Ethyl tert-butyl ether (ETBE) is one of the most promising oxygenates used as high-octane components of fuels. A method to purify ETBE from an ethanol/ETBE azeotropic mixture formed during industrial synthesis is pervaporation. In this study, hybrid membranes containing nanodiamond particles incorporated into the P84 copolyimide matrix have been synthesized for the pervaporation purification of ETBE. The membrane structure has been studied by scanning electron microscopy and via determining the experimental and theoretical density and free volume. The transport properties of the membranes have been determined in sorption and pervaporation experiments. It has been shown that the introduction of up to 1 wt % of nanodiamonds in the P84 matrix leads to an increase in the main mass transfer parameters, namely, the flux and the separation factor of the azeotropic mixture.