Method for purifying nitrogen-containing oxide flue gas

Abstract

This invention discloses a method for denitrification and purification of flue gas containing nitrogen oxides, belonging to the field of waste gas purification technology. It addresses the technical problem that the performance of existing flue gas denitrification methods for nitrogen oxides and the recycling performance of absorbent materials need further improvement. Specifically, it includes the following steps: after the modified ionic liquid reaches the end of its service life, it is passed into a regeneration tank for regeneration and then replenished to the absorption tower for continued use. This invention achieves efficient catalytic oxidation of NO by constructing a composite catalyst of graphene oxide supported on metal oxides. Simultaneously, functionalized modified ionic liquid is introduced as an absorbent to enhance the selective absorption and recycling capacity of NO2. The catalytic oxidation and absorption processes are highly coupled in the process, forming an integrated "catalysis-absorption" denitrification system, thereby improving the performance of flue gas denitrification and the recycling performance of absorbent materials.

Description

Technical Field

[0001] This invention relates to the field of waste gas purification technology, specifically to a method for denitrification and purification of flue gas containing nitrogen oxides. Background Technology

[0002] The development of flue gas denitrification technology for nitrogen oxides has evolved gradually from thermodynamic reduction to highly selective absorption. Early technologies primarily relied on selective catalytic reduction, utilizing ammonia gas under the action of a catalyst to remove NO. x Reduction to nitrogen gas offers high removal efficiency, but it is temperature-sensitive and suffers from ammonia escape and catalyst poisoning. Subsequent non-selective reduction processes simplified the procedure, but had lower removal efficiency. Adsorption, plasma technology, and wet oxidation absorption methods were subsequently proposed, broadening the process's applicability. In recent years, liquid-phase absorption has attracted attention, with absorbents often being alkaline solutions, ferrous chelates, and organic amines, possessing strong NO2 absorption capacity. However, it suffers from limited absorption capacity, poor reaction product stability, and high regeneration energy consumption, limiting recycling efficiency. Current research is gradually focusing on developing novel absorbent materials with high stability and low energy consumption to achieve synergistic optimization of high removal rates and long cycle life.

[0003] However, traditional flue gas denitrification technology systems are relatively mature, but they still face multiple challenges in practical applications. For example, SCR has high denitrification efficiency, but it requires high operating temperature (usually above 300℃), the catalyst is at risk of poisoning and deactivation, and the ammonia escape problem poses a corrosion hazard to downstream equipment. Although SNCR has a simple process, its removal efficiency is limited and it is difficult to meet increasingly stringent environmental standards.

[0004] Wet absorption has a good removal effect on NO2, but its absorption efficiency for NO is low, usually requiring 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, which further affects the continuity of the process and the service life of the materials. Therefore, developing an absorption system that combines high removal efficiency, wide temperature adaptability, and excellent recycling performance has become a key direction for current technological innovation. Summary of the Invention

[0006] The purpose of this invention is to provide a method for denitrification and purification of flue gas containing nitrogen oxides, which addresses the technical problem that the performance of denitrification of flue gas containing nitrogen oxides and the recycling performance of absorption materials in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solution: a method for denitrification and purification of flue gas containing nitrogen oxides, comprising the following steps:

[0008] S1. The pretreated gas is passed into a catalytic reactor loaded with a composite catalyst and catalytically oxidized to obtain gas I;

[0009] The reaction principle for preparing gas I is as follows: oxygen molecules are first activated on the catalyst surface, forming highly reactive adsorbed oxygen species (such as O2). - O2 - NO molecules in the pretreated gas react with surface-activated oxygen species, generating intermediate NO2 via electron transfer. - The intermediate state desorbs to generate NO2 molecules and releases them into the gas phase, achieving an oxidation transformation that converts nitric oxide in the pretreated gas into nitrogen dioxide, thus obtaining gas I.

[0010] S2. Gas I is passed into an absorption tower containing modified ionic liquid, and after purification and absorption, denitrification flue gas is obtained;

[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 strongly polar environment of ionic liquid. The amine groups, carboxyl groups, and substituted imidazole cations in the modified ionic liquid can undergo reversible coordination or addition reactions with NO2 to generate stable complexes or adducts, thereby preparing denitrified flue gas.

[0012] S3. After the modified ionic liquid reaches the end of its service life, it is regenerated in a regeneration tank and then replenished to the absorption tower for continued use.

[0013] The reaction principle of regenerated modified ionic liquid is as follows: the weak interaction between NO2 and ionic liquid is destroyed by thermal desorption, depressurization and inert gas purging, so that NO2 is released efficiently and the ionic liquid can restore its initial absorption activity and form a closed-loop circulation system.

