A method for preparing melamine cyanurate

Abstract

This invention provides a method for preparing melamine cyanurate, comprising the following steps: a) drying and dehydrating urea and melamine; b) adding a polyol auxiliary agent and the dried and dehydrated urea and melamine to a reaction vessel, purging with nitrogen, heating to 160-230°C, and maintaining for 10-60 min to obtain solution A; c) heating solution A to 200-240°C and maintaining for 20-40 min to obtain solution B; d) heating solution B to 280-300°C and maintaining for 60-70 min to obtain crude melamine cyanurate; e) cooling the crude melamine cyanurate to 90-110°C, adding water to the reaction vessel, and maintaining the temperature at 90-110°C for 10 hours to obtain solution C; f) filtering solution C to obtain a filter cake, then washing the filter cake with boiling water until neutral, drying, and pulverizing to obtain melamine cyanurate. The preparation method of this invention lowers the temperature at which urea is pyrolyzed to produce cyanuric acid, thereby reducing the volatilization of urea and increasing the product yield.

Description

Technical Field

[0001] This invention relates to the field of polymer flame retardant materials technology, specifically to a method for preparing melamine cyanurate. Background Technology

[0002] Melamine cyanurate (MCA) is a high-performance nitrogen-based halogen-free flame retardant widely used in high molecular weight materials such as polyamide, rubber, nylon, polyurethane, acrylic emulsion, epoxy resin, polytetrafluoroethylene resin, and plastic products. In addition, MCA can be added to lubricating oils as a solid lubricant additive and to cosmetics as a lubricant. This is because MCA has a layered structure similar to graphite, which gives it excellent lubrication properties.

[0003] Currently, the main industrial methods for preparing MCA from urea include the one-step urea process and the two-step urea process. The two-step urea process uses urea and melamine as raw materials. First, urea is pyrolyzed to produce cyanuric acid, which is then purified and reacted with melamine to produce and purify refined MCA. The reaction equation is as follows:

[0004]

[0005] The one-step urea process involves heating and melting urea and melamine together to obtain crude MCA. The crude MCA is in block form, which is then crushed, acid-cooked, filtered, and dried to obtain refined MCA. The equation for this reaction is as follows:

[0006]

[0007] Whether it's the two-step or one-step urea production process, the reaction principle is the same: urea is first pyrolyzed at high temperature to produce cyanuric acid, which then reacts with melamine. The difference lies in the process itself: in the two-step process, after pyrolysis to produce cyanuric acid, the cyanuric acid is purified before reacting with melamine; while in the one-step process, the cyanuric acid produced by urea pyrolysis reacts directly with melamine at high temperature. Both methods share a common problem: during the high-temperature pyrolysis of urea to produce cyanuric acid, the high temperature leads to a significant amount of urea volatilization, resulting in a low product yield.

[0008] Therefore, there is a need to provide a method for preparing melamine cyanurate to solve the problems existing in the prior art. Summary of the Invention

[0009] In view of this, the present invention provides a method for preparing melamine cyanurate, which lowers the temperature at which urea is pyrolyzed to generate cyanuric acid, thereby reducing the volatilization of urea and thus increasing the yield of the product.

[0010] To achieve the above objectives, the present invention provides a method for preparing melamine cyanurate, employing the following technical solution:

[0011] A method for preparing melamine cyanurate includes the following steps:

[0012] a. Dry and dehydrate urea and melamine for later use;

[0013] b. Add the polyol auxiliaries and the urea and melamine dried and dehydrated in step a to the reaction vessel, introduce nitrogen atmosphere into the reaction vessel, heat to 160-230℃, maintain for 10-60 min, and obtain solution A;

[0014] In this step, urea reacts with a polyol auxiliary agent to obtain carbamate derivatives;

[0015] c. Heat solution A obtained in step b to 200-240℃ and maintain the temperature for 20-40 minutes to obtain solution B;

[0016] In this step, the carbamate derivative is heated and decomposed to obtain cyanuric acid;

[0017] d. Heat the solution B obtained in step c to 280-300℃ and maintain it for 60-70 minutes. Observe that the viscosity of the substance in the reaction vessel increases continuously with the increase of temperature, and obtain white crude melamine cyanuric acid.

[0018] In this step, melamine and cyanuric acid react to obtain a white crude melamine cyanuric acid product.

[0019] e. Cool the crude melamine cyanuric acid obtained in step d to 90-110°C, add water to the reaction vessel, and maintain the temperature at 90-110°C for 10 hours to obtain solution C.

