Wide-distribution water-soluble ammonium polyphosphate and preparation method thereof

Abstract

The invention discloses wide-distribution water-soluble ammonium polyphosphate and a preparation method thereof, and belongs to the technical field of compound fertilizers. When the water-soluble monoammonium phosphate and the urea are subjected to thermal condensation reaction to produce the APP, the water-soluble organic matter is introduced, the chain growth window period before the APP is cured is prolonged, and the high-water-solubility APP powder product with wide polymerization degree distribution is obtained, so that the fertilizer-grade APP product sequence is perfected. The monoammonium phosphate pre-melting process is combined with the APP cold material returning process, so that the operation time is shortened, the productivity is greatly improved, and meanwhile, the problem that a wide-distribution water-soluble product cannot be cured is solved. The organic matters in the APP product, which are combined with phosphorus in situ, have the synergistic potential of chelating trace elements in the soil besides improving the solubility. The method for rapidly producing the wide-distribution water-soluble APP powder is simple in process and convenient for efficient large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of compound fertilizers, and in particular relates to a broadly distributed water-soluble ammonium polyphosphate and a preparation method thereof. Background Art

[0002] Phosphates undergo intermolecular dehydration when heated and can polymerize to form polyphosphates with a POP alternating structure. The general structural formula of ammonium polyphosphate (APP) can be written as (NH4) n+2 P n O 3n+1 . APP used in fertilizers is usually a mixture of oligomers of different chain lengths. APP with an average degree of polymerization n of less than 20 belongs to a water-soluble N and P compound fertilizer, which can desorb and chelate trace elements at the interface between soil solution and aggregates, and promote the diffusion of P and trace elements. APP's resistance to soil fixation, slow release of gradual hydrolysis, and solubility of trace elements in liquid formula fertilizers make the utilization rate of phosphorus by plants generally higher than the application of an equal amount of orthophosphate. The situation of insufficient supply of fertilizer-grade APP has kept the market price of water-soluble APP at more than 8,000 yuan per ton for a long time (as of 2025). Even if expensive industrial monoammonium phosphate (MAP) is used as raw material, the cost of water-soluble APP (including depreciation) is only more than 5,000 yuan / ton. Therefore, water-soluble APP has a broad market potential and profit space recognized by the industry.

[0003] Solid water-soluble APP is the mainstream product of fertilizer-grade APP at present because of its low transportation cost. Domestically, wet phosphoric acid is mostly used to purify and remove impurities to prepare industrial monoammonium phosphate, and then industrial monoammonium phosphate and urea are used as raw materials to prepare APP. In addition, there is a method for preparing APP by phosphoric acid-urea condensation (CN105621381A), but the polymerization system takes a lot of time to evaporate water, the polymerization time is more than 2 hours, and the production intensity is low. There is also a method for producing solid APP by phosphoric acid amination-return material granulation (CN108002357A) in China, which is similar to the TVA process in the United States. It has high requirements for the concentration and purity of raw phosphoric acid and is costly. Patent CN107176597A discloses a method for producing powdered water-soluble APP using a belt conveyor polymerizer, which is similar to the method of continuously producing water-soluble solid APP using a twin-screw extruder in another patent (CN118771924B). The continuous production of solid APP using high-viscosity solid raw materials is their characteristics and advantages, but a large amount of ammonia is volatilized and lost during the transportation and polymerization process, and excess urea is required to ensure solidification. At present, two types of APP grades, 18-58-0 and 14-65-0, have been produced in China, but these highly water-soluble APP solid products cannot achieve a wide molecular weight distribution (also known as polymerization degree distribution) to solubilize more trace elements and meet the needs of crops at different growth stages for APP hydrolysis to orthophosphate. Therefore, it is necessary to invent a method for quickly producing a wide distribution of water-soluble APP powder to solve the above 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 a preparation method thereof, so as to solve the technical problem that the existing ammonium polyphosphate has a narrow molecular weight distribution.

[0005] In order to achieve the above object, 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 until it is melted, then add sodium lignin sulfonate and urea to the molten water-soluble monoammonium phosphate, the amount of sodium lignin sulfonate added is 10% of the mass of water-soluble monoammonium phosphate; then stir and polymerize at 185°C; add urea again after 15 minutes, continue stirring and polymerizing for 25 minutes to obtain a base material; the total amount of urea added is based on the N / P molar ratio of 1.86:1 in the system, and the mass ratio of the two urea additions is 3:4;

[0007] S2: Cool the base material to room temperature in air to obtain the additive material;

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

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

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

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

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

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

[0014] The beneficial effects of the present invention are:

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

[0016] 2. In the present invention, sodium lignin sulfonate is added to the reaction system when preparing ammonium polyphosphate. The aromatic ring organic molecular chain of sodium lignin sulfonate slows down the diffusion of ammonium in the system through the steric hindrance effect, forming a local reaction micro-region, thereby slowing down the process of ammoniation curing, so that the final ammonium polyphosphate powder has a wider molecular weight distribution and sufficient polymerization.

