Pore size MF membrane

Tanny et al. [71] proposed CFMF as a potential solution to the fat removal problem in whey. Using 1.2 p,m pore size MF membrane to clarify sweet cheese whey, Merin et al. [68] observed a permeate that was totally free of fat, while containing aU the other whey components. Compared to the centrifuge-separated and nontreated whey, Merin et al. [68] reported 30% increase in permeation flux when the MF permeate was used as a feed stream in UF to produce WPC. They explained that this is probably due to the absence of small fat globules and casein fines in the MF permeate, which were suggested as major contributors to permeation resistance in the UF of sweet whey. The same group observed reduction of bacteria in the MF permeate by 1 to 2 orders of magnimde. 

It is also claimed that positively charged 1.2 ju pore size MF membranes will retain Pseudomonas diminuta. Data from Pall Corp.18 on their 1.2 ju Nw Posidyne membrane show better than 99.99% retention of Pseudomonas. Their conventional 1.2 ju ULTlPOR N66TM membrane (without the charge) retained less than 50% of the Pseudomonas. In both cases, challenges between 2 x 1010 and 7 x 1012 bacteria per square foot of filter area were used. This means that comparable removal of Pseudomonas can be achieved with more than 10 times the flow rate of a 0.2 ju pore-size membrane. 

A considerable improvement in UF flux (+100%) and stability can be achieved by prefiltering the milk with a 0.4 n pore size MF membrane to remove bacteria, fat, lipoproteins and coagulated (denatured) proteins. The MF must be operated in cross-flow to prevent plugging. 

Membrane Cliaraeterization MF membranes are rated bvtliix and pore size. Microfiltration membranes are imiqiielv testable bv direct examination, but since the number of pores that rnav be obsen ed directlv bv microscope is so small, microscopic pore size determination is rnainlv useful for membrane research and verification of other pore-size-determining methods. Furthermore, the most critical dimension rnav not be obseiA able from the surface. Few MF membranes have neat, cvlindrical pores. Indirect means of measurement are generallv superior. Accurate characterization of MF membranes is a continuing research topic for which interested parties should consult the current literature. 

Membrane Characterization MF membranes are rated by flux and pore size. Microfiltration membranes are uniquely testable by... 

Using 0.1 pm pore size MF ceramic membranes in a Tetra Alcross M-38 system operated at UTMP of 1 bar (100 kPa), 50°C, and crossflow velocity of 5 m s Ardisson-Korat and Rizvi [110] showed that at mass concentration factor of 8, the MF retentate contains up to 30% total solids that can be used for semi-continuous vatless manufacture of LMPS mozzarella cheese. 

Membrane filters are made in a wide variety of pore sizes (Fig. 1). The effective pore size for membranes vary, and membranes can be used in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). RO membranes are widely used in water treatment to remove ionic contaminations from the water. These membranes have an extreme small pore size and, therefore, require excellent pretreatment steps to reduce any fouling or scaling of the membrane, which would reduce the service lifetime. RO membranes are used by extensive pressures on the upstream side of the filter membrane to force the liquids through the pores. 

For MF and UF, membrane selectivity is mainly determined by the pore size of membranes rather than the properties of membrane material itself. However, considering the operating environment and the fouling issue, the selection of polymers as the membrane material is crucial for the practical application of the membranes. In general, polymers used for membrane fabrication through NIPS need to be easily dissolved in some common solvents, resistant to chemical, thermal, and mechanical stresses, and less susceptible to fouling. Common polymers used in NIPS by immersion precipitation and their properties are listed in Table 15.1. 

Pores Even porous membranes can give very high selectivity. Molecular sieve membranes exist that give excellent separation factors for gases. Their commercial scale preparation is a formidable obstacle. At the other extreme, UF,3 separations use Knudsen flow barriers, with aveiy low separation factor. Microfiltration (MF) and iiltrafiltra-tion (UF) membranes are clearly porous, their pores ranging in size from 3 nm to 3 [Lm. Nanofiltration (NF) meiTibranes have smaller pores. 

Chemical Phase Inversion Svmrnetrical phase-inversion membranes (Fig, 22-71) remain the most important commercial MF membranes produced. The process produces tortiioiis-Bow membranes. It involves preparing a concentrated solution of a polvrner in a solvent. The solution is spread into a thin film, then precipitated through the slow addition of a nonsolvent, iisiiallv w ater, sometimes from the vapor phase. The technique is irnpressivelv v ersatile, capable of producing fairlv uniform membranes wFose pore size rnav be varied within broad limits. 

Microfiltration (MF) and ultrafiltration (UF) involve contacting the upstream face ofa porous membrane with a feed stream containing particles or macromolecules (B) suspended in a low molecular weight fluid (A). The pores are simply larger in MF membranes than for UF membranes. In either case, a transmembrane pressure difference motivates the suspending fluid (usually water) to pass through physically observable permanent pores in the membrane. The fluid flow drags suspended particles and macrosolutes to the surface of the membrane where they are rejected due to their excessive size relative to the membrane pores. This simple process... 

Ultrafiltration and microfiltration membranes produce high porosities and pore sizes in the range of 30-100 nanometers (UF) and higher (MF), which enable the passage of larger dissolved particles and even some suspended particles. The separation-filtration mechanism is based on molecule/particle sizes. The nanofiltration membrane lies between the UF and RO membranes, combining the properties of both so that the two mechanisms coexist. In addition, the NF membrane may be... 

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