Membrane Operation

Membrane operation is a specific, but not exotic, operation. In fact it is a "hybrid" of classical heat and mass transfer processes (Figure 4.1). Direct contact mass transfer operations tend to reach equilibrium due to a difference of chemical potential between two phases that are put into contact. In the same way, temperature equilibrium is aimed at during heat transfer operations, for which driving force is a temperature gradient. In contrast, for membrane operations, by using the specific properties of separation of the thin layer material that constitutes the membrane, under the particular driving force that is applied, it is possible to deviate from the equilibrium that prevails at fluid-to-fluid interphase with classical direct contact mass exchange systems and to reorientate the mass transfer properties. In particular, this is the case with classical operations such as microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO), gas separation (GS), pervaporation (PV), dialysis (DI) or electrodialysis (ED), for which a few characteristics are recalled in Table 4.1.

In Table 4.1 L and G refer to liquid and gas phases; dP, Dp, DC and dVare the differences in pressures, partial pressures, concentrations and voltages, respectively; porous and dense refer to the type of the material; and sieving, solubility-diffusion and Donnan are types of mass-transfer mechanism.

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