High-purity urea phosphate and a method for preparing the same

Abstract

The application belongs to the technical field of phosphorus chemical industry, and provides a preparation method of high-purity urea phosphate. The preparation method comprises the following steps: (1) preheating wet-process phosphoric acid, preparing urea aqueous solution and preheating, and preparing calcium hydroxide suspension; (2) adding the calcium hydroxide suspension into the wet-process phosphoric acid drop by drop, keeping the pH of the system at 0.8-1.8, and generating calcium phosphate nanocrystals in situ; (3) adding the urea aqueous solution into the calcium phosphate nanocrystals for reaction, simultaneously starting the nanofiltration membrane system for online circulation impurity removal, and obtaining a reaction liquid; (4) constant-temperature static setting crystallization of the reaction liquid; and (5) separation, washing and drying to obtain the high-purity urea phosphate. The preparation method uses the wet-process phosphoric acid as a raw material, realizes one-step high-purity crystallization through acid in-situ calcium phosphate nanocrystal induction and reaction-nanofiltration collaborative impurity removal, and has no organic additive residue; the high-purity urea phosphate with super-high purity, regular crystal form and extremely low impurities can be prepared, and is suitable for high-end application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus chemical technology, specifically relating to a high-purity urea phosphate and its preparation method. Background Technology

[0002] Urea phosphate is an important organophosphate compound that integrates nitrogen and phosphorus nutrients. It possesses characteristics such as good water solubility, mild acidity, and strong complexing ability, making it irreplaceable in applications such as ruminant feed additives, high-efficiency nitrogen-phosphorus compound fertilizers, industrial acidic cleaning agents, metal surface treatment agents, and flame-retardant material intermediates. With the rapid development of high-end manufacturing, fine chemicals, modern agriculture, and electronic chemicals industries, the market demand for high-purity, high-crystallinity, and low-impurity urea phosphate products continues to increase, especially with more stringent control requirements for harmful impurities such as fluorine, iron, aluminum, and heavy metals.

[0003] Currently, the industrial production of urea phosphate mainly uses wet-process phosphoric acid or thermal-process phosphoric acid as raw materials. These materials undergo a complexation reaction with urea under heating conditions, followed by cooling crystallization, solid-liquid separation, and drying to obtain the final product. Wet-process phosphoric acid is the preferred raw material for large-scale urea phosphate production due to its wide availability, low production cost, and large production capacity. However, existing production technologies have long faced several insurmountable challenges, severely restricting the stable preparation of high-purity urea phosphate.

[0004] First, wet-process phosphoric acid itself contains various trace impurity ions such as fluorine, iron, aluminum, magnesium, sulfate, and heavy metals. During the crystal growth of urea phosphate, these ions can easily enter the crystal through adsorption, encapsulation, and lattice substitution. Conventional methods such as filtration, decolorization, and settling can only remove some suspended impurities and cannot achieve deep removal of ionic impurities. This results in low product purity, high impurity content, and poor storage stability, making it difficult to meet the requirements of high-end applications.

[0005] Secondly, in order to improve crystal form and particle size distribution, traditional processes usually add organic crystallization aids such as polyethylene glycol, polyacrylate, and lignosulfonate. These aids can only play a role in dispersing, reducing viscosity, or inhibiting agglomeration on the crystal surface. They cannot prevent impurities from entering the crystal lattice from the crystal growth mechanism level. There is a clear upper limit to the improvement of purity, making it difficult to achieve stable preparation of ultra-high purity products. In addition, the residue of organic aids will also affect the applicability of the product in electronic and food-grade fields.

[0006] Furthermore, existing crystallization processes generally employ complex operations such as gradient cooling, segmented temperature control, and multi-stage variable-speed stirring. These processes are not only lengthy, energy-intensive, and difficult to control, but also cause uneven crystal growth, increased crystal defects, and exacerbated impurity encapsulation. Simultaneously, impurities accumulate in the mother liquor after multiple cycles, further degrading product quality. This necessitates the discharge of a portion of the mother liquor to maintain system stability, resulting in raw material loss, reduced yield, and environmental pressure.

[0007] Finally, to obtain high-purity urea phosphate, existing technologies often only allow the use of high-cost thermal phosphoric acid as raw material, or secondary or even multiple recrystallizations of the crude product. Although such methods can improve purity to some extent, they significantly increase energy consumption, solvent consumption, and equipment investment, reduce the overall yield, and greatly increase production costs, making it impossible to achieve low-cost, high-efficiency, and green large-scale industrial production.

