Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-11-02
2001-08-28
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S534000, C549S537000
Reexamination Certificate
active
06281370
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a catalyst for the production of ethylene oxide, a method for the production of the catalyst, and a method for the production of ethylene oxide. It relates more particularly to a silver catalyst which excels in catalytic activity, selectivity, and service life and permits production of ethylene oxide at high selectivity for a long time, a method for the production thereof, and a method for the production of ethylene oxide by the use of this silver catalyst.
2. Description of the Related Art
The production of ethylene oxide by the catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst is widely practiced on a commercial scale. Concerning the silver catalyst to be used for the catalytic vapor phase oxidation, numerous inventions covering carriers for the catalyst, methods for depositing the catalyst on such carriers, and reaction promoters used therein have been applied for patent.
U.S. Pat. No. 5,077,256, for example, discloses an idea of using a carrier which is formed by superposing a coating layer of amorphous silica on an &agr;-alumina carrier. JP-A-02-363,139 discloses an idea of using a carrier which is obtained by adding to an &agr;-alumina a compound of one member or two or more members selected from the class consisting of the elements falling in the fourth, fifth, and sixth periods and the IIIa-VIIa and IIIb-Vb groups of the periodical table of the elements (such as, for example, titanium, tin, and hafnium) and calcining the superposed layers.
Though the silver catalysts proposed to date already possess highly advanced levels of selectivity, the desirability of imparting further improved selectivity to these silver catalysts has been finding recognition because the scale of production of ethylene oxide is so large that even an increase of only 1% in the selectivity may result in copiously saving ethylene as a raw material and consequently bring a large economic effect. In the existing circumstances, the development of a silver catalyst possessing a better catalytic efficiency has posed a lasting theme for researchers in the relevant technical field.
The silver catalysts which are disclosed in the patent publications mentioned above, however, are still deficient in selectivity and are not satisfactory in terms of service life.
It is, therefore, an object of this invention is to provide a silver catalyst which possesses an excellent catalytic capacity and permits production of ethylene oxide at a high selectivity for a long time, a method for the manufacture thereof, and a method for the production of ethylene oxide by the use of the silver catalyst.
SUMMARY OF THE INVENTION
The object described above is accomplished by a silver catalyst for the production of ethylene oxide which is formed by depositing silver on a carrier using &agr;-alumina as a main component thereof which comprises silica and a metal or a compound of at least one element selected from the class consisting of the elements of the groups Ib and IIb in the periodical table of the elements.
The object is further accomplished by a method for the manufacture of a catalyst for the production of ethylene oxide, which comprises mixing at least &agr;-alumina, a silicon compound, an organic binder, and a compound of at least one element selected from the elements of the groups Ib and IIb in the periodic table of the elements, then calcining the resultant mixture at a temperature in the range of 1,000°-1,800° C. thereby preparing a carrier, and subsequently depositing at least silver on the carrier.
The object is further accomplished by a method for the production of ethylene oxide, which comprises effecting vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of the catalyst for the production of ethylene oxide mentioned above.
We have been ascertained that a silver catalyst excelling in activity, selectivity, and service life can be obtained by causing a carrier formed mainly of &agr;-alumina to incorporate therein silica and a metal or a compound of at least one element selected from the class consisting of the elements of the groups Ib and IIb in the periodic table of the elements, typically silver oxide. We have eventually perfected this invention based on this knowledge.
The catalyst of this invention for the production of ethylene oxide, therefore, excels in activity, selectivity, and service life and permits ethylene oxide to be produced at a high selectivity for a long time.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The carrier to be used in this invention is formed by using &agr;-alumina as a main component thereof and incorporating in this carrier a metal or a compound of at least one element selected from the class consisting of the elements of the groups Ib and IIb in the periodic table of the elements
The carrier of this construction is obtained by mixing &agr;-alumina particles, a silicon compound, an organic binder, and a metal or a compound of at least one element selected from the elements of the groups Ib and IIb in the periodic table of the elements, optionally molding the resultant mixture in prescribed shape and size, and then calcining the molded mixture at a temperature in the range of 1,000°-1,800° C., preferably 1,400°-1,700° C. The carrier of this invention which has &agr;-alumina as a main component thereof is typically composed of 65-99.5% by weight, preferably 90-99% by weight, of &agr;-alumina, 0-30% by weight, preferably 0-10% by weight, of amorphous alumina, 0-5% by weight, preferably 0.01-4% by weight, (as oxide) of an alkali, and 0-5% by weight, preferably 0.01-3% by weight, of the oxide of a transition metal.
As respects the particle diameter of &agr;-alumina, the primary particles of &agr;-alumina measure 0.01-100 &mgr;m, preferably 0.1-20 &mgr;m, more preferably 0.5-10 &mgr;m, and particularly preferably 1-5 &mgr;m, in diameter. The secondary particles of &agr;-alumina properly measure 0.1-1000 &mgr;m, preferably 1-500 &mgr;m, more preferably 10-200 &mgr;m, and particularly preferably 30-100 &mgr;m, in diameter.
The silver catalyst of this invention is characterized by using a carrier which is formed by causing a carrier formed mainly of &agr;-alumina to incorporate therein silica and a metal or a compound of at least one element selected from the elements of the groups Ib and IIb in the periodic table of the elements.
In this invention, this carrier will be referred to as a “finished carrier”. When the compound of the element mentioned above happens to be silver oxide, for example, after the treatment of this finished carrier with concentrated nitric acid, it will be observed that most of silver compounds are fixed in the carrier by fluorescent x ray analysis. This finised carrier, therefore, is considered to have a structure in which a layer of silica is formed on at least part of the surface of &agr;-alumina and silver oxide is occluded in this silica layer.
As the metals or compounds of the elements of the groups Ib and IIb in the periodic table of the elements, the metals of copper, silver, gold, and zinc or the compounds thereof such as, for example, the oxides may be cited. Among other metals and compounds mentioned above, silver oxide and zinc are particularly favorably usable. Silver oxide is the best choice.
The content of silica is generally in the range of 0.01-15% by weight, preferably 0.1-10% by weight, and more preferably 1-5% by weight, based on the amount of the complete carrier. The content of the metal or compound of at least one element selected from the class consisting of the elements of the groups Ib and IIb in the periodic table of the elements is generally in the range of 0.001-15% by weight, preferably 0.01-10% by weight, and more preferably 0.1-5% by weight as metal.
The production of the finished carrier mentioned above is not particularly discriminated by the kind of method to be adopted therefor. The finished carrier can be easily produced by mixing at least &agr;-alum
Shima Masahide
Takada Hitoshi
Fish & Richardson P.C.
Nippon Shokubai Co. , Ltd.
Trinh Ba K.
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