Ammonium carbamate, its preparation method and use

Abstract

The application discloses ammonium carbamate and a preparation method and application thereof, and relates to the field of chemical industry, and specifically relates to a method for preparing ammonium carbamate, which comprises the following steps: introducing ammonia and carbon dioxide into a closed two-stage fixed-bed reaction tower; reacting the ammonia and the carbon dioxide in a first-stage fixed-bed reaction tower to generate ammonium carbamate slurry; and precipitating ammonium carbamate crystals in a second-stage fixed-bed reaction tower; conveying the crystallized ammonium carbamate slurry to a crystallizer, adding a beta-crystal type stabilizer, and precipitating beta-crystal type dominant ammonium carbamate crystals by cooling; adding a corrosion inhibitor after centrifugal separation, mixing and granulating, and drying to obtain ammonium carbamate denitration agent. The method independently produces ammonium carbamate as a final product, improves the existing ammonium carbamate production process, improves the content of beta-crystal type ammonium carbamate in the product, and improves the stability of the ammonium carbamate product.

Description

Technical Field

[0001] This invention relates to the field of flue gas denitrification agent technology, and in particular to an ammonium carbamate, its preparation method and application. Background Technology

[0002] Against the backdrop of ecological and environmental planning, my country has imposed more stringent requirements on ultra-low emissions in the industrial sector, particularly for industries such as steel, cement, and thermal power. x The emission limit has been reduced to 50 mg / m³ 3 Current mainstream flue gas denitrification technologies (SCR, SNCR) rely on liquid ammonia or urea as reducing agents. However, these technologies have many drawbacks, such as the risk of ammonia escape, which not only generates PM2.5 precursors but also triggers a series of secondary pollution problems. Traditional urea-to-ammonia processes, due to the involvement of water, result in high energy consumption, with the latent heat of water vaporization accounting for approximately 30%-50% of total energy consumption. They also produce byproducts such as isocyanate and biuret, placing a heavy burden on the industry's sustainable development. Unlike the hydrolysis or high-temperature pyrolysis processes of traditional urea-to-ammonia production, ammonium carbamate undergoes a one-step decomposition reaction within the direct pyrolysis range of 280-320℃, directly generating ammonia (NH3) and carbon dioxide (CO2). This makes the reaction process simpler and more efficient. Furthermore, ammonium carbamate is highly efficient as a denitrification agent.

[0003] Ammonium carbamate (NH₂COONH₄) is not produced independently as a final product in industry. Instead, it serves as a key intermediate in urea synthesis, formed by the reaction of liquid ammonia and carbon dioxide under high pressure and medium temperature conditions. Its industrial preparation is closely coupled with the urea production process, primarily achieved through a high-pressure ammonium carbamate condenser. In traditional urea production processes, ammonium carbamate is only used as an intermediate product, not the final product.

[0004] Ammonium carbamate has two crystal structures: α-form and β-form. Studies have shown that α-form ammonium carbamate is more volatile and hydrolyzed, while β-form ammonium carbamate is more stable. However, current ammonium carbamate production processes mainly borrow from urea production, where the formation and crystallization of ammonium carbamate primarily occur in a methylammonium condenser. This results in a complex preparation process, low yield of β-form ammonium carbamate, and low overall efficiency due to the easy decomposition and hydrolysis of α-form ammonium carbamate. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] Therefore, embodiments of the present invention provide an ammonium carbamate, its preparation method, and its application.

[0007] In a first aspect, the present invention provides a method for preparing ammonium carbamate, comprising the following steps:

[0008] (a) Ammonia and carbon dioxide are introduced into a closed two-stage fixed-bed reaction tower. In the first stage of the fixed-bed reaction tower, ammonia and carbon dioxide react to produce ammonium carbamate slurry. In the second stage of the fixed-bed reaction tower, ammonium carbamate crystals precipitate. (b) The crystallized ammonium carbamate slurry is transported to a crystallizer, a β-crystal stabilizer is added, and the temperature is lowered to precipitate β-crystal-dominated ammonium carbamate crystals; (c) After centrifugation, a corrosion inhibitor is added, the mixture is granulated, and dried to obtain ammonium carbamate denitrification agent.

[0009] Furthermore, the molar ratio of ammonia to carbon dioxide is (2-2.4):1.

[0010] Furthermore, the temperature of the first fixed-bed reaction tower is 150-180°C, the pressure is 15-20MPa, and the residence time of the raw materials is 5-10min.

[0011] Furthermore, the temperature of the second-stage fixed-bed reaction tower is 80-100°C, the pressure is 5-8 MPa, and the residence time of the ammonium carbamate slurry is 1-4 hours.