[0008] In summary, how to simplify the crystallization process, improve crystal regularity, and reduce impurity content to prepare high-purity urea phosphate under a low-cost wet phosphoric acid route has become an urgent technical challenge. Summary of the Invention

[0009] To address the aforementioned shortcomings in the existing technology, the present invention aims to provide a high-purity urea phosphate and its preparation method. This preparation method uses wet-process phosphoric acid as raw material and achieves one-step high-purity crystallization through acidic in-situ nano-calcium phosphate seed induction and reaction-nanofiltration synergistic impurity removal, without the need for secondary recrystallization and without organic additive residues. It can prepare urea phosphate with ultra-high purity, regular crystal form, and extremely low impurities, making it suitable for high-end application scenarios.

[0010] To achieve the above objectives, the solution adopted by the present invention is as follows: A method for preparing high-purity urea phosphate includes: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 52%-55% into a reaction vessel and stirring and preheating; preparing a urea aqueous solution with a urea mass fraction of 62%-64% and preheating; preparing a calcium hydroxide suspension with a concentration of 0.5 mol / L; (2) adding calcium hydroxide suspension dropwise to wet phosphoric acid according to a Ca / P molar ratio of 0.01-0.02, maintaining the pH of the system at 0.8-1.8, and generating nano-calcium phosphate seeds with a particle size of 5-20 nm in situ; (3) adding urea aqueous solution to the nano-calcium phosphate seeds according to a phosphoric acid to urea molar ratio of 1:1.02-1.05, and simultaneously turning on the nanofiltration membrane system for online circulation and impurity removal for 2.0-2.5 h to obtain a reaction solution; (4) transferring the reaction solution into a crystallization tank. (5) Crystallize at a constant temperature of 45-50℃ for 2.5-3.5h; (6) Separate, wash and dry to obtain urea phosphate.

[0011] Furthermore, in a preferred embodiment of the present invention, in step (2), the Ca / P molar ratio is 0.015.

[0012] Furthermore, in a preferred embodiment of the present invention, in step (1), wet phosphoric acid is preheated to 65-70°C, stirred at 20-30 r / min, and stirred stably for 10-15 min.

[0013] Furthermore, in a preferred embodiment of the present invention, in step (1), the urea aqueous solution is preheated to 50-60°C.

[0014] Furthermore, in a preferred embodiment of the present invention, in step (2), the reaction temperature is 65-70°C, the stirring speed is 20-30 r / min, the dropping time is 40-60 min, and the stirring is maintained at the temperature for 30 min.

[0015] Furthermore, in a preferred embodiment of the present invention, in step (3), the reaction temperature is 75-80°C, the dropping time is 90-120 min, and the reaction is kept at the temperature for 2 h.

[0016] Furthermore, in a preferred embodiment of the present invention, in step (3), the nanofiltration membrane has a molecular weight cutoff of 100 Da, an operating pressure of 1.2-1.6 MPa, and a circulation flow rate of 40-50 L / h.

[0017] Furthermore, in a preferred embodiment of the present invention, in step (5), the centrifugation speed is 3000-4000 r / min, and the centrifugation time is 10-20 min; the washing water is ultrapure water, and the amount used is 5-10% of the wet mass of the crystal.

[0018] Furthermore, in a preferred embodiment of the present invention, the drying temperature is 55-60℃, the vacuum degree is -0.085--0.095MPa, and the drying time is 2.0-2.5h.

[0019] A high-purity urea phosphate is prepared using the above-described method for preparing high-purity urea phosphate.

