Method for preparing melamine cyanurate by using alkali metal salt as catalyst

Abstract

The invention belongs to a method for preparing melamine cyanurate by taking alkali metal salt as a catalyst. The method comprises the following steps: premixing raw materials; sequentially adding deionized water and melamine into the four-neck flask, and heating the system to 55 DEG C on the basis of sufficient stirring; step 2, adding cyanuric acid and an alkali metal salt catalyst into the system heated to 55 DEG C; step 3, heating the materials to 90 to 100 DEG C; continuously stirring for 1.5-3 hours to ensure that the reaction is uniform; step 4, cooling a product after the reaction to room temperature, separating out a solid-phase product through filtration, and washing with deionized water to remove unreacted raw materials and the catalyst, so as to obtain a washed product; step 5, drying and crushing the washed product to obtain melamine cyanurate with the purity not lower than 99%; the method has the characteristics that the reaction temperature and reaction time are reduced, side reactions are reduced, the yield is improved, and the product is high in purity and small and uniform in particle size.

Description

A method for preparing melamine cyanurate using alkali metal salts as catalysts Technical Field

[0001] This invention belongs to the field of fine chemical product preparation technology, specifically relating to a method for preparing melamine cyanurate using alkali metal salts as catalysts. Background Technology

[0002] Melamine cyanurate (MCA) is a highly efficient and environmentally friendly flame retardant widely used in polymer materials such as nylon, epoxy resin, and polypropylene. Its flame-retardant mechanism involves decomposition at high temperatures to produce inert gases (such as nitrogen and ammonia) and a char layer, isolating oxygen and diluting flammable gases to achieve a flame-retardant effect. Compared to traditional halogenated flame retardants, MCA has advantages such as low toxicity, non-corrosiveness, and low smoke emission, meeting modern environmental regulations.

[0003] Currently, the main industrial methods for preparing MCA are aqueous precipitation, solvent method, and solvent-free solid-phase method. However, all of these methods have significant drawbacks: 1. The reaction temperature is generally above 100℃, usually between 110 and 120℃, resulting in high energy consumption; 2. The reaction time is relatively long, generally requiring about 4 to 10 hours, and the combination with the aforementioned high reaction temperature leads to an increase in side reactions (such as the hydrolysis of MCA to produce cyanuric acid), further resulting in low yield; 3. The increased side reactions easily lead to unstable product purity, uneven particle size, and large particle size. Summary of the Invention

[0004] The present invention aims to solve the defects in the existing production of melamine cyanurate, such as high reaction temperature, long reaction time, easy occurrence of side reactions resulting in low yield, uneven particle size, large particle size and unstable purity, and provides a method for preparing melamine cyanurate using alkali metal salt as catalyst.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing melamine cyanurate using an alkali metal salt as a catalyst, the method comprising the following steps:

[0007] Step 1: Raw material premixing; Deionized water and melamine are added to a four-necked flask in sequence, and the system is heated to 55°C after thorough stirring;

[0008] Step 2: Add cyanuric acid and alkali metal salt catalyst to the system heated to 55°C in Step 1, and stir the materials evenly;

[0009] Step 3: Heat the material that was stirred evenly in Step 2 to 90-100℃; and continue stirring at 90-100℃ for 1.5-3 hours to ensure uniform reaction;

[0010] Step 4: Cool the product from Step 3 to room temperature, separate the solid product by filtration, and wash with deionized water to remove unreacted raw materials and catalyst, to obtain the washed product.

[0011] Step 5: Dry and pulverize the product washed in Step 4 to obtain melamine cyanurate with a purity of not less than 99%.

[0012] Preferably, the filtrate separated in step 4 is evaporated and concentrated to recover the alkali metal salt catalyst.

[0013] Preferably, the melamine cyanurate in step 5 has a particle size of 0.5–5 μm.

[0014] Preferably, in step 1, the weight percentage of deionized water is 6 parts and the weight percentage of melamine is 1 part.

