Catalyst for nitrous oxide removal and ammonia oxidation and method for producing same

Abstract

The proposed invention relates to catalysts for nitrous oxide removal and / or ammonia oxidation in the production of nitric acid. What is proposed is a catalyst for nitrous oxide removal and / or ammonia oxidation which is in the form of a shaped pellet containing an active phase having the composition LaxCeyCozO3, where 0.6≤x≤0.8; 0.2≤y≤0.4; 0.6≤z≤1.4, and the structure of the catalyst pellet forms a connected system of macropores. The invention also includes a method for producing such a catalyst. The technical result of the group of inventions is the production of a catalyst for nitrous oxide removal and / or ammonia oxidation which has high catalytic activity, improved hydrothermal stability and enhanced strength.

Description

[0001] CATALYST FOR THE REMOVAL OF NITRUS OXIDE, AMMONIA OXIDATION AND A METHOD FOR ITS PRODUCTION

[0002] Field of technology

[0003] The present invention relates to catalysts for the removal of nitrous oxide and / or the oxidation of ammonia in nitric acid production. The invention also includes a method for producing such a catalyst.

[0004] Prior art

[0005] In recent years, interest in the decomposition of nitrous oxide has grown, as nitrogen monoxide is a greenhouse gas. N2O is formed, in particular, during the catalytic oxidation of ammonia to produce nitric acid. While nitrous oxide decomposition occurs to some extent at high temperatures, most processes require the use of various types of catalysts for its decomposition.

[0006] Numerous catalysts for the decomposition of N2O are known, and most of them include oxides of various metals as the active component.

[0007] In particular, cobalt oxide is widely known to be active in ammonia oxidation. To improve the activity and selectivity of the cobalt oxide catalyst, it is proposed to incorporate various promoters, such as rare earth metals.

[0008] Thus, patent RU2358901C2, published on 20.06.2009, discloses a catalyst for the oxidation of ammonia and the removal of nitrous oxide of the composition EaCoO3, in which lanthanum is partially replaced (for example, up to 20% mol) by cerium.

[0009] The disadvantage of the proposed catalyst is its low cerium content, which leads to a decrease in the activity and hydrothermal stability of the catalyst.

[0010] For optimal use, a catalyst must be highly stable under reaction conditions. Stability is determined, in particular, by mechanical strength and hydrothermal stability.

[0011] Patent RU2358901C2 does not disclose the catalyst synthesis method, its strength characteristics, or resistance to water at elevated temperatures and / or pressures, which may indicate low strength of the resulting granules and low hydrothermal stability. The closest analogue of the present invention is known from Chinese patent CN86108985B, published on November 23, 1988, which discloses the catalyst composition Lai-xCexCoO3, where x ranges from 0 to 1. The catalyst is obtained by coprecipitation of lanthanum, cerium, and cobalt oxides. The use of the coprecipitation method may result in insufficient homogeneity of the resulting catalyst, which may impair its catalytic performance. In addition, the catalyst is formed into granules by single-stage calcination at 900°C.However, the patent does not specify the catalyst's strength characteristics or resistance to water at elevated temperatures and / or pressures, which may indicate low strength of the resulting granules and low hydrothermal stability. Furthermore, in the case of coprecipitation, it is difficult to control the degree and uniformity of precipitation of individual components.

[0012] Disclosure of invention

[0013] The objective and technical result of the present invention is to obtain a catalyst for removing nitrous oxide and / or oxidizing ammonia with high catalytic activity, increased hydrothermal stability and strength.

[0014] Additionally, the temperature of 98% N2O conversion when using a catalyst does not exceed 693-730°C. After 100 hours of hydrothermal treatment (GHSV = 100,000 h' 1 ) the temperature of 98% N2O conversion does not exceed 712-760°C. The strength of the resulting granules is 129-191 N / granule.

[0015] To solve the stated problem and achieve the technical result, a catalyst for the removal of nitrous oxide and / or oxidation of ammonia is proposed in the form of a molded granule containing an active phase of composition La х Se у SogOz, where

[0016] 0.6<x<0.8;

[0017] 0.2<y<0.4;

[0018] 0.6 <z<l,4, структура гранулы которого образует связную систему макропор.

[0019] By a "connected system of macropores" is meant a connected three-dimensional structure, preferably connected in three dimensions by arches (isthmuses, bridges), that is, any pairs of points of the structure can be connected by a trajectory (here the term "trajectory" is taken in its mathematical definition used in topology), thereby increasing the density of the network of "force chains" bearing a set of mechanical stresses. Unless otherwise specified in individual cases, references to micropores or macropores are given on the basis of the IUPAC classification, according to which micropores are pores with a diameter dp < 2 nm, mesopores are pores with a diameter dp from 2 to 50 nm, and macropores are pores with a diameter greater than 50 nm [Haber et al. IUPAC, Pure and Appl. Chem., 63 (1991) 1227].

