A method for producing water-soluble polyphosphates with a stepped distribution

Abstract

This invention discloses a method for producing water-soluble polyphosphates with a stepped distribution, comprising the following steps: S1: preparing a polyphosphate composition; S2: turning on the stirring and cooling device, adding all the water and then all the alkali into the reaction vessel, and proceeding to step S3 after the temperature inside the vessel drops below 25°C; S3: slowly adding polyphosphate into the reaction vessel to react, controlling the temperature to remain below 70°C; S4: after the reaction is complete, replenishing the water lost due to evaporation, testing the pH value of the solution, and finely adjusting the pH value with polyphosphate or alkali to obtain a clear and transparent water-soluble polyphosphate with a stepped distribution, or one containing some suspended matter. This invention, by precisely preparing the polyphosphate composition and strictly controlling the reaction temperature to below 70°C, can prepare water-soluble polyphosphates with a stepped degree of polymerization, showing promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of fertilizer preparation technology, and specifically to a method for producing water-soluble polyphosphates with a stepped distribution. Background Technology

[0002] Nitrogen, phosphorus, and potassium are essential macronutrients for crops. Water-soluble polyphosphates, as efficient phosphorus sources, are widely used in agriculture. Examples include potassium pyrophosphate and sodium tripolyphosphate, which meet national or industry standards, as well as agricultural ammonium polyphosphate and agricultural potassium polyphosphate, which only have enterprise-specific standards. Crops can only directly absorb non-polymerized orthophosphate (H₂PO₄). - HPO4 2- and PO4 3- It cannot directly absorb polyphosphates (H+). n+ 1P n O 3n+1 - 、H n P n O 3n+1 2- and H n-1 P n O 3n+1 3- (n = 2, 3, 4, 5, 6...), but polyphosphates can be hydrolyzed into orthophosphates by external factors such as temperature, light, water, pH, and soil phosphatases, which can then be absorbed by crops. Polyphosphates are not easily immobilized in the soil, have a chelating effect on certain metal ions in the soil, and have a stronger migration ability in the soil, thus exhibiting higher activity than orthophosphates. The hydrolysis of polyphosphates requires a certain amount of time, and for crops, polyphosphates have a chemically slow-release effect.

[0003] According to relevant literature both domestically and internationally, the complete hydrolysis time of polyphosphates to orthophosphates generally ranges from 7 to 90 days. The longer the molecular chain length (degree of polymerization) of the polyphosphate, the longer the hydrolysis time. This is because the hydrolysis of polyphosphates generally occurs in stages. High-degree-of-polymerization polyphosphates are first hydrolyzed into low-degree-of-polymerization products, which then undergo secondary, tertiary, quaternary, and so on hydrolysis before finally being converted into orthophosphates that can be absorbed by crops. Each stage of hydrolysis requires a certain amount of time, and the cumulative time of each stage is the hydrolysis time of the polyphosphate at that degree of polymerization. For example, potassium pyrophosphate (potassium dipolyphosphate) hydrolyzes in about 7 days, while potassium tripolyphosphate takes up to 30 days.

[0004] The slow-release properties of chemical fertilizers mean that applying polyphosphate products with only a single degree of polymerization (such as potassium pyrophosphate and potassium tripolyphosphate) in agriculture can lead to nutrient deficiency in crops, causing irreparable economic losses. Specifically, crops experience severe phosphorus deficiency immediately after application, and the deficiency only subsides after a long period, severely disrupting normal crop growth patterns. Only fertilizers made from phosphorus sources such as orthophosphate, diphosphate, trimer, tetraphosphate, and pentaphosphate, distributed in a stepped manner in specific proportions, can better meet the needs of crop growth. In polyphosphates with a stepped distribution, orthophosphate can be directly absorbed by crops, addressing the issue of rapid phosphorus release; while polymerized phosphates, after hydrolysis, continuously supply phosphorus to crops, addressing the issues of long-term effectiveness and slow release, making them the most ideal phosphorus source for fertilizers currently available.

