Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2002-09-13
2004-09-14
Cheung, William (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S349000
Reexamination Certificate
active
06790807
ABSTRACT:
STATEMENT OF THE INVENTION
A zirconium/metal oxide fibre comprises zirconium oxide and a metal oxide. The fibre has sufficient structural strength such that for example it may be used as a substitute fibre for glass fibre in the manufacture of paper and paper-like materials. Preferably the fibre's thickness is substantially uniform and has a length in excess of 1 micron.
The metal oxide fibre is made by adding a metal oxide in a suitable form, preferably as a solution of the metal salt (or a colloidal dispersion of the metal) to a colloidal dispersion comprising an amorphous zirconium polymer of the formula:
[Zr
4
(OH)
12
(X)
2
(H
2
O)
4
]
n
(X)
2n
.2
n
H
2
O (I)
wherein X is a zirconium polymer compatible anion and n is a whole number.
The mixed colloidal dispersion is subsequently made into a mixed metal oxide fibre. Preferably the colloidal dispersion of the zirconium polymer of formula (I) is made in accordance with a modification to the process described in U.K. Patent 1,181,794 where, for example, zirconium carbonate or zirconium hydroxide is reacted to form the colloidal dispersion containing the polymer of formula (I).
According to a most preferred embodiment, the invention relates to a zirconium/metal oxide fibre that comprises zirconium oxide and a lanthanide oxide. Preferably, the lanthanide/zirconium oxide fibre is made by adding a solution of a lanthanide, most preferably lanthanide nitrate (or a lanthanide colloidal dispersion) to a colloidal dispersion comprising an amorphous zirconium polymer of the formula:
[Zr
4
(OH)
12
(NO
3
)
2
(H
2
O)
4
]
n
(NO
3
)
2n
0.2
n
H
2
O (I)
The lanthanide nitrate solution is preferably formed by reacting a lanthanide carbonate, hydroxide or oxide with nitric acid.
It was surprisingly found that one could add a highly concentrated solution of a metal salt (or metal oxide colloidal dispersion) to the colloidal dispersion of zirconium polymer of formula (I) creating a mixed colloidal dispersion whereby the charge balance remains intact preventing adverse precipitation within the mixed colloidal dispersion. The preferred ratio of X to zirconium in the polymer of formula (I) is in the range of about 1.0:0.98 to 1.0 to 1.3 to ensure the colloidal dispersion formation although, for reasons later discussed, the ratio may fall outside this range. The pH of the colloidal dispersion is preferably in the range from about 1.5 to about 2. Due to the viscoelastic properties of the zirconium polymer of formula (I), the zirconium polymer of formula (I) can act as a spinning aid such that the concentrated mixed colloidal dispersion has a viscoelasticity that is suitable for fibre formation by techniques such as spray drying, drawing or blow spinning. The resultant green fibres are of a stable dried gel. These green fibres are heat treated to drive off volatiles to form crystalline fibres comprising zirconium oxide and metal oxide.
Although the zirconium polymer of formula (I) has a viscoelasticity that is suitable for fibre formation on its own, other spinning agents may be incorporated into the mixed colloidal dispersion such that the synergistic combination of both the zirconium polymer of formula (I) and at least one other spinning agent facilitates fibre formation. Preferably, these other spinning aids are organic based and are fugitive (volatile) during heat treatment. Examples of exemplary spinning aids include polyethylene oxide and polyvinylpyrrolidone.
