An essentially predictive mathematical model was developed to simulate pervaporation process. The group contribution method UNIFAC was used for calculating the upstream activity coefficients. The diffusion coefficient in the membrane was predicted using free-volume theory. Free-volume parameters were determined with viscosity and temperature data, and the binary interaction solvent-polymer parameter was calculated by a group-contribution lattice-fluid equation of state (GCLF-EOS). A simulator named PERVAP was developed applying the mathematical model. Pervaporation process was simulated for separating bioethanol-water through polyetherimide membrane. The simulated results were validated using experimental data of bioethanol/water separation through polyetherimide membrane. The model presented a satisfactory performance compared to experimental data. Related to the simulation of the studied separation, a 99% molar enriched bioethanol stream was obtained with a recovery of 94%. (c) 2007 Wiley Periodicals, Inc.