Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1996-12-06
2001-03-06
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S432000, C264S045100, C264S045500, C210S500210, C210S490000, C210S502100, C210S506000
Reexamination Certificate
active
06197427
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a process for the production of zeolite membranes which are supported on porous glass, and membranes so produced.
Zeolites are used for their properties of separation by selective adsorption or for their catalytic properties. However, separation using powdered zeolite is a batch process. A zeolite membrane offers the possibility of using a continuous process of economical interest for separating molecules.
A variety of zeolite membrane production processes have already been described. Such membranes are frequently prepared by crystallising a film of zeolite on and/or in a porous support or on a non porous support. There are two possible cases.
In the first case, the support is immersed in a zeolite precursor gel and the ensemble is subjected to hydrothermal conditions to crystallise the zeolite. Japanese patent application JP-A-60/129119, for example, describes a membrane composed of a film of zeolite crystallised on the surface of an alumina support. In U.S. Pat. No. 5,100,596, therefor a membrane is produced by crystallising a molecular sieve on a non porous surface and separating the film from that surface. In European patent EP-A-0 481 660, which concerns a supported zeolite membrane, the zeolite layer is directly bonded to the support. Before crystallising the zeolite, the support is brought into contact with a solution or suspension containing a source of silicic acid to form silicic acid oligomers on the surface. Japanese patent application JP-A-06/321530 describes a process for the production of composite membranes in which the synthesis temperature is increased during crystallisation.
In the second case, the support is brought into contact with a colloidal solution, separated therefrom and placed in saturated steam to crystallise the zeolite from the adsorbed solution. International patent application WO-A-93/17781 describes a process for forming a zeolite membrane by exposing an aqueous or alcoholic colloidal solution deposited on a porous support to saturated steam.
Adhesion of the zeolite to the support must be good in a composite membrane. As a result, the zeolite film must be bonded directly to the support. Treatment of the support surface to increase its reactivity is sometimes necessary. The reactivity can be increased, for example, by forming silicic acid oligomers on the support surface using external reactants. As a result, bonding of these oligomers to the support is decidedly weak and their distribution is not homogeneous.
SUMMARY OF THE INVENTION
The present invention concerns a process for preparing zeolite membranes supported on porous glass. The process comprises a partial hydrolysis step for the silica of the internal and external surfaces of the support before the zeolite crystallisation step. The invention also concerns membranes obtained by this process.
The membranes obtained have certain qualities and can advantageously be used in continuous separation processes. Partial hydrolysis of the silica of the internal and external surfaces of the support apparently produces silanol groups or a silica gel, both of which are more reactive than the initial silica. It may also be that extraction of boron from the glass support leads to a surface which is more accessible to the silicon. Adhesion of the zeolite to the support is thus further improved. Further, the silanol groups or the silica gel formed are chemically bonded to the support surface. As a result, the zeolite crystallised therefrom is directly bonded to the support. This means that the thickness of the zeolite layer is constant and it can be thin.
The zeolite layer is principally located on the external surface of the support. The latter effectively includes pores with a diameter which is too small to contain zeolite crystals.
REFERENCES:
patent: 4699892 (1987-10-01), Suzuki
patent: 5362522 (1994-11-01), Barri
patent: 5474681 (1995-12-01), Fehlner
patent: 5567664 (1996-10-01), Barri
patent: 5712461 (1998-01-01), Zhang
Anstett Martine
Guth Jean-Louis
Le Dred Ronan
Methivier Alain
Streicher Christian
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Speer Timothy M.
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