A modified ozone depleting agent with improved thermal stability and its preparation method

Abstract

This invention discloses a modified ozone depleting agent with improved thermal stability and its preparation method, comprising the following steps: determining the specific pore volume, specific surface area, water absorption rate, and single-particle crushing strength of the basic ozone depleting agent; synthesizing the required amount of modifying adhesive solvent based on the specific pore volume and water absorption rate of the basic ozone depleting agent; uniformly spraying and impregnating the modified adhesive solvent from step two onto the basic ozone depleting agent, aging it, and then transferring it to an oven for drying; calcining the dried ozone depleting agent from step three in an air atmosphere to obtain a modified ozone depleting agent with improved thermal stability. This invention can enhance the thermal stability of the ozone depleting agent under high-temperature conditions, that is, increase the upper limit of the thermal deactivation temperature, with an average deactivation temperature increase of approximately 50°C, while the catalyst particle strength is also improved to a certain extent.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to a modified ozone depleting agent with improved thermal stability and its preparation method. Background Technology

[0002] Ozone is a representative pollutant in photochemical smog, a type of air pollution. Long-term exposure to ozone can cause irreversible damage to the human respiratory tract, including inflammation and neurotoxicity. Even low concentrations of ozone can have adverse effects on human health with prolonged exposure. The Ambient Air Quality Standard (GB3095-2012) stipulates that the daily maximum 8-hour average ozone concentration limit is 100 μg / m³. 3 and 160 μg / m 3 However, ozone-related technologies are also widely used in industrial production, such as water treatment, pulp bleaching, and environmental and drinking water disinfection, where ozone-containing exhaust gases require proper handling. Low-temperature catalytic decomposition, due to its safety, energy efficiency, and ease of operation, is currently the most widely used ozone treatment technology. The key to this technology lies in the use of a high-performance ozone depleting agent, also known as an ozone decomposition catalyst, but it currently suffers from easy deactivation in practical applications, a shortcoming that urgently needs to be overcome from a technical perspective.

[0003] The deactivation of gaseous ozone decomposition catalysts typically occurs through the following mechanisms: 1. Chemical poisoning, such as sulfur and halogen poisoning; 2. Carbon deposition and coking contamination; 3. Water vapor contamination in the feed gas; 4. Gas-phase or solid-phase reactants in the feed gas reacting with the active components to form a non-catalytically active phase; and 5. Inactive phase transformation and sintering caused by high temperatures. Both industry and academia have historically focused on researching and solving deactivation issues in ozone catalysts of types 1-4, while solutions for inactive phase transformation and active site sintering caused by high temperatures are rarely reported and remain in the mechanistic research stage. Hollman and Bertholet et al. determined that ozone decomposition is an antithermal reaction with a reaction heat as high as 123.73-141.12 KJ / mol. Therefore, catalysts operating under high ozone concentrations for extended periods are prone to thermal deactivation. The rapid thermal shock caused by equipment start-up and shutdown at high temperatures can easily lead to the calcareous pulverization and crumbling of the catalyst framework. The mechanisms of thermal deactivation of ozone catalysts can be summarized as follows: 1) Temperature causes the catalytically active components to transform into less active crystal forms; 2) sintering and agglomeration occur during the transformation process; and 3) segregation of non-catalytically active substances onto the catalyst surface hinders contact between the feed gas and the active sites of the catalyst. On the other hand, the decomposition activity of ozone is considered to be positively correlated with the oxygen vacancy concentration on the catalyst surface. High temperatures leading to phase and crystal form transformations often reduce the oxygen vacancy concentration, thereby decreasing the activity of the ozone decomposition catalyst. Based on these mechanisms, the deactivation temperature of commonly used ozone decomposition catalysts in the prior art is 550-650℃. Summary of the Invention

[0004] To address the above technical problems, the purpose of this invention is to provide a modified ozone depleting agent with high deactivation temperature, easy production, and improved thermal stability, as well as its preparation method.

[0005] To achieve the above-mentioned objectives, the technical solution of this invention is a method for preparing a modified ozone depleting agent with improved thermal stability, comprising the following steps:

[0006] Step 1: Determine the physical properties of the basic ozone depleting agent, including specific pore volume, specific surface area, water absorption rate, and single-component crushing strength.

[0007] Step 2: Based on the specific pore volume and water absorption rate of the basic ozone depleting agent, synthesize the required amount of modified adhesive solvent;

[0008] Step 3: The modified adhesive solvent from Step 2 is evenly sprayed onto the base ozone depleting agent, and after aging, it is transferred to an oven to dry.

