A lignite depolymer and its application in photocatalytic denitrification of flue gas

Abstract

This invention relates to the field of lignite resource utilization and environmental protection technology, specifically to a lignite depolymerization product and its application in flue gas photocatalytic denitrification. The invention first prepares an alkali-soluble depolymerization product by pretreating inexpensive lignite with nitric acid and then performing mild oxidative depolymerization. Next, a coating is prepared by mixing the obtained lignite depolymerization product with anatase TiO2 photocatalyst, polyvinyl alcohol, and other additives. This coating is then applied to diatomaceous earth ceramic balls to prepare a flue gas photocatalytic denitrification agent. The prepared lignite depolymerization product possesses the dual functions of promoting TiO2 photocatalysis and absorbing nitrogen oxides. The provided photocatalytic denitrification agent has readily available raw materials, is simple to prepare, low in cost, and has high denitrification efficiency, enabling the high-value utilization of lignite.

Description

Technical Field

[0001] This invention relates to the field of lignite resource utilization and environmental protection technology, specifically to a lignite depolymerization product and its application in flue gas photocatalytic denitrification. Background Technology

[0002] Currently, based on different requirements such as flue gas environment, denitrification cost, and denitrification efficiency, there are mainly two denitrification technologies: dry and wet. Wet denitrification has higher and more stable efficiency, moderate initial investment cost, and is more suitable for high-concentration NO. x Adsorption and removal are necessary for nitrogen oxide removal. However, wet denitrification generates industrial wastewater and waste residue, causing secondary pollution. Furthermore, wet absorbents are highly corrosive, have short equipment lifespans, and high maintenance costs. Dry denitrification, primarily using SNCR and NSCR, is currently the mainstream denitrification technology for coal-fired furnaces. SCR, in particular, boasts a high denitrification rate (stable above 80%), meeting emission standards, but it requires significant investment and incurs high catalyst and operating costs. While SNCR has relatively lower investment and operating costs, its denitrification rate (only 30%-60%) is low, and it suffers from ammonia slip. Therefore, the development of efficient, low-cost ammonia-free flue gas denitrification technology is of great significance.

[0003] NO in industrial waste gas x NO mainly exists in the forms of NO and NO2, especially in coal-fired flue gas where the NO content can reach over 90%. Since NO is insoluble in water and alkaline solutions, it is generally removed by adding reducing agents such as NH3 and urea to convert it into N2, or by generating alkali-soluble NO2 under the action of oxidants such as O2. For example, mainstream denitrification technologies (SNCR and SCR) use ammonia reduction denitrification processes; however, excess ammonia can easily cause ammonia escape, leading to secondary pollution. Oxidative denitrification, primarily using O2, not only requires highly efficient catalysts but also necessitates the re-adsorption or absorption of NO2, making the process complex. With the development of photocatalysis technology, photocatalytic oxidation denitrification based on TiO2 has gradually attracted attention. Under the action of photocatalysts such as TiO2, NO can be oxidized to NO2 at lower temperatures, offering advantages in low-temperature denitrification. However, the generated NO2 still needs to be absorbed by an alkaline solution. Chinese invention patent CN201210365265.2 discloses a humate / nano-titanium dioxide composite adsorbent, which utilizes the photocatalytic oxidation of NO by titanium dioxide to generate NO2, which is then converted into nitric acid and absorbed by the micropores of humate. The denitrified adsorbent can be used as a nitrogen-rich humic acid fertilizer. However, the adsorption capacity of humate is limited, and the physically adsorbed NO2 and HNO3 are easily desorbed, causing secondary pollution.

[0004] Lignite resources are abundant, low in cost, and high in moisture and oxygen content. However, traditional combustion power generation is inefficient and highly polluting. Recent studies have discovered that mild oxidative depolymerization of lignite can yield alkali-soluble depolymers rich in oxygen-containing groups such as carboxyl and phenolic hydroxyl groups, which can be used in environmental remediation and functional material preparation. Although these lignite depolymers exhibit structural characteristics similar to humic acid, they are predominantly aromatic, resulting in higher aromaticity, and the oxygen-containing functional groups are mainly alkali-soluble groups such as carboxyl and phenolic hydroxyl groups. The abundant aromatic rings, acting as chromophores, promote light absorption and have a good sensitizing effect on TiO2 photocatalysis. Simultaneously, the alkaline lignite depolymers (carboxylates and phenolates) can also absorb photocatalytic oxidation products such as NO2. Furthermore, the aromatic structure provides nitration and nitrosation reaction sites for the active intermediates of nitrogen oxides generated by photocatalysis, promoting the chemical absorption of high-valence nitrogen oxides. This provides inspiration for the research of highly efficient ammonia-free photocatalytic denitrification agents.

