Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Silicon containing or process of making
Reexamination Certificate
2001-09-14
2003-08-19
Nguyen, Cam N. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Silicon containing or process of making
C502S241000, C502S260000, C502S314000, C502S327000, C423S027000, C423S028000, C423S068000, C423S086000, C423S098000, C423S109000, C423S132000, C423S150100, C423S280000, C423S594120, C423S605000, C423S658500
Reexamination Certificate
active
06608001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to processes for shaping catalytic material as small spherical particles. The invention also relates to particulate catalysts and catalyst supports prepared by such process.
2. Description of Related Art
The physical and structural properties of a catalyst significantly influence its activity and durability. In many cases, the pore structure of the catalyst support, including size distribution and volume, determines the extent and accessibility of surface area available for contact of the catalytic material and the reactants. Catalytic activity often depends on the rate of diffusion of reactants and products in and out of the interstices of a catalyst. Increased pore size may facilitate the diffusion of reactants and reaction products, but catalytic activity is also a function of surface area and packing density, particularly with fixed bed particular catalysts. Spherically shaped catalyst particles have certain advantages over other shapes because they permit uniform packing so that variations in pressure drop are minimized and the tendency of a reactant stream to channel through the bed without effectively contacting the catalyst is reduced.
After a significant amount of use particulate catalysts and catalyst supports employed in a number of chemical processes tend to break down to smaller particles or fines. This is particularly problematic in fluid catalyst bed systems, where impacts experienced by the particles result in surface abrasion that produces fine particles which can be entrained in the stream of reactants. This usually contributes to a reduction in catalyst activity due to a loss of catalyst in the reactor. Better flow properties are generally obtained with spherical catalyst particles and catalyst attrition tends to be lessened compared to irregularly or non-spherically shaped particle beds.
U.S. Pat. No. 4,318,896 (Schoenover) discusses five general methods of preparing spheroidal particles of a size suitable for commercial operation. Of these, the spray drying method and the method of dropping particles into an oil bath are widely used. According to those methods, drops of a catalyst-forming liquid are produced and allowed to harden. In conventional spray drying techniques the droplet hardening takes place in a stream of air or in a water immiscible liquid such as oil.
A process for manufacturing silica particles is shown in U.S. Pat. No. 3,872,217. Processes for manufacturing alumina particles are shown, for example, in U.S. Pat. No. 4,318,896, and processes for manufacturing silica-alumina particles are described in U.S. Pat. No. 3,986,978. U.S. Pat. No. 2,620,314 (Hoekstra) describes a method for preparing a catalyst support, especially spheroidal alumina particles, by the oil-drop method.
U.S. Pat. No. 4,628,040 (Green) describes a method of making uniform spheroidal catalyst beads in which uniform droplets of a bead-forming liquid are produced by positioning the end of a capillary tube in the throat of a venturi. An immiscible fluid flowing through the venturi detaches the droplets from the end of the capillary tube to produce uniform, spherical droplets which harden into spheroidal beads of uniform size. This is contrasted with other oil-drop methods that initially form irregularly-shaped, non-uniformly sized particles which subsequently assume a spherical shape in the hot oil bath due to surface tension forces. Beads of alumina, silica alumina, and silica of about 200 microns or larger, up to ⅛ inch in diameter are disclosed and compared to typical beads produced in spray drying, which are said to have a diameter of 20 to 150 microns.
U.S. Pat. No. 4,902,666 (Rainis) describes a process for the manufacture of spheroidal bodies by selective agglomeration. These spheroidal particles can have either smooth surfaces or polylobe surfaces depending on the conditions of preparation. They have diameters generally between 1 to 5 mm and are useful as catalysts, or catalyst supports.
U.S. Pat. No. 5,710,093 (Rivas) describes a catalyst support comprising spherical particles of a mixture of at least two refractory inorganic oxides, refractory inorganic carbides, refractory inorganic nitrides, and mixtures of those compounds. The particles have a surface area of at least about 30 m
2
/g, an average pore diameter of at least about 150 Å, and a particle size of at least about 0.1 mm.
U.S. Pat. No. 4,766,101 (Nortier, et al.) describes certain alumina-based catalyst carriers in the form of particles such as spheres, pellets, extrudates and crushed material. The durability of the carriers is improved by stabilizing them by impregnation with an aqueous solution containing silicon, in the form of the silicate ion, and nitrogen in the form of a quaternary ammonium ion, and then drying and activating the impregnated carriers by a calcination which decomposes the organic cation into volatile compounds which diffuse out of the carrier.
U.S. Pat. No. 5,877,381 (Sasaki, et al.) discusses the importance of maintaining a certain particle size distribution of the catalyst in order to maintain a good fluidized state in fluidized bed reactions for syntheses of organic compounds. It is suggested that the catalyst particles tend to be crushed or worn more easily if the particles have a finer particle size, so that the strength of particles having a smaller diameter is particularly important in reducing catalyst loss.
One type of industrial process in which particulate catalysts are employed is in a conventional Fischer-Tropsch process, in which carbon monoxide and hydrogen are converted via an exothermic reaction to the desired C
2
+ hydrocarbon end products. The CO and H
2
reactant gas mixture is referred to as “syngas.” The types and amounts of reaction products, i.e., the lengths of carbon chains, obtained via Fischer-Tropsch synthesis vary dependent upon process kinetics and the choice of catalyst. Slurry phase reactions, particularly those occurring in bubble columns are well-known in the art and have been thoroughly described in the literature for carrying out Fischer-Tropsch hydrogenation reactions. See, for example, Farley et al, The Institute of Petroleum, Vol. 50, No. 482, pp. 27-46, February (1984). In a three-phase slurry reactor a fluidized gas is introduced into a reactor containing catalyst particles slurried in liquid hydrocarbons within a reactor chamber, which is typically a tall column. Syngas is then introduced at the bottom of the column through a distributor plate, which produces small gas bubbles. The gas bubbles migrate up and through the column, causing a beneficial turbulence, while reacting in the presence of the catalyst to produce liquid and gaseous hydrocarbon products. Gaseous products are captured at the top of the reactor, while liquid products are recovered through a filter that separates the liquid hydrocarbons from the catalyst fines.
A variety of catalysts have been described in the literature for enhancing the efficiency and selectively of syngas to liquid hydrocarbons. One common type of catalyst used in Fischer-Tropsch synthesis is a cobalt-based catalyst prepared by loading of the catalytic material on a support using impregnation by incipient wetness or other well known techniques. For example, a titania, silica or alumina support may be impregnated with a cobalt nitrate salt solution, optionally followed or preceded by impregnation with a promoter material. Excess liquid is removed and the catalyst precursor is dried. Following drying, or during continued drying, the catalyst is calcined to convert the salt and promoter to the corresponding metal oxide(s). The oxide is then reduced by treatment with hydrogen or a hydrogen-containing gas for a period of time sufficient to substantially reduce the oxide to the elemental or catalytic form of the metal. Most conventional catalyst production methods do not provide uniform, spherical particles in the micrometer diameter size range (i.e., from less than 1 micrometer up to about 1000 mic
ConocoPhillips Company
Nguyen Cam N.
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