[0020] f. Filter the solution C obtained in step e to obtain a filter cake, then wash the filter cake with boiling water until neutral, dry and crush it to obtain melamine cyanurate.

[0021] In the above preparation method, the polyol auxiliary agent and the urea and melamine after drying and dehydration in step a are added to the reaction vessel at one time. This will not affect the corresponding reaction steps under different reaction conditions, and there is no need to add raw materials step by step, making the operation more convenient. With the participation of the polyol auxiliary agent, the temperature required for urea to pyrolyze into cyanuric acid is lower, thereby reducing the volatilization of urea and improving the product yield.

[0022] Furthermore, in step a, the drying and dehydration temperature is 100-120℃ and the drying and dehydration time is 15-25 minutes.

[0023] Further, in step b, the polyol auxiliaries are one or a mixture of at least two of the following: ethylene glycol, propylene glycol, diethylene glycol, butanediol, pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2-methyl-1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,3-dimethyl-1,4-butanediol, glycerol, glycerol, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 800, polyethylene glycol 1000, polypropylene glycol 200, polypropylene glycol 400, polypropylene glycol 600, dipropylene glycol, and tripropylene glycol.

[0024] Furthermore, in step b, the molar ratio of the polyol auxiliary agent to the urea is 1:1.5-3.0.

[0025] Furthermore, in step b, the molar ratio of urea to melamine is 3:0.85-0.90.

[0026] Furthermore, in step b, the flow rate of the nitrogen atmosphere is 50-70 ml / min.

[0027] Furthermore, in step e, the mass of the water is 7-10 times the mass of the melamine mentioned in step b.

[0028] The above-described technical solution of the present invention has at least the following beneficial effects:

[0029] 1. In the preparation method of the present invention, the participation of polyol auxiliaries reduces the temperature required for urea pyrolysis to generate cyanuric acid, thereby reducing the volatilization of urea and increasing the product yield.

[0030] 2. In the preparation method of the present invention, the polyol auxiliary agent and the urea and melamine after drying and dehydration in step a are added to the reaction vessel at one time. This will not affect the reaction process of the corresponding steps under different reaction conditions, and there is no need to add raw materials in steps, making the operation more convenient.

[0031] 3. In the preparation method of the present invention, before the reaction, urea and melamine are dried and dehydrated to avoid loss of solvent and raw materials due to a small amount of water, thereby improving product yield.

[0032] 4. The preparation method of this invention reduces the deamination of urea, and the content (purity) of the melamine cyanuric acid product obtained after separation is above 99.5%, and the yield is above 95%. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0034] Example 1

[0035] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0036] a. Dry urea and melamine at 110℃ for 15 minutes and set aside.

[0037] b. Add 28g of 2-methyl-1,3-propanediol solvent, 35.0g of dried and dehydrated urea, and 21.62g of melamine to a reaction vessel. Heat to 170°C and, under a nitrogen atmosphere with a flow rate of 55ml / min, stir continuously for 15 minutes to obtain solution A. In this step, urea reacts with 2-methyl-1,3-propanediol to give 2-methyl-1,3-propanediol dicarboxylate. Solution A includes a carbamate derivative (2-methyl-1,3-propanediol dicarboxylate) and melamine.

[0038] c. Solution A is continuously stirred under nitrogen protection and heated to 230℃ for 20 minutes to obtain solution B. In this step, the carbamate derivative is cleaved to obtain cyanuric acid, and solution B contains cyanuric acid and melamine.

[0039] d. Heat solution B to 280℃ and react for 60 minutes. The material will then turn into a white, viscous substance, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0040] e. Cool the crude melamine cyanuric acid to about 100°C, add 190g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0041] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 41.73g of melamine cyanurate product with a yield of 95.6% and a purity of 99.7%.

[0042] Example 2

[0043] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0044] a. Dry urea and melamine at 100℃ for 20 minutes and set aside.

[0045] b. Add 28g of diethylene glycol, 30g of dried and dehydrated urea, and 18.0g of melamine to a reaction vessel, heat to 230℃, and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 60ml / min to obtain solution A. In this step, urea reacts with diethylene glycol to obtain diethylene glycol dicarboxylate, and solution A includes carbamate derivatives (diethylene glycol dicarboxylic acid) and melamine.

