A method for preparing piperazine pyrophosphate by using wet-process phosphoric acid
By reacting wet-process phosphoric acid with melamine to produce melamine phosphate salt, and combining centrifugal separation and high-temperature dehydration, the problems of high production cost and low purity of piperazine pyrophosphate are solved, and high-purity piperazine pyrophosphate is prepared, which is suitable for flame retardant materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YUNNAN YUNTIANHUA
- Filing Date
- 2024-04-10
- Publication Date
- 2026-07-24
AI Technical Summary
Existing technologies for preparing piperazine pyrophosphate suffer from limited raw material sources, high production costs, and low product purity. In particular, wet-process phosphoric acid contains high levels of impurities, which hinders its application in flame-retardant materials.
Unconcentrated wet-process phosphoric acid was reacted with melamine to produce melamine phosphate as an intermediate. The impurity content was reduced by centrifugation and crystallization. Then, it was reacted with piperazine and finally dehydrated at high temperature under a nitrogen atmosphere to prepare piperazine pyrophosphate.
It effectively reduces production costs by 15%-20%, improves the purity and performance of piperazine pyrophosphate, is suitable for flame retardant materials, and reduces the impact of impurity ions.
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Figure CN118324714B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of flame retardants, and more specifically, to a method for preparing piperazine pyrophosphate using wet phosphoric acid. Background Technology
[0002] Wet-process phosphoric acid is produced from apatite-type phosphate rock using strong inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid to decompose the phosphate rock. Compared to the thermal process, wet-process phosphoric acid does not require oxidation and hydration steps, making the process simpler and the equipment cost lower. However, impurities from the phosphate rock can also enter the phosphoric acid, resulting in high impurity content and low acid concentration in wet-process phosphoric acid. It is commonly used for the production of compound phosphate fertilizers, and purification methods such as extraction are required to produce industrial-grade products.
[0003] Piperazine pyrophosphate is a phosphorus-nitrogen-based halogen-free flame retardant. Due to its high flame retardant efficiency, lack of hydroplaning, and high thermal decomposition temperature, it has become a popular research topic both domestically and internationally. There are also many reports on the preparation of piperazine pyrophosphate, which can be roughly divided into two categories: (1) Sodium pyrophosphate acidification method: Patents such as US3810850 and US4599375 disclose the use of sodium pyrophosphate and piperazine in hydrochloric acid solution to generate a water-insoluble precipitate of piperazine pyrophosphate. The piperazine pyrophosphate prepared by this method does not require high-temperature polymerization, so it has a high whiteness. However, the sodium particles and chloride ions brought in by the reaction raw materials cannot be completely removed by washing and other means, which affects the application of piperazine pyrophosphate in materials such as polypropylene. (2) High-temperature dehydration method of piperazine diphosphate: Patent CN102482239A discloses the acid-base neutralization reaction of anhydrous piperazine (or 68% piperazine) and 85% phosphoric acid in a molar ratio of 1:2 to prepare piperazine diphosphate in aqueous solution, and then dehydrated to prepare piperazine pyrophosphate. The piperazine pyrophosphate prepared by this method avoids the influence of impurities on the product, but one of the raw materials, phosphoric acid or concentrated phosphoric acid, is usually obtained by thermal method or by extraction wet method, which is costly.
[0004] Therefore, it is essential to develop a new preparation method with a wider range of raw material sources, lower production costs, and higher product purity. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing piperazine pyrophosphate using wet-process phosphoric acid. Using wet-process phosphoric acid as raw material can effectively reduce production costs and produce a product with better purity.
[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising the following steps:
[0007] S1. Unconcentrated wet-process phosphoric acid is reacted with melamine to obtain a first slurry containing melamine phosphate salt;
[0008] S2. After separating and removing impurities from the first slurry, re-slurry it and react it with piperazine to obtain a second slurry containing piperazine diphosphate;
[0009] S3. After separating the second slurry, the filtrate is crystallized and then dehydrated under a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0010] Furthermore, in other preferred embodiments of the present invention, the concentration of wet-process phosphoric acid is 18wt% to 25wt%.
[0011] Furthermore, in other preferred embodiments of the present invention, the mass ratio of melamine to wet-process phosphoric acid is 1:2 to 6. The mass ratio of melamine, wet-process phosphoric acid, and anhydrous piperazine is 1:2 to 6:0.1 to 0.5, or the mass ratio of melamine, wet-process phosphoric acid, and hexaoctapiperazine is 1:2 to 6:0.2 to 0.8.
[0012] Furthermore, in other preferred embodiments of the present invention, the reaction temperature of melamine and wet-process phosphoric acid is 30–70°C, and the reaction time is 0.5–2 hours.
