DE2751767A1 - Treatment of silver catalysts for ethylene oxide prodn. - by impregnating with soln. contg. heavy alkali metal and nitrogen cpd. - Google Patents

Abstract

A catalyst for ethylene oxide prodn. is prepd. by gas-phase reaction of ethylene with O2. The catalyst comprises a support, 2-12% Ag, and (based on Ag) 0.05-0.35 atom % K, 0.003-0.25 atom % Rb, 0.0005-0.2 atom % Cs or an equiv. amt. of a mixt. of these alkali metals. The process comprises impregnating the Ag-contg. support (opt. also contg. Na and/or Li) with a soln. (pref. alcoholic) contg. a cpd. of K, Rb and/or Cs and an amine and/or ammonia. The presence of an amine and/or ammonia in the impregnation soln. improves the selectively of the catalyst. The process is applicable to fresh catalysts rather than used or thermally stabilised catalysts.

Description

Process for the preparation of an xethylene oxide catalyst

The invention relates to an improved catalyst for manufacture of ethylene oxide, the finely divided silver on a porous support and as a further Components sodium and / or lithium as well as potassium and / or rubidium and / or cesium (heavy alkali metals ") contains and in which on the carrier initially silver and optionally sodium or lithium applied in the form of the relevant salts and heated in the usual way ("activated") and in a subsequent treatment a salt of a heavy alkali metal together with an amine and / or ammonia is applied. The term "heavy alkali metal" refers to the elements potassium, rubidium and cesium.

It is known that after treating a used old Silver catalyst (DT-AS 25 19 599) or one by thermal treatment stabilized silver catalyst (US-PS 40 33 903) with in particular rubidium or Cesium the selectivity of a catalyst for the formation of ethylene oxide from ethylene and oxygen can be improved. The follow-up treatment should be done by a silver catalyst that was used for a time for the synthesis of ethylene oxide and which has formed or stabilized in the process in the synthesis reactor with a solution of one of the heavy alkali metals in a polar organic solvent - e.g. methanol was suggested - impregnated. To improve solubility of the alkali salt, the solvent can contain up to about 10% water.

Treating an unused or unstabilized silver catalyst in this way, almost no improvement in selectivity is achieved or only an improvement in selectivity that is less than that obtained with the use of a previously used or stabilized catalyst is obtained (see comparative example 1). Improving the catalyst selectivity is an object of the invention solves: It has been found that one compared to the previously known Aftertreatment process receives improved catalyst in terms of selectivity, if the after-treatment is carried out with a solution containing a salt of a heavy one Alkali metal, i.

Potassium, but especially rubidium and / or cesium, a polar organic Solvent, in particular an alcohol with 1 to 4 carbon atoms, optionally one contains a small amount of water and, according to the invention, an amine and / or ammonia.

The solution according to the invention can then also be used as a catalyst produce with excellent selectivity if you have an unused catalyst, i.e. treated a catalyst precursor with it. The post-treatment step must therefore also do not take place in the synthesis reactor, but the production of the silver catalyst can including aftertreatment in a conventional for the production of supported catalysts suitable apparatus. Such apparatus and their uses are e.g. in Ullmann's Encyclopedia of Industrial Chemistry, 3rd ed. Vol. 13, p. 517 ff described.

Under the term "used" or "unused but not post-treated" Catalyst should be understood in the following a catalyst based on a commercially available Carrier (e.g.

Aluminum oxide, silica or a silicate) e.g. 2 to 12, in particular 5 to 10 percent by weight silver and, based on the silver content, optionally Contains up to 2 atom% sodium or lithium or mixtures thereof and optionally from a previous treatment still small (less than about 0.1 atom%) amounts of heavy alkali metals.

The improvement achievable according to the invention is achieved independently whether the catalyst to be treated contains sodium or lithium or not, however, it is particularly advantageous if the catalyst present after the aftertreatment about (based in each case on silver) 0.1 to 2 atom% sodium and / or lithium as well either 0.05 to 0.35 atomic percent potassium, 0.003 to 0.25 atom-70 rubidium or 0.0005 to 0.2 atomic cesium or a mixture of the last-mentioned alkali metals contains in the appropriate amount.

