PROCESS FOR HYDROGENATING A MIXTURE IN THE PRESENCE OF A COLORLESS AMINE

Abstract

The present invention relates to a process for hydrogenating a mixture (G1) in the presence of a catalyst, where the mixture (G1) comprises at least one colorless amine and at least one color-imparting component. As a result of the hydrogenation step, the at least one color-imparting component is firstly partially, preferably fully, hydrogenated, while the colorless amine, in particular aniline, is not hydrogenated or hydrogenated to only a very small extent. The color-imparting components which cause the discoloration of the amine which is itself in principle colorless are thus removed by hydrogenation, as a result of which purification of the colorless amine or the mixture (G1) is achieved.

Claims

1: A process for hydrogenating a mixture (G1) which comprises at least one colorless amine and at least one color-imparting component, the process comprising: hydrogenating the mixture (G1) in the presence of a catalyst to obtain a mixture (G2) in which the at least one color-imparting component is at least partially or completely hydrogenated, wherein the at least one color-imparting component is selected from the group consisting of a cycloaliphatic carbonyl compound, a cycloaliphatic amine, a cycloaliphatic imine and a C6-ring aromatic.

2: The process of claim 1, wherein the at least one colorless amine is a primary amine, an aromatic amine and/or a monoamine, optionally wherein the at least one colorless amine comprises aniline.

3: The process of claim 1, wherein the mixture (G2) has a color number L* of at least 90, and/or the mixture (G2) has a color number b* of not more than 20.

4: The process of claim 1, wherein at least 90% by weight of the at least one colorless amine, based on a total amount of the at least one colorless amine comprised in the mixture (G1), is present in the mixture (G2) after the hydrogenating.

5: The process of claim 1, wherein the at least one colorless amine is present in the mixture (G1) in an amount of at least 80% by weight, based on a total weight of the mixture (G1).

6: The process of claim 1, wherein the at least one color-imparting component is present in the mixture (G1) in an amount of not more than 5% by weight, based on a total weight of the mixture (G1).

7: The process of claim 1, wherein the catalyst comprises copper, palladium, cobalt, rhenium and/or manganese.

8: The process of claim 7, wherein the catalyst comprises i) copper in an amount in a range of from 0.1 to 100% by weight, based on a total weight of the catalyst and calculated as metal, and/or ii) palladium in an amount in a range of from 0.1 to 100% by weight, based on a total weight of the catalyst and calculated as metal.

9: The process of claim 7, wherein i) if the catalyst comprises copper, then the copper is present as a metal, a copper compound, a mixture of at least two copper compounds, a mixture of a metal and a copper compound or a mixture of a metal and at least two copper compounds, optionally wherein the copper compounds are selected from the group consisting of copper chromate, copper chromite, copper oxide, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide, copper carbonate, copper acetylacetate, copper alkoxide, copper aryloxide and copper carboxylate, and/or ii) if the catalyst comprises palladium, then the palladium is present as a metal, a palladium compound, a mixture of at least two palladium compounds, a mixture of a metal and a palladium compound or a mixture of a metal and at least two palladium compounds.

10: The process of claim 1, wherein the at least one color-imparting component is selected from the group consisting of a cyclohexylphenylamine derivative, a cyclohexanone derivative, a cyclohexenone derivative, a cyclohexylamine derivative, an N-methylcyclohexylamine derivative, a toluidine derivative, a nitrobenzene derivative, a 2-aminophenol derivative, a 1,2-phenylenediamine derivative, a diphenylamine derivative, an oxidized N-methylaniline derivative and an unoxidized N-methylaniline derivative.

11: The process of claim 1, wherein i) a temperature during the hydrogenating is in a range of from 90 C. to 300 C., and/or ii) a duration of the hydrogenating is in a range of from 1 to 100 hours, and/or iii) the hydrogenating is carried out using hydrogen gas (H.sub.2), and/or iv) the process is carried out continuously or batchwise.

