Water-soluble polyammonium phosphate synthesized by using urea phosphate mother liquor, and synthesis method and application thereof
By heating, filtering, concentrating, and performing high-temperature melt foaming polymerization on urea phosphate mother liquor, water-soluble ammonium polyphosphate is synthesized, solving the problem of low-cost and high-efficiency utilization of urea phosphate mother liquor and realizing the efficient production of water-soluble slow-release fertilizer that meets agricultural standards.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WENGFU (GRP) CO LTD
- Filing Date
- 2024-06-26
- Publication Date
- 2026-07-21
AI Technical Summary
In the existing technology, it is difficult to utilize urea phosphate mother liquor in a low-cost and efficient manner, resulting in low phosphate fertilizer utilization rate. Furthermore, impurities in the mother liquor affect the product quality, making it difficult to achieve industrial production.
Water-soluble ammonium polyphosphate was synthesized by heating, filtering, and concentrating the original raw urea phosphate mother liquor at room temperature to remove water-insoluble precipitates, followed by high-temperature melt foaming polymerization under closed conditions. The synthesis was carried out using a molar ratio of purified urea phosphate powder and urea of 1:(0-0.4).
This method achieves efficient utilization of urea phosphate mother liquor, reduces production costs, improves the utilization rate of phosphate fertilizer, and produces water-soluble slow-release fertilizer that meets agricultural grade requirements and can be used as a water-soluble slow-release fertilizer.
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Figure CN118598098B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of urea phosphate mother liquor recycling and polyphosphate ammonium synthesis, and particularly to a method for synthesizing water-soluble polyphosphate ammonium using urea phosphate mother liquor, and its application. Background Technology
[0002] Water-soluble fertilizers play a vital role in agricultural production. Studies have shown that 70%-80% of phosphate fertilizer applied to the soil is converted into insoluble phosphorus, accumulating and wasting in the soil in an ineffective form, leading to soil salinization and eutrophication of water bodies, among other environmental problems. With traditional phosphate fertilizers, high concentrations of phosphorus are rapidly adsorbed by metal ions such as Al, Fe, and Ca in the soil, reducing phosphorus mobility. Ammonium polyphosphate (APP), a novel water-soluble slow-release fertilizer, can chelate metal ions in the soil and gradually hydrolyzes into PO4 after application. 3- It increases phosphorus migration rate, reduces phosphorus chemical fixation, and continuously provides plants with the phosphorus element they need, thereby improving fertilizer utilization and helping to promote the development of integrated water and fertilizer management and green agriculture.
[0003] Currently, the main methods for preparing water-soluble polyphosphate (APP) include the condensation method of phosphoric acid and urea, the condensation method of ammonium phosphate and urea, the ammoniation method of polyphosphate, and the condensation method of ammonia and diammonium phosphate. In China, the ammonium phosphate-urea condensation method is primarily used for APP synthesis. However, due to the difficulty in transporting the foamed melt in this system, continuous production is not feasible. To address this, the applicant disclosed a highly water-soluble ammonium polyphosphate, its synthesis method, and its application in CN 115108853 A. This synthesis method involves mixing urea phosphate and a phosphorus supplement in a closed environment, followed by melting, foaming polymerization, cooling, and pulverization to obtain highly water-soluble ammonium polyphosphate with an amorphous overall form. The urea phosphate used in this patent application is synthesized from wet-process phosphoric acid and purified by crystallization to obtain industrial-grade urea phosphate, resulting in a relatively high manufacturing cost for APP.
[0004] In addition, the wet-process synthesis of urea phosphate from phosphoric acid produces a large amount of urea phosphate mother liquor as a byproduct, which is rich in nitrogen, P2O5, and metal ions. Currently, there is limited research on the utilization pathways of urea phosphate mother liquor. Most of the mother liquor is directly separated and used as a liquid fast-acting fertilizer. Some studies have used crystallization and extraction processes to separate P2O5 from the mother liquor to prepare highly efficient phosphorus chemical products such as ammonium dihydrogen phosphate. However, these methods are currently only at the experimental level and are difficult to implement in industrial production due to cost and other issues. Existing technologies also utilize urea phosphate mother liquor to prepare phosphorus chemical products, achieving efficient utilization of P2O5 in the mother liquor. However, these processes are complex and costly, making industrial-scale production difficult. Furthermore, the large amount of Ca enriched in the mother liquor... 2+ Mg 2+ Al3+ Fe 3+ SO4 2- F - Impurities such as these make it difficult to solve the problem of low product quality.
[0005] There are few reports on existing technologies for low-cost production of APP using urea phosphate mother liquor. Summary of the Invention
[0006] In view of this, the main objective of the present invention is to provide a low-cost method for synthesizing water-soluble APP using urea phosphate mother liquor, as well as its application.
[0007] The raw urea phosphate mother liquor, a byproduct of the wet-process phosphoric acid synthesis of urea phosphate, is a saturated solution at 40°C and contains Ca. 2+ Mg 2+ Al 3+ Fe 3+ SO4 2- F - Impurities such as urea phosphate will cause a large amount of urea phosphate crystals and a small amount of water-insoluble precipitates to precipitate at room temperature. Therefore, the original urea phosphate mother liquor at room temperature needs to be treated before water-soluble ammonium polyphosphate can be prepared. Therefore, this invention uses the original urea phosphate mother liquor at room temperature as raw material. After heating, filtering, and concentrating, water-soluble APP is synthesized by high-temperature melt foaming polymerization under closed conditions. This achieves efficient utilization of the urea phosphate mother liquor and low-cost synthesis of water-soluble APP.
