A broad distribution water-soluble ammonium polyphosphate and a method for preparing the same

Abstract

The application discloses a kind of wide distribution water-soluble ammonium polyphosphate and preparation method thereof, belong to compound fertilizer technical field.In the production of APP using water-soluble monoammonium phosphate and urea thermal condensation reaction, water-soluble organic matter is introduced, the chain growth window period before APP solidification is extended, and high water-soluble APP powder product with wide distribution of polymerization degree is obtained, so that the fertilizer grade APP product sequence is improved.Monamium phosphate pre-melting combined with APP cold return material process, the operation time is shortened, the production capacity is greatly improved, and the problem of wide distribution water-soluble product cannot be solidified is solved.The organic matter combined with phosphorus in situ in APP product has the potential of chelating trace elements in soil in addition to improving solubility.The method of rapidly producing wide distribution water-soluble APP powder in the application is simple in process, and is convenient for efficient scale production.

Description

Technical Field

[0001] This invention belongs to the field of compound fertilizer technology, specifically relating to a broadly distributed water-soluble ammonium polyphosphate and its preparation method. Background Technology

[0002] Phosphates undergo intermolecular dehydration upon heating, which can polymerize to form polyphosphates with an alternating POP structure. The general structural formula for ammonium polyphosphate (APP) can be written as (NH4). n+2 P n O 3n+1 Phosphorus compounds (APP) used in fertilizers are typically mixtures of oligomers with varying chain lengths. APP with an average degree of polymerization (n) less than 20 is classified as a water-soluble N / P compound fertilizer, capable of desorbing and chelating micronutrients at the interface between soil solution and soil aggregates, promoting the diffusion of phosphorus (P) with micronutrients. APP's resistance to soil fixation, its slow-release properties through gradual hydrolysis, and its solubilizing effect on micronutrients in liquid fertilizer formulations mean that plants typically utilize phosphorus more efficiently than when applying the same amount of orthophosphate. The supply shortage of fertilizer-grade APP has kept the market price of water-soluble APP above 8,000 yuan per ton for a long time (as of 2025). Even using expensive industrial monoammonium phosphate (MAP) as a raw material, the cost of water-soluble APP (including depreciation) is only around 5,000 yuan per ton. Therefore, water-soluble APP has a widely recognized broad market potential and profit margin in the industry.

[0003] Solid water-soluble phosphate (APP) is currently the mainstream fertilizer-grade APP product due to its low transportation cost. In China, the wet process for purifying and removing impurities from phosphoric acid is commonly used to prepare industrial monoammonium phosphate (MAP), which is then used as raw material to produce APP. In addition, there is a method for preparing APP using phosphoric acid-urea condensation (CN105621381A), but the polymerization system requires a significant amount of time to evaporate moisture, with polymerization times exceeding 2 hours, resulting in low production intensity. A method for producing solid APP using phosphoric acid ammoniation-return granulation has also emerged in China (CN108002357A), similar to the US TVA process, which requires high concentration and purity of the raw material phosphoric acid, leading to high costs. Patent CN107176597A discloses a method for producing powdered water-soluble APP using a belt conveyor polymerizer, similar to another patent's method for continuous production of water-soluble solid APP using a twin-screw extruder (CN118771924B). The continuous production of solid APP using high-viscosity solid raw materials is their characteristic and advantage, but a large amount of ammonia is lost during the conveying and polymerization process, requiring excess urea to ensure solidification. Currently, two grades of APP (apple) have been developed in China: 18-58-0 and 14-65-0. However, these highly water-soluble APP solid products cannot achieve a broad molecular weight distribution (also known as a degree of polymerization distribution) to solubilize more micronutrients and meet the needs of crops at different growth stages for APP hydrolysis into orthophosphate. Therefore, it is necessary to invent a method for rapidly producing broadly distributed water-soluble APP powder to solve the above-mentioned technical problems. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a broadly distributed water-soluble ammonium polyphosphate and its preparation method, so as to solve the technical problem of the narrow molecular weight distribution of existing ammonium polyphosphate.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for preparing a broadly distributed water-soluble ammonium polyphosphate, comprising the following steps:

[0006] S1: Heat water-soluble monoammonium phosphate to melt, then add sodium lignosulfonate and urea to the molten water-soluble monoammonium phosphate. The amount of sodium lignosulfonate added is 10% of the mass of water-soluble monoammonium phosphate. Then, stir and polymerize at 185 °C. After 15 min, add urea again and continue stirring and polymerizing for 25 min to obtain the base material. The total amount of urea added is based on the N / P molar ratio in the system being 1.86:1, and the mass ratio of the two urea additions is 3:4.