[0009] Step four: calcine the dried ozone depleting agent from step three in an air atmosphere to obtain a modified ozone depleting agent with improved thermal stability.

[0010] In the above technical solution, in step one, the determination of the specific pore volume of the basic ozone depleting agent is based on T / CPCIF 0140-2021 "Determination of specific surface area and pore volume of catalyst support pseudoboehmite by nitrogen adsorption method".

[0011] Specific surface area was determined according to the national standard GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method".

[0012] The water absorption rate is determined by the following method: the ozone depleting agent is vacuum dried at 150℃ for more than 2 hours, then removed and cooled to room temperature. A certain mass of ozone depleting agent is immersed in deionized water at 40℃ for more than 30 minutes by equal volume impregnation. After filtration and draining, the percentage of the increased weight relative to the weight of the dried ozone depleting agent is measured, which is its water absorption rate.

[0013] The single-particle crushing strength is tested according to the standard test method for the single-particle crushing strength of catalysts and catalyst supports formed by ASTM D4179-11 (2017).

[0014] In the preferred embodiment, the modifying solvent in step two is a solution prepared by the metal sol and the hardness enhancer using the sol-gel method.

[0015] A further technical solution involves using an alkaline sol as the modifying agent, including cordierite sol, zirconium sol, and titanium sol. The effective solid content of this sol accounts for 8-15% of the total mass of the base ozone depleting agent, representing 5-9% of the total weight of the base ozone depleting agent when its pore volume is 0.6 mL / g. The total mass of the modified sol is 75-90% of the water absorption rate of the depleting agent.

[0016] The hardness enhancer is one or more of sodium tetraborate, sodium metaborate and sodium borate, and its usage accounts for 1 to 5% of the mass of the modified adhesive solvent. The total amount of boric acid enhancer accounts for 5 to 9‰ of the total weight of the basic ozone depleting agent.

[0017] Furthermore, since acidic substances inhibit ozone decomposition, cordierite sol is synthesized by an alkaline catalytic method. The specific steps are as follows: tetraethyl orthosilicate (TEOS) and anhydrous ethanol are thoroughly mixed in a mass ratio of 1:3 to 1:4 to obtain a TEOS-ethanol solution; then, aluminum nitrate and magnesium nitrate raw materials in a certain mass ratio are dissolved in water to prepare an aqueous solution.

[0018] The mass ratio of TEOS:aluminum nitrate:magnesium nitrate:water is 1:(1.5~1.7):(0.4~0.5):

[0019] (8-15) The above aqueous solution is slowly added dropwise to a continuously stirred TEOS-ethanol solution, followed by the addition of ammonia as a reaction catalyst. The pH is adjusted to be slightly alkaline (7-8), and the solution is stirred evenly. The solution is then transferred to a 40°C water bath for about 6 hours to obtain a transparent gel-like cordierite sol.

[0020] Since conventional inorganic zirconium as the zirconium source synthesis method leaves a large amount of acidic residues, which inhibits ozone decomposition, zirconium sol uses inorganic zirconium as the zirconium source to synthesize gel. The specific synthesis method is as follows: ethylene glycol is added to an ethanol solution of zirconium propoxide, and then mixed with an equal amount of ethanol solution of a certain amount of deionized water. The mixture is then transferred to a high-pressure reactor and reacted at 150°C for more than 12 hours to obtain nano-sized transparent zirconium gel.

[0021] The mass ratio of zirconium propoxide: ethylene glycol: water: ethanol is 1:(1-2.5):(1-4):(4-20).

[0022] The titanium sol is an alkaline titanium sol synthesized using an organic titanium source and an alkanolamine catalyst. The specific synthesis method is as follows: tetrabutyl titanate is dissolved in a mixed solution of ethanol and ethylene glycol, a certain amount of alkanolamine catalyst is added, the mixed solution is refluxed at 40-70℃ for 2-4 hours, a certain amount of silane coupling agent is added, and stirring and aging are continued to obtain nano-sized transparent alkaline titanium sol.

[0023] The mass ratio of tetrabutyl titanate: ethanol: ethylene glycol: alkanolamine catalyst: silane coupling agent is 1:(4-10):(2-4):(0.05-0.1):(0.001-0.005).

[0024] In the above technical solution, the alkanolamine catalyst is one or more of monoethanolamine, diethanolamine, or triethanolamine.