[0020] The combination of the catalyst's qualitative and quantitative composition and its unique pore distribution with structural connectivity allows it to impart, on the one hand, very high catalytic activity and hydrothermal stability, and on the other, excellent mechanical strength due to the presence of bridges (or vaults) between the particles (crystals). The developed porous structure imparts high catalytic activity.

[0021] The content of Ce at y = 0.2-0.4 is optimal; an increase or decrease in the amount of Ce relative to these values ​​leads to a decrease in activity and hydrothermal stability.

[0022] The Co content is optimal at z = 0.6-1.4; with a decrease in the amount of Co relative to these values, the activity decreases, and an increase in the content leads to a decrease in hydrothermal stability.

[0023] The La content is optimal at x = 0.6-0.8. An increase or decrease in the La content leads to a significant decrease in activity.

[0024] Preferably, the structure of the catalyst granule forms a connected system of macropores throughout the entire volume of the catalyst granule.

[0025] The absence of individual unbound particles in the granule additionally increases the strength of the catalyst.

[0026] Preferably, the macropore size is at least 50 nm, preferably at least 200 nm.

[0027] This macropore size ensures the absence of diffusion limitations when the catalyst operates in the high temperature range, which leads to an additional increase in catalytic activity.

[0028] Preferably, the granule contains at least one meso- and / or micropore system.

[0029] The presence of a system of meso- and / or micropores ensures the absence of diffusion restrictions during catalyst operation at high temperatures, further enhancing catalytic activity. Preferably, the macropores are interconnected by isthmuses, with the length of at least one isthmus being at least 400 nm, preferably at least 1 μm.

[0030] This neck length, related to the pore size, is the most suitable for ensuring both catalytic activity and strength.

[0031] Preferably, the granule comprises a binder in an amount of no more than 50 wt.%, preferably no more than 30 wt.%, even more preferably no more than 20 wt.%, based on the total weight of the catalyst.

[0032] The use of a binder results in a reduction in weight and an additional increase in the porosity of the catalyst.

[0033] Preferably, AlO3 or boehmite is used as a binder.

[0034] Binders such as boehmite and AlO3 provide weight reduction and additional increase in catalyst porosity while maintaining sufficient strength and activity.

[0035] Also, in order to solve the technical problem and achieve the technical result, the present invention proposes a method for producing a catalyst for removing nitrous oxide and / or oxidizing ammonia, comprising a) a step of mixing solutions of metal nitrates: lanthanum, cerium and cobalt with a solution of a polybasic carboxylic acid or amino acid; b) a step of stirring the mixture obtained in step a) until a homogeneous mass is formed; c) a step of drying the sample obtained in step b); d) a step of calcining the sample dried in step c) at 300-550°C for at least 5 hours; e) a step of pressing the sample calcined in step d) to obtain a molded granule; f) a step of calcining the granule obtained in step e) at a temperature of 450-1200°C for at least 5 hours.

[0036] Synthesizing perovskite structures using polybasic acids or amino acids allows for the production of complex multicomponent systems with a given stoichiometry. Mixing metal salts with a polybasic acid or amino acid produces a homogeneous solution that transforms into a resin-like mass in which the metal cations are immobilized within a polymer network, preventing their segregation. A drying step prevents the sample from sticking to the vessel walls. Subsequent calcination removes organic residues, forming a crystalline phase of the perovskite structure with relatively high porosity. Calcination in steps d) and f) for less than five hours increases the occurrence of defects in the crystalline structure, which subsequently negatively impacts the catalyst's stability and activity.

[0037] Preferably, a saturated tricarboxylic acid, preferably citric acid, is used as the polybasic carboxylic acid added in step a); and glycine or ethylenediaminetetraacetic acid (EDTA) is used as the amino acid.

[0038] To achieve the technical result, any polybasic carboxylic acid or amino acid can be used. Using polybasic alpha-hydroxy acids, such as citric acid, results in a more branched polymer network. Furthermore, such acids are more readily available.

[0039] Preferably, the molar ratio of citric acid to the sum of the moles of metals ranges from 0.1 to 2.00, preferably from 0.2 to 1.

[0040] This molar ratio is the most suitable for the completeness of the reaction and also helps to reduce the consumption of organic reagents.

[0041] Preferably, a polyhydric alcohol is added at step a).

