Preparation method of flaky disodium hydrogen phosphate dihydrate

Abstract

The invention discloses a preparation method of flaky disodium hydrogen phosphate dihydrate, which comprises the following steps: melting disodium hydrogen phosphate dodecahydrate to obtain molten disodium hydrogen phosphate dodecahydrate; the preparation method comprises the following steps: evaporating and dehydrating molten disodium hydrogen phosphate dodecahydrate to obtain a slurry material containing disodium hydrogen phosphate dihydrate; and heating the pasty material to enable the disodium hydrogen phosphate dihydrate to be in a molten state, and then transferring the material into a flaker for flaking to obtain the flaky disodium hydrogen phosphate dihydrate. The disodium hydrogen phosphate dihydrate is prepared by adopting a melting and flaking process, no mother liquor is produced, no mother liquor is discharged, no hazardous waste is generated, the obtained flaky product is easy to transport, the risk of integral hardening does not exist, and continuous production can be realized.

Description

Technical Field

[0001] The invention relates to a method for preparing flaky disodium hydrogen phosphate dihydrate, belonging to the technical field of chemical preparation. Background Art

[0002] Disodium hydrogen phosphate dodecahydrate is a common byproduct in the glyphosate industry. Due to the low melting point (35°C) and difficulty in transportation of disodium hydrogen phosphate dodecahydrate, the industry often makes disodium hydrogen phosphate dodecahydrate into disodium hydrogen phosphate dihydrate. At present, disodium hydrogen phosphate dihydrate is mainly prepared by evaporation concentration + centrifugation. The concentration device mostly adopts single effect, multiple effect or MVR. After the evaporation concentrate is thickened, it is separated into disodium hydrogen phosphate dihydrate by centrifuge.

[0003] CN219816218 discloses a device for producing disodium hydrogen phosphate dihydrate from glyphosate byproducts, comprising: a salt dissolving tank, for mixing solid salt with steam condensed water and make-up water into a feed liquid; a salt dissolving heat exchanger, for forcibly circulating and heating the feed liquid in the salt dissolving tank so that it first loses five crystal waters; a salt dissolving material transfer pump, for sending the feed liquid discharged from the salt dissolving tank into a forced circulation system of an evaporation separator; an evaporation separator, for evaporating the feed liquid so that it continues to lose five crystal waters to form disodium hydrogen phosphate dihydrate; an evaporation heat exchanger, for forcibly circulating and heating the feed liquid in the evaporation separator to maintain an evaporation state; a thickening tank and a clarification tank, for performing secondary sedimentation and concentration on the solid-liquid mixture discharged from the evaporation separator; a centrifuge for receiving and separating the concentrated phase of the thickening tank, and disodium hydrogen phosphate dihydrate solid phase salt is discharged from a salt outlet pipe; a feed liquid mother liquid tank, for receiving the clear liquid discharged from the centrifuge and the concentrated phase of the clarification tank and sending them back to the thickening tank for concentration; CN 104986747 B discloses a preparation method of disodium hydrogen phosphate dihydrate, comprising the following steps: dissolving disodium hydrogen phosphate dodecahydrate and water mixed materials at 5-45°C, and after complete liquefaction, placing the mixed materials in a steam heat exchanger to further heat them to above 65°C and then entering a forced circulation evaporator; evaporating, concentrating and crystallizing the mixed materials; the evaporation temperature is 90-95°C, the evaporation time is 1-2h, and secondary steam is generated during the evaporation process; the secondary steam coming out of the crystal separator enters an MVR compression system, and the compressed steam enters an evaporation chamber to heat the mixed materials; in the crystal separator, crystals are generated and form a certain grain size, which is transported to a thickener through a discharge pump to increase the solid content of the crystal concentrate to meet the separation requirements of a centrifuge; the bottom of the thickener is discharged to a centrifuge to separate the disodium hydrogen phosphate dihydrate crystals, and the separation temperature is controlled to be 48-95°C.

[0004] The existing technologies all adopt a route of multi-effect or MVR evaporation followed by a centrifuge to prepare disodium hydrogen phosphate dihydrate. This route has the following disadvantages: (1) The water content of disodium hydrogen phosphate dihydrate discharged from the centrifuge is generally 4-5%. When cooled to room temperature, the material tends to form agglomerates, which cannot be produced continuously for a long time and is not conducive to transportation and use; (2) The mother liquor concentrated by evaporation needs to be discharged after being used to a certain extent, otherwise it will affect the quality of disodium hydrogen phosphate dihydrate. The discharged mother liquor is treated as hazardous waste, which is costly. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing flaky disodium hydrogen phosphate dihydrate. The method is the first to prepare flaky disodium hydrogen phosphate dihydrate from disodium hydrogen phosphate dodecahydrate through a molten flake process, which can realize continuous production without generating hazardous waste and has better environmental protection.

