CZ20131070A3 - Catalyst for removing N20 from waste gases and process for preparing thereof - Google Patents

Abstract

Catalyst for removing N.sub.2 from waste gases containing, besides N.sub.2.sub.2 water vapor, NO.sub.2 O.sub.3 by its decomposition into environmentally harmless components, nitrogen and oxygen, is that the catalyst it consists of calcined cobalt beta-hydroxide impregnated with aqueous solutions of cesium compounds, which are nitrates or carbonates, and the concentration of cesium is in the range of 0.2 to 3% by weight, based on the weight of the catalyst. The process for its preparation consists in treating cobalt nitrate with sodium hydroxide in a molar ratio of NaOH / Co (NO.sub.3), sub = 0.5 to 2.0 at a temperature of 15 to 30 degC with stirring for 5 to 10 minutes to form a crystalline structure of beta-cobalt hydroxide which is dried and calcined at 350-650 degC for 2-8 hours and then impregnated with an aqueous solution of cesium compounds such that the molar ratio of Cs to Co.sub.3 is between 0.003 and 0.060 and is again calcined at 350 to 650 degC for 2 to 8 hours. The catalyst obtained decomposes N.sub.2.sub.2 from the waste gases at temperatures of 350 degC and higher, in the resulting gas a concentration of N.sub.2.sub.2.sub.sub.2 is achieved below 15 < 0 > . at a concentration of N.sub.2 O at the input of 0.1 mol%. and load 0.001 g.sub.katal.n.min ml.sup.-1.n ..

Description

Catalyst for removal of N2O tl waste gases and process for its production

Technical field

The present invention relates to a process for the catalytic decomposition of N2O in waste gases and to the preparation of the catalyst required for its implementation.

BACKGROUND OF THE INVENTION

Azoxide (NiO), formerly known as nitrous oxide, is one of the substances that strongly deplete the stratospheric ozone layer and at the same time it is an important greenhouse gas with a high greenhouse warming potential (GWP = 310). Its long duration in the atmosphere, estimated at 120 to 150 years, is also unfavorable. The largest source of N2O is agriculture, the chemical industry (mainly nitric and adipic acid production) and combustion processes, including emissions from the use of three-way catalysts in automobile transport. In most of the exhaust gas (e.g. from combustion of solid fuels in a fluidized bed or from the production of nitric acid) N2O emissions are accompanied by higher emissions of _NOx (NO and NO2). The current concentration of N2O in the atmosphere is around 612 / zg m ' ³ (312 ppb) and was found to increase by 0.2 + - 0.3% per year [1]. activities. Technologies for reducing N2O emissions from nitric and adipic acid plants are already at the stage of commercial applications, yet it is still desirable to optimize them and develop new technologies.

The choice of a suitable N2O emission reduction method for a given source depends on the process conditions and the waste gas parameters. A simple method of N2O disposal is its direct decomposition into oxygen and nitrogen. The advantage of this method is that the addition of a reducing agent is not necessary and the reaction products are natural components of the atmosphere. However, this method requires sufficiently active, selective and, above all, stable catalysts.

Various catalytic systems have been studied for direct decomposition of N2O. It has been found that the reaction is catalysed by transition metals (Co, Ni, Fe, Cu, Mn, La) and noble metals (Rh, Ru, Pd), and the matrix or carrier type and the oxidation state of the metal play a key role [2]. The most active catalysts are Rh-containing catalysts. However, their use in practice is not economically advantageous due to the high cost of rhodium. Active catalysts also include zeolites with an iron cation content [1], which, however, tend to be less stable in long-term deployment under real conditions. Catalytic decomposition of N ₂ O was also investigated on mixed oxides prepared by calcination of double layered hydroxides, especially of the Co-MnAl type. It was found that the catalytic activity increased significantly after modification of the mixed Co-Mn-Al oxide with alkaline promoters [3].

