METHOD FOR THE HYDROGENATION OF AROMATIC NITRO COMPOUNDS

Abstract

The present invention relates to a process for the preparation of an aromatic amine by hydrogenation of an aromatic nitro compound, comprising the following steps: (I) providing a copper tetramine salt-based impregnation catalyst, in particular an impregnation catalyst obtainable by the incipient wetness method, comprising a metal or metal oxide on a support as a hydrogenation catalyst. At least metallic or oxidic copper (in particular CuO) is present and the mole fraction of Cu based on all metals present is in the range of 075 to 1, and wherein the support comprises shaped silicon-dioxide shaped bodies or silicon-carbide shaped bodies; (II) optionally, activating the hydrogenation catalyst by treating with hydrogen in the absence of the aromatic nitro compound; and (III) reacting the aromatic nitro compound with hydrogen in the presence of the, optionally activated, hydrogenation catalyst to obtain the aromatic amine.

Claims

1. A process for preparing an aromatic amine by hydrogenating an aromatic nitro compound, comprising: (I) providing a tetraamminecopper salt-based impregnated catalyst comprising a metal or metal oxide on a support as hydrogenation catalyst, where at least metallic or oxidic copper is present and the molar proportion of copper, based on all metals present on the catalyst, is 0.75 to 1, and where the carrier comprises shaped silicon dioxide bodies or shaped silicon carbide bodies; (II) optionally activating the hydrogenation catalyst by treating with hydrogen in the absence of the aromatic nitro compound; and (III) reacting the aromatic nitro compound with hydrogen in the presence of the optionally activated hydrogenation catalyst to obtain the aromatic amine.

2. The process as claimed in claim 1, in which step (II) is conducted and the treatment with hydrogen is effected at a temperature of 180° C. to 240° C.

3. The process as claimed in claim 1, in which step (III) is conducted: adiabatically at a temperature of 160° C. to 500° C., or isothermally at a temperature of 180° C. to 550° C.

4. The process as claimed in claim 1, in which step (III) is conducted: adiabatically at a molar ratio of hydrogen to nitro groups of 10 to 200, or isothermally at a molar ratio of hydrogen to nitro groups of 3 to 100.

5. The process as claimed in claim 1, in which the proportion by mass of copper compounds, calculated as metallic Cu, in the hydrogenation catalyst provided in (I), based on the total mass thereof, is 3% to 35%.

6. The process as claimed in claim 1, in which the hydrogenation catalyst used comprises a tetraamminecopper carbonate-based impregnated catalyst.

7. The process as claimed in claim 6, in which the hydrogenation catalyst used comprises a tetraamminecopper carbonate/ammonium carbonate-based impregnated catalyst or a tetraamminecopper carbonate/ammonium acetate-based impregnated catalyst.

8. The process as claimed in claim 1, in which the impregnated catalyst is obtained by a process comprising impregnating the support with an aqueous solution of a tetraamminecopper salt in such a way as not to exceed the maximum absorptivity of the support determined by means of saturation with water.

9. The process as claimed in claim 1, in which step (I) comprises: (a) dissolving a copper salt in aqueous ammonia to obtain an ammoniacal copper salt solution; (b) impregnating the support with the ammoniacal copper salt solution obtained in (a), followed by drying of the impregnated support thus obtained to obtain a catalyst precursor, and (c) calcining the catalyst precursor obtained in (b) to form the tetraamminecopper-based impregnated catalyst.

10. The process as claimed in claim 9, in which the ammoniacal copper salt solution used for impregnation has a pH at 20° C. of 7.0 to 14.

11. The process as claimed in claim 1, in which an aromatic nitro compound of the formula: ##STR00003## is hydrogenated, in which R1 and R2 are independently hydrogen, methyl or ethyl, where R2 may additionally also be NO.sub.2.

12. The process as claimed in claim 9, in which the support in step (b) is impregnated with the ammoniacal copper salt solution obtained in (a) in such a way as not to exceed the maximum absorptivity of the support determined by means of saturation with water.

13. The process as claimed in claim 12, in which the maximum absorptivity of the support is undershot by not more than 5%.

14. The process as claimed in claim 12, in which the maximum absorptivity of the support is undershot by at least 2%.

15. The process as claimed in claim 1, in which the optionally activated hydrogenation catalyst in step (III) is disposed in a fixed catalyst bed.

