A description of the molecular distillation process is made in order to show its principal applications for chemical processes. The transfer process from liquid stage for the falling film and centrifugal molecular distillators is described. The liquid film flows in the conic rotative evaporator of the centrifugal distillator and in the cylindric evaporator of the falling film distillator. The equations that characterize both processes are the mass, energy and momentum balances and the Langmuir rate of evaporation. The equations are solved by the method of finite differences. The effect of several parameters on the distillation rate and on the separation efficiency are studied for binary systems. A comparative analysis between the falling film and centrifugal distillation apparatuses is carried out.