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 producing 2,5-dichloroaniline, the process comprising:
feeding hydrogen and a feed mixture comprising 2,5-dichloronitrobenzene to a hydrogenation zone; and
reacting the 2,5-dichloronitrobenzene with hydrogen in the presence of a heterogeneous hydrogenation catalyst comprising platinum on a support to produce a reaction product comprising 2,5-dichloroaniline, wherein the hydrogenation catalyst has been calcined at a temperature of at least about 500° C.
2. The process of claim 1 wherein the hydrogenation catalyst has been calcined at a temperature of at least about 700° C.
3. The process of claim 1 wherein the hydrogenation catalyst has been calcined at a temperature of from about 500° C. to about 1000° C.
4. The process of claim 1 wherein the hydrogenation catalyst has been calcined at a temperature of from about 700° C. to about 950° C.
5. The process of claim 1 wherein the hydrogenation catalyst has a platinum loading that is no greater than about 5 wt. % of the total catalyst weight.
6. The process of claim 1 wherein the hydrogenation catalyst has a platinum loading that is no greater than about 3 wt. % of the total catalyst weight.
7. The process of claim 1 wherein the hydrogenation catalyst has a platinum loading that is from about 0.1 wt. % to about 5 wt. %, of the total catalyst weight.
8. The process of claim 1 wherein the feed mixture further comprises a solvent.
9. The process of claim 8 wherein the solvent comprises an alcohol.
10. The process of claim 9 wherein the alcohol is selected from the group consisting of methanol, ethanol, propanol, isopropanol, 1-butanol, 2-butanol, t-butanol, and mixtures thereof.
11. The process of claim 8 wherein the solvent comprises water.
12. The process of claim 1 wherein the feed mixture is free or essentially free of additives that function as dehalogenation suppressors.
13. 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.
14. The process of claim 1 wherein the hydrogenation catalyst is essentially free or free of metal catalyst modifiers.
15. The process of claim 1 wherein the reaction product further comprises 2-chloroaniline and 3-chloroaniline.
16. The process of claim 1 wherein the hydrogenation reaction is conducted at a temperature that is from about 20° C. to about 100° C.
17. The process of claim 1 wherein the yield of 2,5-dichloroaniline is at least about 90%.
18. The process of claim 1 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.
19. The process of claim 8 , wherein the solvent comprises an acid.
20. The process of claim 19 , 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.
21. The process of claim 1 , wherein the support having platinum thereon that is calcined comprises unreduced platinum prepared by depositing the platinum onto the support without use of a reducing agent.