Filled Polydimethylsiloxane Membrane Research Articles

ZIF-7/PDMS mixed matrix membranes for pervaporation recovery of butanol from aqueous solution

Abstract In this contribution, zeolitic imidazolate framework (ZIF-7)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) with uniformly dispersed ZIF-7 were fabricated. The homogeneous dispersion of ZIF-7 nanoparticles in PDMS matrix and better interface compatibility were characterized by SEM and EDS. PV performance reveals that the MMMs display increased total flux and the highest separation factor occurs at 20 wt% ZIF-7 loading, which were 1689 g m −2 h −1 and 66 respectively as compared to 1080 g m −2 h −1 and 51 for pure PDMS membrane when separating 1 wt% butanol aqueous solution at 60 °C. The total flux reaches 3496 g m −2 h −1 with 80 wt% butanol in permeate for the enrichment of 5 wt% butanol solution at 60 °C. The enhanced flux may result from enlarged free volume in the polymer matrix caused by the incorporation of ZIF-7 nanoparticles. Moreover, the super-hydrophobic ZIF-7 pore channels and butanol preferential permeation may contribute to the improvement of separation factor. The result also shows that there is a 21.1% reduction of energy barrier for penetrant transportation for 20 wt% ZIF-7 filled PDMS membrane as compared to pristine PDMS membrane. A long period of pervaporation experiment was also carried out to investigate the structure stability of the ZIF-7/PDMS membrane, and the MMM remains intact during the 240 h continuous operation, which is the key to industrial application for membrane-based separation process. All above indicated that ZIF-7 is a good filler to fabricate butanol permselective pervaporation membranes for butanol separation and enrichment.

Sonication-enhanced in situ assembly of organic/inorganic hybrid membranes: Evolution of nanoparticle distribution and pervaporation performance

Organic/inorganic hybrid membranes for separation applications have been widely studied. However, achieving a uniform dispersion of inorganic fillers in the polymer matrix is a primary challenge in the advancement of mixed-matrix membranes (MMMs). In the present study, a method for in situ assembly enhanced by sonication was developed to prepare hydrophobic polydimethylsiloxane (PDMS)/nanoparticle hybrid membranes. Results from scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometry, and atomic force microscopy (AFM) suggest that through ultrasonic cavitation during assembly of the hybrid membrane, this method could effectively avoid nanoscale agglomeration and in turn uniformly disperse inorganic particles within the polymer matrix. This method thus enabled the preparation of an organophilic membrane with higher hydrophobicity and higher performance. For example, the contact angle (CA) of SiO2/PDMS hybrid membrane increased from 135.5° to 146.3°, and the separation factor for the pervaporation of 5% ethanol/water mixture increased from 7.3 to 12.5. Furthermore, the method was used to prepare a zeolite imidazolate framework-8 (ZIF-8)-filled PDMS membrane. The ZIF-8/PDMS hybrid membrane showed high performance in the pervaporation of alcohol/water mixtures. These results further suggest that in situ assembly via sonication is a promising approach to improve the dispersion of inorganic fillers and thus the membrane performance.

Removal of hazardous chlorinated VOCs from aqueous solutions using novel ZSM-5 loaded PDMS/PVDF composite membrane consisting of three hydrophobic layers

Hydrophobic polymer possesses significant potential for selective separation of volatile organic compounds (VOCs) from their aqueous solutions by pervaporation (PV). In the present study mixed matrix hydrophobic membranes of polydimethylsiloxane (PDMS) supported on polyvinylidenefluoride (PVDF) substrate were synthesized by incorporating hydrophobic inorganic ZSM-5 filler. The indigenous membranes were crosslinked with tetraethylorthosilicate (TEOS) for the extraction of volatile chlorinated hydrocarbons such as dichloromethane (DCM), trichloromethane (TCM), 1,2-dichloroethane (DCE), and 1,1,2,2-tetrachloroethane (TeCE), which pose serious environment threat and health hazard. Thermal stability, crosslinking, crystallinity, surface morphology and swelling characteristics of the indigenously developed membranes were determined by TGA, FTIR, XRD, SEM and sorption studies, respectively. Effect of operating parameters such as feed composition and filler concentration on separation performance in terms of flux and selectivity were determined. Flux of DCM, TCM, DCE and TeCE was found to be 0.166, 0.146, 0.141 and 0.06kgm−2h−1 with selectivity of 541, 1068, 917 and 15,000, respectively, for 20% ZSM-5 filled PDMS membrane for aqueous feeds containing 1.33% (w/v) DCM, 0.8% (w/v) TCM, 0.84% (w/v) DCE and 0.28% (w/v) TeCE in water. The membrane exhibited considerable feasibility for scale-up with significant potential for removal of hazardous chlorinated VOCs from aqueous solutions.