[0046] c. Solution A is continuously stirred under nitrogen protection and heated to 220°C for 40 minutes to obtain solution B. In this step, the carbamate derivative is cleaved to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0047] d. Heat solution B to 290℃ and react for 65 minutes. The material will then turn into a white, viscous state, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid undergo a solidification reaction to obtain white crude melamine cyanuric acid.

[0048] e. Cool the crude melamine cyanuric acid to about 100°C, add 280g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0049] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 34.97g of melamine cyanurate product with a yield of 96.0% and a purity of 99.6%.

[0050] Example 3

[0051] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0052] a. Dry and dehydrate urea and melamine at 120°C for 15 minutes, and set aside for later use.

[0053] b. Add 26g of glycerol, 40g of dried and dehydrated urea, and 24.34g of melamine to a reaction vessel, heat to 180℃, and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 65ml / min to obtain solution A. In this step, urea reacts with glycerol to obtain glycerol tricarbamate, and solution A includes a carbamate derivative (glycerol tricarbamate) and melamine.

[0054] c. Solution A is continuously stirred under nitrogen protection and heated to 230°C for 25 minutes for thermal pyrolysis to obtain solution B. In this step, the carbamate derivative is pyrolyzed to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0055] d. Heat solution B to 300℃ and react for 70 minutes. The material will then turn into a white, viscous substance, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0056] e. Cool the crude melamine cyanuric acid to about 100°C, add 230g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0057] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 47.53g of melamine cyanurate product with a yield of 96.5% and a purity of 99.5%.

[0058] Example 4

[0059] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0060] a. Dry and dehydrate urea and melamine at 120°C for 20 minutes, and set aside for later use.

[0061] b. Add 40g of hexanediol, 38g of dried and dehydrated urea, and 24.20g of melamine to a reaction vessel, heat to 190℃, and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 60ml / min to obtain solution A. In this step, urea reacts with hexanediol to obtain hexanediol dicarbamate, and solution A includes a carbamate derivative (hexanediol dicarbamate) and melamine.

[0062] c. Solution A is continuously stirred under nitrogen protection and heated to 240℃ for 25 minutes to obtain solution B. In this step, the carbamate derivative is cleaved to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0063] d. Heat solution B to 290℃ and react for 60 minutes. The material will then turn into a white, viscous product, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0064] e. Cool the crude melamine cyanuric acid to about 100°C, add 240g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0065] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 47.74g of melamine cyanurate product with a yield of 97.5% and a purity of 99.6%.

[0066] Example 5

[0067] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0068] a. Dry urea and melamine at 110℃ for 15 minutes and set aside.

[0069] b. Add 35g of 1,5-pentanediol and polypropylene glycol 400 (mass ratio of 2:1), 38.5g of dried and dehydrated urea, and 23.43g of melamine to a reaction vessel. Heat to 210℃ and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 60ml / min to obtain solution A. In this step, urea reacts with 1,5-pentanediol and polypropylene glycol 400 to obtain 1,5-pentanediol dicarboxylate and polypropylene glycol 400 dicarboxylate. Solution A includes carbamate derivatives (1,5-pentanediol dicarboxylate and polypropylene glycol 400 dicarboxylate) and melamine.

[0070] c. Solution A is continuously stirred under nitrogen protection and heated to 240℃ for 25 minutes to obtain solution B. In this step, the carbamate derivative is cleaved to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0071] d. Heat solution B to 280℃ and react for 60 minutes. The material will then turn into a white, viscous product, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0072] e. Cool the crude melamine cyanuric acid to about 100°C, add 220g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0073] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 45.27g of melamine cyanurate product with a yield of 95.5% and a purity of 99.8%.

[0074] Example 6

[0075] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0076] a. Dry urea and melamine at 100℃ for 20 minutes and set aside.

[0077] b. Add 30g of propylene glycol and glycerol (in a mass ratio of 3:1), 36.5g of dried and dehydrated urea, and 22.68g of melamine to a reaction vessel. Heat to 200℃ and, under a nitrogen atmosphere with a flow rate of 60ml / min, continuously stir for 25 minutes to obtain solution A. In this step, urea reacts with propylene glycol and glycerol to obtain propylene glycol dicarboxylate and glycerol tricarboxylate. Solution A includes carbamate derivatives (propylene glycol dicarboxylate and glycerol tricarboxylate) and melamine.

