A method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid

Abstract

This invention relates to the field of chemical production technology, specifically to a method for preparing feed-grade MDCP by highly mixed defluorinated concentrated phosphoric acid. The method includes the following steps: Defluorinated concentrated phosphoric acid and limestone slurry are added to a trapezoidal premixing reactor at a Ca / P ratio and a specific flow rate for rapid stirring. After passing through a foam-removing screen, a large amount of foam remains in the trapezoidal premixer. The slurry below then enters a maturation reaction tank for thorough reaction. After thorough stirring at 85°C in the maturation reaction tank, the slurry is continuously discharged and dried to obtain the product. This invention uses a trapezoidal premixing reactor for preliminary mixing of raw materials, removing a large amount of foam, allowing the slurry to enter the maturation reaction tank for thorough stirring. The fully reacted MDCP is then dried to obtain the product. This method is simple, highly effective, and allows for a more complete reaction, enabling the preparation of products that meet national standards within a high phosphate MER value range.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, specifically to a method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid. Background Technology

[0002] Over the past decade, China's feed-grade phosphate industry has developed rapidly, becoming the world's largest producer, consumer, and exporter of feed-grade phosphates. Feed-grade dicalcium phosphate (MDCP) is a type of calcium phosphate salt, a mixture of dicalcium phosphate (DCP) and calcium dihydrogen phosphate (MCP). This product contains phosphorus and calcium, two excellent nutrients, and can be used to balance feed nutrition and promote poultry growth and development. Future development can focus on further refinement, functionalization, and specialization.

[0003] The main production processes for bulk feed calcium products include the sulfuric acid process and the hydrochloric acid process. The sulfuric acid process accounts for approximately 95% of total production, while the hydrochloric acid process accounts for about 5%. The sulfuric acid process can be further divided into the dilute acid process and the concentrated acid process. The dilute acid process is limited by the quality of phosphoric acid and is only suitable for producing DCP, while the concentrated acid process can produce various types of feed calcium, including MCP, MDCP, and DCP.

[0004] The concentrated acid method is a process for preparing feed calcium by reacting defluorinated concentrated phosphoric acid with calcium carbonate powder. Based on the phosphorus content requirements of the product, the process involves metering and reacting defluorinated concentrated phosphoric acid and calcium carbonate powder in a specific ratio, followed by granulation and drying to obtain the finished feed calcium. The process is simple. Chinese patent CN100404412C discloses a method for producing feed-grade diced calcium phosphate. The author uses dilute acid and a calcium-containing compound in a reactor for the first step of the liquid-phase reaction. Subsequently, the calcium-containing compound is added to the slurry for further reaction to obtain feed-grade diced calcium phosphate. This method can produce products that meet national standards, but it uses dilute acid for the reaction, resulting in high energy consumption for subsequent drying. Chinese patent CN108910853B discloses a method for producing granular calcium dihydrogen phosphate in one step using concentrated phosphoric acid. The author uses a concentrated acid method to produce the finished product in one step. However, when producing in a tank, because this reaction is a double decomposition reaction and generates a large amount of carbon dioxide, the reaction is particularly violent when two raw materials are added consecutively, producing a large amount of foam that can occupy 2 / 3 of the reaction tank space. At this time, the tank contains a large amount of foam and some product, which may cause the tank to explode. If sufficient stirring is required and the explosion is avoided, a larger volume reaction tank must be used, which will also occupy a lot of space and result in incomplete reaction and low efficiency. Furthermore, this patent primarily targets the reaction of concentrated phosphoric acid in the lower MER value range. This is because concentrated phosphoric acid at lower MER values ​​has fewer impurities, resulting in higher reaction efficiency and the generation of qualified products with shorter residence times. When using phosphoric acid with a higher MER value to produce MDCP, the increased metal impurity ions increase the viscosity of the phosphoric acid, leading to severe encapsulation and exacerbating incomplete reaction. This results in high free acid or high residual calcium carbonate in the product, which in turn causes easy agglomeration and moisture absorption, increasing the likelihood of MDCP products failing quality tests. Moreover, when reacting with concentrated phosphoric acid at a high MER value, the two raw materials will turn into a semi-dry solid within 3 minutes of contact, making discharge difficult. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid, in order to solve the problem in the background art where the use of phosphoric acid with a higher MER value to produce MDCP results in increased phosphoric acid viscosity and severe encapsulation due to the increase of metal impurity ions, which exacerbates the incomplete reaction.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid specifically includes the following steps:

