Vinyl acetate catalyst comprising metallic palladium and...

Details Vinyl acetate catalyst comprising metallic palladium and... Vinyl acetate catalyst comprising metallic palladium and...

1998-06-02

2002-02-26

Geist, Gary (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C560S243000

Reexamination Certificate

active

06350900

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to new and improved catalysts for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid.
2. Background Information Including Description of Related Art
It is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst consisting of metallic palladium and gold supported on a carrier. While the process utilizing such a catalyst is capable of producing vinyl acetate at fair levels of productivity, such productivity levels are limited by the production of undesirable by-products, particularly carbon dioxide. Thus, any expedient capable of achieving reduced production of by-products such as carbon dioxide, expressed as lower percent CO
2
selectivity, is very desirable.
The foregoing catalysts comprising metallic palladium and gold are conventionally prepared by a process including the steps of impregnating a porous support with a single aqueous solution or separate solutions of water-soluble salts of palladium and gold, reacting the impregnated water-soluble salts with an appropriate alkaline compound e.g., sodium hydroxide to “fix” the palladium and gold as water-insoluble compounds, e.g. the hydroxides, and reducing the water insoluble compounds, e.g., with ethylene or hydrazine, to convert the palladium and gold to free metallic form. This type of process has the disadvantage of requiring several steps, sometimes including at least two “fixing” steps.
The following references may be considered material to the invention claimed herein.
U.S. Pat. No. 5,332,710, 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 to precipitate such compounds, and subsequently reducing the compounds to free metallic form.
British Patent No. 1,188,777. published Apr. 22, 1970 discloses a process for the simultaneous production of an unsaturated carboxylic acid ester, e.g. vinyl acetate, from an olefin, carboxylic acid, and oxygen, and the corresponding carboxylic acid, e.g., acetic acid, from its aldehyde, using a single supported catalyst containing a palladium compound, e.g. an oxide or salt, with one or more compounds of any of various metals, e.g. metallic gold or a gold compound such as potassium aurate.
U.S. Pat. No. 5,700,753 discloses vinyl acetate (VA) catalyst prepared by adding organometallic gold complexes to prereduced palladium catalyst prepared from Na
2
PdCl
4
. The organometallic gold compound does not require a fixing procedure.
SUMMARY OF THE INVENTION
In accordance with this invention, a catalyst is provided useful for the production of vinyl acetate (VA) by reaction of ethylene, oxygen and acetic acid with low carbon dioxide selectivity, said catalyst being prepared by steps comprising impregnating a porous support, the porous surfaces of which contain a catalytically effective amount of prereduced metallic palladium, with a solution of potassium aurate, KAuO
2
, and reducing the potassium aurate to a catalytically effective amount of metallic gold. The use of such catalyst often results in lower carbon dioxide and heavy ends selectivities, which are usually accompanied by a higher vinyl acetate productivity, than when various conventional catalysts comprising metallic palladium and gold are employed.
DETAILED DESCRIPTION OF THE INVENTION
Disclosed herein is a process to prepare catalyst useful in the production of VA. Prereduced Pd catalyst were prepared by the impregnation of a support with aqueous solution of Na
2
PdCl
4
followed by fixing with NaOH and reduction of the Pd. A thin shell Pd catalyst was obtained, to which was then contacted with a solution of aqueous KAuO
2
to form a second shell of Au on the support. Ultimately, a shell catalyst of Pd and Au was formed wherein a fixing step for the Au was not necessary. The Pd and Au were distributed as a thin metal shell on the support structure.
As an alternative embodiment, the catalyst may be prepared by first contacting the support with KAuO
2
, followed by contact with Na
2
PdCl
4
. The Pd compound may then be fixed with a precipitating solution such as NaOH, and the Au and Pd reduced with a reducing agent. Alternatively the Au may be reduced before the addition of the Pd solution.
A still further embodiment of the inventive procedure involves use of sodium-free reagents; such as described in U.S. Pat. No. 5,693,586.
The support material in the catalyst of this invention 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, 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 about 2, preferably about 0.4 to about 1.2 ml/g.
In the preparation of the catalyst used in the process of this invention, the support material is first treated to deposit a catalytic amount of palladium on the porous surfaces of the support particles. Any of various methods for accomplishing this purpose may be used, all of which involve the impregnation of the support with an aqueous solution of a water-soluble compound of palladium. Palladium(II) chloride, sodium palladium(II) chloride (i.e., sodium tetrachloropalladium(II), Na
2
PdCl
4
), potassium palladium(II) chloride, palladium(II) nitrate or palladium(II) sulfate are examples of suitable water-soluble palladium compounds. Sodium tetrachloropalladium(II) is the preferred salt for impregnation because of its good water solubility. The impregnation can be accomplished by the “incipient wetness” method wherein an amount of water-soluble metal compound 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 is such that the amount of elemental palladium in the solution absorbed on the support is equal to a desired predetermined amount. The impregnation is such as to provide, for example, about 1 to about 10 grams of elemental palladium per liter of finished catalyst.
After the impregnation of the support with an aqueous solution of water-soluble salt of palladium, the palladium is “fixed”, i.e., precipitated, as a water-insoluble compound such as the hydroxide, by reaction with an appropriate alkaline compound, e.g., an alkali metal hydroxide. silicate, borate, carbonate or bicarbonate, in aqueous solution. Sodium and potassium hydroxides are preferred alkaline fixing compounds. The alkali metal in the alkaline compound should be in an amount of, for example, about 1 to about 2, preferably about 1.1 to about 1.8 times the amount necessary to react with the catalytically active cations present in the water-soluble salt. The fixing of the palladium may be done by the incipient wetness method wherein the impregnated support is dried, e.g., at a temperature of 150° C. for one hour, contacted with an amount of solution of the alkaline material equal to about 95-100% of the pore volume of the support, and allowed to stand for a period of about ½ to about 16 hours; or the roto-immersion method wherein the impregnated support without drying is immersed in a solution of the alkaline material and is

Affiliated with

Also associated with

Rating

Vinyl acetate catalyst comprising metallic palladium and... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Vinyl acetate catalyst comprising metallic palladium and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vinyl acetate catalyst comprising metallic palladium and... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2970427