Hybrid processes of distillation and vapor permeation are considered promising alternatives to azeotropic and extractive distillation. The research is directed toward developing membranes with improved separation properties and longer life times. We show that membranes with very high selectivities are not desirable when a very high purity of the retentate is required. A design methodology was developed to calculate the optimum separation properties for the membranes within hybrid processes. The results of the simulation encourage the use of low-selectivity membranes, especially if the membrane step is coupled to a distillation step. The method is applied to an ethanol dehydration process. However, it can be applied to other membrane separation processes as well.