Simulation study of the fractionation of proteins using ultrafiltration

The effects of module hydrodynamics (cross-flow velocity) and permeate flux (pore velocity) on the selectivity of binary protein fractionation in tangential flow ultrafiltration are examined from a theoretical point of view in this paper. Simulation studies show that, for a given cross-flow velocity, the selectivity depends on the permeate flux, increasing with increase in permeate flux from a value of 1 to a maximum value (at a permeate flux value Jvopt), and then decreasing to a value of 1 at very high permeate flux values. The value of Jvopt depends on the cross-flow velocity; the higher the cross-flow velocity, the higher the value of Jvopt. Selectivity is independent of the cross-flow velocity at very low and very high permeate flux values. In the intermediate permeate flux range (at which most ultrafiltration processes are carried out), the selectivity increases with increase in cross-flow velocity. This cross-flow sensitive range is different for laminar and turbulent flow. In the permeate flux range of 1×10−6 to 1×10−5ms−1, transition from laminar to turbulent flow leads to a very significant increase in selectivity. However, further increase in Reynolds number does not increase the selectivity any significantly further. This trend is similar to earlier experimental observations. For a given system, both permeate flux and cross-flow velocity need to be optimized to obtain high selectivity.