Denitration purification method for flue gas containing nitrogen oxides

Abstract

The invention discloses a denitration purification method for flue gas containing oxynitride, belongs to the technical field of waste gas purification, and aims to solve the technical problem that the denitration performance of the flue gas containing oxynitride and the cycle performance of an absorbing material need to be further improved in the prior art. Introducing the modified ionic liquid into a regeneration tank for regeneration, and then supplementing the modified ionic liquid to the absorption tower for continuous use; according to the invention, efficient catalytic oxidation of NO is realized by constructing a graphene oxide loaded metal oxide composite catalyst, and meanwhile, a functionalized modified ionic liquid is introduced as an absorbent to enhance selective absorption and cyclic regeneration capacity of NO2, and the catalytic oxidation and absorption processes are highly coupled in the process, so that the catalytic oxidation and absorption efficiency is improved. A'catalysis-absorption 'integrated denitration system is formed, and the flue gas denitration performance and the cycle performance of the absorption material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waste gas purification, and in particular to a method for denitrification and purification of flue gas containing nitrogen oxides. Background Art

[0002] The development of flue gas denitrification technology containing nitrogen oxides has experienced a gradual evolution from thermodynamic reduction to highly selective absorption. In the early stage, selective catalytic reduction technology was mainly used, which used ammonia to reduce NO under the action of catalyst. x It is reduced to nitrogen gas, which has a high removal efficiency, but is sensitive to temperature and has problems such as ammonia escape and catalyst poisoning; the non-selective reduction process developed subsequently simplified the process, but the removal efficiency was low. Adsorption, plasma technology and wet oxidation absorption have been proposed to broaden the applicability of the process; in recent years, the liquid phase absorption method has attracted attention. The absorbents are mostly alkaline solutions, ferrous chelates, organic amines, etc., which have strong NO2 absorption capacity, but have limited absorption capacity, poor stability of reaction products, high regeneration energy consumption and other problems, which limit the recycling efficiency; current research is gradually focusing on the development of new absorption materials with high stability and low energy consumption to achieve the synergistic optimization of high removal rate and long life cycle.

[0003] While traditional flue gas denitrification technology systems are relatively mature, they still face multiple challenges in practical application. For example, while SCR offers high denitrification efficiency, it requires high operating temperatures (typically above 300°C), carries risks of catalyst poisoning and deactivation, and ammonia slip poses corrosion risks to downstream equipment. SNCR, while simple to process, has limited removal efficiency, making it difficult to meet increasingly stringent environmental standards.

[0004] Wet absorption has a good effect on removing NO2, but its absorption efficiency for NO is low and usually requires an additional oxidation step. At the same time, traditional absorbents often have problems such as limited absorption capacity, poor cycle stability, and high regeneration energy consumption, resulting in high overall operating costs and insufficient system reliability.

[0005] In addition, some absorbents are prone to degradation, crystallization or deposition of conversion products during long-term operation, further affecting process continuity and material service life. Therefore, the development of an absorption system with high removal efficiency, wide temperature adaptability and excellent recycling and regeneration performance has become a key direction of current technological innovation. Summary of the Invention

[0006] The object of the present invention is to provide a method for denitrification and purification of flue gas containing nitrogen oxides, which is used to solve the technical problem in the prior art that the denitrification performance of flue gas containing nitrogen oxides and the circulation performance of the absorption material need to be further improved.

[0007] The purpose of the present invention can be achieved by the following technical solution: A method for denitrification of flue gas containing nitrogen oxides, comprising the following steps:

[0008] S1, passing the pretreated gas into a catalytic reactor loaded with a composite catalyst, and catalytically oxidizing it to obtain gas I;

[0009] The reaction principle of preparing gas I is as follows: oxygen molecules are first activated on the catalyst surface to form adsorbed oxygen species with high reactivity (such as O - 、O2 - ), NO molecules in the pre-treated gas react with surface activated oxygen species to generate intermediate NO2 through electron transfer - The intermediate state desorption generates NO2 molecules and releases them into the gas phase, realizing oxidation conversion, converting the nitric oxide in the pretreated gas into nitrogen dioxide, and then obtaining gas I.

[0010] S2, passing gas I into an absorption tower loaded with modified ionic liquid to obtain denitrified flue gas through purification and absorption;

[0011] The reaction principle for preparing denitrified flue gas is as follows: nitrogen dioxide, as a polar molecule, can be dispersed with high solubility in the highly polar environment of ionic liquids. The amino groups, carboxyl groups and substituted imidazole cations in the modified ionic liquids can undergo reversible coordination or addition reactions with NO2 to form stable complexes or adducts, thereby preparing denitrified flue gas.

[0012] S3. After the modified ionic liquid reaches its service life, the modified ionic liquid is passed into the regeneration tank for regeneration and then replenished to the absorption tower for continued use.

[0013] The reaction principle of the regenerated modified ionic liquid is to destroy the weak interaction force between NO2 and the ionic liquid through thermal desorption, decompression and inert gas purging, so that NO2 can be released efficiently, and the ionic liquid can restore its initial absorption activity to form a closed-loop circulation system.

[0014] Furthermore, in step S1, the pretreatment step is: after the flue gas passes through a bag filter to remove solid particles with a particle size greater than 5 μm, it is cooled to 80-120°C using a heat exchanger, and then industrial deionized water is sprayed into the flue gas through an atomizing nozzle to control the humidity at 50-70% RH, and the outlet air flow pressure is checked to be maintained at 100-200 Pa to obtain pretreated gas.

