Process for increasing the selectivity of the hydrogenation of 4,4′-diaminodiphenylmethane to 4,4′-diaminodicyclohexylmethane in the presence of an N-alkyl-4,4′-diaminodiphenylmethane
The invention relates to a process for increasing the selectivity of the hydrogenation of 4,4′-diaminodiphenylmethane (4,4′-MDA) to diaminodicyclohexylmethane (4,4′-HMDA) by catalytic hydrogenation of a mixture containing 4,4′-MDA as the main component and its mono-N-methyl derivative as a secondary component. According to the invention, the hydrogenation is terminated before a conversion of 4,4′-MDA to 4,4′-HMDA of 99% is achieved. Under these conditions, a substantially smaller proportion of the N-methyl-4,4′-MDA is hydrogenated to N-methyl-4,4-HMDA.
1. A process for the production of 4,4′-diaminodicyclohexylmethane (4,4′-HMDA) by catalytic hydrogenation of a mixture comprising 4,4′-diaminodiphenylmethane (4,4′-MDA) as the main component and a mono-N-methyl derivative thereof as a secondary component with increased selectivity with regard to the hydrogenation of 4,4′-MDA in the presence of a heterogeneous hydrogenation catalyst at a temperature in the range of 50 to 220° C. and a hydrogen pressure in the range of 1 to 30 MPa,
wherein
the hydrogenation is terminated before a conversion of 4,4′-MDA to 4,4′-HMDA of 99% is achieved.
2. The process according to claim 1 ,
wherein
a crude MDA, comprising at least 70 wt. % 4,4′-diaminodiphenylmethane and 0.01 to 2 wt. % N-methyl-4,4′-diaminodiphenylmethane, is used as said mixture.
3. The process according to claim 2 ,
wherein
said mixture comprises 75–99 wt. % 4,4′-MDA, 1–11 wt. % 2,4′-MDA, less than 2 wt. % 2,2′-MDA and up to 1 wt. % N-methyl-4,4′-MDA.
4. The process according to claim 1 ,
wherein
the hydrogenation of 4,4′-diaminodiphenylmethane to 4,4′-diaminodicyclohexylmethane is terminated at a conversion in the range of 90% to 98.9%.
5. The process according to claim 1 , wherein the hydrogenation is performed at a temperature in the range of 90 to 150° C. and a pressure in the range of 5 to 15 MPa.
6. The process according to claim 1 , wherein an Ru-supported catalyst with an Ru content of 0.5 to 10 wt. % is used.
7. The process according to claim 6 , wherein an Ru-aluminium oxide or Ru-titanium dioxide supported catalyst is used as the Ru supported catalyst, the support having a BET surface area of less than 70 m 2 /g.
8. The process according to claim 1 , wherein the catalytic hydrogenation is performed in the presence of a solvent from the series of the ethers.
9. The process according to claim 1 , wherein the catalytic hydrogenation is performed in a continuous operating method in a fixed bed reactor packed with an Ru supported catalyst, wherein the reactor is operated by a trickle-bed method.
10. The process according to claim 8 , wherein the catalytic hydrogenation is performed in a continuous operating method in a fixed bed reactor packed with an Ru supported catalyst, wherein the reactor is operated by a trickle-bed method.