Recently, references to cobalt oxide catalysts have been found in the scientific literature on the decomposition of N2O. Stelmachowski et al. [4] published data on the high efficiency of commercial CO 3 O 4 impregnated with alkali metal carbonates or nitrates. Pasha et al. [5] prepared CO3O4 by precipitation of a solution of cobalt nitrate with sodium carbonate. The cesium promoter was applied to CO 3 O 4 by impregnation from a cesium nitrate solution. In the same way, using NaOH or Na ₂ CC> 3 as precipitating agents available cesium oxide modified CO3O4 and Ohnishi et al. [6].

In the patent literature, hydrotalcites, cobalt carbonates or hydroxides, most often prepared by precipitation of cobalt nitrate, optionally promoted by other constituents (metals), are mentioned as precursors for the preparation of the cobalt catalyst for the decomposition of N2O. E.g. Japanese Patent JP2012050969-A [7] entitled "Catalyst for decomposing nitrous oxide and method for cleaning nitrous oxide-containing gas by using the same" is Rubidium or Cesium Modified CO 3 O 4. CO 3 O 4 is prepared by precipitation of Co (NO 3) 2, Cs and Rb promoters are deposited by impregnation from nitrate solutions. The catalyst decomposes Ν2Ο even in the presence of CO2 and is active even at low temperatures.

The object of Indian patent 2256389: A [8] is the preparation of CO 3 O 4 by precipitation of Co (NO 3) ₂ , wherein an alkali metal (Na, K, Cs) is used as the promoter. The promoters are deposited on CO 3 O 4 by impregnation from nitrate solutions. Na ₂ CC> 3, (NH ₄ ) ₂ CO ₃ and oxalic acid are protected as precipitating agents. The catalyst decomposes N2O in the presence of moisture and oxygen even at low temperatures (350 ° C).

Japanese Patent JP2007054714-A [9] entitled "Decomposition catalyst of nitrous oxide contained in an exhaust gas ejected from a motor vehicle, containing cobalt oxide having tricobalt tetraoxide as the main component, alkali metal and / or alkaline earth metal" is a catalyst for the decomposition of N2O, consisting of CO 3 O 4 and a promoter (alkali metal or alkaline earth metal) that decomposes N ₂ O at temperatures of 300 ° C or less. The preparation of the catalyst consists of adding an aqueous solution of an alkali metal or alkaline earth metal salt to the cobalt salt and / or cobalt oxide and / or the aqueous solution of the cobalt salt, impregnating the carrier, drying and calcining.

Japanese patent WO 2013047484 A1 [10] entitled "Catalyst for decomposition of nitrous oxide, method for producing catalyst for decomposition of nitrous oxide, and method for processing nitrous oxide-containing gas" protects an N2O decomposition catalyst that effectively decomposes N2O in the presence of NO _X and CO2. It consists of component A (CO 3 O 4 or CoO) and component B (metal from group 5 to 15), B / A molar ratio = 0.0005 to 0.15. The catalyst may also be comprised of component A (cobalt oxide) and component C (at least one metal of Groups 11-15 and Group 2-3). Co (OH) 2 and Co ((OH) 2 --CoCCh yCo), cobalt nitrate, cobalt chloride, cobalt acetate, cobalt carbonate and basic cobalt carbonate are used as starting materials for the preparation of component A. Alkali metals as promoters are not included.

SUMMARY OF THE INVENTION

These disadvantages are overcome by a catalyst for the removal of N2O (azoxide) from waste gases containing, in addition to N2O, water vapor, oxygen and NO _X by decomposing it into environmentally harmless components, nitrogen and oxygen, consisting of calcined cobalt cobalt hydroxide impregnated with aqueous solutions of cesium compounds. The cesium compounds are 6 'nitrates or carbonates and the concentration of cesium ranges from 0.2 to 3 days. %, based on the weight of the catalyst. A process for preparing a catalyst is to treat cobalt nitrate with sodium hydroxide in a molar ratio of NaOH / Co (NO3) 2 = 0.5 to 2.0 at 15 to 30 ° C with stirring for 5 to 10 minutes to form a crystalline The structure of cobalt (II) beta-hydroxyde, which is dried and calcined at 350 to 650 ° C for 2 to 8 hours and then impregnated with an aqueous solution of cesium compounds so that the molar ratio of Cs to CO 3 O 4 is within 0.003 to 0.060 and re-calcined at 350 to 650 ° C for 2 to 8 hours. Method of removing N2O from waste gases containing in addition to N2O, yet water vapor, _NOx and oxygen consists in the fact that the waste gas at temperatures of 350 ° C and higher over the catalyst, which consists of calcined beta hydroxide, cobalt-impregnated with aqueous solutions of compounds of cesium, wherein an N2O concentration in the resulting gas of less than 0.015 mol% is achieved at an N2O inlet concentration of 0.1 mol% and a load of 0.001 gk _ata / min ml ^-1 .