[0017] 3. In the preparation of ammonium polyphosphate, urea is added to the reaction system twice. The first addition of urea (accounting for 3 / 7 of the total mass) quickly initiates a polycondensation reaction at high temperature to form long-chain ammonium polyphosphate, creating a reaction environment with insufficient urea (ammonia) to prevent the ammonium polyphosphate from curing prematurely and terminating the polymerization; the second addition of urea (4 / 7) is mainly to provide the remaining ammonia for the ammoniation curing of the ammonium polyphosphate. At the same time, by controlling the N / P molar ratio to 1.86:1, the ratio of ammonium radicals to phosphate groups is ensured to be at a critical equilibrium point, which can maintain the chain extension power and avoid the excessive urea from lowering the melting point and making it difficult to solidify and form.

[0018] 4. The polymerization reaction of ammonium polyphosphate in the present invention 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 curing proceeds smoothly, thereby obtaining a fully water-soluble ammonium polyphosphate powder with a higher polymerization rate and a wider polymerization degree distribution.

[0019] 5. The present invention introduces water-soluble organic matter sodium lignin sulfonate to delay solidification, and sufficient polymerization broadens the molecular weight distribution of ammonium polyphosphate, improves solubility, and the introduction of organic matter also improves the fertilizer effect of ammonium polyphosphate.

[0020] 6. The present invention introduces ammonium polyphosphate to cool the returned material at the end of the polymerization, and rapidly cools the material to avoid remelting, thereby fully ensuring the quality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the X-ray diffraction (XRD) pattern of the broad distribution water-soluble ammonium polyphosphate obtained in Example 1;

[0022] Figure 2 The ion chromatography (IC) analysis of the broad distribution water-soluble ammonium polyphosphate obtained in Example 1, Example 2, Example 3 and Comparative Example 2, P1~P 10 The peaks represent orthophosphate to decaphosphate. DETAILED DESCRIPTION

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

[0024] Example 1

[0025] A broad distribution 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 °C to fluidize the raw material;

[0027] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 185°C, and then 7.5 kg of sodium lignin sulfonate and a certain amount of solid urea are added, and then stirring is started for stirring polymerization, and the speed of the kneading kettle blade is 35 rpm; after 15 minutes, solid urea is added again, and stirring polymerization is continued for 25 minutes to obtain a base material; the mass ratio of the two urea additions is 3:4, and the total amount of urea added twice makes the N / P molar ratio of the system 1.86:1; part of the base material is removed within 5 minutes and air-cooled to room temperature to obtain an additive material;

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

[0029] Comparative Example 1

[0030] A broad distribution 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 °C to fluidize the raw material;

[0032] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 185°C, and then 7.5 kg of potassium lignin sulfonate and a certain amount of solid urea are added, and then stirring is started for stirring polymerization, and the speed of the kneading kettle blade is 30 rpm; after 15 minutes, solid urea is added again, and stirring polymerization is continued for 25 minutes to obtain a base material; the mass ratio of the two urea additions is 3:4, and the total amount of urea added twice makes the N / P molar ratio of the system 1.57:1; part of the base material is removed within 5 minutes and air-cooled to room temperature to obtain an additive material;

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

[0034] Comparative Example 2

[0035] A broad distribution 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 °C to fluidize the raw material;

[0037] S2: The above melt is fed into a kneading kettle with an inner wall temperature of 165°C, and 7.5 kg of fulvic acid and a certain amount of solid urea are added, and then stirring is started for stirring polymerization, and the speed of the kneading kettle blade is 40 rpm; after 15 minutes, solid urea is added again, and stirring polymerization is continued for 25 minutes to obtain a base material; the mass ratio of the two urea additions is 3:4, and the total amount of urea added twice makes the N / P molar ratio of the system 1.86:1; part of the base material is removed within 5 minutes and air-cooled to room temperature to obtain an additive material;

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

[0039] Comparative Example 3

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

[0041] S1: 75 kg of powdered water-soluble monoammonium phosphate (11% N, 61% P2O5) was fed into a kneading kettle with an inner wall temperature of 185 °C, and then 7.5 kg of sodium lignin sulfonate and a certain amount of solid urea were added, and then stirring was started for stirring polymerization. The speed of the kneading kettle blade was 35 rpm; after 15 minutes, solid urea was added again, and stirring polymerization was continued for 75 minutes to obtain a base material; the mass ratio of the two urea additions was 3:4, and the total amount of urea added twice made the N / P molar ratio of the system 1.86:1; part of the base material was removed within 5 minutes and air-cooled to room temperature to obtain a solid additive;

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

[0043] Comparative Example 4

[0044] A broad distribution 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 °C to fluidize the raw material;