[0006] The specific technical solutions of the present invention are as follows: A method for preparing flaky disodium hydrogen phosphate dihydrate is characterized by comprising the following steps: (1) melting disodium hydrogen phosphate dodecahydrate to obtain molten disodium hydrogen phosphate dodecahydrate; (2) evaporating and dehydrating the molten disodium hydrogen phosphate dodecahydrate to obtain a slurry material containing disodium hydrogen phosphate dihydrate; (3) The slurry material of step (2) is heated to make the disodium hydrogen phosphate dihydrate molten, and then the material is transferred to a flake forming machine for flake forming to obtain flake disodium hydrogen phosphate dihydrate.

[0007] Furthermore, the disodium hydrogen phosphate dodecahydrate used in the present invention can be from any source, preferably from a byproduct of the glyphosate production process, such as a byproduct of glyphosate mother liquor produced by the glycine process, which has a lower cost.

[0008] Furthermore, in step (1), the temperature of disodium hydrogen phosphate dodecahydrate is controlled at 40-80°C, such as 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, so that the disodium hydrogen phosphate dodecahydrate is kept in a molten state. The melting can be carried out in a melting kettle.

[0009] Furthermore, in step (2), a portion of water is removed from the molten disodium hydrogen phosphate dodecahydrate by evaporation, so that the disodium hydrogen phosphate dodecahydrate is dehydrated to form disodium hydrogen phosphate dihydrate. The evaporation can be carried out in an evaporation and dehydration device, and can be carried out by single-effect evaporation, multiple-effect evaporation, MVR evaporation, etc. The evaporation can be atmospheric evaporation or reduced pressure evaporation. Generally, reduced pressure evaporation is used, and the vacuum degree of reduced pressure evaporation is controlled at 0.05 MPa-0.09 MPa, for example, 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa.

[0010] Furthermore, in step (2), the evaporation temperature is 45-85°C, for example, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C.

[0011] Furthermore, in step (2), as the water evaporates, the formed disodium hydrogen phosphate dihydrate will precipitate. In order to ensure the convenience of material transfer, the dehydration ratio must be strictly controlled so that the material finally obtained after evaporation and dehydration is in a slurry with good fluidity. Experimental verification shows that it is better to evaporate and remove 35% to 42% of the total mass of disodium hydrogen phosphate dodecahydrate, such as 35%, 36%, 37%, 38%, 39%, 40%, 41%, and 42%. If the dehydration amount is too low, there is too much free water, and the moisture content of the material is too high, the effective conversion of disodium hydrogen phosphate dodecahydrate cannot be achieved, and the final product will contain other hydrates, which will affect the product yield and product quality, and will also increase the amount of hot air used in the subsequent flake process, increasing costs; if the dehydration amount is too high, the solid content of the material will be too high, which will make material transfer difficult, and the final product will contain a small amount of anhydrous disodium hydrogen phosphate, affecting product quality.

[0012] Furthermore, in step (3), the slurry material containing disodium hydrogen phosphate dihydrate obtained after evaporation and dehydration can be transferred to a melting kettle for melting in a flowing state. Melting is generally carried out under normal conditions, and the melting temperature is controlled at 90-100°C, such as 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, and 100°C. Temperatures greater than 100°C will cause dehydration of disodium hydrogen phosphate dihydrate, so the temperature should not be controlled too high.

[0013] Furthermore, in step (3), during the melting process of disodium hydrogen phosphate dihydrate, the temperature rise will also cause evaporation loss of water, and the dehydrated disodium hydrogen phosphate dihydrate will become anhydrous disodium hydrogen phosphate and precipitate, causing blockage of the components of the flake machine and affecting the subsequent flake process. Therefore, during the melting process, the formed water vapor is preferably converted back into water by condensation and reflux and returned to the system to prevent the disodium hydrogen phosphate dihydrate from losing water and precipitating in the melting kettle. For example, a condenser can be connected to the gas phase outlet of the melting kettle, and the gas phase is condensed to form condensed water and refluxed into the melting kettle.