12: The process of claim 1, wherein i) the catalyst is present in supported or unsupported form, wherein if the catalyst is present in supported form, then the support material is optionally selected from the group consisting of carbon, silicon oxide, aluminum oxide, manganese oxide, cerium oxide, zirconium oxide, lanthanum oxide, titanium oxide and mixtures thereof, and/or ii) the catalyst is used as powder or as shaped bodies.

13: The process of claim 1, further comprising working up the mixture (G2) to isolate the at least one colorless amine, to separate off the catalyst and/or to remove the hydrogenation products from the mixture (G2), optionally wherein the working up comprises distillation.

14: The process of claim 1, further comprising converting the at least one colorless amine comprised in the mixture (G2) into a diphenylmethane derivative, and optionally converting the diphenylmethane derivative into an aromatic isocyanate, optionally by phosgenation.

15: The process of claim 14, wherein the mixture (G2) comprises at least 90% by weight of aniline, and wherein the process further comprises converting the aniline into methylenedianiline (MDA).

16: The process of claim 15, further comprising converting the methylenedianiline (MDA) into methylenedi(phenyl isocyanate) (MDI).

17: The process of claim 1, wherein the mixture (G1) is recycled aniline, where the recycled aniline comprises at least one color-imparting component selected from the group consisting of a cycloaliphatic carbonyl compound, a cycloaliphatic amine, a cycloaliphatic imine and a C6-ring aromatic.

Description

EXAMPLES

[0081] The following examples illustrate, by way of example, how the process of the invention can be carried out. The process of the invention is, however, not restricted to the reactions indicated in the examples.

Examples 1-7: Variation of the Catalyst

General Experimental Procedure

[0082] Aniline (150 g) is introduced into a 300 ml autoclave. Catalyst (1.5 g) is added thereto. The autoclave is flushed a number of times with nitrogen and the nitrogen is then replaced by pure hydrogen. After heating to 100 C., the hydrogen pressure is set to 40 bar and the mixture is stirred at this pressure and temperature for 12 hours. The autoclave is subsequently cooled and vented and the aniline is taken off, and the color number thereof is then determined.

TABLE-US-00001 TABLE 1 Color number of Content of Color number Content of aniline before aniline before after aniline after hydrogenation hydrogenation hydrogenation hydrogenation Example Catalyst L*:a*:b* [GC-% by area] L*:a*:b* [GC-% by area] 1 60% CuO, 67.3:23.3:66.2 96.6 90.3:1.9:11.5 96.1 40% Cr.sub.2O.sub.3 2 65% CuO, 67.3:23.3:66.2 96.6 91.9:1.5:8.2 96.5 5% La, 30% Al.sub.2O.sub.3 3 50% CuO 67.3:23.3:66.2 96.6 96.6:0.5:7.8 96.6 50% Al.sub.2O.sub.3 4 5% Pd 67.3:23.3:66.2 96.6 98.5:0.8:5.2 94.2 95% C 5 65% Co, 67.3:23.3:66.2 96.6 98.2:3.1:12.4 96.0 25% Cu, 10% Mn 6 Raney Ni 67.3:23.3:66.2 97 80:10:30 51 7 5% Ru 67.3:23.3:66.2 97 82:0.5:15 84 95% ZrO.sub.2

[0083] Table 1 shows that the use of Cu-comprising catalysts is particularly advantageous since the color number can be significantly improved and the content of aniline remains virtually unchanged. The use of Ni- or Ru-comprising catalysts, on the other hand, does lead to a loss of aniline, but the color number is improved. Both in table 1 above and also in the following text, the sum of the weight of catalyst is always 100% (calculated as % by weight). If the individual amounts indicated add up to less than 100%, the missing percentages are the support material.

