RU2581166C2 - Method of metal-carbon catalyst synthesis and process of reduction of nitrocompounds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the field of developing catalysts for different processes of hydration of aromatic nitrocompounds into respective amines. A method of palladium-carbon catalyst synthesis for obtaining aromatic amines by the reduction of the aromatic nitrocompounds by hydrogen in a solvent is claimed. The catalyst is obtained by the modification of palladium with triphenylphosphine with its following application on a mesoporous carbon carrier - Kemerit. After that, repeated reduction is carried out with a single catalyst charge.

EFFECT: increase of the process rate and product output with the simultaneous increase of the catalyst stability, which results in the multiple increase of a possibility of its re-application.

4 cl, 4 ex

Description

The invention relates to the field of catalyst development for various processes for the hydrogenation of aromatic nitro compounds to the corresponding amines.

In modern science, one of the relevant areas is the development and study of highly effective and selective catalysts for various processes of hydrogenation of aromatic nitro compounds into the corresponding amines, since the latter are widely used in the manufacture of various dyes, drugs, corrosion inhibitors, antiknock additives to gasoline and motor fuels and other

The invention relates to an improved method for producing aromatic amines by using catalysts based on palladium compounds on a carbon matrix — a mesoporous carbon support — Kemeri, which reduce the diffusion complications of the catalyst support, which sharply increases the rate of reduction reaction.

A known process for the reduction of various nitro compounds (nitrobenzene, 2,4-dinitrotoluene, 1,5-dinitronaphthalene) in a circulation reactor on VPYAPK catalysts with a palladium content of 2 wt. % and 3.5 wt. % The process is carried out in various solvents at a temperature of 60-105 ° C and a pressure of 6-10 atm. The reaction time is 15-84 hours [1]. The disadvantages of the process are quite stringent conditions, low activity of the catalysts and the possibility of side processes.

A known process for producing mono- and bimetallic palladium and platinum catalysts on carbon supports for the hydrogenation of nitro compounds to amines or intermediates [2]. The catalyst has a rather complicated method of preparation: treatment of the carbon support with nitric acid at a temperature of 80 ° C, impregnation of chloride-free palladium or platinum compounds with nitric acid solutions and reduction in a stream of hydrogen at 110-350 ° C.

A known method of reducing nitrobenzene to aniline on palladium catalysts with a palladium content of 1 wt. % on graphite and coke in the gas phase at a temperature of 250-300 ° C. The activity of the catalyst is low [3].

The process of continuous reduction of dinitrotoluene to diaminotoluene on a Pd + Pt + Fe / C catalyst at a temperature of 90 ° C and a pressure of 7 atm in a medium of diaminotoluene and water is recommended, the yield of the target product is 99.1%. With increasing temperature (from 90 to 150-200 ° C) and pressure (up to 10-50 atm), it becomes possible to use the heat of reaction to produce steam [4].

Dow Global Technologies Inc. patented a method for the reduction of dinitrotoluene to diaminotoluene on a Pd / C catalyst (5-10%). The capacity of dinitrotoluene is 18 t / g, the reactor is 30 m ³ . The process is carried out at 135 ° C and a pressure of 4 atm in a medium of water - diaminotoluene. With a small excess of hydrogen (5-10 mol / mol dinitrotoluene), side processes, including hydrogenation to the core, decrease [5].

A characteristic feature of analogues is that the processes of hydrogenation of nitro compounds into the corresponding amines are carried out under rather severe conditions. Such conditions do not allow the formation of a labile, highly dispersed phase of palladium, which leads to a rather low activity of the catalysts. In addition, under severe conditions, the occurrence of side processes is possible. Therefore, supported palladium catalysts for liquid-phase reduction processes operating under mild conditions show very high activity and selectivity.

In this regard, the purpose of this invention was to develop a catalyst operating under mild conditions by using finely divided palladium modified with triphenylphosphine and a carbon carrier with a large surface and porosity, which increases the hydrogenation rate by eliminating diffusion limitations.

