Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1998-05-04
2000-03-07
Drodge, Joseph W.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210 86, 210519, 210521, 210744, 210800, 422256, 422257, 422258, C02F 124, B01D 2124, B01D 2134
Patent
active
060335750
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention provides both a method of mixing and separating two immiscible liquids of different densities, and an apparatus associated with said method. Such apparatus may be referred to as a mixer/separator installation or as a mixer/decanter device. Liquid/liquid extraction is performed therein.
The preferred embodiment of the present invention lies in the context of mixing/separating two liquids as implemented in a mixer/decanter device of the reverse liquid flow type [the decanter being fed from the end of the decanter (its "feed end") that is farthest from the mixer] and with a superposed spout (said mixer and decanter are connected together by a spout disposed above said decanter).
The technical field to which the invention relates is specified a little further on.
The mixing and separating method consists in producing a dispersion of two immiscible liquids, one within the other, that is sufficiently fine to facilitate interchanges between the liquids, and then separating the two immiscible liquids again by decanting (with such separation by decanting being possible providing said two liquids do not have the same density). Generally, one of the liquids is constituted by an impure solution of a given substance while the other liquid is an organic solvent serving either as a solvent that is specific to the substance under consideration or else as a dilution medium for an ion exchanger that is specific to the substance under consideration. The complete installation generally comprises an extraction bank comprising a plurality of mixers/decanters in juxtaposition within which the impure solution of the substance under consideration flows as a counterflow to the organic liquid, followed by a re-extraction bank of identical type in which the organic liquid flows as a counterflow to a pure solution that collects the substance, thereby enabling said organic liquid to be used in a closed circuit.
Each mixer/decanter in the bank essentially comprises a mixer receiving the two liquids, generally via its base, and producing the sought mixture (dispersion) by stirring, followed by a decanter vessel in which said mixture flows slowly and separates progressively, specifically because the liquids are immiscible and the dispersion is not stable. For a given flow rate, it is clear that the size of each mixer depends on the transit time the dispersion requires before going to the separator, which time depends on exchange efficiency, which efficiency increases with increasing fineness of the dispersion. Similarly, the size of each decanter vessel depends on the transit time of the dispersion passing through it, which time is a function of the coalescence speed of the dispersion which, on the contrary, decreases with increasing fineness of the dispersion. Consequently there is always an optimum size for the droplets in the dispersion that provides minimum overall bulk and thus a minimum price for the installation as a whole.
The liquids and mixtures of liquids are generally moved through the installation by means of pumps or pump/stirrers.
Mixing/separating methods and the associated apparatuses are described, in particular, in documents U.S. Pat. No. 4,235,602 and EP-A-0 252 785.
The apparatus described in patent U.S. Pat. No. 4,235,602 is a mixer/decanter of the reverse liquid flow and superposed spout type.
The apparatus described in application EP-A-0 252 785 is a mixer/decanter of the reverse liquid flow and submerged spout type.
To facilitate both the following description of the present invention and also understanding thereof, reference is now made to accompanying FIG. 1 for describing in greater detail the prior art that is closest to the present invention. The present invention comprises an improvement over that prior art. Nevertheless the improvement is not limited solely to that context.
A mixer/decanter of said prior art is shown diagrammatically in FIG. 1. It comprises a mixer/decanter of the type described in patent U.S. Pat. No. 235,602, i.e. of the reverse liquid fl
REFERENCES:
patent: 1176774 (1916-03-01), Morris
patent: 3820954 (1974-06-01), Stonner et al.
patent: 3868335 (1975-02-01), Stonner et al.
patent: 4235602 (1980-11-01), Meyer et al.
patent: 4844801 (1989-07-01), Szanto
patent: 4971692 (1990-11-01), Sklokin et al.
Goodman David
Perret Jean-Claude
Sonntag Alain
Drodge Joseph W.
Krebs & Cie S.A.
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