Design of CNTs/PDMS hybrid membranes with asymmetric filler distribution through electrospraying for enhanced mass transfer of bio-ethanol recovery

Membrane-based pervaporation technology provides an opportunity to meet the growing demand for industrial bio-alcohol recovery. However, current polymer-based membranes still suffer from a low mass transport property and typical permeability-selectivity trade-off effect. Designing membranes with compositionally asymmetric structure has proved a feasible strategy in promoting directional mass transport. Herein, we demonstrated a novel method by combining electrospraying and solution casting to regulate the asymmetric filler distribution in K-CNTs (carbon nanotubes) / PDMS (polydimethylsiloxane) MMMs (mixed matrix membranes) for enhanced bio-ethanol recovery. CNTs were modified with silane coupling agent as K-CNTs before doping in membrane solutions. Electrospray of K-CNTs/PDMS solutions and solution casting of PDMS were then combined to achieve the membranes with K-CNTs enriched on top and bottom area of PDMS selective layer. Correlation between asymmetric distribution of K-CNTs, electrospraying voltage, K-CNTs content, membrane morphology and mass transport property during pervaporation was investigated. Results indicated that the surface-electrosprayed membranes appropriately coordinated the permeability gradient with concentration gradient in membranes by enriching fast-mass transport K-CNTs on top, and thus achieved extraordinary permeating flux about 2390 g·m⁻²·h⁻¹ (2.4 times and 1.9 times that of pure PDMS and conventional MMMs) and separation factor over 10.3 (6 wt% ethanol/water solution at 50 °C). Therefore, we fabricated a high-permeable K-CNTs/PDMS MMM with surface-enriched filler distribution for efficient bio-alcohol separation and proposed a novel strategy to facilitate the mass transport of pervaporation membranes through asymmetric structure design.