[0007] S2: Air cool the base material to room temperature to obtain the additive;

[0008] S3: Add the additive to the base material, the amount of additive is 50% of the mass of the base material, mix well, then air cool to room temperature, then crush and screen to obtain the final product.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, the heating and melting temperature of the water-soluble monoammonium phosphate in S1 is 190 °C.

[0011] Furthermore, the stirring rate for the stirring polymerization in S1 is 30~40 rpm.

[0012] Furthermore, the amount of additive added in S3 is 50% of the mass of the base material.

[0013] The present invention also discloses a broadly distributed water-soluble ammonium polyphosphate, which is prepared by the above-described preparation method.

[0014] The beneficial effects of this invention are:

[0015] 1. This invention pre-melts the water-soluble monoammonium phosphate raw material, saving the melting time of the raw material.

[0016] 2. In the preparation of ammonium polyphosphate, sodium lignosulfonate is added to the reaction system. The aromatic ring organic molecular chain of sodium lignosulfonate slows down the diffusion of ammonium in the system through steric hindrance, forming local reaction micro-regions, thereby slowing down the ammonification and solidification process, so that the final ammonium polyphosphate powder has a wider molecular weight distribution and sufficient polymerization.

[0017] 3. In this invention, urea is added to the reaction system in two stages during the preparation of ammonium polyphosphate. The first addition of urea (3 / 7 of the total mass) rapidly initiates a polycondensation reaction at high temperature, forming long-chain ammonium polyphosphate. This creates a reaction environment with insufficient urea (ammonia) to prevent premature solidification and termination of polymerization. The second addition of urea (4 / 7) is mainly to provide the remaining ammonia for the ammoniation and solidification of the ammonium polyphosphate. Simultaneously, by controlling the N / P molar ratio to 1.86:1, the ratio of ammonium to phosphate groups is ensured to be at a critical equilibrium point, maintaining chain extension motive force while avoiding excessive urea that lowers the melting point and hinders solidification.

[0018] 4. In this invention, the polymerization reaction of ammonium polyphosphate is carried out at 185°C, which just exceeds the reaction energy barrier of pyrophosphate (dimer) developing to a higher polymerization state, and is slightly lower than the melting point of ammonium polyphosphate, so that the ammoniation and solidification can proceed smoothly, thereby obtaining fully water-soluble ammonium polyphosphate powder with a high polymerization rate and a wide degree of polymerization distribution.

[0019] 5. The present invention introduces water-soluble organic sodium lignin sulfonate, which delays solidification, fully polymerizes and broadens the molecular weight distribution of ammonium polyphosphate, improves solubility, and the introduction of organic matter also enhances the fertilizer efficiency of ammonium polyphosphate.

[0020] 6. This invention introduces ammonium polyphosphate for cooling and return at the end of polymerization, which rapidly cools the material to prevent remelting and fully ensures the quality of the product. Attached Figure Description

[0021] Figure 1 The X-ray diffraction (XRD) pattern of the broadly distributed water-soluble ammonium polyphosphate obtained in Example 1;

[0022] Figure 2 For the ion chromatography (IC) analysis of the broadly distributed water-soluble ammonium polyphosphate obtained in Examples 1, 2, 3 and Comparative Example 2, P1~P 10 The spectral peaks represent orthophosphate to decaphosphate. Detailed Implementation

[0023] The focus of this invention is on the process steps for producing water-soluble ammonium polyphosphate and the control of process parameters in the steps. The pre-melting tank (400 L, heated by heat transfer oil between the walls) and the kneading kettle (400 L, heated by heat transfer oil between the walls) are just conventional production tools used to achieve the process objectives of this invention. In order for those skilled in the art to better understand this invention, the invention will be further described below in conjunction with the following embodiments and comparative examples.

