Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Clay
Reexamination Certificate
2001-09-28
2004-09-07
Bos, Steven (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Clay
C502S087000, C502S233000, C502S250000, C502S243000, C502S439000
Reexamination Certificate
active
06787497
ABSTRACT:
The present invention relates to a catalyst carrier, preparation thereof, a slurry for use at preparation thereof, a catalyst comprising such a carrier, and use of the catalyst carrier for producing hydrogen peroxide.
Many chemical processes involve reactions in gas and/or liquid phase in contact with a solid catalyst. Such a catalyst often comprises a carrier on which a catalytically active material is deposited. The carrier serves the purpose of facilitating the handling of the catalyst and rendering the surface to volume ratio high. The carrier can be in the form of particles (orientated with randomness when placed in a catalytic reactor) or in the form of structured bodies (free of randomness when placed in a catalytic reactor).
Structured bodies are particularly easy to handle and can be prepared from a fibre paper impregnated with a support material, on which a catalytically active material can be deposited. WO 97/31710 describes preparation of a catalyst carrier by impregnating a mineral fibre paper with a dispersion of a filling material, a sol and a dispersing medium.
In processes involving gas-liquid reactions the catalyst is subjected to significant mechanical stress and it is hard to produce a structured body having sufficient durability. One examples of such a gas liquid reaction is the hydrogenation of anthraquinones or derivatives thereof, which is an important step in the anthraquinone process for production of hydrogen peroxide.
It is an object of the present invention to provide a catalyst carrier that can be used for preparing a structured catalyst body with high efficiency as well as high and durable mechanical strength.
It is another object of the invention to provide an improved process for performing catalytic reactions in the presence of at least one liquid and preferably at least one gas.
It is still another object to provide an improved process for producing hydrogen peroxide, particularly according to the anthraquinone process.
Thus, in one aspect the invention concerns a catalyst carrier comprising a fibre paper impregnated with a preferably aqueous slurry containing a silica sol, micro fibres and a filler, wherein said micro fibres have an equivalent average particle size, measured with sedigraph method, from about 200 nm to about 30000 nm, preferably from about 500 nm to about 10000 nm. The filler has an average equivalent particle size, measured with sedigraph method, from about 300 to about 10000 nm, preferably from about 1000 to about 4000 nm. In the sedigraph method the equivalent average particle size is determined by sedimentation and evaluated at 50% cumulative mass percent as equivalent spherical diameter in accordance with Stokes Law. Preferably the average length to diameter ratio of the micro fibres is from about 3:1 to about 40:1, most preferably from about 6:1 to about 20:1, as measured on microscope image.
The invention further concerns a method for preparing a catalyst carrier comprising a step of impregnating a fibre paper with a slurry as defined above.
The invention also concerns a slurry as defined above, which can be used for preparing a catalyst carrier.
It has been found that the presence of micro fibres within the above equivalent size and length to diameter ranges significantly improves the durability of structural strength of the catalyst carrier, particularly at long term use in contact with a flowing liquid-gas mixture.
Suitable micro fibres may be selected from glass fibres, ceramic fibres or mineral fibres such as halloysite, palygorskite, wollastonite or mixtures thereof, provided they fulfil the above requirement with respect to equivalent particle size and preferred length to diameter ratio.
The silica both acts as a binder and provides the actual support material with high surface area in the final catalyst carrier on which a catalytically active material can be deposited.
Suitable silica sols are aqueous and preferably have an average particle size from about 5 to about 100 nm, most preferably from about 10 to about 70 nm. The preferred silica sol should have a broad particle size distribution. Suitably the relative standard deviation of the particle size distribution in the sol is at least about 15% by numbers, preferably at least about 30%, and may, for example, be up to about 140% by numbers or more. The relative standard deviation of the particle size distribution corresponds to the ratio between the standard deviation of the particle size distribution and the average particle size by numbers, and may be measured by use of the dynamic light scattering method. It is also possible to use mixtures of silica sols with different average particle size and/or particle size distributions. The average particle size of a silica sol with broad particle size distribution is defined as the particle diameter in a monodispers silica sol with spherical particles having the same surface area (as measured with Sears titration method) per dry weight of silica sol. The silica sols could be anionic, cationic or de-ionised. Preferred silica sols are anionic and mainly stabilised with ions of ammonia, potassium and/or sodium, or mixtures thereof, at a pH above 7. The preferred amount of silica sol (counted as SiO
2
) in the slurry is from about 40% to about 90%, most preferably from about 50% to about 80% by weight (as dry weight).
Suitable fillers may, for example, be selected from talc or clay minerals, such as bentonite or members of the smectite—or kaolin groups, or mixtures thereof. The preferred shape of the filler particles is close to equidimensional, i.e. the shape has no significant elongation. Preferably the average length to diameter ratio of filler particles is less than 3:1, most preferably less than 2:1, as measured on microscope image. It has been found that the presence of a filler both increases the life time of the slurry before sedimentation starts and improves the durability and mechanical strength of the final catalyst carrier.
The preferred total amount of micro fibres and filler in the slurry is from about 10% to about 60%, most preferably from about 20% to about 50% by dry weight. Preferably the weight ratio of filler to micro fibres is from 0 to about 3:1, most preferably from about 1:3 to about 2:1.
The main part of the fibres in the actual fibre paper to be impregnated are preferably longer than the micro fibres used in the impregnation slurry, for examples having a true fibre diameter from about 0.001 to about 0.030 mm, preferably from about 0.002 to about 0.015 mm and a length exceeding about 1 mm, preferably exceeding about 3 mm. There is no critical upper limit on the fibre length, which, for example, may be up to 100 mm, 1000 mm or more. The fibre paper is preferably made of mineral—or glass fibres. Such fibre papers are described in the literature, for example in the above mentioned WO 97/31710 and in U.S. Pat. No. 4,391,667.
The slurry used for impregnating the fibre paper can be prepared by any conventional means, for example by adding, under agitation, the silica sol, the micro fibres and the filler to a liquid, preferably water, to yield a substantially homogeneous slurry with a preferred total dry content from about 35% to about 75%, most preferably from about 45% to about 70%. The fibre paper is impregnated with the slurry by any suitable means, for example by spraying or dipping, and then suitably dried to evaporate water so the silica sol gels, for example at a temperature bellow about 120° C., preferably from about 20° C. to about 100° C. and suitably a sufficiently long time to remove essential all free water. The gelling may be speeded up by adding salts of, for example, acetate or nitrate of aluminium, zirconium, magnesium, calcium and/or ammonia. Although not necessary it is possible to also supply further additives such as silicates, sulfates, phosphates, or carbonates of alkali metals or the corresponding acids, for instance in order to adjust pH. The impregnation and drying steps may be repeated once, twice or several times to increase the amount of solids on the fibre paper. After
Dellve Anna-Carin
Nyström Mats
Tokarz Bozena
Akzo Nobel N.V.
Bos Steven
Serbin David J.
Wright, Sr. William G.
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