Preparation method of large-particle anhydrous calcium hydrogen phosphate

Abstract

The invention provides a preparation method of large-particle anhydrous calcium hydrogen phosphate, and relates to the technical field of phosphate production. According to the method, phosphoric acid and tricalcium phosphate are used as raw materials, an annular rotational flow reactor is adopted, phosphoric acid and tricalcium phosphate react in an annular area of the annular rotational flow reactor to generate reaction slurry, flowing, mass transfer and reaction of a slurry multiphase system are enhanced, then seed crystals are added into the reaction slurry for crystal cultivation, and the obtained calcium hydrophosphate product is large in particle size and high in yield. The particle size distribution is uniform, and the quality batch consistency is high. Reaction conditions in the preparation process are mild, and no carbon dioxide gas is discharged; the preparation process is simple, safe, energy-saving, environment-friendly and easy for industrial production, the product quality can meet the requirements of different industries and special customers, the price is more than two times that of common anhydrous calcium hydrogen phosphate, and a new process technology is provided for production of large-particle calcium hydrogen phosphate.

Description

Technical Field

[0001] The invention relates to the technical field of phosphate production, in particular to a method for preparing large-particle anhydrous calcium hydrogen phosphate. Background Art

[0002] Anhydrous calcium hydrogen phosphate is calcium hydrogen phosphate without crystal water. Its molecular formula is CaHPO4. It is white crystal or powder, odorless and tasteless. It is soluble in dilute hydrochloric acid, nitric acid, acetic acid, slightly soluble in water, and insoluble in ethanol. Its apparent density is 0.9 g / cm3. It is stable in air and decomposes at 370°C. Anhydrous calcium hydrogen phosphate is a stable substance. It has obvious advantages over dihydrated calcium hydrogen phosphate. It is mainly used in the toothpaste industry and the pharmaceutical industry, and is also used in the food industry. Toothpaste manufacturers use it as a friction agent for high-quality toothpaste. Pharmaceutical factories and cosmetics companies use anhydrous calcium hydrogen phosphate as a mineral supplement for medicines, tablet carriers, filling materials or thickeners. At present, anhydrous calcium hydrogen phosphate has shown an increasingly widespread application trend in the domestic and foreign markets, and higher requirements are also put forward for the particle size of anhydrous calcium hydrogen phosphate. The relevant technical standards for pharmaceutical grade large-particle anhydrous calcium hydrogen phosphate products require that the content of the material on the 100 mesh sieve is more than 50% and that the content of the material passing the 325 mesh sieve is no more than 5%.

[0003] After searching, there are two main production processes for anhydrous calcium hydrogen phosphate. The first method is direct calcination, which uses dihydrate calcium hydrogen phosphate as raw material and calcines it at a certain temperature. This method has the following problems: (1) high energy consumption (dihydrate calcium hydrogen phosphate needs to be calcined at high temperature, which consumes a lot of energy and increases costs). (2) many by-products (during the calcination process, dihydrate calcium hydrogen phosphate will undergo intermolecular dehydration, producing by-products such as calcium hydrogen pyrophosphate, which affects product quality). (3) low output (the production efficiency of this process is low, and the output is difficult to meet the needs of large-scale production). The second method is direct neutralization. This method has high requirements for raw materials (it requires calcium carbonate to be of high fineness and free of fine black spots). However, calcium carbonate produced by crushing natural limestone contains impurities and heavy metals, which can easily cause the product arsenic and heavy metals to exceed the standard, limiting its application; particle size improvement is limited: the particle size of the anhydrous calcium hydrogen phosphate produced can generally only reach about 150 mesh. The third method, crystallization process, residual impurities: when preparing direct-compression anhydrous calcium hydrogen phosphate, the added crystallizer is difficult to completely remove in the subsequent process, and the residual impurities will affect the stability of the raw materials; insufficient product performance: the prepared granular anhydrous calcium hydrogen phosphate has high bulk density, irregular shape, and low porosity, and is prone to stratification problems caused by uneven mixing when used in the direct compression process.