[0020] The beneficial effects of the high-purity urea phosphate and its preparation method provided by this invention are: (1) The preparation method of high-purity urea phosphate provided by the present invention generates nano-calcium phosphate seed crystals in situ in the strong acidic system of urea phosphate. The seed crystal structure is stable, insoluble, and does not change crystals. It has a high degree of matching with the orthorhombic crystal system of urea phosphate, and can achieve directional induction from the crystal growth starting point. It excludes impurity ions such as fluorine, iron, aluminum, and magnesium from the inside of the crystal lattice, and solves the industry problem of traditional processes being unable to prevent crystal embedding from the root. It forms a dual guarantee of pretreatment impurity removal and crystal lattice impurity suppression with wet phosphoric acid raw material purification, which significantly improves the purity and crystal integrity of the product. (2) The preparation method of high-purity urea phosphate provided by the present invention combines complexation reaction with online impurity removal by nanofiltration membrane, so as to realize the simultaneous generation and removal of ionic impurities, avoid the accumulation of impurities caused by mother liquor circulation, and form a synergistic impurity removal system of internal repulsion and external removal with seed-induced crystallization; at the same time, constant temperature one-step crystallization is used instead of traditional gradient cooling, so that the crystal growth is more uniform, the crystal shape is more regular, and the particle size is more concentrated, which significantly improves the product's fluidity, water solubility and stability, and no organic additives are used throughout the process, so there is no risk of residue, which can meet the high-purity application scenarios such as electronics, food, and high-end cleaning. (3) The preparation method of high-purity urea phosphate provided by the present invention has a simple process flow, low energy consumption, and is easy to industrialize. The nanofiltration system can realize nearly 100% recycling of the mother liquor, with basically no wastewater discharge, which can greatly reduce raw material loss and environmental pressure. Compared with the prior art, this solution can obtain ultra-high purity products without secondary recrystallization, with lower production costs and better product consistency. It achieves green and efficient production while improving quality, and has significant economic value and industrialization prospects. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] This application provides a method for preparing high-purity urea phosphate, comprising: (1) Pump wet phosphoric acid with a P2O5 mass fraction of 52%-55% into the reactor and stir and preheat to 65-70℃. Turn on the stirring for 20-30 r / min and stir steadily for 10-15 min. Prepare a urea aqueous solution with a urea mass fraction of 62%-64% and preheat to 50-60℃. Prepare a calcium hydroxide suspension with a concentration of 0.5 mol / L. (2) Add calcium hydroxide suspension dropwise to wet phosphoric acid with a Ca / P molar ratio of 0.01-0.02, preferably 0.015, for 40-60 min, maintain the pH of the system at 0.8-1.8, the reaction temperature at 65-70℃, the stirring speed at 20-30 r / min, and keep the mixture warm and stirred for 30 min to generate in situ nano-calcium phosphate seed crystals with a particle size of 5-20 nm; (3) Add urea aqueous solution to the nano calcium phosphate seed crystals according to the molar ratio of phosphoric acid to urea of ​​1:1.02-1.05, the dropwise addition time is 90-120 min, the reaction temperature is 75-80℃, the reaction is kept at the temperature for 2 h, and the nanofiltration membrane system (UNISOL membrane technology (formerly Israel AMS), AMS NanoPro™ A-3011) is turned on at the working pressure of 1.2-1.6MPa and the circulation flow rate is 40-50L / h for online circulation to remove impurities for 2.0-2.5 h to obtain the reaction solution; (4) Transfer the reaction solution to a crystallization tank and let it stand at a constant temperature of 45-50℃ for 2.5-3.5 hours to crystallize; (5) Centrifuge at 3000-4000 r / min for 10-20 min, wash with 5-10% of the wet mass of the crystals with ultrapure water, and dry at 55-60℃ and vacuum degree of -0.085--0.095MPa for 2.0-2.5 h to obtain high-purity phosphoric acid.

[0023] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Example

[0024] A method for preparing high-purity urea phosphate includes: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 54% into a reaction vessel, stirring and preheating to 68°C, starting the stirring at 25 r / min, and stirring stably for 12 min; preparing a urea aqueous solution with a urea mass fraction of 63% and preheating it to 55°C; preparing a calcium hydroxide suspension with a concentration of 0.5 mol / L; (2) adding the calcium hydroxide suspension dropwise to the wet phosphoric acid according to a Ca / P molar ratio of 0.015, with a dropwise addition time of 50 min, and maintaining the pH of the system. 1.2, the reaction temperature is 68℃, the stirring speed is 25r / min, and the stirring is kept warm for 30min to generate nano-calcium phosphate seeds in situ; (3) according to the molar ratio of phosphoric acid to urea of ​​1:1.04, urea aqueous solution is added to the nano-calcium phosphate seeds for reaction, the dropping time is 100min, the reaction temperature is 78℃, the reaction is kept warm for 2h, and the nanofiltration membrane system is turned on at a working pressure of 1.4MPa and a circulation flow rate of 45L / h for online circulation to remove impurities for 2.3h to obtain the reaction solution; (4) the reaction solution is transferred to the crystallization tank and kept at a constant temperature of 48℃ for 3h to crystallize; (5) centrifuged at a centrifugation speed of 3500r / min for 15min, washed with 8% of the wet basis mass of the crystal with ultrapure water, and dried at a temperature of 58℃ and a vacuum degree of -0.09MPa for 2.2h to obtain high-purity urea phosphate. Example