To achieve this goal, palladium acetate, triphenylphosphine are dissolved in acetone and a mesoporous carbon carrier, Kemerit, is added to the solution. The system acquires catalytic properties after treatment with molecular hydrogen.

Closest to the proposed method is the restoration of nitro compounds using a palladium-carbon catalyst modified with triphenylphosphine [6]. Activated carbon, carbon fiber and ultrafine diamond (nanodiamonds) are used as carriers; the most effective carbon carrier is nanodiamonds. Nanodiamond produced by detonation synthesis is isolated under stringent conditions (a mixture of H ₂ SO ₄ and HNO _3, the temperature 180 ° C) and it has a higher value (~ $ 2000 per 1 kg).

Comparative analysis with the prototype [6] shows that the proposed solution is characterized by the use of a cheaper carbon material — a mesoporous carbon carrier — Kemerite — compared to nanodiamonds, which provides higher catalyst efficiency (activity is three times higher than that of nanodiamonds).

The main objective of the invention is to increase the activity of the catalyst through the use of a carbon carrier - Kemerit, which makes it possible to increase the speed of the process and the yield of the product on this type of catalyst and at the same time increase its stability, which greatly increases the possibility of its reuse.

The problem is solved by a method of synthesizing a metal-carbon catalyst for the process of reducing nitro compounds by applying palladium-modified triphenylphosphine onto a carbon carrier, palladium is deposited on a mesoporous carbon carrier — Kemerit.

The catalyst was manufactured as follows:

the calculated amount of palladium acetate Pd (OAc) ₂ (0.085 g) and triphenylphosphine PPh.3 (0.039 g) are loaded into a thermostatic reactor, 80 ml of acetone are added, and the mixture is stirred under argon until the reagents are completely dissolved. Then, in a stream of argon, a weighed portion of the carbon support (2.0 g) is introduced and mixed for 5 minutes. After that, the reaction mixture was purged with hydrogen for 5 minutes without stirring. Then, with stirring, reduction is carried out with molecular hydrogen at 40 ° C for 2 hours. The finished catalyst is filtered off, dried and stored at room temperature in an inert atmosphere.

The method of synthesis of a metal-carbon catalyst for the process of hydrogen reduction of aromatic nitro compounds in a solvent by deposition of palladium modified with triphenylphosphine on a mesoporous carbon carrier - Kemerit and reduction is carried out repeatedly with a single catalyst load.

Recovery is carried out in an aliphatic alcohol medium as a solvent at atmospheric pressure of hydrogen at a temperature of about 40 ° C.

Ethanol or isopropanol are used as the aliphatic alcohol.

The components are supplied for reduction in an atmosphere of an inert gas such as nitrogen or argon.

When calculating the components for the preparation of a palladium catalyst at Kemer, they were guided by the fact that the palladium content should be ~ 2 wt. %, which provides the most economical consumption of palladium and an acceptable rate of hydrogenation of aromatic nitro compounds.

The ratio of triphenylphosphine modifier to palladium acetate (P / Pd) corresponded to 0.4, which ensures the formation of the most stable palladium clusters with phosphorus-containing ligands and the highest rate of hydrogenation of nitro compounds.

The invention is illustrated by the following examples:

Example 1

Catalyst Pd _mod / C (~ 2% Pd), mesoporous carbon support - Kemerit.

5 mg (0.94 · 10 ^-3 mmol of Pd) catalyst, 2.9 mmol of nitrobenzene, 10 ml of ethanol are charged to the reactor under argon (nitrogen) atmosphere and thermostatted for 3-5 min at 40 ° C. Then the system is purged with hydrogen (hydrogen pressure - atmospheric) for 5 minutes, after which intensive mixing begins. The theoretical amount of hydrogen (8.7 mmol) is absorbed in 160 minutes. The next portion of nitrobenzene (2.9 mmol) is hydrogenated in 150 minutes. Then, acting similarly, 5 consecutive portions of 2.9 mmol nitrobenzene were hydrogenated. The theoretical amount of hydrogen per 5 servings of nitrobenzene is absorbed without a noticeable loss of activity in an average of 150 minutes.

