Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Phosphorus or compound containing same
Reexamination Certificate
1999-11-19
2002-03-26
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Phosphorus or compound containing same
C502S247000, C502S214000, C502S353000
Reexamination Certificate
active
06362128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates a process for preparing an improved attrition resistant catalyst. More specifically, but not by way of limitation, the invention relates to a method of imparting attrition resistance to a particulate catalyst or catalyst precursor (e.g., vanadium/phosphorus oxide, V/P/O, solids) by incorporating a large size colloidal sol as the major inorganic metal oxide component in combination with polysilicic acid followed by spray drying and calcining the spray dried product.
2. Description of the Related Art
The use of inert metal oxides such as silica or the like as a support for catalysts or as a binder for catalyst particles is generally well known in the art. In particular, U.S. Pat. No. 4,677,084 discloses and claims a process for producing attrition resistant catalyst or catalyst support particles having an oxide-rich surface layer as well as claims the attrition resistant particles. In a divisional U.S. Pat No. 4,769,477 the use of attrition resistant vanadium/phosphorus oxide catalyst particles (made by the above process) having a SiO
2
-rich surface layer for producing maleic anhydride by oxidation of a hydrocarbon is similarly disclosed and claimed. The method of producing the attrition resistant catalyst particles according to these patents involves the forming of a slurry of catalyst, catalyst precursor or catalyst support particles in a solution containing a solute consisting essentially of the oxide precursor particle (i.e., that which becomes or forms the resulting oxide-rich surface layer; e.g., silicic acid, polysilicic acid or the like). This oxide precursor particle useful in this process is characterized by an average particle size no greater than 5 nanometers and the relative amount of the same is chosen such that the weight of the oxide to be formed as a surface layer is about 3 to 15 percent of the total weight of the resulting attrition resistant particles. This slurry is then spray dried to form porous microspheres which are then calcined to produce attrition resistant catalyst. Both of these patents further contain extensive background reviews of relevant prior patent references and the present invention can be viewed as a further improvement relative to each. As such, U.S. Pat. Nos. 4,677,084 and 4,769,477 are incorporated herein by reference for disclosure purposes.
U.S. Pat. No. 5,302,566 discloses an alternate method for preparing an attrition resistant catalyst described above, particularly vanadium/phosphorus oxide catalyst, having an oxide-rich surface layer. In this alternative method the slurry to be spray dried comprises the catalyst or catalyst precursor particles and a mixture of a solution containing a solute consisting essentially of the oxide precursor particles of less than 5 nm along with a colloidal oxide sol wherein the oxide sol particles have an average size of between 5 and 7 nm. The amount of colloidal oxide sol is selected such as to provide between 50 to 95 percent by weight of the final oxide-rich surface and the polysilicic acid provides 50 to 5 percent. Again, the oxide-rich surface is between 3 and 15 percent by weight of the total weight of resulting attrition resistant catalyst. The resulting catalyst made by this alternative process is shown to be comparable in attrition resistance properties to a catalyst made using only oxide precursor solution as the surface forming oxide source. The mixture of combined oxide precursor solution and 5 to 7 nm colloidal sol, however, is significantly more stable than a solution of oxide precursor alone. Consequently, advantages in terms of shelf-life, storage, and handling are realized particularly when scaling up to commercial production levels. U.S. Pat. No. 5,302,566 is incorporated herein by reference for disclosure purposes.
In a copending and commonly assigned U.S. patent application Ser. No. 09/163,680 filed Sep. 30, 1998, incorporated herein by reference, a further improvement relating to the above described processes is disclosed. In this process the colloidal oxide sol employed has an average size between 10 and 100 nm and the amount used is selected such that from 25 to 50 percent of the resulting weight of attrition resistant catalyst is derived from the colloidal oxide sol. The soluble solute component (e.g., the silicic acid or polysilicic acid) in the slurry prior to spray drying again is characterized by an average particle size no greater than 5 nm and the amount employed is selected such that from 5 to 15 percent of the weight of the attrition resistant catalyst (including the colloidal sol contribution) is derived from the soluble oxide precursor. This particular process and resulting attrition resistant catalyst is intended to alleviate a specific problem associated with transition metal oxide containing catalysts that can expand and shrink during the oxidation and reduction cycles associated with continuous use and the associated increase attrition losses observed during the reduced state.
BRIEF SUMMARY OF THE INVENTION
In view of the above prior art, it has now been discovered that an attrition resistant catalyst exhibiting improved catalytic performance can be prepared by intentionally employing a colloidal oxide sol having an average particle size in excess of ten nanometers as a major contributing component forming the oxide-rich layer. This large dimension colloidal sol is used in combination with a silicic acid or polysilicic acid and/or small colloidal oxide-sol of less than ten nanometers as the other contributing component forming the oxide-rich surface layer. The actual loading of the combined sols on the starting catalyst, catalyst precursor or catalyst support particles is such that the resulting oxide-rich surface layer being deposited represents from 3 to 15 percent by weight of the resulting attrition resistant catalyst. Conceptually, the novel use of the large dimensional oxide sol at this level of loading can be viewed, particularly relative to the previous U.S. Pat. Nos. 4,677,084 and 4,769,477 patents, as an inert yet beneficial diluent to the oxide precursor solution (i.e., the silicic acid, polysilicic acid and the like solution). Although not wanting to limit the observed discovery to any single explanation or mechanistic interpretation, the benefits of the present invention can at least be partially rationalized based on the hypothesis that the small colloidal sol component may serve as a binder while use of the large colloidal sol acts more as a propant and as a pore forming or controlling agent. Nitrogen BET surface area and pore volume data along with thin section high resolution transmission electron micrographs of the attrition resistant catalyst having an oxide-rich surface layer produced according to the process of the present invention tend to support such a view point.
Thus the present invention provides a process for manufacture of an attrition resistant catalyst having an oxide-rich surface layer comprising the steps of:
a) forming a slurry comprising;
i) catalyst, catalyst precursor or catalyst support particles,
ii) a colloidal oxide sol wherein oxide particles in the sol have an average particle size greater than 10 nm; and,
iii) a solution of a solvent and solute wherein the solute is selected from the group consist essentially of a precursor of said oxide-rich surface with average particle size no greater than 5 nm, a colloidal oxide sol wherein oxide particles in the sol have an average size less than 10 nm, and mixtures thereof,
wherein 50 to 95 percent of the weight of the oxide-rich surface layer is derived from said colloidal oxide sol (ii) and remaining 50 to 5 percent of the weight of the oxide-rich surface layer is derived from the solute of said solution (iii), and wherein 3 to 15 percent weight of the attrition resistant catalyst particle is from the oxide-rich surface layer and the remainder is from said catalyst, catalyst precursor or catalyst support particles (i);
b) spray drying the slurry from step (a) to form porous microspheres of attrition r
E. I. du Pont de Nemours and Company
Griffin Steven P.
Johnson Edward M.
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