DE1206400B - Process for the production of zinc or cadmium catalysts on porous carriers - Google Patents

Description

Process for the production of zinc or cadmium catalysts porous supports It is known in the vinyl ester synthesis from a carboxylic acid and acetylene catalysts to be used by applying aqueous solutions of zinc or cadmium salts on porous carriers such as activated carbon, activated aluminum oxide or silica gel. It is used as the active catalyst component expediently the zinc or cadmium salt of the carboxylic acid, the vinyl ester of which is produced shall be. The zinc resp.

The cadmium content of the catalyst should be between 8 and 15 percent by weight lie. In the production of these catalysts, it is very difficult to to achieve such a high zinc or cadmium content on the carrier, since the zinc or cadmium salts of carboxylic acids with increasing carbon number in water always become less soluble. One has therefore the catalysts necessary for the production of vinyl esters whose carboxylic acid radicals have more than 2 carbon atoms are to be used contain, made in such a way that they can be found relatively well in water soluble zinc or cadmium salts of e.g. formic acid or acetic acid, the Carrier impregnated with the optionally hot solution, the catalyst treated in this way dried and then the formic or acetic acid with the carboxylic acid to be vinylated or their anhydride.

This way of working is very time consuming. In addition, part of the Zinc or cadmium also removed from the carrier.

It is also known that catalysts are used for the production of vinyl ester can be produced in the vapor phase by adding a zinc salt to activated carbon in the fluidized bed at temperatures above the sublimation point and below the melting point of the zinc salt. This procedure allows one To apply a high proportion of active catalyst substance to the support, it is but expensive, especially if not in the production of vinyl esters to work according to a fluidized bed process.

It has now been found that zinc or cadmium catalysts are suitable porous supports for the conversion of acetylene with carboxylic acids to vinyl esters in The vapor phase can be produced very easily if you combine porous supports with aqueous-ammoniacal Zinc or cadmium salt solutions of carboxylic acids with 2 to 10 carbon atoms soak and then, optionally under reduced pressure, at temperatures up to dries around 1500 C.

It is surprising that the catalysts prepared in this way with the same Zinc or cadmium content have a much higher activity than before usual. The new catalysts are sufficient to achieve the same activity significantly lower zinc or cadmium concentrations than those used since then. For example, a zinc content of only 7 percent by weight is sufficient for the new catalysts, in order to achieve the same activity that was previously achieved with a catalyst of the 12th Contains percent by weight, has been achieved.

The zinc or cadmium salt solutions can be used in different ways produce. One can e.g.

Zinc oxide in 1 to 2 times the stoichiometric amount of the carboxylic acids Dissolve and for this purpose the 1 to 3 times stoichiometric for the expansion of the diamine salts Add amount of aqueous ammonia.

After adding the ammonia, a clear solution is obtained very quickly, with which then the porous carrier such as aluminum oxide, pumice stone or silica gel, preferably Activated charcoal. But you can also use zinc oxide in an aqueous-ammoniacal one Dissolve the solution of the ammonium salts of the carboxylic acids.

The carboxylic acids that can be used are those that are evaporation do not decompose. So can carboxylic acids with 2 to 10 carbon atoms z. B. aliphatic carboxylic acids such as acetic, propionic, butyric, valeric or capric acid, use.

In contrast to the previously known catalysts, in which the Zinc or cadmium content made up a maximum of about 15 percent by weight, it is after the process according to the invention now very easily possible, catalysts with zinc respectively.

Produce cadmium contents up to about 25 percent by weight. Preferred Zinc and cadmium contents are between about 6 and 20 percent by weight.

The parts given in the examples are parts by weight.

Example 1 190 parts of zinc oxide are added to 285 parts with heating Acetic acid neutralized. The crystal slurry that forms is 600 parts of 200 / above aqueous ammonia and stirred well until everything has gone into solution. 1000 parts of activated carbon preheated to 800 ° C. are impregnated with this solution. Man centrifuged off and dried the filter residue for several hours at 1000 C im Vacuum.

The catalyst contains 16 percent by weight zinc.

Example 2 To a solution of 64 parts of propionic acid and 50 parts 90 parts of 200 / above aqueous ammonia are added to water with thorough stirring. The solution should not boil and should be alkaline after the addition of ammonia has ended react. 32 parts of zinc oxide are added to the hot solution thus obtained and the mixture is stirred about 5 minutes vigorously. The zinc salt solution thus prepared is to 230 parts Activated charcoal, which has been heated beforehand, is applied and, as described in Example 1, treated further. The catalyst contains 12 percent by weight zinc.

Example 3 In a solution of 400 parts of propionic acid and 100 parts 150 parts of cadmium oxide are added to water and the mixture is boiled. Man slowly allows 500 parts of 200% aqueous ammonia to flow in and cooks again about 10 minutes.

The small amount of undissolved residue is then filtered off and 1150 parts of activated charcoal are added to the clear, pale yellow solution. One works, as indicated in Example 1 on. The catalyst prepared in this way contains 11.5 percent by weight Cadmium.

Example 4 346 parts of valeric acid and 25 parts of water become slow 48 parts of 200 / above aqueous ammonia are added. After adding 13.8 parts Zinc oxide is heated for a short time while stirring well until everything is dissolved. The clear one 100 parts of activated charcoal are added to the solution and the catalyst, as in the example 1 described, worked up. A catalyst is obtained which is 12 percent by weight Contains zinc.

Claims (1)

Claim: Process for the production of zinc or cadmium catalysts on porous supports for the conversion of acetylene with carboxylic acids to vinyl esters in the vapor phase, characterized in that one porous carrier with aqueous-ammoniacal Zinc or cadmium salt solutions of carboxylic acids with 2 to 10 carbon atoms soak and then, optionally under reduced pressure, at temperatures up to dries around 1500 C. Documents considered: German Auslegeschrift No. 1134 983.