The kinetics of the formation of a deposited layer during the reverse osmosis of skim milk

Abstract

The kinetics of the permeation of water and dissolved substances in the first phase of the concentration of skim milk were investigated. This phase is characterised by the deposition on the membrane of a layer which becomes rapidly compressed (1 to 2 min) into a membrane-like film forming a barrier against the permeation of water and dissolved substances. However, low molecular weight substances already present at the membrane, are incorporated into the deposited layer as it is being formed and these permeate through the membrane slowly in an equilibration process which may take up to 30 min, while convective transport towards the membrane is reduced by the deposited layer. These processes give the permeation curve its characteristic shape. By varying individual process variables, such as the pressure difference across the membrane, the shear stress at the walls, the temperature and the concentration, the conditions in the first stages of concentration were changed in such a way, that it was possible to determine their effects on the formation of the deposited layer.