Crossflow microfiltration is a frequently applied unit operation in the non-thermic separation or fractionation of complex suspensions. Despite its economic relevance, it still suffers from impaired process efficiency due to fouling. As it is well known, hydrodynamics such as the crossflow velocity or turbulent conditions have a big impact on the particle deposition on the membrane. Deposited particles not only decrease the flux, but also act as secondary active membrane layers and can reduce the factual pore size or cut-off. Product retention and low yields are the consequence.
In order to keep the deposit layer as porous and permeable as possible, the transmembrane pressure plays a major role. However, while a low transmembrane pressure allows a long-term stable product sieving, the flux is unsatisfyingly low and a high transmembrane pressure yields a high flux, but low product sieving. Hence, alternative flow profiles such as pulsatile and alternating crossflow are used in order to maintain an open-pored structure of the deposited material while having a high flux.
We show how this alternating stress influences the structural characteristics of different deposit materials. As model particles we used casein micelles, which are of industrial relevance in food processing and are soft, compressible and can interact with each other. Besides, yeast cells were used to represent the clarification of fermentation broths. It was found that depending on the deposited particles’ characteristics, the transmembrane pressure and the pulsatile flow pattern had a different impact on flux and product sieving. While the long-term flux and protein sieving of the yeast cell suspension could be significantly improved by pulsatile flow conditions, the strong interlinked and gel-like network of the casein micelles impeded particle erosion or cake relaxation by the pulsatile conditions.
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