[0078] c. Solution A is continuously stirred under nitrogen protection and heated to 230°C for 25 minutes for thermal pyrolysis to obtain solution B. In this step, the carbamate derivative is pyrolyzed to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0079] d. Heat solution B to 290℃ and react for 70 minutes. The material will then turn into a white, viscous substance, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0080] e. Cool the crude melamine cyanuric acid to about 100°C, add 210g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0081] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 41.19g of melamine cyanurate product with a yield of 96.3% and a purity of 99.6%.

[0082] As can be seen from Examples 1-6, the content (purity) of melamine cyanurate obtained by the preparation method of the present invention is above 99.5%, and the yield is above 95.5%.

[0083] Comparative Example 1

[0084] The only difference between this comparative example and Example 1 is that in step b, the temperature is raised to 140°C, as detailed below.

[0085] The detailed steps for preparing melamine cyanurate in this comparative example are as follows:

[0086] a. Dry urea and melamine at 110℃ for 15 minutes and set aside.

[0087] b. Add 28g of 2-methyl-1,3-propanediol solvent, 35.0g of dried and dehydrated urea, and 21.62g of melamine to a reaction vessel. Heat to 140℃ and, under a nitrogen atmosphere with a flow rate of 55ml / min, continuously stir for 15min to obtain solution A. In this step, urea reacts with 2-methyl-1,3-propanediol to obtain 2-methyl-1,3-propanediol dicarboxylate. Solution A includes a carbamate derivative (2-methyl-1,3-propanediol dicarboxylate) and melamine.

[0088] c. Solution A is continuously stirred under nitrogen protection and heated to 230℃ for 20 minutes to obtain solution B. In this step, the carbamate derivative is cleaved to obtain cyanuric acid, and solution B contains cyanuric acid and melamine.

[0089] d. Heat solution B to 280℃ and react for 60 minutes. The material will then turn into a white, viscous substance, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0090] e. Cool the crude melamine cyanuric acid to about 100°C, add 190g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0091] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 38.24g of melamine cyanurate product with a yield of 87.4% and a purity of 95.7%.

[0092] The yield of melamine cyanurate obtained in this comparative example was 87.4%, which was significantly lower than that in Example 1.

[0093] Comparative Example 2

[0094] The only difference between this comparative example and Example 2 is that in step b, the temperature is raised to 250°C, as detailed below.

[0095] The detailed steps for preparing melamine cyanurate in this comparative example are as follows:

[0096] a. Dry urea and melamine at 100℃ for 20 minutes and set aside.

[0097] b. Add 28g of diethylene glycol, 30g of dried and dehydrated urea, and 18.0g of melamine to a reaction vessel, heat to 250℃, and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 60ml / min to obtain solution A. In this step, urea reacts with diethylene glycol to obtain diethylene glycol dicarbamate, and solution A includes a carbamate derivative (diethylene glycol dicarbamate) and melamine.

[0098] c. Solution A is continuously stirred under nitrogen protection and kept at 240℃ for 40 minutes to obtain solution B. In this step, diethylene glycol dicarboxylate is cracked to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0099] d. Heat solution B to 290℃ and react for 65 minutes. The material will then turn into a white, viscous state, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0100] e. Cool the crude melamine cyanuric acid to about 100°C, add 280g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0101] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the moisture content is ≤0.2%, pulverize it, and obtain 30.38g of melamine cyanurate product with a yield of 83.4% and a purity of 92.5%.

[0102] The yield of melamine cyanurate obtained in this comparative example was 83.4%, which was significantly lower than that in Example 2.

[0103] Comparative Example 3

[0104] The only difference between this comparative example and Example 3 is that in step b, the temperature is raised to 130°C, as detailed below.

[0105] The detailed steps for preparing melamine cyanurate in this comparative example are as follows:

[0106] a. Dry and dehydrate urea and melamine at 120°C for 15 minutes, and set aside for later use.

[0107] b. Add 26g of glycerol, 40g of dried and dehydrated urea, and 24.34g of melamine to a reaction vessel, heat to 130℃, and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 65ml / min to obtain solution A. In this step, urea reacts with glycerol to obtain glycerol tricarbamate, and solution A includes a carbamate derivative (glycerol tricarbamate) and melamine.

[0108] c. Solution A is continuously stirred under nitrogen protection and heated to 230°C for 25 minutes for thermal pyrolysis to obtain solution B. In this step, the carbamate derivative is pyrolyzed to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0109] d. Heat solution B to 300℃ and react for 70 minutes. The material will then turn into a white, viscous substance, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0110] e. Cool the crude melamine cyanuric acid to about 100°C, add 230g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0111] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 42.60g of melamine cyanurate product with a yield of 86.5% and a purity of 94.8%.