Example 8: Variation of the Reaction Time

General Experimental Procedure

[0084] Aniline (150 g) is introduced into a 300 ml autoclave. A 50% CuO-50% Al.sub.2O.sub.3 catalyst (1.5 g) is added thereto. The autoclave is flushed a number of times with nitrogen and the nitrogen is then replaced by pure hydrogen. After heating to 100 C., the hydrogen pressure is set to 40 bar and the mixture is stirred at this pressure and temperature for the indicated time. The autoclave is subsequently cooled and depressurized and the aniline is taken out, and the color number thereof is then determined.

TABLE-US-00002 TABLE 2 Color number of recycled Content of Color number Content of Reaction aniline before aniline before after aniline after time hydrogenation hydrogenation hydrogenation hydrogenation Example [h] L*:a*:b* [GC-% by area] L*:a*:b* [GC-% by area] 2 12 h 67.3:23.3:66.2 96.6 91.9:1.5:8.2 96.5 8 48 h 67.3:23.3:66.2 96.6 96.8:0.0:8.1 96.4

[0085] The experiments in table 2 show that the reaction time has a great influence on the resulting color number L*, with the latter becoming greater with increasing reaction time and the aniline content remaining the same. However, the proportion of aniline decreases with increasing reaction time.

Examples 9-12: Variation of the Reaction Temperature

General Experimental Procedure

[0086] Aniline (150 g) is introduced into a 300 ml autoclave. A 50% CuO-50% Al.sub.2O.sub.3 catalyst (1.5 g) is added thereto. The autoclave is flushed a number of times with nitrogen and the nitrogen is then replaced by pure hydrogen. After heating to the temperature indicated, the hydrogen pressure is set to 40 bar and the mixture is stirred at this pressure and temperature for 12 hours. The autoclave is subsequently cooled and vented and the aniline is taken out, and the color number thereof is then determined.

TABLE-US-00003 TABLE 3 Color number of Content of Color number Content of Reaction aniline before aniline before after aniline after temperature hydrogenation hydrogenation hydrogenation hydrogenation Example [ C.] L*:a*:b* [GC-% by area] L*:a*:b* [GC-% by area] 2 100 67.3:23.3:66.2 96.6 91.9:1.5:8.2 96.5 9 130 67.3:23.3:66.2 96.6 98.2:0.1:4.9 96.6 10 150 67.3:23.3:66.2 96.6 98.4:0.3:4.9 97.1 11 180 67.3:23.3:66.2 96.6 99.5:0.5:3.0 96.7 12 200 67.3:23.3:66.2 96.6 99.2:0.4:2.5 96.7

[0087] The results in table 3 show that the color number can be improved by increasing the reaction temperature. In addition, the content of aniline is greatest at 150 C. (example 10).

Example 13: Distillation to Improve the Color Number

[0088] The color number of the hydrogenated samples can be increased further by distillation. For this purpose, aniline from example 10 is distilled by means of a short path distillation at 35 mbar and at a temperature at the bottom of 72 C. The main fraction has a color number of L*=100.0, a*=0.1, b*=0.3.

Example 14: Continuous Hydrogenation

[0089] 34 g of catalyst (65% CuO, 5% La, 30% Al.sub.2O.sub.3) are introduced into a tube reactor and the latter is made inert by means of nitrogen. The catalyst is subsequently activated by passing hydrogen over it. The aniline is conveyed through the reactor at varying temperature and a hydrogen pressure of 20 bar and with a varying space velocity over the catalyst. The color number and the composition of the output are determined at regular intervals. Some operating points of this experiment are reported in table 4.