[0004] The present invention summarizes a complete set of large-particle anhydrous calcium hydrogen phosphate production process based on a large number of pilot experiments and detailed analysis of the basic theory of anhydrous calcium hydrogen phosphate: using food-grade tricalcium phosphate and thermal phosphoric acid as raw materials, using a circular cyclone reactor to generate anhydrous calcium hydrogen phosphate slurry, adding crystal seeds to the reaction slurry for crystal cultivation, and then filtering, centrifuging, and drying to obtain a finished product. The anhydrous calcium hydrogen phosphate product prepared by the preparation method has a large particle size, a small particle size distribution range, high purity, low cost, mild reaction conditions, safe operation, no carbon dioxide emissions, and is easy to industrialize. It provides a new process technology for the production of large-particle calcium hydrogen phosphate and has good promotion value. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing large-particle anhydrous calcium hydrogen phosphate. The method is used to prepare anhydrous calcium hydrogen phosphate, and the reaction conditions are mild. The particle size of the material on the 100-mesh sieve can reach more than 60%, and the content of arsenic and heavy metal impurities is low, which fully meets the needs of food, medicine and customers with special requirements on particle size. The mother liquor can be recycled, which is energy-saving and environmentally friendly, and the product quality fully meets the food grade standard and the requirements of high-end customers.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing large-particle anhydrous calcium hydrogen phosphate, comprising the following steps: Step (1) Raw material preparation: first prepare a calcium hydrogen phosphate dihydrate slurry with a mass fraction of 10%-23%, a dilute phosphoric acid solution with a mass fraction of 8%-16%, and a tricalcium phosphate slurry with a mass fraction of 8%-24% respectively; Step (2) feeding and mixing: the calcium hydrogen phosphate dihydrate slurry is circulated in the annular region of the annular cyclone reactor, and the dilute phosphoric acid solution and the tricalcium phosphate slurry are continuously added into the annular region through the feed port at the lower part of one side of the reactor, and the three are fully mixed in the annular region; Step (3) reaction stage: dilute phosphoric acid and tricalcium phosphate react chemically in the annular region to generate monocalcium phosphate. The reaction time is 5-10 minutes and the temperature is controlled at 60-65°C. Step (4) Product discharge: The water vapor generated during the reaction escapes from the gas outlet at the top of the reactor, and the reaction slurry enters the stirred tank reactor from the outlet at the top; Step (5) adding seed crystals for crystal cultivation: adding 0.5-2% of the reaction slurry of anhydrous calcium hydrogen phosphate seed crystals with uniform particle size into the stirred reactor, and stabilizing the pH of the reaction slurry at 5.6-6.2 by an automatic acid or alkali adding device for crystal cultivation, the crystal cultivation time is 30-60 minutes, and the crystal cultivation temperature is 60-65°C; Step (6) Subsequent treatment: The reaction slurry after crystal growth is centrifuged and dried to obtain the finished product of large-particle anhydrous calcium hydrogen phosphate.

[0007] Preferably, the calcium hydrogen phosphate dihydrate slurry in step (1) has a mass fraction of 10%-23%, and is fully stirred to ensure a stable slurry state. It is slowly and steadily injected into the annular area of ​​the annular cyclone reactor through a special conveying pipeline or feeding device so that it can circulate smoothly in the area.

[0008] Preferably, the tricalcium phosphate slurry in step (1) has a mass fraction of 8%-24% and is prepared by adding 325 mesh food grade tricalcium phosphate to pure water; The tricalcium phosphate powder should be fully dispersed in the water at an appropriate stirring speed and duration to form a uniform and fine slurry.

[0009] Preferably, the dilute phosphoric acid solution in step (1) has a mass fraction of 8%-16%, and is prepared by diluting 85% hot phosphoric acid with pure water, and its concentration must be uniform.

[0010] Preferably, the annular cyclone reactor in step (2) is a multiphase flow mixing reactor that combines cyclone and circulation technologies, and is composed of a cyclone trough premixing section, a cyclone reaction section, a flow stabilization cone and a discharge port.

[0011] Preferably, the purity of the raw materials phosphoric acid and tricalcium phosphate should be ensured. If the raw materials contain more impurities, the impurities may be adsorbed on the crystal surface or participate in the crystallization process, interfering with normal crystal growth and thus affecting the particle size. Raw materials with high purity are more conducive to the production of particles of appropriate size.

[0012] Preferably, when preparing the calcium hydrogen phosphate dihydrate slurry, it should be carried out in a special mixing tank with stirring, and it should be fully stirred to ensure the formation of a stable slurry state. Through a special delivery pipeline and a metering pump, it is slowly and steadily injected into the annular area of ​​the annular cyclone reactor so that it can circulate smoothly in this area, creating good conditions for subsequent full mixing and reaction with other raw materials.