[0008] Specifically, a method for synthesizing water-soluble APP using urea phosphate mother liquor includes the following steps:
[0009] Purified urea phosphate mother liquor: The original urea phosphate mother liquor at room temperature is heated and filtered to obtain a clear urea phosphate filtrate mother liquor; the main component of the urea phosphate filtrate mother liquor is urea phosphate, and it also includes metal ions;
[0010] To obtain purified urea phosphate powder: the urea phosphate filtrate mother liquor is concentrated and dehydrated, cooled to obtain urea phosphate crystals, and the urea phosphate crystals are dried and pulverized to obtain purified urea phosphate powder; wherein the concentration and drying temperatures do not exceed 85°C.
[0011] Synthesizing APP: In a closed environment, the purified urea phosphate powder and urea are mixed in a molar ratio of 1:(0-0.4) and then subjected to melt foaming polymerization at a high temperature to synthesize APP. The polymerization temperature is 140-220℃ and the polymerization reaction time is 50-130min.
[0012] The step of purifying the urea phosphate mother liquor is mainly to remove water-insoluble precipitates from the original urea phosphate mother liquor at room temperature, so as not to affect the water-insoluble content of the synthesized ammonium polyphosphate. Specifically, the original urea phosphate mother liquor at room temperature is heated to form a urea phosphate crystal solution, resulting in a heated original urea phosphate mother liquor. A vacuum filtration device is then used to perform solid-liquid separation on the heated original urea phosphate mother liquor, filtering out the insoluble phosphate precipitates in the original urea phosphate mother liquor at room temperature, obtaining the clarified urea phosphate filter mother liquor. The preferred heating temperature for the original urea phosphate mother liquor at room temperature is 40-50℃. The main metal ion in the urea phosphate filter mother liquor is Ca. 2+ Mg 2+ Al 3+ Fe 3+ wait.
[0013] The original urea phosphate mother liquor at room temperature is obtained by cooling the original byproduct of the wet-process urea phosphate synthesis process to room temperature.
[0014] The main purpose of the step of obtaining purified urea phosphate powder is to obtain dry, purified urea phosphate powder. Because moisture in urea phosphate hinders the condensation reaction between urea phosphate and urea, increasing the energy required for the reaction, removing moisture from the original urea phosphate mother liquor at room temperature can reduce the impact of water on the polymerization product. Therefore, the step of obtaining purified urea phosphate powder must involve drying. The drying method can be atmospheric pressure drying, vacuum drying, freeze drying, etc. Furthermore, because urea phosphate undergoes high-temperature decomposition, the drying temperature should not exceed 85°C.
[0015] On the other hand, the water removed from the original urea phosphate mother liquor at room temperature forms distilled water, which can be used for other purposes to achieve zero discharge of process wastewater in industry.
[0016] Specifically, the step of obtaining purified urea phosphate powder includes: first, concentrating the urea phosphate filtrate mother liquor by vacuum rotary evaporation, and then cooling and crystallizing it to form urea phosphate crystals; then drying and pulverizing the urea phosphate crystals to obtain purified urea phosphate powder with a particle size of 0-75 μm.
[0017] Furthermore, to facilitate industrial implementation of this step, the step of obtaining purified urea phosphate powder includes: placing the clarified urea phosphate mother liquor into a vacuum rotary evaporator, evaporating and concentrating it at 60℃-80℃ for 45-90 minutes in a vacuum environment and at a rotation speed of 50-70 r / min, cooling and crystallizing to obtain urea phosphate crystals; first drying the urea phosphate crystals at 60℃-80℃, and then pulverizing them with a pulverizer to obtain purified urea phosphate powder with a particle size of 0-75 μm.
[0018] In the step of synthesizing APP, under a closed environment and high temperature, urea phosphate molecules decompose into urea and phosphate ions with externally supplied energy, which participate in the chain growth process respectively. After cooling, the aforementioned amorphous APP is synthesized. According to the above mechanism, dimer, trimer, tetramer, and even higher degrees of polymerization of APP are gradually generated. The chain growth process is shown below.
[0019]
[0020] To ensure full utilization of phosphorus in the raw materials, in the APP synthesis step, the molar ratio of purified urea phosphate powder to urea is preferably 1:(0-0.2), and the polymerization temperature is preferably 140-200℃. More preferably, the molar ratio of purified urea phosphate powder to urea is preferably 1:(0.05-0.2).
[0021] This invention discloses a water-soluble APP prepared by the above method, which has an amorphous structure, with ammonium polyphosphate as its main component, and includes trace elements with a mass percentage not exceeding 3%. The ammonium polyphosphate has a polymerization rate of 85%-96% and an average degree of polymerization of 3.0-3.8. The trace elements include Ca. 2+ Mg 2+ Al 3+ Fe 3+ SO4 2- F - Ingredients such as...
[0022] The total phosphorus content and total nitrogen content in the above-mentioned water-soluble APP are 48.20%-51.45% and 19.18-20.08%, respectively. According to the national standard HG / T 5939-2021 "Fertilizer Grade Ammonium Polyphosphate", the above-mentioned water-soluble APP meets the requirements of agricultural grade Class II products.
[0023] Therefore, another object of the present invention is to provide an application of the above-mentioned water-soluble APP in the field of fertilizer.