[0024] Example 1

[0025] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0026] S1: Place 75 kg of water-soluble monoammonium phosphate (11% N, 61% P2O5) into a pre-melting tank and heat it to melt at a tank wall temperature of 190 ℃ to fluidize the raw material;

[0027] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 185 ℃, and then 7.5 kg of sodium lignosulfonate and a certain amount of solid urea are added. Then, stirring is started for stirring polymerization, and the kneading kettle impeller speed is 35 rpm. After 15 min, solid urea is added again, and stirring polymerization is continued for 25 min to obtain the base material. The mass ratio of urea added in the two additions is 3:4, and the total amount of urea added in the two additions makes the N / P molar ratio of the system 1.86:1. A portion of the base material is removed within 5 min and air-cooled to room temperature to obtain the additive.

[0028] S3: Add the additive to the base material to quickly cool it down and prevent remelting. The amount of additive added is 50% of the mass of the base material. Then air cool it to room temperature, crush it, and sieve it to obtain the broadly distributed water-soluble ammonium polyphosphate.

[0029] Comparative Example 1

[0030] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0031] S1: Place 75 kg of water-soluble monoammonium phosphate (11% N, 61% P2O5) into a pre-melting tank and heat it to melt at a tank wall temperature of 200 ℃ to fluidize the raw material;

[0032] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 185 ℃, and then 7.5 kg of potassium lignosulfonate and a certain amount of solid urea are added. Then, stirring is started for polymerization, and the kneading kettle impeller speed is 30 rpm. After 15 min, solid urea is added again, and stirring and polymerization are continued for 25 min to obtain the base material. The mass ratio of urea added in the two additions is 3:4, and the total amount of urea added in the two additions makes the N / P molar ratio of the system 1.57:1. A portion of the base material is removed within 5 min and air-cooled to room temperature to obtain the additive.

[0033] S3: Add the additive to the base material to quickly cool it down and prevent remelting. The amount of additive added is 50% of the mass of the base material. Then air cool it to room temperature, crush it, and sieve it to obtain the broadly distributed water-soluble ammonium polyphosphate.

[0034] Comparative Example 2

[0035] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0036] S1: Place 75 kg of water-soluble monoammonium phosphate (11% N, 61% P2O5) into a pre-melting tank and heat it to melt at a tank wall temperature of 170 ℃ to fluidize the raw material;

[0037] S2: The above melt was fed into a kneading kettle with an inner wall temperature of 165 ℃, and 7.5 kg of fulvic acid and a certain amount of solid urea were added. Then, stirring was started for polymerization, and the kneading kettle impeller speed was 40 rpm. After 15 min, solid urea was added again, and stirring and polymerization continued for 25 min to obtain the base material. The mass ratio of urea added in the two additions was 3:4, and the total amount of urea added in the two additions made the N / P molar ratio of the system 1.86:1. A portion of the base material was removed within 5 min and air-cooled to room temperature to obtain the additive.

[0038] S3: Add the additive to the base material to quickly cool it down and prevent remelting. The amount of additive added is 50% of the mass of the base material. Then air cool it to room temperature, crush it, and sieve it to obtain the broadly distributed water-soluble ammonium polyphosphate.

[0039] Comparative Example 3

[0040] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0041] S1: 75 kg of water-soluble monoammonium phosphate powder (11% N, 61% P2O5) was fed into a kneading kettle with an inner wall temperature of 185 ℃. Then, 7.5 kg of sodium lignosulfonate and a certain amount of solid urea were added. The stirring was then started for polymerization, with the kneading kettle impeller speed at 35 rpm. After 15 min, solid urea was added again, and the polymerization was continued for 75 min to obtain the base material. The mass ratio of urea added in the two additions was 3:4, and the total amount of urea added in the two additions made the N / P molar ratio of the system 1.86:1. A portion of the base material was removed within 5 min and air-cooled to room temperature to obtain the solid additive.

[0042] S2: Add the additive to the base material to quickly cool it down and prevent remelting. The amount of additive added is 50% of the mass of the base material. Then air cool it to room temperature, and then crush and screen it to obtain the broadly distributed water-soluble ammonium polyphosphate.

