SU1625520A1 - Method for passivating catalyst of ammonia synthesis - Google Patents

Abstract

This invention relates to catalytic chemistry, in particular to the passivation of an ammonia synthesis catalyst. The goal is to reduce the passivation time, reduce the consumption of the passivating agent, reduce the degree of oxidation of the catalyst, and maintain the autothermal mode. Passivation is carried out by treating the pyrophoric catalyst with a gas mixture containing carbon dioxide and oxygen at a ratio of them, vol.%: (88.0-96.5); (3.5-12.0). 2 tab.

Description

1W

fe

This invention relates to catalyst technology, in particular, passivation of pyrophoric metal catalysts.

The purpose of the invention is to reduce the passivation time, reduce the consumption of the passivating agent, decrease the degree of oxidation of the catalyst and maintain the autothermal mode by changing the ratio of reagents in the passivating mixture.

Example 1. A sample of a commercial catalyst CA-1B (with a weight of 8 g, fraction of 2-3 mm) is reduced with hydrogen in a laboratory reactor with a stepped temperature rise to 530-550 ° C. It is kept at this temperature for 1 hour. After that, the heating of the reactor is stopped and the catalyst starts to cool in a hydrogen stream. When the catalyst reaches the required temperature (380 ° C), the supply of hydrogen is stopped and a passivation mixture is fed to the catalyst at a rate of 250 hours. The catalyst is treated with a mixture flow (Table 1) for 5 minutes and then cooled in a stream of pure CO2 to room temperature. The stability of the passivating film is judged by the heating temperature of the catalyst-treated catalyst by passing air through it. The temperature should not exceed 90 ° С.

Examples 2-17. Passivation is carried out in a similar way, changing the composition of the passivating mixture and the temperature.

Examples 1-9 (Table 1) show that the mixture containing 88.0 - 96.5% by volume of CO2 and 3.5 - 12.0% by volume 02. effectively passivates the catalyst in the temperature range of 380-530 ° C (residual pyrophoricity does not exceed 4 ° C). Moreover, the higher the oxygen content in the mixture, the less residual pyrophore. Heating during passivation does not exceed 28 ° C.

At temperatures below 380 ° C (examples 10 and 11), heating during passivation increases to 46 ° C and, accordingly, the degree of oxidation of the catalyst increases. Oxidation occurs not only the surface of the catalyst, but its entire mass. At temperatures above 530 ° C (examples 12 and 13), heating increases when passivated to 39 ° C. The temperature of the catalyst reaches 560-580 ° C. The activity of the catalyst passaged under these conditions decreases. A mixture containing less than 3.5% 02 (examples 14 and 15) does not passivate the catalyst in the temperature range of 380-530 ° C. When the oxygen content in the mixture is more than 12.0 vol.% (Examples 16 and 17), the degree of oxidation of the catalyst increases and its activity decreases.

Compared with the known (Table 2), the proposed method reduces the passivation time (5 minutes instead of 30), saves the passivation mixture (flow rate 250 instead of 5000 hT), and with a lower degree of oxidation of the catalyst (and no carbidization), the stability of the protective layer is achieved (residual pyrophoricity below). The catalyst activity corresponds to the standard sample.

Note. The composition of the catalyst is CA 1B. %: Fe 70.0; Cao 0.7-1.2; 3.0-3.1,

CaO 1.9-2.1; FeO is not normalized.

The composition of the catalyst is CA 1,%: FeO 29.0-36; toO 0,7-TH; AlaOa 3.0-3.1;

CaO 1.9-2.1; Fe is not normalized.

The proposed composition of the passivating mixture allows the passivation process to be carried out without heat being supplied from the outside, i.e. in the autothermal mode, and according to a known method, due to the small thermal effect, heat is required to maintain the reaction temperature required for passivation.

Claims (1)

Invention Formula A method for passivating an ammonia synthesis catalyst by treating a pyrophoric catalyst with a gas mixture containing carbon dioxide and oxygen, characterized in that, in order to shorten the passivation time, reduce the consumption of the passivating agent, reduce the degree of oxidation of the catalyst and maintain the autothermal regime, carbon dioxide and oxygen in the gas mixture used in the following ratio, vol.%: Carbon Dioxide88.0-96.5 Oxygen3,5-12,0 Table 1 table 2