A method for catalyzing low-concentration ozone oxidation of NO by using ammonium salt modified SAPO-34 molecular sieve
The preparation of NH4-SAPO-34 catalyst by modifying SAPO-34 molecular sieve with ammonium salt solves the problem of lack of metal-modified molecular sieves in the catalytic oxidation of NO with low concentration ozone, realizes low-temperature high-efficiency catalysis and catalyst regeneration, and reduces production and waste gas treatment costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WENZHOU UNIV
- Filing Date
- 2023-11-30
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, metal-modified molecular sieve catalysts are rarely used in the catalytic oxidation of NO with low concentrations of ozone, and there is a lack of research on non-metal-modified molecular sieves, resulting in high costs and environmental unfriendliness.
NH4-SAPO-34 catalyst was prepared by ion exchange using ammonium salt-modified SAPO-34 molecular sieve for catalyzing the oxidation of NO with low concentration ozone. This method avoids the introduction of metal elements, is simple to prepare, and is environmentally friendly.
This method achieves high-efficiency catalysis under low-temperature conditions, reduces production costs, and improves catalyst recycling rate and reduces waste gas treatment costs by regenerating the catalyst through high-temperature calcination.
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Figure CN117732237B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for catalytic oxidation of NO with low concentrations of ozone using ammonium salt-modified SAPO-34 molecular sieve. Background Technology
[0002] During coal combustion, a large amount of flue gas is generated. NO and SO2, as major pollutants, cause a series of environmental problems, including acid rain, photochemical smog, and ozone layer depletion. NO in the flue gas is poorly soluble in water, while high-valence nitrogen oxides such as NO2, N2O3, and N2O5 can react with water to form HNO2 or HNO3. If NO is pre-oxidized, the oxidation products can then dissolve in water along with the more water-soluble SO2, achieving simultaneous desulfurization and denitrification. Catalytic low-concentration ozone ([O3] / [NO] molar ratio <1) oxidation technology can reduce the dependence of oxidation reactions on ozone. On the one hand, under low temperature conditions (<100℃), the catalyst catalyzes ozone to generate oxidants with faster reaction rates and stronger oxidizing power (such as surface oxygen atoms, hydroxyl radicals, etc.) to oxidize NO. On the other hand, when the oxidation degree of NO ([NO] / [NO]+[NO2]) reaches 50-60%, it can provide the optimal oxidation degree required for subsequent alkaline absorption and denitrification. At this time, the utilization efficiency of ozone reaches the highest level, and the residual ozone concentration is very low, which decomposes quickly in the environment.
[0003] Molecular sieves possess advantages such as large ion exchange capacity, regular pore structure, and large specific surface area, making them ideal materials for catalyzing ozone oxidation. Most research on using molecular sieves as catalysts for ozone oxidation focuses on the effects of added metals (such as transition metals, noble metals, and alkali metals) or metal oxides on the modified catalysts, while the effects of non-metals on molecular sieve modification are rarely considered. NH4 + As a nonmetallic cation, NH4+ exhibits pseudo-alkali metal properties in catalytic reactions. A few studies have demonstrated that NH4+... + The modified molecular sieves exhibit a certain degree of selective oxidizing activity in catalytic oxidation reactions, which is attributed to the compensating cation NH4 within the molecular sieve. + The resulting electrostatic field, generated by unshielded cations in the molecular sieve, can catalyze the reaction of adsorbed molecules through polarization bonds or enhanced electron transfer. However, NH4... + The application of modified molecular sieves in the catalytic oxidation of NO by ozone has not been reported, and there is no experimental evidence to prove their properties.
[0004] Therefore, it is necessary to provide a method for catalytic oxidation of NO with low concentrations of ozone using SAPO-34 molecular sieve modified with inorganic ammonium salts. +As an active component, it can not only reduce dependence on costly and environmentally unfriendly metal elements, but also provide new ideas for the research of non-metallic modified molecular sieve catalytic ozone oxidation reaction. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing ammonium salt modified SAPO-34 molecular sieve. The prepared catalyst is used to catalyze the oxidation of NO with low concentration ozone, thus filling the gap in research on non-metallic modified molecular sieves in the catalytic ozone oxidation system.