[0013] Preferably, when preparing tricalcium phosphate slurry, tricalcium phosphate is slowly added to water, and a stirring device is turned on at the same time, and the tricalcium phosphate powder is fully dispersed in the water at an appropriate stirring speed and duration to form a uniform and fine slurry, which is finally stored and prepared to be added to the reactor from the corresponding feed port.

[0014] Preferably, when preparing the dilute phosphoric acid solution, a dilute phosphoric acid solution with a mass concentration of 8%-16% should be accurately prepared. Strictly follow the stoichiometry, measure phosphoric acid with a concentration of 85%, carefully add an appropriate amount of water to dilute, and continue stirring to make its concentration uniform. After preparation, it is stored in a high-level metering tank, waiting for subsequent feeding through the dilute phosphoric acid feed port at the lower part of one side of the annular cyclone reactor.

[0015] Preferably, the dilute phosphoric acid solution is fed into the annular region at a set flow rate at a constant speed through a dilute phosphoric acid feed port at the lower part of one side of the annular cyclone reactor in a stable and continuous manner by means of a special delivery pump or other equipment. This flow rate is determined by prior process tests and calculations to ensure that it can fully react with tricalcium phosphate without causing problems such as runaway reaction due to excessive flow rate.

[0016] Preferably, the tricalcium phosphate slurry enters the annular region in a continuous and stable state from the tricalcium phosphate feed port at the lower part of the other side of the annular cyclone reactor by means of a matching feed device. During the feeding process, attention should be paid to the feed pressure, flow rate and other parameters to ensure the stability of the feed.

[0017] Preferably, when dilute phosphoric acid and tricalcium phosphate meet in the annular area, a chemical reaction will occur rapidly. The entire reaction process will last about 10-15 minutes, during which the reaction temperature must be accurately controlled within the range of 60-65°C by the temperature control system of the reactor. For example, a jacketed heating or cooling device can be used to automatically adjust the flow of the heating or cooling medium according to the temperature conditions monitored in real time to maintain a suitable reaction temperature, so that the reaction can be carried out efficiently and stably, ensuring that the generated reaction slurry meets the requirements of subsequent processes.

[0018] Preferably, the generated reaction slurry should flow along the flow channel inside the annular cyclone reactor, through the outlet located at the top of the annular cyclone reactor, and flow into the stirred tank reactor in an orderly manner by gravity or by means of pumping, so as to prepare for the subsequent seeding and crystal cultivation. During the slurry transfer process, it is necessary to ensure that the pipeline is unobstructed to prevent the slurry from clogging the pipeline and affecting the continuity of the entire production process.

[0019] Preferably, the size of the added seed crystals should be small and uniform, so that the calcium hydrogen phosphate particles grown on this basis are easier to grow and have a more uniform size; if the seed crystals have uneven particle sizes, the size of the generated particles will also vary greatly. If too much seed crystal is added, too many crystal cores will be formed, so that each core has limited material available for growth, and the final particles will be small; adding a proper amount of seed crystals is conducive to controlling the expected growth of particles.

[0020] Preferably, sufficient crystal growth time is given to allow the anhydrous calcium hydrogen phosphate crystals to grow fully. If the time is too short, the crystals will be separated before they have time to grow, resulting in smaller particles. Reasonable extension of the reaction time and the combination of other conditions can produce larger particles of the product.

[0021] Compared with the prior art, the present invention provides a method for preparing large-particle anhydrous calcium hydrogen phosphate, which has the following beneficial effects: 1. The preparation method of large-particle anhydrous calcium hydrogen phosphate, the prepared large-particle anhydrous calcium hydrogen phosphate, has a particle size of more than 60% on a 100-mesh sieve and no more than 3% passing a 325-mesh sieve, and a uniform particle size distribution, which can fully meet the technical standard requirements of pharmaceutical-grade anhydrous calcium hydrogen phosphate.

[0022] 2. The preparation method of the large-particle anhydrous calcium hydrogen phosphate has low arsenic and heavy metal impurity content, which can meet the needs of different industries and different customers. The product price is 2-3 times that of ordinary anhydrous calcium hydrogen phosphate.

[0023] 3. The preparation method of large-particle anhydrous calcium hydrogen phosphate has mild reaction conditions, is energy-saving and environmentally friendly, and provides a new process technology for the production of large-particle anhydrous calcium hydrogen phosphate.

