Composite denitration agent for out-of-furnace phase change process and preparation method of composite denitration agent

Abstract

The invention belongs to the technical field of denitration agents, and particularly discloses a composite denitration agent for an out-of-furnace phase change process and a preparation method of the composite denitration agent. The preparation method comprises the following steps: mixing 60-80 parts of urea, 20-30 parts of a hydrolysis accelerant and 5-15 parts of amino modified zeolite to obtain the composite denitration agent for the external phase change process; the hydrolysis accelerant is coated ammonium carbamate, and the amino-modified zeolite is obtained by modifying an amino-containing silane coupling agent. The prepared composite denitration agent can promote forward proceeding of urea hydrolysis, the conversion rate of urea is increased, and the ammonia yield is increased; the amino modified zeolite can adsorb and activate urea molecules, urea decomposition is transferred to a low temperature, the activation energy of urea decomposition is remarkably reduced, and the reaction rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of denitrification agents, and in particular to a composite denitrification agent for an out-of-furnace phase change process and a preparation method thereof. Background Art

[0002] Phase change denitrification technology outside the furnace is one of the important methods for industrial flue gas denitrification. Its core principle is to inject a reducing agent (such as ammonia or urea solution) into the flue gas to convert nitrogen oxides (NO x ) is selectively reduced to nitrogen (N2) and water (H2O), thereby achieving efficient removal of pollutants. At present, urea has become a commonly used ammonia source precursor in the off-site denitrification process due to its safety and ease of use. Urea is hydrolyzed or pyrolyzed to produce ammonia (NH3), which then reacts with NO x Catalytic reduction reaction occurs to achieve denitrification. Urea ammonia production technology mainly includes two processes: thermal decomposition and hydrolysis. Among them, hydrolysis is more economical.

[0003] However, the urea hydrolysis method faces problems such as low urea conversion rate, slow ammonia production rate and poor operation stability in practical applications. In terms of reaction mechanism, urea hydrolysis is an endothermic reversible reaction. Limited by thermodynamic equilibrium, the theoretical conversion rate under normal conditions can only reach 80-90%. In actual operation, due to factors such as uneven heat transfer and insufficient reaction residence time, the conversion rate often drops below 70%, resulting in waste of raw materials and increased operating costs. In terms of ammonia production rate, traditional heating methods have obvious thermal hysteresis, the reactor heating time is long, and it is difficult for urea to quickly reach activation energy, resulting in slow dynamic response and difficulty in meeting rapidly changing ammonia demand, which has become a key bottleneck restricting the application of hydrolysis method for ammonia production in flexible scenarios.

[0004] Therefore, how to provide a composite denitrification agent for an off-furnace phase change process and a preparation method thereof, improve the hydrolysis conversion rate of urea, reduce the activation energy of the reaction, and improve the stability of ammonia production is a difficult problem to be solved urgently in this field. Summary of the invention

[0005] In view of this, the present invention provides a composite denitrification agent for an off-furnace phase change process and a preparation method thereof, so as to solve the problems existing in the existing urea hydrolysis method such as low conversion rate, slow ammonia production rate and poor stability.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A composite denitrification agent for an out-of-furnace phase change process comprises the following components in parts by mass:

[0008] 60-80 parts of urea, 20-30 parts of hydrolysis accelerator, 5-15 parts of amino-modified zeolite;

[0009] The hydrolysis promoter is coated ammonium carbamate.

[0010] Preferably, the preparation method of the hydrolysis promoter comprises the following steps:

[0011] At room temperature, ammonium carbamate is coated with a mixed emulsion of polyvinyl alcohol and ethyl cellulose. After the coating treatment is completed, it is dried with cold air to obtain coated ammonium carbamate.

[0012] Preferably, the mass ratio of polyvinyl alcohol to ammonium carbamate in the mixed emulsion of polyvinyl alcohol and ethyl cellulose is 0.1-0.3:10; the mass concentration of polyvinyl alcohol is 5-8%;

[0013] The mass ratio of polyvinyl alcohol to ethyl cellulose is 90-95:5-10.

[0014] Preferably, the preparation steps of the amino-modified zeolite are as follows:

[0015] 1) Activate natural zeolite to obtain activated natural zeolite;

[0016] 2) Mix the activated natural zeolite, a silane coupling agent containing an amino group and an organic solvent, and carry out an amino-modification reaction to obtain amino-modified zeolite.