We have now found that when a cobalt catalyst - CO 3 O 4 is prepared by calcination at a temperature of 350 to 650 ° C from a precursor of a specific crystal structure, in particular from cobalt cobalt hydroxide prepared by sodium hydroxide on cobalt nitrate, cesium catalyst which allows high N ₂ O conversions (greater than 85%) at temperatures below 350 ° C, even in the presence of O ₂ and H ₂ O.

The method according to the invention represents a simple, low-tech way removing N2O from waste gases containing water vapor, _NOx and oxygen so as to obtain component benign environment (oxygen and nitrogen).

Overview of pictures

Figure 1 shows the powder diffractograms of precursors A, B and C. Identified crystalline phases: precursor A - double layered Co (II) -Co (III) hydroxide admixed with βCo (OH) 2; precursor B - β-Οο (ΟΗ) 2; precursor C - hydrated basic cobalt carbonate, Co (CO 3) 0.5 (OH) 0.1 IH 2 O.

Figure 2 shows the powder diffractograms of catalysts A, B and C. A single crystalline phase - CO 3 O 4 - was identified in all samples. Catalysts A, B, and C were prepared by calcining precursors A, B, and C at 500 ° C.

Examples

The invention is further illustrated by the following examples.

Example 1

Preparation of CO 3 O 4 catalysts from various precursors

Precursor A was prepared as follows: To an air-bubbled solution of sodium hydroxide prepared by dissolving 5.60 g of NaOH in 700 ml of distilled water was added at room temperature and vigorous stirring a solution of cobalt nitrate prepared by dissolving 81.50 g of Co (NO3) 2'6H2O in distilled water. NaOH / Co (NO3) 2 molar ratio = 0.50. The resulting suspension was maintained at room temperature for 18 hours with stirring and air bubbling. Subsequently, the solid product was filtered off, washed with distilled water and dried at 30 ° C. The powder diffractogram of the dried precursor A showed diffraction peaks characteristic of double layered Co (II) -Co (III) type hydroxide. A very small amount of β-Οο (ΟΗ) 2 was also detected in the sample (Figure 1).

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Precursor B was prepared in the following manner: air-sparged sodium hydroxide solution prepared by dissolving 22.40 g of NaOH in 700 ml of distilled water, at room temperature and with vigorous stirring a solution of cobalt nitrate prepared by dissolving 81.50 g of Co (NO3) 2 ^- 6H2O in distilled water. The NaOH / Co (NO 3) 2 molar ratio = 2. The resulting suspension was stirred and bubbled through air at room temperature for 5 minutes, then the solid product was filtered off, washed with distilled water and dried at 30 ° C. The powder diffraction pattern of the dried precursor B showed diffraction peaks characteristic of the beta-modification of cobalt hydroxide, p-Co (OH) 2 (Figure 1).

Precursor C was prepared as follows: A stirred reactor containing 200 ml of distilled water heated to 60 ° C the rate of 5.5 ml ^min-1 added 400 ml of a solution of cobalt nitrate prepared by dissolving 116.40 g of Co (NO3) 2 ^- 6H2O in distilled water. Simultaneously, sodium carbonate solution having a concentration of c (Na 2 CO 3) = 2.65 mol Γ ^{1 was added} at such a rate that the pH of the reaction mixture was maintained at 9.5 ± 0.1. The precipitation reaction was carried out with vigorous stirring at 60 ° C. After the entire amount of cobalt nitrate solution was added, the resulting suspension was stirred at 60 ° C for an additional 30 minutes. Subsequently, the solid product was filtered off, washed with distilled water and dried at 30 ° C. In the powder diffractogram of the dried precursor C, a basic hydrated cobalt carbonate of the composition Co (CO3) ₀ was identified. ₅ (OH) · 0.11H ₂ O (Figure 1).

