CS234642B1 - Process for stabilizing activated hydrogen cobalt catalyst - Google Patents

Abstract

The activated catalyst, promoted by one carbonate from the group of alkali metal carbonates and containing 25 to 60 wt. % of cobalt, is first cooled to a temperature below 55 °C by a stream of hydrogen and, after flushing with a stream of inert gas, is stabilized at an initial temperature of 15 °C to 55 °C by a stream of an inert gas-oxygen gas mixture, the initial inlet oxygen concentration of which is 0.3 vol. % is gradually increased up to 21 vol. %, while the maximum temperature in the catalyst layer must not exceed 70 °C.

Description

The invention relates to a method for stabilizing a cobalt catalyst for the selective hydrogenation of aniline to cyclohexylamine.

Cobalt, nickel and some other metal hydrogenation catalysts are pyrophoric in the activated state and therefore unstable in air. Their activation is therefore most often carried out in equipment intended for the catalytic process. Stabilized types of metal catalysts are used in technologies whose reaction temperature is significantly lower than the catalyst activation temperature. Stabilized catalysts have a significant part of the active component already in the activated state, which is protected against rapid and uncontrolled oxidation by atmospheric oxygen by a layer of surface-sorbed oxygen. Reactivation of stabilized catalysts can then be carried out at temperatures comparable to or lower than the reaction temperature of the catalyzed reaction.

The principle of stabilization, i.e. the protection of the active metal surface from uncontrolled oxidation by atmospheric oxygen, is generally known. Known stabilization procedures are in many cases specific not only to the type of catalyst, but also to the technological process. Storing Raney types of catalysts under solvents or treating their surfaces with various organic substances are patented stabilization procedures /Brit. Pat. 791 658, USA Pat. 4 176.092/, the application of which is linked to hydrogenations taking place in the liquid phase and technologically most often implemented in batch reactors. Metal catalysts used in hydrogenations in the gas phase are most often stabilized by thermal desorption of hydrogen in a stream of inert gas or by temperature and partial pressure of oxygen controlled by removal of hydrogen from the catalyst surface, or by a combination of both methods /Ger. Pat. 157 161/. The cited procedures protect

234,642 exclusively describes methods for stabilizing nickel catalysts. The implicitly stated possibility of stabilizing cobalt catalysts is not supported by either examples or specification of stabilization conditions.

The gap in the area of stabilization of cobalt hydrogenation catalysts is eliminated by the proposed stabilization procedure, characterized in that a layer of activated cobalt catalyst, promoted by one carbonate from the group of alkali metal carbonates and containing 2.5 to 60 wt. % cobalt, is first cooled to a temperature below 55 °C by a stream of hydrogen and, after flushing with a stream of inert gas, is stabilized at an initial temperature of 15 to 55 °C by a stream of a gaseous mixture of inert gas and oxygen, the initial oxygen concentration of which is 0.3 vol. % is gradually increased up to 21 vol. %, while the maximum temperature in the catalyst layer must not exceed 70 °C.

The described stabilization procedure removes the pyrophoric properties of the activated cobalt catalyst and allows its long-term storage /5,000 hours/ and manipulation in an air atmosphere without changing its initial catalytic activity. The effectiveness of stabilization was assessed by evaluating the catalytic activity of the stabilized and long-term stored catalyst in an air atmosphere after its reactivation in a hydrogen stream for one hour at a temperature of 200 °C. The stabilization method and its effectiveness are documented in the following examples.

Example 1 g of commercial cobalt catalyst was activated for 10 hours by a stream of pure hydrogen with a volume velocity of 1,000 m^/m? h at a temperature of 260 °C. The activated catalyst layer was first flushed with nitrogen after cooling in a stream of hydrogen to a temperature of 18 °C and then stabilized at an initial temperature of 18 °C by a stream of nitrogen-oxygen gas mixture. The initial inlet concentration of oxygen in the gas mixture was 0.3 vol. %. The stabilization process was monitored by measuring the axial temperature profile of the stabilized catalyst layer. The partial pressure of oxygen /at a total pressure of 0.1 MPa/ was increased stepwise from the initial value of 0.3 kPa through 1.2 kPa to

- 3 234 642 value of 21 kPa always after achieving isothermality along the entire length of the stabilized catalyst layer. The volumetric flow rate of the gas mixture was 850 m^/m^ h throughout the stabilization period. The efficiency of stabilization is documented by the values of the relative catalytic activity of the stabilized and stored cobalt catalyst in the air atmosphere /table 1/.

