Process for catalytic hydrogenation of halonitroaromatics
The present invention generally relates to processes for the catalytic hydrogenation of halonitroaromatics. In particular, the present invention includes processes for the catalytic hydrogenation of halonitroaromatics such as 2,5-dicloronitrobenzene to 2,5-dichloroaniline over a platinum-containing catalyst. The present invention also relates to processes for producing 3,6-dichloro-2-methoxybenzoic acid.
1. A process for preparing a haloaminoaromatic compound, the process comprising:
feeding hydrogen and a feed mixture comprising a halonitroaromatic compound to a hydrogenation zone; and
reacting the halonitroaromatic compound with hydrogen in the presence of a hydrogenation catalyst comprising a noble metal on a support to produce a reaction product comprising the haloaminoaromatic compound, wherein the hydrogenation catalyst has been calcined at a temperature of at least about 500° C.;
wherein the process further comprises one or more of the following features:
(1) the feed mixture further comprises a solvent comprising an acid; and/or
(2) the support having noble metal thereon that is calcined comprises unreduced noble metal prepared by depositing the noble metal onto the support without use of a reducing agent.
2. The process of claim 1 , wherein the acid comprises an organic acid selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, citric acid, and mixtures thereof.
3. The process of claim 1 , wherein the acid comprises acetic acid.
4. The process of claim 3 , wherein the halonitroaromatic compound comprises a halonitrobenzene and the haloaminoaromatic compound comprises a haloaniline and the process further comprising cooling the reaction product to a temperature of about 15° C. or less.
5. The process of claim 4 , wherein the reaction product is cooled to a temperature between about 0° C. and about 15° C.
6. The process of claim 1 , wherein the hydrogenation catalyst has been calcined at a temperature of at least about 700° C.
7. The process of claim 1 , wherein the hydrogenation catalyst has been calcined at a temperature of from about 500° C. to about 1000° C.
8. The process of claim 1 , wherein the hydrogenation catalyst has been calcined at a temperature of from about 700° C. to about 950° C.
9. The process of claim 1 , wherein the noble metal comprises platinum, palladium, or combinations thereof.
10. The process of claim 9 , wherein the noble metal comprises platinum.
11. The process of claim 10 , wherein the support comprises carbon.
12. The process of claim 11 , wherein the hydrogenation catalyst has a platinum loading that is no greater than about 5 wt. % of the total catalyst weight.
13. The process of claim 11 , wherein the hydrogenation catalyst has a platinum loading that is from about 0.1 wt. % to about 5 wt. %, of the total catalyst weight.
14. The process of claim 1 , wherein the solvent further comprises water.
15. The process of claim 1 , wherein the feed mixture is free or essentially free of additives that function as dehalogenation suppressors.
16. The process of claim 1 , wherein the feed mixture is free or essentially free of hydroxides or oxides of magnesium, cycloaliphatic amines, and acidic phosphorous compounds.
17. The process of claim 1 , wherein the hydrogenation catalyst is essentially free or free of metal catalyst modifiers.
18. The process of claim 1 , wherein the hydrogenation catalyst is an unmodified hydrogenation catalyst.
19. The process of claim 1 , wherein the hydrogenation reaction is conducted at a temperature that is from about 20° C. to about 100° C.
20. The process of claim 11 , wherein the hydrogenation catalyst comprises platinum metal particles of a size up to 10 nm in their largest dimension and no more than about 50% (number basis) of the platinum metal particles are less than 2 nm in their largest dimension.