[0013] Furthermore, in other preferred embodiments of the present invention, wet-process phosphoric acid is first subjected to pressure filtration to remove solid impurities, with a solid content of less than 0.05%, and then reacted with melamine.
[0014] Furthermore, in other preferred embodiments of the present invention, the first slurry is centrifuged to separate the solid phase components, and washed multiple times to obtain high-purity melamine phosphate salt. After adding water and slurrying again, melamine phosphate slurry is obtained, and then reacted with piperazine.
[0015] Furthermore, in other preferred embodiments of the present invention, the reaction temperature of the melamine phosphate slurry with piperazine is 80-100°C, and the reaction time is 1-2 hours.
[0016] Furthermore, in other preferred embodiments of the present invention, the second slurry is centrifuged to separate the liquid phase component, which is then concentrated and cooled to crystallize, yielding piperazine diphosphate crystals. These crystals are then separated and subjected to a dehydration reaction. After concentration at 120°C until crystals appear, crystallization is carried out at 20°C.
[0017] Furthermore, in other preferred embodiments of the present invention, piperazine diphosphate is dehydrated by heating to 250–350°C in a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0018] Reaction mechanism:
[0019]
[0020] Compared with the prior art, the beneficial effects of the present invention are:
[0021] This invention uses unconcentrated wet-process phosphoric acid as a raw material to synthesize piperazine pyrophosphate. The raw material is inexpensive and stable, and the process is easier than traditional phosphoric acid methods. The high-temperature dehydration method for piperazine diphosphate reduces costs by 15%–20%. In the reaction process, wet-process phosphoric acid is first reacted with melamine to obtain a melamine phosphate slurry. The resulting melamine phosphate salt is used as an intermediate, effectively reducing impurity ions present in the wet-process phosphoric acid and improving product purity. After reacting with piperazine, the filtrate is crystallized and dehydrated at high temperature to obtain piperazine pyrophosphate without affecting its performance as a flame retardant material. Attached Figure Description
[0022] Figure 1 This is a flowchart of the present invention. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0024] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0025] Example 1
[0026] This embodiment provides a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising:
[0027] S1. Unconcentrated wet-process phosphoric acid (concentration 20wt%) is filtered through a plate and frame filter press to remove solid impurities such as phosphogypsum from the acid, with a solid content of less than 0.05%.
[0028] S2. Add 100 kg of filtered wet-process phosphoric acid to the reactor, maintain the temperature at 50°C, add 20 kg of melamine evenly, and stir for 0.5 h to obtain the first slurry containing melamine phosphate salt.
[0029] S3. The first slurry is centrifuged to remove unreacted phosphoric acid and most of the impurities dissolved in the liquid phase. The solid phase component is collected and washed multiple times to obtain high-purity melamine phosphate salt.
[0030] S4. Place the melamine phosphate salt obtained in step S3 into a reactor, add 200 kg of water for re-slurrying, heat to 80°C, add 5.5 kg of anhydrous piperazine, and continue stirring for 2 hours to obtain a second slurry containing piperazine diphosphate.
[0031] S5. Centrifuge the second slurry to remove the solid phase melamine and collect the liquid phase component, namely piperazine diphosphate solution.
[0032] S6. Concentrate the piperazine diphosphate solution at 120°C until crystals precipitate to obtain a supersaturated piperazine diphosphate solution; transfer the supersaturated piperazine diphosphate solution into a crystallization tank, cool and crystallize at 20°C, and obtain piperazine diphosphate after centrifugation and drying.
[0033] S7. Add the piperazine diphosphate obtained in step S6 to the reactor, and dehydrate and condense it at 250°C for 4 hours in a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0034] Example 2
[0035] This embodiment provides a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising:
[0036] S1. Unconcentrated wet-process phosphoric acid (concentration 20wt%) is filtered through a plate and frame filter press to remove solid impurities such as phosphogypsum from the acid, with a solid content of less than 0.05%.
[0037] S2. Add 100 kg of filtered wet-process phosphoric acid to the reactor, maintain the temperature at 50°C, add 20 kg of melamine evenly, and stir for 2 hours to obtain the first slurry containing melamine phosphate salt.
[0038] S3. The first slurry is centrifuged to remove unreacted phosphoric acid and most of the impurities dissolved in the liquid phase. The solid phase component is collected and washed multiple times to obtain high-purity melamine phosphate salt.
[0039] S4. Place the melamine phosphate salt obtained in step S3 into a reactor, add 200 kg of water for re-slurrying, heat to 80°C, add 4 kg of anhydrous piperazine, and continue stirring for 2 hours to obtain a second slurry containing piperazine diphosphate.