[0014] Furthermore, in step (3), the molten disodium hydrogen phosphate dihydrate is preferably sprayed into the flaker through a distributor. The molten disodium hydrogen phosphate dihydrate should be quickly transferred into the flaker for flake formation. If it is not quickly transferred, the disodium hydrogen phosphate dihydrate will lose a small amount of water and become disodium hydrogen phosphate, which will not only affect the product quality, but also clog the distributor. The function of the distributor is to evenly spread the molten disodium hydrogen phosphate dihydrate onto the conveyor belt of the flaker. The distributor can be a spraying distribution device of the prior art.

[0015] Furthermore, in step (3), the flaker includes a housing, and the housing includes a conveyor belt. The front section of the conveyor belt is a hot air section for blowing away excess free water, and the rear section is a cold air section for cooling and solidifying the flakes. The length of the hot air section can be freely set according to the moisture required to be removed from the material, and the length of the cold air section ensures that the material is cooled and solidified into flakes. The hot air section and the cold air section are separated by a baffle, which is close to the conveyor belt and can be freely adjusted with a spacing of 2 to 5 mm. An air outlet is also provided on the top of the flaker.

[0016] Furthermore, in step (3), a suitable material distribution speed and conveyor belt speed are set so that the molten material is spread on the conveyor belt to form a liquid film with a thickness of about 0.5 to 1.5 mm, for example, 0.5 mm, 1.0 mm, or 1.5 mm.

[0017] Furthermore, in step (3), the liquid film first passes through the hot air section, and the excess free water is removed by hot air blowing. After dehydration in the hot air section, the molten disodium hydrogen phosphate dihydrate enters the cold air section, and is cooled by cold air blowing. The disodium hydrogen phosphate dihydrate is cooled and solidified on the conveyor belt, and is sliced ​​to form flaky disodium hydrogen phosphate dihydrate. The temperature of the hot air section is 90~120℃, for example, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, and the material is purged until the moisture content is ≤5%. The cold air section is dry cold air purging, and the temperature is 2~15℃, for example, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 11℃, 12℃, 13℃, 14℃, 15℃, and the material is purged until it is cooled and solidified.

[0018] The present invention has the following beneficial effects: 1. The present invention adopts a molten flake process to prepare disodium hydrogen phosphate dihydrate. The obtained flake product is easy to transport, has no overall agglomeration risk, and can achieve continuous production.

[0019] 2. The molten flake process of the present invention does not produce any mother liquor, does not discharge any mother liquor, and does not generate any hazardous waste.

[0020] 3. The flaky disodium hydrogen phosphate dihydrate obtained by the present invention has high quality, with a disodium hydrogen phosphate dihydrate content of ≥95%, a sodium chloride content of ≤0.2%, and a free water content of ≤5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The schematic diagram of the structure of the system used for preparing flaky disodium hydrogen phosphate dihydrate of the present invention.

[0022] In the figure, 1. disodium hydrogen phosphate dodecahydrate melting kettle; 2. first feed pump; 3. evaporation device; 31. liquid outlet pipe; 32. liquid return pipe; 4. steam compressor; 5. heat exchanger; 6. circulation pump; 7. condenser B; 8. disodium hydrogen phosphate dihydrate melting kettle; 9. second feed pump; 10. flake machine; 11. first three-way pipe; 12. second three-way pipe. DETAILED DESCRIPTION

[0023] The following is a description of exemplary embodiments of the present invention, including various details of the embodiments of the present invention to aid understanding, which should be considered as merely exemplary. Therefore, it should be appreciated by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Likewise, for clarity and simplicity, descriptions of well-known functions, operations, and structures are omitted in the following description.