[0015] The principle of preparing pretreated gas is: by controlling the particle concentration, temperature, humidity and airflow state, the risk of catalyst poisoning is reduced and the reaction efficiency is improved. The removal of particulate matter reduces the interference with the catalyst and absorbent. Temperature regulation ensures that NO reacts in the appropriate kinetic range. Humidity affects the generation and absorption performance of active species. The airflow stability determines the uniformity and continuity of the reaction system, thereby obtaining pretreated gas.

[0016] Furthermore, in step S1, the bed temperature of the catalytic reactor is 150-250°C, and the inlet space velocity of the pretreated gas is 10,000-20,000 h -1 , the oxygen content in the pre-treated gas is 3-5%;

[0017] Furthermore, in step S2, the absorption tower is a rotary spray tower, the operating temperature of the rotary spray tower is 30-50°C, and the liquid-gas ratio is 2-4 L / m 3 , pH value is 5-8, and the continuous use period of the modified ionic liquid is 48-72h;

[0018] Furthermore, in step S3, during the regeneration process, the operating pressure of the regeneration tank is 20-50 kPa, the temperature is 80-100°C, and argon gas is introduced for purging and assisted desorption. The desorbed nitrogen oxide gas is centrally incinerated, and the ionic liquid is cooled to room temperature and then replenished to the absorption tower for continued use.

[0019] Furthermore, in step S1, the preparation method of the composite catalyst comprises the following steps:

[0020] A1. Add 0.1 mol / L Ce(NO3)3 aqueous solution, 0.1 mol / L Mn(NO3)2 aqueous solution, and 0.1 mol / L Fe(NO3)3 aqueous solution into a reactor and stir. Raise the temperature of the reactor to 60-70°C and adjust the pH of the reaction system to 10-11 using saturated sodium hydroxide aqueous solution. Keep the temperature and stir for 2 hours, then naturally age for 12 hours and post-treat to obtain a mixed powder.

[0021] A2. calcining the mixed powder to obtain a catalyst precursor;

[0022] A3. Add the catalyst precursor and graphene oxide dispersion into the reactor and stir. Raise the temperature of the reactor to 60-70° C., keep stirring for 3-4 hours, and perform post-treatment to obtain the composite catalyst.

[0023] The reaction principle for preparing the composite catalyst is: Ce 3+ 、Mn 2+ and Fe 3+The corresponding hydroxide precipitates are generated in an alkaline aqueous solution to form a mixed precipitate containing multiple metal elements. After heat treatment, these hydroxides undergo dehydration and phase change, converting into composite metal oxides. Subsequently, the obtained metal oxide precursor is mixed with a graphene oxide dispersion, and the precursor is loaded on the graphene oxide sheet by means of physical adsorption and surface forces. Finally, its structure is fixed by heat treatment to form a composite catalyst.

[0024] Furthermore, in step A1, the dosage ratio of 0.1 mol / L Ce(NO3)3 aqueous solution, 0.1 mol / L Mn(NO3)2 aqueous solution, and 0.1 mol / LFe(NO3)3 aqueous solution is 1 mL:1 mL:1 mL, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, the reaction mixture is filtered to collect the filter cake, the filter cake is washed 3-5 times with anhydrous ethanol and deionized water, and the filter cake is transferred to a drying oven at a temperature of 80°C and vacuum dried to constant weight to obtain a mixed powder;

[0025] Furthermore, in step A2, the calcination operation is as follows: adding the mixed powder into a muffle furnace, heating the muffle furnace to 300° C. at a heating rate of 5° C. / min, keeping the temperature for 4 hours, and then naturally cooling to room temperature to obtain a catalyst precursor;

[0026] Furthermore, in step A3, the amount ratio of the catalyst precursor and the graphene oxide dispersion is 1g:40-50mL, wherein the graphene oxide dispersion is obtained by mixing deionized water and graphene oxide in a ratio of 40-50mL:0.2-0.3g, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, the reaction mixture is filtered to collect the filter cake, and the filter cake is washed 3-5 times with anhydrous ethanol and deionized water. After that, the filter cake is transferred to a drying oven at a temperature of 80°C and vacuum dried to constant weight, and then the material is transferred to a muffle furnace, and the muffle furnace is heated to 300°C at a heating rate of 3°C / min. After heat treatment for 2h, it is naturally cooled to room temperature to obtain a composite catalyst.

[0027] Furthermore, in step S2, the preparation method of the modified ionic liquid includes the following steps:

[0028] B1. Add 1-methylimidazole, ethyl bromide and anhydrous acetone into a reactor and stir. Heat the reactor to reflux and then keep stirring for 10-12 hours. Post-treat to obtain an ionic liquid precursor.

[0029] B2. Add the ionic liquid precursor and anhydrous acetonitrile into a reactor and stir. After the temperature of the reactor is raised to 55-65° C., add potassium thiocyanate into the reactor, keep the temperature and stir for 5-7 hours, and perform post-treatment to obtain a modified ionic liquid.

[0030] The reaction principle for preparing modified ionic liquids is as follows: 1-methylimidazole and ethyl bromide undergo a nucleophilic substitution reaction in anhydrous acetone. Ethyl bromide acts as an alkylating agent, and the carbon atom on its ethyl group is attacked by the nitrogen atom in the 1-methylimidazole molecule to generate 1-ethyl-3-methylimidazole bromide, thereby obtaining an ionic liquid precursor. Furthermore, bromide ions and thiocyanate ions undergo an anion exchange reaction in anhydrous acetonitrile. Potassium thiocyanate dissociates into thiocyanate ions (SCN) in the solution. - ), the bromide ions in the original imidazole salt are replaced by a bimolecular ion exchange process to obtain 1-ethyl-3-methylimidazolium thiocyanate, and then a modified ionic liquid is prepared.

