Emulsions settling tank

Separation of two liquid phases, immiscible or partially miscible liquids, is a common requirement in the process industries. For example, in the unit operation of liquid-liquid extraction the liquid contacting step must be followed by a separation stage (Chapter 11, Section 11.16). It is also frequently necessary to separate small quantities of entrained water from process streams. The simplest form of equipment used to separate liquid phases is the gravity settling tank, the decanter. Various proprietary equipment is also used to promote coalescence and improve separation in difficult systems, or where emulsions are likely to form. Centrifugal separators are also used. 

One problem with acidulation in the integrated facility concerns the emulsion tendencies of certain products, especially phosphatides removed as gums. As indicated earlier, if the gums are not removed from the soapstock stream, but are allowed to enter the acidulation system, a third phase may be evident in the settling tanks. This phase is extremely difficult to split into separate oil and aqueous phases and may require several passes through the system until the emulsion is broken. 

Agitation. The effectiveness of any demulsifier added to a treatment system is directly dependent upon its making optimum contact with the emulsion. Therefore, the emulsion must be sufficiently agitated after the chemical demulsifier has been added. Increased mild agitation, such as in flow lines and in settling tanks, is beneficial in promoting coalescence. Re-... 

The behavior of emulsions is considered in Section V in connection with the process of oil dehydration. Actual problems of drop integration in emulsions are discussed. It is shown that this process occurs most effectively if the emulsion is subjected to an electric field. In this context, the behavior of conducting drops in emulsions, the interaction of drops in an electric field, and the coalescence of drops in emulsions are examined in detail. In terms of applications, processes of emulsion separation in settling tanks, electro dehydrators, and electric filters are considered. 

The stirred batch reactors are easy to operate and their configurations avoid temperature and concentration gradient (Table 5). These reactors are useful for hydrolysis reactions proceeding very slowly. After the end of the batch reaction, separation of the powdered enzyme support and the product from the reaction mixture can be accomplished by a simple centrifugation and/or filtration. Roffler et al. [114] investigated two-phase biocatalysis and described stirred-tank reactor coupled to a settler for extraction of product with direct solvent addition. This basic experimental setup can lead to a rather stable emulsion that needs a long settling time. 

The other major type of catalytic reactor is a situation where the fluid and the catalyst are stirred instead of having the catalyst fixed in a bed. If the fluid is a liquid, we call this a slurry reactor, in which catalyst pellets or powder is held in a tank through which catalyst flows. The stirring must obviously be fast enough to mix the fluid and particles. To keep the particles from settling out, catalyst particle sizes in a slurry reactor must be sufficiently small. If the catalyst phase is another Hquid that is stirred to maintain high interfacial area for reaction at the interface, we call the reactor an emulsion reactor. These are shown in Figure 74. 

Demulsifiers are quite effective at clearing fuel of water-initiated haze. Occasionally, upon clearing the fuel, the water will be removed by interacting with a demulsifier to form an emulsion. This emulsion will precipitate from the fuel and settle to the bottom of a fuel storage tank. This emulsion can plug filters and clog small lines if not removed from the tank with the water bottoms. 

Removal of EDC emulsions. A commonly occurring alkaline (pH of 12-13) process waste stream in VCM plants contains emulsions of EDC, water and inorganic solids such as calcium/iron hydroxides. The emulsion which settles between the heavier (bottom) EDC layer and the lighter (top) water layer in a tank can create deficiency in the stripping and distillation towers by causing fouling and corrosion. As indicated in Table 6.12, the amount of emulsified EDC varies from 2 to 4% and that of metal hydroxides from I to 15% by volume. 

Concepts applied to regular emulsions still apply with reverse emulsions. Emulsifying agents or charges must be neutralized to permit coalescence of the oil. Adequate settling time for the oil to rise out of the water phase must be available. Skim tanks and API separators are used for this purpose. A variety of flotation units will accomplish the same goals at an accelerated rate. 

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