[0008] S10: Defluorinated concentrated phosphoric acid and limestone slurry are added to the trapezoidal premixing reactor at a specific flow rate according to the Ca / P ratio and are rapidly stirred. After the slurry passes through the foam-removing screen, a large amount of foam remains in the trapezoidal premixer. The slurry below enters the maturation reaction tank for full reaction.

[0009] S20: The slurry enters the maturation reaction tank and is thoroughly stirred at 85°C before being continuously discharged and dried to obtain the product.

[0010] Preferably, the trapezoidal premixing reactor is equipped with a stirrer.

[0011] Preferably, the Ca / P ratio added in step S10 is in the range of 0.5-1.0.

[0012] Preferably, the temperature of the defluorinated concentrated phosphoric acid and limestone slurry in step S10 is between 60-120°C.

[0013] Preferably, the stirring speed of the trapezoidal premixing reactor in step S10 is 100-500 rpm.

[0014] Preferably, the reaction residence time in the trapezoidal premixed reactor in step S10 is 1 min to 5 min.

[0015] Preferably, the diameter of the mesh size of the foam-cutting mesh in step S10 is 5-15 cm. If the mesh size is too small, it will hinder the flow of slurry and cause accumulation and blockage; if the mesh size is too large, it will not be effective in cutting off the foam layer.

[0016] Preferably, the ratio of the upper to lower diameter of the trapezoidal premixer in step S10 is 1.1-4:1.

[0017] Preferably, the type of agitator in the maturation reaction tank in step S20 is an anchor agitator, a frame agitator, a ribbon agitator, a propeller agitator, a paddle agitator, or a turbine agitator.

[0018] Preferably, the residence time of the ripening reaction tank in step S20 is 10-50 min, and the MER value of concentrated phosphoric acid is 0.08-0.14.

[0019] Reaction mechanism:

[0020] The reaction mechanism of this invention mainly utilizes the neutralization reaction between defluorinated concentrated phosphoric acid and calcium carbonate to produce dicalcium phosphate (MDCP) at a certain Ca / P ratio. The main reaction equations are shown below:

[0021] 2H3PO4+CaCO3+H2O→Ca(H2PO4)2·H2O+CO2; (1)

[0022] H3PO4+CaCO3+H2O→CaHPO4·2H2O+CO2; (2)

[0023] Ca(H2PO4)2+CaCO3+3H2O→2CaHPO4·2H2O+CO2. (3)

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This method for preparing feed-grade MDCP using highly mixed defluorinated concentrated phosphoric acid utilizes concentrated phosphoric acid with a high MER value. By employing a trapezoidal premixing reactor, a large amount of foam is retained within the premixer, significantly reducing the pressure on the maturation reaction tank and providing ample space for maturation over a certain period. After maturation, the resulting MDCP exhibits better fluidity, facilitating discharge and ensuring a thorough reaction. Furthermore, the two raw materials can directly contact each other during the trapezoidal premixing process, increasing reaction efficiency. The slurry from the trapezoidal premixer is then thoroughly stirred before being continuously discharged and dried to obtain fully reacted feed-grade MDCP.