[0024] The nitrogen and phosphorus in the water-soluble APP reach agricultural grade and can be used as a water-soluble slow-release fertilizer, which has the functions of lowering the pH of alkaline soil and slow-releasing PO4. 3- It has the effects of reducing nitrogen and phosphorus loss. Additionally, the Ca in the urea phosphate mother liquor... 2+ Mg 2+ Al 3+ Fe 3+ SO4 2- F - After impurities are converted into the product APP, they can be used as micronutrients for plants to absorb, which is beneficial for promoting plant growth. Therefore, the water-soluble APP can be used to prepare water-soluble slow-release fertilizers.
[0025] The method for synthesizing water-soluble APP provided by this invention uses room-temperature raw urea phosphate mother liquor as raw material. After heating, filtration, and concentration, water-soluble APP is synthesized by high-temperature melt foaming polymerization under sealed conditions. The raw materials used in the above method are cheaper and more readily available than those in existing APP preparation processes, and it can solve the problem of difficult utilization of mother liquor in urea phosphate production. In addition, the above method is simpler and facilitates the efficient and low-cost industrial preparation of agricultural water-soluble APP products.
[0026] Furthermore, the method for synthesizing water-soluble APP provided by this invention enables full utilization of phosphorus in the raw materials. In the polymerization reaction, using purified urea phosphate powder as the raw material, the phosphorus utilization rate can reach 95%–99.9%, achieving full utilization of the urea phosphate mother liquor and fully recovering P2O5 from it. In addition to recovering nitrogen and phosphorus from the urea phosphate mother liquor, some trace elements, such as Ca, are also recovered. 2+ Mg 2+ Al 3+ Fe 3+ SO4 2- F - This reduces the cost of recovering urea phosphate mother liquor, thereby lowering the production cost of water-soluble APP; moreover, the entire synthesis process generates less exhaust gas, making it environmentally friendly. Furthermore, the water-soluble APP produced by the method provided by this invention can be used as a water-soluble slow-release fertilizer.
[0027] Therefore, the method provided by the present invention and the water-soluble APP synthesized by the above method realize the efficient recycling of urea phosphate mother liquor, which not only improves the economic added value of urea phosphate mother liquor, but also reduces the production cost of water-soluble APP fertilizer and enables industrial production. Attached Figure Description
[0028] Figure 1 A flowchart illustrating the preparation process of water-soluble APP provided in this embodiment of the invention.
[0029] Figure 2 The graph shows the effect of different polymerization reaction temperatures on the total phosphorus, polymerization rate, total nitrogen, and average degree of polymerization in the water-soluble APP product, as provided in the embodiments of the present invention.
[0030] Figure 3 This is a comparison chart showing the effect of different polymerization reaction temperatures on the sustained-release performance of water-soluble APP products, provided in an embodiment of the present invention.
[0031] Figure 4 The graph shows the effect of different raw material molar ratios on the total phosphorus, polymerization rate, total nitrogen, and average degree of polymerization of water-soluble APP in the product, as provided in the embodiments of the present invention.
[0032] Figure 5 The graph shows the effect of different reaction times on the total phosphorus, polymerization rate, total nitrogen and average degree of polymerization of water-soluble APP in the product, as provided in the embodiments of the present invention.
[0033] Figure 6 This is a photograph of water-soluble APP prepared by the synthesis method provided in the embodiments of the present invention.
[0034] Figure 7 This is a SEM-EDS analysis diagram of water-soluble APP synthesized under optimal process conditions according to the embodiments of the present invention.
[0035] Figure 8 This is a mapping analysis diagram of water-soluble APP synthesized under optimal process conditions according to the embodiments of the present invention.
[0036] Figure 9 The image shows the XRD spectrum of water-soluble APP synthesized under optimal process conditions according to the embodiments of the present invention.
[0037] Figure 10 The image shows the FT-IR spectrum of water-soluble APP synthesized under optimal process conditions according to the embodiments of the present invention.
[0038] Figure 11 APP provided for embodiments of the present invention 自制 A diagram showing the effect of pH on different soil types.
[0039] Figure 12 APP provided for embodiments of the present invention 自制 Figures showing the changes in available phosphorus content and water-soluble phosphorus content in hydrolyzed soils; Figure (a) shows the changes in available phosphorus content in alkaline soils, (b) in neutral soils and (c) in acidic soils, and Figure (d) shows the changes in water-soluble phosphorus content in alkaline soils, (e) in neutral soils and (f) in acidic soils.
[0040] Figure 13 APP provided for embodiments of the present invention 自制 A diagram showing the nitrogen and phosphorus leaching characteristics of Henan alluvial soil. Detailed Implementation
[0041] The technical solution of the present invention will be further described in detail below through specific embodiments.
[0042] Unless otherwise specified, all terms used in this invention are commonly used in the relevant field. The technical means employed in the embodiments, such as preparation processes and testing methods, are conventional methods well-known to those skilled in the art. All reagents and products used are commercially available. The source, trade name, and, where necessary, the components of any reagents are indicated upon their first appearance.
[0043] The measurement methods for the parameters or indicators involved in the following embodiments are as follows:
[0044] Total nitrogen: The nitrogen content in ammonium polyphosphate products was determined by titration after distillation, in accordance with standard GB / T 8572-2010.
[0045] Total phosphorus: The content of total phosphorus P2O5 in APP products was determined by the quinomolybdate gravimetric method (arbitration method) according to standard HG / T 2770-2020.
[0046] PO4 3- The PO4 content in the product was determined using the molybdenum yellow colorimetric method. 3- content.