[0005] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of photocatalytic efficiency and NO2 absorption in existing photocatalytic denitrification technologies, and to provide a lignite depolymerizer and its application in flue gas photocatalytic denitrification.

[0007] To achieve the above objectives, this invention discloses a method for preparing lignite depolymers, comprising the following steps:

[0008] S1, lignite is added to nitric acid solution, stirred and heated, kept at a constant temperature, cooled, filtered and separated, and dried to obtain pretreated lignite;

[0009] S2, pretreated lignite is mixed with KOH solution, stirred and dispersed, then O2 is introduced, heated and oxidized to depolymerize, cooled and filtered, and the filtrate is evaporated and concentrated to obtain alkali-soluble lignite depolymerized product.

[0010] In step S1, the concentration of the nitric acid solution is 0.5 mol / L, the stirring and heating temperature is 40~60 ℃, and the constant temperature treatment time is 4h.

[0011] In step S2, the solid-liquid ratio during mixing is 10-20, and the mass ratio of pretreated lignite to KOH is 1:0.5-1.1.

[0012] In step S2, the amount of O2 introduced is 1~3 MPa, the heating temperature for oxidation and depolymerization is 120 ℃, and the time is 1~3 h.

[0013] This invention also discloses the application of the lignite depolymerized material prepared by the above method in photocatalytic denitrification of flue gas. The specific application method includes the following steps:

[0014] A1. Nanoscale anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, lignite depolymerization and polyvinyl alcohol solution are added and stirred evenly to obtain a mixture for preparing photocatalytic coating.

[0015] A2. Transfer the mixture obtained in step A1 to a constant temperature shaker, add diatomaceous earth ceramic balls to it, swirl and shake, and then dry to obtain the denitrification agent;

[0016] A3. Fill the photocatalytic reaction tube with the denitrifying agent obtained in step A2, excite it with an ultraviolet light source, and introduce flue gas to carry out photocatalytic denitrification at room temperature.

[0017] In step A1, the photocatalytic coating comprises the following components by mass percentage: 50-65% lignite depolymerization, 25-35% TiO2, and 10-15% polyvinyl alcohol; the particle size of the nano-sized anatase TiO2 is 25-100 nm.

[0018] In step A2, the mass ratio of photocatalyst coating to diatomaceous earth ceramic balls is 1:10, the particle size of the diatomaceous earth ceramic balls is 2~3 mm, the swirling and shaking time is 2h, the drying temperature is 110 ℃, and the drying time is 8h.

[0019] In step A3, the wavelength of the ultraviolet light source is 250~350 nm, and the space velocity of the flue gas is 0.5~1.5. The O2 content of the flue gas should not be less than 6%.

[0020] The lignite depolymer of this invention is used as a TiO2 photocatalytic denitrification promoter and absorbent. Its principle is as follows:

[0021] (1) Due to the low degree of metamorphism, high reactivity, and abundance of oxygen-containing functional groups in lignite, mild oxidation can break the macromolecular structure of lignite and generate a large number of carboxyl groups, thus obtaining aromatic alkali-soluble depolymers. Pretreatment with nitric acid can introduce oxidizing groups such as nitro and nitroso groups, promoting the absorption of nitrogen oxides. At the same time, oxidation under mild conditions can avoid excessive oxidation and the generation of CO2, thereby increasing the yield of depolymers.

[0022] (2) Since lignite is mainly composed of 1-3 aromatic rings connected by bridging bonds such as methylene groups, and contains a large number of phenolic hydroxyl and carboxyl groups, the resulting depolymers are rich in a variety of chromophores and auxochromes, which can provide strong sensitization for TiO2 photocatalysts, increase the wavelength range of photoresponse, and improve photocatalytic efficiency. In particular, the nitro and nitroso groups introduced during the nitric acid pretreatment process further enhance the photosensitizing effect of the depolymers.