Catalysts A, B and C were prepared by calcining the dried precursors A, B and C in air at 500 ° C for 4 hours. In the diffractograms of all calcined products, CO 3 O 4 was detected as a single crystalline phase (Figure 2). For the catalytic tests, the catalysts were formed into tablets and, after crushing, a 0.160-0.315 mm particle size fraction was sieved.

Example 2

Catalytic test of the decomposition of N ₂ O in nitrogen in the presence of catalysts A, B and C

Catalysts A, B and C prepared as described in Example 1 were sequentially placed into a heated tube reactor made of stainless steel or glass (internal diameter 5 mm) and placed in contact with the exhaust gas flow rate of 100 ml ^min-1 containing 0.1 mol % N ₃ O, followed by 5 mol% O 2 and 2 mol% H 2 O, the remainder of the gas mixture being nitrogen. The catalyst bed contained 0.1 g of catalyst in the form of 0.160-0.315 mm grains. The connections between the reactor and the individual parts were made using capillaries heated to 120 ° C. The N2O concentration at the inlet and outlet of the reactor was measured by a continuous infrared analyzer (Sick), eventual NO _X formation was checked by an infrared analyzer (Siemens) with a catalytic converter NO2 / NO, temperature and relative gas humidity were measured by a probe (GREISINGER Electronic GmbH) .

N2O conversion obtained under these conditions are summarized in Table 1, the highest conversion of N ₃ O in N2O decomposition in nitrogen (96%) in the presence of O2 and H2O (45%) was achieved with Catalyst B which was prepared from Precursor / 3- Co (OH) 2.

Table 1

Results of catalytic tests of N2O decomposition in the presence of catalysts A, B and C

Catalyst N2O conversion in inert ¹⁾ (%) N2O conversion in the presence of O ₂ + H ₂ O ²⁾ (%) 450 ° C 400 ° C 450 ° C 400 ° C Catalyst A 92 49 16 3 Catalyst B 96 62 45 15 Dec Catalyst C not measured not measured 41 4

^υ 0.1 mol% N ₂ O in N ₂ , spatial time 0.001 kg min Γ ^{1 2)} 0.1 mol% N ₂ O, 5 mol% O ₂ , 2 mol% H ₂ O in N ₂ , spatial time 0.001 kg min Γ ¹

Example 3

Preparation of cesium modified CO3O4 catalysts

Catalyst B prepared from precursor / S-Co (OH) 2 (precursor B) according to the procedure described in Example 1 was impregnated for water absorption with an aqueous solution of CSNO 3 or CS 2 CO 3 to a content of 0.2, 1, 2, 3 and 4 wt. % Cs. The molar CS / CO 3 O 4 ratio ranged from 0.003 to 0.060. Then, the wet product was dried at 130 ° C for 4 h and calcined at 500 ° C for 4 h. The catalyst thus prepared was formed into tablets, crushed, and a 0.160-0.315 mm particle size fraction was sieved from the sample, which was further used in catalytic tests. Promotion of the catalyst podle prepared according to Example 1 by calcination of precursor B with a structure of βCo (OH) 2 with cesium salt gave catalysts with the physical properties listed in Table 2.

Table 2

Physico-chemical properties of catalysts prepared by calcination of cobalt cobalt hydroxide and subsequently modified with varying amounts of cesium

Catalyst Content What*' (wt%) Content Cs * ' (wt%) Hz-TPR ¹ 25-2500 ° C (mmol g ^-1 ) H ₂ -TPR ²⁾ x T _m (° C) Bet (m ² g ') B / CsO 67.5 0.2 13.02 375 407 14.3 B / Csl 67.0 0.8 13.38 370 409 12.6 B / Cs2 67.3 1,8 13.73 337 406 10.7 B / Cs3 64.2 2.9 14.18 349 412 10.6 B / Cs4 64.5 3.4 13.83 353 425 10.9

