Liquid purification or separation – Casing divided by membrane into sections having inlet – Planar membrane
Patent
1991-08-12
1992-11-03
Silverman, Stanley S.
Liquid purification or separation
Casing divided by membrane into sections having inlet
Planar membrane
21032164, 21032167, 21032175, 21050022, 21050021, 21050042, 210489, 210492, 210407, 210785, 210488, B01D 6308, B01D 6502, B01D 6906, B01D 6910
Patent
active
051606160
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to filtering apparatus.
In industrial and laboratory separation processes, particularly as part of an analytical procedure or in the biotechnological and pharmaceutical industries, it is often a necessary part of the purification procedure for any product to pass through one or more stages of filtration. Thus, an essential part of many processing activities is that of separating microparticles from a suspension. By "microparticle" is meant a particle of dimension no greater than about 50 microns with the term "particle" intended to include cells, viruses and macromolecules. The need for filtering systems is thus seen as an important tool in the extraction of products and by-products or in purification procedures.
Where the filtration system is primarily a barrier of fixed diameter pores, the effect is merely to prevent all microparticles larger than the maximum pore size from being transported by the carrier flow across the filter. As the residue builds up, the transport efficiency becomes worse because of pore blocking. Blocking cuts down flow and has the effect of progressively reducing the particle size transported, being eventually far smaller than the original pore diameter. Multi-stage filtration, using a series of filters with different pore sizes, alleviates the rapid loss common to single filters, but eventually requires replacement as with single units. Such methods are costly and in many circumstances impracticable.
Ideally, a filtration system should be programmable to a range of pore sizes and be able to clear fouling without disassembly. It is an object of this invention to provide approved filtering apparatus meeting these desiderata.
It should be recognised that, in a different field, U.S. Pat. No. 2,315,651 discloses an adjustable screen for a shaker assembly, the screen having top and bottom plates each with an array of square apertures. A screw thread arrangement is provided for sliding the top plate, to vary the registration of the top and bottom apertures. This is intended to reduce the time needed to adjust the equipment to meet varying sifting requirements.
SUMMARY OF THE INVENTION
Accordingly, the present invention consists in filtering apparatus for the selective filtration of microparticles comprising first and second filter elements each having a planar working surface and a plurality of filter apertures opening to said working surface in a regular array, the filter elements being arranged with the respective working surfaces substantially in contact, such that relative displacement of the elements in a direction in the plane of the working surfaces serves to bring the apertures of the first filter element into greater or lesser register with the apertures of the second filter element, the relative position of the filter elements corresponding with the maximum registry providing an effective pore size of the apparatus of up to about 50 microns; and control means for controlled relative displacement of the filter elements in said direction.
Preferably, at least one of the filter elements includes piezoelectric material and said control means includes means for applying an electrical potential to said piezoelectric material.
The essential principle of the method is that of producing an occlusion or masking of a pore by the relative shift of another located above (or below) and which was previously axially registered with it. Consider two thin sheets of material both having perfectly regular arrays of holes in a cubic pattern, that is with each hole equidistant from the other. The sheets are dimensionally identical. If now, the two sheets are overlayed then each pore centre will have the same axis as the one above or below. So long as the pitch (spacing) between pores is greater than the pore diameter, then sufficient lateral displacement along the line of the pores will result in a condition where any one pore is facing the blank material between pores in the other membrane. When the pores on both sheets are registered axially
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Lithgow Thomas M.
Public Health Laboratory Service Board
Silverman Stanley S.
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