[0040] S5. Centrifuge the second slurry to remove the solid phase melamine and collect the liquid phase component, namely piperazine diphosphate solution.
[0041] S6. After concentrating the piperazine diphosphate solution at 120°C until crystals precipitate, a supersaturated piperazine diphosphate solution is obtained; the supersaturated piperazine diphosphate solution is transferred to a crystallization tank, cooled and crystallized at 20°C, and then centrifuged and dried to obtain piperazine diphosphate.
[0042] S7. Add the piperazine diphosphate obtained in step S6 to the reactor, and dehydrate and condense it at 250°C for 4 hours in a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0043] Example 3
[0044] This embodiment provides a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising:
[0045] S1. Unconcentrated wet-process phosphoric acid (concentration 25wt%) is filtered through a plate and frame filter press to remove solid impurities such as phosphogypsum from the acid, with a solid content of less than 0.05%.
[0046] S2. Add 100 kg of filtered wet-process phosphoric acid to the reactor, maintain the temperature at 70°C, add 50 kg of melamine evenly, and stir for 2 hours to obtain the first slurry containing melamine phosphate salt.
[0047] S3. The first slurry is centrifuged to remove unreacted phosphoric acid and most of the impurities dissolved in the liquid phase. The solid phase component is collected and washed multiple times to obtain high-purity melamine phosphate salt.
[0048] S4. Place the melamine phosphate salt obtained in step S3 into a reactor, add 450 kg of water for re-slurrying, heat to 80°C, add 15 kg of anhydrous piperazine, and continue stirring for 1.5 h to obtain a second slurry containing piperazine diphosphate.
[0049] S5. Centrifuge the second slurry to remove the solid phase melamine and collect the liquid phase component, namely piperazine diphosphate solution.
[0050] S6. After concentrating the piperazine diphosphate solution at 120°C until crystals precipitate, a supersaturated piperazine diphosphate solution is obtained; the supersaturated piperazine diphosphate solution is transferred to a crystallization tank, cooled and crystallized at 20°C, and then centrifuged and dried to obtain piperazine diphosphate.
[0051] S7. Add the piperazine diphosphate obtained in step S6 to the reactor, and dehydrate and condense it at 300°C for 2.5 h in a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0052] Example 4
[0053] This embodiment provides a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising:
[0054] The filtrate from the supersaturated piperazine diphosphate solution in step S6 of Example 1 was mixed with water and then re-slurried for reuse, with all other conditions remaining unchanged.
[0055] Example 5
[0056] This embodiment provides a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising:
[0057] S1. Unconcentrated wet-process phosphoric acid (concentration 25wt%) is filtered through a plate and frame filter press to remove solid impurities such as phosphogypsum from the acid, with a solid content of less than 0.05%.
[0058] S2. Add 100 kg of filtered wet-process phosphoric acid to the reactor, maintain the temperature at 70°C, add 25 kg of melamine evenly, and stir for 2 hours to obtain the first slurry containing melamine phosphate salt.
[0059] S3. The first slurry is centrifuged to remove unreacted phosphoric acid and most of the impurities dissolved in the liquid phase. The solid phase component is collected and washed multiple times to obtain high-purity melamine phosphate salt.
[0060] S4. Place the melamine phosphate salt obtained in step S3 into a reactor, add 200 kg of water to slurry, heat to 80°C, add 20 kg of piperazine, and continue stirring for 1.5 h to obtain a second slurry containing piperazine diphosphate.
[0061] S5. Centrifuge the second slurry to remove the solid phase melamine and collect the liquid phase component, namely piperazine diphosphate solution.
[0062] S6. After concentrating the piperazine diphosphate solution at 120°C until crystals precipitate, a supersaturated piperazine diphosphate solution is obtained; the supersaturated piperazine diphosphate solution is transferred to a crystallization tank, cooled and crystallized at 20°C, and then centrifuged and dried to obtain piperazine diphosphate.
[0063] S7. Add the piperazine diphosphate obtained in step S6 to the reactor and dehydrate it at 300°C under a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0064] Comparative Example 1
[0065] This comparative example provides a method for preparing piperazine pyrophosphate using wet phosphoric acid, comprising:
[0066] S1. Unconcentrated wet-process phosphoric acid (concentration 20wt%) is filtered through a plate and frame filter press to remove solid impurities such as phosphogypsum from the acid, with a solid content of less than 0.05%.
[0067] S2. Add 100 kg of filtered wet phosphoric acid to the reactor, heat to 80°C, add 15 kg of anhydrous piperazine, and continue stirring for 2 hours to obtain a second slurry containing piperazine diphosphate.
[0068] S3. Centrifuge the second slurry to collect the liquid phase component, namely piperazine diphosphate solution.
