such as good hydrophobicity, excellent permeate flux and high separation factor in pervaporation (PV). In order to overcome the aggregation of inorganic nanofillers in membrane and the leakage of inorganic nanoparticles from hybrid membrane in separation process, the polymers of intrinsic microporosity (PIMs) materials with unique properties were successfully synthesized and employed as organic microporous fillers owning good affinity with polymer matrix. The PIM-1/polydimethylsiloxane (PDMS) hybrid pervaporation membranes were then fabricated by mutual combination of the rigidity of PIM-1 and the flexibility of PDMS. The organophilic PIM materials were discovered to provide definite improvements in enhancing the interfacial compatibility and solvent resistance ability to achieve defect-free membrane. Various techniques including FTIR, SEM, EDS, NMR, GPC, contact angle goniometry, N2 absorption/desorption, pervaporation measurements and swelling tests were used to characterize and evaluate the properties of PIMs and membranes. Compared with the pristine PDMS membrane, the prepared PIM-1/PDMS pervaporation membrane exhibited superior permeate flux of 1425.3 g m−2 h−1 and competitive separation factor of 30.7 in the separation of n-butanol–water system under a very low concentration of 1.0 wt%. Moreover, the membrane displayed excellent stability and integrity even over 240 hour’s long-term continuous operation, which showed great potential for industrial application.

PDMS modified membranes by 1-dodecanol and its effect on ethanol removal by pervaporation

Abstract Hydrophobic polydimethylsiloxane (PDMS) membranes in pervaporation are used to remove ethanol compounds from aqueous solutions as fermentation broths. Conventional PDMS membranes, which have been extensively studied, have high fluxes but relatively low selectivities. A new technique to modified PDMS pervaporation membranes is proposed, where a high molecular weight and hydrophobic compound (1-dodecanol) is inserted in the PDMS polymeric layer at several concentrations. The effect of 1-dodecanol concentration in the PDMS layer on flux and selectivity for ethanol removal has been measured. The unmodified and modified PDMS layers were analyzed by SEM to study the membrane layer morphology. Also, TGA and DTG were performed to estimate the 1-dodecanol composition in the PDMS layer remaining after membrane deposition and curing. Pervaporation experiments were carried out at 31 °C for ethanol concentrations in aqueous solutions of 40, 80 and 170 g/L to identify the performance as a function of 1-dodecanol load in the separation layer. The separation factor increases with the concentrations of 1-dodecanol in the polymeric layer while total flux decreases. It is known that although PDMS is a hydrophobic material a high water permeation occurs due to swelling and the molecular interaction between ethanol and water during the ethanol mass transfer across the membrane. The high hydrophobicity of 1-dodecanol reduces this behavior. This new approach presents a strategy to obtain more selective polymeric membranes or with modified properties.

Hydrosilylation-based UV-curable polydimethylsiloxane pervaporation membranes for n-butanol recovery

UV-cured polydimethylsiloxane (PDMS) pervaporation membranes (pristine and mixed matrix membranes (MMMs) containing silicalite-1 particles) were fabricated by using a new class of hydrosilylation-based UV-curable PDMS to facilitate the manufacturing process as well as to enhance performance for n-butanol recovery. Unlike the pristine (heat- and UV-cured) PDMS membranes which showed no discernible difference in their morphology, the UV-cured MMM exhibited a more loosely-packed structure with a rougher surface due to the protuberant features compared to the conventional heat-cured MMM. It was attributed presumably to the different curing mechanisms as well as the different compositions and chemical structures of the PDMS used. Importantly, the UV-cured MMM exhibited a higher permeate flux with a similar separation factor compared to the heat-cured counterpart. Our UV-cured MMM further enhanced separation performance at the elevated temperature with the highest flux of ∼1,520 g m2 h−1 and separation factor of ∼19.8 at 60 °C. This flux enhancement of the UV-cured MMM was explained by its unique morphology (higher surface roughness and loosely-packed structure) and more pronounced temperature-dependent diffusivity enhancement. Our proposed strategy could provide a more efficient and commercially viable route to fabricate highly permeable PDMS-based pervaporation membranes for efficient butanol recovery in the bio-butanol production process.