[0031] Furthermore, in step B1, the ratio of 1-methylimidazole, ethyl bromide and anhydrous acetone is 8.1-8.3 g:10.8-11.0 g:100 mL, and the post-treatment includes: cooling to room temperature after the reaction, removing the solvent by rotary evaporation, adding anhydrous ether to wash the product 3-5 times, and continuing to rotary evaporation to remove anhydrous ether to obtain an ionic liquid precursor;

[0032] Furthermore, in step B2, the ratio of the amount of the ionic liquid precursor, anhydrous acetonitrile and potassium thiocyanate is 9.6g-9.7g:100mL:14.5-14.7g, and the post-treatment includes: cooling to room temperature after the reaction, removing the solvent by rotary evaporation, and then transferring the reaction solution to a drying oven at a temperature of 60°C and vacuum drying for 10-12h to obtain a modified ionic liquid.

[0033] The present invention has the following beneficial effects:

[0034] 1. The modified ionic liquid introduced in the present invention enhances the reversible absorption capacity of NO2 by introducing polar functional groups with complexing ability (such as amino, carboxyl, and imidazole substituents). At the same time, relying on its low volatility and thermal stability, it has good circulation potential. A composite catalyst with Ce-Mn-Fe as the main component is introduced into the absorption system to improve the selective conversion rate of NO to NO2, thereby avoiding NO from entering the absorption system directly without being fully oxidized, thereby inducing free radical side reactions in the modified ionic liquid, attacking organic functional groups such as imidazole rings and amino groups, causing molecular skeleton fractures, and seriously damaging its structural stability and absorption function; and the catalyst carrier such as graphene oxide further promotes the synergy of the gas-solid-liquid three-phase interface, improving the overall denitrification efficiency. Ultimately, the front-end purification effect of the composite catalyst complements the absorption-regeneration function of the ionic liquid, significantly extending the cycle life of the absorbent and ensuring the stable operation of the process.

[0035] 2. The present invention utilizes Ce 3+ 、Mn 2+ with Fe 3+Under alkaline conditions, multi-metal hydroxides are co-precipitated and converted into composite metal oxides after heat treatment. They have excellent oxidation ability and can effectively catalyze the oxidation of NO into more easily absorbed NO2. The composite metal oxides are further loaded on graphene oxide sheets, and their excellent dispersibility and conductivity are used to enhance the catalytic reaction interface and improve the conversion efficiency of NO to NO2. On this basis, modified ionic liquids are introduced as absorbents. By regulating their cationic structure and introducing polar functional groups (such as carboxyl, hydroxyl, imidazole ring, etc.), the solubility and complexation ability of NO2 are significantly enhanced. In terms of process, key parameters such as gas temperature and humidity, flow rate and particulate matter filtration are controlled to provide a stable environment for multiphase reactions. Finally, through the high synergy of catalytic oxidation and absorption processes, the whole system effectively improves NO x absorption capacity.

[0036] 3. The present invention introduces Ce-Mn-Fe composite metal oxides and synergistically constructs a stable crystal structure, which significantly improves the structural integrity of the catalyst under high-speed airflow and high-temperature conditions, reduces the loss of active components, and effectively delays the deactivation process of the catalyst due to wear. Among them, CeO2 has excellent oxygen storage and release capabilities, which can relieve oxidation stress in high-temperature environments; MnO x The introduction of Fe2O3 enhances the overall mechanical strength and sintering resistance of the catalyst. Secondly, the catalyst is loaded on the surface of the graphene oxide (GO) carrier. GO has a high specific surface area and flexibility, which can effectively disperse the active components, prevent their agglomeration and slow down the particle shedding caused by airflow scouring during the reaction. At the same time, the two-dimensional layered structure of GO can serve as a "buffer base" to absorb mechanical energy and reduce the direct damage of external forces to catalytic particles, thereby improving the overall wear resistance. Finally, through the complementarity of multiple components in microstructure and performance, the dual improvement of structural stability and mechanical strength is achieved, providing a reliable guarantee for the long-term operation of the catalyst in a complex reaction environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 This is a SEM image of the mixed powder prepared in Example 3 of the present invention;

[0039] Figure 2 This is a SEM image of the composite catalyst prepared in Example 3 of the present invention;

[0040] Figure 3 This is the FTIR image of the composite catalyst prepared in Example 3 of the present invention;

[0041] Figure 4 This is the FTIR spectrum of the modified ionic liquid prepared in Example 6 of the present invention. DETAILED DESCRIPTION

[0042] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] The graphene oxide used in the present invention was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with the brand name G476339.

[0044] Example 1

[0045] This embodiment provides a method for preparing a composite catalyst for denitration and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0046] Step I: Preparation of mixed powder

[0047] Weigh: 1L 0.1 mol / L Ce(NO3)3 aqueous solution, 1L 0.1 mol / L Mn(NO3)2 aqueous solution, and 1L 0.1mol / L Fe(NO3)3 aqueous solution and add them into the reactor and stir. The temperature of the reactor is raised to 60°C and the pH of the reaction system is adjusted to 10 using saturated sodium hydroxide aqueous solution. After keeping warm and stirring for 2 hours, it is naturally aged for 12 hours. After the reaction is completed, the temperature of the reactor is lowered to room temperature, the reaction mixture is filtered and the filter cake is collected. After washing the filter cake 3 times with anhydrous ethanol and deionized water, the filter cake is transferred to a drying oven at 80°C and vacuum dried to constant weight to obtain a mixed powder.