¹¹ Hydrogen consumption at temperature programmed reduction in temperature range 25 * 500 ° C ²¹ Maximum peak temperature at temperature programmed reduction --¾ * 'Determined in calcined catalyst

Example 4

Catalytic decomposition tests of N ₂ O in the presence of cesium-modified catalysts B

Catalysts B / C prepared according to the procedure described in Example 3 were sequentially placed into a heated tube reactor made of stainless steel or glass (internal diameter 5 mm) and placed in contact with the exhaust gas flow rate of 100 ml ^min-1 containing 0.1 mol%. N ₂ O, 5 mol% O ₂ and 2 mol% H ₂ O, the remainder of the gas mixture was nitrogen. The catalyst bed contained 0.1 g of catalyst in the form of 0.160-0.315 mm grains. The connections between the reactor and the individual parts were made using capillaries heated to 120 ° C. The concentration of N ₂ O at the inlet and outlet of the reactor was measured by a continuous infrared analyzer (Sick), eventual NO _X formation was controlled by an infrared analyzer (Siemens) with a catalytic converter NO ₂ / NO, temperature and relative humidity of the gas was measured by a probe (GREISINGER Electronic GmbH). The N ₂ O conversions achieved under these conditions are summarized in Table 3.

Table 3

Results of catalytic tests of N2O decomposition in the presence of cesium modified B catalysts

Catalyst Content Cs (wt%) N2O conversion in the presence of O2 + H2O (%) t ₈₅ ²⁾ (° C) 450 ° C 400 ° C 360 ° C B / CsO 0.2 86 63 42 450 B / Csl 0.8 100 ALIGN! 100 ALIGN! 91 349 B / Cs2 1,8 100 ALIGN! 88 58 392 B / Cs2 * ³⁾ 1.9 100 ALIGN! 87 56 393 B / Cs3 2.9 100 ALIGN! 86 52 395 B / Cs 3 * ^3> 2.8 100 ALIGN! 85 53 396 B / Cs4 3.4 93 47 16 437

0.1 mol% N ₂ O, 5 mol% O ₂ , 2 mol% H ₂ O in N ₂ , space time 0.001 kg min Γ ²¹ Ts ₅ : temperature required for 85% N ₂ O conversion, 0.1 mol% N ₂ 0.5 mol% of O ₂ , 2 mol% of H ₂ O in N ₂ , space time 0.001 kg min Γ ¹ 'An aqueous solution of Cs ₂ CO _{3 was} used for impregnation

The results show that the B / Csl catalyst prepared by calcination of the precursor B (δ-Co (OH) 2) promoted with 0.8 wt% Cs shows the highest catalytic activity. The temperature T 5 ₈ required to achieve 85% conversion of N2O, the catalyst is very favorable (349 ° C).

Example 5

Stability of Catalyst B / Cs1 (Cs3O4 modified Cs) in catalytic decomposition of N2O

Catalyst B / Csl prepared by calcination of precursor B (β-Co (OH) 2) and modified by the addition of 0,8% wt. cesium according to the procedure described in Example 3 was compressed with the addition of graphite to 5 ^X 5 mm tablets, placed in a heated tubular reactor (32 cm ID) with integral catalyst bed and contacted with real off-gas from HNO3 production at a flow rate of 600 kg h ^{- 1} having an average of 47 · 10 ^-3 mol% N2O ^-3 1,8-10 mole% NO, 5,6-10 ^-3 mol%, NO2, O? and water vapor. The catalyst bed contained 75.9 kg of catalyst. Concentration

N2O reactor inlet and at the outlet thereof was measured continuously by an infrared analyzer (ABB Uras), the _NOx concentration was measured by a photometric analyzer (ABB Limas). The catalytic reaction was carried out at an average temperature of 437 ° C, the stability of the catalyst under these conditions was monitored for 336 hours. The average conversion value was 89%, and there was no decrease in N2O conversion during the experiment. This experiment showed excellent stability of the B / Csl catalyst prepared by calcination of the βCo (OH) 2 precursor and modified with 0.8 wt%. MS in real conditions of waste gas from nitric acid production.

