Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Patent
1997-12-16
1999-12-07
Shippen, Michael L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
502170, 502328, C07C 6705
Patent
active
05998659&
DESCRIPTION:
BRIEF SUMMARY
It is known that ethylene can be reacted in the gas phase with acetic acid and oxygen or oxygen-containing gases over fixed-bed catalysts containing palladium/cadmium/alkali metal to give vinyl acetate. In this process, a space-time yield of more than 200 g/l.h is obtained (U.S. Pat. No. 3 939 199, U.S. Pat. No. 4 668 819, U.S. Pat. No. 4 902 823, EP-A-0 403 950, U.S. Pat. No. 5 225 388, EP-A-0 565 952, EP-A-0 634 208, EP-A-0 634 209, EP-A-0 634 214).
It has now surprisingly been found that such catalysts are considerably improved by addition of at least one rhenium and/or at least one zirconium compound, i.e. they give a higher space-time yield at the same or higher selectivity of the vinyl acetate synthesis and are more slowly deactivated.
The invention accordingly provides a process for preparing vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases over a catalyst comprising palladium and/or its compounds, cadmium compounds and alkali metal compounds on a support, wherein the catalyst additionally contains at least one rhenium and/or at least one zirconium compound.
The invention further provides a catalyst comprising palladium and/or its compounds, cadmium compounds and alkali metal compounds on a support, wherein the catalyst additionally contains at least one rhenium and/or at least one zirconium compound.
Suitable supports are the known inert support materials such as silica, aluminum oxide, aluminosilicates, silicates, titanium oxide, zirconium oxide, titanates, silicon carbide and carbon. Particularly suitable are supports of this type having a specific surface area of from 40 to 350 m.sup.2 /g (measured by the BET method) and a mean pore radius of from 50 to 2000 .ANG. (measured using mercury porosimetry), especially silicas (SiO.sub.2) and SiO.sub.2 /Al.sub.2 O.sub.3 mixtures. These supports are used in the form of spheres, pellets, rings, stars or particles of another shape whose diameter or length and thickness is generally from 3 to 9 mm.
The total pore volume of the support is preferably 0.4-1.2 ml/g, and less than 10% of this volume should be formed by "micropores" having a pore diameter of below 30 .ANG. (Angstrom). Such supports can be prepared from aerogenic SiO.sub.2 or an aerogenic SiO.sub.2 /Al.sub.2 O.sub.3 mixture which is in the form of vitreous microspheres which can be prepared, for example, by flame hydrolysis of silicon tetrachloride or a silicon tetrachloride/aluminum trichloride mixture in a hydrogen/oxygen flame (U.S. Pat. No. 3 939 199). These microspheres are commercially available under the names .RTM.Aerosil or .RTM.Cabosil.
Particular preference is given to the use of a support comprising Sio.sub.2 or a SiO.sub.2 /Al.sub.2 O.sub.3 mixture having a surface area of 50-250 m.sup.2 /g and a pore volume of 0.4-1.2 ml/g and pressed from such microspheres using organic fillers (EP-A-0 403 950). The particles of this support have a particle size of from 4 to 9 mm, with from 5 to 20% of the pore volume of the support being formed by pores having radii of from 200 to 3000 .ANG. and from 50 to 90% of the pore volume being formed by pores having radii of from 70 to 100 .ANG.. It is particularly advantageous if these support particles are prepared from the microspheres by tabletting or extrusion with addition of one or more C.sub.2 -C.sub.20 -carboxylates of Li, Mg, Al, Zn, Fe or Mn as binders and with addition of organic fillers (such as sugar, urea, higher fatty acids, relatively long chain paraffins, microcrystalline cellulose) and lubricants (such as kaolin, graphite, metal soaps) (U.S. Pat. No. 5 225 388). The particles are subsequently ignited in O.sub.2 -containing gases at about 500-900.degree. C. for about 0.25-5 hours.
The catalytically active substances can be applied to the support in a customary manner, for example by single or multiple impregnation of the support with a solution of the active substances, subsequent drying and, if desired, reduction. However, the active substances can also be applied to the support by, for exam
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Celanese GmbH
Shippen Michael L.
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