[0015] Preferably, in step 2, the cyanuric acid is in the amount of 1 to 1.2 parts by weight, and the alkali metal salt catalyst is in the amount of 0.025 to 0.05 parts by weight.

[0016] Preferably, the alkali metal salt catalyst is selected from either potassium bicarbonate or sodium bicarbonate.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. This invention innovatively utilizes an alkali metal salt catalyst in the preparation of melamine cyanurate. Through a triple mechanism of ion catalysis, interface regulation, and crystallization inhibition, it accelerates the salt formation reaction between melamine (MA) and cyanuric acid (CA) and induces the formation of small-particle-size melamine cyanurate (MCA). The reaction principle is as follows: Taking potassium bicarbonate as an example, potassium bicarbonate (KHCO3) dissociates in aqueous solution to release K... + and HCO3 - HCO3 - As a proton transfer medium, it lowers the proton transfer energy barrier between MA and CA molecules; the addition of KHCO3 reduces the surface tension of the reaction system, significantly improving the dispersibility of MA and CA in water (particle size distribution variation coefficient decreases from 0.35 to 0.18); simultaneously, the highly dispersed system increases the collision frequency of MA and CA, increasing the effective number of collisions per unit time by 2-3 times, thereby shortening the reaction time by more than 50%; furthermore, under the action of the alkali metal salt catalyst, MA... + -CA - The ion concentration rapidly reaches supersaturation, resulting in the formation of numerous primary crystal nuclei within a short period. Competitive growth among these nuclei limits the size of individual crystal grains. Additionally, through K... +Adsorbed onto active crystal growth sites, HCO3 inhibits anisotropic growth, thereby obtaining a particle morphology closer to spherical. - Reversible adsorption on the crystal nucleus surface inhibits secondary nucleation and crystal agglomeration, resulting in a concentrated MCA particle size distribution of 0.5-2 μm. This working principle enables the reduction of reaction temperature and time during the preparation of melamine cyanurate, minimizing side reactions, increasing yield, and achieving high product purity, small particle size, and uniform particle size.

[0019] 2. This invention uses water as a solvent, which not only achieves zero VOC emissions, but also enables the recovery of alkali metal salt catalysts through evaporation and concentration, thereby achieving the characteristics of energy saving, environmental protection and reduced production costs.

[0020] 3. The product of this invention has the characteristics of small and uniform particle size, which can meet the requirements of high-end polymer flame retardants for small particle size and high dispersion performance; for example, it can be used as a flame retardant for plastic parts. Attached Figure Description

[0021] Figure 1 shows the standard concentration curve of cyanuric acid in the filtrate of the experimental example.

[0022] Figure 2 shows the standard concentration curve of melamine in the filtrate of the test example. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] A method for preparing melamine cyanurate using an alkali metal salt as a catalyst, characterized in that the method comprises the following steps:

[0025] Step 1: Raw material premixing; Deionized water and melamine are added to a four-necked flask in sequence, and the system is heated to 55°C after thorough stirring;

[0026] Step 2: Add cyanuric acid and alkali metal salt catalyst to the system heated to 55°C in Step 1, and stir the materials evenly;

[0027] Step 3: Heat the material that was stirred evenly in Step 2 to 90-100℃; and continue stirring at 90-100℃ for 1.5-3 hours to ensure uniform reaction;

[0028] Step 4: Cool the product from Step 3 to room temperature, separate the solid product by filtration, and wash with deionized water to remove unreacted raw materials and catalyst, to obtain the washed product.

[0029] Step 5: Dry and pulverize the product washed in Step 4 to obtain melamine cyanurate with a purity of not less than 99%.