. Example 2 g of commercial cobalt catalyst was activated by the same procedure as in Example 1. The activated catalyst layer was first flushed with nitrogen after cooling in a hydrogen stream to a temperature of 40 °C and then stabilized at the same temperature with a stream of nitrogen-oxygen gas mixture. The initial partial pressure of oxygen in the gas mixture of 0.3 kPa was then gradually increased to 1.2 kPa and 21 kPa. The partial pressure of oxygen was always increased only after the isothermal regime in the catalyst layer had stabilized. The volumetric flow rate of the gas mixture was 1,000 m5/m^ h throughout the stabilization period. The stabilization efficiency was assessed analogously to Example 1.

Example 3

2.4 kg of commercial cobalt catalyst was activated for 10 hours by a stream of 99% hydrogen at a volume velocity of 1,110 m^/m^ h at a temperature of 260 °C. After cooling in a stream of hydrogen to a temperature of 26 °C, the activated catalyst layer was first flushed with nitrogen and then stabilized at an initial temperature of 26 °C by a stream of a nitrogen-oxygen gas mixture. The partial pressure of oxygen in the gas mixture was adjusted stepwise to values from 0.3 to 1.2 to 5.0 to 21.0 kPa. The stated values of the partial pressure of oxygen were adjusted according to the maximum temperature in the catalyst layer, which did not exceed 53 °C during the entire stabilization period. The partial pressure of oxygen was always increased after the isothermal regime in the stabilized catalyst layer had stabilized. The volumetric flow rate of the gas mixture was 1,780 m/m ^y h throughout the stabilization period. The stabilization efficiency was assessed by evaluating the catalytic activity of an average sample taken from the stabilized layer and is documented by the data given in Table II.

- 4 Table I

234,642

Relative catalytic activity of stabilized cobalt catalyst stored in air atmosphere for gas-phase hydrogenation of aniline .. \

Catalyst Exposure time for catalyst stability in air /days/ Relative catalytic activity /k/ - /and/ 1.00 ⁰ /b/ 1.10 0 /b/ 1.28 1 1.16 7 1.12 14 1.14 42 1.05 49 1.06 - ' /a/ unstabilized catalyst

/b/ catalyst immediately after stabilization reactivated w

p..inverse of space velocity

S, X ... symbols, assigning the described quantities to the standard or evaluated catalyst x ... conversion

- 5 Table II ²³⁴

Activity of stabilized cobalt catalyst stored under various conditions for the hydrogenation of aniline to cyclohexylamine

Catalyst Storage conditions for stable catalyst in air atmosphere Relative catalytic activity /A/ time /h/ ON time /h/ UN ~ /a/ /and/ 1.00 100 - 1.45 - 100 1.45 1000 - 1.52 - 1000 1.54 5000 - 0.86 - . 5000 1.54 5000 0.99 - 5000 1.50

ON ... open storage container

UN ... hermetically sealed storage container Other symbols are identical to those in Table I

Claims (1)

SUBJECT OF THE INVENTION Process for stabilizing an activated cobalt hydrogenation catalyst, characterized in that the activated catalyst, promoted by one of the alkali metal carbonates and containing 25 to 60 wt. is stabilized at an initial temperature of 15 ° C to 55 ° C by an inert gas-oxygen gas mixture whose initial oxygen concentration of 0,5% by volume increases gradually up to 21% by volume, the maximum temperature in the catalyst layer not exceeding 70 ° C. ⁽ Printed by Moravian Printing Works, plant 12, Leninova 21, Olomouc Price: 2,40 Kčs Correction in the printed descriptions of the invention In the description of the invention for the copyright notice $ · 2M 642 <W X4X> * S | Correctly also the method of stabilizing the activated organobutane cobalt catalyst