[0012] Furthermore, carbon tetrachloride is added to the second fixed-bed reaction tower, wherein the amount of carbon tetrachloride added is 0.5-2 wt% of the ammonium carbamate slurry.

[0013] Furthermore, the β-crystal stabilizer includes at least one of sodium polyacrylate, sodium citrate, and disodium EDTA.

[0014] Furthermore, the amount of the β-crystal stabilizer added is 5-20 wt% of the ammonium carbamate slurry.

[0015] Furthermore, in step (b), the cooling process involves cooling to 10°C at a rate of 0.5-1.0°C / min.

[0016] Furthermore, the corrosion inhibitor includes at least one of benzotriazole, sodium molybdate, and sodium tungstate.

[0017] Furthermore, the amount of the corrosion inhibitor added is 2-3 wt% of the ammonium carbamate crystals.

[0018] Furthermore, the particle size of the ammonium carbamate denitrifying agent is 1-3 mm.

[0019] Further, in step (c), the mixing is carried out at 50-60°C for 40-50 minutes.

[0020] Furthermore, in step (c), the drying process involves drying at 60-90°C for 2-4 hours.

[0021] Secondly, the present invention provides ammonium carbamate prepared by the method proposed in the first aspect above.

[0022] Thirdly, the present invention proposes the application of ammonium carbamate prepared by the method proposed in the first aspect or the ammonium carbamate proposed in the second aspect as a denitrification agent in flue gas denitrification.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: The method of the present invention produces ammonium carbamate as a final product independently, which improves the existing production process of ammonium carbamate, increases the content of β-crystal ammonium carbamate in the product, and improves the stability of the ammonium carbamate product. Attached Figure Description

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart of the preparation method of ammonium carbamate according to the present invention. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The following description, in conjunction with the accompanying drawings, describes the ammonium carbamate proposed in this invention, its preparation method, and its applications.

[0027] like Figure 1 As shown, the ammonium carbamate of the present invention and its preparation method include the following steps: (a) Ammonia and carbon dioxide are introduced into a closed two-stage fixed-bed reaction tower. In the first stage of the fixed-bed reaction tower, ammonia and carbon dioxide react to produce ammonium carbamate slurry. In the second stage of the fixed-bed reaction tower, ammonium carbamate crystals precipitate. (b) The crystallized ammonium carbamate slurry is transported to a crystallizer, a β-crystal stabilizer is added, and the temperature is lowered to precipitate β-crystal-dominated ammonium carbamate crystals; (c) After centrifugation, a corrosion inhibitor is added, the mixture is granulated, and dried to obtain ammonium carbamate denitrification agent.

[0028] In step (a), the molar ratio of ammonia to carbon dioxide is (2-2.4):1, with a slight excess of ammonia to prevent the side reaction of ammonium bicarbonate from being generated due to excessive ammonia, which would interfere with the β crystal form.

[0029] The first stage of the fixed-bed reactor operates at a temperature of 150-180°C and a pressure of 15-20 MPa; the second stage operates at a temperature of 80-100°C and a pressure of 5-8 MPa. Carbon tetrachloride is added to the second stage at a rate of 0.5-2 wt% of the ammonium carbamate slurry. The primary purpose of the first stage's high-temperature, high-pressure fixed bed is to ensure a high reaction rate between ammonia and carbon dioxide. The second stage's low-temperature, low-pressure fixed bed primarily controls crystal growth and introduces carbon tetrachloride to provide heterogeneous nucleation sites, inducing the growth of β-form ammonium carbamate. Simultaneously, the hydrophobicity of carbon tetrachloride reduces moisture interference and forms a suspension system, dispersing crystals and preventing agglomeration. Maintaining the temperature of the second stage fixed-bed reactor at 80-100°C inhibits α-form nucleation and promotes the dominant growth of β-form.

[0030] Regarding the control of reaction time, the first-stage fixed-bed reaction tower can achieve continuous feeding and discharging, with a raw material residence time of 5-10 minutes; the residence time of ammonium carbamate slurry in the second-stage fixed-bed reaction tower is controlled at 1-4 hours, allowing ammonium carbamate to slowly precipitate crystals.

[0031] In step (b), the β-crystal stabilizer includes at least one of sodium polyacrylate, sodium citrate, and disodium ethylenediaminetetraacetate, and the amount of β-crystal stabilizer added is 5-20 wt% of the ammonium carbamate slurry. The cooling process involves cooling to 10°C at a rate of 0.5-1.0°C / min to precipitate β-crystal-dominant ammonium carbamate crystals.