[0025] A method for preparing high-purity urea phosphate includes: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 52% into a reaction vessel, stirring and preheating to 70°C, starting the stirring at 20 r / min, and stirring stably for 15 min; preparing a urea aqueous solution with a urea mass fraction of 62% and preheating it to 60°C; preparing a calcium hydroxide suspension with a concentration of 0.5 mol / L; (2) adding the calcium hydroxide suspension dropwise to the wet phosphoric acid according to a Ca / P molar ratio of 0.01, with a dropwise addition time of 60 min, and maintaining the pH of the system. 0.8, reaction temperature is 70℃, stirring speed is 20r / min, keep warm and stir for 30min, and generate nano calcium phosphate seed crystals in situ; (3) according to the molar ratio of phosphoric acid to urea is 1:1.05, add urea aqueous solution to nano calcium phosphate seed crystals for reaction, drop time is 90min, reaction temperature is 80℃, keep warm and react for 2h, and simultaneously turn on the nanofiltration membrane system at working pressure of 1.2MPa, circulation flow rate of 50L / h for online circulation to remove impurities for 2.0h, and obtain reaction solution; (4) transfer the reaction solution into the crystallization tank, keep it at constant temperature of 50℃ for 2.5h; (5) centrifuge at a speed of 4000r / min for 10min, wash with 10% of the wet basis mass of crystals with ultrapure water, and dry at a temperature of 55℃ and a vacuum degree of -0.095MPa for 2.0h to obtain high purity urea phosphate. Example

[0026] A method for preparing high-purity urea phosphate includes: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 55% into a reaction vessel, stirring and preheating to 65°C, starting the stirring at 30 r / min, and stirring steadily for 10 min; preparing a urea aqueous solution with a urea mass fraction of 64% and preheating it to 50°C; preparing a calcium hydroxide suspension with a concentration of 0.5 mol / L; (2) adding the calcium hydroxide suspension dropwise to the wet phosphoric acid according to a Ca / P molar ratio of 0.02, with a dropwise addition time of 40 min, and maintaining the pH of the system. 1.8, the reaction temperature is 65℃, the stirring speed is 30r / min, and the stirring is kept warm for 30min to generate nano calcium phosphate seeds in situ; (3) according to the molar ratio of phosphoric acid to urea of ​​1:1.02, urea aqueous solution is added to the nano calcium phosphate seeds for reaction, the drop time is 120min, the reaction temperature is 75℃, the reaction is kept warm for 2h, and the nanofiltration membrane system is turned on at a working pressure of 1.6MPa and a circulation flow rate of 40L / h for online circulation to remove impurities for 2.5h to obtain the reaction solution; (4) the reaction solution is transferred to the crystallization tank and kept at a constant temperature of 45℃ for 3.5h to crystallize; (5) centrifuged at a centrifugation speed of 3000r / min for 20min, washed with 5% of the wet basis mass of the crystal with ultrapure water, and dried at a temperature of 60℃ and a vacuum degree of -0.085MPa for 2.5h to obtain high-purity urea phosphate.

[0027] Comparative Example 1 This comparative example provides a method for preparing high-purity urea phosphate, including: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 54% into a reactor and stirring and preheating it to 68°C, turning on the stirrer at 25 r / min and stirring steadily for 12 min; preparing a urea aqueous solution with a urea mass fraction of 63% and preheating it to 55°C; (2) according to a Ca / P molar ratio of 0.015, maintaining the reactor temperature at 78°C, slowly adding the urea aqueous solution dropwise for 100 min, and keeping the reaction temperature for 2 h after the addition is completed; (3) after the reaction is completed, directly cooling the liquid from 80°C to 25°C naturally, maintaining the stirring speed at 15 r / min, and the total crystallization time is 3 h; (4) separation and drying: centrifuging the crystallization liquid at 3500 r / min for 15 min, washing it with ultrapure water, the washing water volume being 8% of the wet basis mass of the crystal; placing the washed crystal in a vacuum drying oven at 58°C and a vacuum degree of -0.09 MPa. The product was dried under the specified conditions for 2.5 hours to obtain urea phosphate.

