초록

An improved porous substrate for zeolite membranes is formed by coating the substrate with a layer of zeolite particles of a narrow particle distribution size of between 20 and 0.01 microns.

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1. A method of treating a porous substrate which has tubular conduits formed within it, which method comprises mixing together zeolite particles of different size distributions having a diameter of between 20 μm and 0.1 μm to form a suspension of the particles, passing the suspension of zeolite part

1. A method of treating a porous substrate which has tubular conduits formed within it, which method comprises mixing together zeolite particles of different size distributions having a diameter of between 20 μm and 0.1 μm to form a suspension of the particles, passing the suspension of zeolite particles down through the tubular conduits and out through the walls of the tubular conduits so as to deposit a layer of zeolite particles on the inner surface of the tubular conduits. 2. A method as claimed in claim 1 which comprises forming a mixture of zeolite particles of different size distributions and water and grinding the mixture in a grinder until the particles are of the requisite size to obtain the mixture of zeolite particles. 3. A method as claimed in claim 2 which comprises pulverising zeolite particles and mixing the pulverised particles with unground particles to obtain the mixture of zeolite particles. 4. A method as claimed in claim 1 in which the zeolite particles of different size distributions are mixed together to obtain a distribution of particles which conforms approximately to a Fuller curve to form the mixture of zeolite particles. 5. A method as claimed in claim 1 in which the porous substrate is formed of a substrate selected from metal, ceramic, glass, mineral, carbon or polymer fibres, cellulosic, organic or inorganic polymers, a mesh or sintered metal particles, alumina, a carbide, a clay, a silicate, silicon carbide or porous silica. 6. A method as claimed in claim 5 in which the porous support has a pore size of 0.1 to 20 microns. 7. A method of forming a zeolite membrane on the inner surface of tubular conduits formed within a porous substrate, which method comprises (i) forming a mixture of zeolite particles having a range of diameters of between 20 μm and 0.1 μm (ii) passing a suspension of the mixture down through the tubular conduits and out through the walls of the tubular conduits so as to deposit a layer of zeolite particles on the inner surface of the tubular conduits and (iii) depositing or crystallising a zeolite membrane on the zeolite particles by gel crystallisation. 8. A method as claimed in claim 7 which comprises forming a mixture of zeolite particles of different size distributions and water and grinding this mixture in a grinder until the particles are of the requisite size to obtain the mixture of zeolites particles. 9. A method as claimed in claim 7 which comprises pulverising zeolites particles and mixing these pulverised particles with unground particles to obtain the mixture of zeolites particles. 10. A method as claimed in claim 7 in which the zeolite particles of different size distributions are mixed together to obtain a distribution of particles which conforms approximately to a Fuller curve to form the mixture of zeolites particles. 11. A method as claimed in claim 7 in which the porous substrate is formed of a substrate selected from metal, ceramic, glass, mineral, carbon or polymer fibres, cellulosic or organic or inorganic polymers, a mesh or sintered metal particles, alumina, carbide, clay, silicate, silicon carbide or porous silica. 12. A method as claimed in claim 11 in which the porous support has a pore size of 0.1 to 20 microns.