Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1996-03-21
2003-01-28
Norton, Nadine G. (Department: 1764)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S325000, C502S326000, C502S330000, C502S344000
Reexamination Certificate
active
06511938
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silver-containing, supported catalysts for the epoxidation of alkene, especially ethylene, to the corresponding alkylene oxide, e.g., ethylene oxide, which contain a stability and/or efficiency and/or activity enhancing amount of a cobalt-containing component.
BACKGROUND TO THE INVENTION
Ethylene oxide is commercially produced by the epoxidation of ethylene over silver-containing catalyst at elevated temperature. Considerable research efforts have been devoted to providing catalysts that increase the efficiency, or selectivity, of the process to ethylene oxide.
The manufacture of ethylene oxide by the reaction of oxygen or oxygen-containing gases with ethylene in the presence of a silver catalyst is an old and developed art. For example, U.S. Pat. No. 2,040,782, patented May 12, 1936, describes the manufacture of ethylene oxide by the reaction of oxygen with ethylene in the presence of silver catalysts which contain a class of metal-containing promoters. In Reissue U.S. Pat. No. 20,370, dated May 18, 1937, Leforte discloses that the formation of olefin oxides may be effected by causing olefins to combine directly with molecular oxygen in the presence of a silver catalyst. From that point on, the prior art has focused its efforts on improving the catalyst's efficiency in producing ethylene oxide.
In characterizing this invention, the terms “conversion”, “selectivity”, and “yield” are employed as defined in U.S. Pat. No. 3,420,784, patented Jan. 7, 1969, at column 3, lines 24-35 inclusive. This definition of “selectivity” is consistent with that disclosed in U.S. Pat. No. 2,766,261 at column 6, lines 5-22, and U.S. Pat. No. 3,144,916, lines 58-61. The definitions of “yield” and “conversion” have more varied meaning in the art and are not to be employed as defined, for example, in the aforementioned U.S. Pat. No. 2,766,261. The terms “efficiency” and “selectivity”, as used throughout the specification and claims are intended to be synonymous.
Silver catalysts employed in the manufacture of ethylene oxide have undergone significant changes since their initial period of development. As reported by the art, silver particles were first deposited upon support materials with little attention being paid to support properties, such as surface area, pore volume and chemical inertness. As the art evolved, there developed special technologies related to carriers or supports containing silver that were more effective for the reaction of ethylene with oxygen to produce ethylene oxide. Today, most supports for the silver catalysts are shaped particulate materials which can be loaded in the interior of a reactor wherein the reacting gases and the gaseous products of the reaction are capable of flowing in and about these particulate materials to pass through the reactor and be recovered. The size and shape of the support are variable factors and the particular size and shape selected are peculiar to the reactor employed, the gas flow required, and the pressure drop across the reactor, with other factors also being considered.
The carriers that have been employed are typically made of inorganic materials, generally of a mineral nature. In most cases, the preferred carrier is made of alpha-alumina, such as has been described in the patent literature: see for example, U.S. Pat. Nos. 2,294,383; 3,172,893; 3,332,887; 3,423,328; and 3,563,914.
The carriers which are employed for the manufacture of most, if not all, commercially employed ethylene oxide catalysts are produced by companies who do not produce such catalysts. As a rule, the methods of making such carriers are trade secrets of significant value to the carrier manufacturers. Consequently, the catalyst manufacturer cannot know how the carrier is made. Critical to making a carrier which proves uniquely desirable for the manufacture of a successful catalyst can be a number of factors, such as the purity and other physical/chemical properties of raw materials used to make the carrier and the method by which the carrier is made.
The silver that is deposited on these carriers is thought to be in the form of small particles because that is all that can be seen by current microscopic techniques. The patent literature indicates that the size of the silver is a factor in the effectiveness of the catalyst and in most cases fine particle silver is obtained utilizing the standard processes in the art; see, for example, U.S. Pat. Nos. 2,554,459; 2,831,870; 3,423,328 (specifies that silver particles of 150-400 Angstroms are employed); U.S. Pat. No. 3,702,259 (disclosed a preparation procedure for forming silver particles less than 1 micron in diameter) and U.S. Pat. No. 3,758,418 (discloses silver particles having a diameter less than 1000 Angstroms). Improvements in microscopic examinations of silver catalysts enable the observation that the particle size ranges to even smaller values.
The deposition of silver onto the carrier can be achieved by a number of techniques but the two techniques which are most frequently employed involve, in one case, the impregnation of the support with a silver solution followed by heat treatment of the impregnated support to effect deposition of the silver on the support and, in the other case, the coating of the silver on the support by the precipitation of silver or the preformation of silver into a slurry such that the silver particles are deposited on the support and adhere to the support surface when the carrier or support is heated to remove the liquids present. These various procedures are exemplified in various U.S. Patents such as U.S. Pat. Nos. 2,773,844; 3,207,700; 3,501,407; 3,664,970 (see British Patent 754,593) and U.S. Pat. No. 3,172,893.
The surface area provided by the support has been the subject of considerable interest in the development of silver catalysts. Disclosures concerning the surface area of the catalyst carrier can be found in U.S. Pat. No. 2,766,261 (which discloses that a surface area of 0.002-10 m
2
/gm is suitable); U.S. Pat. No. 3,172,893 which depicts a porosity of 35-65% and a pore diameter of 80-200 microns); U.S. Pat. No. 3,725,307 which depicts a surface area of less than 1 sq.m/gm and an average pore diameter of 10-15 microns); U.S. Pat. No. 3,664,970 (which utilizes a support having a minimum porosity of about 30%, at least 90% of the pores having diameters in the range of 1-30 microns, and the average of such diameters being in the range of 4-10 microns); and U.S. Pat. No. 3,563,914 which utilizes a catalyst support having a surface area of less than 1 sq. m/gm, a volume of 0.23 ml/gm and a particle size between 0.074 and 0.30 mm). Low surface area, inert alpha-alumina is favored by the prior art.
It has been known for a long time that impurities present in the catalyst and/or the gas phase can materially impact upon the reaction. In the early development of the art, there were no techniques available for identifying or measuring such impurities. Consequently, one could not isolate the role that such impurities played. However, even in the earliest periods of the development of the art, the use of alkali metals as promoters for the silver catalyzed production of ethylene oxide was extremely well known in the art. U.S. Pat. No. 2,177,361, issued October 1939, has a teaching of the use of alkali metals in silver catalysts. U.S. Pat. No. 2,238,471 discloses that lithium is very desirable as a promoter but that potassium and cesium are detrimental when used in amounts of essentially 10% by weight of potassium hydroxide or cesium hydroxide to the silver oxide employed in making the catalyst. Later, U.S. Pat. No. 2,404,438 states that sodium and lithium are effective promoters for this reaction. Essentially the same teaching can be found in U.S. Pat. No. 2,424,084. U.S. Pat. No. 2,424,086 generalizes about alkali metals as promoters and specifies sodium in particular. In U.S. Pat. No. 2,671,764 (the Sacken sulfate patent), the patentees believe that alkali metals in the form of their sulfates are effective as promoters for such silve
Liu Albert Cheng-Yu
McCain James Herndon
Minahan David Michael
Soo Hwaili
Thorsteinson Erlind Magnus
Choo Tai-Sau
Hampilos Gus
Norton Nadine G.
Union Carbide Chemicals & Plastics Technology Corporation
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