[0032] In step (c), the mixing process is carried out at 50-60℃ for 40-50 minutes, and the drying process is carried out at 60-90℃ for 2-4 hours. The corrosion inhibitor includes at least one of benzotriazole, sodium molybdate, or sodium tungstate, and the amount of corrosion inhibitor added is 2-3 wt% of ammonium carbamate crystals. The particle size of the ammonium carbamate denitrification agent is 1-3 mm.

[0033] The ammonium carbamate of the present invention is prepared by the preparation method of the ammonium carbamate of the present invention, and the ammonium carbamate of the present invention is used as a denitrification agent in flue gas denitrification.

[0034] The present invention will now be described in detail with reference to specific embodiments.

[0035] Example 1 Ammonia gas with a purity ≥99.5% and carbon dioxide with a purity ≥99.0% were introduced into the first-stage high-temperature, high-pressure reaction tower (pressure controlled at 18 MPa, temperature 180℃) at a molar ratio of 2.05:1 and reacted for 10 minutes to obtain a slurry. The slurry was then transferred to the second-stage low-temperature, low-pressure reaction tower (pressure controlled at 6 MPa, temperature 80℃), with carbon tetrachloride added at 1% of the slurry mass, and crystals were stably precipitated for 3 hours.

[0036] After crystallization, the slurry is fed into a crystallizer, and sodium polyacrylate (10% of the slurry mass) is added as a β-crystal stabilizer. The slurry is then cooled to 10℃ at a rate of 0.5℃ / min to crystallize.

[0037] After centrifugation, it is mixed with benzotriazole (3% of the mass of ammonium carbamate crystals) at 55°C for 45 minutes, shaped into 1-3 mm particles by a disc granulator, and dried at 80°C for 2 hours to obtain white spherical denitrification agent.

[0038] The white spherical denitrification agent was tested, and the results were as follows: β crystal form accounted for 54.5%, the decomposition rate was only 1.2% after 30 days at 25℃ and 40% relative humidity, and the compressive strength was ≥15N / particle.

[0039] Example 2 Ammonia gas with a purity ≥99.5% and carbon dioxide with a purity ≥99.0% were introduced into the first-stage high-temperature, high-pressure reaction tower (pressure controlled at 18 MPa, temperature 180℃) at a molar ratio of 2.05:1 and reacted for 10 minutes to obtain a slurry. The slurry was then transferred to the second-stage low-temperature, low-pressure reaction tower (pressure controlled at 6 MPa, temperature 80℃), with carbon tetrachloride added at 2% of the slurry mass, and crystals were stably precipitated for 3 hours.

[0040] After crystallization, the slurry is fed into a crystallizer, and sodium polyacrylate (10% of the slurry mass) is added as a β-crystal stabilizer. The slurry is then cooled to 10℃ at a rate of 0.5℃ / min to crystallize.

[0041] After centrifugation, it is mixed with benzotriazole (3% of the mass of ammonium carbamate crystals) at 55°C for 45 minutes, shaped into 1-3 mm particles by a disc granulator, and dried at 80°C for 2 hours to obtain white spherical denitrification agent.

[0042] The white spherical denitrification agent was tested, and the results were as follows: β crystal form accounted for 63.4%, the decomposition rate was only 1.0% after 30 days at 25℃ and 40% relative humidity, and the compressive strength was ≥15N / particle.

[0043] Example 3 Ammonia gas with a purity ≥99.5% and carbon dioxide with a purity ≥99.0% were introduced into the first-stage high-temperature, high-pressure reaction tower (pressure controlled at 18 MPa, temperature 180℃) at a molar ratio of 2.05:1 and reacted for 10 minutes to obtain a slurry. The slurry was then transferred to the second-stage low-temperature, low-pressure reaction tower (pressure controlled at 6 MPa, temperature 80℃), with carbon tetrachloride added at 0.5% of the slurry mass, and crystals were stably precipitated for 3 hours.

[0044] After crystallization, the slurry is fed into a crystallizer, and sodium polyacrylate (10% of the slurry mass) is added as a β-crystal stabilizer. The slurry is then cooled to 10℃ at a rate of 0.5℃ / min to crystallize.

[0045] After centrifugation, it is mixed with benzotriazole (3% of the mass of ammonium carbamate crystals) at 55°C for 45 minutes, shaped into 1-3 mm particles by a disc granulator, and dried at 80°C for 2 hours to obtain white spherical denitrification agent.

[0046] The white spherical denitrification agent was tested, and the results were as follows: β crystal form accounted for 52.8%, the decomposition rate was only 1.6% after 30 days at 25℃ and 40% relative humidity, and the compressive strength was ≥ 15N / particle.