Industrial applicability

The invention can be used in removing undesirable N2O gases from falling away chemical plants for producing nitric acid and other plants producing emissions of N ₂ O.

References

1. Pérez-Ramirez, J .; Kapteijn, F .; Schoffel, K .; Moulijn, J.A. Appl. Catal. B 44 (2003) 117-151.

2. Kapteijn, F .; Rodriguez-Mirasol, J .; Moulijn, J.A .; Appl. Catal. B 9 (1996) 25-64.

3. Obalova, L .; Jiratova, K .; Kovanda, F. Oxidic catalyst, especially for removal of N ₂ O from waste industrial gases. Patent CZ 300807 (2009).

4. Stelmachowski, P .; Maniac, G; Kotarba, A; Sojka, Z .; Catal. Commun. 10 (2009) 1062-1065.

5. Pasha, N .; Lingaiah, N .; Babu, N.S .; Reddy, P.S.S .; Prasad, P.S.S .; Catal. Commun 10 (2009) 132-136.

6. Ohnishi, C .; Asano, K .; Iwamoto, S .; Chikama, K .; Inoue, M .; Catal. Today 120 (2007) 145-150.

7. Nishina Akira, Morita Atsushi, Morishima Atsushi, Kirishiki, Masaru, NIPPON SHOKUBAI CO LTD, JP2012050969-A;

8. Putluru Gray Sankar Reddy, Nakka Lingaiah, Potharaju Seetharamanjaneya Sal Prasad, Kommasani Bhupal Reddy, Nayeem Pasha, Catalysis Division Indian Institute of Chemical Technology, Hyderabad, India, Indian Patent Number 2256389: A (Indian Patent Application Number 593 / DEL / 2007 ), A catalyst useful for decomposition of nitrous oxide to nitrogen and oxygen.

9. Inoue Masashi, Shiotani Yasushi, Chikama Katsumi, Kyoto University, Sud-Chemie Catalysts Inc, Nissan Chem. Indian. Ltd JP2007054714-A, Nitrous oxide decomposition and nitrous oxide decomposition method using the catalyst.

10. Shinya Kitaguchi, Akira Nishina, Nippon Shokubai Co., Ltd., WO 2013047484 A1, Catalyst for decomposition of nitrous oxide, a method for producing a catalyst for decomposition of nitrous oxide, and a method for processing nitrous oxide-containing gas.

Claims (5)

PATENT CLAIMS Catalyst for the removal of N2O from waste gases containing, in addition to N2O, water vapor, NO _X and oxygen by decomposing it into nitrogen and oxygen, characterized in that it is consisting of calcined cobalt hydroxide, impregnated with aqueous solutions of cesium compounds. · - ·. ’ 2. Catalyst according to claim l · _f indicated that cesium compounds are nitrates or carbonates. </ 3. The catalyst of claim 1, wherein _f / in that the cesium concentration ranges from between 0.2 to 3 wt. %, based on the weight of the catalyst. A process for the production of a catalyst according to claim 1, characterized in that the cobalt nitrate is treated with sodium hydroxide in a molar ratio NaOH / Co (NC> 3) 2 = 0.5 to 2.0 at 15 to 30 ° C with stirring for 5 to 10 minutes to form a crystalline structure of cobalt (II) hydroxide, which is dried and calcined at 350 to 650 ° C for 2 to 8 hours after which it is impregnated with an aqueous solution of cesium compounds to form a molar. the ratio of Cs to CO 3 O 4 was within the range of 0.003 to 0.060 and again subjected to calcination at 350 to 650 ° C for 2 to 8 / hours. 5. A method of removing N2O-containing flue gases besides water vapor, N2O, NO _X and the acidic ^ characterized in that the waste gas at temperatures of 350 ° C and higher over the catalyst according to claim 1, wherein the N2O concentration is achieved in the resulting gas under 15-10 ^-3 mol% at an N 2 O concentration at 0.1 mol% input and a load of 0.001 g katai min ml ¹ .