[0023] (3) In lignite oxidative depolymers, acidic oxygen-containing functional groups such as carboxyl and phenolic hydroxyl groups exist in the form of salts, which can absorb acidic nitrogen oxides. At the same time, a large number of aromatic structures can also undergo nitration and nitrosation reactions for the active nitrogen oxides generated by photooxidation, thereby realizing the chemical absorption of photocatalytic oxidation products.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention provides an alkali-soluble depolymerized product obtained from the selective oxidation of lignite as a promoter and absorbent. By regulating the aromatic structure and functional groups in the depolymerized product, light absorption is promoted, thus improving the efficiency of TiO2 photocatalytic denitrification. Simultaneously, the aromatic structure in the depolymerized product also enables the chemical absorption of NO2, eliminating the secondary pollution risks associated with physical adsorption.

[0026] 2. This invention provides a low-temperature, high-efficiency photocatalytic denitrification agent for flue gas, with a stable denitrification efficiency of over 80%. For NO with an initial concentration not exceeding 500 mg / L, the NO in the outlet tail gas... x Emissions below 50 mg / L meet the standards.

[0027] 3. This invention provides a method for preparing a photocatalytic denitrification agent for flue gas, which has the technical advantages of simple operation, low cost, and environmental friendliness, and can be used for NO removal. x End-of-pipe treatment;

[0028] 4. This invention provides a low-temperature, high-efficiency photocatalytic denitrification agent for flue gas, which can be used as a high-nitrogen organic fertilizer after use, without secondary pollution. Attached Figure Description

[0029] Figure 1 A flowchart illustrating the preparation process of lignite depolymers and their application in photocatalytic denitrification of flue gas;

[0030] Figure 2 These are SEM images of the denitrification agent before and after denitrification in Example 1 of this invention;

[0031] Figure 3 The diagram shows the denitrification effect of Example 1 and the comparative example of the denitrification agent of the present invention. Detailed Implementation

[0032] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0033] Example 1

[0034] Process flow as follows Figure 1 As shown:

[0035] (1) Lignite pretreatment: Zhaotong lignite was added to a 0.5 mol / L nitric acid solution, heated to 50°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0036] (2) Oxidation and depolymerization of pretreated lignite: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:20 (by weight) (pretreated lignite:KOH = 1:0.6). After stirring and dispersing, 1 MPa O2 was introduced, and the mixture was heated to 120 °C for oxidative depolymerization for 2 h, then cooled and filtered. The filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0037] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0038] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0039] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a wavelength of 1.0 nm. 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification. The morphology and structure of the denitrification agent remained stable before and after denitrification. Figure 2 The denitrification effect was significantly better than that of the control group ( Figure 3 ).

[0040] Example 2

[0041] Process flow as follows Figure 1 As shown:

[0042] (1) Lignite pretreatment: Baoqing lignite was added to a 0.5 mol / L nitric acid solution, heated to 60°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0043] (2) Oxidation and depolymerization of pretreated lignite: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:20 (by weight) (pretreated lignite:KOH = 1:1.1). After stirring and dispersing, 3 MPa O2 was introduced, and the mixture was heated to 120 ℃ for oxidative depolymerization for 3 h, then cooled and filtered. The filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0044] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0045] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken continuously for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0046] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a wavelength of 1.0 nm. 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0047] Example 3

[0048] Process flow as follows Figure 1 As shown:

[0049] (1) Lignite pretreatment: Mile lignite was added to a 0.5 mol / L nitric acid solution, heated to 40°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0050] (2) Oxidation and depolymerization of pretreated lignite: In a pressure vessel, the pretreated coal obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:20 (by weight) (pretreated lignite:KOH = 1:0.9). After stirring and dispersing, 2 MPa O2 was introduced, and the mixture was heated to 120 ℃ for oxidative depolymerization for 2 h, then cooled and filtered. The filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0051] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0052] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0053] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a wavelength of 1.0 nm. 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0054] Example 4

[0055] Process flow as follows Figure 1 As shown:

[0056] (1) Lignite pretreatment: Zhaotong lignite was added to a 0.5 mol / L nitric acid solution, heated to 40°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0057] (2) Oxidative depolymerization of pretreated coal: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:10 (by weight) (pretreated lignite:KOH = 1:0.5). After stirring and dispersing, 2 MPa O2 was introduced, and the mixture was heated to 120 ℃ for oxidative depolymerization for 3 h, then cooled and filtered. The filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0058] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0059] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0060] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a 1.5 nm wavelength. 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0061] Example 5

[0062] Process flow as follows Figure 1 As shown:

[0063] (1) Lignite pretreatment: Zhaotong lignite was added to a 0.5 mol / L nitric acid solution, heated to 50°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0064] (2) Depolymerization of pretreated lignite: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:20 (by weight) (pretreated lignite:KOH = 1:0.9). After stirring and dispersing, 1 MPa O2 was introduced, and the mixture was heated to 120 °C for oxidative depolymerization for 1 h, followed by cooling and filtration. The resulting filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0065] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0066] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0067] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a 0.5 nm wavelength. 500 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0068] Example 6