[0017] Preferably, the activation in step 1) includes acid activation and calcination activation;

[0018] The particle size of the natural zeolite is 10-500 μm.

[0019] Preferably, the acid activation is: soaking natural zeolite in an acid solution for 1.5-2.5 h to complete the activation of natural zeolite;

[0020] The acid solution includes hydrochloric acid solution and / or sulfuric acid solution, and the molar concentration of the acid solution is 1-2 mol / L.

[0021] Preferably, the calcination activation is: calcining natural zeolite to complete the activation of natural zeolite;

[0022] The temperature of the calcination is 400-500 °C, and the calcination time is 1.5-2 h.

[0023] Preferably, the mass-volume ratio of the activated natural zeolite, the silane coupling agent containing an amino group and the organic solvent in step 2) is 5 g:2-5 mL:200-300 mL;

[0024] The silane coupling agent containing an amino group includes 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane;

[0025] The organic solvent includes one or more of ethanol, methanol, and tetrahydrofuran.

[0026] Preferably, in step 2), the temperature of the amino modification reaction is 50-70 °C, and the time of the amino modification reaction is 6-12 h.

[0027] Another object of the present invention is to provide a preparation method of a composite denitration agent for an out-of-furnace phase change process, comprising the following steps:

[0028] Mix urea, a hydrolysis promoter, and amino-modified zeolite to obtain a composite denitration agent for an out-of-furnace phase change process.

[0029] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. In the composite denitration agent containing urea of the present invention, a hydrolysis promoter (coated ammonium carbamate) is introduced. After the hydrolysis promoter dissolves in water, it will release ammonium carbamate, which can promote the forward hydrolysis of urea, improve the conversion rate of urea, and increase the ammonia production.

[0031] 2. The composite denitration agent disclosed in the present invention also contains amino-modified zeolite. The porous structure of the zeolite provides a high specific surface area and abundant active sites, which can adsorb and activate urea molecules, transfer the decomposition of urea to a lower temperature, can significantly reduce the activation energy of urea decomposition, and accelerate the reaction rate; the present invention also conducts amino graft modification on the zeolite to improve the hydrophilicity of the zeolite. In addition, the amino group can act as a proton acceptor to promote the cleavage of the amide bond in the urea molecule, further promoting the hydrolysis of urea. Specific Embodiments

[0032] The present invention provides a composite denitration agent for an out-of-furnace phase change process, comprising the following components in parts by mass:

[0033] 60-80 parts of urea, 20-30 parts of a hydrolysis promoter, 5-15 parts of amino-modified zeolite; under the ratio disclosed in the present invention, the specific addition parts of urea can be 62 parts, 65 parts, 68 parts, 70 parts, 72 parts, 75 parts, 78 parts, the specific addition parts of the hydrolysis promoter can be 22 parts, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, and the specific addition parts of the amino-modified zeolite can be 6 parts, 8 parts, 10 parts, 12 parts, 14 parts.

[0034] In the present invention, the hydrolysis promoter is coated ammonium carbamate.

[0035] In the present invention, the preparation method of the hydrolysis promoter comprises the following steps:

[0036] At room temperature, ammonium carbamate is coated with a mixed emulsion of polyvinyl alcohol and ethyl cellulose. After the coating treatment is completed, it is dried with cold air to obtain coated ammonium carbamate.

[0037] In the present invention, the coating treatment can improve the storage stability of ammonium carbamate and avoid the decomposition of ammonium carbamate.

[0038] In the present invention, the mass ratio of polyvinyl alcohol to ammonium carbamate in the mixed emulsion of polyvinyl alcohol and ethyl cellulose is 0.1 - 0.3:10, preferably 0.15 - 0.25:10, and more preferably 0.2:10; the mass concentration of polyvinyl alcohol is 5 - 8%, 5.5%, 6%, 6.5%, 7%, 7.5%; the mass ratio of polyvinyl alcohol to ethyl cellulose is 90 - 95:5 - 10, preferably 91 - 94:6 - 8, and more preferably 92 - 93:7.

[0039] In the present invention, the solvent of the polyvinyl alcohol emulsion includes ethanol and / or acetonitrile.

[0040] In the present invention, polyvinyl alcohol and ethyl cellulose can form a biphasic structure, effectively blocking moisture and providing effective protection for ammonium carbamate.

[0041] In the present invention, the temperature of the cold air drying ≤ 30°C, specifically it can be 15°C, 18°C, 20°C, 22°C, 25°C, 26°C, 28°C.

