Uniform transmembrane pressure

Microfiltration with uniform transmembrane pressure Commercial and developing liquid phase applications Gas separations using inorganic membranes... 

It is interesting to note that the problem of operation with large pressure differences between the feed/retentate side and the permeate compartment of membrane filtration modules was identified long ago. The concept of operation under low uniform transmembrane pressure (UTMP) was pioneered and first... 

Vadi, P.K. and Rizvi, S.S.H., Experimental evaluation of a uniform transmembrane pressure crossflow microfiltration unit for the concentration of micellar casein from skim milk, J. Membr. Sci., 189, 69, 2001. 

Nonuniform TMP values over the filtration surface area may cause substantial (up to 50%) reduction in the product recovery in the permeate. A novel approach to improving the flux and/or product recovery utilizes the concept of a uniform transmembrane pressure. lf This is achieved by varying the permeate side pressure with an independent recirculation pump to adjust the TMP to a constant value. A schematic of the UTP and conventional cross-flow configuration is shown in Figs. 11 and 12, respectively. The TMP profiles for the two operational modes are shown in Fig. 13. Flux improvements up to 500% have been achieved compared with the conventional cross-flow mode in many important food, beverage and biotechnology applications. 

Figure 11. Schematic of microfiltration with uniform transmembrane pressure.

Figure 13. Transmembrane pressure profiles (a) uniform transmembrane pressure operation, and (b) conventional cross-flow operation.

The virgin whey harvested from the MF, which does not contain cheesanaking remnants, fats, or spores, contained about 5.3% TS, about 6% of which is WPs. Brandsma and Rizvi [94], Punidadas and Rizvi [108], Solanki and Rizvi [109], and Ardisson-Korat and Rizvi [110] showed that the virgin whey s composition is consistent at MCF of 8. Brandsma and Rizvi [107] suggested uniform transmembrane pressure (UTMP) operation... 

Permeate Flux Values in the MF of Skim Milk at Different Processing Conditions under Uniform Transmembrane Pressure Mode... 

Since selectivity is a function of the local permeate flux, and thus the local transmembrane pressure, selectivity can be further improved by maintaining a nearly uniform and low transmembrane pressure throughout the ultrafiltration module. Following the early work from Sandblom, HPTFF technology uses, when required, a cocurrent permeate flow that is accomplished by the addition of a coflow loop and pump on the permeate side. 

Porous membranes used for reactant feed are typically mesoporous or macro-porous. Two problems arise control of the rate of addition and distribution of reactant B, and back-diffusion of reactant A. To control the uniformity of the distribution of B, we want the membrane to present enough resistance to equalize pressure on the reactant B side, giving a constant transmembrane pressure drop along the tube. This may mean modification of thin y-alumina mesoporous membranes or use of Vycor glass tubes.A higher pressure drop also helps reduce the driving force for back-diffusion, which was exploited in the pneumatic... 

In this reaction scheme, P is the desired product and S is the undesired byproduct. In the case the reaction rates are proportional to the partial pressure of reactant B (ri = kiPB and t 2 = p y respectively) the kinetics are favourable if nlslow reaction 2 more than reaction 1, inducing an increased selectivity for the desired product P. For this purpose, mainly porous membranes are used. To control the uniformity of the distribution of B, the membrane should have sufficient resistance to equalize the pressure on the reactant side, i.e. a constant transmembrane pressure drop along the tube [15, 16]. Another problem to tackle in this type of systems is back diffusion of reactant A and product(s) P and S. Here also, an increased pressure drop across the membrane will be advantageous, although it also decreases the permeation rate of B, which potentially leads to problems balancing the feed rate to the reaction rate 1. 

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