Pervaporation of azeotropic mixtures ethanol/ethyl tert-butyl ether: influence of membrane conditioning and operation variables on pervaporation flux

This work reports the pervaporative separation of ethanol from ethanol –ethyl ter butyl ether mixtures using a commercial membrane, PERVAP 2256, that previously showed an interesting behavior in the separation of methanolMTBE mixtures. Pervaporation flux has been obtained and analyzed as a function of feed composition in the range of ethanol concentration of 30–50 wt % and temperature in the range of 50–70ºC whereas permeate pressure was kept constant in all the experiments and equal to 3 mmHg. Pervaporation fluxes showed an exponential dependence with both variables, that in the case of temperature fitted to an Arrhenius type expression. Achievement of steady state conditions referred to the pervaporation flux needed of long times that depended on the previous history of the membrane; thus new membranes needed a long conditioning period before reaching steady state that was considerably shortened in subsequent changes of the operation conditions.

This work reports the analysis of the pervaporation flux of ethanol in the separation from ethanol-ethyl tert-butyl ether mixtures using the commercial membrane Pervap 2256. The membrane had been previously used for the separation of methanol-methyl tert-butyl ether allowing high methanol flux values as well as high permeate selectivities, but needing of higher conditioning times than other dehydration membranes types [2]. The study of the time needed to reach steady state flux data has been performed starting with new membranes as well as with membranes that had been already used under different operation conditions. Finally the dependence of s.s. flux data on feed composition in the range 30–50 wt% of ethanol and temperature in the range 50–70ºC has been studied working at a constant permeate pressure of 3 mmHg. Both variables showed an exponential influence on the permeate flux, fitting the influence of temperature to an Arrhenius type expression.