Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-11-05
2004-09-07
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06787656
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Pursuant to 35 USC § 119, this application claims the benefit of Japan Patent Application No. 2001-340572 filed Nov. 6, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a catalyst obtained by depositing a silver component on a carrier containing specific elements and then heat-treating the resultant composite and used for the production of ethylene oxide, a method for the production thereof, and a method for the production of ethylene oxide by the use of the catalyst.
2. Description of the Related Art
Numerous reports covering catalysts to be used for producing ethylene oxide by the gas phase oxidation of ethylene with a molecular oxygen-containing gas and carriers therefor have been heretofore published in literature.
JP-A-06-47278, for example, discloses a catalyst carrier for use in the production of ethylene oxide which comprises at least 85 mass % of &agr;-alumina (calculated as oxide), 0.001-6 mass % (calculated as oxide) of calcium oxide or magnesium oxide, 0.01-5 mass % (calculated as silica) of silicon oxide, and 0-10 mass % (calculated as oxide) of zirconium oxide.
The same patent publication also discloses a method for producing a catalyst carrier for use in the production of ethylene oxide by mixing &agr;-alumina powder of high purity, a calcium compound or a magnesium compound or a magnesium oxide, a silicon compound, and a zirconium compound with water and a binder in specific quantities to give a final carrier containing not less than 85 mass % of &agr;-alumina, extrusion molding the resultant mixture into pellets, and calcining the pellets at a temperature of not lower than 1300° C.
The carrier mentioned above is effective for a catalyst which has particularly silver, an alkali metal activator, a rhenium activator, and an arbitrary rhenium coactivator deposited therein. Such an alkaline earth metal as mentioned above functions as a catalytic base in the absence of rhenium and forms an isomerizing active site in an excess quantity, with the result that the produced ethylene oxide will entail the problem of succumbing to successive oxidation and consequently lowering the selectivity.
JP-A-05-84440 discloses a catalyst characterized by having a catalytically effective quantity of silver, a promoting quantity of an alkali metal, and a promoting quantity of rhenium deposited on a carrier comprising at least 85 wt. % of &agr;-alumina, 0.05-6 wt. % (determined as oxide MO) of an alkaline earth metal in the form of an oxide, 0.01-5 wt. % (determined as dioxide) of silicon in the form of an oxide, and 0 1-10 wt. % (determined as dioxide) of zirconia in the form of an oxide.
We have proposed a carrier for a catalyst obtained by using refractory inorganic particles as seeds and depositing a refractory inorganic powder and zirconia sol on the seeds and a method for the production thereof (JP-A-02-290257), a catalyst for the production of ethylene oxide using an &agr;-alumina carrier having the outer surface of the carrier and the surface of pores in the carrier coated with amorphous silica (JP-A-02-194839), and a catalyst for the production of ethylene oxide using an &agr;-alumina carrier having the outer surface of the carrier and the surface of pores in the carrier coated with amorphous silica-alumina (JP-A-05-329368).
Thus, the desirability of materializing further improvement of the selectivity, improvement of the activity, and long-time stabilization of the life performance has been finding enthusiastic popular approval.
These catalysts are excellent in catalytic performance and satisfactory to a certain extent from the industrial point of view. According to SRI published in January, 1997, the annual production of ethylene oxide in the whole world is about 12 million tons. The quantity of ethylene to be used as the raw material therefor is estimated to be about 9,500,000 tons when the selectivity of the catalyst used for the production of ethylene oxide is 80% or about 8,500,000 tons when the selectivity is 90%, indicating that an improvement of 10% in the selectivity results in saving about 1 million tons of ethylene annually in the world. Even such a minute improvement as 0.1% in the selectivity, therefore, brings a huge cost merit because this improvement permits a saving of about 10,000 tons of ethylene in the whole world.
When the reaction temperature of the catalyst to be used for the production of ethylene oxide is unduly high, the production requires the plant used therefor to satisfy a very high design pressure which some of the existing plants may possibly fail to meet. Further, since the high reaction temperature results in lowering the tolerable oxygen concentration for explosion limits and consequently heightening the degree of danger, the actual commercial operation of the plant is preferred to proceed at a temperature of not higher than 250° C. from the viewpoint of both performance and safety of the plant.
This invention, therefore, has for an object thereof the provision of a catalyst of the ethylene oxide production grade materializing preparation of a catalyst for the production of ethylene oxide excellent in catalyst properties, namely activity, selectivity, and life, a method for the production thereof, and a method for the production of ethylene oxide by the use of the catalyst.
SUMMARY OF THE INVENTION
The various objects mentioned above accomplished by the following items (1)-(3).
(1) A catalyst for the production of ethylene oxide, having silver deposited on a carrier which comprises 90.0-98.9 mass % of &agr;-alumina, 0.01-1 mass % (calculated as oxide) of a compound of at least one metal selected from the group consisting of potassium and iron, 0.1-5 mass % (calculated as oxide) of a silicon compound, and 1-5 mass % (calculated as oxide) of zirconium compound.
(2) A method for the production of a catalyst set forth in the preceding item (1), characterized by depositing silver and an alkali metal on a carrier comprising 90.0-98.9 mass % of &agr;-alumina, 0.01-1 mass % (calculated as oxide) of a compound of at least one metal selected from the group consisting of potassium and iron, 0.1-5 mass % (calculated as oxide) of a silicon compound, and 1-5 mass % (calculated as oxide) of zirconium compound in inner portion thereof, drying the resultant composite, and subjecting the dried composite to a heat treatment performed in the presence of an oxygen-containing gas at a temperature in the range of 60-450° C. and a heat treatment performed in the atmosphere of an inert gas at a higher temperature in the range of 450-700° C.
(3) A method for the production of ethylene oxide, characterized by effecting gas phase oxidation of ethylene with a molecular oxygen-containing gas by the use of a catalyst set forth in the item (1) or a catalyst produced by the method set forth in the item (2).
Since the catalyst contemplated by this invention for the production of ethylene oxide is possessed of such a construction as described above, it brings an improvement in the selectivity for ethylene oxide, an improvement in the activity, and an improvement in the long-time life performance as compared with the conventional countertype.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The catalyst carrier contemplated by this invention for the production of ethylene oxide is prepared from &agr;-alumina powder of high purity, a compound affording potassium oxide and/or iron oxide, silica sol, a compound affording zirconia (arbitrary components) and conventional binder/perfect combustion agent.
The &agr;-alumina which is used for the preparation of the catalyst has an assay approximating to 98 mass %, preferably exceeding 98.5 mass % and has a sodium impurity content not exceeding about 0.06 mass %, specifically falling in the range of 0.02-0.06 mass %. The alumina comprises &agr;-crystals having an average particle size preferably in the range of about 0.5—about 5 &mgr;m, preferably in the range of about 1—about 4 &mgr;m. These crystals are preferred to aggregate and form particles having an average part
Shima Masahide
Takada Hitoshi
Fish & Richardson P.C.
McKane Joseph K.
Nippon Shokubai Co. , Ltd.
Solola Taofiq A.
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