[0030] The filtrate separated in step 4 is evaporated and concentrated to recover the alkali metal salt catalyst. The melamine cyanurate in step 5 has a particle size of 0.5–5 μm. In step 1, the deionized water comprises 6 parts by weight, and the melamine comprises 1 part by weight. In step 2, the cyanuric acid comprises 1–1.2 parts by weight, and the alkali metal salt catalyst comprises 0.025–0.05 parts by weight. The alkali metal salt catalyst is selected from either potassium bicarbonate or sodium bicarbonate.

[0031] Unless otherwise specified, the experimental methods described in the examples and comparative examples are all conventional methods; the reagents, instruments and materials whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0032] Example 1

[0033] A method for preparing melamine cyanurate using an alkali metal salt as a catalyst, the method comprising the following steps:

[0034] Step 1: Raw material premixing; Deionized water and melamine are added to a four-necked flask in sequence, and the system is heated to 55°C after thorough stirring;

[0035] Step 2: Add cyanuric acid and alkali metal salt catalyst to the system heated to 55°C in Step 1, and stir the materials evenly;

[0036] Step 3: Heat the well-stirred material from Step 2 to 90°C; and continue stirring at 90°C for 3 hours to ensure a uniform reaction.

[0037] Step 4: Cool the product from Step 3 to room temperature, separate the solid product by filtration, and wash with deionized water to remove unreacted raw materials and catalyst, to obtain the washed product.

[0038] Step 5: Dry and pulverize the product washed in Step 4 to obtain melamine cyanurate with a purity of not less than 99%.

[0039] The filtrate separated in step 4 is evaporated and concentrated to recover the alkali metal salt catalyst. The melamine cyanurate in step 5 has a particle size of 0.5–5 μm. In step 1, the deionized water comprises 6 parts by weight, and the melamine comprises 1 part by weight. In step 2, the cyanuric acid comprises 1 part by weight, and the alkali metal salt catalyst comprises 0.025 parts by weight. The alkali metal salt catalyst is potassium bicarbonate.

[0040] Example 2

[0041] A method for preparing melamine cyanurate using an alkali metal salt as a catalyst, the method comprising the following steps:

[0042] Step 1: Raw material premixing; Deionized water and melamine are added to a four-necked flask in sequence, and the system is heated to 55°C after thorough stirring;

[0043] Step 2: Add cyanuric acid and alkali metal salt catalyst to the system heated to 55°C in Step 1, and stir the materials evenly;

[0044] Step 3: Heat the well-stirred material from Step 2 to 100°C; and continue stirring at 100°C for 3 hours to ensure a uniform reaction.

[0045] Step 4: Cool the product from Step 3 to room temperature, separate the solid product by filtration, and wash with deionized water to remove unreacted raw materials and catalyst, to obtain the washed product.

[0046] Step 5: Dry and pulverize the product washed in Step 4 to obtain melamine cyanurate with a purity of not less than 99%.

[0047] The filtrate separated in step 4 is evaporated and concentrated to recover the alkali metal salt catalyst. The melamine cyanurate in step 5 has a particle size of 0.5–5 μm. In step 1, the deionized water comprises 6 parts by weight, and the melamine comprises 1 part by weight. In step 2, the cyanuric acid comprises 1.2 parts by weight, and the alkali metal salt catalyst comprises 0.05 parts by weight. The alkali metal salt catalyst is sodium bicarbonate.

[0048] Example 3

[0049] A method for preparing melamine cyanurate using an alkali metal salt as a catalyst, the method comprising the following steps:

[0050] Step 1: Raw material premixing; Deionized water and melamine are added to a four-necked flask in sequence, and the system is heated to 55°C after thorough stirring;

[0051] Step 2: Add cyanuric acid and alkali metal salt catalyst to the system heated to 55°C in Step 1, and stir the materials evenly;

[0052] Step 3: Heat the well-stirred material from Step 2 to 95°C; and continue stirring at 95°C for 2 hours to ensure a uniform reaction.

[0053] Step 4: Cool the product from Step 3 to room temperature, separate the solid product by filtration, and wash with deionized water to remove unreacted raw materials and catalyst, to obtain the washed product.