[0043] Comparative Example 4

[0044] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0045] S1: Place 75 kg of water-soluble monoammonium phosphate (11% N, 61% P2O5) into a pre-melting tank and heat it to melt at a tank wall temperature of 190 ℃ to fluidize the raw material;

[0046] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 185 ℃, and a certain amount of solid urea is added. Then, stirring is started for stirring and polymerization, and the kneading kettle impeller speed is 35 rpm. After 15 min, solid urea is added again, and stirring and polymerization is continued for 15 min to obtain the base material. The mass ratio of urea added in the two additions is 3:4, and the total amount of urea added in the two additions makes the N / P molar ratio of the system 1.86:1. A portion of the base material is removed within 5 min and air-cooled to room temperature to obtain the solid additive.

[0047] S3: Add the additive to the base material to quickly cool it down and prevent remelting. The amount of additive added is 50% of the mass of the base material. Then air cool it to room temperature, crush it, and sieve it to obtain the broadly distributed water-soluble ammonium polyphosphate.

[0048] Comparative Example 5

[0049] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0050] S1: Place 75 kg of water-soluble monoammonium phosphate (11% N, 61% P2O5) into a pre-melting tank and heat it to melt at a tank wall temperature of 190 ℃ to fluidize the raw material;

[0051] S2: The above melt was fed into a kneading kettle with an inner wall temperature of 185 ℃, and 11.25 kg of sodium lignosulfonate and a certain amount of solid urea were added. Then, stirring was started for polymerization, and the kneading kettle impeller speed was 35 rpm. After 15 min, solid urea was added again, and stirring and polymerization continued for 85 min to obtain the base material. The mass ratio of urea added in the two additions was 3:4, and the total amount of urea added in the two additions made the N / P molar ratio of the system 1.86:1. The state of the material was observed at 10-minute intervals during the polymerization process. After 100 min, it was still not solidified. Part of the base material was air-cooled to room temperature to obtain the additive.

[0052] S3: Add the additive to the base material to obtain a broadly distributed water-soluble ammonium polyphosphate.

[0053] Comparative Example 6

[0054] A broadly distributed water-soluble ammonium polyphosphate is prepared by the following steps:

[0055] S1: Place 75 kg of water-soluble monoammonium phosphate (11% N, 61% P2O5) into a pre-melting tank and heat it to melt at a tank wall temperature of 190 ℃ to fluidize the raw material;

[0056] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 185 ℃, and then 7.5 kg of sodium lignosulfonate and a certain amount of solid urea are added. Then, stirring is started for stirring polymerization, and the kneading kettle impeller speed is 35 rpm. After 15 min, solid urea is added again, and stirring polymerization is continued for 25 min to obtain the base material. The mass ratio of urea added in the two additions is 3:4, and the total amount of urea added in the two additions makes the N / P molar ratio of the system 1.86:1.

[0057] S3: The base material partially remelts within 5 minutes, and the resulting paste is cooled to obtain a broadly distributed water-soluble ammonium polyphosphate.

[0058] Experimental Example

[0059] The process conditions for producing broadly distributed water-soluble ammonium polyphosphate in the above experimental examples and comparative examples, as well as the product parameters of the obtained broadly distributed water-soluble ammonium polyphosphate, are shown in Table 1.

[0060] Table 1 Process conditions and product parameters

[0061] N / P (molar ratio) Temperature of the inner wall of the kneading vessel (°C) Pre-melted Organic matter addition (%MAP) Is it necessary to return materials? Is it cured? Curing time (min) Curing duration (min) Solubility (g / 100g water) N（%） <![CDATA[P2O5(%)]]> Weight-average degree of polymerization PDI Example 1 1.86 185 yes 10 yes yes 40 30 200 16 56 4.33 1.34 Comparative Example 1 1.57 185 yes 10 yes yes 40 30 170 14 55 3.07 1.23 Comparative Example 2 1.86 165 yes 10 yes yes 40 30 170 15 54 2.95 1.19 Comparative Example 3 1.86 185 no 10 yes yes 90 30 190 14 56 3.78 1.28 Comparative Example 4 1.86 185 yes 0 yes yes 30 30 100 18 59 2.21 1.14 Comparative Example 5 1.86 185 yes 15 yes no - - 230 15 55 4.55 1.35 Comparative Example 6 1.86 185 yes 10 no yes 40 5 210 14 55 4.28 1.31

[0062] The nitrogen and phosphorus content and degree of polymerization were measured according to the chemical industry standard "HG / T 5939—2021 Fertilizer Grade Ammonium Polyphosphate". PDI refers to polydispersity index, which is the ratio of the weight average molecular weight to the number average molecular weight of the product. The higher the PDI, the wider the degree of polymerization distribution and the richer the phosphorus species.

