Milk protein fractionation by custom-made prototypes of spiral-wound microfiltration membranes operated at extreme crossflow velocities
Compared to tubular membranes, spiral-wound membranes (SWM) cannot be operated at very high crossflow velocities due to mechanical instabilities of the module. We therefore applied a novel approach using custom- made microfiltration SWM modules to study the effects of crossflow velocities beyond the level currently applicable for commercial SWM. First, we used a modified industrial SWM (0.96 m) to measure flux and protein permeation spatially resolved within the limits of crossflow conditions applied in routine operation (maximum Δ DpL of 1.3 bar). Secondly, we applied a short SWM (0.24 m) to assess the effect of extreme crossflow velocities with a corresponding Δ DpL of up to 2.8 bar m-1. The goal was to investigate the effects of deposit formation reduced to the minimum, and thus, to measure the theoretically achievable improvement of flux and protein permeation even though this is currently not practicable. As key result, we found a critical crossflow velocity up to which a significant increase of protein mass flow could be achieved; beyond which, however, no further reduction in filtration resistance caused by deposit formation was observed. The filtration became independent of the transmembrane pressure. Based on these findings, more rigid modules could potentially improve the performance of SWM.
Crossflow velocity; deposit layer; microfiltration; milk protein fractionation; spiral-wound membrane