16. The process as claimed in claim 13, in which the maximum absorptivity of the support is undershot by at least 2%.

Description

EXAMPLES

General Methods

Determination of Maximum Absorptivity of the Support

[0102] The absorptivity maximum is determined by weighing the shaped bodies before and after absorption of water, as described hereinafter. For this purpose, the support material is weighed out and, in a vessel that enables visual observation (e.g. glass beaker), left to stand (without moving the vessel) blanketed with demineralized water until no further air bubbles ascend. The supernatant water is decanted, and the surface of the still-moist shaped bodies is dried. This is done by absorbing the moisture adhering to the surface with filter paper, which, according to the shape of the shaped bodies, can be performed by rolling on or dabbing with the filter paper. This drying step removes water adhering to the surface, but not water that has been absorbed into the pores of the support. By weighing the contents and subtracting the starting weight, the water absorption in grams is obtained, corresponding to the absorptivity maximum of the shaped body used.

[0103] In all examples for catalyst preparation, the amount of the metal salt solution to be used for impregnation was adjusted such that it was 2% below the maximum absorptivity (incipient wetness method).

Starting Materials

[0104] Cu(NO.sub.3).sub.2 solution from Poletto Aldo with a density at 20° C. of 1.48 g/ml, a Cu content of (14.5±0.5)% by mass and a pH (measured at ambient temperature, 20 to 25° C.) of 3.5±0.5.

[0105] Shaped silicon dioxide bodies, 3×5 mm cylinders, absorptivity 1.13 ml/g, bulk density 417 g/l.

Example 1

Preparation of a Copper Nitrate-Based Impregnated Catalyst as Comparative Catalyst

[0106] 100 ml of the silicon dioxide support was impregnated with the Cu(NO.sub.3).sub.2 solution. This involved agitating the mixture until the liquid had been completely absorbed by the support material. The impregnated shaped bodies were dried to constant mass at 120° C. and then calcined at 450° C. in air atmosphere for 4 h. The catalyst had a proportion by mass of copper compounds, calculated as metallic copper, of about 24.0%.

Example 2

Hydrogenation of Nitrobenzene With the Catalyst From Example 1 (Comparison)

[0107] The catalyst from example 1 was transferred into a fixed bed reactor in the oxidized state, and nitrogen was passed through it until the remaining oxygen had been driven out. The temperature was adjusted to a value in the range from 200° C. to 240° C., and the activation was commenced by metering in hydrogen. The exothermicity caused by the reaction should be kept as low as possible. On conclusion of the activation, nitrogen was passed through the catalyst to remove the excess hydrogen. For the reaction, nitrobenzene (NB) was metered into the activated catalyst, successively increasing and adjusting the amount of nitrobenzene to the target load of 0.9 g.sub.NB ml.sub.cat.sup.−1 h.sup.−1. The molar hydrogen:nitrobenzene ratio was 10:1. The reaction was conducted polytropically, with removal of the heat formed in the reaction by a heat carrier. The hydrogenation was conducted in each case until breakthrough of nitrobenzene was observed.

[0108] The catalyst described in example 1 showed a service life of 60 h and an average aniline selectivity of 99.2%.

Example 3

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention

[0109] Compositions used for a solution with a proportion by mass of Cu of (12.7±0.5)% at pH=9.2±1.0: [0110] ammonium carbonate 65.785 g [0111] basic copper carbonate 74.6 g [0112] ammonia 81.7 g [0113] demineralized water 100 g

[0114] First of all, the starting materials were cooled to below 5° C. in a refrigerator. Water and ammonia were mixed in a closable vessel. The solids were weighed out together in a dish and added rapidly to the cooled ammonia solution, and they were mixed together with the lid closed until the salts had dissolved.

[0115] 100 ml of the silicon dioxide support was impregnated with an amount of the tetraamminecopper carbonate solution thus prepared corresponding to the absorptivity of the support. This involved agitating the mixture until the liquid had been completely absorbed by the support material. The impregnated shaped bodies were dried to constant mass at 120° C. and then calcined at 450° C. for 4 h.

[0116] The catalyst had a proportion by mass of copper compounds, calculated as metallic copper, of about 14.8%.

Example 4

Hydrogenation of Nitrobenzene With the Catalyst From Example 3 (Inventive)

[0117] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 295 h and the average aniline selectivity 99.6%.

