Change in molecular weight retention curves of ultrafiltration membranes with respect to lignosulfonates under gel formation conditions

The paper considers ultrafiltration of lignosulfonates (LS) under predominantly the gel formation conditions. An effort is to determine the molecular weight retention (MWR) curves of a series of ultrafiltration membranes differing in their pore size under in turn different operating pressures (1–32 bar). The initial separative properties (both retentivity and volume flux) of all membranes are shown to change because of gel formation occurring actually instantly as a cake layer placed mostly onto the membrane surface. The transmembrane pressure-drop sets up primarily these properties but the initial hydrodynamic permeability coefficient of a membrane (i.e. its mean pore size) is also of concern. As a result, an increase in that pressure results in a shift of the molecular weight retention curves of all membranes under study towards lower molecular weights: the more, the higher their mean pore size. Further, these curves become more abrupt in their form, and such a change depends on the mean pore size of a membrane as well.