[0025] The silane coupling agent is one or both of vinyltriethoxysilane and γ-aminopropylethoxysilane.

[0026] In the preferred technical solution, the specific method for uniformly spraying and impregnating the modified adhesive solvent onto the base ozone destructor in step three is as follows: a certain amount of base ozone destructor is placed in a disc-type rolling granulator. The granulator is equipped with an atomizing spray gun for spray impregnation. A modified adhesive solvent equivalent to 75-95% of the theoretical water absorption rate of the destructor is uniformly sprayed onto the surface of the base ozone destructor rotating at a low speed. When the modified adhesive solvent is used up, the surface of the ozone destructor should still remain dry.

[0027] In the preferred technical solution, the aging conditions in the oven in step three are 40℃ for more than 12 hours.

[0028] In the preferred technical solution, the drying conditions in step three are 150℃ for 12 hours or more.

[0029] In the preferred technical solution, the calcination conditions in step four are calcination at 450-600℃, with the highest temperature holding time being 4-8 hours. After calcination, the temperature is lowered to below 150℃, and the product can be removed and further cooled to room temperature to obtain the modified ozone destructive agent.

[0030] In the above technical solution, the ozone removal rate of the modified ozone destructor product does not change by more than 8%; under the same working conditions, the local maximum temperature of the ozone destructor bed decreases by more than 15%; the local specific surface area and specific pore volume change does not exceed 30%; when the above conditions are met, if the single particle crushing strength increases, it is a beneficial effect; if it decreases, it shall not exceed 5%.

[0031] The advantages of this invention are:

[0032] 1. This invention can enhance the thermal stability of ozone depleting agents under high-temperature conditions, that is, increase the upper limit of thermal deactivation temperature, and increase the average deactivation temperature by about 50°C.

[0033] 2. Under the same operating conditions, the local maximum temperature of the bed layer of this invention can be reduced by about 15-40℃, preventing local overheating of the bed layer, i.e., the specific heat capacity or heat conduction capacity of the ozone destructor bed layer.

[0034] 3. This invention aims to maintain or even enhance catalytic activity, i.e., ozone removal efficiency;

[0035] 4. This invention can maintain or even enhance the strength of the ozone depleting agent skeleton;

[0036] 5. This invention eliminates the need to add raw materials during the ozone depletion agent molding process, allowing direct modification of already molded ozone depletion agents. This facilitates formulation control and the process is simple and easy to operate.

[0037] 6. The raw materials used in the modified formulations of this invention are readily available or easy to prepare, and no waste is generated during the process. Detailed Implementation

[0038] Example 1:

[0039] The ozone depleting agent molded body uses an ozone depleting agent product (sample 1) from a manufacturer in Hunan Province, with a specific surface area >190m². 2 / g, specific pore volume >0.4mL / g, single particle crushing strength >45N, theoretical water absorption rate 45%, and thermal deactivation temperature above 650℃.

[0040] The modified ozone depleting agent used was formulated with zirconium sol as the metal sol and sodium borate as the hardness enhancer. Specifically, it was a mixed solution of zirconium propoxide, diethylene glycol, water, and ethanol in a mass ratio of 1:1.2:2:4. This solution was reacted in a high-pressure water bath at 150°C for 14 hours. Then, sodium borate, equivalent to 2% of the total mass of the depleting agent, was added and mixed thoroughly to obtain the modified ozone depleting agent. The amount of the ozone depleting agent used for spray impregnation was approximately 40% of the total mass of the depleting agent. The surface of the depleting agent remained dry after spraying and was aged at 40°C for 12 hours before being transferred to a calcining furnace and calcined at 550°C for 4 hours. The final product was a modified ozone depleting agent with improved thermal stability (modified sample 1). The changes in specific pore volume and specific surface area before and after the reaction were compared. The calcination conditions for improved thermal deactivation performance were determined to be 700°C for 6 hours.

[0041] Example 2:

[0042] The ozone depleting agent molded body uses an ozone depleting agent product (sample 2) from a manufacturer in Jiangxi Province, with a specific surface area >140m². 2 / g, specific pore volume >0.3mL / g, single particle crushing strength 50-60N, theoretical water absorption rate 30%, and thermal deactivation temperature above 550℃.