[0014] Furthermore, in step S1, the pretreatment step is as follows: after removing solid particles with a diameter greater than 5μm from the flue gas through a bag filter, the temperature is reduced to 80-120℃ using a heat exchanger, and then industrial deionized water is sprayed into the flue gas through an atomizing nozzle to control the humidity at 50-70%RH, and the outlet airflow pressure is checked to maintain at 100-200Pa, thus obtaining pretreated gas.

[0015] The principle of preparing pretreated gas is as follows: by controlling particulate matter 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 interference with the catalyst and absorbent. Temperature regulation ensures that NO reacts within a suitable kinetic range. Humidity affects the generation and absorption performance of active species. 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℃, and the inlet space velocity of the pretreated gas is 10000-20000 h⁻¹. -1 The oxygen content in the pretreated gas is 3-5%;

[0017] Furthermore, in step S2, the absorption tower is a rotary spray tower, and the operating temperature of the rotary spray tower is 30-50℃, and the liquid-to-gas ratio is 2-4L / m³. 3 The 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℃, and argon gas is introduced for purging to assist 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 includes 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 to a reaction vessel and stir. Raise the temperature of the reaction vessel to 60-70℃ and adjust the pH of the reaction system to 10-11 using saturated sodium hydroxide aqueous solution. After stirring at this temperature for 2 hours, allow it to age naturally for 12 hours. The resulting powder is then post-processed.

[0021] A2. After calcining the mixed powder, a catalyst precursor is obtained;

[0022] A3. Add the catalyst precursor and graphene oxide dispersion to the reactor and stir. Raise the reactor temperature to 60-70℃ and keep it at that temperature for 3-4 hours. Then, perform post-treatment to obtain the composite catalyst.

[0023] The reaction principle for preparing composite catalysts is: Ce 3+ Mn 2+ and Fe 3+In an alkaline aqueous solution, corresponding hydroxide precipitates are generated to form a mixed precipitate containing multiple metal elements. After heat treatment, these hydroxides undergo dehydration and phase transformation, transforming into composite metal oxides. Subsequently, the obtained metal oxide precursors are mixed with graphene oxide dispersions, and the precursors are loaded onto graphene oxide sheets by means of physical adsorption and surface interaction forces. Finally, their structure is fixed by heat treatment to form a composite catalyst.

[0024] Further, in step A1, the ratio of 0.1 mol / L Ce(NO3)3 aqueous solution, 0.1 mol / L Mn(NO3)2 aqueous solution, and 0.1 mol / L FFe(NO3)3 aqueous solution is 1 mL:1 mL:1 mL. The post-processing includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, filter the reactants to collect the filter cake, wash the filter cake 3-5 times with anhydrous ethanol and deionized water, and then transfer the filter cake to a drying oven at 80°C and vacuum dry it to constant weight to obtain a mixed powder.

[0025] Furthermore, 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, the temperature is held for 4 hours, and then naturally cooled to room temperature to obtain the catalyst precursor.

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

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

[0028] B1. Add 1-methylimidazolium, bromoethane and anhydrous acetone to a reaction vessel and stir. Heat the reaction vessel to reflux and stir for 10-12 hours. Post-process to obtain the ionic liquid precursor.

[0029] B2. Add the ionic liquid precursor and anhydrous acetonitrile to the reactor and stir. After the reactor temperature is raised to 55-65℃, add potassium thiocyanate to the reactor and keep it at this temperature for 5-7 hours. The modified ionic liquid is then obtained through post-treatment.

[0030] The reaction principle for preparing modified ionic liquids is as follows: 1-methylimidazolium reacts with bromoethane in anhydrous acetone via a nucleophilic substitution reaction. Bromoethane acts as the alkylating agent, and the carbon atom on its ethyl group is attacked by the nitrogen atom in the 1-methylimidazolium molecule, generating 1-ethyl-3-methylimidazolium bromide, thus yielding the ionic liquid precursor. Further, bromide ions and thiocyanate ions undergo an anion exchange reaction in anhydrous acetonitrile. Potassium thiocyanate dissociates in solution to release thiocyanate ions (SCN). - ), by replacing the bromide ions in the original imidazole salt through a bimolecular ion exchange process, 1-ethyl-3-methylimidazolium thiocyanate is obtained, and then the modified ionic liquid is prepared.

