Mass Transfer Models Across Membranes

Models for mass transfer across membranes are divided into those in which the membrane represents the main transport resistance and others in which additional resistances are formed by concentration boundary layers and particle layers. Since mainly porous membranes are used in AO, the pore model is derived for membrane-controlled mass transfer. Concentration boundary layers may develop if permeable components are diffusively transported along a gradient from bulk to wall concentration, or if impermeable components concentrate at the membrane surface. By establishing mass flow balances around a differential membrane cross section (a membrane element), equations are derived describing the removal rates of solvents and dissolved or dispersed molecules and its dependencies on geometrical and operational parameters. These equations will be used for the different processes in AO.