Pervaporation of ethanol/water mixture by organophilic nano-silica filled PDMS composite membranes

A novel organophilic nano-silica (ONS) filled polydimethylsiloxane (PDMS) composite membrane was prepared and characterized for the pervaporation (PV) of ethanol from water. The sorption and diffusion behaviors of ethanol and water in the composite membranes were investigated. The results showed that with increasing ONS concentration from 0wt.% to 10wt.%, the solubility selectivity and the diffusion selectivity increased from 21.87 to 38.85 and from 1.87 to 6.18, respectively. When the temperature ranged from 30°C to 70°C, the solubility selectivity increased but the diffusion selectivity first increased and then decreased. The effects of ONS content, feed temperature and permeate-side vacuum on the PV performance of the composite membrane for the pervaporation of 5 wt.% ethanol–water mixture were studied. The examinations showed that the composite membranes exhibited striking advantages in total flux and separation factor as compared with unfilled PDMS membrane. When ONS loading was 5 wt.%, the PDMS composite membrane showed the best PV performances with the permeate flux (J) of 114g/(m2·h), the separation factor (α) of 30.1 and permeate separate index (PSI), of 3420, respectively. With an increase of the feed temperature from 30 to 70°C, the total flux of filled PDMS membrane with 5 wt.% ONS increased apparently from 11.1 to 210g/(m2·h), and the maximum separation factor of 30.1 was observed at 60°C. With an increase of vacuum in permeate-side from 0.075 to 0.100MPa, both separation factor and total flux increased for filled PDMS membrane with 5 wt.% ONS.

Pervaporative enrichment of 2,3‐butanediol from its mixture with 1‐butanol using a polydimethylsiloxane and ZSM‐5 mixed matrix membrane: Effects of ethanol as a by‐product

AbstractA ZSM‐5 filled polydimethylsiloxane membrane with 44.4 wt.% zeolite loading was used in the pervaporative removal of 1‐butanol from its mixtures with 1‐butanol. A small quantity of ethanol was added to the feed as a by‐product to test the response of the membrane. It was found that the permeation behaviour of other feed components was changed and membrane selectivity decreased. This change was attributed to the frequently‐observed inter‐component coupled transport in multi‐component feed systems. The impact of ethanol on recovery of 2,3‐butanediol was evaluated using a simulated continuous operation, which enriched 2,3‐butanediol to 99.5 wt.% from a feed containing 5 wt.% 2,3‐butanediol and less than 1.0 wt.% ethanol. It was observed that membrane selectivity improves as ethanol concentration decreases in the stream due to its preferential removal. The final recovery of 2,3‐butanediol was not significantly reduced as the concentration of ethanol was below 1.0 wt.%. © 2011 Canadian Society for Chemical Engineering

Organophilic Modification and Application of Nano-Fumed Silica in Pervaporation of Ethanol / Water Mixture

Fumed Silica was modified with hexamethyldisiazane (HMDZ, modifier) and dimethyldiethoxysilane (DMDEOS, co-modifier) by grafting method. The structure of organo-functionnalized nanoparticles was characterized by fourier transform infrared spectrum (FT-IR) and transmission electron microscopy (TEM). Functional nanosilica-filled polydimethylsiloxane(PDMS) composites membrane were prepared. Scanning electron microscopy (SEM) observations of composites revealed good dispersion of the silica nanoparticles and the pervaporation performance of the filled PDMS membranes is better than that of the unfilled PDMS membranes.