[0031] Further, in step B1, the ratio of 1-methylimidazole, bromoethane, and anhydrous acetone is 8.1-8.3 g: 10.8-11.0 g: 100 mL. The post-treatment includes: cooling to room temperature after the reaction, removing the solvent by rotary evaporation, washing the product with anhydrous diethyl ether 3-5 times, and continuing to remove the anhydrous diethyl ether by rotary evaporation to obtain the ionic liquid precursor.

[0032] Furthermore, in step B2, the ratio of the ionic liquid precursor, anhydrous acetonitrile, and potassium thiocyanate is 9.6g-9.7g:100mL:14.5-14.7g. 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 60°C for vacuum drying for 10-12 hours to obtain the modified ionic liquid.

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

[0034] 1. The modified ionic liquid introduced in this invention enhances the reversible absorption capacity of NO2 by introducing polar functional groups with complexing ability (such as amino, carboxyl, and imidazole substituents). Simultaneously, relying on its low volatility and thermal stability, it possesses good cycling potential. Furthermore, the introduction of a composite catalyst with Ce-Mn-Fe as the main component into the absorption system improves the selective conversion rate of NO to NO2, preventing NO from directly entering the absorption system without being fully oxidized. This avoids the induction of free radical side reactions in the modified ionic liquid, which attack organic functional groups such as imidazole rings and amino groups, leading to molecular skeleton breakage and severely damaging its structural stability and absorption function. Moreover, the catalyst support, such as graphene oxide, further promotes synergistic effects at 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 stable process operation.

[0035] 2. This invention utilizes Ce 3+ Mn 2+ with Fe 3+Under alkaline conditions, a polymetallic hydroxide is co-precipitated and then converted into a composite metal oxide after heat treatment. This composite metal oxide possesses excellent oxidizing capabilities, effectively catalytically oxidizing NO to the more readily absorbed NO2. This composite metal oxide is further loaded onto graphene oxide sheets, utilizing its excellent dispersibility and conductivity to enhance the catalytic reaction interface and improve the conversion efficiency of NO to NO2. Based on this, a modified ionic liquid is introduced as an absorbent. By controlling its cationic structure and introducing polar functional groups (such as carboxyl, hydroxyl, and imidazole rings), its solubility and complexation ability for NO2 is significantly enhanced. Furthermore, in the process, key parameters such as gas temperature and humidity, flow rate, and particulate filtration are controlled to provide a stable environment for the multiphase reaction. Ultimately, through the highly synergistic effect of catalytic oxidation and absorption, the overall system's ability to absorb NO is effectively improved. x Absorption capacity.

[0036] 3. This invention significantly improves the structural integrity of the catalyst under high-speed gas flow and high-temperature conditions by introducing Ce-Mn-Fe composite metal oxides and synergistically constructing a stable crystal structure. This reduces the loss of active components and effectively delays the deactivation process caused by catalyst wear. CeO2 possesses excellent oxygen storage and release capabilities, which can alleviate oxidative stress under high-temperature environments; MnO... x The introduction of Fe2O3 enhances the overall mechanical strength and anti-sintering ability of the catalyst. Secondly, the catalyst is supported on the surface of graphene oxide (GO). 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 during the reaction. At the same time, the two-dimensional layered structure of GO can act as a "buffer substrate" to absorb mechanical energy and reduce the direct damage of external forces to the catalyst particles, thereby improving the overall wear resistance. Finally, through the complementarity of the microstructure and performance among the multiple components, the dual improvement of structural stability and mechanical strength is achieved, providing a reliable guarantee for the long-term operation of the catalyst in complex reaction environments. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[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 The FTIR spectrum of the composite catalyst prepared in Example 3 of this invention is shown below.

[0041] Figure 4 The FTIR spectrum of the modified ionic liquid prepared in Example 6 of this invention is shown. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The graphene oxide used in this invention was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and its grade is G476339.

[0044] Example 1

[0045] This embodiment provides a method for preparing a composite catalyst for denitrification and purification of nitrogen-containing oxygen-containing flue gas, including the following steps:

[0046] Step I: Preparation of mixed powder

[0047] Weigh out 1 L of 0.1 mol / L Ce(NO3)3 aqueous solution, 1 L of 0.1 mol / L Mn(NO3)2 aqueous solution, and 1 L of 0.1 mol / L Fe(NO3)3 aqueous solution and add them to the reaction vessel. Stir the mixture, raise the temperature of the reaction vessel to 60℃, and adjust the pH of the reaction system to 10 using saturated sodium hydroxide aqueous solution. After stirring at this temperature for 2 hours, allow the mixture to age naturally for 12 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, filter the reactants, collect the filter cake, wash the filter cake three times with anhydrous ethanol and deionized water, and then transfer the filter cake to a drying oven at 80℃ and vacuum dry it to constant weight to obtain a mixed powder.