[0048] Step II: Preparation of catalyst precursor

[0049] 20.0 g of the mixed powder was weighed and added into a muffle furnace. The temperature of the muffle furnace was raised to 300° C. at a heating rate of 5° C. / min. After heat preservation for 4 h, the mixture was naturally cooled to room temperature to obtain a catalyst precursor.

[0050] Step III: Preparation of composite catalyst

[0051] Weigh 400.0 mL of deionized water and 2.0 g of graphene oxide to obtain a graphene oxide dispersion.

[0052] Weigh: 10.0 g of catalyst precursor and 400.0 mL of graphene oxide dispersion were added to the reactor and stirred. The temperature of the reactor was raised to 60°C and stirred for 3 hours. After the reaction was completed, the temperature of the reactor was lowered to room temperature, the reaction mixture was filtered and the filter cake was collected. The filter cake was washed 3 times with anhydrous ethanol and deionized water, and then the filter cake was transferred to a drying oven at a temperature of 80°C and vacuum dried to constant weight. The material was then transferred to a muffle furnace, and the muffle furnace was heated to 300°C at a heating rate of 3°C / min. After insulation treatment for 2 hours, it was naturally cooled to room temperature to obtain a composite catalyst.

[0053] Example 2

[0054] This embodiment provides a method for preparing a composite catalyst for denitration and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0055] Step I: Preparation of mixed powder

[0056] Weigh: 1L 0.1 mol / L Ce(NO3)3 aqueous solution, 1L 0.1 mol / L Mn(NO3)2 aqueous solution, and 1L 0.1mol / L Fe(NO3)3 aqueous solution and add them into the reactor and stir. The temperature of the reactor is raised to 70°C and the pH of the reaction system is adjusted to 11 using saturated sodium hydroxide aqueous solution. After keeping warm and stirring for 2 hours, it is naturally aged for 12 hours. After the reaction is completed, the temperature of the reactor is lowered to room temperature, the reaction mixture is filtered and the filter cake is collected. After washing the filter cake with anhydrous ethanol and deionized water 5 times, the filter cake is transferred to a drying oven at 80°C and vacuum dried to constant weight to obtain a mixed powder.

[0057] Step II: Preparation of catalyst precursor

[0058] 20.0 g of the mixed powder was weighed and added into a muffle furnace. The temperature of the muffle furnace was raised to 300° C. at a heating rate of 5° C. / min. After heat preservation for 4 h, the mixture was naturally cooled to room temperature to obtain a catalyst precursor.

[0059] Step III: Preparation of composite catalyst

[0060] Weigh 500.0 mL of deionized water and 3.0 g of graphene oxide to obtain a graphene oxide dispersion.

[0061] Weigh: 10.0 g of catalyst precursor and 500.0 mL of graphene oxide dispersion were added to the reactor and stirred. The temperature of the reactor was raised to 70°C and kept stirring for 4 hours. After the reaction was completed, the temperature of the reactor was lowered to room temperature, the reaction mixture was filtered and the filter cake was collected. The filter cake was washed 5 times with anhydrous ethanol and deionized water, and then the filter cake was transferred to a drying oven at a temperature of 80°C and vacuum dried to constant weight. The material was then transferred to a muffle furnace, and the muffle furnace was heated to 300°C at a heating rate of 3°C / min. After insulation treatment for 2 hours, it was naturally cooled to room temperature to obtain a composite catalyst.

[0062] Example 3

[0063] This embodiment provides a method for preparing a composite catalyst for denitration and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0064] Step I: Preparation of mixed powder

[0065] Weigh: 1L 0.1 mol / L Ce(NO3)3 aqueous solution, 1L 0.1 mol / L Mn(NO3)2 aqueous solution, and 1L 0.1mol / L Fe(NO3)3 aqueous solution and add them into the reactor and stir. The temperature of the reactor is raised to 65°C and the pH of the reaction system is adjusted to 11 using saturated sodium hydroxide aqueous solution. After keeping warm and stirring for 2 hours, it is naturally aged for 12 hours. After the reaction is completed, the temperature of the reactor is lowered to room temperature, the reaction mixture is filtered and the filter cake is collected. After washing the filter cake 4 times with anhydrous ethanol and deionized water, the filter cake is transferred to a drying oven at 80°C and vacuum dried to constant weight to obtain a mixed powder.

[0066] Step II: Preparation of catalyst precursor

[0067] 20.0 g of the mixed powder was weighed and added into a muffle furnace. The temperature of the muffle furnace was raised to 300° C. at a heating rate of 5° C. / min. After heat preservation for 4 h, the mixture was naturally cooled to room temperature to obtain a catalyst precursor.

[0068] Step III: Preparation of composite catalyst

[0069] Weigh 450.0 mL of deionized water and 2.5 g of graphene oxide to obtain a graphene oxide dispersion.

[0070] Weigh: 10.0 g of catalyst precursor and 450.0 mL of graphene oxide dispersion were added to the reactor and stirred. The temperature of the reactor was raised to 65°C and kept stirring for 4 hours. After the reaction was completed, the temperature of the reactor was lowered to room temperature, the reaction mixture was filtered and the filter cake was collected. The filter cake was washed 4 times with anhydrous ethanol and deionized water, and then the filter cake was transferred to a drying oven at a temperature of 80°C and vacuum dried to constant weight. The material was then transferred to a muffle furnace, and the muffle furnace was heated to 300°C at a heating rate of 3°C / min. After insulation treatment for 2 hours, it was naturally cooled to room temperature to obtain a composite catalyst.