[0024] 4. The preparation method of large-particle anhydrous calcium hydrogen phosphate has high production capacity, low energy consumption, no pollution, low manufacturing cost, obvious economic and environmental benefits, and is easy to promote and apply on a large scale.

[0025] 5. The preparation method of large-particle anhydrous calcium hydrogen phosphate has good mixing effect: the swirl trough is used to strengthen the gas-liquid mixing, and the swirl blades cut the bubbles, which plays the role of weak swirl field on multiphase flow mixing reaction and the turbulence strengthening reaction of strong swirl field, so that the flow state inside the guide tube becomes turbulent, which is beneficial to the heat transfer, mass transfer and momentum transfer of the fluid, and improves the uniformity of gas phase distribution. 6. The preparation method of large-particle anhydrous calcium hydrogen phosphate has a long residence time: The two-stage guide tube constructed by the guide tube and the tube shell structure has an inner spiral and an outer spiral flow structure, which increases the flow resistance of the fluid system and prolongs the residence time of the reaction materials, which is beneficial to improve the conversion rate of the reaction, reduce coking in the reactor, and facilitate the fluid-solid separation process in the subsequent process. 7. The preparation method of large-particle anhydrous calcium hydrogen phosphate is flexible in operation: the number of reactor stages can be increased or decreased according to the needs of multiphase flow reaction, and the reactors are connected in series through steady flow cones to achieve a cascade mixing reaction inside and outside the reactor. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] A method for preparing large-particle anhydrous calcium hydrogen phosphate comprises the following steps: Step (1) Raw material preparation: first prepare a calcium hydrogen phosphate dihydrate slurry with a mass fraction of 10%-23%, a dilute phosphoric acid solution with a mass fraction of 8%-16%, and a tricalcium phosphate slurry with a mass fraction of 8%-24% respectively; Step (2) feeding and mixing: the calcium hydrogen phosphate dihydrate slurry is circulated in the annular region of the annular cyclone reactor, and the dilute phosphoric acid solution and the tricalcium phosphate slurry are continuously added into the annular region through the feed port at the lower part of one side of the reactor, and the three are fully mixed in the annular region; Step (3) reaction stage: dilute phosphoric acid and tricalcium phosphate react chemically in the annular region to generate monocalcium phosphate. The reaction time is 5-10 minutes and the temperature is controlled at 60-65°C. Step (4) Product discharge: The water vapor generated by the reaction escapes from the gas outlet at the top of the reactor, and the reaction slurry enters the stirred tank reactor from the outlet at the top; Step (5) adding seed crystals for crystal cultivation: adding 0.5-2% of the reaction slurry of anhydrous calcium hydrogen phosphate seed crystals with uniform particle size into the stirred reactor, and stabilizing the pH of the reaction slurry at 5.6-6.2 by an automatic acid or alkali adding device for crystal cultivation, the crystal cultivation time is 30-60 minutes, and the crystal cultivation temperature is 60-65°C; Step (6) Subsequent treatment: The reaction slurry after crystal growth is centrifuged and dried to obtain the finished product of large-particle anhydrous calcium hydrogen phosphate.

[0028] The calcium hydrogen phosphate dihydrate slurry in step (1) has a mass fraction of 10%-23%, and should be fully stirred to ensure a stable slurry state. It is slowly and steadily injected into the annular area of ​​the annular cyclone reactor through a special conveying pipeline or feeding device so that it can circulate smoothly in the area.

[0029] The tricalcium phosphate slurry in step (1) has a mass fraction of 8%-24% and is prepared by adding 325 mesh food grade tricalcium phosphate to pure water; The tricalcium phosphate powder should be fully dispersed in the water at an appropriate stirring speed and duration to form a uniform and fine slurry.

[0030] The dilute phosphoric acid solution in step (1) has a mass fraction of 8%-16% and is prepared by diluting 85% hot phosphoric acid with pure water. The concentration of the solution must be uniform.

[0031] The annular cyclone reactor in step (2) is a multiphase flow mixing reactor that combines cyclone and circulation technologies, and is composed of a cyclone trough premixing section, a cyclone reaction section, a flow stabilization cone and a discharge port.

