BG67064B1 - SPINEL-TYPE Cu-Zn-Al CATALYST FOR DECOMPOSITION OF N2О TO N2 AND O2 AND A METHOD FOR PREPARATION THEREOF - Google Patents

Abstract

The invention relates to a process for preparation of copper-zinc-aluminum spinel-like "secondary" catalyst for decomposition of N2О (nitrous oxide) to N2 (nitrogen) and О2 (oxygen), which ifinds application in the production of nitric acid. The catalyst, designated БN2ОК, is prepared by a method characterized by the use of available source materials (copper, zinc, aluminum, nitric acid, ammonia and carbon dioxide) and easily feasible technological processes, the most important of which is the precipitation process, which does not use a precipitating reagent, for example NaOH (sodium hydroxide) or Nа2СО3 (sodium carbonate), and the role of precipitating reagent is performed by some of the ingredients of the catalyst composition. The method ensures the production of an active, selective and long-cycle catalyst for the decomposition of N2О to N2 and О2 under conditions that do not require both technical and technological changes in the plant for the production of НNО3 (nitric acid).

Description

The invention relates to a spinel-like Cu-Zn-Al type catalyst for the decomposition of N ₂ O (nitrous oxide) to N ₂ (nitrogen) and O ₂ (oxygen) and a method for its preparation.

High requirements for greenhouse gas emissions into the atmosphere, especially N _; O. which has 310 times higher emission factor than that of CO ₂ , (carbon dioxide) predetermines the need to remove it from emissions in the production of nitric acid. The decomposition of N ₂ O from 01.01.2013 is a mandatory element in the technology for obtaining nitric acid by the method of Ostwald [1].

Of the two possible technologies for eliminating N ₂ O - "secondary" and "tertiary", the catalyst, designated as BN ₂ OK is from the group "secondary" (the terms refer to the sequence of catalytic devices in the process). The process conditions in this variant do not require technological changes in the production of nitric acid. The decomposition of N ₂ O takes place at the temperature and the corresponding volumetric oxidation rates in the contact devices. This predetermines high requirements for the qualities that the catalyst must have:

- the components of the catalyst composition have a high Taman temperature;

- to be in optimal proportion and finely distributed;

- to have as large an external (geometric) surface as possible and good porosity;

- there are no components in the composition (eg Na-sodium, K-potassium) that accelerate the aging process (sintering) of the catalyst.

The removal of N ₂ O from waste gases emitted into the atmosphere in the production of nitric acid can be carried out catalytically in several ways.

It is known [1] that the DeNOx technology - NSCR (Non-selective catalytic reduction) of NOx, concomitantly decomposes N ₂ O to residual levels of 0.1-0.2%. Disadvantages of this technology are:

- the need to introduce energy to increase the temperature of the gases, carried out by burning methane (emission of CO _{2 -} greenhouse gas);

- the use of a reducing agent CH4 (methane) in excess, they. again the emission of a greenhouse gas such as methane.

These disadvantages are avoided in German patent DE 198 19 882 A1 [2], where this is realized by catalytic means using a copper-spinel catalyst, immediately after the contact networks on which the oxidation of NH ₃ (ammonia) to NO takes place. The process of decomposition of N ₂ O therefore takes place on the catalyst, which is located in the space between the networks and the boiler utilizer, they. the realization of the process is not associated with the need for technological change in the production of nitric acid by the method of Ostwald.

A similar solution is described in U.S. Pat. No. 5,478,549 [3] with the difference that the catalyst is ZrO (zirconium oxide). The process is designed for installations operating at a pressure of 4 kg / cm ² , a temperature of 600 ° C and a volumetric velocity of 30000 h ¹ .

Yara France [4] describes a process for the decomposition of naN ₂ O with a catalyst based on CsO (cesium oxide) promoted with Co (cobalt). The catalyst is described in [5].

Krupp-Uhde GmbH [6] considered the “tertiary” variant, in which the decomposition of naN ₂ O takes place simultaneously or sequentially with the removal of ΝΟ _χ from the waste gas. The method is catalytic and is carried out with a reducer ΝΗ ₃ and CH ₄ at a temperature of 350 ° C.

In source [7] there is information about a cesium catalyst promoted with CuO (copper oxide) for decomposition of naN ₂ O in the waste gases at a temperature up to 400 ° С. The study was performed with a model gas having a similar composition to the waste gas from nitric acid production.

Similar studies have been done in [8]. Spinel-like catalysts based on oxides - MgO (magnesium oxide) were studied here; Cr ₂ O ₃ (dichromic trioxide); CuO; FeO (iron oxide), Fe ₂ O ₃ (iron trioxide) and others.

In [9] there is data on the catalytic activity against the decomposition of N _; O with model gas, with a similar waste gas composition, with a Co-catalyst promoted with Fe ₃ O ₄ (iron iron tetraoxide).

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Descriptions of issued patents for inventions № 05.2 / 29.05.2020

The invention relates to:

1. Structure and composition of a catalyst for the decomposition of N ₂ O to N ₂ and O ₂ with a spinel-like structure based on oxides of Cu, Zn and A1 with high catalytic activity and selectivity.

2. A process for the preparation of a spinel-like catalyst based on oxides of Cu, Zn and Al with high catalytic activity and selectivity, having a long operating cycle under the conditions of its use for the decomposition of N ₂ O in the production of nitric acid.

The method object of the present invention is characterized by the following:

1. Preparation of the starting precursors in the form of ammonia-carbonate solutions containing Cu and Zn and of A1 in the form of a nitrate solution.