[0071] The FTIR spectrum of the composite catalyst is as follows Figure 1 As shown, at 670cm -1 A strong absorption peak appears, which is the characteristic stretching vibration of the Fe-O bond, indicating that Fe is stably embedded in the structural network in the form of oxygen bridges. The peak is full, corresponding to Fe 3+ Typical patterns in octahedral coordination;

[0072] 580cm -1 The peak is attributed to the Mn-O stretching vibration, which is an important indicator of the formation of manganese-oxygen cluster structure, confirming that Mn 2+ / Mn 3 + It is embedded in the framework in an oxygen-coordinated manner; this peak is clearly separated in the spectrum, eliminating the possibility of overlap with Fe-O;

[0073] At 500cm -1 A medium-strong absorption peak appears at the Ce-O bond, which is attributed to the symmetrical stretching of the Ce-O bond, reflecting that the Ce element is Ce 3+ / Ce 4+ The covalent coordination form is embedded in the inorganic part. Its peak position is stable and the binding energy is high, which proves its stable bonding state during the synthesis process;

[0074] In addition, 470cm -1 The shoulder peak can be attributed to the cooperative vibration of the heterocoordinate bond in the bridging structure formed between Fe-O-Mn or Fe-O-Ce, showing the spectral manifestation of a multi-metal nested structure, which is indirect evidence of tri-metal cooperative construction;

[0075] In addition to the metal oxygen bond region, 1110 cm -1 A strong absorption peak appears at , which corresponds to the COC or PO bond in the organic fragment of the material, and is a direct characterization of the embedding of organic ionic liquid fragments.

[0076] Others such as 3440cm -1 、1620cm -1 、1384cm -1 The isosbestic peaks correspond to -OH stretching vibration, aromatic C=C structure and NO3 -The presence of heteroatomic groups.

[0077] Example 4

[0078] This embodiment provides a method for preparing a modified ionic liquid for denitrification and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0079] Step 1: Preparation of ionic liquid precursor

[0080] Weigh 81.0 g of 1-methylimidazole, 108.0 g of ethyl bromide, and 1000.0 mL of anhydrous acetone into a reactor and stir. The reactor was heated to reflux and stirred for 10 h. After the reaction was completed, it was cooled to room temperature and the solvent was removed by rotary evaporation. The product was washed with anhydrous ether three times and the anhydrous ether was removed by rotary evaporation to obtain an ionic liquid precursor.

[0081] Step ②, preparation of modified ionic liquid

[0082] Weigh: 96.0 g of ionic liquid precursor and 1000.0 mL of anhydrous acetonitrile were added to the reactor and stirred. After the temperature of the reactor was raised to 55°C, 145.0 g of potassium thiocyanate was added to the reactor and stirred for 5 hours. After the reaction was completed, it was cooled to room temperature and the solvent was removed by rotary evaporation. The reaction solution was then transferred to a drying oven at a temperature of 60°C and vacuum dried for 10 hours to obtain a modified ionic liquid.

[0083] Example 5

[0084] This embodiment provides a method for preparing a modified ionic liquid for denitrification and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0085] Step 1: Preparation of ionic liquid precursor

[0086] Weigh 83.0 g of 1-methylimidazole, 110.0 g of ethyl bromide, and 1000.0 mL of anhydrous acetone into a reactor and stir. Heat the reactor to reflux and keep stirring for 12 h. After the reaction is completed, cool to room temperature and remove the solvent by rotary evaporation. Add anhydrous ether to wash the product 5 times, and continue to rotary evaporation to remove anhydrous ether to obtain an ionic liquid precursor.

[0087] Step ②, preparation of modified ionic liquid

[0088] Weigh: 97.0 g of ionic liquid precursor and 1000.0 mL of anhydrous acetonitrile were added to the reactor and stirred. After the temperature of the reactor was raised to 65°C, 147.0 g of potassium thiocyanate was added to the reactor and stirred for 7 hours. After the reaction was completed, it was cooled to room temperature and the solvent was removed by rotary evaporation. The reaction solution was then transferred to a drying oven at a temperature of 60°C and vacuum dried for 12 hours to obtain a modified ionic liquid.

[0089] Example 6

[0090] This embodiment provides a method for preparing a modified ionic liquid for denitrification and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0091] Step 1: Preparation of ionic liquid precursor

[0092] Weigh 82.0 g of 1-methylimidazole, 109.0 g of ethyl bromide, and 1000.0 mL of anhydrous acetone into a reactor and stir. The reactor was heated to reflux and stirred for 11 h. After the reaction was completed, it was cooled to room temperature and the solvent was removed by rotary evaporation. The product was washed with anhydrous ether four times and the anhydrous ether was removed by rotary evaporation to obtain an ionic liquid precursor.

[0093] Step ②, preparation of modified ionic liquid

[0094] Weigh: 97.0 g of ionic liquid precursor and 1000.0 mL of anhydrous acetonitrile were added to the reactor and stirred. After the temperature of the reactor was raised to 60°C, 146.0 g of potassium thiocyanate was added to the reactor and stirred for 6 hours. After the reaction was completed, it was cooled to room temperature and the solvent was removed by rotary evaporation. The reaction solution was then transferred to a drying oven at a temperature of 60°C and vacuum dried for 12 hours to obtain a modified ionic liquid.