[0024] In the following examples and comparative examples, the disodium hydrogen phosphate dodecahydrate used is the disodium hydrogen phosphate dodecahydrate by-product of the glyphosate mother liquor produced by the glycine process, and the indicators are as follows: Example 1 When preparing the flaky disodium hydrogen phosphate dihydrate, the present invention can use Figure 1 The system shown comprises a disodium hydrogen phosphate dodecahydrate melting kettle 1, an evaporation device 3, a disodium hydrogen phosphate dihydrate melting kettle 8 and a flake forming machine 10. The inlet of the melting kettle 1 is a solid feed port of disodium hydrogen phosphate dodecahydrate, which is arranged at the top, and the outlet is arranged at the bottom. The disodium hydrogen phosphate dodecahydrate can continuously enter the disodium hydrogen phosphate dodecahydrate melting kettle, and the molten liquid disodium hydrogen phosphate dodecahydrate continuously enters the evaporation device. The evaporation device 3 can be one of single effect, multi-effect, MVR, etc. The evaporation device 3 is provided with a liquid outlet pipe 31 and a liquid return pipe 32. The liquid outlet pipe 31 is connected to the pipe side inlet of the heat exchanger 5, and the liquid return pipe 32 is connected to the pipe side outlet of the heat exchanger; the liquid outlet pipe 31 is provided with a circulation pump 6, and a first three-way pipe 11 is provided on the pipeline connecting the evaporation device and the circulation pump, and the first three-way pipe is connected to the disodium hydrogen phosphate dodecahydrate melting kettle 1, and a second three-way pipe 12 is provided between the circulation pump and the heat exchanger 5, and the second three-way pipe is connected to the disodium hydrogen phosphate dihydrate melting kettle 8. The top of the evaporator is provided with an air outlet, which is connected to the shell side inlet of the heat exchanger through a pipeline, and the shell side outlet of the heat exchanger 5 is connected to the condenser A. A steam compressor 4 is provided on the pipeline connecting the air outlet of the evaporator and the heat exchanger. After the dehydration amount in the evaporator meets the requirements, the material enters the disodium hydrogen phosphate dihydrate melting kettle through the second three-way pipe.

[0025] The disodium hydrogen phosphate dihydrate melting kettle 8 is provided with a jacket, which is heated by steam inside and has insulation measures outside. The disodium hydrogen phosphate dihydrate melting kettle 8 is provided with a condenser B7 to condense the gas phase produced by the melting kettle, so that the water vapor is condensed into water and directly flows back into the kettle, ensuring that the disodium hydrogen phosphate dihydrate will not be converted into anhydrous disodium hydrogen phosphate and precipitate due to water loss during the melting process.

[0026] The discharge port of the disodium hydrogen phosphate dihydrate melting kettle 8 is connected to the inlet of the second feed pump 9, and the outlet of the second feed pump 9 is connected to the feed port of the flaker 10. The flaker includes a shell, and the shell includes a conveyor belt. The front section of the conveyor belt (near the feed port section) is a hot air section for blowing excess free water, and the rear section of the conveyor belt is a cold air section for cooling and solidifying the flakes. The length of the hot air section can be freely set according to the moisture required to be removed from the material, and the length of the cold air section ensures that the material is solidified and flakes. The hot air section and the cold air section are separated by a baffle, which is close to the conveyor belt and can be freely adjusted with a general interval of 2~5mm. Hot air enters from one side of the flaker feed port, and cold air enters from one side of the flaker discharge port. A distributor is provided at the flaker feed port. The molten material entering from the feed port is evenly sprayed on the conveyor belt through the distributor. The appropriate distribution speed and conveyor belt speed are set. The molten material is spread on the conveyor belt to form a layer of liquid film with a thickness of about 0.5~1.5mm. There are two gas phase outlets on the top of the flaker, one for discharging hot and humid air and the other for discharging cold and dry air. A slicing device is provided at the end of the conveyor belt. The flaker outlet is connected to the finished product bin, and the disodium hydrogen phosphate dihydrate that has been sliced ​​into flakes enters the finished product bin.

[0027] The above-mentioned devices can be directly purchased from the market.