[0043] The modified adhesive solvent used was formulated with alkaline cordierite sol as the metal sol and sodium metaborate as the hardness enhancer. Specifically, tetraethyl orthosilicate (TEOS): anhydrous ethanol: aluminum nitrate: magnesium nitrate: water were prepared into a mixed solution in a mass ratio of 1:3:1.5:0.4:8. Ammonia was slowly added dropwise until the pH reached 8, and the mixture was reacted in a 40°C water bath for 6 hours. Then, sodium metaborate, equivalent to 2.5% of the total mass of the destructive agent, was added and mixed thoroughly to obtain the modified adhesive solvent. The amount of adhesive solvent used for spray impregnation was approximately 28% of the total mass of the destructive agent. The surface of the destructive agent remained dry after spraying. After aging at 40°C for 24 hours, it was transferred to a calcining furnace and calcined at 480°C for 4 hours. Finally, a modified ozone destructive agent with improved thermal stability (modified sample 2) was obtained. The changes in specific pore volume and specific surface area before and after were compared, and the calcination conditions for improved thermal deactivation performance were determined to be 600°C for 6 hours.

[0044] Example 3: The ozone depleting agent molded body uses the OD-3 ozone depleting agent product (sample 3) from Jiangsu Zhishui Youshu Environmental Protection Technology Co., Ltd., with a specific surface area >220m². 2 / g, specific pore volume >0.42mL / g, single particle crushing strength >50N, theoretical water absorption rate 35%, and thermal deactivation temperature above 680℃.

[0045] The modified adhesive solvent formulation used was as follows: alkaline titanium sol was used as the metal sol, and sodium borate was used as the hardness enhancer. Specifically, the mass ratio of tetrabutyl titanate:ethanol:ethylene glycol:diethanolamine was 1:3:2:0.05. The mixed solution was refluxed at 60°C for 4 hours, and then 3‰ vinyltriethoxysilane coupling agent (equivalent to tetrabutyl titanate) and 1.5% sodium borate (equivalent to the total weight of the destructive agent) were added. The mixture was stirred and aged for another 6 hours to obtain the modified adhesive solvent. The amount of adhesive solvent used for spray impregnation was approximately 34% of the total mass of the destructive agent. The surface of the destructive agent remained dry after spraying. After aging at 40°C for 24 hours, it was transferred to a calcining furnace and calcined at 500°C for 4 hours. The final product was a modified ozone destructive agent with improved thermal stability (modified sample 3). The changes in specific pore volume and specific surface area before and after the modification were compared. The calcination condition for improved thermal deactivation performance was 730°C for 6 hours.

[0046] Example 4:

[0047] The ozone depleting agent molded body uses an ozone depleting agent product (sample 4) from a manufacturer in Jiangsu Province. The product has a specific surface area >150m2 / g, a specific pore volume >0.32mL / g, a single particle crushing strength of 40-70N, a theoretical water absorption rate of about 36%, and a thermal deactivation temperature of over 630℃.

[0048] The modified adhesive solvent formulation used consisted of zirconium sol as the metal sol and sodium metaborate as the hardness enhancer. Specifically, it was a mixed solution of zirconium propoxide, diethylene glycol, water, and ethanol in a mass ratio of 1:1.5:3:3. This solution was reacted in a high-pressure water bath at 120°C for 14 hours. Then, sodium metaborate, equivalent to 2% of the total mass of the destructive agent, was added and mixed thoroughly to obtain the modified adhesive solvent. The amount of adhesive solvent used for spray impregnation was approximately 32% of the total mass of the destructive agent. The surface of the destructive agent remained dry after spray impregnation. After aging at 60°C for 24 hours, it was transferred to a calcining furnace and calcined at 500°C for 6 hours. The final product was a modified ozone destructive agent with improved thermal stability (modified sample 4). Comparison of changes in specific pore volume and specific surface area before and after the reaction showed that the calcination conditions for improved thermal deactivation performance were 680°C for 6 hours.

[0049] Table 1

[0050]

[0051] Comparing the ozone removal rate, local maximum temperature of the bed, and deactivation temperature of samples 1-4 and modified samples 1-4 in Examples 1-4, the local maximum temperature of the bed decreased significantly, and the deactivation temperature increased significantly. The ozone catalyst after calcination at the deactivation temperature can still maintain an ozone removal rate of over 80%.

[0052] Ozone removal rate evaluation conditions: inlet concentration 80mg / L, flow rate 2L / min, ozone destructive agent bed volume 50mL, height-to-diameter ratio 3:1, removal rate % = (1 - outlet concentration / inlet concentration) × 100%.

[0053] The local maximum temperature is the highest temperature of the destructor bed near the gas inlet of the reaction vessel.