Example 5

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10

[0118] Proceeding from example 3, a catalyst was prepared that was prepared at pH=10. The following amounts were used: [0119] ammonium carbonate: 15.8 g [0120] basic copper carbonate: 18.18 g [0121] ammonia: 32.60 g [0122] demineralized water: 33.42 g

[0123] First of all, the starting materials were cooled to below 5° C. in a refrigerator. Water and ammonia were mixed in a closable vessel. The solids were weighed out together in a dish and added rapidly to the cooled ammonia solution, and they were mixed together with the lid closed until the salts had dissolved.

[0124] 100 ml of the silicon dioxide support was impregnated with an amount of the tetraamminecopper carbonate solution thus prepared corresponding to the absorptivity of the support. This involved agitating the mixture until the liquid had been completely absorbed by the support material. The impregnated shaped bodies were dried to constant mass at 120° C. and then calcined at 450° C. for 4 h. The catalyst had a proportion by mass of Cu of about 12.4%.

Example 6

Hydrogenation of Nitrobenzene With the Catalyst From Example 5 (Inventive)

[0125] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 240 h and the average aniline selectivity 99.6%.

Example 7

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10 Including “Aging”

[0126] A catalyst was prepared analogously to example 5, except that the catalyst, in the impregnation process, was left to stand in the wet state for one week prior to drying.

Example 8

Hydrogenation of Nitrobenzene With the Catalyst From Example 7 (Inventive)

[0127] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 240 h and the average aniline selectivity had a value of 99.5%.

Example 9

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10 With Multiple Impregnation

[0128] The procedure was analogous to example 5, except that a higher copper content was achieved by double impregnation. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 22%.

Example 10

Hydrogenation of Nitrobenzene With the Catalyst From Example 9 (Inventive)

[0129] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 360 h and the average aniline selectivity 99.6%.

Example 11

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 9.2 With Multiple Impregnation at Lower Metal Concentration

[0130] The procedure was analogous to example 5, except that a double impregnation was conducted at a lower metal content of the impregnation solution. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 15.3%.

Example 12

Hydrogenation of Nitrobenzene With the Catalyst From Example 11 (Inventive)

[0131] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 290 h and the average aniline selectivity had a value of 99.6%.

Example 13

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 9.2 on an Alternative Silica Support

[0132] The procedure was analogous to example 3, except that an alternative silica support material having a lower specific surface area of 80 m.sup.2/g was used. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 12.9%.

Example 14

Hydrogenation of Nitrobenzene With the Catalyst From Example 13 (Inventive)

[0133] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 260 h and the average aniline selectivity had a value of 99.5%.

Example 15

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10 on a “Trilobe” Shaped Body

[0134] The procedure was analogous to example 5, except that the support material used was a silica-based trilobe shaped body. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 11.6%.

Example 16

Hydrogenation of Nitrobenzene With the Catalyst From Example 15 (Inventive)

[0135] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 240 h and the average aniline selectivity 99.7%.

Example 17

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10 With Multiple Impregnation on a “Trilobe” Shaped Body

[0136] The procedure was analogous to example 5, except that the support material used was a silica-based trilobe shaped body and a multiple impregnation was conducted. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 19.6%.

Example 18

Hydrogenation of Nitrobenzene With the Catalyst From Example 17 (Inventive)

[0137] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 300 h and the average aniline selectivity had a value of 99.7%.

Example 19

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10 With Multiple Impregnation on a Silicon Carbide Support of Comparatively Low Purity (about 99.5% SiC)

[0138] The procedure was analogous to example 5, except that the support material used was a silicon carbide support (about 99.5% SiC) and a multiple impregnation was conducted. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 10.3%.

Example 20

Hydrogenation of Nitrobenzene With the Catalyst From Example 19 (Inventive)

[0139] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 290 h and the average aniline selectivity had a value of 99.8%.

Example 21

Preparation of a Tetraamminecopper-Based Impregnated Catalyst as Hydrogenation Catalyst for the Process of the Invention at pH 10 With Multiple Impregnation on a Silicon Carbide Support of Hither Purity Compared to Example 19 (≥99.85% SiC)

[0140] The procedure was analogous to example 5, except that the support material used was a silicon carbide support (≥99.85% SiC) and a multiple impregnation was conducted. The proportion by mass of copper compounds, calculated as metallic copper, after calcination was about 10.1%.

Example 22

Hydrogenation of Nitrobenzene With the Catalyst From Example 21 (Inventive)

[0141] Apart from the catalyst, the experiment was conducted analogously to example 2; the service life was 240 h and the average aniline selectivity had a value of 99.8%.