[0028] Example 2 The system of Example 1 is used to prepare disodium hydrogen phosphate dihydrate in flake form, wherein the hot air section length in the flake forming machine is 9 m, and the cold air section length is 6 m, and the steps are as follows: 1. Melting of disodium hydrogen phosphate dodecahydrate: add disodium hydrogen phosphate dodecahydrate into the melting kettle at a flow rate of 5 t / h and keep it at 70°C until all the disodium hydrogen phosphate dodecahydrate becomes molten; 2. Evaporation and dehydration of disodium hydrogen phosphate dodecahydrate: The disodium hydrogen phosphate dodecahydrate melting kettle is connected to the MVR device, and the molten disodium hydrogen phosphate dodecahydrate is pumped into the MVR through a pump. The vacuum degree of the MVR device is controlled at 0.07Mpa, and the evaporation temperature is 65~68℃. 35% of the water of the total mass of disodium hydrogen phosphate dodecahydrate is evaporated and removed. Disodium hydrogen phosphate dihydrate solid is precipitated. At this time, the material is in a slurry that is easy to flow; 3. Pump the above slurry material into the disodium hydrogen phosphate dihydrate melting kettle at normal pressure and control the kettle temperature at 100°C to make all the disodium hydrogen phosphate dihydrate molten; 4. After the disodium hydrogen phosphate dihydrate becomes molten, it quickly enters the flake machine through the distributor. The distribution speed and the conveyor belt speed are controlled to form a liquid film with a thickness of 1.5 mm on the conveyor belt of the flake machine. The hot air section of the flake machine uses hot air blowing, and the hot air temperature is 110°C. The cold air section uses cold air blowing, and the cold air temperature is 5°C. The liquid film after cold air blowing is cooled and solidified, and sliced ​​to form flaky disodium hydrogen phosphate dihydrate. The obtained flaky disodium hydrogen phosphate dihydrate is produced at a flow rate of 2.6t / h. According to the provisions of 5.6 in HG / T2965-2009, the flaky disodium hydrogen phosphate dihydrate is tested. The content of disodium hydrogen phosphate dihydrate is 95.5%, the free water content is 1.3%, the sodium chloride content is 0.2%, and the content of other substances is 3.0%.

[0029] Example 3 The system of Example 1 is used to prepare disodium hydrogen phosphate dihydrate in flake form, wherein the hot air section length in the flake forming machine is 9 m, and the cold air section length is 6 m, and the steps are as follows: 1. Melting of disodium hydrogen phosphate dodecahydrate: add disodium hydrogen phosphate dodecahydrate into the melting kettle at a flow rate of 5 t / h and keep it at 60°C until all the disodium hydrogen phosphate dodecahydrate becomes molten; 2. Evaporation and dehydration of disodium hydrogen phosphate dodecahydrate: The disodium hydrogen phosphate dodecahydrate melting kettle is connected to the MVR device, and the molten disodium hydrogen phosphate dodecahydrate is pumped into the MVR through a pump. The vacuum degree of the MVR device is controlled at 0.08Mpa, and the evaporation temperature is 55-58℃. 40% of the water of the total mass of disodium hydrogen phosphate dodecahydrate is evaporated and removed. Disodium hydrogen phosphate dodecahydrate solid is precipitated. At this time, the material is in a slurry that is easy to flow; 3. Pump the above slurry material into the disodium hydrogen phosphate dihydrate melting kettle at normal pressure and control the kettle temperature at 95°C to make all the disodium hydrogen phosphate dihydrate molten; 4. After the disodium hydrogen phosphate dihydrate becomes molten, it quickly enters the flake machine through the distributor. The distribution speed and the conveyor belt speed are controlled to form a liquid film with a thickness of 1mm on the conveyor belt of the flake machine. The hot air section of the flake machine uses hot air blowing, and the hot air temperature is 100℃. The cold air section uses cold air blowing, and the cold air temperature is 8℃. The liquid film after cold air blowing is cooled and solidified, and sliced ​​to form flaky disodium hydrogen phosphate dihydrate. The obtained flaky disodium hydrogen phosphate dihydrate is produced at a flow rate of 2.56t / h. According to the provisions of 5.6 in HG / T2965-2009, the flaky disodium hydrogen phosphate dihydrate is tested. The content of disodium hydrogen phosphate dihydrate is 97.2%, the free water content is 1.15%, the sodium chloride content is 0.15%, and the content of other substances is 1.5%.