[0042] In the present invention, the room temperature is conventionally understood as 25°C (this temperature is used in all embodiments of the present invention), and it can also include 15 - 25°C, specifically it can be 16°C, 18°C, 20°C, 22°C, 24°C.

[0043] In the present invention, the coating operation is preferably carried out using a coating machine. The rotation speed of the coating is preferably 50 - 200 rpm, specifically it can be 60 rpm, 80 rpm, 100 rpm, 120 rpm, 150 rpm, 180 rpm; the coating time is preferably 0.5 - 2 h, specifically it can be 0.8 h, 1 h, 1.2 h, 1.5 h, 1.8 h.

[0044] In the present invention, the preparation steps of the amino - modified zeolite are as follows:

[0045] 1) Activate natural zeolite to obtain activated natural zeolite;

[0046] 2) Mix the activated natural zeolite, a silane coupling agent containing an amino group, and an organic solvent, and carry out an amino - modification reaction to obtain amino - modified zeolite.

[0047] In the present invention, the particle size of the natural zeolite is 10 - 500 μm, specifically it can be 20 μm, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm.

[0048] In the present invention, the activation in step 1) includes acid activation and calcination activation.

[0049] In the present invention, the acid activation is as follows: immersing the natural zeolite in an acid solution for 1.5 - 2.5 h to complete the activation of the natural zeolite. The holding time can specifically be 1.6 h, 1.8 h, 2 h, 2.2 h, 2.4 h.

[0050] The acid solution includes hydrochloric acid solution and / or sulfuric acid solution, and the molar concentration of the acid solution is 1 - 2 mol / L, specifically it can be 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L.

[0051] In the present invention, the calcination activation is as follows: calcining the natural zeolite to complete the activation of the natural zeolite.

[0052] In the present invention, the temperature of the calcination is 400 - 500 °C, specifically it can be 420 °C, 440 °C, 450 °C, 460 °C, 480 °C; the calcination time is 1.5 - 2 h, specifically it can be 1.6 h, 1.7 h, 1.8 h, 1.9 h.

[0053] In the present invention, in step 2), the mass - volume ratio of the activated natural zeolite, the silane coupling agent containing an amino group, and the organic solvent is 5 g: 2 - 5 mL: 200 - 300 mL, preferably 5 g: 3 - 4 mL: 220 - 280 mL, and further preferably 5 g: 3.5 mL: 250 mL.

[0054] In the present invention, the silane coupling agent containing an amino group includes 3 - aminopropyltriethoxysilane and / or 3 - aminopropyltrimethoxysilane.

[0055] In the present invention, the organic solvent includes one or more of ethanol, methanol, and tetrahydrofuran.

[0056] In the present invention, in step 2), the temperature of the amino - modification reaction is 50 - 70 °C, specifically it can be 52 °C, 54 °C, 55 °C, 56 °C, 58 °C, 60 °C, 62 °C, 65 °C, 68 °C; the time of the amino - modification reaction is 6 - 12 h, specifically it can be 7 h, 8 h, 9 h, 10 h, 11 h.

[0057] The present invention also provides a preparation method of a composite denitration agent for an out - of - furnace phase - change process, comprising the following steps:

[0058] Mix urea, hydrolysis promoter and amino-modified zeolite to obtain a composite denitration agent for out-of-furnace phase change process.

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0060] Example 1

[0061] Under room temperature conditions, place ammonium carbamate in a coating machine, spray a mixed emulsion of polyvinyl alcohol and ethyl cellulose (the solvent is ethanol, the mass concentration of polyvinyl alcohol is 6%, and the mass ratio of polyvinyl alcohol to ethyl cellulose is 95:5), perform coating treatment at 100 rpm for 1 h (the mass ratio of polyvinyl alcohol to ammonium carbamate is 0.2:10), and then perform cold air drying (20 °C) to obtain coated ammonium carbamate, which is reserved as a hydrolysis promoter.

[0062] Take natural zeolite with a particle size of 100 - 200 μm and calcine it at 450 °C for 2 h to complete the activation of natural zeolite. Then mix the activated natural zeolite with 3-aminopropyltriethoxysilane and ethanol (the dosage ratio of activated natural zeolite, 3-aminopropyltriethoxysilane and ethanol is 5 g:2 mL:250 mL), and carry out amino modification reaction at 60 °C for 8 h to obtain amino-modified zeolite.

