Facial build-up of acid-resistance skin for high-stability zeolite NaA membrane

Abstract

Zeolite NaA membranes have been widely used in dehydration of alcohols by pervaporation because of their excellent permeability and selectivity. However, the zeolite NaA membranes were criticized for the poor performance in acidic condition. Herein, we report a simple and effective method to enhance acid stability of zeolite NaA membranes. The key is a positively charged polyelectrolyte complex (PEC) was impregnated on the surface of zeolite NaA membranes. The PEC was synthesized from chitosan (CS) and sodium poly (vinyl sulfonate) (PVS). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that the zeolite NaA membranes suffered from severe damage in both morphology and crystal structure after contact with acid, while the PEC/NaA composite membranes remained intact. Accordingly, the PEC/NaA composite membranes（1.5 wt% PEC in solution） exhibited excellent water permeability and selectivity in acid solution. For acidic 90 wt% ethanol/water (pH = 3) mixture separation, the permeate flux was 875 g/(m2 h), the water content in permeate was as high as 99.8 wt% at 40 °C. Meanwhile, the composite membranes showed a good acid stability for more than 200 h and this was attributed to the barrier effect of PEC layer, as well as the protonation ability of -NH2 groups in PEC. This method is expected to offer great opportunities for the dehydration of organics under acidic conditions.