[0047] Comparative Example 1 Ammonia gas with a purity ≥99.5% and carbon dioxide with a purity ≥99.0% were introduced into the first-stage high-temperature, high-pressure reaction tower (pressure controlled at 18 MPa, temperature 180℃) at a molar ratio of 2.05:1 and reacted for 10 minutes to obtain a slurry. The slurry was then transferred to the second-stage low-temperature, low-pressure reaction tower (pressure controlled at 6 MPa, temperature 80℃) without the addition of carbon tetrachloride, and crystals were stably precipitated for 3 hours.

[0048] After crystallization, the slurry is fed into a crystallizer, and sodium polyacrylate (10% of the slurry mass) is added as a β-crystal stabilizer. The slurry is then cooled to 10℃ at a rate of 0.5℃ / min to crystallize.

[0049] After centrifugation, it is mixed with benzotriazole (3% of the mass of ammonium carbamate crystals) at 55°C for 45 minutes, shaped into 1-3 mm particles by a disc granulator, and dried at 80°C for 2 hours to obtain white spherical denitrification agent.

[0050] The white spherical denitrification agent was tested, and the results were as follows: β crystal form accounted for 36.4%, the decomposition rate was only 4.8% after 30 days at 25℃ and 40% relative humidity, and the compressive strength was ≥15N / particle.

[0051] According to Examples 1-3 and Comparative Example 1, when carbon tetrachloride was added in Examples 1-3, the proportion of β-crystal form in the ammonium carbamate denitrifying agent was relatively high, while in Comparative Example 1, when carbon tetrachloride was not added, the proportion of β-crystal form in the ammonium carbamate denitrifying agent was relatively low. It can be seen that the addition of carbon tetrachloride helps to increase the proportion of β-crystal form in the ammonium carbamate denitrifying agent.

[0052] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0053] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0054] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing ammonium carbamate, characterized in that, Includes the following steps: (a) Ammonia and carbon dioxide are introduced into a closed two-stage fixed-bed reaction tower. In the first stage of the fixed-bed reaction tower, ammonia and carbon dioxide react to produce ammonium carbamate slurry. In the second stage of the fixed-bed reaction tower, ammonium carbamate crystals precipitate. (b) The crystallized ammonium carbamate slurry is transported to a crystallizer, a β-crystal stabilizer is added, and the temperature is lowered to precipitate β-crystal-dominated ammonium carbamate crystals; (c) After centrifugation, a corrosion inhibitor is added, the mixture is granulated, and dried to obtain ammonium carbamate denitrification agent.

2. The method for preparing ammonium carbamate as described in claim 1, characterized in that, The molar ratio of ammonia to carbon dioxide is (2-2.4):

1.

3. The method for preparing ammonium carbamate as described in claim 1, characterized in that, The temperature of the first stage fixed-bed reaction tower is 150-180°C, the pressure is 15-20MPa, and the residence time of the raw materials is 5-10min; And / or, the temperature of the second fixed-bed reaction tower is 80-100°C, the pressure is 5-8MPa, and the residence time of the ammonium carbamate slurry is 1-4h.

4. The method for preparing ammonium carbamate as described in claim 1, characterized in that, Carbon tetrachloride is added to the second fixed-bed reaction tower, and the amount of carbon tetrachloride added is 0.5-2 wt% of the ammonium carbamate slurry.

5. The method for preparing ammonium carbamate as described in claim 1, characterized in that, The β-crystal stabilizer includes at least one of sodium polyacrylate, sodium citrate, and disodium EDTA. And / or, the amount of the β-crystal stabilizer added is 5-20 wt% of the ammonium carbamate slurry.

6. The method for preparing ammonium carbamate according to claim 1, characterized in that, In step (b), the cooling process involves cooling down to 10°C at a rate of 0.5-1.0°C / min.

7. The method for preparing ammonium carbamate according to claim 1, characterized in that, The corrosion inhibitor includes at least one of benzotriazole, sodium molybdate, and sodium tungstate; And / or, the amount of the corrosion inhibitor added is 2-3 wt% of the ammonium carbamate crystals; And / or, the particle size of the ammonium carbamate denitrifying agent is 1-3 mm.

8. The method for preparing ammonium carbamate as described in claim 1, characterized in that, In step (c), the mixing is carried out at 50-60°C for 40-50 minutes. And / or, the drying in step (c) is performed at 60-90°C for 2-4 hours.

9. An ammonium carbamate, characterized in that, Prepared by the method described in any one of claims 1 to 8.

10. The application of ammonium carbamate prepared by the method according to any one of claims 1 to 8 or ammonium carbamate according to claim 9 as a denitrification agent in flue gas denitrification.

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