[0047] Degree of polymerization: The average degree of polymerization of the synthesized APP product was determined by end-group titration.
[0048] Polymerization rate: The percentage of polymerized phosphorus in the product relative to the total phosphorus content, i.e., the ratio of the difference between the total phosphorus content and the orthophosphate content (both calculated as P2O5) to the former. Refer to standard HG / T5939-2021.
[0049] Phosphorus utilization rate: The ratio of total phosphorus content in ammonium polyphosphate products to total phosphorus content in mother liquor raw materials.
[0050] Phosphorus speciation analysis: The phosphorus speciation of ammonium polyphosphate was analyzed using the ion exchange resin method.
[0051] Solubility: The solubility of the sample was determined using a dynamic method based on solvent quantification.
[0052] Slow-release performance (static water slow-release): Under constant temperature conditions, a fixed mass of the product fertilizer is added to a certain volume of water for cultivation, and the nutrient dissolution is measured at a specific time. For details, please refer to the standard GB / T23348-2009.
[0053] Please see Figure 1 This invention provides a method for synthesizing water-soluble APP, comprising:
[0054] I. Purification of urea phosphate mother liquor
[0055] A raw urea phosphate mother liquor, a byproduct of a wet synthesis of phosphoric acid, is provided. This mother liquor is cooled to room temperature to obtain a room-temperature raw urea phosphate mother liquor. The composition of the raw urea phosphate mother liquor is shown in Table 1.
[0056] First, the original urea phosphate mother liquor at room temperature was heated to 45°C to dissolve the urea phosphate crystals, resulting in a heated urea phosphate mother liquor. Then, under room temperature conditions, a vacuum filtration device was used to separate the solid and liquid phases of the heated urea phosphate mother liquor, filtering out the insoluble white phosphate precipitate and collecting the clear urea phosphate filtrate. The solid and liquid phases of the urea phosphate filtrate mother liquor were analyzed, and the composition results are shown in Table 2.
[0057] Table 1 Composition of the original urea phosphate mother liquor
[0058]
[0059] Table 2 Solid-liquid mass fraction of urea phosphate filtration mother liquor
[0060] Filter residue 8.70 filtrate 91.30
[0061] II. Obtaining purified urea phosphate powder
[0062] The clarified urea phosphate filtrate mother liquor was placed in a vacuum rotary evaporator, with the volume of the mother liquor approximately one-third of the evaporator's volume. Using a vacuum pump to provide vacuum conditions, the mixture was heated at 70°C for 60 minutes at a rotary evaporator speed of 60 r / min, followed by cooling and crystallization to obtain urea phosphate crystals. These crystals were then dried at 80°C and pulverized using a rotary pulverizer to obtain purified urea phosphate powder with a particle size of 0-75 μm. The main component of this powder is urea phosphate, along with small amounts of phosphate and sulfate.
[0063] III. Synthesizing Apps
[0064] The purified urea phosphate powder and urea are mixed in a molar ratio of 1:(0-0.4) and placed in a closed reactor. The product APP is synthesized by melt foaming polymerization in a closed high-temperature environment. The polymerization temperature is 140-220℃ and the polymerization reaction time is 50-130min. The APP produced from the high-temperature reactor is cooled and pulverized to obtain APP powder.
[0065] Studies have revealed that polymerization temperature, the ratio of purified urea phosphate powder and urea as raw materials, and polymerization time all significantly influence the preparation of water-soluble APP. The following single-factor analysis further illustrates the impact of these factors on the water-soluble APP product.
[0066] (1) Effect of polymerization reaction temperature
[0067] Experimental conditions: The purified urea phosphate powder was used as the raw material, without the addition of urea as a condensing agent. The polymerization reaction temperatures were 120℃, 140℃, 160℃, 180℃, 200℃, and 220℃, and the polymerization reaction time was 90 min.
[0068] The total phosphorus, polymerization rate, total nitrogen, and average degree of polymerization of the water-soluble APP prepared under the above experimental conditions were tested, and the effect of polymerization temperature on its sustained-release performance was also measured. Figures 2-3 As shown.
[0069] from Figure 2 As can be seen, as the reaction temperature gradually increases, the amount of ammonia volatilization gradually increases, leading to a gradual increase in the mass fraction of total phosphorus in the reaction system, while the mass fraction of total nitrogen gradually decreases, but the overall difference is not significant.
[0070] from Figure 2 (a) It can be seen that when the temperature is 120℃, the polymerization rate of the product is relatively low at 87.54%. This is because the reaction temperature is too low, and the energy provided for the polymerization reaction is insufficient, which prevents the raw materials from undergoing a good polymerization and foaming reaction. As the reaction temperature gradually increases, the polymerization rate of the product gradually increases and gradually tends to stabilize. However, when the temperature is greater than 200℃, the polymerization rate of the product shows a decreasing trend. This is because the metal ions in the purified urea phosphate powder combine with phosphate ions to form phosphates, which prevents the polymerization reaction from proceeding.
[0071] from Figure 2 (b) It can be seen that the average degree of polymerization of the product shows a trend of first increasing and then decreasing. When the temperature is below 160℃, as the temperature increases, the polymerization reaction rate gradually accelerates, the ammonia overflow rate increases, and the ammonia partial pressure increases, promoting the forward polymerization reaction and leading to a gradual increase in the average degree of polymerization of the product. When the reaction temperature is above 160℃, the polycondensation reaction first occurs on the inner wall of the polytetrafluoroethylene lining of the high-pressure hydrothermal reactor, generating highly polymerized APP. Highly polymerized APP is a good flame retardant material, which prevents heat transfer to intermediate materials, resulting in incomplete polymerization at the raw material center, thus causing a downward trend in the average degree of polymerization of the product.