TABLE-US-00004 TABLE 4 Proportion of aniline Space velocity in the Temper- over the catalyst mixture Time on ature [kg of feed/l [GC-% by stream [ C.] of cat*h] area] L* a* b* Feed 95.4 92.9 5.5 40.7 238 100 0.30 95.5 94.1 0.1 15.5 309 100 1.00 95.3 95.3 0.1 10.8 380 150 0.30 95.4 98.1 0.7 5.6 479 125 0.30 95.4 97.1 0.4 7.9 551 125 1.00 95.4 95.2 0.2 11.5 575 150 1.00 95.4 96.9 0.7 9.0 671 170 0.65 95.1 95.3 1.1 10.8 695 185 0.65 94.5 97.3 1.1 8.7 719 200 0.65 94.1 97.9 0.9 6.8 815 200 1.00 94.9 97.1 0.5 8.5 860 150 0.65 95.3 97.0 0.2 6.8 884 150 0.65 95.3 96.8 0.1 7.7 912 150 0.65 95.4 97.4 0.2 6.0 1028 150 0.65 95.3 96.9 0.1 7.6 1148 150 0.65 95.4 95.9 0.0 9.7 1202 150 0.65 95.4 95.7 0.1 11.5

[0090] The experiments reported in table 4 show that the catalyst used is stable in the long term.

Ex. 15: Continuous Hydrogenation

[0091] 21 g of catalyst (50% CuO, 50% Al.sub.2O.sub.3) are introduced into a tube reactor and the latter is made inert by means of nitrogen. The catalyst is subsequently activated by passing hydrogen over it. The recycled aniline is conveyed through the reactor at varying temperature and a hydrogen pressure of 20 bar and with a varying space velocity over the catalyst. The color number and the composition of the output are determined at regular intervals. Some operating points of this experiment are reported in table 5.

TABLE-US-00005 TABLE 5 Proportion of aniline Space velocity in the Temper- over the catalyst mixture Time on ature [kg of feed/l [GC-% by stream [ C.] of cat*h] area] L* a* b* Feed 95.5 86.6 1.2 59.6 113 150 0.65 95.2 88.6 1.6 29.0 139 170 0.65 95.1 89.9 0.6 25.8 161 190 0.65 94.7 91.6 0.1 22.8 281 190 0.65 95.0 84.4 2.5 25.0 305 200 0.65 94.8 93.5 1.3 19.7 401 210 0.65 94.8 94.9 0.3 14.3 427 220 0.65 94.9 94.30 0.4 16.6

[0092] At the same space velocity over the catalyst, the L* value becomes greater with increasing temperature, but the proportion of aniline decreases.

Example 16: Synthesis of MDI Using Color-Improved Aniline

[0093] Aniline is converted into MDI according to the following method.

[0094] The synthesis of MDA is carried out in a 2l double-wall reactor equipped with a propeller stirrer. The aniline from example 13 is admixed with aqueous hydrochloric acid (32% by weight) and heated to 90 C. A 36.5% strength by weight aqueous formaldehyde solution is then added, with the reaction temperature being maintained at 90 C. After all the formaldehyde had been added, the reaction mixture is heated to 120 C. for 2 hours and then neutralized using 50% strength by weight aqueous NaOH solution and subsequently washed twice with water.

[0095] The MDA obtained in this way is added to 1300 ml of monochlorobenzene and added dropwise to a solution of monochlorobenzene and phosgene (100 g) at 50 C. over a period of 60 minutes. The reaction mixture is subsequently heated at 100 C. for 30 minutes until it is clear. The excess phosgene is removed by application of a reduced pressure of 20 mbar at 75 C. The MDI obtained is dechlorinated firstly for 60 minutes at 100 C. and 50 mbar, then for 60 minutes at 180 C. and 20 mbar. After cooling to room temperature, the color number and also the NCO number and the chlorine content are determined.

TABLE-US-00006 TABLE 6 Color number of NCO number Example Aniline the MDI L*:a*:b* of the MDI 11 Aniline 84.3:3.2:54.9 32.4 13 Aniline from 95.0:7.2:33.2 32.7 example 11

[0096] The examples in table 6 show that the color of the MDI can be significantly improved by the use of hydrogenated aniline. The NCO number, an important quality criterion for MDI, remains virtually unchanged.