[0005] Currently, commercially available agricultural phosphorus sources can generally be divided into two categories: orthophosphates produced by traditional crystallization methods without polymerized phosphorus, such as monoammonium phosphate, diammonium phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate; and newer polyphosphates produced by high-temperature polycondensation methods with a single degree of polymerization, such as potassium pyrophosphate, potassium tripolyphosphate, and ammonium polyphosphate. To achieve a certain degree of polymerization distribution in the phosphorus source, it is only possible to achieve this through physical mixing of the aforementioned phosphorus sources. However, physically mixed products have poor uniformity and a narrow degree of polymerization distribution. For example, while mixing potassium dihydrogen phosphate with potassium pyrophosphate or potassium tripolyphosphate results in the presence of polymerized phosphorus, it lacks tetrameric, pentamer, or higher-polymerized phosphates, leading to less than ideal practical application results. Furthermore, the high-temperature polyphosphate process is complex, energy-intensive, and costly, limiting its application in agriculture. Summary of the Invention

[0006] This invention overcomes the technical problem that existing methods for producing water-soluble polyphosphates cannot obtain polyphosphate products with multiple degrees of polymerization and distributed in a certain proportion to meet agricultural needs, and provides a method for producing water-soluble polyphosphates with a stepped distribution.

[0007] To solve the above problems, the present invention adopts the following technical solution:

[0008] A method for producing a water-soluble polyphosphate with a stepped distribution includes the following steps:

[0009] S1: Based on the degree of polymerization distribution of the target product water-soluble polyphosphate, formulate the required polyphosphate combination and calculate the amount of alkali and water required for the reaction;

[0010] S2: Turn on the stirring and cooling device, add all the water into the reactor, then add all the alkali. Wait until the temperature inside the reactor drops below 25°C before proceeding to step S3.

[0011] S3: Slowly add polyphosphoric acid of different concentrations into the reactor in sequence, and keep the temperature below 70°C throughout the reaction process. If the temperature approaches the limit during the reaction, stop adding polyphosphoric acid and wait for the material in the reactor to cool down to below 25°C before resuming the addition until all polyphosphoric acid has been added.

[0012] S4: After the reaction is complete, replenish the water lost due to evaporation, test the pH value of the solution, and fine-tune it with polyphosphoric acid or alkali to make the pH between 4 and 11. This will yield a clear and transparent water-soluble polyphosphate with a stepped distribution containing some suspended matter.

[0013] Furthermore, the water-soluble polyphosphate with a stepped distribution obtained in S4 can be freeze-dried to obtain a solid water-soluble polyphosphate with a stepped distribution.

[0014] Furthermore, in S1, the concentration of the polyphosphoric acid is 100%-123%, and the polyphosphoric acid combination is a combination of one or more polyphosphoric acids with a concentration of 100%-123% in a specific proportion according to the degree of polymerization distribution of phosphorus in the target product to form the polyphosphoric acid raw material required for the reaction.

[0015] Furthermore, the alkali is one or more of the following: hydroxides, oxides, carbonates, bicarbonates, basic carbonates, and sulfides corresponding to potassium, sodium, ammonium, calcium, magnesium, copper, iron, manganese, and zinc.

[0016] Furthermore, in S1, polyphosphoric acid is calculated as P2O5, ammonium as N, and other bases as oxides. The base required for the reaction is calculated according to the molar ratio of phosphorus pentoxide to base of 0.3:1 to 1:1.

[0017] Furthermore, in S3, the temperature of the reaction is preferably controlled between 10 and 50°C.

[0018] Another object of the present invention is to protect the water-soluble polyphosphate with a stepped distribution obtained by the above-described method for producing water-soluble polyphosphate with a stepped distribution.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] As is known to those skilled in the art, polyphosphoric acid can undergo a neutralization reaction with a base (represented by MOH) under certain conditions, and the chemical reaction equation can be expressed as follows:

[0021] H n+2 P n O 3n+1 +MOH=MH n+1 P n O 3n+1 +H2O

[0022] Polyphosphoric acid of different concentrations has a stable degree of polymerization distribution. Table 1 below shows the degree of polymerization distribution of some polyphosphoric acids.

[0023] Table 1

[0024]

[0025] Note: In Table 1, P1, P2, P3, P4, P5, P6, P7 and P8 represent orthophosphoric acid, diphosphoric acid, triphosphoric acid, tetraphosphoric acid, pentaphosphoric acid, hexaphosphoric acid, heptaphosphoric acid and octaphosphoric acid, respectively.

[0026] For example, a 105% concentration of polyphosphoric acid contains approximately 54% orthophosphoric acid, 41% diphosphoric acid, and 5% triphosphoric acid. If the reaction of polyphosphoric acid with an alkali does not involve hydrolysis, the product is a polyphosphate with the same degree of polymerization distribution as the original polyphosphoric acid. However, this reaction contains water, and the reaction is mostly exothermic. The large amount of heat of reaction overcomes the energy barrier for product hydrolysis, leading to the product MH. n+1 P n O 3n+1 Hydrolysis transforms polyphosphates into orthophosphates with no degree of polymerization, such as MH2PO4, MHPO4, or MPO4. However, this invention, by strictly controlling the reaction temperature below 70°C, preferably between 10 and 50°C, produces polyphosphates that are essentially free from hydrolysis, and whose degree of polymerization distribution closely matches that of the polyphosphate raw materials involved in the reaction. Therefore, by accurately preparing various combinations of polyphosphates and reacting them with an alkali at temperatures below 70°C, polyphosphate products with the desired degree of polymerization distribution can be obtained. Alternatively, the required combination of polyphosphates can be calculated by reverse engineering based on the expected degree of polymerization distribution of the target product. This invention features simple equipment and processes, eliminates the need for high-temperature reactions, and achieves significant results by strictly controlling the reaction temperature to obtain polyphosphates with a specific degree of polymerization distribution. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments and experiments.

