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 tang ential flow ultrafiltration are examined from a theoretical point of view i n 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 val ue J(v)(opt)), and then decreasing to a value of 1 at very high permeate fl ux values. The value of J(v)(opt) depends on the cross-flow velocity; the h igher the cross-flow velocity, the higher the value of J(v)(opt). Selectivi ty is independent of the cross-flow velocity at very low and very high perm eate Bur values. In the intermediate permeate flux range (at which most ult rafiltration processes are carried out), the selectivity increases with inc rease in cross-flow velocity. This cross-flow sensitive range is different for laminar and turbulent flow. In the permeate flux range of 1 x 10(-6) to 1 x 10(-5) m s(-1), transition from laminar to turbulent flow leads to a v ery significant increase in selectivity. However, further increase in Reyno lds number does not increase the selectivity any significantly further. Thi s 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. (C) 2000 Elsevier Science B.V. All rights reserved.