[0048] Step II: Preparation of catalyst precursor

[0049] Weigh 20.0g of the mixed powder and add it to a muffle furnace. The muffle furnace is heated to 300℃ at a heating rate of 5℃ / min. After holding at this temperature for 4 hours, it is naturally cooled to room temperature to obtain the catalyst precursor.

[0050] Step III: Preparation of composite catalyst

[0051] Weigh out 400.0 mL of deionized water and mix with 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 and add them to the reactor. Stir the reactor and raise the temperature to 60 °C. Keep the temperature and stir for 3 h. After the reaction is complete, wait for the reactor temperature to drop to room temperature, filter the reactants and collect the filter cake. Wash the filter cake three times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 80 °C and vacuum dry it to constant weight. Then transfer the material to a muffle furnace and heat it to 300 °C at a heating rate of 3 °C / min. Keep the temperature for 2 h and then cool it naturally to room temperature to obtain the composite catalyst.

[0053] Example 2

[0054] This embodiment provides a method for preparing a composite catalyst for denitrification and purification of nitrogen-containing oxygen-containing flue gas, including the following steps:

[0055] Step I: Preparation of mixed powder

[0056] Weigh out 1 L of 0.1 mol / L Ce(NO3)3 aqueous solution, 1 L of 0.1 mol / L Mn(NO3)2 aqueous solution, and 1 L of 0.1 mol / L Fe(NO3)3 aqueous solution and add them to the reaction vessel. Stir the mixture, raise the temperature of the reaction vessel to 70℃, and adjust the pH of the reaction system to 11 using saturated sodium hydroxide aqueous solution. After stirring at this temperature for 2 hours, allow the mixture to age naturally for 12 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, filter the reactants, collect the filter cake, wash the filter cake 5 times with anhydrous ethanol and deionized water, and then transfer the filter cake to a drying oven at 80℃ and vacuum dry it to constant weight to obtain a mixed powder.

[0057] Step II: Preparation of catalyst precursor

[0058] Weigh 20.0g of the mixed powder and add it to a muffle furnace. The muffle furnace is heated to 300℃ at a heating rate of 5℃ / min. After holding at this temperature for 4 hours, it is naturally cooled to room temperature to obtain the catalyst precursor.

[0059] Step III: Preparation of composite catalyst

[0060] Weigh out 500.0 mL of deionized water and mix with 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 and add them to the reactor. Stir the reactor and raise the temperature to 70 °C. Keep the temperature and stir for 4 h. After the reaction is complete, wait for the reactor temperature to drop to room temperature, filter the reactants and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 80 °C and vacuum dry it to constant weight. Then transfer the material to a muffle furnace and heat it to 300 °C at a heating rate of 3 °C / min. Keep the temperature for 2 h and then cool it naturally to room temperature to obtain the composite catalyst.

[0062] Example 3

[0063] This embodiment provides a method for preparing a composite catalyst for denitrification and purification of nitrogen-containing oxygen-containing flue gas, including the following steps:

[0064] Step I: Preparation of mixed powder

[0065] Weigh out 1 L of 0.1 mol / L Ce(NO3)3 aqueous solution, 1 L of 0.1 mol / L Mn(NO3)2 aqueous solution, and 1 L of 0.1 mol / L Fe(NO3)3 aqueous solution and add them to the reaction vessel. Stir the mixture, raise the temperature of the reaction vessel to 65℃, and adjust the pH of the reaction system to 11 using saturated sodium hydroxide aqueous solution. After stirring at this temperature for 2 hours, allow the mixture to age naturally for 12 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, filter the reactants, collect the filter cake, wash the filter cake four times with anhydrous ethanol and deionized water, and then transfer the filter cake to a drying oven at 80℃ and vacuum dry it to constant weight to obtain a mixed powder.

[0066] Step II: Preparation of catalyst precursor

[0067] Weigh 20.0g of the mixed powder and add it to a muffle furnace. The muffle furnace is heated to 300℃ at a heating rate of 5℃ / min. After holding at this temperature for 4 hours, it is naturally cooled to room temperature to obtain the catalyst precursor.

[0068] Step III: Preparation of composite catalyst

[0069] Weigh out 450.0 mL of deionized water and mix with 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 and add them to the reactor. Stir the reactor temperature to 65 °C and maintain the temperature for 4 h. After the reaction is complete, wait for the reactor temperature to drop to room temperature, filter the reactants and collect the filter cake. Wash the filter cake four times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 80 °C and vacuum dry it to constant weight. Then transfer the material to a muffle furnace and heat it to 300 °C at a heating rate of 3 °C / min. After holding the temperature for 2 h, allow it to cool naturally to room temperature to obtain the composite catalyst.