[0006] To achieve the above objectives, the main technical solution adopted by this invention includes: a method for catalytic oxidation of NO with low-concentration ozone using ammonium salt-modified SAPO-34 molecular sieve, comprising the following steps:
[0007] (1) The template agent-removed SAPO-34 molecular sieve was mixed with a certain concentration of inorganic ammonium salt solution in a round-bottom flask. Under water bath heating, the mixture was stirred continuously for a certain period of time. Then, the solid-liquid mixture was filtered through a Buchner funnel and washed with water until the pH of the lower filtrate was neutral. After drying in an electric thermostatic drying oven, the above steps were repeated several times to obtain NH4-SAPO-34.
[0008] (2) Place the product from step (1) into a tablet press and press it into tablets under certain conditions. After forming, crush and sieve to obtain a catalyst with a certain particle size.
[0009] (3) The product of step (2) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The concentration of the gas after the reaction is detected by a detector.
[0010] Preferably, the inorganic ammonium salt in step (1) includes, but is not limited to, inorganic soluble ammonium salts such as ammonium nitrate, ammonium chloride, ammonium sulfate, and ammonium carbonate.
[0011] Preferably, in step (1), the inorganic ammonium salt contains NH4 + The concentration range is 0.1 mol / L–8.0 mol / L, and the ratio of SAPO-34 molecular sieve to ammonium salt solution is 1 g: 10 mL–30 mL.
[0012] Preferably, in step (1), the SAPO-34 molecular sieve and the ammonium salt solution undergo ion exchange under water bath heating conditions, with a reaction time of 1–24 h and a reaction temperature of 30℃–90℃.
[0013] Preferably, the solid washed in step (1) is dried in an electric thermostatic drying oven at a temperature of 60℃-120℃ for 6–24 hours.
[0014] Preferably, in step (1), the above steps are repeated several times to obtain NH4-SAPO-34, wherein the number of ion exchanges is 1-5 times.
[0015] Preferably, the tableting conditions in step (2) are: pressure 5–15 MPa, 5–60 s, crushing through an 8–12 mesh sieve to obtain a catalyst with an average particle size of about 1–2 mm for later use.
[0016] Preferably, the simulated flue gas preparation conditions in step (3) are: NO concentration of 50–1000 ppm, SO2 concentration of 0–600 ppm, molar ratio of O3 to NO of 0.1–1, and water vapor volume fraction of 0–20%.
[0017] Preferably, the catalytic reaction conditions in step (3) are: reaction temperature 20℃–100℃, and catalyst residence time 0.5–6s.
[0018] (1) This invention uses SAPO-34 molecular sieve as a support to prepare an ammonium salt-modified molecular sieve catalyst NH4-SAPO-34 by ion exchange, and applies it to the catalytic oxidation of NO by low-concentration ozone. + As the active site of the catalyst, it avoids the introduction of metal elements, and the preparation method is simple, which not only reduces the production cost of the catalyst, but also makes the prepared catalyst more environmentally friendly.
[0019] (2) The NH4-SAPO-34 catalyst prepared in this invention, after undergoing a sulfidation reaction, produces ammonium sulfate or ammonium bisulfate. Since ammonium sulfate completely decomposes upon high-temperature calcination above 550°C, and SAPO-34 molecular sieve exhibits strong hydrothermal stability, maintaining its crystal structure even at high temperatures up to 800°C, the sulfidated catalyst only requires high-temperature calcination (>550°C) for a certain period to regenerate the molecular sieve. The catalyst can be repeatedly reused through re-preparation, further reducing production costs.
[0020] Instruction manual illustrations
[0021] Figure 1 The invention examples 1-4 and the comparative examples demonstrate the catalytic ozone oxidation effect of NO.
[0022] Figure 2 This describes the effect of SO2 on catalytic oxidation efficiency in Example 1 of the present invention.
[0023] Figure 3These are the FT-IR spectra of Embodiments 1 and 4 of the present invention. Detailed Implementation
[0024] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.
[0025] Comparative example:
[0026] (1) Mix 10g of SAPO-34 molecular sieve (with template removed) with 100mL of deionized water in a round-bottom flask. Heat in an 80℃ water bath and stir continuously for 3h. Then filter the solid-liquid mixture using a Buchner funnel and wash with water until the pH of the lower filtrate is neutral. Dry in an electric thermostatic drying oven at 105℃ for 12h.
[0027] (2) Place the product from step (1) in a tablet press and press it into tablets at a pressure of 10 MPa. After 10 seconds of tableting, crush the tablets and pass them through an 8-12 mesh sieve to obtain a catalyst with an average particle size of about 2 mm.
[0028] (3) The product of step (2) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The gas after the reaction is detected by a detector.