[0069] Process flow as follows Figure 1 As shown:

[0070] (1) Lignite pretreatment: Zhaotong lignite was added to a 0.5 mol / L nitric acid solution, heated to 60°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0071] (2) Depolymerization of pretreated lignite: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:15 (by weight) (pretreated lignite:KOH = 1:0.6). After stirring and dispersing, 1 MPa O2 was introduced, and the mixture was heated to 120 °C for oxidative depolymerization for 2 h, followed by cooling and filtration. The resulting filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0072] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0073] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0074] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a wavelength of 1.0 nm. 100 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0075] As shown in Table 1, the composition and yield of lignite depolymers from Examples 1-6 are high, all exceeding 70%. Furthermore, Table 2 shows the photocatalytic denitrification effect; the provided lignite depolymers used to prepare denitrification agents all achieve photocatalytic denitrification rates exceeding 80%, significantly reducing NO in the denitrified flue gas. x The concentrations were all below 50 mg / L, demonstrating good photocatalytic denitrification ability. Furthermore, the denitrification agent prepared from nitric acid-pretreated coal depolymers exhibited even better denitrification performance.

[0076] Table 1. Composition and yield of lignite depolymers in Examples 1-6

[0077]

[0078] Comparative Example 1

[0079] Unlike the examples, this comparative example demonstrates the denitrification effect of the denitrification agent provided under non-photo-excitation conditions.

[0080] (1) Lignite pretreatment: Zhaotong lignite was added to a 0.5 mol / L nitric acid solution, heated to 50°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0081] (2) Oxidative depolymerization of pretreated coal: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:20 (by weight) (pretreated lignite:KOH = 1:0.6). After stirring and dispersing, 1 MPa O2 was introduced, and the mixture was heated to 120 ℃ for oxidative depolymerization for 2 h, then cooled and filtered. The filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0082] (3) Preparation of photocatalytic coating: According to the dry composition: 60% alkali-soluble polymer, 30% TiO2, and 10% polyvinyl alcohol, nano-sized anatase TiO2 is ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, the alkali-soluble polymer and polyvinyl alcohol solution obtained in step (2) are added and stirred evenly.

[0083] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0084] (5) Catalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, the ultraviolet light source is turned off, and the reaction is carried out at room temperature with a reaction rate of 1.0 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature non-photocatalytic denitrification.

[0085] Comparative Example 2 (Non-photocatalysis)

[0086] Unlike the examples, this comparative example demonstrates the denitrification effect without TiO2 denitrification agent.

[0087] (1) Lignite pretreatment: Zhaotong lignite was added to a 0.5 mol / L nitric acid solution, heated to 50°C with constant stirring, kept at a constant temperature for 4 h, cooled, filtered and separated, and dried to obtain pretreated lignite.

[0088] (2) Oxidation and depolymerization of pretreated lignite: In a pressure vessel, the pretreated lignite obtained in (1) was mixed with KOH solution at a solid-liquid ratio of 1:20 (by weight) (pretreated lignite:KOH = 1:0.6). After stirring and dispersing, 1 MPa O2 was introduced, and the mixture was heated to 120 °C for oxidative depolymerization for 2 h, then cooled and filtered. The filtrate was concentrated by evaporation to obtain lignite alkali solubles.

[0089] (3) Preparation of photocatalytic coating: According to the dry composition: 90% alkali-soluble polymer and 10% polyvinyl alcohol, the two are mixed and stirred evenly.

[0090] (4) Preparation of denitrification agent: The mixture obtained in step (3) is transferred to a constant temperature shaker, and diatomaceous earth ceramic balls (weight ratio 1:10) are added to it and shaken for 2 h. Then, the mixture is placed at 110 ℃ and dried continuously for 8 h to obtain the solid denitrification agent.

[0091] (5) Photocatalytic denitration: The denitrifying agent prepared in step (4) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a wavelength of 1.0 nm. 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0092] Comparative Example 3

[0093] Unlike the examples, this comparative example demonstrates the denitrification effect of a denitrification agent that does not contain lignite depolymerization products.

[0094] (1) Preparation of photocatalytic coating: Nanoscale anatase TiO2 is ultrasonically dispersed in isopropanol solution, stirred to form TiO2 suspension, and then polyvinyl alcohol solution is added and stirred evenly.