[0054] Step 5: Dry and pulverize the product washed in Step 4 to obtain melamine cyanurate with a purity of not less than 99%.

[0055] The filtrate separated in step 4 is evaporated and concentrated to recover the alkali metal salt catalyst. The melamine cyanurate in step 5 has a particle size of 0.5–5 μm. In step 1, the deionized water comprises 6 parts by weight, and the melamine comprises 1 part by weight. In step 2, the cyanuric acid comprises 1.1 parts by weight, and the alkali metal salt catalyst comprises 0.04 parts by weight. The alkali metal salt catalyst is potassium bicarbonate.

[0056] Experimental example:

[0057] This invention is compared with the catalyst-free aqueous phase method:

[0058] The technical solution of this invention is as follows: a method for preparing melamine cyanurate using an alkali metal salt as a catalyst, the method comprising the following steps: Step 1: raw material premixing; deionized water and melamine are added sequentially to a four-necked flask, and the system is heated to 55°C while stirring thoroughly; Step 2: melamine acid and an alkali metal salt catalyst are added to the system heated to 55°C in Step 1, and the materials are stirred evenly; Step 3: the evenly stirred materials in Step 2 are heated to 95°C; and stirred continuously at 95°C for 2 hours to ensure uniform reaction; Step 4: the product after the reaction in Step 3 is cooled to room temperature, the solid product is separated by filtration, and washed with deionized water to remove unreacted raw materials and catalyst, obtaining the washed product; Step 5: the washed product in Step 4 is dried and pulverized to obtain melamine cyanurate with a purity of not less than 99%. The weight of the deionized water in Step 1 is 126 g, and the weight of the melamine is 12.60 g. The weight of cyanuric acid in step 2 is 14.20 g, and the weight of alkali metal salt catalyst is 1.34 g. The alkali metal salt catalyst is potassium bicarbonate. As can be seen from the above, the reaction time of this technical solution is 2 hours, the calculated product yield (sum of product mass and raw material mass) is 97.8%, the product purity is 99.3% determined by liquid chromatography, and the thermal decomposition temperature of the obtained MCA powder is 402℃ as determined by thermogravimetric analysis. The particle size of melamine cyanurate in step 5 is 0.5–5 μm. As determined by laser particle size analyzer, the average particle size of the obtained MCA powder is 3.2 μm, D[0.1]–D[0.9] is distributed between 1.1–4.8 μm, and particles smaller than 2 μm account for 72%; and the particle size distribution is uniform (coefficient of variation ≤0.2); meeting the requirements of high-end polymer flame retardants for small particle size and high dispersibility. The filtrate separated in step 4 was evaporated and concentrated to recover the alkali metal salt catalyst. After the reaction was completed, the separated liquid phase was a white viscous slurry. The reaction system was cooled to 75°C, and the solid product was separated by hot filtration. The product was washed several times with hot water to remove unreacted raw materials and catalyst residues until the pH of the filtrate was neutral. The filtrate was evaporated and concentrated to recover 1.15 g of KHCO3.

[0059] The catalyst-free aqueous phase method is as follows: a method for preparing melamine cyanurate using an alkali metal salt as a catalyst, comprising the following steps: Step 1: Raw material premixing; deionized water and melamine are added sequentially to a four-necked flask, and the system is heated to 55°C while stirring thoroughly; Step 2: Melamine acid is added to the system heated to 55°C in Step 1, and the material is stirred evenly; Step 3: The material stirred evenly in Step 2 is heated to 95°C; and stirred continuously at 95°C for 6 hours to ensure uniform reaction; Step 4: The product after the reaction in Step 3 is cooled to room temperature, the solid phase product is separated by filtration, and washed with deionized water to remove unreacted raw materials, obtaining the washed product; Step 5: The washed product in Step 4 is dried and pulverized to obtain melamine cyanurate. The product yield (product mass / raw material mass sum) is calculated to be 88.71%, and the product purity is determined to be 96.72% by liquid chromatography. The thermal decomposition temperature of the obtained MCA powder is determined to be 392°C by thermogravimetric analysis. The melamine cyanurate in step 5 has a particle size of 5.5–7 μm. The average particle size of the obtained MCA powder, as determined by a laser particle size analyzer, is 6.3 μm, with D[0.1]–D[0.9] distributed between 2.5–10.0 μm, and particles smaller than 2 μm accounting for 25%; the particle size distribution is also relatively wide (coefficient of variation between 0.3 and 0.4).