The total conversion of nitrobenzene per 1 g of palladium is 1520 g (11.8 mol). The yield of aniline is 99.5% (chromatographic analysis data).

Speed at Kemeri: 9-13.2 lN ₂ / g Pd min.

Example 2

Catalyst Pd _mod / C (~ 2% Pd), mesoporous carbon support - Kemerit.

5 mg (0.94 · 10 ^-3 mmol Pd) of catalyst, 2.9 mmol of para-nitrophenol, 10 ml of ethanol are charged into the reactor under argon atmosphere and thermostatted for 3-5 min at 40 ° C. Then the system is purged with hydrogen (hydrogen pressure - atmospheric) for 5 minutes, after which intensive mixing begins. The theoretical amount of hydrogen (8.7 mmol) is absorbed in 310 minutes. The average absorption rate of 6.5 nH ₂ / gPd min. A decrease in the activity of the catalyst during the reaction is not observed. The yield of p-aminophenol is 99% according to chromatographic analysis.

Example 3

Catalyst Pd _mod / C (~ 2% Pd), mesoporous carbon support - Kemerit.

10 mg (1.88 · 10 ^-3 mmol Pd) of catalyst, 2.9 mmol of ludigol, 10 ml of ethanol are loaded into the reactor under argon atmosphere and thermostated for 3-5 min at 40 ° C. Then the system is purged with hydrogen (hydrogen pressure - atmospheric) for 5 minutes, after which intensive mixing begins. The theoretical amount of hydrogen (8.7 mmol) is absorbed in 140 minutes. The average absorption rate of 3.8 lN ₂ / gPd min. A decrease in the activity of the catalyst during the reaction is not observed. The yield of amine is close to quantitative (by absorption of hydrogen).

Example 4

Catalyst Pd _mod / C (~ 2% Pd), mesoporous carbon support - Kemerit.

5 mg (0.94 · 10 ^-3 mmol Pd) of catalyst, 2.9 mmol of nitrobenzene, 10 ml of ethanol are loaded into the reactor under argon atmosphere and thermostated for 3-5 min at 40 ° C. Then the system is purged with hydrogen (hydrogen pressure - atmospheric) for 5 minutes, after which intensive mixing begins. The theoretical amount of hydrogen (8.7 mmol) is absorbed in 110 minutes. The average absorption rate of 19.8 ln ₂ / gPd min. A decrease in the activity of the catalyst during the reaction is not observed. The yield of aniline is 99.5% according to chromatographic analysis.

Information sources

1. Pat. RF 2316394, B01J21 / 18, 02/10/208.

2. US patent 5304525, 1994.

3. Kozlov A.I., Zbarsky V.L. Grew up. Chem. J. 2006. V. 50, No. 3, p. 131-139.

4. US patent 5563296, 1996.

5. US patent 6565053, 2005.

6. Prototype - Obraztsova II, Efimov OA, Simenyuk G.Yu., Minkov A.I. Tr. Int. scientific-practical conference "Chemistry - XXI century: new technologies, new products." Kemerovo, December 5-8, 2000 Kemerovo, 2000.S. 62-66.

Claims (4)

1. A method of synthesizing a metal-carbon catalyst for the process of reducing nitro compounds by applying palladium on a carbon carrier, characterized in that palladium is modified with triphenylphosphine, applied to a mesoporous carbon carrier — Kemerit and reduction are carried out repeatedly with a single catalyst load. 2. The method according to p. 1, characterized in that the recovery is carried out in an environment of aliphatic alcohol as a solvent at atmospheric pressure of hydrogen at a temperature of about 40 ° C. 3. The method according to p. 1 or 2, characterized in that ethanol or isopropanol is used as an aliphatic alcohol. 4. The method according to PP. 1, 2 or 3, characterized in that the supply of components for recovery is carried out in an atmosphere of inert gas, such as nitrogen or argon.