Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1985-06-10
1988-02-09
Cintins, Ivars
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
2105101, 501 80, 501127, 501153, B01D 3920
Patent
active
047240784
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a porous material made from sintered inorganic particles, and also to a tubular filter made of said material and suitable, in particular, for filtering liquids and gases.
Filter mediums of this type have already been proposed, but they are generally of relatively low efficiency since although they are highly permeable to fluids they are not capable of withstanding the relatively high head loss that would be required to obtain a high flow rate per unit area of filter, or for enabling recovery of the solid material collected on the surface of the filter by exerting pressure in the opposite direction to that taken by the fluid flow during filtering. They are also incapable of satisfactorily withstanding the high mechanical or thermo-mechanical stresses which often appear during assembly and during operation. If they are made thick enough to withstand high mechanical stresses, they are of low permeability and thus of low efficiency.
An object of the present invention is thus to provide a porous material which is both highly permeable and very strong with respect to mechanical and thermo-mechanical stresses, said material being usable for manufacturing mechanically strong filters of high efficiency.
The porous material in accordance with the invention is characterized in that it has an open porosity of 30% to 40% by volume and a crushing strength, measured under conditions of isostatic compression, of 4.times.10.sup.8 to 5.times.10.sup.8 N/m.sup.2.
It preferably includes at least one of the following characteristics:
Its bending strength lies in the range 2.5 to 3.5.times.10.sup.7 N/m.sup.2 ;
The average diameter of its pores lies in the range 2 to 20 microns;
Its permeability to water at 20.degree. C. ranges from 0.6 to 60 m.sup.3 /h.m.sup.2.bar for a wall thickness of 1 cm, and as the average pore diameter goes from 2 to 20 microns.
It is composed of a mixture of metal oxides including more than 20% by weight alumina;
It is constituted by alumina which is at least 99.9% by weight pure.
A tubular filter in accordance with the invention is characterized in that it comprises a thick porous layer constituting a support layer in a material such as defined above, together with at least one thin porous filter layer made from inorganic particles which are sintered to one another and to the internal or external surface of the support layer, the pores of the filter layer having a diameter of less than 10 microns and being smaller than the those of the support layer, the radial thickness of each filter layer not exceeding a few tens of microns.
The filter preferably includes at least one of the following characteristics:
The average pore diameter of the layer having the finest pores is about 0.2 microns;
The support layer includes at least two sub-layers of different pore diameters which are connected to one another by sintering, the sub-layer having the finest pores being disposed between the filter(s) and the other sub-layer;
The ratio of the outside diameter of the tube to its radial thickness lies in the range 4 to 20;
Its resistance to internal pressure ranges from 30 bars to 240 bars as the ratio of the outside diameter to the radial thickness ranges from 20 to 4.
The preparation and the main physical and mechanical properties of tubular filters in accordance with the invention is described below by way of example.
EXAMPLE 1
A paste is prepared comprising a mixture of:
40% electro-melted alumina having an average grain size of 29 microns;
30% electro-melted alumina having an average grain diameter of 17 microns;
30% alumina having a average grain diameter of 2.5 microns;
9% industrial vaseline;
16% of an aqueous gel constituted by 1.5% methyl-hydroxylpropyl cellulose and 14.5% water.
These quantities are expressed in weight percent relative to the dry alumina content.
The paste prepared in this manner is extruded at a pressure of 120 bars in the form of tubes having a diameter of 20 mm and a thickness of 2 mm.
The tubes are then dried to eliminate the organic binders and then ba
REFERENCES:
patent: 1081573 (1913-12-01), Boeck
patent: 2464517 (1949-03-01), Kurtz
patent: 4278544 (1981-07-01), Takashima
Auriol Alain
Gillot Jacques
Ceraver
Cintins Ivars
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