Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1997-09-16
1999-10-05
Drodge, Joseph W.
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210 85, 210243, 21032184, 210511, 21050026, 210644, 210746, 210748, B01D 1100
Patent
active
059618329
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for carrying out a process between first and second immiscible fluids, for example mass transfer from one fluid to another.
The use of membranes in liquid/liquid mass transfer processes is known. EP-A-0246065 and Kiani et al, Journal of Membrane Science, 20 (1984) 125-145 "Solvent Extraction with Immobilised Interfaces in a Microporous Hydrophobic Membrane" both disclose the transfer of a solute between two immiscible liquids, wherein the interface between the liquids is defined by a membrane. The mass transfer actually takes place in the pores of the membrane, and a typical membrane used in this process is a Celgard (Registered Trade Mark) 2400 microporous polypropylene film. The membranes are typically of the order of 25 micrometers thick and with an effective pore diameter of 0.02 micrometers. Thus the pores in which the mass transfer takes place are essentially very long and thin. Kiani discloses an hydrophobic membrane. An aqueous phase on one side of the membrane is at a higher pressure than an organic phase on the other side of the membrane and the liquid interface is stabilised on the aqueous side of the membrane.
A problem with such arrangements is that the liquid in the pores at the interface is essentially stationary. With respect to fluid flow on either side of the membrane, the membrane functions as a solid wall so that fluid velocities are essentially zero at the membrane fluid boundaries. This provides unfavourable conditions for interphase transport as the stationary fluid held in the membrane pores extends the distance for diffusion of the transferring entity. Additionally such stagnant regions can accumulate debris and undesirable reaction products which may interfere with inter phase transport of the diffusing solute.
SUMMARY OF THE INVENTION
The present invention is based on the concept of providing for a diffusive transfer process an apertured or foraminous sheet wherein the apertures in the sheet in which fluid interfaces are created between two immiscible fluids on either side of the sheet are such that within either or both fluids flow essentially parallel to the interfaces is continuous up to and at the interface within each aperture and rapid diffusion can take place across the interface.
The present invention provides in a first aspect apparatus for carrying out a diffusive transfer process between first and second immiscible fluids, including first and second fluid flow paths for respective first and second fluids disposed on opposite sides of a foraminous sheet means, wherein an interface between the fluids is formed in use at or in each aperture, characterised in that a minimum height of each of at least the greater part of the apertures, as measured perpendicular both to the direction of fluid flow and to the thickness of the sheet means, is less than 200 micrometers, wherein each aperture has a form such as to permit fluid to flow into the aperture without interfering with fluid flow out of the aperture thereby to permit a significant component of fluid flow immediately adjacent the interface, and wherein outside of the region of the sheet means, the first and second flow paths are separated to permit the respective first and second fluids to flow into and out of said region without mixing.
In a further aspect, the invention provides a method of carrying out a process of diffusive transfer of an entity from a first fluid to a second fluid immiscible with the first, the method comprising: across a foraminous sheet means, a maximum height of at least the greater part of the apertures in the sheet means being less than 200 micrometers as measured at an interface position in a direction perpendicular both to the direction of fluid flow and to the width of the sheet means, and wherein each aperture has a form such as to permit fluid to flow into the aperture without interfering with fluid flow out of the aperture, second flow paths such that, at least in the region of the sheet means, the flow of the fluids is essentially
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"Solvent Extraction With Immobilized Interfaces in a Microporous Hydrophobic Membrane", A. Kiani et al., Journal of Membrane Science, 20 (1984) pp. 125-145.
Bull Adrian James
Holmes Robert George Godfrey
Shaw John Edward Andrew
Simper Adrian Mark
Simpson Richard Iain
Central Research Laboratories Limited
Drodge Joseph W.
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