[0063] As shown in Table 1, the broadly distributed water-soluble ammonium polyphosphate prepared using the process of this invention (Example 1) not only has a high degree of polymerization but also a broad degree of polymerization distribution (PDI = 1.34). The chelating properties of this broadly distributed water-soluble ammonium polyphosphate with organic matter result in a solubility of 200 g / 100 mL water. X-ray diffraction analysis of the broadly distributed water-soluble ammonium polyphosphate obtained in Example 1 yielded the following results: Figure 1 As shown, the broadly distributed water-soluble ammonium polyphosphate prepared in Example 1 is a type I crystal. Furthermore, ion chromatography (IC) analysis was performed on the broadly distributed water-soluble ammonium polyphosphate prepared in Example 1, Comparative Examples 1-2, and Comparative Example 4, and the results are as follows: Figure 2 As shown in the figure, the degree of polymerization of the broadly distributed water-soluble ammonium polyphosphate prepared in Example 1 ranges from orthophosphate (P1) to decaphosphate (P2). 10 )coexist.

[0064] Compared with Example 1, Comparative Example 3 did not use pre-melting technology. All raw materials were mixed and reacted in a kneading kettle, and the total operation time, including the raw material melting time, was extended from 40 min to 90 min, which greatly reduced production efficiency. At the same time, because the urea decomposition temperature was low, the ammonia loss in Comparative Example 3 was severe, and the nitrogen content of the product decreased from 16% to 14% (Table 1).

[0065] Compared to Example 1, Comparative Example 4, due to the absence of water-soluble organic matter, had an earlier curing time, preventing chain growth and the development of a broadly distributed APP, thus terminating the polymerization reaction. Consequently, its degree of polymerization and PDI were both lower, and its solubility was only 100 g / 100 mL of water (Table 1). Figure 2 ).

[0066] Compared with Example 1, Comparative Example 5 could not be solidified at the reaction temperature due to the excessive addition of low-melting-point organic matter, and the subsequent crushing and sieving operations could not be carried out (Table 1).

[0067] Compared with Example 1, Comparative Example 6 did not use cooled ammonium polyphosphate as a return cooling material at the end of polymerization. The inner wall temperature of the kneading kettle was maintained at 185 °C, which is higher than the melting point of APP. The product melted again after 5 minutes, and subsequent crushing and screening operations could not be carried out (Table 1).

[0068] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing a broadly distributed water-soluble ammonium polyphosphate, characterized in that, Includes the following steps: S1: Heat water-soluble monoammonium phosphate to melt, then add sodium lignosulfonate and urea to the molten water-soluble monoammonium phosphate. The amount of sodium lignosulfonate added is 10% of the mass of water-soluble monoammonium phosphate. Then, stir and polymerize at 185 °C. After 15 min, add urea again and continue stirring and polymerizing for 25 min to obtain the base material. The total amount of urea added is based on the N / P molar ratio in the system being 1.86:1, and the mass ratio of the two urea additions is 3:

4. S2: Remove a portion of the base material within 5 minutes and air-cool it to room temperature to obtain the additive; S3: Add the additive to the base material, mix well, then air cool to room temperature, then crush and sieve to obtain the final product; the amount of additive added is 50% of the mass of the base material.

2. The preparation method according to claim 1, characterized in that: The heating and melting temperature of water-soluble monoammonium phosphate in S1 is 190 ℃.

3. The preparation method according to claim 1, characterized in that: The stirring speed for polymerization in S1 is 30~40 rpm.

4. A broadly distributed water-soluble ammonium polyphosphate, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 3.

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