Centrifuges immiscible-liquid separations

A cyUndrical or, preferably, a pear-shaped separatory funnel (Fig. II, 1, 5, e and d) of 10-15 ml. capacity is usually employed for the separation of immiscible liquids. For separations on a smaller scale, a dropper pipette may be used the upper layer is best removed with a bent pipette as in Fig. XII, 1,3. For liquids which tend to emulsify, centrifugation (a hand centrifuge is satisfactory) will usually produce a clean line of demarcation between two immiscible liquids. 

Centrifugation, for immiscible liquid or solid separation and recovery... 

High-speed, vertical axis, tubular bowl centrifuges are used for the separation of immiscible liquids, such as water and oil, and for the separation of fine solids. The bowl is driven at speeds of around 15,000 rpm (250 Hz) and the centrifugal force generated exceeds 130,000 N. 

If the centrifuge is separating two immiscible liquids, Figure 13.486, the pressure will be given by ... 

Coalescence. Coalescence by gravity in simple settling devices can often be used to separate immiscible liquid-liquid mixtures. The coalescence can be enhanced by the use of mesh pads and centrifugal forces, as discussed in Chapter 8. 

The problem of separating immiscible liquids in a centrifuge can best be understood by first considering the static gravity separation of immiscible liquids, as illustrated in Fig. 12-5, where the subscript 1 represents the lighter liquid and 2 represents the heavier liquid. In a continuous system, the static head of the heavier liquid in the overflow pipe must be balanced by the combined head of the lighter and heavier liquids in the separator, i.e.,... 

Another way to extract pore water is to use a displacement method, which is usually applied in the laboratory. In this method, a solvent immiscible with water is applied to the soil in a column or centrifuge tube, and gravity or centrifugation is used to move the solvent through the soil, displacing pore water. The displaced water can then be separated from the immiscible liquid and analyzed. 

In a sedimenting centrifuge, a continuous liquid phase moves through the rotor. To accomplish a useful separation, the discontinuous phase, either the insoluble solids or the immiscible liquid drops (or both), must move in a direction different from the flow of the continuous liquid. Stokes law is usually applied to describe this relationship. The effective force accelerating the particle in a centrifugal field is then given as ... 

Outlets of both solids and liquids, if not properly chosen, may adversely affect separation to the extent that it may even be impossible to effect separation in the bowl. Because choosing the correct outlet size can be critical, most sedimenting centrifuges are designed so that at least the liquid outlet radius can be changed relatively easily. Selecting the appropriate outlet radius is particularly important in separating immiscible liquids because two must be chosen. ... 

Centrifuges may be batch, batch automatic, or continuous. Handling of the separated solids is the primary reason for the difference in operating modes. Therefore, a centrifuge type may be a batch operation when separating solids from liquids, but a continuous one when separating two immiscible liquids. 

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