Predicting mass fluxes in the pervaporation process using Maxwell-Stefan diffusion coefficients

Alicyclic Polyimide/SiO2 Mixed Matrix Membranes for Water/n-Butanol Pervaporation

Alicyclic polyimides (PIs) have excellent properties in solubility, mechanical strength, thermal property, etc. This study developed two types of alicyclic PI-based mixed matrix membranes (MMMs) for water/n-butanol pervaporation application, which have never been investigated previously. The fillers were hydrophilic SiO₂ nanoparticles. The synthesized PI was mixed with SiO₂ nanoparticles in DMAc to make the casting solution, and a liquid film was formed over PET substrate using doctor blade. A dense MMM was fabricated at 80 °C and further treated via multi-stage curing (100–170 °C). The prepared membranes were characterized by FTIR, TGA, FE-SEM, water contact angle, and solvent swelling. The trends of pure solvent swelling effects agree well with the water contact angle results. Moreover, the pervaporation efficiencies of alicyclic PI/SiO₂ MMMs for 85 wt% n-butanol aqueous solution at 40 °C were investigated. The results showed that BCDA-3,4′-ODA/SiO₂ MMMs had a larger permeation flux and higher separation factor than BCDA-1,3,3-APB/SiO₂ MMMs. For both types of MMMs, the separation factor increased first and then decreased, with increasing SiO₂ loading. Based on the PSI performance, the optimal SiO₂ content was 0.5 wt% for BCDA-3,4′-ODA/SiO₂ MMMs and 5 wt% for BCDA-1,3,3-APB/SiO₂ MMMs. The overall separation efficiency of BCDA-3,4′-ODA-based membranes was 10–30-fold higher.

Double-Crosslinked GO Interlayer Framework as a Pervaporation Hybrid Membrane with High Performance

Graphene oxide (GO), as a two-dimensional structure material, has attracted widespread attention in the field of molecule sieving. However, GO-based membranes usually exhibit undesirable separation performance because the microstructure of GO is difficult to adjust. Herein, a novel double-crosslinking strategy for tuning the interlayer spacing of GO is reported. The hybrid membrane fabricated by the double-crosslinking strategy was used for pervaporation (PV) dehydration of isopropanol. To achieve high-performance of the PV hybrid membranes, the effects of operating cycles, chitosan concentration, and GO concentration were systematically investigated. The PV hybrid membranes were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, water contact angle measurement, and scanning electron microscopy. The results demonstrate that the interlayer of GO can be adjusted successfully by the double-crosslinking strategy. The fabricated hybrid membrane containing 0.1 wt % GO exhibited excellent performance with a flux of 4391 g/m2h and a separation factor of 1491, which indicated that the double-crosslinking strategy may extend the applications of GO in the field of membrane separation.

Composition dependent transport diffusion in non-ideal mixtures from spatially resolved nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is a well-established technique for the measurement of intra-diffusion coefficients. Recently, such information has been used as a basis of predictive models to extrapolate to the Fick diffusion coefficient of liquid mixtures. The present work presents a new approach to directly access the Fick diffusion coefficient by spatially resolved NMR experiments. The Fick diffusion coefficient of the binary mixture TEA/H2O was determined at two temperatures, 283.2 K and 275.2 K. The results are consistent with values previously reported either from optical experiments or predictive Darken-type models developed for this system. The proposed methodology adds high-resolution NMR to the toolbox for the study of the transport diffusion of multicomponent mixtures. It is, however, still limited to mixtures with liquid-liquid equilibrium phase separation.