A SIMULATION STUDY OF THE ADSORPTION CONCENTRATION POLARIZATION INTERPLAY IN PROTEIN ULTRAFILTRATION

A theoretical approach to study the adsorption-polarisation interplay in ultrafiltration is presented. The model is based on transient mass transfer in the boundary layer, with an appropriate ''source term'' to account for adsorption on the wall boundary of the membrane. The membrane is assumed to be totally selective and of homogeneous surface porosity. Permeate flux is modelled as J = (DELTAP - DELTAPI)/(R(m) + R(ad)), where both DELTAPI, the osmotic term, and R(ad), the additional resistance due to adsorption, are time-dependent. This approach is basically different from that of the semi-empirical models currently employed. The transient mass transfer equation is solved numerically using a tridiagonal matrix algorithm. The evolution of flux and wall concentration over time is obtained for selected values of the polarisation and adsorption parameters involved, particularly in reference to protein ultrafiltration. However, the model can also be applied in a more general way. The characteristic trend for the interplay of the two phenomena, as the simulation results indicate, is for the wall concentration to increase initially for a very short time and then decrease towards a steady-state or quasi-steady-state level in the long term. Preliminary experiments carried out yielded results in close agreement with the model concerning flux as a function of time and steady-state flux as a function of pressure.