ULTRAFILTRATION OF A LARGE POLYELECTROLYTE

We present a model of polarisation at an ultrafiltration membrane. The feed is an aqueous solution of a large polyelectrolyte (such as a pro tein) and small co- and counter-ions. Small ions can pass the membrane ; the large ones cannot. This causes electrical effects in the polaris ation layer and at the membrane interface. Equilibrium at the interfac e then yields a pressure drop. The relation between this pressure drop and the flux is similar to that seen in practice. So are the salt ret ention and the effects of protein concentration, salt concentration an d pH (charge of the protein).