Process for producing a supported silver catalyst

1. A process for producing a supported silver catalyst, which comprises

(a) reacting oxalic acid with an alkali metal base in a solvent to the second equivalence point of oxalic acid to give alkali metal oxalate;

(b) reacting the alkali metal oxalate obtained according to (a) with a silver salt in a solvent to give silver oxalate;

(c) forming a complex of the silver oxalate obtained according to (b) with a diamine compound in a solvent to give a diamine-silver oxalate complex.

2. The process according to claim 1 , wherein the alkali metal base used in (a) is an alkali metal hydroxide, and wherein the silver salt used in (b) is silver nitrate.

3. The process according to claim 1 , wherein (a) comprises:

(a1) reacting oxalic acid with up to 98.5% of the equimolar amount based on oxalic acid of alkali metal base in aqueous solution;

(a2) bringing the aqueous solution obtained according to (a1) to a temperature in the range from 40 to 50° C.;

(a3) adding alkali metal base to the heated aqueous solution according to (a2) to the second equivalence point of oxalic acid, with the aqueous solution being maintained at a temperature in the range from 40 to 50° C. during the addition.

4. The process according to claim 3 , wherein (b) comprises:

(b1) adding the aqueous solution obtained according to (a3) to an aqueous solution of the silver salt having a temperature in the range from 40 to 50° C. to give a suspension comprising the silver oxalate;

(b2) separating the silver oxalate from the suspension and washing of the silver oxalate which has been separated off with deionized water as washing water until the washings have an electrical conductivity of not more than 60 microsiemens/cm;

(b3) concentrating the silver oxalate.

5. The process according to claim 1 , wherein the diamine compound used in (c) is an alkylene diamine having from 2 to 5 carbon atoms.

6. The process according to claim 1 , wherein the temperature in the reaction mixture present in the reaction according to (c) is set to values in the range from 10 to 30° C.

7. The process according to claim 1 , wherein the solution obtained according to (c) has a silver content, calculated as elemental silver, in the range from 25 to 32% by weight, based on the total weight of the solution.

8. The process according to claim 1 , which additionally comprises

(d) adding at least one promoter to the solution obtained according to (c).

9. The process according to claim 8 , wherein lithium, cesium, tungsten, rhenium and sulfur are added as promoters and the solution obtained according to (d) has a lithium content in the range from 50 to 700 ppm by weight, a cesium content in the range from 50 to 1500 ppm by weight, a tungsten content in the range from 10 to 800 ppm by weight, a rhenium content in the range from 50 to 1200 ppm by weight and a sulfur content in the range from 2 to 100 ppm by weight.

10. The process according to claim 1 , which additionally comprises

(e) providing a porous support material which preferably comprises alpha-aluminum oxide;

impregnating the porous support material with the solution obtained according to (c) or (d).

11. The process according to claim 10 , wherein the porous support material has a cylindrical geometry.

12. The process according to claim 10 , which additionally comprises

(g) calcining the impregnated support material obtained according to (f).

13. The process according to claim 1 , which comprises

(a) reacting oxalic acid with an alkali metal base in a solvent to the second equivalence point of oxalic acid to give alkali metal oxalate;

(b) reacting the alkali metal oxalate obtained according to (a) with a silver salt in a solvent to give silver oxalate;

(c) forming a complex of the silver oxalate obtained according to (b) with a diamine compound in a solvent to give a diamine-silver oxalate complex;

and which additionally comprises

(d) adding at least one promoter to the solution obtained according to (c);

(e) providing a porous support material;

impregnating the porous support material with the solution obtained according to (c) or (d);

(g) calcining the impregnated support material obtained according to (f).

14. The process according to claim 1 , which comprises

(a) reacting oxalic acid with an alkali metal base in a solvent to the second equivalence point of oxalic acid to give alkali metal oxalate;

(b) reacting the alkali metal oxalate obtained according to (a) with a silver salt in a solvent to give silver oxalate;

(c) forming a complex of the silver oxalate obtained according to (b) with a diamine compound in a solvent to give a diamine-silver oxalate complex;

and which additionally comprises

(d) adding at least one promoter to the solution obtained according to (c);

(e) providing a porous support material;

(f) impregnating the porous support material with the solution obtained according to (c) or (d);

(g) calcining the impregnated support material obtained according to (f);

wherein (a) comprises:

(a1) reacting oxalic acid with up to 98.5% of the equimolar amount based on oxalic acid of alkali metal base in aqueous solution;

(a2) bringing the aqueous solution obtained according to (a1) to a temperature in the range from 40 to 50° C.;

(a3) adding alkali metal base to the heated aqueous solution according to (a2) to the second equivalence point of oxalic acid, with the aqueous solution being maintained at a temperature in the range from 40 to 50° C. during the addition;

and wherein (b) comprises:

(b1) adding the aqueous solution obtained according to (a3) to an aqueous solution of the silver salt having a temperature in the range from 40 to 50° C. to give a suspension comprising the silver oxalate;

(b2) separating the silver oxalate from the suspension and washing of the silver oxalate which has been separated off with deionized water as washing water until the washings have an electrical conductivity of not more than 60 microsiemens/cm;

(b3) concentrating the silver oxalate, preferably to a residual moisture content of the silver oxalate in the range from 10 to 25% by weight, based on silver oxalate.

15. The process according to claim 1 , which comprises

(a) reacting oxalic acid with an alkali metal base in water to the second equivalence point of oxalic acid to give alkali metal oxalate;

(b) reacting the alkali metal oxalate obtained according to (a) with a silver salt in water to give silver oxalate;

(c) forming a complex of the silver oxalate obtained according to (b) with a diamine compound in water to give a diamine-silver oxalate complex;

and which additionally comprises

(d) adding at least one promoter to the solution obtained according to (c);

(e) providing a porous support material which comprises at least 98% by weight of alpha-aluminum oxide;

(f) impregnating the porous support material with the solution obtained according to (c) or (d);

(g) calcining the impregnated support material obtained according to (f), at a temperature in the range from 270 to 295° C.;

wherein (a) comprises:

(a1) reacting oxalic acid with from 90 to 98.5%, of the equimolar amount based on oxalic acid of alkali metal base in aqueous solution;

(a2) bringing the aqueous solution obtained according to (a1) to a temperature in the range from 40 to 45° C.;

(a3) adding alkali metal base to the heated aqueous solution according to (a2) to the second equivalence point of oxalic acid, with the aqueous solution being maintained at a temperature in the range from 40 to 45° C., during the addition;

and wherein (b) comprises:

(b1) adding the aqueous solution obtained according to (a3) to an aqueous solution of the silver salt having a temperature in the range from 40 to 45° C., to give a suspension comprising the silver oxalate;

(b2) separating the silver oxalate from the suspension and washing of the silver oxalate which has been separated off with deionized water as washing water until the washings have an electrical conductivity of not more than 60 microsiemens/cm;

(b3) concentrating the silver oxalate to a residual moisture content of the silver oxalate in the range from 10 to 25% by weight, based on silver oxalate.

16. The process according to claim 1 , wherein the diamine compound used in (c) is ethylene diamine.