[0054] Ozone removal rate after calcination: The ozone destructive agent was calcined at a temperature 50°C or higher than the deactivation temperature for 6 hours, and its ozone removal rate was determined under the above-mentioned ozone removal rate evaluation conditions.

[0055] Table 2

[0056] Ozone depleting agents <![CDATA[Specific surface area, m 2 / g]]> Specific pore volume, ml / g Single particle crushing strength, N Sample 1 >190 >0.4 >45 Modified Sample 1 >160 0.39 117 Sample 2 >140 >0.3 50-60 Modified Sample 2 >110 0.35 98 Sample 3 >220 >0.42 >50 Modified Sample 3 >190 0.47 107 Sample 4 >150 >0.32 40-70 Modified Sample 4 >130 0.36 89

[0057] As shown in Table 2, the surface area, specific pore volume and single crushing strength of sample 1-4 of Examples 1-4 and modified sample 1-4 were compared (average value of 10 samples were tested). The specific surface area decreased significantly, the specific pore volume increased slightly, and the single crushing strength increased significantly.

Claims

1. A method for preparing a modified ozone depleting agent with improved thermal stability, characterized in that, Includes the following steps: Step 1: Determine the physical properties of the basic ozone depleting agent, including specific pore volume, specific surface area, water absorption rate, and single-particle crushing strength. Step 2: Based on the specific pore volume and water absorption rate of the basic ozone depleting agent, synthesize the required amount of modified adhesive solvent. The modified adhesive solvent is a solution prepared by the sol-gel method using a metal sol and a hardness enhancer. The metal sol is cordierite sol, zirconium sol, and titanium sol; the hardness enhancer is one or more of sodium tetraborate, sodium metaborate, and sodium borate. The cordierite sol is synthesized by thoroughly mixing tetraethyl orthosilicate (TEOS) with anhydrous ethanol at a mass ratio of 1:3 to 1:4 to obtain a TEOS-ethanol solution. Then, a certain mass ratio of aluminum nitrate and magnesium nitrate is dissolved in water to prepare an aqueous solution. The mass ratio of TEOS:aluminum nitrate:magnesium nitrate:water is 1:(1.5~1.7):(0.4~0.5):(8~15). The above aqueous solution is slowly added dropwise to the continuously stirred TEOS-ethanol solution. Then, ammonia water is added dropwise as a reaction catalyst, the pH is adjusted to slightly alkaline 7-8, stirred evenly, and then transferred to a 40℃ water bath for 6 hours to obtain a transparent gel-like cordierite sol; the synthesis method of the zirconium sol is to add ethylene glycol to an ethanol solution of zirconium propoxide, then mix it with an equal amount of ethanol solution of a certain amount of deionized water, transfer it to a high-pressure reactor and react at 150℃ for more than 12 hours to obtain a transparent zirconium gel, wherein the mass ratio of zirconium propoxide: ethylene glycol: water: ethanol is 1:(1~2.5):(1~4):(4~20); the synthesis method of the titanium sol is to dissolve tetrabutyl titanate in a mixed solution of ethanol and ethylene glycol, add an alkanolamine catalyst, reflux the mixed solution at 40-70℃ for 2~4 hours, then add a silane coupling agent, continue stirring and aging, and finally obtain a transparent titanium sol; wherein tetrabutyl titanate: The mass ratio of ethanol:ethylene glycol:alloamine catalyst:silane coupling agent is 1:(4~10):(2~4):(0.05~0.1):(0.001~0.005). Step 3: The modified adhesive solvent from Step 2 is evenly sprayed onto the base ozone depleting agent, and after aging, it is transferred to an oven to dry. Step four: calcine the dried ozone depleting agent from step three in an air atmosphere to obtain a modified ozone depleting agent with improved thermal stability.

2. The method for preparing a modified ozone depleting agent with improved thermal stability according to claim 1, characterized in that, The amount of the hardening agent used accounts for 1-5% of the mass of the modified adhesive solvent, and the total amount of the hardening agent accounts for 5-9% of the total weight of the basic ozone depleting agent.

3. The method for preparing a modified ozone depleting agent with improved thermal stability according to claim 1, characterized in that, In step three, the aging conditions in the oven are 40°C for more than 12 hours; in step four, the calcination conditions are 450-600°C, with the highest temperature held for 4-8 hours, and the temperature is reduced to below 150°C after calcination.

4. A modified ozone depleting agent with improved thermal stability, characterized in that, It is prepared by the method of any one of claims 1-3 for the preparation of a modified ozone depleting agent with improved thermal stability.

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