Helically microstructured spacers improve mass transfer and fractionation selectivity in ultrafiltration

The separation performance of ultrafiltration processes is strongly affected by the hydrodynamic flow conditions in the feed channel close to the membrane surface. In particular, spacer mats required to separate the membranes have a strong influence on the mass transport in the bulk liquid towards the membrane surface. Commercially available net-spacers have proven to influence mass transport advantageously depending on their geometrical structure: spacers improve mixing phenomena, diminish concentration polarization and increase mass transfer coefficients. Little is known about the effect of such spacers on the mass transfer in multi-component mixtures with respect to the separation between different solutes dissolved in a solvent. This paper investigates new 3D-printed helically microstructured spacers in comparison to state-of-the-art net spacers. In particular, we report the influence of fluid hydrodynamics on mass transport enhancement and process selectivity. Ultrafiltration experiments with well-defined Dextran solutions focus on the molecular weight cut-off and the separation quality at various operating conditions. Compared to net-spacers, the application of the micro-structured spacers resulted in significant improvements of the overall mass transfer coefficient as well as process selectivity. A higher overall performance at equal cross flow power consumption is obtained as well.