This paper presents the design of a pervaporator in order to separate water from an azeotropic mixture, light oil. This mixture is composed of five alcohols ranging from C-2-C-5. From the mass transfer equations obtained from our experimental results, we develop three basic equations governing the pervaporation process formulating mass and energy balance. A very simple heat balance is used considering the vaporization enthalpy of the permeate supplied by the feed mixture under adiabatic conditions. It was clearly seen that the membrane area required to obtain a specific final concentration neglecting the feed temperature drop was underestimated. The membrane surface area is important because the pervaporation modules called stages have higher surface area.