High-flux membrane separation using fluid skimming dominated convective fluid flow

We here report on the separation of yeast cells, with micro-engineered membranes having pores that are typically five times larger than the cells. The separation is due to neither shear-induced diffusion, nor initial lift, but to an effect similar to fluid skimming. The separation performance is linked to the ratio between cross-flow and transmembrane flux, and could be captured with a dimensionless number relating those. On the basis of this dimensionless number, flux and transmission of the cells could be predicted. The mechanism rests on having a sufficiently high cross-flow velocity, such that particles are not dragged too deep in the pore, but are dragged with the cross-flow back into the feed stream. The separation factor can simply be changed by changing the ratio between crossflow velocity and transmembrane flux. Since the membranes have very large pores, fouling does not play a role. Constant high transmembrane flux values of 200–2200 L/m2 h were reached for transmembrane pressures ranging from 0.02 to 0.4 bar (typical industrial fluxes are 150 L/m2 h bar with a maximum of 2000 L/m2 h bar for short periods of time, comparable to 50–400 L/m2 h ). Although the effect is strongest with monodispersed pores, it will be possible to exploit the mechanism with conventional membranes. As such, it may open up a new route towards non-fouling crossflow microfiltration.