Cross-flow Microfiltration Of Skim Milk Research Articles

Influence of twisted tape turbulence promoter on fouling reduction in microfiltration of milk proteins

Membrane filtration has become one of the major technologies in the food industry. It is widely applied in the dairy industry, and it is mostly used for the concentration and fractionation of milk proteins and for the whey processing. Of all pressure driven membrane processes, ultrafiltration is the most widely used. The major disadvantage of pressure driven membrane processes is severe fouling of membrane during filtration particularly when the fluids containing proteins are processed. Fouling with proteins is complex phenomenon because it occurs at the membrane surface as well as in the pores of membrane, and depends on the operating conditions and on the interactions of proteins and membrane material. In order to reduce fouling of the membrane different techniques have been developed, and one of them relies on the changing of the hydrodynamic conditions in the membrane or module. In this study, influence of twisted tape turbulence promoters on the fouling reduction in cross-flow microfiltration of skim milk was investigated. Twisted tapes with tree characteristic ratios of helix element length to the tape diameter (aspect ratio) were studied. It was shown that twisted tapes with different aspect ratios reduce fouling of membrane by a factor of three or more. The presence of twisted tape induces changes in the flow patterns from straight to helicoidally thus producing turbulence flow at the lower cross-flow rates. Turbulence intensification prevents accumulation of proteins at membrane surface enabling reduction in reversible fouling what results in the reduction of overall membrane fouling. The best performance was achieved using a twisted tape with the lowest aspect ratio of 1.0. This promoter reduces fouling seven times at low transmembrane pressure and low cross-flow velocity. The twisted tape with aspect ratio 1.0 induces the most intensive turbulence, the longest helicoidal flow path, and appearance of vortices near the membrane surfaces, so the scouring of proteins from the membrane surface is the most intensive in that case.

Separation of casein micelles from whey proteins by high shear microfiltration of skim milk using rotating ceramic membranes and organic membranes in a rotating disk module

This paper investigates the microfiltration of skim milk in order to separate caseins micelles from two whey proteins, α-lactalbumin (α-La) and β-lactoglobulin (β-Lg), using a modified dynamic filtration pilot (MSD) consisting in 6 ceramic 9-cm diameter membrane disks of 0.2 μm pores, rotating around a shaft inside cylindrical housing. A comparison was made with another dynamic filtration module consisting in a disk rotating near a fixed PVDF 15.5 cm diameter membrane with 0.15 μm pores. Maximum permeate fluxes were 120 L h−1 m−2 with the MSD module at 1930 rpm and at 40 °C, and 210 L h−1 m−2 at 2500 rpm and 45 °C, with the rotating disk module. Casein rejection was around 99% at high speed for both membranes. α-La transmission decreased with increasing transmembrane pressure (TMP) from 75% to 60% for ceramic membranes and from 25% to 10% for the PVDF one. β-Lg transmissions were lower, ranging from 23% to 15% for ceramic membranes and from 20% to 5% for the PVDF one. In a concentration test with the PVDF membrane at 2000 rpm, the flux decayed from 200 L h−1 m−2 at initial concentration to 80 L h−1 m−2 at VRR = 3.2 and 22.1% of the initial α-La mass was recovered in the permeate, against 8.1% for β-Lg. Permeate fluxes in the mass transfer limited regime (Jlim) of the MSD and rotating disk module operated at various speeds were well correlated by the equation Jlim = 17.13 Vav where Vav denoted the disk azimuthal velocity averaged over the membrane area. Measurements of Jlim, taken from Ref. [G. Samuelsson, P. Dejlmek, G. Tragardh, M. Paulsson, Minimizing whey protein retention in crossflow microfiltration of skim milk. Int. Dairy J. 7 (1997) 237–242] during MF of skim milk using tubular ceramic membranes at velocities from 1.5 to 8 m s−1 with permeate co-current recirculation were found to obey the same correlation.

Static turbulence promoter in cross-flow microfiltration of skim milk

The efficiency of cross-flow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The objective of this study was to investigate the influence of static turbulence promoter on permeate flux during skim milk microfiltration and the potential application of this arrangement for an industrial development. Experimental investigations were performed on 100 nm ceramic membrane using the Kenics static mixer as a turbulence promoter. The insertion of the Kenics static mixer caused improvement of permeate flux of more than 700% at the same feed flow rate. Although the hydraulic dissipated power was significantly increased (about 6 times), the decrease of more than 25% in specific energy consumption was obtained by the use of the static mixer. Moreover, the presence of the static mixer in the membrane tube provided the similar permeate flux values at about 5 times lower cross-flow velocity, thus reducing the energy consumption for more than 80%. Additional energy saving was achieved using the Kenics static mixer with the aspect ratio (ratio of element length to mixer diameter) greater than 1, especially at the volumetric concentration factors greater than 2.