To produce solutions that can be used according to the invention, i.a.

the concentration of "heavy" alkali metals chosen such that after soaking up some of the solution in the catalyst and removing it of the non-absorbed part, the effective amount of alkali metals according to the invention on the catalytic converter.

Amines in the context of the invention are preferably aliphatic Amines, i.e. mono-, di- or trialkylamines, alkanolamines and polyvalent amines such as the alkylenediamines, piperazines and the like are used; they are e.g. in a crowd of up to 30 vol. «, based on the solution intended for post-treatment, used. An amount of 0.1 to 10 vol. Is favorable.

The conversion of the treated catalyst or precursor into the active form takes place as usual by heating, optionally in the presence of the usual gaseous reaction mixture of ethylene and oxygen.

Example 1 139 g of silver nitrate are added in a mixture of 120 g of sec-butylamine and 4 g dissolved in an aqueous solution of 0.57 g lithium and 0.38 g sodium nitrate. The solution is made up to a volume that corresponds to the liquid absorbency of the intended carrier. With the prepared solution 1 kg of aluminum oxide become impregnated in spherical shape (carrier from NORTON, Akron, U.S.A., type SA 5551). The catalyst precursor obtained is after storage for one day at room temperature dried in a convection oven at 220 ° C. and the silver deposited on the carrier. The catalyst contains 8.0 weight percent silver, 0.55 atomic percent sodium and 1.0 Atom% lithium. The catalyst is given the designation A.

10 ml of crushed catalyst A are in a test reactor with Built-in 5 mm inside diameter and consisting of 30 Nl / h of a gas mixture at 15 bar pressure from 28% ethylene, 8% oxygen, 2 ppm vinyl chloride (remainder nitrogen) through the Catalyst sent. The temperature is regulated so that a 50% oxygen conversion is achieved. Having reached a constant level of activity after a few days is, the experiment is interrupted and the catalyst in the reactor at room temperature with a methanolic solution of 400 ppm CsN03, 5 fi sec-butylamine and 0.5% Water soaked. After one hour of exposure, the excess solution is drained off and by passing nitrogen through and heating the reactor, the catalyst dried. The catalyst treated in this way is given the designation B. With the one previously The gas mixture used is an activity and selectivity test at 50% O2 conversion carried out. The result is shown in the table.

Example 2 100 ml of catalyst A are mixed with a methanolic solution, which contains 350 ppm CsOH and 2% concentrated aqueous ammonia, impregnated and then dried at 220 ° C. in a convection oven.

The catalyst obtained (designation C) is the activity and Subject to selectivity test (table).

Example 3 The procedure described above is repeated; the impregnation solution contains 330 ppm Cs2CO3, 2% xthylenediamine, 1% concentrated aqueous ammonia in methanol; the catalyst is identified with the letter D. The result of the performance test can be found in the table.

Comparative Example 1 The production takes place as in Example 1, however, there is no sec-butylamine in the impregnation solution. Catalyst M, table.

Comparative Example 2 The production takes place as in Example 2, but the ammonia is missing in the impregnation solution. Catalyst N, table.

Table of catalyst comparison temperature + selectivity + oC B 221 81.5 C 217 80.5 D 218 80.5 M (comparison) 223 78.5 N (comparison) 218 77.5 A (comparison) 217 76.5 with 50% oxygen conversion

Claims (2)

Claims 1. A method for producing a catalyst for Production of ethylene oxide by reacting ethylene oxide and oxygen in the Gas phase containing about 2 to 12% elemental silver and alkali metals on a carrier or their compounds, where at least one of the alkali metals potassium, Rubidium or cesium applies to the catalyst support in such a way that the already containing silver in reduced form and optionally sodium and / or lithium Catalyst with a preferably alcoholic solution of a compound of potassium, Treated rubidium and / or cesium, and the solution used in such an amount as that the solution absorbed by the catalyst contains an amount of (based on silver) 0.05 to 0.35 atomic percent potassium, 0.003 to 0.25 atomic percent rubidium, or 0.0005 to 0.2 Atom% corresponds to cesium or corresponding amounts of a mixture of these alkali metals and, where appropriate, amounts of the alkali metals already present on the catalyst be taken into account, characterized in that a solution is used that also contains an amine and / or ammonia. 2. The method according to claim 1, characterized in that as Alumina catalyst support used.