Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1987-01-06
1988-05-31
Tufariello, T. M.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204307, B01D 1104
Patent
active
047479213
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods and apparatus for effecting liquid-liquid contact, for instance in the field of liquid-liquid extraction.
The invention involves the simultaneous use of high voltage fields and high shear mixing to promote coalescence and redispersion, respectively, when there is differential contact between two liquid phases. More particularly, the invention relates to applying a form of DC or AC voltage to an insulation coated electrode that is concentric with, but displaced on the central axis from, a high shear mixer at earth potential such that an electrostatic field is generated between the ring, electrode and the mixer assembly. The electrostatic field causes coalescence of the drops leaving the mixer thereby permitting high speed mixing and rapid creation of new interface without the production of very small drops that normally renders such an approach unacceptable.
According to the present invention there is provided a method for effecting contact between two immiscible liquids having different electrical conductivities, the method comprising providing contact between the two liquids wherein the relatively more conducting liquid is dispersed within the less conducting liquid characterised in that th liquids are subjected to intense mechanical agitation in a first zone to reduce the droplet size of the dispersed phase and, at least in a second, immediately adjacent zone, to a varying electrostatic field to cause coalescence of the droplets, whereby the liquid-liquid interfaces undergo rapid changes and droplet size is maintained at a desirably high magnitude at least outside said first zone.
The present invention also provides apparatus for effecting contact between two immiscible liquids having different elecrical conductivities, the apparatus comprising means for effecting contact between two immiscible liquids having different electrical conductivities wherein the relatively more conducting liquid is dispersed within the less conducting liquid characterised in that the apparatus includes means for subjecting the liquids to intense mechanical agitation in a first zone to reduce the droplet size of the dispersed phase, and means for applying, in a second, immediately adjacent zone, a varying electrostatic field to cause coalescence of the droplets, said agitation means and said means for applying an electrostatic field being such that the liquid-liquid interfaces undergo rapid changes and droplet size is maintained at a desirably high magnitude at least outside said first zone.
In a preferred arrangement of apparatus of the invention, a drive shaft along the central axis facilitates multiple arrangements of the mixer and electrode assemblies in a manner analogous to that found with rotors and stators in mechanically agitated liquid-liquid extraction columns such as the Rotating Disc Contactor, Kuhni column and Oldeshue-Rushton column.
In liquid-liquid extraction a solute is transferred from one liquid solvent to another across the phase boundary. Distribution data give information on concentration levels in the conjugate phases at equilibrium but provide no indication of the rate at which this equilibrium is established. When two liquid phases are contacted which contain a solute at such concentration levels that the ratio is not equal to the distribution coefficient, the solute will transfer between the two phases until its chemical potential becomes the same in each phase. Industrial equipment for liquid-liquid extraction can be classified into two groups, depending on the way this concentration driving force is arranged in practice. The terms used to describe the two categories are differential and stagewise contators.
A stagewise contactor provides a number of discrete stages in which the two phases are brought to equilibrium, separated, and passed countercurrent to the adjoining stages. In contrast, a differential contactor provides continuous coutercurrent contact between the two phases; such that the concentration profiles of the two phases ensure that a driving force for m
REFERENCES:
patent: 2395011 (1946-02-01), Perkins
patent: 4161439 (1979-07-01), Warren
Chemie-Ing.-Techn., vol. 35, No. 12, 1963, pp. 851-853.
Bailes Philip J.
Stitt Edmund H.
Tufariello T. M.
University of Bradford
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