[0026] 2. This method for preparing feed-grade MDCP through high-level mixing of defluorinated concentrated phosphoric acid utilizes rapid stirring in a trapezoidal premixing reactor to quickly mix the slurry, shortening the reaction time and improving production efficiency. Sufficient reaction in a maturation tank ensures complete maturation of the slurry, improving product quality. Thorough stirring at 85℃ reduces energy consumption and improves energy utilization efficiency. Continuous discharge drying reduces labor intensity and increases production efficiency. This process uses defluorinated concentrated phosphoric acid and limestone slurry as raw materials, contains no harmful substances, and is environmentally friendly. It offers advantages such as improved production efficiency, product quality, reduced energy consumption, reduced labor intensity, and reduced environmental pollution, making it an environmentally friendly, efficient, and sustainable preparation method. Attached Figure Description

[0027] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are explained in detail together with the embodiments of the invention, but do not constitute a limitation thereof.

[0028] Figure 1 This is a schematic diagram of the structure of the present invention;

[0029] The meanings of the labels in the diagram are as follows: 1. Mixer; 2. Trapezoidal premixing reactor; 3. Foam trap. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] The steps for preparing MDCP from defluorinated concentrated phosphoric acid in this embodiment are as follows:

[0033] First, prepare a certain concentration of defluorinated concentrated phosphoric acid (MER value 0.08) at 85℃ and limestone emulsion. Add the raw materials at a Ca / P ratio of 0.65 into a trapezoidal premixing reactor to react, cutting off a large amount of foam. The stirring speed is 200 rpm and the residence time is 1 min. The premixed slurry flows down into a maturation reactor and is thoroughly stirred at 85℃ using a frame agitator at a stirring speed of 150 rpm and a residence time of 30 min. After discharge, the MDCP is dried to obtain the final product.

[0034] The trapezoidal premixer, as Figure 1 As shown, its shell is an inverted trapezoid with a larger upper opening and a smaller lower opening. The ratio of the upper opening diameter to the lower opening diameter is 1.1-4:1. A mixer 1 is installed in the middle, and a foam-removing screen 3 with a mesh diameter of 5-15cm is installed at the bottom. After defluorinated concentrated phosphoric acid and limestone slurry are added to the trapezoidal premixer 2, they are mixed and reacted while flowing to the bottom under the action of the mixer 1. After most of the foam is removed by the foam-removing screen 3, they enter the maturation tank for further stirring and reaction to obtain crude MDCP.

[0035] Example 2

[0036] The steps for preparing MDCP from defluorinated concentrated phosphoric acid in this embodiment are as follows:

[0037] First, prepare a certain concentration of defluorinated concentrated phosphoric acid (MER value 0.08) and limestone emulsion at 85℃, and add them at a Ca / P ratio of 0.70. The raw materials are added to a trapezoidal premixing reactor for reaction, where excessive foaming is controlled. The stirring speed is 250 rpm and the residence time is 2 min. The premixed slurry is then added to a maturation reactor and thoroughly stirred at 85℃ using a paddle agitator at a stirring speed of 100 rpm and a residence time of 25 min. After drying, the MDCP discharged yields the final product.

[0038] Example 3

[0039] The steps for preparing MDCP from defluorinated concentrated phosphoric acid in this embodiment are as follows:

[0040] First, prepare a certain concentration of defluorinated concentrated phosphoric acid (MER value 0.1) at 90℃ and limestone emulsion, and add the raw materials at a Ca / P ratio of 0.8. The reaction is carried out in a premixing reactor, where excessive foaming is controlled. The stirring speed is 200 rpm and the residence time is 2 min. The premixed slurry is then added to a maturation reactor and thoroughly stirred at 85℃ using a ribbon agitator at a stirring speed of 150 rpm and a residence time of 25 min. The discharged MDCP is then dried to obtain the final product.

[0041] Example 4

[0042] The steps for preparing MDCP from defluorinated concentrated phosphoric acid in this embodiment are as follows:

[0043] First, prepare a certain concentration of defluorinated concentrated phosphoric acid (MER value 0.09) and limestone emulsion at 85℃, and add them at a Ca / P ratio of 0.75. The raw materials are added to a premixing reactor for reaction, where excessive foaming is controlled. The stirring speed is 300 rpm and the residence time is 1.5 min. The premixed slurry is then added to a maturation reactor and thoroughly stirred at 85℃ using a frame stirrer at a stirring speed of 150 rpm and a residence time of 20 min. After drying, the MDCP discharged yields the final product.

