FILTRATION IN A CENTRIFUGE

If dP is the pressure difference across a small thickness d/ of cake, the velocity of flow of the filtrate is given by equation 7.2, and  

If the centrifugal force is large compared with the gravitational force, the filtrate will flow in an approximately radial direction, and will be evenly distributed over the axial length of the bowl. The area available for flow will increase towards the walls of the bowl. If dV is the volume of filtrate flowing through the filter cake in time dt, then  

If the resistance of the cloth is negligible, —AP is equal to the centrifugal pressure. More generally, if the cloth, considered together with the supporting wall of the basket, is equivalent in resistance to a cake of thickness L, situated at the walls of the basket, the pressure drop —A P across the cloth is given by  

Thus the total pressure drop across the filter cake and the cloth (—AP), say, is given by  

Before this equation can be integrated it is necessary to establish the relation between r and V. If v is the bulk volume of incompressible cake deposited by the passage of unit volume of filtrate, then  

---

PRINCIPLES OF CENTRIFUGAL FILTRATION. The basic theory of constant-pressure filtration can be modified to apply to filtration in a centrifuge. The treatment applies after the cake has been deposited and during flow of clear filtrate or freshwater through the cake. Figure 30.18 shows such a cake. In this figure,... 

Figure 14.2 Filtration in a centrifugal field. A close relationship exists in the pressure filtration, the only difference being the forced sedimentation in the centrifugal field. The entire amount of mother phase has to filter through the entire filter cake.

A Pyrex micro filter (Fig. XII, 2, 18) of 8 ml. capacity and furnished with a sintered glass disc is useful for the filtration of hot or boihng hquids. The long cylindrical tube reduces evaporation. The filter may be inserted into a test-tube with side arm (Fig. XII, 2, 13) and the filtrate collected in a centrifuge tube or semimicro test-tube receiver. 

For cakes of high permeabihty, the capillary drain height may be an insignificant fraction of cake thickness, and film drainage becomes the controlling factor in a centrifugal field (7). Under unsteady-state conditions, equation 18 represents the drainable Liquid left in the cake as a function of the centrifugal filtration parameters ... 

An extract from the soluble stromal proteins of purified and intact spinach-leaf chloroplasts was prepared by lysis of the cells in buffer, centrifugation of the suspension of broken cells, and concentration of the supernatant with removal of insoluble material. This extract contained all of the enzymes involved in the condensation of the cyclic moieties of thiamine, thiazole, and pyramine. Thus, the synthesis of thiamine in this extract following the addition of pyramine and putative precursors was a proof that the system had the possibility of building the thiazole. It was found that L-tyrosine was the donor of the C-2 carbon atom of thiazole, as in E. coli. Also, as in E. coli cells, addition of 1 -deoxy-D-f/irco-pen-tulose permitted synthesis of the thiamine structure. The relevant enzymes were localized by gel filtration in a fraction covering the 50- to 350-kDa molecular-mass range. This fraction was able to catalyze the formation of the thiazole moiety of thiamine from 0.1 -mM 1-deoxy-D-t/ireo-pentulose at the rate of 220 pmol per mg of protein per hour, in the presence of ATP and Mg2+. 

Protein precipitation by filtration in a 96-well format has been used as a high-throughput, easy-to-automate alternative to the traditional centrifugation-based protocol. However, most filter plates... 

Haruni and Storrow(4) have carried out an extensive investigation into the flow of liquid through a cake formed in a centrifuge and have concluded that, although the results of tests on a filtration plant and a centrifuge are often difficult to compare because of the effects of the compressibility of the cake, it is frequently possible to predict the flowrate... 

The acid is allowed to run into a container of 3 m3 capacity where it is neutralized with gaseous ammonia while the temperature is raised to 70°C. The cyclonite thus formed is separated on a vacuum filter, and the filtrate is cooled when about two-thirds of the ammonium nitrate crystallizes. The latter is separated in a centrifuge, and used in the preparation of explosive mixtures. The small amounts of hexamine... 

Transfer the filtrate to centrifuge tubes. Be sure each pair of centrifuge tubes is carefully balanced (use a Harvard triple-beam balance) before they are placed in a centrifuge rotor. 

---