Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-11-17
2001-10-16
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S327000, C502S332000, C502S333000, C502S339000, C502S344000
Reexamination Certificate
active
06303537
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to new and improved catalysts comprising metallic palladium and gold, which are useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid.
2. Description of the Related Art
It is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst comprising palladium and gold, supported on a carrier. While the process utilizing such a catalyst is capable of producing vinyl acetate at relatively high levels of productivity, any expedient which could possibly result in even greater productivity or a decrease in by products would be very desirable.
The following references may be considered material to the invention claimed herein.
U.S. Pat. No. 3,775,342 issued Nov. 27, 1973, and U.S. Pat. No. 3,822,308 issued Jul. 2, 1974, both to Kronig et al., each discloses a method of making vinyl acetate catalysts comprising treating a support simultaneously or successively with a solution A containing dissolved salts of noble metals such as palladium and gold and a solution B containing compounds able to react on the support with the noble metal salts to form water-insoluble compounds, treating such water-insoluble compounds with a reducing agent to convert the water-insoluble noble metal compounds to the free metals, washing the catalyst to remove water-soluble compounds, and applying an alkali metal compound, e.g., an alkali metal carboxylate before or after treatment with the reducing agent. Solution A can optionally also contain salts of other metals such as magnesium, calcium, barium and copper.
U.S. Pat. No. 5,322,710, issued Jul. 26, 1994, to Nicolau et al., discloses a method of preparing a catalyst useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising impregnating a porous support with water soluble salts of palladium and gold, fixing the palladium and gold as insoluble compounds on the support by immersing and tumbling the impregnated support in a reactive solution for at least ½ hour to precipitate such compounds, and subsequently reducing the compounds to free metallic form.
U.S. Pat. No. 5,347,046, issued Sept. 13, 1994 to White et al., discloses catalysts for the production of vinyl acetate by reaction of ethylene, oxygen, and acetic acid, comprising a palladium group metal and/or a compound thereof, gold and/or a compound thereof, and copper, nickel, cobalt, iron, manganese, lead or silver, or a compound thereof, preferably deposited on a support material.
Suslick, K. S., “Organometallic Sonochemistry,”
Advances in Organometallic Chemistry
25, 73-119 (1986) is a general article on the application of ultrasound waves to organometalic reactions.
Suslick, K. S.; Fang, M.; Hyeon, T.; and Cichowlas, A. A., “Nanostructured Fe-Co Catalysts Generated by Ultrasound,”
Materials Research Society Symposia Proceedings,
351, 443-448 (1994), discuss the preparation and activity of Fe-Co catalysts generated with ultrasound waves.
Okitsu, K.; Bandow, H.; and Maeda, Y.; “Sonochemical Preparation of Ultrafine Palladium Particles,”
Chemistry of Materials
8, 315-317 (1996) discuss the sonochemical reduction of Pd (II) in the presence of protective agents such as surfactants to produce ultrafine Pd particles and state that colloidal dispersion of these particles “exhibit interesting catalytic activity.”
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, a catalyst effective for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising a porous support on the porous surfaces of which is deposited catalytically effective amounts of metallic palladium and gold, and optionally, one or more additional catalytically active metals, is prepared by steps comprising impregnating the support with one or more aqueous solutions of water-soluble compounds of the metals, fixing the metals on the support as water-insoluble compounds in one or more fixing steps by reaction with an appropriate alkaline compound, and reducing the water-insoluble compounds of the catalytically active metals to their free metallic form in one or more reducing steps, at least one of such reducing steps being carried out in an aqueous medium containing a reducing agent dissolved therein or through which a gaseous reducing agent is bubbled, and in which the support containing the fixed water-insoluble metal compounds is immersed while sonicating, i.e., applying ultrasound waves to, such aqueous medium.
Catalysts may be prepared by the method of this invention utilizing sonication in the reducing step, which are capable of implementing the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid with somewhat reduced selectivities to CO
2
and/or heavy ends such that the use of such catalysts may result in greater vinyl acetate productivity than when any of various catalysts known in the art is employed.
DETAILED DESCRIPTION OF THE INVENTION
In preparing the catalysts under this invention, the catalyst support material is composed of particles having any of various regular or irregular shapes, such as spheres, tablets, cylinders, rings, stars, or other shapes, and may have dimensions such as diameter, length, or width of about 1 to about 10 mm., preferably about 3 to 9 mm. Spheres having a diameter of about 4 to about 8 mm. are preferred. The support material may be composed of any suitable porous substance, e.g., silica, alumina, silica-alumina, titania, zirconia, silicates, aluminosilicates, titanates, spinel, silicon carbide, or carbon and the like.
The support material may have a surface area within the range, for example, of about 10 to about 350, preferably about 100 to about 200 m
2
/g, an average pore size in the range, for example, of about 50 to about 2000 angstroms, and a pore volume in the range, for example, of about 0.1 to 2, preferably about 0.4 to about 1.2 ml/g.
In the preparation of the catalysts of this invention, the support material may be treated to deposit catalytic amounts of palladium, gold, and any additional catalytically active metal, if any, on the porous surfaces of the support particles. Any of various methods for accomplishing this purpose may be used, all of which involve simultaneous or separate impregnations of the support with one or more aqueous solutions of water-soluble compounds of the catalytically active metals. Palladium(II)chloride, sodium palladium(II)chloride, potassium palladium(II)chloride, palladium(II)nitrate or palladium(II)sulfate are examples of suitable water-soluble palladium compounds; and an alkali metal, e.g., sodium or potassium salt of auric(III)chloride or tetrachloroauric(III)acid can be used as the water-soluble gold compound. An alkali metal salt of tetrachloroauric(III)acid and sodium palladium(II)chloride are preferred salts for impregnation of gold and palladium respectively because of their good water solubility.
In preparing the catalyst, the impregnations of the support material with solutions of water-soluble salts of the catalytically active metals may be effected by any method known to those skilled in the art. Preferably, however, such impregnations are accomplished by the “incipient wetness” method wherein an amount of water-soluble salt solution used for the impregnation is from about 95 to about 100 percent of the absorptive capacity of the support material. The concentration of the solution or solutions is such that the amounts of catalytically active metals in the solution or solutions absorbed on the support is equal to a desired predetermined amount. If more than one such impregnation is carried out, then each impregnation may contain water soluble compound equivalent to all or only a portion of the amount of one or any combination of the catalytically active metals desired in the final catalyst, as long as the amounts of such metals in the total of the impregnating solutions absorbed are equal to the final desired amounts. The impregnations are such as to provide, for example, about 1 to about
Broussard Jerry A.
Gerberich H. Robert
Wang Tao
Celanese International Corporation
Griffin Steven P.
Nguyen Cam N.
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