2. Precipitation with solutions under fixed conditions: pH, temperature, concentration, precipitation time and maturation of the sediment. The resulting precipitate is characterized by high dispersion and homogeneous chemical and phase composition, not requiring the use of a precipitating reagent (NaOH or Na ₂ CO ₃ ), whose Na ⁺ is difficult to remove, and their complete removal is practically impossible.

3. After ripening, the precipitate is filtered, washed, dried and annealed. The resulting mass is molded into tablets or extruded with subsequent annealing at a higher temperature.

The catalyst, designated BN ₂ OK, has high activity and selectivity and a long operating cycle at temperatures of 80 (H950 ^o C, volumetric velocity up to 20000 h ¹ at a pressure of 1 kg / cm ² and 60000 h ¹ at a pressure of 3 M kg / cm ² .

Example 1.

Copper-zinc ammonia-carbonate solution with a concentration of components in the range of 60-90 g / 1 CuO, 60-90 g / 1 ZnO, 160-180 g / 1 NH ₃ and 120-140 g / 1 CO ₂ is mixed with a solution of A1 (NO ₃ ) _{3 with} a concentration in the range of 120-180 g / l A1 ₂ O ₃ at a temperature of 80 ° C for 15 min with vigorous stirring, maintaining the pH in the range of 5-7. The resulting precipitate was allowed to mature at the same temperature for 35 minutes. During the precipitation and maturation of the precipitate, CO ₂ is fed into the suspension. The precipitate was filtered off, washed with NO ₃ , dried at 120N to 50 ° C and annealed at 350-600 ° C for 3-6 hours. The contact mass has a composition of SiA1 ₂ O ₄ and ΖηΑ1 ₂ Ο4, in the ratio Cu: Zn: Al = 1: 1: 4, with nanosized particles - 3 nm and a specific surface - 145 m ² / g. It is treated with binders (urea, carboxymethylcellulose) and mixed with graphite. It is formed on a tablet machine in the form of tablets (rings) with dimensions 12x6x6 ± 1 mm (DxdxH).

The tableted catalyst is reheated for 3-6 hours at 600-1000 ° C. The catalyst has nanosized particles of ~ 25 nm and a specific surface area S = 62 m ² / g. The catalyst tablets have a size of 11x5x5 ± 1 mm, an outer (geometric) surface F> 5 cm ² / g and a porosity> 28%.

Example 2.

The catalyst obtained in Example 1 was tested for catalytic activity in a laboratory reactor under the following conditions:

volume of the catalyst - 4 ml with dimensions 0,63 ^ -0,8 mm (kinetic regime) gas - taken after the contact networks from an industrial installation for production of nitric acid by Oswald method volume velocity - 8000 h ¹ and 16000 h ¹ temperature - 830 ° C input concentration of N ₂ O - 1200-4400 ppm.

The activity of the catalyst, expressed by degree of decomposition - a _p and selectivity - a _c is: for 8000 h ¹ - o, = 0,98 and a = 1 for 16000 h ¹ - a = 0,95 and a = 1.

Example 3.

Under the conditions of Example 2, the catalyst obtained in Example 1 was tested in a pilot reactor in a volume of 100 ml with dimensions 11x5x5 mm (diffusion mode).

The catalytic activity of the catalyst is:

at 8000 h ¹ - o, = 0.92 and a = 1 at 16000 h ¹ - a, = 0.90 ia = 1.

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Descriptions of issued patents for inventions № 05.2 / 29.05.2020

Example 4.

The catalyst obtained in Example 1 was industrially used under the following conditions:

catalyst volume - 560 1 volumetric speed - 8500 h ¹ pressure - 1 bar abe.

temperature - 835 ° С inlet concentration of N ₂ O - 1400 ppm layer resistance - 12 mm Н ₂ О at Н = 200 mm

The catalytic activity of BN ₂ OK is:

a = 0.95 and a = 1

Claims (4)

Spinel-like copper-zinc-aluminum catalyst for decomposition of N ₂ O to N ₂ and O ₂ , characterized in that it contains active phase - CuA1 ₂ O ₄ and stabilizing phase - ΖηΑ1 ₂ Ο ₄ in the ratio Cu: Zn: Al = 1: 1: 4 with nanosized particles. Spinel-like copper-zinc-aluminum catalyst for the decomposition of N ₂ O to N ₂ and O ₂ according to Claim 1, characterized in that it is formed in the form of cylindrical rings with bases in the form of one and a half or part thereof, with dimensions 11x5x5 (± 1 mm), with external (geometric) surface F = 5 cm ² / g and porosity> 30. Spinel-like copper-zinc-aluminum catalyst for the decomposition of N ₂ O to N ₂ and O ₂ according to claims 1 and 2, characterized in that it is used in industrial plants for the production of nitric acid based on the oxidation of ammonia with air at atmospheric or elevated pressure, immediately after the contact networks in the oxidation reactor itself. A process for the preparation of a spinel-like copper-zinc-aluminum catalyst for the decomposition of N ₂ O to N ₂ and O ₂ according to claims 1, 2 and 3, characterized in that it is carried out by direct synthesis from the ammonia complexes of Cu, Zn when mixing copper-zinc-ammonia-carbonate solution with concentration of components in the range of 60-90 g / 1 CuO, 60-90 g / 1 ZnO, 160-180 g / 1 NH ₃ and 120-140 g / 1 CO ₂ and aqueous solution of A1 (NO ₃ ) ₃ with a concentration in the range of 120-180 g / Ι A1 ₂ O ₃ at a temperature of 80 ° C for 50 min, filtration of the contact mass, annealing at a temperature of 350 to 600 ° C for 3-6 h and molding.