Chemistry of inorganic compounds – Miscellaneous process
Patent
1995-09-05
1998-04-07
Straub, Gary P.
Chemistry of inorganic compounds
Miscellaneous process
264 13, 264659, 23313R, B29B 900, B01J 3508
Patent
active
057361185
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of producing spherical particles made from inorganic oxides, to the particles obtained according to this method as well as to their use.
Spherical particles made from inorganic oxides, for example, from silicon dioxide, aluminum oxide, alumosilicate, magnesium oxide, titanium dioxide or zirconium dioxide, are used on a large scale as catalysts, catalyst supports, adsorbents, drying agents or ion exchange materials. For most of the indicated purposes, particles are required which have a uniform spherical shape and a narrow grain spectrum in order to therefore permit a packing which is as uniform as possible and a packing density which is as high as possible, for example, in the fixed-bed reactor. If the particles are used in the moving-bed reactor, an increased resistance to wear is also expected of the particles. If the particles are to be used in catalysts or catalyst supports, they must, in addition to a narrow grain spectrum, also have defined specific surface and a specific pore volume.
Normally, spherical particles are obtained from inorganic oxides, for example, from silicon dioxide, aluminum oxide, alumosilicates and/or other oxides according to the generally known sol/gel process. According to this process, as described, for example, in German Patent Document DE-AS 1 667 669, the production of spherical silicon dioxide particles takes place in that an aqueous solution of an alkali metal silicate is mixed with an aqueous solution of an acid. A sol is obtained in this manner which is converted into drop-shaped particles when are then caused to gel in a so-called forming oil. The forming oil used in this case is usually a fluid which cannot be mixed with water, such as mineral oil, crude petroleum or kerosine. In a further process step, a so-called cation exchange is then carried out in which the alkali metal content of the obtained particles is reduced in an aqueous medium to less than 1% in weight, relative to the dry substance. The particles will then be washed, dried and calcined. According to this process, the shaping of the formed particles depends on the rate at which the sol drops fall through the forming oil, in which case the falling speed of the sol drops is a function of the specific weight and of the viscosity of the fluid used as the forming oil. According to another method, which is known per se, the shaping of the particles may also take place in that the sol drops obtained after the alkali metal silicate solution is added to the aqueous acid solution, is caused to fall through an air column under the force of gravity, in which case the drops will gel during the fall. According to this method, the gelling time and the falling height must be precisely coordinated with one another. If the drops are not sufficiently presolidified, there is the risk that they may be deformed when they impact on the reaction fluid.
According to International Patent Document WO 92/07653, a sol/gel process is known according to which spherical particles are produced from aluminum oxide. In this case, spherical drops made from an aluminum oxide hydrosol are produced by a nozzle plate which is caused to vibrate, are then presolidified by being exposed to a lateral blowing-on of ammonia gas and are then collected in an aqueous ammonia solution. When particles are produced which have a larger diameter, the particles must normally be caused to pass through a foam layer so that the impact of the particles on the ammonia solution is slowed down in order to this prevent a deformation or breaking-apart of the drops. According to this process, the used aluminum oxide sol or the aluminum oxide suspension should have a defined viscosity in the range of from 10 to 500 mPa at room temperature.
In U.S. Pat. No. 2,652,371, a method is described of producing and classifying the sizes of silicon dioxide particles, in which sodium silicate sol drops are sprayed at an oblique angle in which case, by means of a blowing-on of an inert gas, are wide ray of sol drops of different sizes is pr
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Bretz Karl-Heinz
Derleth Helmut
Solvay Deutschland GmbH
Straub Gary P.
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