[0072] from Figure 3 It can be seen that as the synthesis temperature increases, the hydrolysis rate of the APP product decreases, while the sustained-release performance gradually increases. When the reaction temperature is 120℃ and 140℃, the sustained-release trend is similar, with the total phosphorus content hydrolyzed after 21 days reaching 17.328% and 15.478%, respectively. When the temperature exceeds 160℃, the hydrolysis rate gradually decreases, and the sustained-release performance is significantly better than that of the APP product prepared at lower temperatures. The polymerization rates of APP synthesized at 160℃ and 180℃ are similar, and the difference in their hydrolysis and sustained-release performance is not significant.
[0073] Therefore, considering the entire APP synthesis system, reaction energy consumption, and economic cost, a reaction temperature of 160℃ is the optimal reaction temperature. Under these conditions, the synthesized product APP has a total phosphorus content of 52.32% and a total nitrogen content of 19.83%, a polymerization rate of 92.72%, and an average degree of polymerization of 3.22.
[0074] (2) Influence of raw material ratio
[0075] During the polymerization reaction, the partial pressure of ammonia gas affects the relevant properties of the product APP. Urea decomposes upon heating, releasing ammonia gas, which provides a certain partial pressure for the reaction and can partially neutralize polyphosphoric acid, thus contributing to an increase in the average degree of polymerization.
[0076] Experimental conditions: polymerization temperature was 160℃, polymerization time was 90 min, and the molar ratio of the purified urea phosphate powder to urea was 1:0, 1:0.1, 1:0.2, 1:0.3, and 1:0.4, respectively. The effect of the raw material ratio on the synthesized product APP is shown in the figure below. Figure 4 As shown.
[0077] from Figure 4 It can be seen that as the amount of urea added gradually increases, the total phosphorus mass fraction of the product APP gradually decreases, while the total nitrogen mass fraction gradually increases. The average degree of polymerization and polymerization rate of APP both show a trend of first increasing and then decreasing, because when the urea molar ratio increases, NH... 4+ The increased content provides more adsorption sites for phosphorus. Urea acts as a condensing agent; the ammonia gas released during thermal decomposition provides a certain ammonia partial pressure for the condensation reaction, which is beneficial for the forward reaction and helps form long APP chains, thus increasing the average degree of polymerization. However, as the urea molar ratio continues to increase, the average degree of polymerization and polymerization rate show a decreasing trend. The main reason is that with increased urea content, the polymerization reaction requires more external energy, resulting in less complete reaction under the same reaction time and temperature. Furthermore, with increased urea addition, two molecules of urea will generate the byproduct biuret, leading to decreased product purity, affecting the normal progress of the polymerization process, and causing a downward trend in the average degree of polymerization and polymerization rate, ultimately reducing the quality of the APP product.
[0078] As Figure 4 As shown, with the gradual increase of the molar ratio of urea phosphate to urea, the residual urea content in the APP synthesis system gradually increases. From the comprehensive analysis of the average degree of polymerization and polymerization rate of APP, the optimal molar ratio of urea phosphate to urea is 1:0.1. Under this condition, the total phosphorus content and total nitrogen content of the product APP are 51.45% and 20.08%, respectively, the polymerization rate is 93.78%, and the average degree of polymerization is 3.66.
[0079] (3) Effect of polymerization reaction time
[0080] Experimental conditions: polymerization temperature was 160℃, molar ratio of urea phosphate to urea was 1:0.1, and polymerization times were 50 min, 70 min, 90 min, 110 min, and 130 min, respectively. The effect of polymerization time on the synthesized product APP is shown in the figure. Figure 5 As shown.
[0081] from Figure 5 It can be seen that when the polymerization reaction time is 50 min, the provided heat is insufficient to allow the materials to react, resulting in incomplete foaming and a lower product polymerization rate and average degree of polymerization. As the reaction time increases, the total phosphorus mass fraction gradually increases, while the total nitrogen mass fraction gradually decreases. This is because the amount of ammonia escaping gradually increases with the increase in reaction time. The average degree of polymerization of APP shows a trend of first increasing and then decreasing. This is partly because, with the increase in reaction time, the mass of the byproduct biuret gradually increases, affecting the quality of the APP product and leading to a gradual decrease in the average degree of polymerization. On the other hand, excessive heating time can cause the generated product to coke and turn yellow, thus affecting the improvement of the average degree of polymerization. The polymerization rate of the APP product tends to plateau after 90 min, possibly because the ammonia atmosphere in the reaction system is maintained in a relatively balanced state, with NH4... + The adsorption sites are basically saturated with phosphorus, which leads to a slow increase in the polymerization rate of the product APP, which almost reaches a plateau.
[0082] Without affecting the quality of water-soluble APP products, the APP products polymerized in this embodiment of the invention basically meet the requirements of agricultural grade Class II products. To increase the phosphorus and nitrogen content of the APP products and meet the P2O5 content requirements for Class II APP as specified in HG / T 5939-2021, an orthogonal experiment was designed below to further investigate the optimal reaction parameters of this embodiment of the invention.
[0083] According to the APP synthesis method provided in the embodiments of the present invention, the parameters of its orthogonal experiment are shown in Table 3, and the orthogonal experimental design and results of the synthesized APP are shown in Table 4.