[0042] When mixing metal salts with a polybasic acid and a polyhydric alcohol, a polyesterification reaction occurs with the formation of a homogeneous solution, which contributes to an additional reduction in the consumption of organic components.

[0043] Preferably, a dihydric alcohol, preferably ethylene glycol, is used as the polyhydric alcohol.

[0044] Any polyhydric alcohol can be used to achieve the technical result. Ethylene glycol is the most preferred due to its widespread availability.

[0045] Preferably, the molar ratio of ethylene glycol to the sum of the moles of metals ranges from 0.1 to 1.

[0046] Reducing the consumption of organic components reduces the total mass of the initial mixture during calcination per unit of catalyst, further enhancing the efficiency of the proposed method. Furthermore, CO2 emissions are reduced, reducing the carbon footprint, further enhancing the environmental friendliness of the technology.

[0047] Preferably, in step b) the mixture is heated with stirring to a temperature of 60-120°C, preferably 90-110°C. Heating the mixture in the specified temperature range ensures the greatest homogeneity of the solution, which further improves the catalytic characteristics of the catalyst.

[0048] Preferably, the calcination in step d) is carried out for 5-20 hours, preferably for 8-15 hours.

[0049] The dried sample is calcined by slowly raising the temperature to provide additional control and flexible regulation of the heating.

[0050] Preferably, calcination in step e) is carried out for 5-20 hours, preferably for 8-15 hours.

[0051] The pressed sample is calcined, slowly raising the temperature, to form a homogeneous, highly ordered perovskite structure with fewer lattice defects.

[0052] Preferably, calcination in step d) is carried out in such a way that the rate of temperature increase from room temperature to the calcination temperature of the dried sample is 50-100°C / hour.

[0053] The dried sample is calcined by slowly raising the temperature to provide additional control and flexible regulation of the heating.

[0054] Preferably, calcination in step f) is carried out in such a way that the rate of temperature increase from room temperature to the calcination temperature of the pressed sample is 50-100°C / hour.

[0055] The pressed sample is calcined, slowly raising the temperature, to form a homogeneous, highly ordered perovskite structure with fewer lattice defects.

[0056] Brief description of the drawings

[0057] Fig. 1 - XRF spectra of samples 1-5

[0058] Fig. 2 - X-ray diffraction spectra of samples 6-7

[0059] Fig. 3 - X-ray diffraction spectra of samples 8-11

[0060] Fig. 4 - SEM image of sample 3 (resolution 2 µm)

[0061] Fig. 4a - SEM image of sample Za (resolution 2 µm)

[0062] Fig. 5 - SEM image of sample 3 (resolution 1 µm)

[0063] Fig. 6 - X-ray diffraction spectra of samples 1, 3, 5 after hydrothermal treatment (HT)

[0064] Fig. 7 - distribution of reaction products for sample 3

[0065] Fig. 8 - X-ray diffraction spectra of sample 3* after adding boehmite Best embodiments of the invention

[0066] The described embodiments are provided for illustrative purposes only. Those skilled in the art will readily recognize that other embodiments are possible without changing the essence of the invention.

[0067] Obtaining a catalyst

[0068] To obtain the catalyst, a mixture of lanthanum, cerium, and cobalt nitrates was dissolved in distilled water. A previously dissolved polybasic acid or amino acid was added to the resulting solution. In some cases, a polyhydric alcohol was also added. This mixture was heated with stirring to temperature T1 (80-120°C) and maintained at this temperature until a homogeneous resin-like mass formed. The resulting sample was kept in a drying oven. The dried sample was calcined in a muffle furnace at T2 (300-550°C) for at least five hours. The rate of temperature increase (VI) from room temperature to T2 was 50-100°C / hour. The calcined catalyst was pressed into a tablet (granule). The resulting tablet (granule) was again calcined in a muffle at a temperature of T3 (450-1200°C) for at least five hours at a heating rate of V2 (50-100°C / hour).

[0069] The composition of the obtained samples 1-11, as well as the conditions of their production are given in Tables 1-2.

[0070] It will be obvious to a specialist that in order to obtain the composition Ьа х Se у SogOz, where

[0071] 0.6<x<0.8;

[0072] 0.2<y<0.4;

[0073] 0.6 <z<l,4, мольные соотношения нитратов металлов варьировали в пределах: нитрат лантана: нитрат церия:нитрат кобальта = (0,6-0,8):(0,2-0,4):(0,6-1,4).