[0046] S2: The melt is fed into a kneading kettle with an inner wall temperature of 185°C, and a certain amount of solid urea is added, and then stirring is started for stirring polymerization, and the speed of the kneading kettle blade is 35 rpm; after 15 minutes, solid urea is added again, and stirring polymerization is continued for 15 minutes to obtain a base material; the mass ratio of the two urea additions is 3:4, and the total amount of urea added twice makes the N / P molar ratio of the system 1.86:1; part of the base material is removed within 5 minutes and air-cooled to room temperature to obtain a solid additive;

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

[0048] Comparative Example 5

[0049] A broad distribution 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 °C to fluidize the raw material;

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

[0052] S3: Add the additives into the base material to obtain broad distribution water-soluble ammonium polyphosphate.

[0053] Comparative Example 6

[0054] A broad distribution 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 °C to fluidize the raw material;

[0056] S2: The above melt was fed into a kneading kettle with an inner wall temperature of 185 °C, and 7.5 kg of sodium lignin sulfonate and a certain amount of solid urea were added, and then stirring was started for stirring polymerization. The speed of the kneading kettle blade was 35 rpm. After 15 minutes, solid urea was added again, and stirring polymerization was continued for 25 minutes to obtain a base material. The mass ratio of the two urea additions was 3:4, and the total amount of urea added twice made 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 broad distribution water-soluble ammonium polyphosphate in the above experimental examples and comparative examples and the product parameters of the obtained broad distribution water-soluble ammonium polyphosphate are shown in Table 1.

[0060] Table 1 Process conditions and product parameters

[0061] N / P (molar ratio) Inner wall temperature of kneading kettle (°C) Whether pre-melting Organic matter addition amount (%MAP) Whether recycling Whether curing Curing time (min) Curing maintenance time (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] Indicators such as nitrogen and phosphorus content and degree of polymerization are measured according to the chemical industry standard "HG / T 5939-2021 Fertilizer Grade Ammonium Polyphosphate". PDI refers to the polydispersity index, which is the ratio of the product weight-average molecular weight to the number-average molecular weight. The higher the PDI, the wider the degree of polymerization distribution and the richer the phosphorus species.

[0063] As can be seen from Table 1, the broad distribution water-soluble ammonium polyphosphate prepared by the process of the present invention (Example 1) not only has a high degree of polymerization, but also has a wide degree of polymerization distribution (PDI=1.34). The chelating property of the broad distribution water-soluble ammonium polyphosphate with organic matter enables its solubility to reach 200 g / 100 mL water. X-ray diffraction analysis of the broad distribution water-soluble ammonium polyphosphate obtained in Example 1 is performed, and the results are as follows: Figure 1 As shown, it can be seen that the broad distribution water-soluble ammonium polyphosphate prepared in Example 1 is type I crystal; in addition, the broad distribution water-soluble ammonium polyphosphate prepared in Example 1 and Comparative Examples 1-2 and Comparative Example 4 were subjected to ion chromatography (IC) analysis, and the results are as follows Figure 2 As shown in the figure, it can be seen that the wide distribution water-soluble ammonium polyphosphate prepared in Example 1 has a polymerization degree distribution ranging from orthophosphate (P1) to decaphosphate (P 10 )coexist.

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

[0065] Compared with Example 1, Comparative Example 4 did not add water-soluble organic matter, the curing time was advanced, and there was no time for the chain to grow and develop into a widely distributed APP, and the polymerization reaction was terminated. Therefore, the degree of polymerization and PDI were both low, and the solubility was only 100 g / 100 mL water (Table 1, Figure 2 ).

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

[0067] Compared with Example 1, in Comparative Example 6, because no cooled ammonium polyphosphate was used as a return cooling material at the end of the polymerization, the inner wall temperature of the kneading kettle was maintained at 185°C, which was 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 the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for preparing a broadly distributed water-soluble ammonium polyphosphate, characterized in that: The following steps are involved: S1: Heat water-soluble monoammonium phosphate until it is melted, then add sodium lignin sulfonate and urea to the molten water-soluble monoammonium phosphate, the amount of sodium lignin sulfonate added is 10% of the mass of water-soluble monoammonium phosphate; then stir and polymerize at 185°C; add urea again after 15 minutes, continue stirring and polymerizing for 25 minutes to obtain a base material; the total amount of urea added is based on the N / P molar ratio of 1.86:1 in the system, and the mass ratio of the two urea additions is 3:4; S2: Cool the base material to room temperature in air to obtain the additive material; S3: Add the additives to the base material, mix well, then air cool to room temperature, and then crush and sieve to obtain.

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

3. The preparation method according to claim 1, characterized in that: The stirring rate of the stirred polymerization in S1 is 30-40 rpm.

4. The preparation method according to claim 1, characterized in that: The amount of additives added in S3 is 50% of the mass of the base material.

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

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