Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Patent
1998-11-02
2000-09-05
Geist, Gary
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
502102, 502103, 502202, 502207, C07C 6705, B01J 3100
Patent
active
061145718
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The present invention relates to a catalyst comprising palladium, gold and an alkali metal compound, a process for its preparation and its use for preparing vinyl acetate from acetic acid, ethylene and oxygen or oxygen-containing gases.
It is known from the prior art that vinyl acetate can be prepared from ethylene, oxygen and acetic acid by reaction over catalysts comprising palladium, gold and an alkali metal compound on a support material (for instance silicon dioxide). Such catalysts display good activity and generally form little carbon dioxide and ethyl acetate. Although high-boilers are formed as further by-products in amounts which appear to be small, they nevertheless present a problem from process and ecological points of view. The term high-boilers here refers to, in particular, the compounds ethylidene diacetate, ethylene glycol and diacetoxyethylenes.
Literature references which disclose the preparation of such catalysts for the commercial production of vinyl acetate generally describe methods of depositing the noble metals in a shell on the catalyst support.
U.S. Pat. No. 4,048,096 describes the preparation of a catalyst for vinyl acetate production in which the dissolved noble metal salts are adsorbed by the support from a solution which has the same volume as the pores of the support material, with the support particles being agitated in a rotating vessel. The salts are then fixed using alkalis, without drying the support beforehand.
U.S. Pat. No. 5,332,710 discloses the preparation of a catalyst for vinyl acetate production where the insoluble noble metal salts are precipitated onto the support particles by agitating these in a rotating drum for at least half an hour during the precipitation by means of alkalis.
THE INVENTION
It has now surprisingly been found that the addition of boron or boron compounds improves the selectivity of the catalyst, with, in particular, the formation of high-boilers being significantly reduced. High-boilers are, in particular, the compounds mentioned in the introduction.
The invention provides a catalyst for preparing vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases with, at the same time, low high-boiler formation, which catalyst comprises palladium and/or its compounds, gold and/or its compounds and alkali metal compounds on a particulate support, wherein the catalyst further comprises boron or boron compounds.
In a preferred embodiment, the catalyst is prepared by insoluble compounds by means of an alkaline solution; means of a reducing agent in the liquid phase;
The invention also relates to a process for preparing vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases while at the same time, there is a low boiler formation over a catalyst as defined above.
The invention accordingly provides, on the one hand, a process for preparing a catalyst for the production of vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases with, at the same time, low high-boiler formation, which catalyst comprises palladium and/or its compounds, gold and/or its compounds and alkali metal compounds on a particulate support, where the catalyst is prepared by insoluble compounds by means of an alkaline solution; means of a reducing agent in the liquid phase; final drying.
On the other hand, the invention provides a process for preparing vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases with, at the same time, low high-boiler formation over the catalyst of the invention.
The boron content of the catalyst is preferably from 0.01 to 1 % by weight, in particular from 0.01 to 0.2% by weight. The boron is applied to the support in the form of its compounds, preferably in the form of borates. The application can be carried out in the abovementioned step a) together with the soluble palladium and gold compounds, in step b) together with the alkaline solution, or using a borate solution as alkal
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Abel Roland
Hopf Erich
Kiemel Rainer
Nicolau Ioan
Celanese GmbH
Deemie Robert W.
Geist Gary
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