[0028] Example 1

[0029] A method for producing a water-soluble polyphosphate with a stepped distribution, comprising the following steps:

[0030] S1: Based on the mass of the materials, take 27.3 parts of polyphosphoric acid with a concentration of 111%, 26.2 parts of potassium hydroxide, and 46.5 parts of water.

[0031] S2: Turn on the stirring and cooling device, add 46.5 parts of water to the reactor, then add 26.2 parts of potassium hydroxide. After the potassium hydroxide is added, cool the temperature to below 25°C and proceed to step S3.

[0032] S3: Slowly add 111% polyphosphoric acid, maintaining the temperature below 50℃ during the addition process. If the temperature reaches 50℃, stop adding polyphosphoric acid and resume adding it once the temperature of the liquid in the reactor drops below 25℃, continuing until all 27.3 parts of 111% polyphosphoric acid have been added. After replenishing the lost water, test the pH of the liquid. Add a small amount of potassium hydroxide or polyphosphoric acid to bring the pH to 7.0. This will yield a clear, transparent, water-soluble liquid potassium polyphosphate product with a content of 22% P2O5 and 22% K2O.

[0033] Example 2

[0034] A method for producing a water-soluble polyphosphate with a stepped distribution, comprising the following steps:

[0035] S1: Based on the mass of the materials, take 28.9 parts of polyphosphoric acid with a concentration of 105%, 18.7 parts of sodium hydroxide, and 52.4 parts of water.

[0036] S2: Turn on the stirring and cooling device, add 52.4 parts of water to the reactor, then add 18.7 parts of sodium hydroxide. After the sodium hydroxide is added, cool the temperature to below 25°C and proceed to step S3.

[0037] S3: Slowly add 105% polyphosphoric acid, maintaining the temperature below 70℃ during the addition process. Stop adding polyphosphoric acid when the temperature reaches 70℃, and resume adding once the temperature of the liquid in the reactor drops below 25℃, until all 28.9 parts of polyphosphoric acid have been added. After replenishing the lost water, test the pH value of the liquid. Add a small amount of sodium hydroxide or polyphosphoric acid to bring the pH to 7.0. This will yield a clear, transparent, water-soluble liquid sodium polyphosphate product with a content of P2O5: 22% and Na2O: 14.5%.

[0038] Example 3

[0039] A method for producing a water-soluble polyphosphate with a stepped distribution, comprising the following steps:

[0040] S1: Based on the mass of the materials, take 39.3 parts of polyphosphoric acid with a concentration of 123%, 40 parts of ammonium bicarbonate, and 20.7 parts of water.

[0041] S2: Turn on the stirring and cooling device, add 20.7 parts of water to the reactor, then add 40 parts of ammonium bicarbonate. After the ammonium bicarbonate is added, cool the temperature to below 25°C and proceed to step S3.

[0042] S3: Slowly add 123% polyphosphoric acid, maintaining the temperature below 25℃ during the addition process. Stop adding polyphosphoric acid when the temperature reaches 25℃, and resume adding once the temperature of the liquid in the reactor drops below 25℃, until all 39.3 parts of polyphosphoric acid have been added. After replenishing the lost water, test the pH value of the liquid. Add a small amount of ammonium bicarbonate or polyphosphoric acid to bring the pH to 4.0. This will yield a clear, transparent, water-soluble liquid ammonium polyphosphate product with a content of 7% N and 35% P2O5.

[0043] Example 4

[0044] A method for producing a water-soluble polyphosphate with a stepped distribution, comprising the following steps:

[0045] S1: Based on the mass of the materials, take 16.5 parts of polyphosphoric acid with a concentration of 109%, 21.9 parts of sodium hydroxide, and 38.4 parts of water.

[0046] S2: Turn on the stirring and cooling device, add 38.4 parts of water to the reactor, then add 21.9 parts of sodium hydroxide. After the sodium hydroxide is added, cool the temperature to below 25°C and proceed to step S3.