BACKGROUND OF THE INVENTION
It is known that metal oxide catalysts can be incorporated on the surface of various types of fibres for decomposing various compositions or for purifying exhaust gases. For example, U.S. Pat. No. 5,094,222 describes a mixture of ceramic fibres containing an oxidation catalyst for decomposition of fats and oils. The ceramic fibres are made from at least one of the following oxides: silicon oxide, zirconium oxide and aluminum oxide. The oxidation catalyst can be selected from at least one of a variety of metal oxides. U.S. Pat. No. 5,165,899 describes a porous fibrous structure for purification of exhaust gases. The fibrous structure is made of metal alloy fibrils of the MCrAlX type where M is a matrix chosen from iron, and/or nickel and/or cobalt and X is chosen from zirconium, yttrium, cerium and lanthanum metal. Japanese Patent 3,060,738 describes cerium oxide mixed and other components which were mixed with an alumina-silica ceramic fibre to provide a catalyst that decomposes soot. Also, U.S. Pat. No. 3,860,529 describes Group III B metal oxide impregnated zirconia fibres.
Metal oxide catalysts have also been used in an extruded form. Canadian Patent 2,274,013 describes an extruded form of a ceria/zirconia mixture to treat exhaust gases.
Similarly, metal oxide catalysts can also be used as coatings on various types of fibres for primarily purifying exhaust gases. See for example U.S. Pat. Nos. 5,040,551; 5,075,275; 5,195,165; 5,759,663; 5,944,025; 5,965,481 and U.K. Patent 2,236,493. For instance, to purify exhaust gas, U.S. Pat. No. 5,075,275 describes a catalyst carrier, such as porous heat resistant fibres, which have been coated with cerium and barium oxides. U.S. Pat. No. 5,759,663 describes a high temperature resistant lath of woven ceramic where the fibres of the lath are coated with chromium oxide, silicone carbide and cerium oxide. U.K. Patent 2,236,493 describes a honeycomb filter impregnated with cesium, copper, and cerium or lanthanum to oxidize carbonaceous particles.
All of the above-mentioned references either refer to metal oxides as incorporated on the surface of fibres, as an extruded form, as coatings on fibres, or as impregnating the fibre. Several references exist that refer to metal oxides in fibre form only and further describe various processes for making such fibres. For instance, U.S. Pat. No. 5,911,944 describes a fibre made by dispersing a raw material containing at least one metal hydrate and hydrated metal compound in an alcohol-based solvent (Bpt.>70° C.) forming a colloidal dispersion. The colloidal dispersion is heated not higher than 100° C., which produces a polymer of the raw material. The polymer is converted to a complex. The complex is concentrated until it has spinnability. The colloidal dispersion is stretched to form a fibre precursor that causes gelation. The gelatinized fibre precursor is heated to produce a fibre. U.S. Pat. No. 3,846,527 describes making inorganic fibres that normally would not be spinnable. This was done by dry spinning a solution or colloidal dispersion with a linear polymeric fibre-forming material. U.K. Patent 1,402,544 describes the preparation of mixed metal oxide fibres by using metal alkoxide(s) capable of converting to spinels. Rare-earth metals are not known to form spinels. U.K. Patent 1,322,723 describes a process for producing fibrous material wherein zirconium oxide is capable of reacting chemically with silica fibrils to assist in bonding the fibrils together.
U.K. Patent 2,059,933 describes the preparation of alumina or zirconia fibres by spinning an aqueous solution of the corresponding metal salt, a precursor to the metal oxide fibre. The specific examples relate only to formation of alumina fibres. These particular fibres can be made from an aqueous solution containing other metals whose salts are hydrolysed at a pH less than 7 to yield a mixed metal fibre. To prevent gelling or precipitation within the aqueous solution, aliphatic or aromatic amines are added to the solution to remove excess anions to create a more desirable solution for fibre formation. In the present invention, however, excess nitrate anions within the zirconium polymer colloidal dispersion, as described in U.K. Patent 1,181,794, result in formation of spheres that would be detrimental to formation of our desired mixed metal oxide fibres.
Several patents have dealt with a Group IIA, a Group IIIA or a lanthanide metal oxide colloidal dispersion that can form gels, which can be used to make ceramic materials as described in U.S. Pat. No. 4,181,532. These colloid
Banner & Witcoff , Ltd.
Cheung William
Rothmans, Benson & Hedges Inc.
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