[0063] Fully mix 65 parts of urea, 25 parts of hydrolysis promoter and 10 parts of amino-modified zeolite to obtain a composite denitration agent.

[0064] Example 2

[0065] The difference between this example and Example 1 is only that acid activation is used instead of calcination activation.

[0066] The specific steps of acid activation are as follows:

[0067] Immerse natural zeolite in a 1.5 mol / L hydrochloric acid solution for 2 h to complete the activation of natural zeolite.

[0068] Example 3

[0069] Under room temperature conditions, place ammonium carbamate in a coating machine, spray in a mixed emulsion of polyvinyl alcohol and ethyl cellulose (the solvent is ethanol, the mass concentration of polyvinyl alcohol is 5%, and the mass ratio of polyvinyl alcohol to ethyl cellulose is 92:8), perform coating treatment at 100 rpm for 1 h (the mass ratio of polyvinyl alcohol to ammonium carbamate is 0.1:10), and then perform cold air drying (20 °C) to obtain coated ammonium carbamate, which is reserved as a hydrolysis promoter.

[0070] Take natural zeolite with a particle size of 150 - 400 μm and calcine it at 400 °C for 2 h to complete the activation of the natural zeolite. Then mix the activated natural zeolite with 3-aminopropyltriethoxysilane and ethanol (the dosage ratio of activated natural zeolite, 3-aminopropyltriethoxysilane, and ethanol is 5 g:4 mL:300 mL), and carry out an amino modification reaction at 50 °C for 10 h to obtain amino-modified zeolite.

[0071] Fully mix 70 parts of urea, 20 parts of hydrolysis promoter, and 15 parts of amino-modified zeolite to obtain a composite denitration agent.

[0072] Example 4

[0073] Under room temperature conditions, place ammonium carbamate in a coating machine, spray in a mixed emulsion of polyvinyl alcohol and ethyl cellulose (the solvent is ethanol, the mass concentration of polyvinyl alcohol is 8%, and the mass ratio of polyvinyl alcohol to ethyl cellulose is 90:10), perform coating treatment at 100 rpm for 1 h (the mass ratio of polyvinyl alcohol to ammonium carbamate is 0.3:10), and then perform cold air drying (20 °C) to obtain coated ammonium carbamate, which is reserved as a hydrolysis promoter.

[0074] Take natural zeolite with a particle size of 50 - 200 μm and calcine it at 500 °C for 1.5 h to complete the activation of the natural zeolite. Then mix the activated natural zeolite with 3-aminopropyltrimethoxysilane and ethanol (the dosage ratio of activated natural zeolite, 3-aminopropyltrimethoxysilane, and ethanol is 5 g:3 mL:250 mL), and carry out an amino modification reaction at 65 °C for 7 h to obtain amino-modified zeolite.

[0075] Fully mix 80 parts of urea, 20 parts of hydrolysis promoter, and 10 parts of amino-modified zeolite to obtain a composite denitration agent.

[0076] Comparative Example 1

[0077] The difference between this comparative example and Example 1 is only that no hydrolysis promoter is added.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 1 is only that natural zeolite (100 - 200 μm) of equal mass is used instead of amino-modified zeolite.

[0080] Experimental Example 1

[0081] The ammonia production performance of the composite denitration agents prepared in Examples 1-4 and Comparative Examples 1-2 was detected respectively. The detection method was as follows: the above composite denitration agents were fully mixed with water respectively (the solid-liquid ratio of the mixture was 1 kg: 1 L), and then heated to 140 °C, and the hydrolysis reaction was carried out at 0.3 MPa. The urea decomposition rate was detected after 1 h of hydrolysis reaction (the residual concentration of urea was detected by using an ultraviolet spectrophotometer). The urea decomposition rates are shown in Table 1.

[0082] Table 1 Urea decomposition rates of Examples 1-4 and Comparative Examples 1-2

[0083] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Decomposition rate 99％ 99％ 99％ 99％ 95％ 94％

[0084] It can be seen from Table 1 that the urea decomposition rate of the composite denitration agent prepared in the examples of the present invention is higher. Different catalyst modification methods can all achieve the amino modification of the catalyst (Examples 1 and 2), and can all promote the decomposition of urea. In Comparative Example 1, since the hydrolysis promoter (ammonium carbamate) was not added, the urea decomposition rate was relatively low. In Comparative Example 2, the catalyst was not amino-modified, which was not conducive to the dispersion of the catalyst and could not play the role of a proton acceptor, resulting in a relatively low urea decomposition rate.