[0047] S3: Slowly add 109% polyphosphoric acid, maintaining the temperature below 40℃ during the addition process. Stop adding polyphosphoric acid when the temperature reaches 40℃, and resume adding it once the temperature of the liquid in the reactor drops below 25℃, until all 16.5 parts of polyphosphoric acid have been added. After replenishing the lost water, test the pH value of the liquid. Add a small amount of sodium hydroxide or polyphosphoric acid to bring the pH to 11.0, thus obtaining a clear and transparent water-soluble liquid sodium polyphosphate product with a content of P2O5:13% and Na2O:17%.

[0048] Example 5

[0049] A method for producing a water-soluble polyphosphate with a stepped distribution, comprising the following steps:

[0050] S1: Based on the mass of the materials, take 14.3 parts of polyphosphoric acid with a concentration of 107%, 13 parts of polyphosphoric acid with a concentration of 116%, 26.2 parts of potassium hydroxide, and 46.5 parts of water.

[0051] S2: Turn on the stirring and cooling device, add 46.5 parts of water to the reactor, then add 26.2 parts of potassium hydroxide. After the potassium hydroxide is added, cool the temperature to below 25°C and proceed to step S3.

[0052] S3: Slowly add 107% polyphosphoric acid, maintaining the temperature below 50℃ during the addition process. If the temperature reaches 50℃, stop adding polyphosphoric acid and resume adding it once the temperature of the solution in the reactor drops below 25℃, continuing this process until all 14.3 parts of 107% polyphosphoric acid have been added. After the 107% polyphosphoric acid addition is complete, slowly add 116% polyphosphoric acid, maintaining the temperature below 50℃ during the addition process. If the temperature reaches 50℃, stop adding polyphosphoric acid and resume adding it once the temperature of the solution in the reactor drops below 25℃, continuing this process until all 13 parts of 116% polyphosphoric acid have been added. After replenishing the lost water, test the pH value of the solution. Add a small amount of potassium hydroxide or 116% polyphosphoric acid to bring the pH to 7.0, thus obtaining a P2O5 content of 22%.

[0053] K2O: 22%, a clear and transparent water-soluble liquid potassium polyphosphate product.

[0054] Example 6

[0055] A method for producing a water-soluble polyphosphate with a stepped distribution, comprising the following steps:

[0056] S1: Based on the mass of the materials, take 17.8 parts of polyphosphoric acid with a concentration of 109%, 10 parts of zinc oxide, and 72.2 parts of water.

[0057] S2: Turn on the stirring and cooling device, add 72.2 parts of water to the reactor, then add 10 parts of zinc oxide. After the zinc oxide is added, cool the temperature to below 25°C and proceed to step S3.

[0058] S3: Slowly add 109% polyphosphoric acid, maintaining the temperature below 50℃ during the addition process. If the temperature reaches 50℃, stop adding polyphosphoric acid and resume adding it once the temperature of the liquid in the reactor drops below 25℃, continuing until all 17.8 parts of 109% polyphosphoric acid have been added. After replenishing the lost water, test the pH of the liquid. Add a small amount of zinc oxide or polyphosphoric acid to bring the pH to 4.5, thus obtaining a clear, transparent, water-soluble liquid zinc polyphosphate product with a content of 14% P2O5 and 8% ZnO.

[0059] Control group 1

[0060] The temperature during the feeding process is controlled below 90°C. If the temperature reaches 90°C, the addition of polyphosphoric acid is stopped. The addition is resumed after the temperature of the liquid in the reactor is below 25°C. The rest is the same as in Example 1.

[0061] Control group 2

[0062] After the polyphosphoric acid was added, the pH was adjusted to 3.0 with 111% polyphosphoric acid, and the rest was the same as in Example 1.

[0063] Control group 3

[0064] S1: Based on the mass of the materials, take 47 parts of 85% phosphoric acid, 27 parts of sodium hydroxide, and 26 parts of water.

[0065] S2: Start stirring, add 26 parts of water to the reactor, then add 27 parts of sodium hydroxide. After the sodium hydroxide is added, proceed to step S3.

[0066] S3: Add 85% phosphoric acid to react. After the reaction is complete, dry the material with hot air. Continue to heat the dried material to 420℃ and keep it at that temperature for 2 hours to obtain a white powdery sodium tripolyphosphate product with a content of P2O5: 58% and Na2O: 42%.

[0067] The degree of polymerization distribution of phosphorus in the products obtained from the above-mentioned Examples 1 to 6 and Control Groups 1 to 3 is shown in Table 2.