[0095] The FTIR spectra of the modified ionic liquid samples are shown in Figure 2. Figure 2 As shown, in the high wave number region (3100–3200 cm -1 ), respectively at 3160cm -1 and 3110cm -1 Two groups of medium-intensity stretching vibration absorption peaks were observed at the 100 nm region, which were attributed to the sp 2 Hybrid stretching vibrations confirmed the existence of the imidazole core structure;

[0096] In the spectrum, at 1575 cm -1 A strong absorption peak appears at , which can be attributed to the conjugated skeleton vibration of C=N and C=C bonds, further supporting the stable construction of the aromatic structure of the imidazole ring;

[0097] At 1465cm -1 The CH bending vibration peak was observed at 1250 cm -1 and 1170cm -1 The CN and CO stretching vibration peaks at indicate the successful introduction of functional substituents on the side chain, which is consistent with the structural characteristics of alkoxy or ether modification groups in the modification design.

[0098] 1050cm -1 The strong absorption peak at corresponds to -SO3 - or -OSO3 -The antisymmetric stretching vibration of the S=O bond in the structure indicates that the sulfonic acid or sulfonic acid-like groups have been effectively grafted, supporting the introduction of modified anions or functional groups;

[0099] In addition, at 750cm -1 and 690cm -1 There are two strong absorption bands at 2100 cm-1, which can be attributed to the characteristic peaks of CH bending vibration outside the plane of imidazole ring, which is the auxiliary verification basis of aromatic heterocyclic structure; -1 A significant absorption peak appears near the surface of the nanostructured carbon molecule, which is commonly found in the C≡N or metal-carbon double bond intermediate region after the introduction of organic-inorganic covalent structure or the loading of metal coordination center, indirectly characterizing the synergistic modification process of some multifunctional sites.

[0100] Example 7

[0101] This embodiment provides a method for denitrification of flue gas containing nitrogen oxides, comprising the following steps:

[0102] Step 1: Prepare pre-treated gas

[0103] After the flue gas passes through a bag filter to remove solid particles with a particle size greater than 5μm, it is cooled to 80℃ using a heat exchanger, and then industrial deionized water is sprayed into the flue gas through an atomizing nozzle to control the humidity at 50%RH. The outlet air flow pressure is checked to be maintained at 100Pa to obtain pretreated gas.

[0104] Step 2: Preparation of Gas I

[0105] The pre-treated gas was introduced into a catalytic reactor loaded with the composite catalyst prepared in Example 1. The bed temperature of the catalytic reactor was 150°C and the inlet space velocity of the pre-treated gas was 10000 h -1 The oxygen content in the pretreated gas is 3%, and gas I is obtained by catalytic oxidation.

[0106] Step 3: Preparation of denitrification flue gas

[0107] The gas I was introduced into the rotary spray tower loaded with the modified ionic liquid prepared in Example 4. The operating temperature of the rotary spray tower was 30°C and the liquid-gas ratio was 2 L / m 3 , pH value is 5, and the continuous use cycle of the modified ionic liquid is 48h, and denitrified flue gas is obtained after purification and absorption.

[0108] Step 4: Regeneration of modified ionic liquid

[0109] After the modified ionic liquid has been used for 48 hours, the modified ionic liquid is passed into the regeneration tank for regeneration. The operating pressure of the regeneration tank is 20 kPa and the temperature is 80°C. Argon gas is introduced for purge-assisted desorption. The desorbed nitrogen oxide gas is centrally incinerated. The ionic liquid is cooled to room temperature and then replenished to the absorption tower for continued use.

[0110] Example 8

[0111] This embodiment provides a method for denitrification of flue gas containing nitrogen oxides, comprising the following steps:

[0112] Step 1: Prepare pre-treated gas

[0113] After the flue gas passes through a bag filter to remove solid particles with a particle size greater than 5μm, it is cooled to 120℃ using a heat exchanger, and then industrial deionized water is sprayed into the flue gas through an atomizing nozzle to control the humidity at 70%RH. The outlet air flow pressure is checked to be maintained at 200Pa to obtain pretreated gas.

[0114] Step 2: Preparation of Gas I

[0115] The pre-treated gas was introduced into a catalytic reactor loaded with the composite catalyst prepared in Example 2. The bed temperature of the catalytic reactor was 250°C and the inlet space velocity of the pre-treated gas was 20,000 h / min. -1 The oxygen content in the pretreated gas is 5%, and gas I is obtained by catalytic oxidation.

[0116] Step 3: Preparation of denitrification flue gas

[0117] Gas I was introduced into a rotary spray tower loaded with the modified ionic liquid prepared in Example 5. The operating temperature of the rotary spray tower was 50°C, and the liquid-gas ratio was 4 L / m 3 , pH value is 8, and the continuous use cycle of the modified ionic liquid is 72h, and denitrified flue gas is obtained after purification and absorption.

[0118] Step 4: Regeneration of modified ionic liquid

[0119] After the modified ionic liquid has been used for 72 hours, the modified ionic liquid is passed into a regeneration tank for regeneration. The operating pressure of the regeneration tank is 50 kPa and the temperature is 100°C. Argon gas is introduced for purge-assisted desorption. The desorbed nitrogen oxide gas is centrally incinerated. The ionic liquid is cooled to room temperature and then replenished to the absorption tower for continued use.

[0120] Example 9

[0121] This embodiment provides a method for denitrification of flue gas containing nitrogen oxides, comprising the following steps:

[0122] Step 1: Prepare pre-treated gas

[0123] After the flue gas passes through a bag filter to remove solid particles with a particle size greater than 5μm, it is cooled to 100℃ using a heat exchanger, and then industrial deionized water is sprayed into it through an atomizing nozzle to control the humidity at 60%RH. The outlet air flow pressure is checked to be maintained at 150Pa to obtain pretreated gas.