[0028] Comparative Example 2 This comparative example provides a method for preparing high-purity urea phosphate, including: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 52% into a reactor and stirring and preheating it to 70°C, turning on the stirrer at 20 r / min and stirring steadily for 15 min; preparing a urea aqueous solution with a urea mass fraction of 62% and preheating it to 60°C; (2) according to a Ca / P molar ratio of 0.01, maintaining the reactor temperature at 78°C, slowly adding the urea aqueous solution dropwise for 100 min; after the dropwise addition is completed, adding 0.08% of the total mass of PEG-400 as a crystallization aid, and stirring and reacting for 2 h; (3) three-stage gradient cooling crystallization: first stage: cooling from 80°C to 62°C at a uniform rate, and nucleating at a constant temperature for 1 h; second stage: cooling from 62°C to 42°C at a uniform rate, and growing at a constant temperature for 2.5 h; third stage: cooling from 42°C to 20°C at a uniform rate, and maturing at a constant temperature for 1.5 h; stirring speed throughout the process is 15 r / min; (4) The crystallization solution was centrifuged at 3500 r / min for 15 min, washed with ultrapure water (8% of the wet mass of the crystals), and then placed in a vacuum drying oven and dried at 58℃ and a vacuum of -0.09 MPa for 2.5 h to obtain urea phosphate product.

[0029] Comparative Example 3 This comparative example provides a method for preparing high-purity urea phosphate, comprising: (1) pumping wet phosphoric acid with a P2O5 mass fraction of 50% into a reaction vessel, stirring and preheating to 80°C, starting the stirring at 15 r / min, and stirring steadily for 20 min; preparing a urea aqueous solution with a urea mass fraction of 65% and preheating it to 65°C; and preparing a calcium hydroxide suspension with a concentration of 0.2 mol / L; (2) adding the calcium hydroxide suspension dropwise to the wet phosphoric acid according to a Ca / P molar ratio of 0.015, with a dropwise addition time of 70 min, and maintaining the pH of the system. 1.2, the reaction temperature is 80℃, the stirring speed is 40r / min, and the stirring is kept warm for 20min to generate nano-calcium phosphate seeds in situ; (3) according to the molar ratio of phosphoric acid to urea of ​​1:1.04, urea aqueous solution is added to the nano-calcium phosphate seeds for reaction, the dropping time is 80min, the reaction temperature is 90℃, the reaction is kept warm for 3h, and the nanofiltration membrane system is turned on at a working pressure of 1.8MPa and a circulation flow rate of 35L / h for online circulation to remove impurities for 3h to obtain the reaction solution; (4) the reaction solution is transferred to the crystallization tank and kept at a constant temperature of 40℃ for 4h to crystallize; (5) centrifuged at a centrifugation speed of 4500r / min for 25min, washed with 12% of the wet basis mass of the crystal with ultrapure water, and dried at a temperature of 65℃ and a vacuum degree of -0.08MPa for 3h to obtain high-purity urea phosphate.

[0030] Comparative Example 4 This comparative example provides a method for preparing high-purity urea phosphate, which differs from Example 1 in that: in step (2), the molar ratio of Ca / P is 1:0.05.

[0031] Comparative Example 5 This comparative example provides a method for preparing high-purity urea phosphate, which differs from Example 1 in that the molar ratio of Ca / P in step (3) is 1:1.01.

[0032] Experimental Example 1 The purity (wt%), F⁻ (wt%), Fe³⁺ (wt%), average particle size (μm), and crystal state of the urea phosphate products prepared in Examples 1-3 and Comparative Examples 1-5 are as follows: (1) Purity of urea phosphate: Acid-base titration method: Accurately weigh a certain amount of sample, completely dissolve it in deionized water, add phenolphthalein indicator, titrate with sodium hydroxide standard solution at room temperature until the solution turns a stable light red color and does not disappear within 30 seconds, record the volume of standard solution consumed, and calculate the mass fraction of urea phosphate based on the stoichiometric relationship of chemical reaction. (2) F⁻: Refer to GB / T 21057-2007 "General Method for Determination of Fluorine Content in Inorganic Chemical Products - Ion Selective Electrode Method", and determine it by ion chromatography: Dissolve the sample to be tested in ultrapure water and make up to the mark, shake well and filter through a microporous membrane to remove insoluble impurities, and detect it with an ion chromatograph. Plot a standard curve with fluoride ion standard working solution, and calculate the mass fraction of fluoride ions in the sample by external standard method. (3) Fe³⁺: Refer to GB / T 3049-2006 "General Method for Determination of Iron Content in Industrial Chemical Products 1,10-Phenanthroline Spectrophotometric Method", and determine it by atomic absorption spectrophotometry: Weigh the sample and place it in a volumetric flask, acidify and dissolve it with dilute nitric acid solution and make up to volume, filter it and then use a flame atomic absorption spectrophotometer to measure the absorbance at the characteristic wavelength. Use iron standard solution to establish a standard curve and calculate the mass fraction of iron ions in the sample based on the absorbance value. (4) Average particle size: The average particle size was determined by laser particle size scattering method: Take an appropriate amount of crystal sample, use anhydrous ethanol as the dispersion medium, and after ultrasonic dispersion, use a laser particle size analyzer for wet detection. Set appropriate shading rate and test parameters, and the instrument will automatically output particle size distribution data. The D50 volume average particle size is used as the measurement result. (5) Crystal form: Characterization was performed using a 400x polarizing microscope combined with XRD: A small amount of the crystal to be tested was placed on a glass slide, and anhydrous ethanol was added and dispersed evenly. The appearance, edge integrity, surface condition and aggregation of the crystal were observed under a 400x polarizing microscope. The regularity of the crystal form, the presence or absence of defects, inclusions and impurities were recorded.