[0029] Example 1:
[0030] (1) 10 g of SAPO-34 molecular sieve with template removed was mixed with 100 mL of 3.6 mol / L ammonium nitrate solution in a round-bottom flask. The mixture was heated in an 80°C water bath and stirred continuously for 3 h. The solid-liquid mixture was then filtered through a Buchner funnel and washed with water until the pH of the lower filtrate was neutral. After drying in an electric thermostatic drying oven at 105°C for 12 h, the above steps were repeated, and the NH4-SAPO-34 catalyst was obtained by ion exchange twice.
[0031] (2) Place the product from step (1) in a tablet press and press it into tablets at a pressure of 10 MPa. After 10 seconds of tableting, crush the tablets and pass them through an 8-12 mesh sieve to obtain a catalyst with an average particle size of about 2 mm.
[0032] (3) The product of step (2) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The gas after the reaction is detected by a detector.
[0033] Example 2:
[0034] (1) 10 g of SAPO-34 molecular sieve with template removed was mixed with 100 mL of 3.6 mol / L ammonium chloride solution in a round-bottom flask. The mixture was heated in an 80°C water bath and stirred continuously for 3 h. The solid-liquid mixture was then filtered through a Buchner funnel and washed with water until the pH of the lower filtrate was neutral. After drying in an electric thermostatic drying oven at 105°C for 12 h, the above steps were repeated, and the NH4-SAPO-34 catalyst was obtained by ion exchange twice.
[0035] (2) Place the product from step (1) in a tablet press and press it into tablets at a pressure of 10 MPa. After 10 seconds of tableting, crush the tablets and pass them through an 8-12 mesh sieve to obtain a catalyst with an average particle size of about 2 mm.
[0036] (3) The product of step (2) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The gas after the reaction is detected by a detector.
[0037] Example 3:
[0038] (1) 10 g of SAPO-34 molecular sieve with template removed was mixed with 100 mL of 1.8 mol / L ammonium sulfate solution in a round-bottom flask. The mixture was heated in an 80°C water bath and stirred continuously for 3 h. The solid-liquid mixture was then filtered through a Buchner funnel and washed with water until the pH of the lower filtrate was neutral. After drying in an electric thermostatic drying oven at 105°C for 12 h, the NH4-SAPO-34 catalyst was obtained by one ion exchange.
[0039] (2) Place the product from step (1) in a tablet press and press it into tablets at a pressure of 10 MPa. After 10 seconds of tableting, crush the tablets and pass them through an 8-12 mesh sieve to obtain a catalyst with an average particle size of about 2 mm.
[0040] (3) The product of step (2) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The gas after the reaction is detected by a detector.
[0041] Example 4:
[0042] (1) 10 g of SAPO-34 molecular sieve with template removed was mixed with 100 mL of 3.6 mol / L ammonium chloride solution in a round-bottom flask. The mixture was heated in an 80°C water bath and stirred continuously for 3 h. The solid-liquid mixture was then filtered through a Buchner funnel and washed with water until the pH of the lower filtrate was neutral. After drying in an electric thermostatic drying oven at 105°C for 12 h, the NH4-SAPO-34 catalyst was obtained by one ion exchange.
[0043] (2) The product from step (1) was placed in a muffle furnace and calcined at 550°C for 4 hours at a heating rate of 10°C / min to remove NH4. + H-SAPO-34 molecular sieve was obtained.
[0044] (3) Place the product from step (2) in a tablet press and press it into tablets at a pressure of 10 MPa. After 10 seconds of forming, crush it and pass it through an 8-12 mesh sieve to obtain a catalyst with an average particle size of about 2 mm.
[0045] (4) The product of step (3) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The gas after the reaction is detected by a detector.
[0046] Test example:
[0047] The catalytic ozone oxidation activity of NO in Examples 1-4 and the comparative example was tested. The simulated flue gas preparation conditions were: NO concentration 400 ppm, [O3] / [NO] molar ratio 0.3, and water vapor volume fraction 4%. The flue gas was preheated and then reacted with the catalyst at 80°C for a residence time of 1 s. The resulting gas was detected by a detector. The experimental results are as follows: Figure 1 As shown, the comparative example and Example 4 lack the active component NH4. + The results were similar to those of the simple ozone oxidation of NO. Examples 1-3 confirmed that the ammonium salt modified SAPO-34 molecular sieve has a catalytic oxidation effect on NO.