[0032] To ensure the purity of the annual raw materials phosphoric acid and tricalcium phosphate, if the raw materials contain more impurities, the impurities may be adsorbed on the crystal surface or participate in the crystallization process, interfering with normal crystal growth and thus affecting the particle size. Raw materials with high purity are more conducive to the production of particles of appropriate size.

[0033] When preparing dihydrate calcium hydrogen phosphate slurry, it should be carried out in a special mixing tank with stirring, and it should be fully stirred to ensure the formation of a stable slurry state. Through a special delivery pipeline and metering pump, it is slowly and steadily injected into the annular area of ​​the annular cyclone reactor so that it can circulate smoothly in this area. Create good conditions for subsequent full mixing and reaction with other raw materials.

[0034] When preparing tricalcium phosphate slurry, slowly add tricalcium phosphate into the water and turn on the stirring device at the same time. Use appropriate stirring speed and duration to allow the tricalcium phosphate powder to be fully dispersed in the water to form a uniform and fine slurry. Finally, store it and prepare to add it to the reactor from the corresponding feed port.

[0035] When preparing dilute phosphoric acid solution, it is necessary to accurately prepare a dilute phosphoric acid solution with a mass concentration of 8% -16%. Strictly follow the chemical measurement, measure 85% phosphoric acid, carefully add an appropriate amount of water to dilute, and continue to stir to make the concentration uniform. After preparation, store it in a high-level metering tank and wait for subsequent feeding through the dilute phosphoric acid feed port at the lower side of the annular cyclone reactor.

[0036] The dilute phosphoric acid solution is fed into the annular area at a set flow rate at a constant speed through the dilute phosphoric acid feed port at the lower part of one side of the annular cyclone reactor in a stable and continuous manner with the help of a special delivery pump and other equipment. This flow rate is determined through prior process tests and calculations to ensure that it can fully react with tricalcium phosphate without causing problems such as runaway reaction due to excessive flow.

[0037] The tricalcium phosphate slurry relies on the supporting feeding device to enter the annular area from the tricalcium phosphate feeding port at the lower part of the other side of the annular cyclone reactor in the same continuous and stable state. During the feeding process, attention should be paid to the feeding pressure, flow rate and other parameters to ensure the stability of the feeding.

[0038] When dilute phosphoric acid and tricalcium phosphate meet in the annular area, a chemical reaction will occur rapidly. The entire reaction process will last about 10-15 minutes. During this period, the reaction temperature must be accurately controlled within the range of 60-65°C through the temperature control system of the reactor. For example, the flow of the heating or cooling medium can be automatically adjusted by a jacketed heating or cooling device according to the real-time monitored temperature to maintain a suitable reaction temperature, so that the reaction can be carried out efficiently and stably, ensuring that the generated reaction slurry meets the requirements of subsequent processes.

[0039] The generated reaction slurry should flow along the flow channel inside the annular cyclone reactor through the outlet located at the top of the annular cyclone reactor, relying on gravity or pumping, and flow into the stirred tank reactor in an orderly manner to prepare for the subsequent seeding and crystal cultivation. During the slurry transfer process, it is necessary to ensure that the pipeline is unobstructed to prevent the slurry from clogging the pipeline and affecting the continuity of the entire production process.

[0040] The size of the added seed crystals should be small and uniform, so that the calcium hydrogen phosphate particles grown on this basis will be easier to grow and more uniform in size; if the seed crystals have uneven particle sizes, the generated particles will also have large differences in size. If too much seed crystal is added, too many crystal cores will be formed, so that each core has limited material available for growth, and the final particles will be small; adding a proper amount of seed crystals is conducive to controlling the expected growth of particles.

[0041] Providing enough crystal growth time can allow the anhydrous calcium hydrogen phosphate crystals to grow fully. If the time is too short, the crystals will be separated before they have time to grow, resulting in smaller particles. Prolonging the reaction time reasonably and meeting other conditions can produce larger particles.

