Ultrathin zeolite X membranes for pervaporation dehydration of ethanol

► An ultrathin zeolite X membrane was grown from a well-defined seed monolayer. ► The membrane displayed good performance for dehydration of ethanol–water mixture. ► The performance of ultrathin membrane was still limited by pressure drop in support. ► The limitation of membrane performance was explored by a mathematical model. Discrete Faujasite zeolite nanocrystals with an average size of about 60nm were attached as a well-defined monolayer on the surface of porous graded alumina supports. Ultrathin zeolite X films with a total thickness of about 1μm were grown from the seed monolayers by hydrothermal treatment in clear synthesis solutions. One of the membranes showed a total flux of 3.37±0.08kgm−2h−1 and a separation factor of 296±4 for dehydration of a 90/10wt.% ethanol/water mixture by pervaporation at 65°C. Moreover, the membranes displayed stable performance during pervaporation for 5.5h operation. A mathematical model indicated that the flux and selectivity of the membranes were limited by pressure drop in the supports. Therefore, in order to obtain higher flux, the permeability of the support must be improved.