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

[0072] 580cm -1 The peak value is attributed to the Mn-O stretching vibration, which is an important indicator of the formation of manganese-oxygen cluster structures, confirming the presence of Mn. 2+ / Mn 3 + It is embedded in the framework via oxygen coordination; the peak is clearly separated in the spectrum, ruling out the possibility of overlap with Fe-O;

[0073] At 500cm -1 The presence of a medium-strong absorption peak at this point is attributed to the symmetric stretching of the Ce-O bond, reflecting the presence of Ce as an element. 3+ / Ce 4+ It is covalently integrated into the inorganic part. Its peak position is stable and its binding energy is high, which supports its stable bonding state during the synthesis process;

[0074] In addition, 470cm -1 The shoulder peaks can be attributed to the coordinated vibrations of heterocoordinate bonds in the bridging structures formed between Fe-O-Mn or Fe-O-Ce, exhibiting the spectral characteristics of a multi-metal nested structure, which is indirect evidence of trimetallic coordinated construction.

[0075] Besides the metal-oxygen bond region, 1110 cm -1 A strong absorption peak appears at a certain point, corresponding to the COC or PO bonds in the organic fragments of the material, which is a direct characterization of the embedding of organic ionic liquid fragments.

[0076] Others, such as 3440cm -1 1620cm -1 1384cm -1 The isoabsorption peaks correspond to the -OH stretching vibration, the aromatic C=C structure, and NO3, respectively. -The presence of heteroatom groups, etc.

[0077] Example 4

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

[0079] Step ①: Preparation of ionic liquid precursor

[0080] Weigh out 81.0 g of 1-methylimidazole, 108.0 g of bromoethane and 1000.0 mL of anhydrous acetone and add them to the reaction vessel. Stir the reaction vessel and heat it to reflux. Keep it at this temperature and stir for 10 h. After the reaction is completed, cool it to room temperature and remove the solvent by rotary evaporation. Add anhydrous diethyl ether to wash the product three times and continue to remove the anhydrous diethyl ether by rotary evaporation to obtain the 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 and add them to the reaction vessel and stir. After the temperature of the reaction vessel is raised to 55℃, add 145.0 g of potassium thiocyanate to the reaction vessel and keep it at this temperature for 5 h. After the reaction is completed, cool to room temperature, remove the solvent by rotary evaporation, and then transfer the reaction solution to a drying oven at 60℃ and vacuum dry for 10 h to obtain the modified ionic liquid.

[0083] Example 5

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

[0085] Step ①: Preparation of ionic liquid precursor

[0086] Weigh out 83.0 g of 1-methylimidazole, 110.0 g of bromoethane and 1000.0 mL of anhydrous acetone and add them to the reaction vessel. Stir the reaction vessel and heat it to reflux. Keep it at this temperature and stir for 12 h. After the reaction is completed, cool it to room temperature and remove the solvent by rotary evaporation. Add anhydrous diethyl ether to wash the product 5 times and continue to remove the anhydrous diethyl ether by rotary evaporation to obtain the 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 and add them to the reaction vessel and stir. After the temperature of the reaction vessel is raised to 65℃, add 147.0 g of potassium thiocyanate to the reaction vessel and keep it at this temperature for 7 h. After the reaction is completed, cool to room temperature, remove the solvent by rotary evaporation, and then transfer the reaction solution to a drying oven at 60℃ and vacuum dry for 12 h to obtain the modified ionic liquid.

[0089] Example 6

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

[0091] Step ①: Preparation of ionic liquid precursor

[0092] Weigh out 82.0 g of 1-methylimidazole, 109.0 g of bromoethane and 1000.0 mL of anhydrous acetone and add them to the reaction vessel. Stir the reaction vessel and heat it to reflux. Then keep it at this temperature and stir for 11 h. After the reaction is completed, cool it to room temperature and remove the solvent by rotary evaporation. Add anhydrous diethyl ether to wash the product 4 times and continue to remove the anhydrous diethyl ether by rotary evaporation to obtain the 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 and add them to the reaction vessel and stir. After the temperature of the reaction vessel is raised to 60℃, add 146.0 g of potassium thiocyanate to the reaction vessel and keep it at this temperature for 6 h. After the reaction is completed, cool to room temperature, remove the solvent by rotary evaporation, and then transfer the reaction solution to a drying oven at 60℃ and vacuum dry for 12 h to obtain the modified ionic liquid.

