Augmenting the Efficacy of a Polyvinyl Alcohol Selective Layer Coated on Polyvinylidene Fluoride Support Membranes with Kaolinite Introduction for Improved Pervaporation Dehydration of Epichlorohydrin/Isopropanol/Water Ternary Systems.

Composite membranes with a polyvinyl alcohol (PVA) selective layer composed of well-dispersed hydrophilic kaolinite particles coated on a polyvinylidene fluoride (PVDF) support were developed. They were applied to the pervaporation dehydration of the industrially important epichlorohydrin (ECH)/isopropanol (IPA)/water ternary mixture. In comparison with raw kaolinite (RK), hydrophilic kaolinite (HK) enhanced the mechanical properties, hydrophilicity, and thermal stability of the PVA selective layer, as confirmed by universal testing, the contact angle, and TGA analyses, respectively. The pervaporation results revealed that the addition of HK particles significantly enhanced the separation factor (3-fold). Only a marginal reduction in flux was observed with ECH/IPA/water, 50/30/20 (w/w %) at 40 °C. An HK particle concentration of 4 wt.% with respect to PVA delivered the highest flux performance of 0.86 kg/m2h and achieved a separation factor of 116. The PVA-kaolinite composite membrane exhibited pronounced resistance to the ECH-containing feed, demonstrating a sustained flux and separation factor throughout an extended pervaporation stability test lasting 250 h.

Synergistic pervaporation dehydration of ethanol/water mixture: Exploring the potential of a covalently designed hybrid membrane structure of polyacrylic acid grafted carbon nitride and polyvinyl alcohol.

Polyacrylic acid (PAA) grafted CN sheet (P-g-CN) was synthesized to enhance the dispersive properties of carbon nitride (CN) in the membrane. A successful PAA grafting to the CN was confirmed from FTIR, TGA, and Zeta potential and XRD analyses. The A PVA membrane embedded P-g-CN, including a covalently constructed polymer-filler network, was developed to separate ethanol-water mixtures using pervaporation (PV). XPS study has confirmed a covalent attachment of P-g-CN sheets to the PVA matrix. Thereby, a defect-free membrane matrix was observed in the FESEM analysis. A 10 wt% loaded PVA-P-g-CN10 composite membrane was compared to the pristine PVA membrane, demonstrating improved PV dehydration performance. The flux decreased from 0.21 kg/m2h of pristine PVA membrane to 0.17 kg/m2h of PVA-P-g-CN10 membrane, while the separation factor improved from 49 to 176 in a 90/10 wt % ethanol/water feed at 40 °C. This improvement can be attributed to the selective diffusion of water through the P-g-CN interlayer spacing and tiny triangular nanopores in the s-triazine network, along with their dispersibility in the PVA matrix, resulting in well-ordered membrane morphology. Furthermore, PVA-P-g-CN10 exhibited higher water permeance (43.31-86.07 GPU) than ethanol (1.18-10.47 GPU) as the feed temperature increased from 30 to 70 °C, suggesting P-g-CN successfully inhibits swelling in the feed solution through proper interaction with PVA. In a long-term PV test lasting 250 h, the PVA-P-g-CN10 membrane displayed excellent structural stability and maintained its performance.