Isomerization of MDACH

Abstract

A method for isomerizing a starting mixture comprising 2,4-diamino-1-methylcyclohexane, 2,4-MDACH for short, 2,6-diamino-1-methylcyclohexane, 2,6-MDACH for short, or mixtures thereof, wherein the isomerization is carried out in the presence of a supported catalyst with zirconium dioxide as support and ruthenium as active metal.

Claims

1. An isomerization method, comprising: hydrogenating a composition comprising at least one of 2,4-diaminotoluene and 2,6-diaminotoluene, to obtain a starting mixture comprising at least one of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane; separating the starting mixture to obtain a cis-enriched or trans-enriched mixture comprising at least one of the 2,4-diamino-1-methylcyclohexane and the 2,6-diamino-1-methylcyclohexane; and isomerizing the cis-enriched or trans-enriched mixture in the presence of a supported catalyst with zirconium dioxide as support and ruthenium as active metal, to obtain a product mixture, wherein the isomerizing is a cis/trans isomerization that alters the cis/trans ratio of the product mixture relative to the cis-enriched or trans-enriched mixture.

2. The method according to claim 1, wherein the cis-enriched or trans-enriched mixture comprises at least one of the 2,4-diamino-1-methylcyclohexane and the 2,6-diamino-1-methylcyclohexane in a content of more than 95% by weight.

3. The method according to claim 1, wherein the cis-enriched or trans-enriched mixture comprises 5 to 95% by weight of the 2,4-diamino-1-methylcyclohexane and 5 to 95% by weight of the 2,6-diamino-1-methylcyclohexane, based on a total weight of the 2,4-diamino-1-methylcyclohexane and the 2,6-diamino-1-methylcyclohexane.

4. The method according to claim 1, wherein the isomerization is carried out at a temperature of 80 to 200 C.

5. The method according to claim 1, wherein the isomerization is carried out continuously.

6. The method according to claim 1, wherein the isomerizing occurs in the presence of hydrogen.

7. The method according to claim 1, wherein the isomerizing alters the cis/trans ratio by increasing the proportion of trans isomers in the product mixture relative to the proportion of trans isomers in the cis-enriched or trans-enriched mixture.

8. The method according to claim 1, wherein the isomerizing alters the cis/trans ratio by increasing the proportion of cis isomers in the product mixture relative to the proportion of trans isomers in the cis-enriched or trans-enriched mixture.

Description

EXAMPLES

(1) Various catalysts were tested in the method of isomerization of MDACH and, at the end of the isomerization, the isomer distribution and the selectivity were measured. The proportion of cis and trans MDACH in the MDACH starting mixture, the reaction conditions, the selectivity and the ratio of cis to trans MDACH at the end of the isomerization are reported in Table 1.

(2) The isomer ratio and the selectivity were determined in this case by gas chromatography by measuring the areas after assigning the signals to the individual isomers.

(3) Cis- or trans-enriched MDACH starting mixtures were initially charged in an autoclave and the amount of catalyst specified was added. Subsequently, the autoclave was tightly sealed and flushed with hydrogen. After adjusting the temperature according to Table 1, the system was pressurized (with hydrogen) according to Table 1 and the reaction mixture was stirred for the time specified. At the end of the reaction time, the autoclave was vented to room pressure and cooled to room temperature.

(4) The composition of the starting mixtures and the end products were investigated by gas chromatography (GC). For this purpose, the mixture is dissolved in dioxane. This solution is injected into the gas chromatograph with the aid of a syringe. The gas chromatograph is equipped with a 30 m long column having an internal diameter of 0.25 mm and a film thickness of 0.5 m. The column itself comprises as stationary phase 35% by weight diphenyl- and 65% by weight dimethylpolysiloxane (RTX35 Amine column from Resteck Corporation). Helium is used as carrier gas or mobile phase. The helium flow rate is adjusted to 40 ml/min so that a split ratio set to 40:1 gives constant flow of 1 mL/min helium through the column. To determine the substances to be investigated, the gas chromatograph has a flame ionization detector which is operated at 280 C. The column in the gas chromatograph is operated at a temperature in the range of 100 to 250 C.

(5) In order to be able to determine the percentages by weight of the peaks to be determined, a defined amount of a standard (dodecane) is added to the mixture dissolved in dioxane. The mixture thus obtained is injected onto the column at an injection temperature of 100 C. and an inlet pressure of 1 bar. A heating rate of 1 C./min is initially set which is maintained until a column temperature of 120 C. is reached. As soon as this temperature is reached, the column heating rate is readjusted to 5 C./min and maintained up to a final temperature of 250 C. The column temperature is then maintained at 250 C. for 10 minutes.

(6) Catalysts Used

(7) Catalyst 1:

(8) 13% by weight Ni, 13% by weight Co, 20% by weight Cu and 54% by weight Al.sub.2O.sub.3 (support)

(9) Catalyst 2

(10) 50% by weight Ni and 50% by weight ZrO.sub.2

(11) Catalyst 3

(12) 5% by weight Ru and 95% by weight ZrO.sub.2

(13) TABLE-US-00001 Ratio Ratio cis:trans cis:trans in the Amount Pressure Temperature Time Selectivity in the starting product Catalyst [%] [bar] [ C.] [h] [%] mixture mixture 1 1 100 160 12 96 75:25 66:34 2 1 100 160 12 95 75:25 65:35 3 1 100 160 12 99.7 75:25 65:35 3 1 100 160 12 99 20:80 64:36 3 1 100 160 12 99 100:0 55:45

Example 2

(14) 8 mL of the ruthenium supported catalyst according to the invention (5% by weight Ru on ZrO.sub.2) were filled into a tubular reactor heated with an external jacket (5 m height, 2 mm internal diameter). The reactor is then firstly flushed with hydrogen and subsequently fed with cis-enriched MDACH. It was isomerized at varying temperature and hydrogen pressure, wherein the catalyst hourly space velocity was 1 kg MDACH/kg cat*h, and the reactor was operated with recirculation, i.e. a portion of the output is recycled into the reactor. The reaction outputs were analyzed by gas chromatography and the isomer distribution was determined.

(15) TABLE-US-00002 Run time Temperature Pressure Selectivity [h] [ C.] [bar] Ratio cis-trans [%] Reactant 99:1 24 130 150 89:11 99 72 150 150 71:28 99 96 160 150 65:35 99 121 150 50 72:28 99 146 150 100 72:28 99 171 150 150 71:29 99 384 150 150 71:29 99 432 155 150 69:31 99