Kenics Static Mixer as Turbulence Promoter in Cross-Flow Microfiltration of Skim Milk

The efficiency of cross-flow membrane filtration processes is limited by membrane fouling and concentration polarization. The question of membrane fouling and membrane pore blocking during microfiltration is much more important than in the traditional ultrafiltration, not only for the maintenance of acceptable flux but also for the adequate recovery of the permeate components. The objective of this study was to demonstrate that use of a static mixer as turbulence promoter results in enhanced cross-flow microfiltration of skim milk. Experimental investigations were performed on 50-nm and 100-nm ceramic tubular membranes. The use of a static mixer provided a significant reduction of membrane fouling and an increase of more than 700% in permeate flux for both membranes compared with that obtained without a static mixer at the same feed flow rate. The similar flux enhancement indicates that surface layer resistance dominates the overall fouling resistance. Although the power consumption was significantly increased by using a static mixer, a decrease of more than 25% in specific energy consumption for both membranes was achieved with static mixer as compared to arrangement without static mixer in experiments performed at the same cross-flow velocity.

The effect of turbulence promoter on cross-flow microfiltration of skim milk

The effect of turbulence promotion on cross-flow microfiltration of skim milk was studied experimentally. The use of Kenics static mixer as turbulence promoter in inorganic (Membralox™) membranes with pore sizes 50, 100 and 200 nm provided a significant permeate flux improvement. In experiments at the same Reynolds number, the flux improvements of more than 500% were achieved for Re numbers in the range 3000–10 000. The increase of power consumption for fluid flow due to the insertion of turbulence promoter was also discussed. The effect of turbulence promoter on microfiltration performance was checked at the same hydraulic dissipated power. The flux improvements of more than 300% were achieved for hydraulic dissipated power in the range from 0.13 to 0.95 W indicating that using the turbulence promoter is more energy efficient than operation without the turbulence promoter. The fouling resistance analysis approved that resistance of the surface micellar layer dominates the overall fouling resistance. The use of turbulence promoter caused a large scouring of the membrane surface provided significant reduction of reversible fouling. Also, when the turbulence promoter was used, the membrane cleaning efficiency was improved compared with experiment without the promoter.

Protein composition of micellar casein obtained by cross-flow micro-filtration of skimmed milk

In this study of the products of cross-flow micro-filtration of unheated skim milk, it was found that some lactoferrin, serum albumin and immunoglobulins were retained with the casein fraction. An acid-soluble casein, identified as proteose peptone component 5, also remained associated with the micellar fraction during micro-filtration.

Minimizing whey protein retention in cross-flow microfiltration of skim milk

The feasibility of fractionating casein and whey protein in skim milk was studied by measuring the permeation of whey protein in a laboratory microfiltration set-up in relation to temperature, circulation velocity, transmembrane pressure (TMP) and permeate flux. A tubular, ceramic membrane from Tech-Sep with a nominal pore size of 0.14 μm was used. The protein content in the permeate was found to be independent of TMP up to 190 kPa for the highest circulation velocity, 8 m s−1, at 55 °C. For lower circulation velocities and at 15 °C, the protein content decreased when the TMP was increased. For every circulation velocity, a lowest value of the TMP corresponding to a limiting flux was found. The value of the limiting flux increased with increasing temperature and circulation velocity. The highest value for the limiting flux was 145 L h−1 m−2 for the circulation velocity 8 m s−1 at 55 °C. All results could be roughly correlated as limiting flux = 0.0025 Re.

On the conventional cross-flow microfiltration of skim milk for the production of native phosphocaseinate

Abstract The use of conventional microfiltration for the production of native phosphocaseinate was studied at 50 °C using a microporous ceramic membrane of 0.22 μm pore diameter at a flow velocity of 6.9 m s−1 and a transmembrane pressure of 190 kPa. Flux declined by approximately 50% from an initial value of 180 L h−1 m−2 over the course of 3× concentration. Batch diafiltrations after dilution of the retentate with distilled water or 0.08 M Nad at pH 7.0 raised the flux for both media to the initial value or higher, followed by a similar pattern of flux decline during the concentration step. The procedure allowed the preparation of native phosphocaseinate containing 79% protein with a casein to total protein nitrogen ratio over 0.91.