[0074] It will be obvious to a specialist that the catalyst granule can have any shape known from the prior art and capable of providing minimal gas-dynamic resistance of the bed, high strength of the granules and resistance to cyclic thermal loads, wear resistance of the catalyst throughout the entire service life. In particular, the shape of a cylinder, quadralob, trilob, sphere, having a diameter and height of 6-20 mm; as well as 1-10 channels with a diameter of 1-5 mm. In addition, the catalyst can be made in the form of thin-walled finned tubes with 3-15 fins. In addition, the catalyst can be made in the form of a honeycomb of various shapes and heights. The phase composition of the synthesized samples 1-11 was studied by X-ray phase analysis (XRD). Diffraction patterns were obtained on a DRON-4 diffractometer (N1P1 "Burevestnik", Russia) using Cu-K radiation а (Ni filter, wavelength X=1.54059 nm). Filming was carried out in the range of angles of 15-75° (29) with a step of 0.02° (29) and an exposure time of 3 sec.

[0075] The XRD results confirming the production of samples 1-11 are shown in Figs. 1-3.

[0076] Also, samples la-11a with the same qualitative and quantitative composition as samples 1-11, respectively, were obtained using the method disclosed in the closest analogue.

[0077] Catalyst characteristics

[0078] It was unexpectedly discovered that the catalyst obtained by the method of the present invention has greater mechanical strength than the catalyst obtained by the method proposed in the closest analogue.

[0079] Strength was measured using a LinteL® PC-21 catalyst strength tester, manufactured according to NTVR 441336.965 TU. The measurement was conducted in accordance with ASTM D4179 Standard Test Method for Single Pellet Crush Strength of Formed Catalysts and Catalyst Carriers.

[0080] The strength characteristics of samples 1-11 and la-11a are given in Table 3.

[0081] Samples 3 and 3a were examined by scanning electron microscopy (SEM) using a Hitachi Scanning Electron Microscope SU3599.

[0082] When examining the SEM images of samples 3 and 3a (shown in Figs. 4 and 4a), significant structural differences were discovered. For example, the structure of sample 3 is characterized by a connected system of macropores. That is, any two points in the structure can be connected by a continuous line of isthmuses (arches). If we look at the micrograph of sample 3a, we can see that the sample's structure is a collection of unconnected individual particles.

[0083] It is further noted that both micrographs were taken on the same instrument (Hitachi Scanning Electron Microscope SU3599) at the same resolution (2 µm).

[0084] It will be obvious to a skilled technician that, despite the identical qualitative and quantitative composition of samples 3 and 3a, their structure is fundamentally different, a consequence of differences in their production methods. That is, the granule structure, characterized by a connected system of macropores, is not a characteristic objectively inherent to a catalyst characterized solely by its qualitative and quantitative composition. SEM images of sample 3, taken at 2 μm and 1 μm resolution, show that the neck length can be at least 400 nm. Individual neck lengths exceed 1 micron (Fig. 4 and Fig. 5).

[0085] Mercury porosimetry was used to determine macropore diameters in the present invention. Gas adsorption was used to determine meso- and micropore sizes. Sample pore sizes are presented in Table 4.

[0086] The catalytic activity of the catalyst samples was studied using a flow-through setup equipped with a tubular quartz and fixed catalyst bed. The gas mixture composition was: 6.00% Ch; 0.20% N2O; 9.0% NO; 9% H2O; the rest was N2. The space velocity was 100,000 h' 1 The tests were carried out with the temperature increasing from 120 to 900°C at a rate of 5°C / min. A Fourier transform infrared spectrometer was used to determine the concentrations of NO, NO2, N2O, and H2O.

[0087] The activity of the catalyst samples was assessed by the conversion value (X) of N2O, calculated using the formula: where [N2O]BX and [N2O]Bbix are the concentrations of nitrous oxide at the inlet and outlet of the reactor, respectively.

[0088] Table 5 shows the temperatures of 98% nitrogen monoxide conversion for samples 1-11. It can be seen that the temperature does not exceed 730°C, and in some cases it is less than 700°C.

[0089] To study the stability of the catalyst samples, they were first subjected to hydrothermal treatment (HTT). The reactor was placed in a horizontal furnace heated to 800-1000°C at a rate of 5°C / min. The total HTT time for the samples was 100 hours. The flow composition was 10% H2O in air.

[0090] As can be seen from Fig. 6, the structure of samples 1, 3, 5 did not change after the GTO.

[0091] Table 5 shows the temperatures of 98% conversion of nitrogen monoxide for samples 1-11 after GTO.

[0092] You can see that the temperature does not exceed 760°C. And in some cases it is no more than 712°C.

[0093] In another embodiment of the invention, the following composition of the gas mixture was used to study sample 3: 0.1% N2O, 0.25% NO, 0.07% T4H3, 5% O2, 9% H2O, the rest - N2. In Fig. 7 it can be seen that ammonia is completely oxidized at T> 350 °C, while in the range of 400-850 °C oxidation occurs to NO.