[0112] The yield of melamine cyanurate obtained in this comparative example was 86.5%, which was significantly lower than that in Example 3.

[0113] Comparative Example 4

[0114] The only difference between this comparative example and Example 4 is that in step b, the temperature is raised to 240°C, as detailed below.

[0115] The detailed steps for preparing melamine cyanurate in this embodiment are as follows:

[0116] a. Dry and dehydrate urea and melamine at 120°C for 20 minutes, and set aside for later use.

[0117] b. Add 40g of hexanediol, 38g of dried and dehydrated urea, and 24.20g of melamine to a reaction vessel, heat to 240℃, and stir continuously for 25 minutes under a nitrogen atmosphere with a flow rate of 60ml / min to obtain solution A. In this step, urea reacts with hexanediol to obtain hexanediol dicarbamate, and solution A includes a carbamate derivative (hexanediol dicarbamate) and melamine.

[0118] c. Solution A is continuously stirred under nitrogen protection and heated to 240℃ for 25 minutes to obtain solution B. In this step, the carbamate derivative is cleaved to obtain cyanuric acid, and solution B includes cyanuric acid and melamine.

[0119] d. Heat solution B to 290℃ and react for 60 minutes. The material will then turn into a white, viscous product, which is crude melamine cyanuric acid. In this step, melamine and cyanuric acid react to obtain white crude melamine cyanuric acid.

[0120] e. Cool the crude melamine cyanuric acid to about 100°C, add 240g of water, and maintain the temperature at about 100°C. Stir for 10 hours to obtain solution C.

[0121] f. Filter solution C while it is hot to obtain a filter cake. Then wash the filter cake with boiling water until it is neutral, dry it until the water content is ≤0.2%, pulverize it, and obtain 40.94g of melamine cyanurate product with a yield of 83.6% and a purity of 92.5%.

[0122] The yield of melamine cyanurate obtained in this comparative example was 83.6%, which was significantly lower than that in Example 4.

Claims

1. A method for preparing melamine cyanurate, characterized in that, Includes the following steps: a. Dry and dehydrate urea and melamine for later use; b. Add the polyol auxiliary agent, the urea and melamine dried and dehydrated in step a to a reaction vessel, introduce a nitrogen atmosphere into the reaction vessel, heat to 160-230℃, maintain for 10-60 min, and obtain solution A; In step b, the molar ratio of the polyol auxiliary agent to the urea is 1:1.5-3.0; c. Heat solution A obtained in step b to 200-240℃ and maintain the temperature for 20-40 minutes to obtain solution B; d. Heat the solution B obtained in step c to 280-300℃ and maintain it for 60-70 minutes. Observe the viscosity of the substance in the reaction vessel continuously increasing to obtain white crude melamine cyanuric acid. e. Cool the crude melamine cyanuric acid obtained in step d to 90-110°C, add water to the reaction vessel, and maintain the temperature at 90-110°C for 10 hours to obtain solution C. f. Filter the solution C obtained in step e to obtain a filter cake, then wash the filter cake with boiling water until neutral, dry and crush it to obtain melamine cyanurate.

2. The method for preparing melamine cyanurate according to claim 1, characterized in that, In step a, the drying and dehydration temperature is 100-120℃ and the drying and dehydration time is 15-25 minutes.

3. The method for preparing melamine cyanurate according to claim 1, characterized in that, In step b, the polyol auxiliaries are one or a mixture of at least two of the following: ethylene glycol, propylene glycol, diethylene glycol, butanediol, pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2-methyl-1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,3-dimethyl-1,4-butanediol, glycerol, glycerol, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 800, polyethylene glycol 1000, polypropylene glycol 200, polypropylene glycol 400, polypropylene glycol 600, dipropylene glycol, and tripropylene glycol.

4. The method for preparing melamine cyanurate according to claim 1, characterized in that, In step b, the molar ratio of urea to melamine is 3:0.85-0.

90.

5. The method for preparing melamine cyanurate according to claim 1, characterized in that, In step b, the flow rate of the nitrogen atmosphere is 50-70 ml / min.

6. The method for preparing melamine cyanurate according to claim 1, characterized in that, In step e, the mass of the water is 7-10 times the mass of the melamine mentioned in step b.

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