A molecule within the nonporous polymeric membrane moves in response to the local driving force and has no memory of how it entered the membrane or how the local gradients were generated. This means that a properly formulated model of transport within the membrane should be equally applicable to dialysis, pervaporation or vapour permeation. The phenomenological approach of irreversible thermodynamics was used to develop transient models of dialysis and pervaporation. The model developed in this study were validated against transient dialysis and pervaporation data for ethanol-water/silicone rubber system. A critical assessment was obtained by recovering the model parameters from the dialysis data and using the same parameters to predict the transient pervaporation performance. The equilibria for the system under study was separately described in terms of Flory-Huggins model with constant interaction parameters where the interaction parameters were found from a nonlinear fit to the available relative sorption data. It was shown the average phenomenological diffusion coefficients recovered from dialysis data can give a good qualitative prediction of pervaporation performance provided the diffusion coefficients satisfy the Onsagar reciprocal relationships. However, a quantitative prediction requires the explicit inclusion of the concentration dependence of the diffusivities as well as a better description of polymer phase equilibria, which is difficult to handle in the framework of irreversible thermodynamics formalism and best achieved within the mechanistic Stefan-Maxwell formulation and deferred to the forthcoming article.