Herein, the numerical simulation of polymeric membrane formation is investigated when a coupling between phase separation and solvent evaporation occurs. A binary polymer/solvent system is considered and simulations were performed in 2D geometries, first in a horizontal 2D plan, then in a vertical cross-section plan. The phase separation was simulated using Cahn-Hilliard equations and the Flory-Huggins theory was used to describe the thermodynamics of the binary system. The solvent evaporation was coupled to the phase separation using a continuous mass flux at the upper interface of the system, whose magnitude is controlled by a mass transfer driving force. The simulated patterns were analyzed using Minkowski descriptors and Fourier analysis. The results exhibit a strong influence of solvent evaporation in the vicinity of the upper interface, leading to the formation of a dense skin, whose kinetics in concentration and thickness was shown to depend on the initial polymer concentration and the mass transfer coefficient. Beneath the dense layer, the system tends to relax to minimize its free energy so that the phase separation in the bulk solution was found homogeneous and weakly affected by the solvent evaporation.