[0084] Table 3 Orthogonal experimental design for APP preparation
[0085] 1 140 1:0 70 2 160 1:0.1 90 3 180 1:0.2 110 4 220 1:0.3 130
[0086] Table 4. Orthogonal experimental design and results of APP synthesis
[0087] 1 A1 B1 C1 52.95 87.59 --- 2 A1 B2 C2 52.15 89.95 --- 3 A1 B3 C3 51.58 90.56 --- 4 A2 B1 C2 52.53 92.58 3.223 5 A2 B2 C3 51.70 94.21 3.796 6 A2 B3 C1 50.55 93.47 --- 7 A3 B1 C3 52.58 92.74 3.052 8 A3 B2 C1 50.45 92.99 --- 9 A3 B3 C3 50.38 93.65 ---
[0088] To obtain APP products with superior performance and higher total phosphorus content, making them more competitive in the market, we selected products with a total phosphorus content greater than 51% and a polymerization rate greater than 91% as the benchmarks. We screened products with conditions 4, 5, and 7, and then tested the sustained-release performance of these products.
[0089] The optimal process conditions were determined to be a reaction temperature of 160℃, a urea phosphate / urea molar ratio of 1:0.1, and a reaction time of 110 min.
[0090] Therefore, considering the results of the single-factor and orthogonal experiments, the optimal process conditions are: a reaction temperature of 160℃, a raw material ratio of purified urea phosphate powder to urea of 1:0.1, and a reaction time of 110 min. Under this synthesis process, the product APP has the following appearance: Figure 6 As shown, it is a white powder. The SEM-EDS analysis results of the product APP are as follows: Figure 7 As shown, the mapping analysis results are as follows: Figure 8 As shown. From Figure 7 and Figure 8 As can be seen from the data, the APP synthesized under the optimal process includes elements such as P, O, Mg, Al, Ca, and Fe. The total phosphorus content and total nitrogen content are 51.70% and 19.46%, respectively, the polymerization rate is 94.21%, and the average degree of polymerization is 3.79.
[0091] The XRD and FT-IR spectra of APP synthesized under these optimal process conditions are as follows: Figure 9 and Figure 10 As shown. Among them, Figure 9 The XRD spectrum shown further indicates that the APP product synthesized by the method provided by this invention is different from the currently available crystalline type I and crystalline type II products; it is an amorphous state and lacks a specific crystal structure. Figure 10 The FT-IR spectrum shown shows that at 3030 cm⁻¹ -1 The broad absorption peak centered on NH4 is considered to be NH4 + The asymmetric stretching peak is at 1240 cm⁻¹. -1 The peak is caused by the tensile vibration of P=O, 600-900 cm⁻¹ -1 The nearby peak corresponds to the tensile vibration of the POP. Furthermore, at 1690 cm⁻¹... -1 The nearby C=O absorption peak represents residual urea in the reaction system.
[0092] Furthermore, experiments measuring water-insoluble matter revealed that the synthesized APP product meets the standards for use as a water-soluble fertilizer, and it exhibits good slow-release properties, capable of releasing calcium that can be absorbed by crops. 2+ Mg 2+ Al3+ Fe 3+ It contains trace nutrients and can be used as a water-soluble APP fertilizer.
[0093] application
[0094] This embodiment provides an application of the aforementioned water-soluble APP in the fertilizer field. Specifically, the following experiments further verify that the water-soluble APP provided by this invention has significant application prospects in water-soluble slow-release fertilizers.
[0095] The tested soils included calcareous strongly alkaline soil, alluvial weakly alkaline to neutral soil, and weakly acidic soil, selected from Shihezi City, Xinjiang Uygur Autonomous Region (44°22′N, 85°99′E), Zhengzhou City, Henan Province (44°22′N, 85°99′E), and Sanyuan City, Fujian Province (26°13′N, 117°36′E), respectively. All three types of soils are typical soils widely distributed in China. The basic physicochemical properties of the soils are shown in Table 5.
[0096] Table 5 Basic Physicochemical Properties of Soil
[0097]
[0098] The following experiments use APP synthesized under the optimal process described in the above examples. 自制 Using traditional fertilizers such as ammonium dihydrogen phosphate (MAP, Tianjin Kemeio Chemical Reagent Co., Ltd.) and urea (Urea, Anyang Chemical Group Co., Ltd.), as well as similar products on the market such as ammonium polyphosphate (APP), the samples were analyzed. 市售 (Yunnan Tianyao Chemical Co., Ltd.) is used as a control. The basic properties of the fertilizer are shown in Table 6.
[0099] Table 6. Basic physicochemical properties of the tested fertilizers
[0100]
[0101] The following further illustrates the hydrolysis characteristics of the self-made APP provided by the embodiments of the present invention in different soil environments and the leaching and loss patterns of different types of fertilizers in typical alluvial soil in Henan.
[0102] (1) APP 自制 The product's effect on the pH of alkaline soils
[0103] APP has a regulatory effect on soil pH, and pH is an important indicator reflecting the physicochemical properties of soil. (The last sentence appears to be incomplete and possibly refers to a different product / service.) 自制An equal amount of soil was applied to the test soil, and the soil was weighed every two days. Deionized water was added to maintain a field water holding capacity of 40%. Soil was extracted with deionized water at a ratio of 1:2.5 at incubation periods of 2, 5, 8, 15, 20, 30, 35, and 40 days. The pH value of the extract was measured using a precision pH meter. The results are as follows: Figure 11 As shown.
