Using concentration polarization factors to determine the mass transfer resistance in vacuum membrane distillation

Abstract

Vacuum membrane distillation, like any membrane distillation process, is a thermally driven process in which the convective mass transfer is the dominant mechanism for mass transfer. The driving force is maintained by applying vacuum at the downstream side to keep the pressure at this side below the equilibrium vapor pressure (see Fig. 1), The membrane in this process is a physical support for the vapor-liquid interface and does not affect the selectivity associated with the vapor-liquid equilibrium. Vacuum membrane distillation has the potential to be one of the most common techniques, in environmental engineering, used to separate dilute aqueous mixtures, such as in the removal of ethanol from fermentation broth to prevent the inhibition of the microorganisms used in fermentation, and for the removal of trace concentrations of VOC's. In addition to that, VMD can be used when the feed contains non-volatile salt as in desalination. The objective of this article is to determine the most important mass transfer resistance in vacuum membrane distillation in the case of removal of trace VOC's. Simple criteria used without the need to solve the mathematical model.