Performances of skimmed milk crossflow microfiltration: Comparison of ceramic membraneconfigurations

International audience

anglais. Microfiltration is largely applied in the food sector for the separation and concentration of proteins. For example, skimmed milk 0.1 μm microfiltration is implemented in the industry to separate casein micelles (retentate) from serum proteins (filtrate) and to obtain high-purity serum protein fractions before furtherprocessing (ultrafiltration and spray-drying). The efficiency of the process, and especially the serum protein transmission, depends on the accumulation of casein micelles at the membrane surface. To overcome this problem, milk microfiltration is operated with specific ceramic tubular membrane configurations. The Uniform Transmembrane Pressure (UTP) configuration makes it possible to get a low transmembrane pressure (TP) along the membrane with an additional pump on the permeate side. The Graded Permeability (GP) configuration uses a membrane designed to create uniform permeate flux along the membrane (higher hydraulic resistance at the inlet, when TP is higher). Unfortunately, the performances of these configurations have never been compared in a wide range of operating conditions. This study proposes a comparison of the performances (permeability selectivity, energy consumption) of the UTP and GP configurations in the case of milk 0.1 μm microfiltration operating in feed and bleed mode, at 50°C. Parametric study, that consisted in TP steps (0.8 - 2 bar), was performed in a large range of VRR, volume reduction ratio (1.0-3.5) and retentate pressure drop (2.0 - 2.6 bar). Despite the fact that both configurations used membranes with similar filtering layers, the performances of the two ceramic membrane configurations show large discrepancies, especially at high VRR (3.0-3.5) where fouling is more severe: at a TP=1 bar for instance, the transmission of serum proteins was higher with UTP (60%) compared to GP (44%) configuration. The results are discussed considering the difference in membrane configurations features. The optimal performances are not obtained under the industrially recommended conditions, which leaves room for significant improvements of existingfiltration plants. The results allow the definition of optimal operating conditions for each volume reduction factor and each stage of an industrial skimmed milk plant using ceramic membranes.