[0042] Example 1

[0043] A method for preparing large-particle anhydrous calcium hydrogen phosphate, the specific steps of which are as follows: (1) Raw material preparation: Use pure water and a special mixing tank with stirring to prepare 10% calcium hydrogen phosphate dihydrate slurry, 8% dilute phosphoric acid solution and 8% tricalcium phosphate slurry, and store them in high-level metering tanks for standby use; (2) Feeding and mixing: The calcium hydrogen phosphate dihydrate slurry is slowly and steadily injected into the annular area of ​​the annular cyclone reactor through a special delivery pipeline and metering pump, so that it circulates smoothly in the area, creating good conditions for subsequent sufficient mixing and reaction with other raw materials; The dilute phosphoric acid solution and tricalcium phosphate slurry are continuously added into the annular area through the feed port at the lower part of one side of the reactor with the help of special conveying pipes and metering pumps and other equipment. The three are fully mixed in the annular area. The stability and continuity of the feed must be maintained, and they must enter the annular area at a uniform speed according to a preset flow rate. This flow rate is determined through prior process tests and calculations to ensure that they can fully react with tricalcium phosphate without causing problems such as reaction out of control due to excessive flow.

[0044] (3) Reaction stage: When dilute phosphoric acid and tricalcium phosphate meet in the annular area, a chemical reaction will occur rapidly. When tricalcium phosphate reacts with phosphoric acid, the reaction of Ca3(PO4)2+4H3PO4=3Ca(H2PO4)2 will first occur to generate monocalcium phosphate. Monocalcium phosphate is converted into calcium hydrogen phosphate: As the reaction proceeds, monocalcium phosphate continues to react with tricalcium phosphate, that is, Ca(H2PO4)2+Ca3(PO4)2=4CaHPO4, thereby generating monocalcium phosphate. The entire reaction process will last about 15 minutes. During this period, the reaction temperature must be accurately controlled within the range of 60-65℃ through the temperature control system of the reactor. Through the jacketed heating or cooling device, the flow rate of the heating or cooling medium is automatically adjusted according to the real-time monitored temperature conditions to maintain the appropriate reaction temperature, so that the reaction can be carried out efficiently and stably, ensuring that the generated reaction slurry meets the subsequent process requirements.

[0045] The annular cyclone reactor forms a high-speed rotating vortex of reactants, generates a strong centrifugal force, separates materials of different densities and particle sizes in the radial direction, and highly disperses solid particles or bubbles, increases the contact area and collision probability between reactants, accelerates the reaction, and thus accelerates mass transfer; the shear force and turbulence of the cyclone break the diffusion layer on the surface of the reactants, improves the mass transfer efficiency, and the reactor can better control the reaction temperature and maintain it in an appropriate range, providing good heat transfer conditions for the reaction, so that the reaction can proceed efficiently and stably. The heat transfer efficiency is improved.

[0046] (4) Product discharge: The generated reaction slurry should flow along the flow channel inside the annular cyclone reactor through the outlet located at the top of the annular cyclone reactor, relying on gravity or pumping, and flow into the stirred tank reactor in an orderly manner, so as to prepare for the subsequent seeding and crystal cultivation. During the slurry transfer process, it is necessary to ensure that the pipeline is unobstructed to prevent the slurry from clogging the pipeline and affecting the continuity of the entire production process.

[0047] (5) Adding seed crystals for crystal cultivation: Add 1% of the reaction slurry system of anhydrous calcium hydrogen phosphate seed crystals with a particle size of 200 mesh into the stirred reactor, and stabilize the pH of the reaction slurry at 5.8 through an automatic acid or alkali adding device for crystal cultivation. The crystal cultivation time is 30-40 minutes and the crystal cultivation temperature is 60-65°C.

[0048] (6) Subsequent treatment: The reaction slurry after crystallization is filtered, centrifuged and dried in a fixed fluidized bed to obtain the finished product of large-particle anhydrous calcium hydrogen phosphate.

[0049] The dried anhydrous calcium hydrogen phosphate is passed through a 30-mesh sieve to remove the bulky material to obtain the finished anhydrous calcium hydrogen phosphate.

[0050] The physical and chemical indicators of the samples taken for testing are as follows: content 98.9%, particle size above 100 mesh sieve 60.5%, and pass rate of 325 mesh sieve 3.23%. Other physical and chemical indicators meet the requirements of GB1886.3-2021, FCC-V, E341 (ii), and USP-30 standards.

[0051] Example 2

[0052] A method for preparing large-particle anhydrous calcium hydrogen phosphate, the specific steps of which are as follows: (1) Raw material preparation: Use pure water and a special mixing tank with stirring to prepare 20% calcium hydrogen phosphate dihydrate slurry, 13% dilute phosphoric acid solution and 18% tricalcium phosphate slurry, and store them in high-level metering tanks respectively.

