Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1996-09-24
1998-10-20
Drodge, Joseph W.
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
55523, 75234, 75235, 96 4, 210496, 2105101, 419 2, 419 32, 419 33, 419 41, B01D 6910, C22C 2912, B22F 100, B22F 104
Patent
active
058242201
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FR96/00128, filed on Jan. 25, 1996.
FIELD OF THE INVENTION
The present invention relates to the technical field of separating molecules or particles by implementing separator elements generally called "membranes" made of inorganic materials and constituted by a porous support on which at least one separator layer is deposited having nature and morphology adapted to perform separation of molecules or particles contained in the fluid medium to be treated.
More precisely, the invention seeks to provide inorganic porous supports constituting inorganic membranes.
PRIOR ART
Conventionally, a membrane is defined by associating together a porous support of ceramic material on which layers of inorganic material are deposited, which layers are bonded to one another and to the support by sintering. The role of the layers is to separate the molecular or particulate species, while the role of the support is to provide the mechanical strength necessary for making layers that are thin. Thus, the support must provide mechanical strength without participating in the hydraulic resistance of the membrane, while the layer must define permeability without participating in the mechanical strength.
Numerous types of support exist in the state of the art. The commonest type is a support made of pure alumina. Its manufacture comprises operations of mixing alumina with various additives such as an organic binder enabling the grains to hold together prior to sintering, a lubricant facilitating flow of the paste through the die during shaping, or a wetting agent making the particles easier to wet by the liquid in which they are in suspension. The resulting paste is then subjected to a shaping operation via a die whose shape is adapted to the future geometry of the support. After the extruded substance has dried, it is baked to begin reaction between the particles of alumina and also, in particular, to eliminate all organic matter which could inhibit the sintering reaction. Thereafter, it is sintered by heat treatment at a high temperature. For alumina, the sintering temperature is about 1800.degree. C.
Conventionally, sintering corresponds to solid state reaction between inorganic particles which, in simplified manner, can be considered as being spherical in shape. After the shaping and drying operations, the particles are in contact with one another. Each contact point defines a kind of neck of practically zero diameter, and the volume around a neck can be thought of as the concave portion of a capillary meniscus. During heat treatment, the particles are subjected to changes of state. Two main parameters govern sintering, firstly the equivalent diameter of the concave portion around each neck, which depends on particle size, and secondly the viscosity of the material and also its partial pressure, which depend on the temperature of the heat treatment. Thus, the smaller the size of the particle, the smaller the equivalent diameter of the concave portions. High viscosity is therefore sufficient to form necks, such that the temperature of heat treatment is low. Conversely, the larger the size of the particles, the lower the viscosity, thus requiring a high sintering temperature. Nevertheless, increasing the quantity of energy supplied gives rise to a sintered support whose density is equal to that of its particles, such that its porosity is zero.
To obtain a body that is porous after sintering, it is therefore necessary to limit the quantity of heat energy so as to obtain necks of sufficient volume for porosity to be large and for mechanical strength to be high. It should be assumed that the higher the sintering temperature, the thicker the necks, thereby obtaining a support of increased mechanical strength and low porosity.
In an attempt to remedy this contradiction, patent application FR 2 693 921 proposes making an inorganic support whose raw material composition comprises thermally stable alumina associated with an oxide of titanium. Bonding between the particles of alumina is provided by the
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Grangeon Andre
Lescoche Philippe
Drodge Joseph W.
T.A.M.I. Industries
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