[0048] The sulfur resistance of the sample from Example 1 was tested under the following conditions: NO concentration of 400 ppm, SO2 concentration of 300 ppm, [O3] / [NO] molar ratio of 0.3, and water vapor volume fraction of 4%. The flue gas was preheated and then reacted with the catalyst at 80°C for a residence time of 1 s. The resulting gas was detected by a detector. The experimental results are as follows: Figure 2As shown, under the conditions of 300 ppm SO2 and 4% water vapor, the NO oxidation rate of NH4-SAPO-34 decreased by only 4% after 5 hours of reaction.
[0049] Furthermore, the NH4-SAPO-34 catalyst prepared in this invention can generate ammonium sulfate or ammonium bisulfate products after a sulfidation reaction.
[0050] Because ammonium sulfate completely decomposes upon high-temperature calcination above 550℃, and SAPO-34 molecular sieve has strong hydrothermal stability, it can still maintain the integrity of its crystal structure at high temperatures of 800℃.
[0051] Therefore, the sulfided catalyst only needs to be calcined at high temperature (>550℃) for a certain period of time to regenerate the molecular sieve. The catalyst can be re-prepared and reused by the method of this invention, further reducing production costs.
[0052] As shown in the results of the experimental group above Figure 1-3 It can be seen that the molecular sieve catalyst proposed in this invention has the significant advantage of non-metallic elements participating in reducing secondary pollution caused by metallic elements compared with the prior art. Moreover, after use, the molecular sieve catalyst can be regenerated through secondary processing, which enhances its recyclability and reduces the cost of waste gas treatment. It has significant progress and promising prospects for promotion.
[0053] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for catalytic oxidation of NO with low-concentration ozone using ammonium salt-modified SAPO-34 molecular sieve, comprising the following steps: (1) The SAPO-34 molecular sieve with the template agent removed was mixed with an inorganic ammonium salt solution of a certain concentration and placed in a round-bottom flask. Under water bath heating conditions, the mixture was continuously stirred for a certain period of time. Then, the solid-liquid mixture was filtered by Buchner funnel and washed with water until the pH of the lower filtrate was neutral. After drying in an electric thermostatic drying oven, the above steps were repeated several times to obtain NH4-SAPO-34. (2) Place the product from step (1) into a tablet press and press it into tablets under certain conditions. After forming, crush and sieve to obtain a catalyst with a certain particle size. (3) The product of step (2) is placed in a fixed bed reactor for activity testing. The simulated flue gas preparation conditions include a certain concentration of NO, SO2, ozone, water vapor and carrier gas N2. After the flue gas is preheated, it reacts with the catalyst under certain temperature and residence time conditions. The concentration of the gas after the reaction is detected by a detector.
2. The method according to claim 1, characterized in that: The inorganic ammonium salts mentioned in step (1) include ammonium nitrate, ammonium chloride, ammonium sulfate, and ammonium carbonate.
3. The method according to claim 1, characterized in that: In step (1), the inorganic ammonium salt contains NH4 + The concentration range is 0.1 mol / L–8.0 mol / L, and the ratio of SAPO-34 molecular sieve to ammonium salt solution is 1 g: 10 mL–30 mL.
4. The method according to claim 1, characterized in that: In step (1), the SAPO-34 molecular sieve and the ammonium salt solution undergo ion exchange under water bath heating conditions, with a reaction time of 1–24 h and a reaction temperature of 30℃–90℃.
5. The method according to claim 1, characterized in that: The solid washed with water in step (1) is dried in an electric thermostatic drying oven at a temperature of 60℃-120℃ for 6–24 hours.
6. The method according to claim 1, characterized in that: In step (1), the above steps are repeated several times to obtain NH4-SAPO-34, wherein the number of ion exchanges is 1-5 times.
7. The method according to claim 1, characterized in that: The tableting conditions in step (2) are: pressure 5–15 MPa, 5–60 s, crushing through an 8–12 mesh sieve to obtain a catalyst with an average particle size of about 1–2 mm for later use.
8. The method according to claim 1, characterized in that: The simulated flue gas preparation conditions in step (3) are as follows: NO concentration is 50–1000 ppm, SO2 concentration is 0–600 ppm, the molar ratio of O3 to NO is 0.1–1, and the volume fraction of water vapor is 0–20%.
9. The method according to claim 1, characterized in that: The catalytic reaction conditions described in step (3) are: reaction temperature 20℃–100℃, and catalyst residence time 0.5–6s.