[0053] (2) Feeding and mixing: The calcium hydrogen phosphate dihydrate slurry is slowly and steadily injected into the annular area of ​​the annular cyclone reactor through a special delivery pipeline and metering pump, so that it circulates smoothly in the area, creating good conditions for subsequent sufficient mixing and reaction with other raw materials; The dilute phosphoric acid solution and tricalcium phosphate slurry are continuously added into the annular area through the feed port at the lower part of one side of the reactor with the help of special conveying pipes and metering pumps and other equipment. The three are fully mixed in the annular area. The stability and continuity of the feed must be maintained, and they must enter the annular area at a uniform speed according to a preset flow rate. This flow rate is determined through prior process tests and calculations to ensure that they can fully react with tricalcium phosphate without causing problems such as reaction out of control due to excessive flow.

[0054] (3) Reaction stage: When dilute phosphoric acid and tricalcium phosphate meet in the annular area, a chemical reaction will occur rapidly. When tricalcium phosphate reacts with phosphoric acid, the reaction of Ca3(PO4)2+4H3PO4=3Ca(H2PO4)2 will first occur to generate monocalcium phosphate. Monocalcium phosphate is converted into calcium hydrogen phosphate: As the reaction proceeds, monocalcium phosphate continues to react with tricalcium phosphate, that is, Ca(H2PO4)2+Ca3(PO4)2=4CaHPO4, thereby generating calcium hydrogen phosphate. The entire reaction process will last about 15 minutes. During this period, the reaction temperature must be accurately controlled within the range of 60-65°C through the temperature control system of the reactor. For example, a jacketed heating or cooling device can be used to automatically adjust the flow rate of the heating or cooling medium according to the real-time monitored temperature to maintain a suitable reaction temperature, so that the reaction can be carried out efficiently and stably, ensuring that the generated reaction slurry meets the subsequent process requirements.

[0055] The annular cyclone reactor forms a high-speed rotating vortex of reactants, generates a strong centrifugal force, separates materials of different densities and particle sizes in the radial direction, and highly disperses solid particles or bubbles, increases the contact area and collision probability between reactants, accelerates the reaction, and thus accelerates mass transfer; the shear force and turbulence of the cyclone break the diffusion layer on the surface of the reactants, improves the mass transfer efficiency, and the reactor can better control the reaction temperature and maintain it in an appropriate range, providing good heat transfer conditions for the reaction, so that the reaction can proceed efficiently and stably. The heat transfer efficiency is improved.

[0056] (4) Product discharge: The generated reaction slurry should flow along the flow channel inside the annular cyclone reactor through the outlet located at the top of the annular cyclone reactor, relying on gravity or pumping, and flow into the stirred tank reactor in an orderly manner, so as to prepare for the subsequent seeding and crystal cultivation. During the slurry transfer process, it is necessary to ensure that the pipeline is unobstructed to prevent the slurry from clogging the pipeline and affecting the continuity of the entire production process.

[0057] (5) Adding seed crystals for crystal cultivation: Add 1% of the reaction slurry system of anhydrous calcium hydrogen phosphate seed crystals with a particle size of 200 mesh into the stirred reactor, and stabilize the pH of the reaction slurry at 5.8 through an automatic acid or alkali adding device for crystal cultivation. The crystal cultivation time is 50 minutes and the crystal cultivation temperature is 60°C.

[0058] (6) Subsequent treatment: The reaction slurry after crystallization is filtered, centrifuged and dried in a fixed fluidized bed to obtain the finished product of large-particle anhydrous calcium hydrogen phosphate.

[0059] The dried anhydrous calcium hydrogen phosphate is passed through a 30-mesh sieve to remove the bulky material to obtain the finished anhydrous calcium hydrogen phosphate.

