An energy-saving separation process by vapor permeation (VP) membrane is proposed for the concentration of aqueous ethanol solutions and an explicit design model for vapor permeation systems, based on the solution-diffusion mechanism, is presented. In order to concentrate aqueous ethanol solution from 30 to 99.6 wt.% with ethanol recovery more than 98 wt.%, a computer simulation is performed by changing the operating conditions and the optimum operating factors and the required membrane area are investigated. (C) 2000 Elsevier Science B.V. All rights reserved.