[0094] The space velocity was 100,000 h . Tests were carried out with the temperature increasing from 120 to 900°C at a rate of 5°C / min. A Fourier transform infrared spectrometer was used to determine the concentration of substances.

[0095] In the third embodiment of the invention, a binder, boehmite, was added to sample 3* (with the same active phase composition as sample 3) in an amount of 15 wt.% based on the total weight of the catalyst. The structure of the resulting sample is shown in Fig. 8. The density of sample 3* decreased by 22% compared to the density of sample 3 (which obviously led to a decrease in weight), and the porosity increased by 11%. Also, based on Table 5, it can be concluded that with the addition of boehmite, the activity and stability after hydrothermal treatment of the sample change insignificantly. Thus, the proposed group of inventions provides a catalyst for the removal of nitrous oxide and / or oxidation of ammonia with high catalytic activity, increased hydrothermal stability and strength.

[0096] Table 1. Composition and conditions for obtaining the studied samples

[0097] Table 2. Conditions for obtaining the test samples

[0098] Table 3. Strength characteristics of the studied samples

[0099] Table 4. Porosity characteristics of the studied samples

[0100] Table 5. Activity characteristics of the studied samples

Claims

Invention formula 1. A catalyst for the removal of nitrous oxide and / or oxidation of ammonia, in the form of a molded granule, including an active phase of composition La х Se у SogOz, where 0.6 <х<0,8; 0,2 <у<0,4; 0,6 <z<l,4, структура гранулы которого образует связную систему макропор.

2. The catalyst according to claim 1, characterized in that the structure of the catalyst granule forms a connected system of macropores throughout the entire volume of the catalyst granule.

3. The catalyst according to claim 1, characterized in that the diameter of the macropores is at least 50 nm, preferably at least 200 nm.

4. The catalyst according to claim 1, characterized in that the granule contains at least one system of meso- and / or micropores.

5. The catalyst according to claim 1, characterized in that the macropores are connected to each other by isthmuses, wherein the length of at least one isthmus is at least 400 nm, preferably at least 1 μm.

6. The catalyst according to claim 1, characterized in that the molded granule additionally includes a binder in an amount of no more than 50% by weight, preferably no more than 30% by weight, even more preferably no more than 20% by weight, based on the total weight of the catalyst.

7. The catalyst according to item 6, characterized in that boehmite is used as a binder.

8. A method for producing a catalyst for removing nitrous oxide and / or oxidizing ammonia according to any of paragraphs 1-7, comprising a) a step of mixing solutions of metal nitrates: lanthanum, cerium and cobalt with a solution of a polybasic carboxylic acid or amino acid; b) a step of mixing the mixture obtained in step a) until a homogeneous mass is formed; c) a step of drying the sample obtained in step b); d) a step of calcining the sample dried in step c) at 300-550°C for at least 5 hours; e) a step of pressing the sample calcined in step d) to obtain a shaped granule; f) a step of calcining the granule obtained in step e) at a temperature of 450-1200°C for at least 5 hours.

9. The method according to claim 8, characterized in that a saturated tribasic carboxylic acid, preferably citric acid, is used as the polybasic carboxylic acid added in step a); and glycine or ethylenediaminetetraacetic acid (EDTA) is used as the amino acid.

10. The method according to item 9, characterized in that the molar ratio of citric acid to the sum of the moles of metals varies from 0.1 to 2, preferably from 0.2 to 1.

11. The method according to item 8, characterized in that at stage a) a polyhydric alcohol is added.

12. The method according to item 11, characterized in that a dihydric alcohol, preferably ethylene glycol, is used as the polyhydric alcohol.

13. The method according to item 12, characterized in that the molar ratio of ethylene glycol to the sum of the moles of metals varies from 0.1 to 1.

14. The method according to item 8, characterized in that in step b) the mixture is heated with stirring to a temperature of 60-120°C, preferably 90-110°C.

15. The method according to item 8, characterized in that calcination in step d) is carried out for 5-20 hours, preferably for 8-15 hours.

16. The method according to item 8, characterized in that calcination in step e) is carried out for 5-20 hours, preferably for 8-15 hours.

17. The method according to item 8, characterized in that calcination in step d) is carried out in such a way that the rate of temperature increase from room temperature to the calcination temperature of the dried sample is 50-100°C / hour.

18. The method according to item 8, characterized in that calcination in stage f) is carried out in such a way that the rate of temperature increase from room temperature to the calcination temperature of the pressed sample is 50-100°C / hour. < / у<0,4; < / х<0,8;

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