Theoretical approach is tried to predict flux changes in nanofiltration of dairy whey. Solute quantities (
A) in whey are considered to classify into two parts namely one part is membrane permeable solute (
Ap) and another part is membrane non-permeable solute (
Ar).
Whey solution (0.1 ton of weight and solids concentration 5.34%) to solve the commercial whey powder, was concentrated by means of nanofiltration unit (Element's effective membrane area is 7.4 m
2) up to 2.2 folds by weight in batch concentration system. The flux changes were measured during nanofiltration concentration under the operating conditions of 10°C, 1.2 MPa and feed rate of whey solution to nanofiltration element 1 m
3/h.
The analytical results show that total solute in the initial whey solution are 20.92 mol, and 0.391 of molar ratio of total solute is the permeable solute and residual 0.609 of molar ratio is the non-permeable solute. The permeability coefficient of permeable solute was determined 0.737 from it's concentration per water. A permeable solute will show some osmotic pressure difference through membrane, but it is considered that a permeable solute does not show concentration-polarization phenomena, and a non-permeable solute is considered to form concentration-polarization phenomena.
In this concept, nanofiltration of whey can be analyzed as reverse osmosis concentration of non-permeable solute in whey regarding flux changes.
To calculate osmotic pressure using freezing-point depression analysis, Morse and Frazer's equation showed better coincidence with data than van't Hoff's equation.
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