Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1984-01-10
1985-12-31
Richman, Barry S.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
260705, 422234, 422259, 562513, 562600, C07B 5142
Patent
active
045622884
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of operating a mixer-settler.
More particularly, the invention concerns a method of efficiently operating a mixer-settler extractor in the extraction of a solute from its aqueous solution with the aid of an organic extractant which contains a tertiary amine.
BACKGROUND ART
Mixer-settler extractors have problems including generally higher construction cost and larger holdup in the system than tower extractors. For extractions in a limited number of stages, however, they call for less investments for equipment than the tower type. Especially with systems which involve low extraction rates or wide oil-water viscosity difference, or in cases where ingress of impurities can take place, they exhibit quite excellent characteristic performance.
In the extraction of a solute from its aqueous solution by the use of an organic extractant, such as a mixture of a tertiary amine and an organic diluent, the solvent viscosity is so high and the rate of solute travel is so low that it is not customary to employ a tower extractor, typically a perforated-plate or packed tower, which is devoid of any mechanically working part. For such an application the tower extractor must be tall enough to accommodate the very high actual height of each theoretical plate. Moreover, in order to prevent troubles such as flooding, the operation range is limited and a large-diameter extraction tower must be used, thereby causing economic disadvantage.
Thus, if efficient extraction is to be done using an organic solvent, especially an extractant system containing a tertiary amine, it is advisable to employ an extractor of, e.g. a mixer-settler type, which is designed to accelerate the frequencies of dispersion and coalescence of liquid droplets.
For the extracting operation of a mixer-settler extractor, attainment of the highest possible rate of mixed liquids separation in the settler is of prime importance. The higher the separation rate the smaller the settler size may be. The smaller settler will accordingly require a narrower installation area and may hold less liquid than ordinary settlers. These are substantial economic advantages where the organic solvent for use as an extractant and/or the construction material for the settler is expensive.
DISCLOSURE OF INVENTION
In view of the above, diversified technical investigations have been made so as to attain increased separation rates of liquids in settlers. We have extensively studied the separability of liquids in the settler of a mixer-settler extractor for the recovery of a solute from its aqueous solution using an organic extractant which consists of a tertiary amine and an organic diluent. As a result, it has been found that the most effective factor for the improvement of the separation rate is to maintain the disperse phase in the mixer in the form of a solvent phase, that is, to operate the mixer with a solvent dispersion inside.
According to our finding, operation of the mixer holding an aqueous phase as the disperse phase (that is, an aqueous dispersion) causes separation of the liquids in the settler in such a relation that water droplets fall by gravity out of the solvent phase, against the continuous upward flow of the solvent phase. This relation is commonly given, for example, by Stokes' relationship, and the quantity of the aqueous phase to be entrained by the solvent phase can be determined from that equation. Generally speaking, the liquid droplet distribution that occurs inside a mixer tends to be relatively broad, though it depends on the agitating condition in the vessel. In such a situation, the fine water droplets are inevitably entrained by the solvent phase, with the consequence that the separation in the settler becomes insufficient and the extraction efficiency drops. It is therefore essential for the enhancement of the separation efficiency of the settler to narrow down the range of the dispersed droplet size distribution in the mixer and yet increase the average droplet diameter. Exactly the same applies t
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CA 90:154097g, "Study of the Dimensional Distribution of Drops in `Water in Oil` Emulsions in a Box-Type Mixing Settling Extractor", Nezhdanov, A. A., 1977.
CA 92:13162m, "Solvent Properties of Organic Bases for Extraction of Acid from Water", Ricker, N. L., 1979.
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Koga Kunio
Samejima Mutsumi
Sasaki Yukihiro
Daicel Chemical Industries Ltd.
Ledbetter, Jr. Titus B.
Richman Barry S.
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