[0069] S4. After concentrating the piperazine diphosphate solution at 120°C until crystals precipitate, a supersaturated piperazine diphosphate solution is obtained. The supersaturated piperazine diphosphate solution is transferred to a crystallization tank and cooled and crystallized at 20°C. After centrifugation and drying, piperazine diphosphate is obtained.
[0070] S5. Add the piperazine diphosphate obtained in step S6 to the reactor and dehydrate it at 250°C under a nitrogen atmosphere to obtain piperazine pyrophosphate.
[0071] Test case
[0072] This experimental example uses the methods for preparing piperazine pyrophosphate provided in Examples 1-4 and Comparative Example 1 to prepare piperazine pyrophosphate. The obtained piperazine pyrophosphate is compared with commercially available piperazine pyrophosphate (control example). The comparison results are shown in Table 1:
[0073] Table 1. Performance Tests of Piperazine Pyrophosphate
[0074]
[0075]
[0076] As shown in Table 1, the piperazine pyrophosphate prepared using the methods of Examples 1-5 of this invention exhibits similar properties to commercially available products in terms of content, solubility, pH, thermal decomposition temperature, and whiteness, with some indicators even slightly superior. This invention significantly improves the purity of the piperazine pyrophosphate product by using melamine to purify wet-process phosphoric acid, with the highest purity reaching 99%.
[0077] In addition, in Comparative Example 1, we also tried reacting wet-process phosphoric acid directly with anhydrous piperazine without using melamine. It can be seen that the product content and yield were significantly reduced, and the final product contained significantly less Ca, Mg, Al, Fe, and SO4. 2- The impurity content was significantly higher than in the examples, severely impacting product quality. The control example product was a commercially available product.
[0078] In summary, this invention uses unconcentrated wet-process phosphoric acid as a raw material to synthesize piperazine pyrophosphate. The raw material is inexpensive and stable, and the process is easier than traditional phosphoric acid methods. The high-temperature dehydration method for piperazine diphosphate reduces costs by 15%–20% (this cost reduction is the price difference between the wet-process phosphoric acid price required to produce the same amount of piperazine pyrophosphate plus purification costs and the price reduction of thermal phosphoric acid). During the reaction, wet-process phosphoric acid is first reacted with melamine to generate melamine phosphate as an intermediate, effectively reducing impurity ions present in the wet-process phosphoric acid and improving product purity. After reacting with piperazine, the filtrate is crystallized and dehydrated at high temperature to obtain piperazine pyrophosphate without affecting its performance as a flame retardant material.
[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing piperazine pyrophosphate using wet-process phosphoric acid, characterized in that, Includes the following steps: S1. Unconcentrated wet-process phosphoric acid is reacted with melamine to obtain a first slurry containing melamine phosphate salt; the concentration of the wet-process phosphoric acid is 18wt% to 25wt%. S2. After separating and removing impurities from the first slurry, re-slurry it and react it with piperazine to obtain a second slurry containing piperazine diphosphate; S3. After separating the second slurry, the filtrate is crystallized and then dehydrated under a nitrogen atmosphere to obtain the piperazine pyrophosphate.
2. The method according to claim 1, characterized in that, The piperazine is anhydrous piperazine or hexaoctapiperazine; the mass ratio of melamine, wet-process phosphoric acid and anhydrous piperazine is 1:2 to 6:0.1 to 0.5; the mass ratio of melamine, wet-process phosphoric acid and hexaoctapiperazine is 1:2 to 6:0.2 to 0.
8.
3. The method according to claim 2, characterized in that, The reaction temperature of the melamine and the wet-process phosphoric acid is 30–70°C, and the reaction time is 0.5–2 h.
4. The method according to claim 1, characterized in that, The wet-process phosphoric acid is first filtered to remove solid impurities before reacting with the melamine.
5. The method according to claim 1, characterized in that, The first slurry was centrifuged to separate the solid phase components, and the solid phase components were collected. After washing multiple times, high-purity melamine phosphate salt was obtained. After adding water and slurrying again, melamine phosphate slurry was obtained, and then it was reacted with piperazine.
6. The method according to claim 5, characterized in that, The reaction temperature of the melamine phosphate slurry with the piperazine is 80-100°C, and the reaction time is 1-2 hours.
7. The method according to claim 1, characterized in that, The second slurry is centrifuged to separate the liquid phase components, which are then concentrated and cooled to crystallize, yielding the piperazine diphosphate crystals. These crystals are then separated and subjected to a dehydration reaction.
8. The method according to claim 1, characterized in that, The piperazine diphosphate was dehydrated by heating it to 250–350°C in a nitrogen atmosphere to obtain the piperazine pyrophosphate.