[0095] FTIR spectra of modified ionic liquid samples as follows Figure 2 As shown, in the high wavenumber region (3100–3200 cm⁻¹) -1 ), respectively at 3160cm -1 With 3110cm -1 Two sets of moderate-intensity stretching vibration absorption peaks were observed, which are attributed to the sp bonds of the CH bonds on the imidazole ring. 2 Hybridized tensile vibrations confirmed the existence of the imidazole core structure;

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

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

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

[0099] In addition, at 750cm -1 With 690cm -1 Two strong absorption bands exist at 2100 cm⁻¹, which can be attributed to the out-of-plane CH bending vibration characteristic peaks of the imidazole ring, providing auxiliary verification of the aromatic heterocyclic structure; -1 A significant absorption peak appears nearby, which is commonly seen in the C≡N or metal-carbon double bond intermediate regions after the introduction of organic-inorganic covalent structures or loaded metal coordination centers, indirectly characterizing the synergistic modification process of some multifunctional sites.

[0100] Example 7

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

[0102] Step 1: Preparation of pretreatment gas

[0103] After the flue gas is passed through a bag filter to remove solid particles larger than 5μm, it is cooled to 80℃ using a heat exchanger. Then, industrial deionized water is sprayed through an atomizing nozzle to control the humidity at 50%RH, and the outlet airflow pressure is checked to maintain 100Pa, thus obtaining pretreated gas.

[0104] Step 2: Preparation of Gas I

[0105] The pretreated 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 pretreated gas was 10,000 h⁻¹. -1 The oxygen content in the pretreated gas is 3%, and gas I is obtained by catalytic oxidation.

[0106] Step 3: Preparation of denitrified flue gas

[0107] Gas I was introduced into a rotary spray tower containing the modified ionic liquid prepared in Example 4. The operating temperature of the rotary spray tower was 30°C, and the liquid-to-gas ratio was 2 L / m³. 3 The pH value is 5, and the continuous use cycle of the modified ionic liquid is 48 hours. After purification and absorption, denitrification flue gas is obtained.

[0108] Step 4: Regenerating the modified ionic liquid

[0109] After the modified ionic liquid has been used for 48 hours, it is regenerated in a regeneration tank. The operating pressure of the regeneration tank is 20 kPa and the temperature is 80°C. Argon gas is introduced for purging to assist desorption. The desorbed nitrogen oxide gas is centrally incinerated. After the ionic liquid is cooled to room temperature, it is returned to the absorption tower for continued use.

[0110] Example 8

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

[0112] Step 1: Preparation of pretreatment gas

[0113] After the flue gas is passed through a bag filter to remove solid particles larger than 5μm, it is cooled to 120℃ using a heat exchanger. Then, industrial deionized water is sprayed through an atomizing nozzle to control the humidity at 70%RH, and the outlet airflow pressure is checked to maintain 200Pa, thus obtaining pretreated gas.

[0114] Step 2: Preparation of Gas I

[0115] The pretreated 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 pretreated gas was 20,000 h⁻¹. -1 The oxygen content in the pretreated gas is 5%, and gas I is obtained by catalytic oxidation.

[0116] Step 3: Preparation of denitrified flue gas

[0117] Gas I was introduced into a rotary spray tower containing the modified ionic liquid prepared in Example 5. The operating temperature of the rotary spray tower was 50°C, and the liquid-to-gas ratio was 4 L / m³. 3 The pH value is 8, and the continuous use cycle of the modified ionic liquid is 72 hours. After purification and absorption, denitrification flue gas is obtained.

[0118] Step 4: Regenerating the modified ionic liquid

[0119] After the modified ionic liquid has been used for 72 hours, it is regenerated in a regeneration tank. The operating pressure of the regeneration tank is 50 kPa and the temperature is 100°C. Argon gas is introduced for purging to assist desorption. The desorbed nitrogen oxide gas is centrally incinerated. After the ionic liquid is cooled to room temperature, it is returned to the absorption tower for continued use.

[0120] Example 9

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

[0122] Step 1: Preparation of pretreatment gas

[0123] After the flue gas is passed through a bag filter to remove solid particles larger than 5μm, it is cooled to 100℃ using a heat exchanger. Then, industrial deionized water is sprayed through an atomizing nozzle to control the humidity at 60%RH, and the outlet airflow pressure is checked to maintain 150Pa, thus obtaining pretreated gas.