[0124] Step 2: Preparation of Gas I

[0125] The pre-treated gas was introduced into the catalytic reactor loaded with the composite catalyst prepared in Example 3. The bed temperature of the catalytic reactor was 200°C and the inlet space velocity of the pre-treated gas was 15000 h -1 The oxygen content in the pretreated gas is 4%, and gas I is obtained by catalytic oxidation.

[0126] Step 3: Preparation of denitrification flue gas

[0127] The gas I was introduced into the rotary spray tower loaded with the modified ionic liquid prepared in Example 6. The operating temperature of the rotary spray tower was 40°C and the liquid-gas ratio was 3 L / m 3 , pH value is 6, and the continuous use cycle of the modified ionic liquid is 54h, and denitrified flue gas is obtained after purification and absorption.

[0128] Step 4: Regeneration of modified ionic liquid

[0129] After the modified ionic liquid has been used for 54 hours, the modified ionic liquid is passed into a regeneration tank for regeneration. The operating pressure of the regeneration tank is 35 kPa and the temperature is 90°C. Argon gas is introduced for purge-assisted desorption. The desorbed nitrogen oxide gas is centrally incinerated. The ionic liquid is cooled to room temperature and then replenished to the absorption tower for continued use.

[0130] Comparative Example 1

[0131] The difference between this comparative example and Example 9 is that step III is omitted during the preparation of the composite catalyst used in step II.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 9 is that step ② is omitted during the preparation of the modified ionic liquid used in step 3.

[0134] Comparative Example 3

[0135] The difference between this comparative example and Example 9 is that step 2 is omitted.

[0136] Performance testing:

[0137] Referring to the standard DL / T 1286-2021 "Technical Specifications for Testing Flue Gas Denitrification Catalysts in Thermal Power Plants", the wear rates of the composite catalysts used in Examples 7-9 and Comparative Examples 1-3 were tested;

[0138] With reference to the standard GB 13271-2014 "Boiler Air Pollutant Emission Standard", the nitrogen oxide concentration of the denitrified flue gas prepared in Examples 7-9 and Comparative Examples 1-3 was measured;

[0139] The modified ionic liquid recycled 5, 50, and 100 times was added to the rotary spray tower, and the concentration of nitrogen oxides in the denitrified flue gas obtained after denitrification by recycling the modified ionic liquid 5, 50, and 100 times was measured with reference to the standard GB13271-2014 "Boiler Air Pollutant Emission Standard". The specific data are shown in Table 1.

[0140] Table 1 - Performance test data of each sample

[0141]

[0142] Data Analysis:

[0143] After comparing and analyzing the data in Table 1, the wear rate of the composite catalyst used in this denitrification process is 0.040%·kg -1 The concentration of nitrogen oxides in the denitrification tail gas is 33 mg·m 3 The concentration of nitrogen oxides in the denitrified tail gas after the modified ionic liquid was circulated 5 times for denitrification was 34 mg·m 3 The nitrogen oxide concentration in the denitrification tail gas after 50 cycles of denitrification is 36 mg·m 3 The nitrogen oxide concentration in the denitrified tail gas after 100 cycles of denitrification is 38 mg·m 3 , all data are better than the comparative example, indicating that:

[0144] The composite catalyst used in Comparative Example 1 did not incorporate graphene oxide to construct a composite structure, but directly used a calcined metal oxide precursor. Due to the loss of graphene oxide's synergistic effects in structural stability, electronic conductivity, and active site dispersion, the overall specific surface area of ​​the catalyst decreased significantly, the pore size distribution was uneven, and the active species were poorly dispersed, prone to agglomeration. At the same time, the conductivity and redox buffering capacity of graphene oxide itself help to increase the catalytic oxidation rate of NO. Its absence prevented the catalyst from effectively converting NO to NO₂. As a result, the catalyst was insufficiently active during the reaction, the residual NO content increased, the NO₂ concentration entering the downstream absorption step was insufficient, and the absorption efficiency decreased simultaneously.

[0145] The absorbent used in Comparative Example 2 is unmodified 1-ethyl-3-methylimidazolium bromide, which has not been modified with functional groups. As a result, its solubility and reactivity for NO2 are poor, and the unmodified ionic liquid has low polarity and lacks the ability to form a stable complex with NO2. It also does not have sufficient electron acceptor structure to promote reversible addition reaction. Therefore, the absorption process mostly relies on physical dissolution rather than chemical reaction, resulting in limited absorption capacity and slow rate. At the same time, such ionic liquids are prone to problems such as adsorption site saturation, increased viscosity, and accumulation of reaction by-products during continuous recycling, affecting regeneration efficiency.

[0146] In Comparative Example 3, the catalytic oxidation step was completely omitted, and NO gas was directly introduced into the modified ionic liquid absorber, attempting to rely solely on the absorbent to remove NO. However, NO molecules are non-polar, small-molecule gases with extremely low reactivity. Without catalytic oxidation "activation," they rarely react with the absorbent and have extremely low solubility. Although the modified ionic liquid itself has excellent performance and good NO2 absorption and regeneration capabilities, its absorption effect on unoxidized NO is almost ineffective. The results show that in the absence of the NO conversion step, the NO concentration at the absorber outlet remains almost unchanged, and accelerated absorption liquid circulation cannot improve the removal effect.