[0033] The test results are shown in Table 1:

[0034] As shown in Table 1, compared with the conventional wet process provided in Comparative Example 1, the traditional PEG additive process provided in Comparative Example 2 can significantly improve the purity of urea phosphate and greatly reduce the content of F⁻ and Fe³⁺ impurities, while obtaining high-quality crystals with uniform particle size, complete crystal form and no agglomeration in Examples 1-3 of this application. Meanwhile, compared with Comparative Examples 4-5, Examples 1-3 of this application have better purity of urea phosphate, content of F⁻ and Fe³⁺ impurities, and crystal structure, indicating that the process parameters, Ca / P molar ratio, phosphoric acid / urea molar ratio, etc., in this application are necessary and unique, and this application needs to be carried out under specific technical conditions.

[0035] In summary, the high-purity urea phosphate and its preparation method provided in this application use wet-process phosphoric acid as raw material. Through acidic in-situ nano-calcium phosphate seed induction and reaction-nanofiltration synergistic impurity removal, a one-step high-purity crystallization is achieved without secondary recrystallization or organic additive residues. It can prepare urea phosphate with ultra-high purity, regular crystal form, and extremely low impurities, making it suitable for high-end application scenarios.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity urea phosphate, characterized in that: include: (1) Pump wet phosphoric acid with a P2O5 mass fraction of 52%-55% into the reactor and stir and preheat it; prepare a urea aqueous solution with a urea mass fraction of 62%-64% and preheat it; prepare a calcium hydroxide suspension with a concentration of 0.5mol / L. (2) Add the calcium hydroxide suspension dropwise to the wet-process phosphoric acid with a Ca / P molar ratio of 0.01-0.02, maintain the pH of the system at 0.8-1.8, and generate nano-sized calcium phosphate seeds with a particle size of 5-20 nm in situ; (3) Add the urea aqueous solution to the nano-calcium phosphate seed crystals according to the molar ratio of phosphoric acid to urea of ​​1:1.02-1.05, and simultaneously turn on the nanofiltration membrane system to circulate and remove impurities online for 2.0-2.5 h to obtain the reaction solution; (4) Transfer the reaction solution into a crystallization tank and let it stand at a constant temperature of 45-50℃ for 2.5-3.5h to crystallize; (5) Separate, wash and dry to obtain the urea phosphate.

2. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (2), the Ca / P molar ratio is 0.

015.

3. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (1), the wet-process phosphoric acid is preheated to 65-70°C, stirred at 20-30 r / min, and stirred stably for 10-15 min.

4. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (1), the urea aqueous solution is preheated to 50-60°C.

5. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (2), the reaction temperature is 65-70℃, the stirring speed is 20-30r / min, the dropping time is 40-60min, and the temperature is maintained and stirred for 30min.

6. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (3), the reaction temperature is 75-80℃, the dropping time is 90-120 min, and the reaction is kept at the temperature for 2 h.

7. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (3), the nanofiltration membrane has a molecular weight cutoff of 100 Da, an operating pressure of 1.2-1.6 MPa, and a circulation flow rate of 40-50 L / h.

8. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (5), the centrifugation speed is 3000-4000 r / min, and the centrifugation time is 10-20 min; ultrapure water is used for washing, and the amount used is 5-10% of the wet mass of the crystal.

9. The method for preparing high-purity urea phosphate according to claim 1, characterized in that: In step (5), the drying temperature is 55-60℃, the vacuum degree is -0.085--0.095MPa, and the drying time is 2.0-2.5h.

10. A high-purity urea phosphate, characterized in that: It was prepared using the method for preparing high-purity urea phosphate as described in any one of claims 1-9.

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