Solvent Recovery from Soybean Oil/Hexane Miscella by PDMS Composite Membrane

Traditional solvent recovery in the extraction step of edible oil processing is distillation, which consumes large amounts of energy. If the distillation is replaced by membrane process, the energy consumption can be reduced greatly. In this work, two kinds of membrane, PDMS (polydimethylsiloxane) composite membrane and Zeolite filled PDMS membrane were prepared, in which asymmetric microporous PVDF (polyvinylidenefluoride) membrane prepared with phase inversion method was functioned as the microporous supporting layer in the flat-plate composite membrane. The different function compositions of the PDMS/PVDF composite membranes were characterized by reflection Fourier transform infrared (FTIR) spectroscopy. The surface and section of PDMS/PVDF composite membranes were investigated by scanning electron microscope (SEM). The PDMS NF (nanofiltration) membranes were then applied in the recovery of hexane from soybean oil/hexane miscellas (1:3, mass ratio). The effects of pressure (0.5-1.5 MPa), cross-linking temperature and PDMS layer thickness on membrane performances were investigated. The results indicated that both two kinds of NF membranes were promising for solvent recovery, and zeolite filled in PDMS NF membrane could enhance the separation performance.

Improved performance of PDMS/ceramic composite pervaporation membranes by ZSM-5 homogeneously dispersed in PDMS via a surface graft/coating approach

A homogeneous dispersion of inorganic fillers in polymer matrix is a primary challenge for the advancement of mixed matrix membranes (MMMs) in pervaporation and gas separation. In this work, a surface graft/coating approach was developed for homogeneously dispersing ZSM-5 zeolite in polydimethylsiloxane (PDMS) for preparing ZSM-5 filled PDMS mixed matrix/ceramic composite membranes. Molecular dynamics simulations were carried out to calculate the interaction energy between zeolite and PDMS. It was found that surface modification of zeolite particles could highly improve their interaction with PDMS matrix. The SEM images confirmed the uniform dispersions of surface-modified ZSM-5 particles in PDMS matrix even at highest zeolite loading of 40 wt.%. As revealed in the FT-IR analysis and contact angle measurements, the prepared ZSM-5 filled PDMS membranes exhibited less hydroxyl groups and became more hydrophobic with increasing zeolite loading. The pervaporation experiment in 5 wt.% ethanol–water solution indicated that the homogeneously incorporated ZSM-5 particles improved the selectivity of PDMS membrane, and the separation factor of surface-modified ZSM-5 filled PDMS membrane increased gradually with zeolite loading. This effective dispersion method could be instructive for the fabrication of organic–inorganic composite materials.

Pervaporation of acetic acid/water mixtures through silicalite filled polydimethylsiloxane membranes

The preferential pervaporation of acetic acid over water is achieved with silicalite filled polydimethylsiloxane (PDMS) membranes. The effect of silicalite addition is not positive at the feed temperature of 25°C, but improves with increasing feed temperature. At a feed temperature of 45°C, silicalite addition enhances not only the separation factor but also the permeation flux of the pervaporation. This improvement may be attributed to the reduction in kinetic limitation on sorption/desorption processes and the enlargement of sorption difference between acetic acid and water towards silicalite. At 25°C, the sorption ratio of acetic acid to water is 3.9, but 4.9 at 45°C. It is further found that at a silicalite loading of 49.9 wt.%, the separation factor versus feed acetic acid concentration curve exhibits a maximum and this maximum shifts to lower feed acetic acid concentrations with increasing feed temperature. Further increasing the silicalite loading to 69.2 wt.%, results in the formation of connected pores in the membrane and thus failure of the membrane in providing a separative pervaporation. The addition of silicalite is also found to enhance the thermal stability of the membrane. The pervaporation behavior of the silicalite filled PDMS membrane seems to fall in between those of pure PDMS and pure silicalite membranes.