Effect of flow channel number in multi-channel tubular ceramic microfiltration membranes on flux and small protein transmission in milk protein fractionation

Ceramic multi-channel microfiltration (MF) membrane elements exist in various configurations, partially with high numbers of flow channels to increase the active membrane surface area and flux. The open question was how multi-channel membranes with different channel numbers perform in applications of protein fractionation, where not only flux, but more importantly, also transmission of components counts as decisive criteria. In this study, ceramic membrane elements with 1-, 7-, 19-, and 37-channels with the same outer diameter were compared with the task of milk protein fractionation in their main fractions (casein micelles, about d = 180 nm in diameter, and whey proteins, 4–8 nm in size) using 0.1 μm MF as technical example. Flux and therefore the advective protein transport towards the membrane surface was expected to differ between outer and inner channels owing to the different resistance to flow of the permeate from the inner channels to the outer rim of the ceramic element. In fact, the fouling intensity exerted by the retained biopolymers differed. Permeate flux, as well as whey protein transmission, depend on number and position of the individual channels. The 37-channel membrane element with more inner channels was found superior in terms of permeate volume flow and whey protein transmission. The results can be explained by the less pronounced deposit layer formation on the inner channels due to the higher backpressure for the permeate, which reduces the flux and, thus, the intensity of deposit layer formation of retained casein micelles rendering the membrane surface more open for whey protein transmission.