[0124] Step 2: Preparation of Gas I

[0125] The pretreated gas was introduced into a 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 pretreated gas was 15000 h⁻¹. -1 The oxygen content in the pretreated gas is 4%, and gas I is obtained by catalytic oxidation.

[0126] Step 3: Preparation of denitrified flue gas

[0127] Gas I was introduced into a rotary spray tower containing the modified ionic liquid prepared in Example 6. The operating temperature of the rotary spray tower was 40°C, and the liquid-to-gas ratio was 3 L / m³. 3 The pH value is 6, and the continuous use cycle of the modified ionic liquid is 54 hours. After purification and absorption, denitrification flue gas is obtained.

[0128] Step 4: Regenerating the modified ionic liquid

[0129] After the modified ionic liquid has been used for 54 hours, it is regenerated in a regeneration tank. The operating pressure of the regeneration tank is 35 kPa and the temperature is 90°C. Argon gas is introduced for purging to assist desorption. The desorbed nitrogen oxide gas is centrally incinerated. After the ionic liquid is cooled to room temperature, it is returned 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 in the preparation process of the composite catalyst used in step two.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 9 is that step ② is omitted in the preparation process 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 two is omitted.

[0136] Performance testing:

[0137] The wear rate of the composite catalysts used in Examples 7-9 and Comparative Examples 1-3 was tested in accordance with the standard DL / T 1286-2021 "Technical Specification for Testing Catalysts for Flue Gas Denitrification in Thermal Power Plants".

[0138] Referring to standard GB 13271-2014 "Emission Standard of Air Pollutants for Boilers", the nitrogen oxide concentrations of the denitrified flue gas prepared in Examples 7-9 and Comparative Examples 1-3 were measured.

[0139] Modified ionic liquids that have been recycled 5, 50, and 100 times were added to a rotary spray tower, and the concentration of nitrogen oxides in the denitrification flue gas obtained after denitrification with the modified ionic liquids recycled 5, 50, and 100 times was measured in accordance with the standard GB13271-2014 "Emission Standard of Air Pollutants for Boilers". The specific data are shown in Table 1.

[0140] Table 1 - Performance Test Data for Each Sample

[0141]

[0142] Data Analysis:

[0143] After comparing and analyzing the data in Table 1, the attrition 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 was 33 mg·m³. 3 Furthermore, the concentration of nitrogen oxides in the denitrification tail gas after five cycles of the modified ionic liquid used for denitrification was 34 mg·m³. 3 The nitrogen oxide concentration in the denitrification tail gas after 50 cycles of denitrification was 36 mg·m³. 3 Simultaneously, after 100 cycles of denitrification, the nitrogen oxide concentration in the denitrified exhaust gas is 38 mg·m³. 3 All data points are better than the comparative data, indicating that:

[0144] In Comparative Example 1, the composite catalyst did not incorporate graphene oxide to construct the composite structure; instead, it directly used calcined metal oxide precursors. Due to the loss of the synergistic effects of graphene oxide in structural stability, electronic conductivity, and active site dispersion, the overall specific surface area of ​​the catalyst significantly decreased, the pore size distribution was uneven, and the active species exhibited poor dispersion, making aggregation likely. Simultaneously, the conductivity and redox buffering capacity of graphene oxide itself help to enhance the catalytic oxidation rate of NO; ​​its absence resulted in the catalyst's inability to effectively convert NO to NO2. Consequently, the catalyst exhibited insufficient reactivity during the reaction, leading to increased NO residue, insufficient NO2 concentration entering the downstream absorption step, and a simultaneous decrease in absorption efficiency.

[0145] The absorbent used in Comparative Example 2 was unmodified 1-ethyl-3-methylimidazolium bromide. Since it was not modified with functional groups, its solubility and reactivity for NO2 were poor. Furthermore, the unmodified ionic liquid had low polarity and lacked the ability to form stable complexes with NO2. It also lacked sufficient electron acceptor structure to promote reversible addition reactions. Therefore, the absorption process mostly relied on physical dissolution rather than chemical reaction, resulting in limited absorption capacity and slow rate. At the same time, this type of ionic liquid is prone to problems such as adsorption site saturation, increased viscosity, and accumulation of reaction byproducts during continuous recycling, which affects the 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 absorption tower, attempting to rely on the absorbent alone to remove NO. However, NO molecules are nonpolar small molecules with extremely low reactivity. Without catalytic oxidation to "activate" them, they hardly react with the absorbent and have extremely low solubility. Although the modified ionic liquid itself has excellent performance and good absorption and regeneration capabilities for NO2, its absorption effect is almost ineffective for unoxidized NO. The results show that, in the absence of the NO conversion step, the NO concentration at the outlet of the absorption tower hardly changes, and accelerating the circulation of the absorbent cannot improve the removal effect.