[0044] Example 5

[0045] The steps for preparing MDCP from defluorinated concentrated phosphoric acid in this embodiment are as follows:

[0046] First, prepare a certain concentration of defluorinated concentrated phosphoric acid (MER value 0.09) and limestone emulsion at 90℃, and add them at a Ca / P ratio of 0.7. The raw materials are added to a premixing reactor for reaction, where excessive foaming is controlled. The stirring speed is 250 rpm and the residence time is 2.5 min. The premixed slurry is then added to a maturation reactor and thoroughly stirred at 85℃ using a frame stirrer at a stirring speed of 200 rpm and a residence time of 25 min. After drying, the MDCP is ready to obtain the final product.

[0047] Example 6

[0048] The steps for preparing MDCP from defluorinated concentrated phosphoric acid in this embodiment are as follows:

[0049] First, prepare a certain concentration of defluorinated concentrated phosphoric acid (MER value 0.12) and limestone emulsion at 90℃, and add them at a Ca / P ratio of 0.69. The raw materials are added to a premixing reactor for reaction, where excessive foaming is controlled. The stirring speed is 300 rpm and the residence time is 2 min. The premixed slurry is then added to a maturation reactor and thoroughly stirred at 85℃ using a ribbon agitator at a stirring speed of 200 rpm and a residence time of 25 min. After discharge, the MDCP is dried to obtain the final product.

[0050]

[0051]

[0052] In summary, this invention utilizes premixed defluorinated concentrated phosphoric acid with a high MER value to fully react with limestone slurry in a reactor, resulting in feed-grade dicalcium phosphate that meets industry standards. The reaction reduces free acid and residual calcium carbonate in the product, ensuring quality. This method generates no waste residue or wastewater, is economical and environmentally friendly, and has a simple process. This invention's method for preparing feed-grade MDCP through highly mixed defluorinated concentrated phosphoric acid utilizes concentrated phosphoric acid with a high MER value range to produce products that meet industry standards.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid, characterized in that: Specifically, the steps include the following: S10: Defluorinated concentrated phosphoric acid and limestone slurry are added to the trapezoidal premixing reactor (2) at a Ca / P ratio of 0.5-1.0 and stirred rapidly. After the slurry passes through the foam-removing screen (3), a large amount of foam remains in the trapezoidal premixer. The slurry at the bottom enters the maturation reaction tank for full reaction. The reaction residence time of the trapezoidal premixing reactor is 1 min-5 min. The diameter of the mesh size of the foam-removing screen (3) is 5-15 cm. The diameter ratio of the upper opening to the lower opening of the trapezoidal premixer is 1-4:

1. S20: The slurry enters the maturation reaction tank and is thoroughly stirred at 85℃ before being continuously discharged and dried to obtain the product; the residence time in the maturation reaction tank is 10-50 min, and the MER value of concentrated phosphoric acid is 0.08-0.

14.

2. The method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid according to claim 1, characterized in that: A mixer (1) is installed on the trapezoidal premixing reactor (2).

3. The method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid according to claim 1, characterized in that: In step S10, the temperature of the defluorinated concentrated phosphoric acid and limestone slurry is between 60-120℃.

4. The method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid according to claim 1, characterized in that: In step S10, the stirring speed of the trapezoidal premix reactor is 100-500 rpm.

5. The method for preparing feed-grade MDCP by highly mixing defluorinated concentrated phosphoric acid according to claim 1, characterized in that: In step S20, the type of agitator in the maturation reaction tank is an anchor agitator, a frame agitator, a ribbon agitator, a propeller agitator, a paddle agitator, or a turbine agitator.

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