Separation of dimethyl carbonate/methanol azeotropic mixture by pervaporation with dealcoholized room temperature-vulcanized silicone rubber/nanosilica hybrid active layer

Abstract Less pollution, low toxicity, high binding force, dealcoholization-type, room temperature-vulcanized (RTV) silicone rubber and alkyl-modified nanosilica were applied to obtain a nano SiO2/RTV pervaporation (PV) hybrid active layer. The layer is applied to the PV membrane separation technology of dimethyl carbonate (DMC)/methanol azeotrope given its flexible molecular chain and its structure that is conducive to the transmission of DMC. The nanoSiO2/RTV active layer was characterized by reflection infrared spectroscopy, X-ray diffraction, thermogravimetry, and swelling analyses. The PV membrane was characterized by scanning electron microscopy and contact angle measurement. The permeation flux, separation factor, swelling/diffusion selectivity, and activation energy of the hybrid membrane were evaluated by PV test. Results showed that the alkyl-modified nanosilica reduced the order of RTV and the contact angle with the azeotrope, facilitated the preferential infiltration of DMC, and increased the permeation flux of DMC during PV. The separation factor increased first and then decreased with increasing amount of alkyl nanosilica. This finding could be due to the following: the alkyl group on the surface of nanosilica has DMC selection ability, the excessively high content of nanosilica causes the free volume of the active layer to increase, and methanol can penetrate quickly. NanoSiO2/RTV hybrid membrane M-30 possessed a permeation flux of 3.8 kg/m2h at 50 °C and a separation factor of 4.42; whereas M-15 had a separation factor of 5.60 at 30 °C and a permeation flux of 1.2 kg/m2h. It is preferentially separated from DMC compared with the results reported in literature. The overall separation efficiency reached a new height.