CS253798B1 - A method for increasing the selectivity of the catalytic hydrogenation process of aniline to cyclohexylamine - Google Patents

Abstract

A method for increasing the selectivity of the catalytic hydrogenation of aniline to cyclohexylamine consists in that it takes place in the presence of a selective cobalt catalyst, the nickel and copper content of which is less than 0.05 wt.%, and the catalyst grain has the shape of rings with a wall thickness of 1.5 to 2.5 mm.

Description

The invention relates to a process for increasing the selectivity of the catalytic hydrogenation process of aniline to cyclohexylamine.

Cyclohexylamine is most commonly produced by gas-phase catalytic hydrogenation of aniline in the presence of supported metal catalysts. Depending on the reaction conditions, the type of metal used and the acid-base properties of the selected carrier, the composition of the reaction mixture and thus the selectivity of the process vary. While cobalt catalysts provide reaction mixtures with a predominant cyclohexylamine content, nickel catalysts prefer the formation of secondary amines, that is, phenylcyclohexylamine and especially dicyclohexylamine. Acid carriers such as gamma-Al2O4, SiO2, alumosilicates and the like promote the subsequent condensation of the imine with amines and thus alter the composition of the reaction mixture in favor of secondary amines.

One possibility of increasing the selectivity of the process is to shift the complex thermodynamic equilibrium of the reactions occurring during the aniline hydrogenation to the primary amine by increasing the ammonia concentration in the circulating gaseous reaction mixture. This method of influencing selectivity is the subject of an owl patent. No. 112,394 (1956). A disadvantage of this process is that as the partial pressure of ammonia in the reaction mixture increases, the reaction rate of hydrogenation and thus the performance of the apparatus decreases.

For the production of cyclohexylamine is a selective catalyst whose composition and use is described in U.S. Pat. 101 477 and 101 478. The precursor of the active ingredient of this, but also of other cobalt catalysts, is the oxides -Co 4 O 4 and CoO, furthermore cobalt (II) hydroxide, carbonate or carbonate dihydroxide. By studying the properties of cobalt catalysts in detail, we found that the impurities contained in the raw materials for their production may affect the selectivity of the hydrogenation of aniline to cyclohexylamine and that the quality and amount of undesirable impurities depends on the origin or technological process of the starting process. cobalt raw materials.

This drawback removes the proposed process for increasing the selectivity of the aniline hydrogenation process to cyclohexylamine in the presence of a cobalt catalyst, characterized in that the catalytic hydrogenation takes place in the presence of a selective catalyst having a nickel and copper content of less than 0.05% by weight. and the catalyst grain is in the form of rings having a wall thickness of 1.5 to 2.5 mm. The ring diameter is preferably chosen in the range of 5 to 6 mm. By selecting the starting material or precursor itself, the content of unwanted impurities, especially nickel and copper, can be reduced and thereby contribute to an increase in process selectivity. We have further found that in addition to the targeted selection of catalyst preparation raw materials, the selectivity of the reaction can be increased by using a catalyst of suitable geometric shape.

An advantage of the described method of improving the selectivity of hydrogenation of aniline is that it can only be achieved by selecting the active ingredient precursor of the required quality and forming the catalyst mass into a designed geometric shape, i.e. the composition of the catalyst used in the process under consideration.

The influence of the nickel content of the active ingredient precursor and the geometric shape of the grain on the selectivity of the cyclohexylamine process is illustrated by the examples below.

Example 1

The industrial catalyst used for the selective hydrogenation of aniline to cyclohexylamine is a mechanical mixture of substances containing 45 wt. % cobalt, 3-4 wt. % sodium carbonate and 51 to 52 wt. calcium carbonate. The precursor of the active ingredient is a mixture of cobalt-cobalt oxide and dihydroxydicobalt carbonate. The results of Table I illustrate the influence of variable nickel content in samples of the indicated catalyst type, same composition, bulk density and grain size on the process selectivity. The selectivity is characterized by the dicyclohexylamine content of the reaction mixture samples of mutually comparable conversion. The change of nickel in the catalyst samples was accomplished using cobalt-cobalt oxide from various manufacturers, with varying degrees of nickel contamination.

Table I

Influence of NiO on dicyclohexylamine formation rate during hydrogenation of aniline to cyclohexylamine

Designation of the catalyst Conversion (») DCA content (mass%) NiO content in catalyst (mass i) K-l 99.58 0.23 0.040 K-2 99.41 0.38 0,076 K-3 99.53 0.59 0.120 K-4 99.48 1,28 0.296

The selectivity data were obtained by studying the course of the reaction in an integral reactor at a cooling bath temperature of 180 ° C, a hydrogen: aniline molar ratio of 20 and a catalyst loading of 815 g ^ 1 to catalyst in the form of granules having a grain size of 1.4 to 1.6 mm.

Example2

The catalyst mass of the same composition as in Example 1 was shaped into a technically useful form by compression into tablets having a diameter of 5 nun and a height of 5 mm. Rings of 5x1x5 mm were prepared by pressing from a part of the catalyst mass. From comparable reaction conditions, i.e. at a cooling bath temperature of 160 ° C, a molar ratio of hydrogen: aniline = 20 and a conversion of 90%, the process selectivity was compared and the results obtained are summarized in Tab. II.

Table II

Influence of cobalt catalyst grain geometry on selectivity of aniline hydrogenation process

Catalyst form grain size (mm) Conversion (%) DCA content (mass%) Catalyst load (g 'i ^-1 , .h' ^: i ³ A cat tablets 5x5 90 0.32 425 rings 5x1x5 90 . 0.12 880

SUBJECT OF THE INVENTION

Claims (1)

A process for increasing the selectivity of the catalytic hydrogenation process of aniline to cyclohexylamine in the lean phase on a cobalt supported catalyst, characterized in that the catalytic hydrogenation is carried out in the presence of a selective catalyst having a nickel and copper content of less than 0.05% by weight. and the catalyst grain is in the form of rings having a wall thickness of 1.5 to 2.5 mm.