Process for the preparation of toluenediamine
Toluenediamine is produced and separated from by-products of the reaction by: a) hydrogenating dinitrotoluene in the presence of a catalyst, b) separating the catalyst, water and optionally solvent from the hydrogenation reaction mixture to give crude toluenediamine, and c) separating by distillation the crude toluenediamine in a separating wall column into at least four product streams P 1 , P 2 , P 3 and P 4 . The product stream P 1 is a stream containing low boilers. The product stream P 2 is a stream containing o-toluenediamine. The product stream P 3 is a stream containing m-toluenediamine. The product stream P 4 is a stream containing high boilers and m-toluenediamine.
1. A process for the preparation of m-toluenediamine comprising:
a) hydrogenating dinitrotoluene in the presence of a catalyst,
b) separating the catalyst, water and optionally solvent from the product of a) to obtain crude toluenediamine, and
c) distilling the crude toluenediamine in a distillation column having a separating wall to separate the crude toluenediamine into at least four product streams P 1 , P 2 , P 3 and P 4 wherein
(i) the product stream P 1 comprises low boilers,
(ii) the product stream P 2 comprises o-toluenediamine,
(iii) the product stream P 3 comprises m-toluenediamine, and
(iv) the product stream P 4 comprises high boilers and m-toluenediamine.
2. The process of claim 1 in which the crude toluenediamine is introduced into the distillation column in a region near the separating wall.
3. The process of claim 1 in which the crude toluenediamine is introduced into the distillation column from above the separating wall for preliminary separation of the crude toluenediamine.
4. The process of claim 1 in which the crude toluenediamine is introduced into the distillation column at a side of the separating wall.
5. The process of claim 4 in which the crude toluenediamine is introduced into a separating segment of the distillation column with the separating segment having (a) an upper edge which is below the separating wall's upper edge by a distance which is at least 10% of the total height of the separating wall and (b) a lower edge which is above the separating wall's lower edge by a distance which is at least 10% of the total height of the separating wall.
6. The process of claim 1 in which the stream P 4 is withdrawn from the distillation column's bottom.
7. The process of claim 1 in which the stream P 3 is withdrawn from the distillation column in a region of the separating wall.
8. The process of claim 1 in which the product stream P 2 withdrawn from the distillation column as a side stream.
9. The process of claim 1 in which a vapor stream withdrawn from the top of the distillation column is condensed, and one portion of this condensate is withdrawn as the product stream P 2 and another portion of this condensate is introduced into the distillation column as reflux.
10. The process of claim 9 in which only a portion of the vapor stream is condensed.
11. The process of claim 1 in which the product stream P 4 is withdrawn from the distillation column's bottom and further treated to remove m-toluenediamine.
12. The process of claim 11 in which the m-toluenediamine is removed from stream P 4 by evaporation in a kneader dryer.
13. The process of claim 11 in which withdrawn product stream P 4 is introduced into a second distillation column at its top and at least a portion of product stream P 2 is introduced into the second distillation column at a point below that where the product stream P 4 is introduced, and a stream S is withdrawn from the second distillation column and recycled into the distillation column with the separating.
14. A process for the production of m-toluene diisocyanate comprising phosgenating m-toluenediamine prepared by the process of claim 1 .