ABSTRACT
Abstract Two international patents and also recent results have shown that polymeric membranes containing cationic groups are highly efficient for the removal of protic species (e.g., alcohols) from organic mixtures, with an important potential application for the purification of ethyl-tert-butyl ether (ETBE). By an appropriate tax policy for the past ten years, the European Union has been strongly encouraging to produce this alkyl ether from bio-ethanol. Due to its specific advantages and its much better biodegradability than methyl-tertbutyl ether (MTBE), ETBE is currently considered as one of the most promising bio-fuels. Nevertheless, its industrial synthesis process leads to an azeotropic mixture containing 20 wt% of ethanol which has to be removed for ETBE purification. Taking advantage of our former experience with polyimide block copolymers for this separation, we have recently synthesized and characterized 3 families of new ion-containing polyimide copolymers, with a control of the number of their cationic ammonium groups, the length of their alkyl side chain and the type of their counter-ions. On the basis of sorption and permeability results obtained for the purification of ETBE, the membrane features are discussed in terms of structure-property relationships. In particular, it is shown that simply changing the chemical structure of the cationic groups enables to increase sharply the permeability with a very low impact on selectivity, therefore overcoming the usual permeability/selectivity trade-off.
