Ring hydrogenation of aromatic amines using Group 6 and Group 8 metals carried on a support is well known. Two aspects in the hydrogenation process are problematic. First, contaminants in the aromatic amine substrate can poison the catalyst thus impacting catalyst activity and catalyst life. Second, catalyst attrition can occur thereby resulting in catalyst loss and plugging of catalyst filtration equipment.
Representative patents which illustrate various processes for the hydrogenation of aromatic amines, including methylenedianiline are as follows:
U.S. Pat. Nos. 2,606,925 and 2,606,927 disclose the hydrogenation of nitroaromatics and aromatic amines. The '925 patent shows the use of ruthenium oxide as a catalyst whereas the '927 discloses the use of cobalt on alumina.
U.S. Pat. Nos. 3,636,108 and 3,697,449 disclose the hydrogenation of aromatic compounds, and particularly 4,4′-methylenedianiline, to produce a product referred to as PACM, using an alkali metal-moderated ruthenium catalyst. The catalyst is formed by depositing a ruthenium compound on a support from an aqueous solution of sodium or potassium bicarbonate, hydroxide, or the like. A wide variety of carriers such as calcium carbonate, rare earth oxides, alumina, barium sulfate, kieselguhr and the like are shown as candidate supports. The '449 patent discloses the in situ alkali moderation of the supported ruthenium catalyst using lithium hydroxide.
U.S. Pat. No. 3,959,376 discloses a process for the preparation of mixed isomeric methylene bridged polycyclohexylpolyamines by the hydrogenation of methylenedianiline feedstocks. The patentees report feed mixtures having upwards of 25% isomeric methylene diamines, i.e., feedstocks having an average functionality of from 2.0 to 3.3 can be employed if one uses a pretreatment comprising effecting an initial hydrogenation in the presence of nickel followed by hydrogenation with ruthenium.
U.S. Pat. No. 3,959,374 discloses a process for the direct hydrogenation of a methylene bridged polyphenylamine feed that contains trace impurities and oligomers. A crude MDA feed containing these impurities and oligomers is initially treated with hydrogen in the presence of a nickel catalyst prior to hydrogenation in the presence of a ruthenium catalyst.
U.S. Pat. No. 4,754,070 discloses an improved process for the hydrogenation of methylenedianiline contaminated with catalyst poisoning impurities. A catalyst comprised of rhodium and ruthenium was found to be effective in the hydrogenation of a crude methylenedianiline (MDA-85), i.e., one containing oligomers in an amount up to about 15 to 20%. Alkali moderation via addition of lithium hydroxide activation was shown to be effective for the combined catalyst. Carriers suited for the rhodium/ruthenium catalyst included alumina, carbonates, etc.
U.S. Pat. No.5,545,756 discloses a process for the hydrogenation of aromatic amines, whether mononuclear or polynuclear, using a catalyst of rhodium carried on a titania support. Examples of titania supports include TiAl2O5, TiSiO4 and TiSrO3. The titania support permitted the use of rhodium alone as the active metal in the hydrogenation of crude methylenedianiline. Rhodium carried on titania in combination with ruthenium on alumina was also suited as a catalyst. Lithium hydroxide addition resulted in enhanced activity.
U.S. Pat. No. 6,184,416 discloses a process for hydrogenating methylenedianiline and other aromatic amines using a catalyst comprised of rhodium and ruthenium carried on a lithium aluminate support. The hydrogenation of feedstocks of methylenedianiline and impurity laden methylenedianiline (referred to as MDA-85) wherein the feedstock contains up to about 15 to 20% of an oligomer function is described. Oligomers are three, four and five ring products.
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