[0147] The results show that Comparative Example 1 omitted the graphene oxide composite structure, leading to a decrease in catalyst specific surface area, reduced electrical conductivity, uneven distribution of active sites, and a significant reduction in NO oxidation efficiency, directly affecting subsequent absorption steps. Comparative Example 2 used an unmodified ionic liquid, lacking functional groups such as thiocyanate, which prevented it from forming a stable complex with NO2, resulting in decreased absorption capacity, slower reaction rate, and unsatisfactory regeneration performance, limiting the long-term recycling of the absorbent. Comparative Example 3 directly removed the catalytic oxidation step, attempting to rely on the modified ionic liquid to directly absorb NO, but due to the low polarity and poor reactivity of NO, it was almost insoluble in the absorbent, causing a significant decline in overall denitrification efficiency. In conclusion, 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 a highly efficient and stable integrated "catalysis-absorption" system.

[0148] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for denitrification and purification of flue gas containing nitrogen oxides, characterized in that, Includes the following steps: S1. The pretreated gas is passed into a catalytic reactor loaded with a composite catalyst and catalytically oxidized to obtain gas I; S2. Gas I is passed into an absorption tower containing modified ionic liquid, and after purification and absorption, denitrified flue gas is obtained; 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 returned to the absorption tower for continued use. The preparation method of the composite catalyst includes 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 / L FFe(NO3)3 aqueous solution to the reaction vessel and stir. Raise the temperature of the reaction vessel to 60-70℃ and adjust the pH of the reaction system to 10-11 using saturated sodium hydroxide aqueous solution. After stirring at this temperature for 2 hours, allow it to age naturally for 12 hours. The resulting powder is then obtained through post-processing. A2. After calcining the mixed powder, a catalyst precursor is obtained; A3. Add the catalyst precursor and graphene oxide dispersion to the reactor and stir. Raise the reactor temperature to 60-70℃ and keep it at that temperature for 3-4 hours. Then, after post-treatment, the composite catalyst is obtained. The preparation method of the modified ionic liquid includes the following steps: B1. Add 1-methylimidazolium, bromoethane and anhydrous acetone to a reaction vessel and stir. Heat the reaction vessel to reflux and stir for 10-12 hours. Post-process to obtain the ionic liquid precursor. B2. Add the ionic liquid precursor and anhydrous acetonitrile to the reactor and stir. After the reactor temperature is raised to 55-65℃, add potassium thiocyanate to the reactor and keep it at this temperature for 5-7 hours. The modified ionic liquid is then obtained through post-treatment.

2. The method for denitrification and purification of nitrogen-containing oxygen-containing flue gas according to claim 1, characterized in that, In step S1, the pretreatment step is as follows: after removing solid particles with a diameter greater than 5μm from the flue gas through a bag filter, the temperature is reduced to 80-120℃ using a heat exchanger, and then industrial deionized water is sprayed into the flue gas through an atomizing nozzle to control the humidity at 50-70%RH. The outlet airflow pressure is checked and maintained at 100-200Pa to obtain the pretreated gas.

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

4. The method for denitrification and purification of nitrogen-containing oxygen-containing flue gas according to claim 1, characterized in that, In step S2, the absorption tower is a rotary spray tower, and the operating temperature of the rotary spray tower is 30-50℃, and the liquid-to-gas ratio is 2-4L / m³. 3 The pH value is 5-8, and the continuous use period of the modified ionic liquid is 48-72h.

5. The method for denitrification and purification of nitrogen-containing oxygen-containing flue gas 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℃, and argon gas is introduced for purging to assist 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.

6. The method for denitrification and purification of nitrogen-containing oxygen-containing flue gas according to claim 1, characterized in that, In step A1, the ratio of 0.1 mol / L Ce(NO3)3 aqueous solution, 0.1 mol / L Mn(NO3)2 aqueous solution, and 0.1 mol / L FFe(NO3)3 aqueous solution is 1 mL:1 mL:1 mL. 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℃ at a heating rate of 5℃ / min, held at that temperature for 4 hours, and then naturally cooled to room temperature to obtain the catalyst precursor. In step A3, the ratio of the catalyst precursor to the graphene oxide dispersion is 1 g:40-50 mL, wherein the graphene oxide dispersion is obtained by mixing deionized water and graphene oxide at a ratio of 40-50 mL:0.2-0.3 g.

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

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