Investigation on Three-Dimensional Solubility Parameters for Explanation and Prediction of Swelling Degree of Polydimethylsiloxane Pervaporation Membranes

Using polydimethylsiloxane (PDMS) as a basic matrix to prepare ethanol and butanol permselective pervaporation membranes is a vibrant field. Many studies have verified that the three-dimensional Hansen solubility parameters (HSP) theory offers a valid explanation for the swelling performance of ethanol and butanol in PDMS. Five parameters (δD, δP, δH, δt, and Ra) are defined in HSP theory which can be individually used to explain the interaction strength between a solvent and a polymer. However, for the above five parameters, which one is the most effective parameter for deciding the swelling degree still needs to be determined. In this study, a commonly used hydroxy-terminated PDMS precursor was adopted to prepare the PDMS network. The HSP of the chosen PDMS precursor was measured by an advanced “solubility-rating” method. The special software package HSPiP (4.1.03), purchased from the HSPiP team, was used to process the “solubility-rating” results. The equilibrium swelling degree (Q value) of the PDMS network in water, ethanol, butanol, and toluene was measured and the relationships between the five HSP parameters of the solvents and the logarithmic equilibrium swelling degree, log(Q), were discussed. It was found that the measured polar parameter, δP, of PDMS was 0.12 MPa0.5. The measured hydrogen bonding parameter, δH, was larger than δP, attaining a value of 8.6 MPa0.5, because the hydroxy groups directly contributed to the hydrogen bonding solubility parameter, δH. With respect to the relationships between log(Q) and δD, δP, δH, δt, and Ra, linear relationships existed after plotting log(Q) vs. δP and log(Q) vs. δH. The linear relation degree of the fitted lines was 0.995 and 0.989, respectively. Their standard deviations were 0.149 and 0.232, respectively. Therefore, a better linear relationship existed between log(Q) and δP than the other solubility parameters. This indicated that the polar interaction was the main effect for deciding the swelling degree of the PDMS network in water and alcohol systems.

High performance polydimethylsiloxane pervaporative membranes with hyperbranched polysiloxane as a crosslinker for separation of n-butanol from water

Novel hyperbranched polysiloxane crosslinkers, HPSiO, were synthesized to prepare high performance polydimethylsiloxane pervaporation membranes HPSiO-c-PDMS membranes for recoveringn-butanol from aqueous solution by pervaporation.

Effect of pH, CO2, and High Glucose Concentrations on Polydimethylsiloxane Pervaporation Membranes for Ethanol Removal

Previous studies have shown that hybrid fermentation–pervaporation systems can be attractive for ethanol production. Simultaneous removal of the ethanol produced promises to improve yield and to reduce operation time and the energy required for ethanol purification. This paper experimentally explores the effect of pH (3–5.7), CO2 (at saturated conditions), and high glucose concentrations (50–400 g/L) on the flux and selectivity of PDMS (polydimethylsiloxane) pervaporation membranes at several ethanol concentrations (50–100 g/L) and temperatures (278–313 K). Membrane performance has been simulated using a Henry solution model combined with a Maxwell–Stefan description of mass transport through the membrane. By adjusting the model to the water–ethanol experimental data, it was possible to calculate the relative solubility and diffusion between ethanol and water in the polymeric membrane. Experimental results showed that the higher the glucose concentration is, the higher the membrane selectivity to ethanol will be due to a reduction on water flux. However, at a glucose concentration of 400 g/L a strong drop of total flux was measured. CO2 permeates through the PDMS membrane, but it does not have any effect on ethanol or water flux and, consequently, on selectivity. On the contrary, as pH is reduced so does selectivity while the total flux increases. Low pH values produce a decrease in membrane hydrophobicity, increasing water transport. The results presented in this paper contribute to the design of hybrid fermentation and pervaporation units, especially those that can operate at high glucose concentrations.

Experimental Study and Mass Transport Modeling of Ethanol Separation from Aqueous Solutions by Pervaporation

Polydimethylsiloxane pervaporation membrane was employed to remove ethanol from aqueous solutions. The influences of feed flow rate, temperature, permeate-side pressure, and ethanol concentration on the membrane performance were investigated. The feed flow rate was shown to have no significant effect on either flux or ethanol selectivity whereas the feed concentration, temperature, and permeate-side pressure had highly significant effects. Sorption and desorption experiments were also performed to provide data for analysis of mass transport based on resistance-in-series model. The analysis of transport resistances revealed that the mass transport of the system was controlled by the transport resistance of components in the membrane active layer.

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

A new technique for preparation of PDMS pervaporation membrane for VOC removal

To improve the low flux and low selectivity in composite membranes for the removal of volatile organic components (VOC), a new composite membrane, which adopted polydimethylsiloxane (PDMS) as a top layer and non-woven fabric treated with polyethylene glycol (PEG) solution as a support layer, was developed. The preparation variables and the performance of the new membrane were investigated through a permeation test with toluene as a representative VOC. Intrusion thickness, which has a greater effect on membrane performance than the top layer thickness does, decreased when the concentration of PDMS and PEG increased, so that the permeation flux increased. The toluene flux of the new membrane with PEG-treated non-woven fabric showed a maximum increase of 37.4% over a composite membrane with polysulfone (PSf) and a 41.4% increase over that with non-woven fabric.