Contribution of sorption to global mass transfer during pervaporation of ethyl tert-butyl ether–ethanol mixtures through a polyurethaneimide film

Abstract

The pervaporation of ethyl tert-butyl ether–ethanol mixtures through a polyurethaneimide block-copolymer film has been investigated over the entire composition range. Experiments revealed the system to be unstable at a critical feed mixture, inducing strong flux oscillations. Pervaporation selectivity towards ethanol is higher than that of the sorption method. The features of sorption were examined in relation to the corresponding pervaporation properties and analysed in terms of the activity of each penetrant to take account of the system non-ideality. Original sorption isotherms could be expressed in terms of a single linear relationship for ethyl tert-butyl ether and two linear relationship in the case of ethanol. The discontinuity in the EtOH isotherm corresponds to the composition of the critical feed mixture and was ascribed to the complete monosolvation of the polymer's most basic sites, i.e. urethane groups, by the protic penetrant.