[0085] Based on the above conditions, the ammonia concentration in the mixed gas generated by the ammonia production of the composite denitration agent was detected, and the test results are shown in Table 2.

[0086] Table 2 Ammonia concentrations of Examples 1-4 and Comparative Examples 1-2

[0087]

[0088]

[0089] The ammonia concentration of the composite denitration agent prepared in the present invention is also higher than that of Comparative Example 1 and Comparative Example 2, which is beneficial to the subsequent denitration reaction.

[0090] The mixed gas obtained in Example 1 was diluted to an ammonia concentration of 6% for denitration testing. The denitration conditions were 400 mg / m 3 NO x , the flue gas flow rate was 500 m 3 / h, the temperature was 900 °C, and the denitration rate was 92%, proving that the present invention can achieve excellent denitration effect. In addition, after the hydrolysis reaction, the amino-modified zeolite can be regenerated and then used again for the preparation of the composite denitration agent, reducing the preparation cost of the denitration agent.

[0091] In the present specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts among the various embodiments can be referred to each other.

[0092] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite denitrification agent for an out-of-furnace phase change process, characterized in that: The composition includes the following components in parts by weight: 60-80 parts of urea, 20-30 parts of hydrolysis accelerator, 5-15 parts of amino-modified zeolite; The hydrolysis accelerator is coated ammonium carbamate.

2. A composite denitrification agent for an out-of-furnace phase change process according to claim 1, characterized in that: The preparation method of the hydrolysis promoter comprises the following steps: At room temperature, the mixed emulsion of polyvinyl alcohol and ethyl cellulose is used to coat the ammonium carbamate. After the coating is completed, cold air drying is performed to obtain the coated ammonium carbamate.

3. The composite denitrification agent for an out-of-furnace phase change process according to claim 2, characterized in that: The mass ratio of polyvinyl alcohol to ammonium carbamate in the mixed emulsion of polyvinyl alcohol and ethyl cellulose is 0.1-0.3:10; the mass concentration of the polyvinyl alcohol is 5-8%; The mass ratio of the polyvinyl alcohol to the ethyl cellulose is 90-95:5-10.

4. A composite denitrification agent for an out-of-furnace phase change process according to any one of claims 1 to 3, characterized in that: The preparation steps of the amino-modified zeolite are as follows: 1) activating natural zeolite to obtain activated natural zeolite; 2) The activated natural zeolite, the silane coupling agent containing amino group and the organic solvent are mixed to carry out amino modification reaction to obtain the amino modified zeolite.

5. The composite denitrification agent for an out-of-furnace phase change process according to claim 4, characterized in that: The activation in step 1) includes acid activation and calcination activation; The particle size of the natural zeolite is 10 to 500 μm.

6. The composite denitrification agent for an out-of-furnace phase change process according to claim 5, characterized in that: The acid activation comprises: immersing the natural zeolite in an acid solution for 1.5 to 2.5 hours to complete the activation of the natural zeolite; The acid solution includes hydrochloric acid solution and / or sulfuric acid solution, and the molar concentration of the acid solution is 1-2 mol / L.

7. The composite denitrification agent for an out-of-furnace phase change process according to claim 5, characterized in that: The calcination activation comprises: calcining the natural zeolite to activate the natural zeolite; The calcination temperature is 400-500° C., and the calcination time is 1.5-2 hours.

8. A composite denitrification agent for an out-of-furnace phase change process according to claim 6 or 7, characterized in that: The mass volume ratio of the activated natural zeolite, the amino-containing silane coupling agent and the organic solvent in step 2) is 5 g: 2-5 mL: 200-300 mL; The amino-containing silane coupling agent includes 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane; The organic solvent includes one or more of ethanol, methanol and tetrahydrofuran.

9. The composite denitrification agent for an out-of-furnace phase change process according to claim 8, characterized in that: The temperature of the amino modification reaction in step 2) is 50-70° C., and the time of the amino modification reaction is 6-12 hours.

10. The method for preparing a composite denitrification agent for an out-of-furnace phase change process according to any one of claims 1 to 9, characterized in that: The steps include: The urea, the hydrolysis accelerator and the amino-modified zeolite are mixed to obtain a composite denitrification agent for an out-of-furnace phase change process.

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