[0147] Finally, it is explained that Comparative Example 1 omits the graphene oxide composite structure, resulting in a decrease in the specific surface area of ​​the catalyst, a decrease in electrical conductivity, an uneven distribution of active sites, and a significant decrease in the NO oxidation efficiency, which directly affects the subsequent absorption step; Comparative Example 2 uses unmodified ionic liquid, which lacks the assistance of functional groups such as thiocyanate and cannot form a stable complex with NO2, resulting in a decrease in absorption capacity, a slow reaction rate, and unsatisfactory regeneration performance, which limits the long-term recycling of the absorbent; Comparative Example 3 directly removes the catalytic oxidation step and attempts to rely on modified ionic liquid to directly absorb NO, but due to the low polarity and poor reactivity of NO, it is almost insoluble in the absorbent, resulting in a significant decline in the overall denitrification efficiency; In summary, the composite structure of the catalyst, the functional design of the ionic liquid and the synergistic mechanism between the two are indispensable in the denitrification process, and the three together construct an efficient and stable "catalysis-absorption" integrated system.

[0148] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for denitrification of flue gas containing nitrogen oxides, characterized in that: The following steps are involved: S1, passing the pretreated gas into a catalytic reactor loaded with a composite catalyst, and catalytically oxidizing it to obtain gas I; S2, passing gas I into an absorption tower loaded with modified ionic liquid to obtain denitrified flue gas through purification and absorption; S3, after the modified ionic liquid reaches the end of its service life, the modified ionic liquid is passed into the regeneration tank for regeneration and then replenished to the absorption tower for continued use; The preparation method of the composite catalyst comprises the following steps: A1. Add 0.1 mol / L Ce(NO3)3 aqueous solution, 0.1 mol / L Mn(NO3)2 aqueous solution, and 0.1 mol / LFe(NO3)3 aqueous solution into a reactor and stir. Raise the temperature of the reactor to 60-70°C and adjust the pH of the reaction system to 10-11 using saturated sodium hydroxide aqueous solution. Keep the mixture warm and stir for 2 hours, then naturally age for 12 hours and post-treat to obtain a mixed powder. A2. calcining the mixed powder to obtain a catalyst precursor; A3. Add the catalyst precursor and graphene oxide dispersion into a reactor and stir. Raise the temperature of the reactor to 60-70°C, keep stirring for 3-4 hours, and perform post-processing to obtain a composite catalyst. The preparation method of the modified ionic liquid comprises the following steps: B1. Add 1-methylimidazole, ethyl bromide and anhydrous acetone into a reactor and stir. Heat the reactor to reflux and then keep stirring for 10-12 hours. Post-treat to obtain an ionic liquid precursor. B2. Add the ionic liquid precursor and anhydrous acetonitrile into a reactor and stir. After the temperature of the reactor is raised to 55-65° C., add potassium thiocyanate into the reactor, keep the temperature and stir for 5-7 hours, and perform post-treatment to obtain a modified ionic liquid.

2. The method for denitrification of flue gas containing nitrogen oxides according to claim 1, characterized in that: In step S1, the pretreatment step is as follows: after the flue gas passes through a bag filter to remove solid particles with a particle size greater than 5 μm, it is cooled to 80-120°C using a heat exchanger, and then industrial deionized water is sprayed into the flue gas through an atomizing nozzle to control the humidity at 50-70% RH, and the outlet air flow pressure is checked to be maintained at 100-200 Pa to obtain pretreated gas.

3. The method for denitrification of flue gas containing nitrogen oxides according to claim 1, characterized in that: In step S1, the bed temperature of the catalytic reactor is 150-250°C, and the inlet space velocity of the pre-treated gas is 10000-20000h -1 , the oxygen content in the pretreated gas is 3-5%.

4. The method for denitrification of flue gas containing nitrogen oxides according to claim 1, characterized in that: In step S2, the absorption tower is a rotary spray tower, the operating temperature of the rotary spray tower is 30-50°C, the liquid-gas ratio is 2-4L / m 3 , pH value is 5-8, and the continuous use period of the modified ionic liquid is 48-72h.

5. The method for denitrification of flue gas containing nitrogen oxides according to claim 1, characterized in that: In step S3, during the regeneration process, the operating pressure of the regeneration tank is 20-50 kPa, the temperature is 80-100°C, and argon gas is introduced for purging and assisted desorption. The desorbed nitrogen oxide gas is centrally incinerated, and the ionic liquid is cooled to room temperature and then replenished to the absorption tower for continued use.

6. The method for denitrification of flue gas containing nitrogen oxides according to claim 1, characterized in that: In step A1, the amount ratio of 0.1 mol / L Ce(NO3)3 aqueous solution, 0.1 mol / L Mn(NO3)2 aqueous solution, and 0.1 mol / LFe(NO3)3 aqueous solution is 1mL:1mL:1mL; in step A2, the calcination operation is as follows: the mixed powder is added to a muffle furnace, the muffle furnace is heated to 300°C at a heating rate of 5°C / min, and after heat treatment for 4 hours, it is naturally cooled to room temperature to obtain a catalyst precursor; in step A3, the amount ratio of the catalyst precursor and the graphene oxide dispersion is 1g:40-50mL, wherein the graphene oxide dispersion is obtained by mixing deionized water and graphene oxide in a ratio of 40-50mL:0.2-0.3g.

7. The method for denitrification of flue gas containing nitrogen oxides according to claim 1, characterized in that: In step B1, the usage ratio of 1-methylimidazole, ethyl bromide and anhydrous acetone is 8.1-8.3 g:10.8-11.0 g:100 mL; in step B2, the usage ratio of the ionic liquid precursor, anhydrous acetonitrile and potassium thiocyanate is 9.6 g-9.7 g:100 mL:14.5-14.7 g.

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