Influence of support layer and PDMS coating conditions on composite membrane performance for ethanol/water separation by pervaporation

Abstract

A systematic study was performed on the combination of support properties and polydimethylsiloxane (PDMS) coating conditions for the lab-scale preparation of a defect-free, thin film composite membrane for organophilic pervaporation. Support layers having comparable surface porosities were prepared from three polymers with different chemical composition (PVDF, PSF, PI). Their exact role on the deposition of the PDMS coating (i.e., wetting and intrusion) and the final membrane performance (i.e., effect on mass transfer of the permeants) was studied. The crosslinking behavior of dilute PDMS solutions was studied by viscosity measurements to optimize the coating layer thickness, support intrusion and wetting. It was found essential to pre-crosslink the PDMS solution for a certain time prior to the coating. Dip time for coating the PDMS solution on the supports was varied by using automated dip coating machine. The performance of the synthesized membranes was tested in the separation of ethanol/water mixtures by pervaporation. Both flux and selectivity of the membranes were clearly influenced by the support layer. Resistance of the support layers increased by increasing the polymer concentration in the casting solutions of the supports. Increasing the dip time of the PDMS coating solution led to increased selectivity of the composite membranes. Scanning Electron Microscopy analysis of the composite membranes showed that this leads to a minor increase in the thickness of the PDMS top layer. Top layer thickness increased linearly with the square root of the dip time (t 0.5 ) at a constant withdrawal speed of the support.

Enhanced Pervaporation Properties of PVA-Based Membranes Modified with Polyelectrolytes. Application to IPA Dehydration

“…Despite the generally accepted opinion that the porous substrate of supported membranes does not significantly affect the mass transfer of low-molecular-weight components in pervaporation, the substrate polymer type, as well as substrate porosity, can have a significant effect on the transport properties of the supported membrane [46][47][48]. In this section, to understand the mechanism of mass transfer in pervaporation, the characteristics of commercial porous substrates PAN and UPM-20 were studied by SEM, AFM, the standard porosimetry method, contact-angle measurements, and ultrafiltration experiments.…”

“…Thus, based on the obtained pervaporation data on the separation of the isopropanol-water mixture and data on the characterization of commercial porous substrates, it can be concluded that a supported membrane with a thin selective layer based on PVA-PAH deposited on porous PAN substrate and modified with 10 PEL bilayers via LbL deposition (PVA-PAH/LbL-10 PAN membrane) has the best selective properties with respect to water. On the other hand, the UPM-20 substrate, characterized by a much higher porosity, did not limit the mass transport of the low-molecular-weight component, which logically favored a higher permeance [46]. Nevertheless, at the same time, the water selectivity was reduced due to the coupling effect of several parameters: a more open pore structure, a rougher and more hydrophobic surface, and facilitated diffusion of iPrOH in UPM-20 (compared to PAN).…”

“…The SEM cross-sectional micrographs of industrial PAN and UPM-20 substrates are presented in Figure 8. The presented microphotographs in Figure 8 demonstrate that the bulk porosity of the PAN substrate is much smaller than for the UPM-20 substrate, which is one of key factors for permeation flux decrease and the increase in water content in the permeate with the use of a PAN membrane as the substrate compared to the UPM-20 substrate [46].…”

Thin film composite membranes with desirable support layer for MeOH/MTBE pervaporation

“…Although the morphology and chemical nature of the selective layer mainly control the membrane performance, according to many studies in this field, the pore size, pore length, porosity, hydrophilicity, and reactivity of the sublayer might influence the final properties of the prepared membranes. Some studies have proved the significant effects of the sublayer on pervaporation. While the sublayer should preserve the mechanical stability of the membrane, the selective layer is responsible for high flux and selectivity .…”

“…Some studies have proved the significant effects of the sublayer on pervaporation. While the sublayer should preserve the mechanical stability of the membrane, the selective layer is responsible for high flux and selectivity . Hence, the development of a porous support with high mechanical and chemical stability, proper porosity, and flexibility is required.…”