Liquid purification or separation – Filter – Material
Patent
1992-06-10
1993-08-03
Sever, Frank
Liquid purification or separation
Filter
Material
21050026, 210509, 2105101, E01D 7102, E01D 7104
Patent
active
052325989
DESCRIPTION:
BRIEF SUMMARY
This invention concerns porous inorganic membranes. Such membranes are well known and widely used for filters, catalyst supports and other purposes. They have various advantages over organic membranes, including chemical inertness, thermal stability, high flux and uniform pore size.
EPA 348041 published Dec. 27, 1989 describes and claims a composite membrane comprising an inorganic support having interstices, and porous inorganic films of sintered non-metallic particles carried by the support and bridging the interstices. The support may be a mesh of fibres, particularly a woven metal mesh. Interstices are distinguished from pores and are defined as having diameters greater than 5 .mu.m and lengths preferably less than 10 times their diameters. The interstices are bridged by porous films of inorganic material carried by the support, preferably substantially coplanar with the support, the minimum film thickness across the interstices being not more than about twice the thickness of the support. Preferably the films bridging the interstices have concave menisci.
These composite membranes have interesting properties. Because the supports are inherently flexible and because the films bridging the interstices are in longitudinal compression at ambient temperature, the composite membranes can be bent, often sharply without serious loss of filter performance. By virtue of their metal or other support, the membranes are also much easier to fix in position than prior membranes with ceramic supports.
These composite membranes may be prepared by dipping a woven metal mesh or other support in a slurry of the inorganic non-metallic particles, so as to create films bridging the interstices, and drying and heating the films to a temperature sufficient to partly sinter the particles. The temperature required for partial sintering must not be so high as to damage the support. This may place limitations, either on the material of the support, or on the nature and size of the inorganic particles used and hence on the pore size of the composite membrane. There is a need for porous membranes or films of inorganic particles that do not require excessively high temperatures in their preparation.
It is an object of this invention to provide porous inorganic membranes, based on particles of inorganic material, that do not require heating to the temperatures necessary to bond the particles by sintering alone. This object is achieved by the use of inorganic adhesives. A difference between the use of inorganic adhesives and sintering is that with inorganic adhesives there is essentially no long range transport of material of the particles.
The invention provides a composite membrane comprising a support having interstices of diameter greater than 5 .mu.m and length less than ten times their diameters, and porous inorganic films carried by the support and bridging the interstices thereof, wherein the films comprise more than 50% by weight of particles of an inorganic material bonded together by means of less than 50% by weight of an inorganic adhesive. Preferably the films are substantially coplanar with the support. Preferably the films bridging the interstices have concave menisci. Preferably the support is inorganic, although organic polymers are possible. Preferably the support is a woven metal mesh, although glass and other refractory fibres can be used. Preferably the support is as described in the aforesaid EPA 348041.
The particulate inorganic material may be chosen to achieve desired properties, e.g. chemical and thermal resistance, in the membrane. Suitable materials include refractory materials such as alumina, magnesia, beryllia, zirconia, thoria, titania, chromium oxide, tin oxide, silica, silicon carbide, silicon nitride, boron nitride, boron carbide, titanium carbode, titanium nitride, chemical stoneware, chemical porcelain and zeolites; also carbon and silicon and metals such as aluminium.
The pore size of the porous films is related to the particle size. Large particles, above about 1 .mu.m in diameter, tend to result
Steward Nigel I.
Sturgeon Andrew J.
Thomas Michael P.
Ceramesh Limited
Laughlin Richard T.
Sever Frank
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