[0104] Figure 11 Indicates: APP 自制 The application of this product has a good effect on improving alkaline soils. APP 自制 Fifteen days after application to the soil, the pH value of the alkaline soil decreased to 7.71. As time went on, APP... 自制 The effect of APP on soil pH improvement continued to strengthen. After 40 days of application, the pH value of alkaline soil decreased from 8.96 to 7.39, a reduction of 1.57. Overall, APP... 自制 It has different effects on the pH value of different soil types: the regulating effect is more obvious on alkaline soils, while the improving effect on acidic soils is relatively weaker on alkaline soils.
[0105] (2) Soil slow-release characteristics of the product
[0106] Three typical soil samples were air-dried, plant debris and stones were removed, and the samples were sieved through a 2mm standard soil sieve. The tested fertilizers were applied as basal fertilizers in a single application to culture cups (11.0cm long, 11.0cm wide, 11.0cm high), specifically: control (CK) without phosphate fertilizer, ammonium dihydrogen phosphate (MAP), and ammonium polyphosphate (APP). 市售 )APP 自制 Each treatment was repeated twice, for a total of 288 cups. An equal amount of P2O5 was maintained and mixed with 300g of soil, and each cup was incubated at 25℃. Samples were weighed every two days, and deionized water was added to maintain field capacity at 40%. Soil samples were collected after 2, 5, 8, 15, 20, 30, 35, 40, 50, 60, 70, and 80 days, and the contents of available phosphorus and water-soluble phosphorus were determined. The results are as follows: Figure 12 As shown.
[0107] from Figure 12 (a) to 12(e) show that: relative to MAP, APP 市售 and APP 自制 It belongs to the category of slow-release polyphosphate fertilizers. Its slow hydrolysis release mechanism helps reduce the chance of phosphate fertilizer binding with metal ions in the soil. In the early stages after application, it mainly moves in the soil as polymerized phosphorus, interacting almost no with mineral particles. As the cultivation time increases, APP... 市售 and APP 自制As the phosphorus gradually hydrolyzes, the content of both available phosphorus and water-soluble phosphorus shows a slow upward trend.
[0108] After 50 days of cultivation, the APP 市售 The available phosphorus content increased from 30.89 mg / kg to 111.45 mg / kg in alkaline, 32.85 mg / kg to 115.29 mg / kg in neutral, and 35.87 mg / kg to 105.63 mg / kg in acidic soils; the water-soluble phosphorus content increased from 22.32 mg / kg to 51.87 mg / kg in alkaline, 15.76 mg / kg to 35.76 mg / kg in neutral, and 11.25 mg / kg to 27.50 mg / kg in acidic, neutral, and 35.76 mg / kg in neutral, and 35.76 mg / kg in acidic soils. 自制 The available phosphorus content increased from 35.41 mg / kg to 148.23 mg / kg in alkaline, neutral, and acidic soils, from 33.69 mg / kg to 128.76 mg / kg, from 39.54 mg / kg to 110.79 mg / kg, and from 23.58 mg / kg to 72.75 mg / kg in alkaline, neutral, and acidic soils, from 17.63 mg / kg to 42.99 mg / kg, and from 11.25 mg / kg to 27.50 mg / kg, respectively.
[0109] In acidic soils, APP 市售 With APP 自制 The difference in slow-release performance is not significant. However, the difference in slow-release performance gradually increases with increasing alkalinity. This is because alkaline soils contain higher levels of salt ions, which affect fertilizer decomposition and increase the rate of phosphorus hydrolysis. The rate of phosphorus fixation in soil mainly depends on phosphorus concentration. Acidic soils promote the decomposition of APP, leading to an increase in PO4. 3- As the concentration increases, a large amount of phosphorus is fixed by metal ions, thus reducing the increase in phosphorus content. APP 市售 APP 自制 Compared to MAP, both can significantly improve phosphorus availability. They are more suitable for alkaline soils, with available phosphorus content in alkaline soils increasing by 22.75% and 29.46% respectively compared to acidic soils.
[0110] Therefore, at 25°C, compared to MAP, APP 市售 and APP 自制 It can significantly improve the availability of phosphate fertilizer in alkaline soils, slow down the rate of phosphorus fixation, and polymerized phosphorus will complex with calcium, aluminum, iron and other ions to form effective phosphorus aggregates. These aggregates will gradually hydrolyze into PO4 in the soil. 3- It is available for plants to absorb and utilize.
[0111] (3) The nitrogen and phosphorus leaching characteristics of the product on Henan soil
[0112] An existing leaching column device filled with soil from Chaoyang, Henan Province, was used to simulate 100 mL of rainfall. Leachate was collected and tested on the same day after 24 hours when there was no significant leakage. To prevent soil moisture evaporation during the intervals between leaching operations, the PVC pipe was sealed with plastic wrap. Leaching was performed at 1, 3, 5, 10, 15, 20, 25, 30, and 40 days, and the total nitrogen and PO4 content of the leachate was measured. 3- The content, the results are as follows Figure 13 As shown.
