Experimental evaluation of a uniform transmembrane pressure crossflow microfiltration unit for the concentration of micellar casein from skim milk

Abstract A uniform transmembrane pressure (UTMP) crossflow microfiltration (CFMF) system maintains a low but uniform transmembrane pressure (Δ P TM ) with high crossflow velocity (CFV), which reduces fouling and cake build-up, and improves the utilization of available filtration area. A CFMF system, with a 0.2 μm nominal pore size ceramic filter, filtration area 0.184 m 2 , was operated in both UTMP and non-UTMP modes. The two modes were compared for their effectiveness in maintaining a steady flux during the separation of casein micelles from skim milk up to a concentration factor (CF) 10 at 50°C. Experiments were performed at an average CFV of 7.2 m s −1 and Δ P TM from 89 to 380 kPa. Up to CF 4 the non-UTMP mode maintained a slightly better flux and process time than the UTMP mode, but reached the minimally acceptable flux (below 0.005 kg m −2  s −1 ) at CF 6. Depending upon the Δ P TM maintained, the UTMP mode approached the minimal flux at CF 7 or 10 depending upon the combination of Δ P TM and CFV used. Cake resistance ( R cm ) was modified to include the effect of an increase in retentate viscosity with concentration. R cm increased for the non-UTMP mode and decreased for the UTMP mode with a decrease in the ratio of permeation flux/wall shear stress ( J p / τ w ) (which occurred as the retentate gets concentrated). This indicated that the cake formed during the non-UTMP mode of operation was more compact and durable (harder to erode) than in the UTMP mode. A central composite rotatable design estimated the optimal operating region at a CFV of 7.1 m s −1 and Δ P TM of 241±10 kPa to achieve maximum flux and a high concentration.

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