[0095] (2) Preparation of denitrification agent: The mixture obtained in step (1) was transferred to a constant temperature shaker, diatomaceous earth ceramic balls were added to it, and the mixture was shaken for 2 h. Then, the mixture was dried at 110 ℃ for 8 h to obtain the solid denitrification agent.

[0096] (3) Photocatalytic denitration: The denitrifying agent prepared in step (2) is filled into the photocatalytic reaction tube, and excited by a 275 nm ultraviolet light source at room temperature with a wavelength of 1.0 nm. 200 ppm NO at airspeed x Simulated flue gas containing (90% NO + 10% NO2) + 6% O2 was subjected to room temperature photocatalytic denitrification.

[0097] The implementation effects of Comparative Examples 1-3 are shown in Table 2. Comparative Examples 1-2 show that the lignite depolymerization denitrification agent provided by this invention is a photocatalytic denitrification agent. However, in the absence of photoexcitation and a photocatalyst, the denitrification effect of the prepared denitrification agent is poor. Comparative Example 3 shows that the photocatalytic denitrification agent without the provided lignite depolymerization agent has a significantly lower denitrification efficiency than the examples, and the NO content in the exhaust gas after denitrification is also lower. x The content is too high to meet the direct emission standards.

[0098] Table 2. Implementation Results of Comparative Examples 1-3

[0099]

[0100] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing lignite depolymers, characterized in that, Includes the following steps: S1, lignite is added to nitric acid solution, stirred and heated, kept at a constant temperature, cooled, filtered and separated, and dried to obtain pretreated lignite; S2, pretreated lignite is mixed with KOH solution, stirred and dispersed, then O2 is introduced, heated and oxidized to depolymerize, cooled and filtered, and the filtrate is evaporated and concentrated to obtain alkali-soluble lignite depolymerized product.

2. The method for preparing lignite depolymers as described in claim 1, characterized in that, In step S1, the concentration of the nitric acid solution is 0.5 mol / L, the stirring and heating temperature is 40~60 ℃, and the constant temperature treatment time is 4h.

3. The method for preparing lignite depolymers as described in claim 1, characterized in that, In step S2, the solid-liquid ratio during mixing is 10-20, and the mass ratio of pretreated lignite to KOH is 1:0.5-1.

1.

4. The method for preparing lignite depolymers as described in claim 1, characterized in that, In step S2, the amount of O2 introduced is 1~3 MPa, the heating temperature for oxidation and depolymerization is 120 ℃, and the time is 1~3 h.

5. A lignite depolymerized product prepared by the preparation method according to any one of claims 1 to 4.

6. An application of the lignite depolymer as described in claim 5 in photocatalytic denitrification of flue gas, characterized in that, The specific application method includes the following steps: A1. Nanoscale anatase TiO2 was ultrasonically dispersed in isopropanol solution and stirred to form TiO2 suspension. Then, lignite depolymerization and polyvinyl alcohol solution were added and stirred evenly to obtain photocatalytic coating. A2, the photocatalytic coating obtained in step A1 is transferred to a constant temperature shaker, diatomaceous earth ceramic balls are added to it, the mixture is swirled and shaken, and then dried to obtain the denitrification agent; A3. Fill the photocatalytic reaction tube with the denitrifying agent obtained in step A2, excite it with an ultraviolet light source, and introduce flue gas to carry out photocatalytic denitrification at room temperature.

7. The application of lignite depolymer as described in claim 6 in photocatalytic denitrification of flue gas, characterized in that, In step A1, the photocatalytic coating comprises the following components by mass percentage: 50-65% lignite depolymerization, 25-35% TiO2, and 10-15% polyvinyl alcohol; the particle size of the nano-sized anatase TiO2 is 25-100 nm.

8. The application of lignite depolymer as described in claim 6 in photocatalytic denitrification of flue gas, characterized in that, In step A2, the mass ratio of photocatalyst coating to diatomaceous earth ceramic balls is 1:10, the particle size of the diatomaceous earth ceramic balls is 2~3 mm, the swirling and shaking time is 2h, the drying temperature is 110 ℃, and the drying time is 8h.

9. The application of lignite depolymer as described in claim 6 in photocatalytic denitrification of flue gas, characterized in that, In step A3, the wavelength of the ultraviolet light source is 250~350 nm, and the space velocity of the flue gas is 0.5~1.

5. The O2 content of the flue gas should not be less than 6%.

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