[0060] The physical and chemical indicators of the samples taken for testing are as follows: content 98.9%, particle size above 100 mesh sieve 60.5%, and pass rate of 325 mesh sieve 3.23%. Other physical and chemical indicators meet the requirements of GB1886.3-2021, FCC-V, E341 (ii), and USP-30 standards.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing large-particle anhydrous calcium hydrogen phosphate, characterized in that: The following steps are involved: Step (1) Raw material preparation: first prepare a calcium hydrogen phosphate dihydrate slurry with a mass fraction of 10%-23%, a dilute phosphoric acid solution with a mass fraction of 8%-16%, and a tricalcium phosphate slurry with a mass fraction of 8%-24% respectively; Step (2) feeding and mixing: the calcium hydrogen phosphate dihydrate slurry is circulated in the annular region of the annular cyclone reactor, and the dilute phosphoric acid solution and the tricalcium phosphate slurry are continuously added into the annular region through the feed port at the lower part of one side of the reactor, and the three are fully mixed in the annular region; Step (3) reaction stage: dilute phosphoric acid and tricalcium phosphate react chemically in the annular region to generate monocalcium phosphate. The reaction time is 5-10 minutes and the temperature is controlled at 60-65°C. Step (4) Product discharge: The water vapor generated during the reaction escapes from the gas outlet at the top of the reactor, and the reaction slurry enters the stirred tank reactor from the outlet at the top; Step (5) adding seed crystals for crystal cultivation: adding 0.5-2% of the reaction slurry of anhydrous calcium hydrogen phosphate seed crystals with uniform particle size into the stirred reactor, and stabilizing the pH of the reaction slurry at 5.6-6.2 by an automatic acid or alkali adding device for crystal cultivation, the crystal cultivation time is 30-60 minutes, and the crystal cultivation temperature is 60-65°C; Step (6) Subsequent treatment: The reaction slurry after crystal growth is centrifuged and dried to obtain the finished product of large-particle anhydrous calcium hydrogen phosphate.

2. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 1, characterized in that: The calcium hydrogen phosphate dihydrate slurry in step (1) has a mass fraction of 10%-23%, and should be fully stirred to ensure a stable slurry state. It is slowly and steadily injected into the annular area of ​​the annular cyclone reactor through a special conveying pipeline or feeding device so that it can circulate smoothly in the area.

3. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 1, characterized in that: The tricalcium phosphate slurry in step (1) has a mass fraction of 8%-24% and is prepared by adding 325 mesh food grade tricalcium phosphate to pure water; The tricalcium phosphate powder should be fully dispersed in the water at an appropriate stirring speed and duration to form a uniform and fine slurry.

4. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 1, characterized in that: The dilute phosphoric acid solution in step (1) has a mass fraction of 8%-16% and is prepared by diluting 85% hot phosphoric acid with pure water. The concentration of the solution must be uniform.

5. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 1, characterized in that: The annular cyclone reactor in step (2) is a multiphase flow mixing reactor that combines cyclone and circulation technologies, and is composed of a cyclone trough premixing section, a cyclone reaction section, a flow stabilization cone and a discharge port.

6. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 5, characterized in that: The cyclone tank premixing section includes an outer cylinder shell, a liquid phase feed port, a gas feed port, a gas chamber, a liquid phase cyclone tank and a gas distributor. The outer cylinder shell serves as an external supporting structure of the reactor and accommodates internal components. The liquid feed port and the gas feed port are used to introduce liquid and gas phase materials respectively; The gas chamber and the liquid phase swirl groove, the gas chamber is located at the bottom of the outer cylinder shell and is connected to the gas feed port, the liquid phase swirl groove is a spiral channel in the annular gap between the inner wall of the outer cylinder shell and the outer wall of the gas chamber, and the liquid phase feed port is connected to the liquid phase swirl groove; Gas distributor: The gas distributor is installed on the top of the gas chamber to evenly disperse the gas into the liquid phase cyclone tank and fully contact and mix with the liquid phase.

7. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 6, characterized in that: The cyclone reaction section includes a shell connected to the top of the cyclone tank premixing section, and contains components such as the primary and secondary cyclone reactors; The primary cyclone reactor comprises a guide tube and a plurality of cyclone blades, the lower end of the guide tube does not contact the shell, the outer peripheral side of the cyclone blades is fixed to the inner wall surface of the guide tube, the width of the cyclone blades is smaller than the inner radius of the guide tube, and a cylindrical fluid channel is formed on the inner peripheral side of the cyclone blades; The secondary swirl flow reactor comprises a cylindrical shell structure and swirl guide vanes. The swirl guide vanes are arranged between the outer wall surface of the cylindrical shell structure and the inner wall surface of the shell. The upper end of the cylindrical shell structure does not contact the shell.

8. The method for preparing large-particle anhydrous calcium hydrogen phosphate according to claim 7, characterized in that: The flow stabilizing cone is arranged between the guide tube and the shell structure, with the cone tip facing the guide tube, and a flow gap is left between the guide tube, the shell structure and the flow stabilizing cone; The discharge port is located at the top of the shell, and the reacted materials are discharged from here.