[0113] Figure 13 The results showed that urea and MAP had cumulative total nitrogen leaching losses of up to 67.53% and 50.72% respectively on day 1. The cumulative percentage of total nitrogen loss from urea stabilized on day 10 and reached 73.1% after 40 days of leaching; the cumulative percentage of total nitrogen leaching from MAP reached 74.20% after 40 days. Compared to urea and MAP, APP... 市售 and APP 自制 It showed good performance in reducing nitrogen leaching loss, with cumulative total nitrogen loss percentages of 55.55% and 56.71% over 40 days, respectively. (APP) 市售 and APP 自制 Compared to urea, the cumulative percentage of total nitrogen loss decreased by 24.00% and 22.42%, respectively; APP 市售 and APP 自制 Compared to MAP, the cumulative percentage of total nitrogen loss decreased by 25.13% and 23.57%, respectively. The data demonstrates that the product APP (App) provided in this embodiment of the invention... 自制 Compared to traditional fertilizers, it can reduce nitrogen loss to a certain extent.
[0114] Traditional fertilizers like MAP showed similar trends in phosphorus and nitrogen loss concentrations, with phosphorus loss reaching a high of 341.28 mg / 100 mL on day 1, gradually decreasing and stabilizing thereafter. APP, on the other hand... 市售 APP 自制 The phosphorus loss concentration showed a gradual upward trend. This is because both fertilizers contain polymerized phosphorus, and over time, the fertilizer undergoes hydrolysis, leading to an increase in PO4 concentration in the soil. 3- Increased phosphorus content. Phosphorus flows into lakes via runoff, posing a risk of environmental pollution; therefore, attention should be paid to fertilizer application rates. Furthermore, phosphorus leaching is lower than nitrogen leaching because phosphorus is more easily fixed in the soil and converted into occluded phosphorus, exhibiting poor mobility.
[0115] In summary, the method for synthesizing water-soluble APP provided in this embodiment of the invention uses room-temperature raw urea phosphate mother liquor as raw material. After heating, filtration, and concentration, water-soluble APP is obtained by high-temperature melt foaming polymerization under sealed conditions. The water-soluble APP synthesized by the above method has an amorphous structure, and its main component is ammonium polyphosphate, and it includes trace elements with a mass percentage not exceeding 3%. The polymerization rate of the ammonium polyphosphate is 85%-96%, and the average degree of polymerization is 3.0-3.8. The trace elements include at least Ca. 2+ Mg 2+ Al 3+ Fe 3+ SO4 2- F - It can be used as a water-soluble slow-release fertilizer.
[0116] Therefore, the method provided in this embodiment of the invention has the advantages of readily available raw materials and simple process, realizing the efficient recovery and utilization of urea phosphate mother liquor and solving the problem of the difficulty in utilizing urea phosphate mother liquor during production. The above method converts the metal ion impurities in the existing urea phosphate mother liquor into micronutrients that can be absorbed by plants in water-soluble APP products, which is beneficial to promoting plant growth. The above synthesis method not only increases the economic added value of urea phosphate mother liquor but also reduces the production cost of water-soluble APP fertilizer and enables industrial-scale production.
[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.
Claims
1. A method for synthesizing water-soluble ammonium polyphosphate using urea phosphate mother liquor, comprising the following steps: Purification of urea phosphate mother liquor: The original urea phosphate mother liquor at room temperature is heated to 40-50℃ to dissolve the urea phosphate crystals, forming a heated original urea phosphate mother liquor; the heated original urea phosphate mother liquor is then subjected to solid-liquid separation using a vacuum filtration device to filter out the insoluble phosphate precipitate from the original urea phosphate mother liquor at room temperature, yielding a clear urea phosphate filtrate mother liquor; the metal ion in the urea phosphate filtrate mother liquor is Ca. 2+ Mg 2+ Al 3+ Fe 3+ ; To obtain purified urea phosphate powder: The urea phosphate filtrate mother liquor was concentrated and dehydrated using vacuum rotary evaporation. After cooling, urea phosphate crystals were obtained. These crystals were then dried and pulverized to obtain purified urea phosphate powder with a particle size greater than 0 and less than or equal to 75 μm. The temperature of the concentration and drying processes shall not exceed 85°C; Synthesis of ammonium polyphosphate: In a closed environment, the purified urea phosphate powder and urea are mixed at a molar ratio of 1:(0.05-0.2), and a melt foaming polymerization reaction is carried out at high temperature to synthesize amorphous ammonium polyphosphate. The polymerization rate of the ammonium polyphosphate is 85%-96%, the average degree of polymerization is 3.0-3.8, and it includes trace elements with a mass percentage not exceeding 3%. The polymerization temperature is 140-200℃, and the polymerization reaction time is 50-130 min.
2. The method according to claim 1, characterized in that, The steps for obtaining purified urea phosphate powder include: placing the clarified urea phosphate mother liquor into a vacuum rotary evaporator, evaporating and concentrating it at 60℃-80℃ for 45-90 min in a vacuum environment and at a rotation speed of 50-70 r / min, cooling and crystallizing to obtain urea phosphate crystals; first drying the urea phosphate crystals at 60℃-80℃, and then pulverizing them with a pulverizer to obtain the purified urea phosphate powder.
3. The method according to claim 1 or 2, characterized in that, The original urea phosphate mother liquor at room temperature is obtained by cooling the original byproduct of the wet-process urea phosphate synthesis process to room temperature.
4. A water-soluble ammonium polyphosphate synthesized by the method described in any one of 1-3.
5. The water-soluble ammonium polyphosphate according to claim 4, characterized in that, The trace elements include at least Ca. 2+ Mg 2+ Al 3+ Fe 3+ SO4 2- F - .
6. The application of the water-soluble ammonium polyphosphate as described in claim 4 or 5 in the field of fertilizers.
7. The application according to claim 6, wherein the water-soluble ammonium polyphosphate is used in the preparation of water-soluble slow-release fertilizer.