[0068] Table 2

[0069]

[0070] Note: In Table 2, P2, P3, P4, P5, P6, P7, and P8 represent dipolyphosphate, tripolyphosphate, tetrapolyphosphate, pentapolyphosphate, hexapolyphosphate, heptapolyphosphate, and octapolyphosphate, respectively. The degree of polymerization distribution of phosphorus was tested according to GB / T 9984 standard, and pH was tested according to NY / T 1973 standard. The data for each group of tests are the average values ​​of 5 parallel tests.

[0071] As shown in Table 2, the degree of polymerization distribution of phosphorus in the products of Examples 1 to 6 is very close to that of phosphoric acid in polyphosphoric acid. The reaction process is a simple acid-base neutralization reaction. The polymerized phosphorus does not undergo obvious hydrolysis. The degree of polymerization distribution of polyphosphate products is determined by the composition of polyphosphoric acid raw materials.

[0072] As can be seen from the comparison between Example 1 and Control Groups 1 to 2, both excessively high reaction temperature and excessively low pH will lead to product hydrolysis. The present invention controls the reaction temperature and the pH value of the product to obtain polyphosphate with a stepwise distribution, and the effect is very obvious.

[0073] As can be seen from Examples 1 to 6 compared with Control Group 3, the polyphosphate products produced by the traditional high-temperature polycondensation method have a very simple composition and a narrow degree of polymerization distribution. It is impossible to formulate polyphosphate products with multiple degrees of polymerization coexisting and exhibiting a stepped distribution suitable for agricultural applications.

[0074] Comparing Example 1 and Example 5, although the weighted average concentration of polyphosphoric acid in Example 5 is the same as that in Example 1, the degree of polymerization distribution of the products in the two examples is significantly different. By combining different concentrations of polyphosphoric acid, the degree of polymerization distribution of polyphosphate products can be adjusted to meet the requirements.

[0075] This invention preserves the degree of polymerization distribution of phosphorus in polyphosphoric acid by strictly controlling the temperature and pH value of the reaction process between polyphosphoric acid and alkali, thereby obtaining a polyphosphate product with a degree of polymerization distribution similar to that of the polyphosphoric acid raw material. By combining polyphosphoric acid of different concentrations, the degree of polymerization distribution of phosphorus in the product can be adjusted to obtain a water-soluble polyphosphate product with a stepwise distribution. This invention is carried out at low temperature, has a simple process, significant effects, and outstanding technical benefits.

[0076] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for producing water-soluble polyphosphates with a stepped distribution, characterized in that, Includes the following steps: S1: Based on the degree of polymerization distribution of the target product water-soluble polyphosphate, prepare the required polyphosphate combination and calculate the amount of alkali and water required for the reaction; the polyphosphate combination is prepared by combining one or more polyphosphates with a concentration of 100% to 123% in a specific ratio according to the degree of polymerization distribution of phosphorus in the target product to form the polyphosphate raw material required for the reaction; the polyphosphate is calculated as P2O5, ammonium is calculated as N, and other alkalis are calculated as oxides, and the alkali required for the reaction is calculated according to the molar ratio of phosphorus pentoxide to alkali of 0.3:1 to 1:1; S2: Turn on the stirring and cooling device, add all the water into the reactor, then add all the alkali. Wait until the temperature inside the reactor drops below 25°C before proceeding to step S3. S3: Slowly add polyphosphoric acid of different concentrations into the reactor in sequence, and keep the temperature below 70°C throughout the reaction process. If the temperature approaches the limit during the reaction, stop adding polyphosphoric acid and wait for the material in the reactor to cool down to below 25°C before resuming the addition until all polyphosphoric acid has been added. S4: After the reaction is complete, replenish the water lost due to evaporation, test the pH value of the solution, and fine-tune it with polyphosphoric acid or alkali to make the pH value between 4 and 11. This will yield a clear and transparent water-soluble polyphosphate with a stepped distribution containing some suspended matter.

2. The method for producing a water-soluble polyphosphate with a stepped distribution as described in claim 1, characterized in that, The water-soluble polyphosphate with a stepped distribution obtained by S4 can be freeze-dried to obtain a solid water-soluble polyphosphate with a stepped distribution.

3. The method for producing a water-soluble polyphosphate with a stepped distribution as described in claim 1, characterized in that, The alkali is one or more of the following: hydroxides, oxides, carbonates, bicarbonates, basic carbonates, and sulfides of potassium, sodium, ammonium, calcium, magnesium, copper, iron, manganese, and zinc.

4. The method for producing a water-soluble polyphosphate with a stepped distribution as described in claim 1, characterized in that, In S3, the temperature of the reaction is controlled between 10 and 50°C.

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