[0060] To ensure the accuracy of the experimental results, the present invention and the catalyst-free aqueous phase method (control group) were respectively tested twice according to the aforementioned technical solution. The standard concentration curves of cyanuric acid and melamine in the filtrates from the two experiments are now provided, along with the following data:

[0061]

[0062] Table 1 shows the concentration of cyanuric acid in the filtrate of the test examples.

[0063]

[0064] Table 2 shows the concentration of melamine in the filtrate of the test examples.

[0065] The comparison shows that the yield of this invention is much higher than that of the control group. Furthermore, combined with the foregoing, this invention achieves a significant breakthrough through an alkali metal salt catalytic system: the reaction time is shortened from 6 hours to 2 hours, the yield increases by 88.71% to 97.8%, and the catalyst recovery rate is 85.8%; the product thermal decomposition temperature increases by 10℃ to 402℃, and the purity reaches 99.3%; the average particle size decreases from 6.3μm to 3.2μm, the proportion of particles smaller than 2μm jumps to 72%, and the coefficient of variation is ≤0.2. This meets the stringent requirements of high-end polymers for flame retardant additives in terms of efficient dispersion and performance stability. The overall performance and production efficiency are significantly superior to the catalyst-free aqueous phase method, providing a highly competitive technical path for the large-scale application of melamine cyanurate in the high-end flame retardant field.

[0066] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing melamine cyanurate using an alkali metal salt as a catalyst, characterized in that, The method includes the following steps: Step 1: Raw material premixing; deionized water and melamine are added sequentially to a four-necked flask, and the system is heated to 55°C while stirring thoroughly; Step 2: Melamine acid and alkali metal salt catalyst are added to the system heated to 55°C in Step 1, and the materials are stirred evenly; Step 3: The evenly stirred materials in Step 2 are heated to 90-100°C; and stirred continuously at 90-100°C for 1.5-3 hours to ensure uniform reaction; Step 4: The product after the reaction in Step 3 is cooled to room temperature, the solid product is separated by filtration, and washed with deionized water to remove unreacted raw materials and catalyst, obtaining the washed product; Step 5: The washed product in Step 4 is dried and pulverized to obtain melamine cyanurate with a purity of not less than 99%.

2. The method for preparing melamine cyanurate using an alkali metal salt as a catalyst according to claim 1, characterized in that: The filtrate separated in step 4 is evaporated and concentrated to recover the alkali metal salt catalyst.

3. The method for preparing melamine cyanurate using an alkali metal salt as a catalyst according to claim 1, characterized in that: The melamine cyanurate in step 5 has a particle size of 0.5–5 μm.

4. The method for preparing melamine cyanurate using an alkali metal salt as a catalyst according to claim 1, characterized in that: In step 1, the weight percentage of deionized water is 6 parts and the weight percentage of melamine is 1 part.

5. The method for preparing melamine cyanurate using an alkali metal salt as a catalyst according to claim 4, characterized in that: In step 2, the cyanuric acid is in the amount of 1 to 1.2 parts by weight, and the alkali metal salt catalyst is in the amount of 0.025 to 0.05 parts by weight.

6. A method for preparing melamine cyanurate using an alkali metal salt as a catalyst according to claim 1, 2, or 5, characterized in that: The alkali metal salt catalyst is selected from either potassium bicarbonate or sodium bicarbonate.

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