[0030] Example 4 The system of Example 1 is used to prepare disodium hydrogen phosphate dihydrate in flake form, wherein the hot air section length in the flake forming machine is 9 m, and the cold air section length is 6 m, and the steps are as follows: 1. Melting of disodium hydrogen phosphate dodecahydrate: add disodium hydrogen phosphate dodecahydrate into the melting kettle at a flow rate of 5 t / h and keep it at 50°C until all the disodium hydrogen phosphate dodecahydrate becomes molten; 2. Evaporation and dehydration of disodium hydrogen phosphate dodecahydrate: The disodium hydrogen phosphate dodecahydrate melting kettle is connected to the MVR device, and the molten disodium hydrogen phosphate dodecahydrate is pumped into the MVR through a pump. The vacuum degree of the MVR device is controlled at 0.09Mpa, and the evaporation temperature is 45~50℃. 42% of the total mass of disodium hydrogen phosphate dodecahydrate is evaporated and dehydrated. Disodium hydrogen phosphate dihydrate solid is precipitated. At this time, the material is in a slurry that is easy to flow; 3. Pump the above slurry material into the disodium hydrogen phosphate dihydrate melting kettle at normal pressure and control the kettle temperature at 92°C to make all the disodium hydrogen phosphate dihydrate molten; 4. After the disodium hydrogen phosphate dihydrate becomes molten, it quickly enters the flake machine through the distributor. The distribution speed and the conveyor belt speed are controlled to form a liquid film with a thickness of 0.5 mm on the conveyor belt of the flake machine. The hot air section of the flake machine uses hot air blowing, and the hot air temperature is 95°C. The cold air section uses cold air blowing, and the cold air temperature is 13°C. The liquid film after cold air blowing is cooled and solidified, and sliced ​​to form flaky disodium hydrogen phosphate dihydrate. The obtained flaky disodium hydrogen phosphate dihydrate is produced at a flow rate of 2.6t / h. According to the provisions of 5.6 in HG / T2965-2009, the flaky disodium hydrogen phosphate dihydrate is tested. The content of disodium hydrogen phosphate dihydrate is 95.5%, the free water content is 2.2%, the sodium chloride content is 0.2%, and the content of other substances is 2.1%.

[0031] Comparative Example 1 The flake disodium hydrogen phosphate dihydrate was prepared according to the method of Example 4, except that: in step 2, the disodium hydrogen phosphate dodecahydrate melting kettle was connected to the MVR device, the molten disodium hydrogen phosphate dodecahydrate was pumped into the MVR through a pump, the vacuum degree of the MVR device was controlled at 0.09 MPa, the evaporation temperature was 45-50° C., 30% of the total mass of the disodium hydrogen phosphate dodecahydrate was evaporated to remove water, and disodium hydrogen phosphate dihydrate solid was precipitated. At this time, the material was in a slurry that was easy to flow.

[0032] The final obtained flake disodium hydrogen phosphate dihydrate is produced at a flow rate of 3.24t / h. According to the provisions of 5.6 of HG / T2965-2009, the flake disodium hydrogen phosphate dihydrate is tested. The content of disodium hydrogen phosphate dihydrate is 76.8%, the free water content is 3.0%, the sodium chloride content is 0.18%, and the content of other substances is 20.2% (other substances may contain disodium hydrogen phosphate dodecahydrate and disodium hydrogen phosphate heptahydrate). It can be seen that if the evaporated water content is less than 35%, the water content will be high and the quality of disodium hydrogen phosphate dihydrate will be reduced.

[0033] Comparative Example 2 The flake disodium hydrogen phosphate dihydrate was prepared according to the method of Example 4, except that: in step 2, the disodium hydrogen phosphate dodecahydrate melting kettle was connected to the MVR device, the molten disodium hydrogen phosphate dodecahydrate was pumped into the MVR through a pump, the vacuum degree of the MVR device was controlled at 0.09 MPa, the evaporation temperature was 45-50° C., 45% of the total mass of the disodium hydrogen phosphate dodecahydrate was evaporated and removed, and disodium hydrogen phosphate dihydrate solid was precipitated. At this time, the material was in a paste state in the MVR device, and the material transfer was difficult. If the temperature during the material transfer process dropped below 40° C., the material was easy to solidify and block the pipeline.

[0034] The final flaky disodium hydrogen phosphate dihydrate was produced at a flow rate of 2.50 t / h. The flaky disodium hydrogen phosphate dihydrate was tested in accordance with the provisions of 5.6 of HG / T2965-2009. The content of disodium hydrogen phosphate dihydrate was 92.3%, the content of free water was 1.2%, the content of sodium chloride was 0.15%, and the content of other substances was 6.35% (other substances may be anhydrous disodium hydrogen phosphate).

[0035] Comparative Example 3 The flake disodium hydrogen phosphate dihydrate was prepared according to the method of Example 4, except that no condenser was installed on the disodium hydrogen phosphate dihydrate melting kettle. As the melting proceeded, solids precipitated in the kettle, which would block the distributor.

Claims

1. A method for preparing flaky disodium hydrogen phosphate dihydrate, characterized in that The following steps are involved: (1) melting disodium hydrogen phosphate dodecahydrate to obtain molten disodium hydrogen phosphate dodecahydrate; (2) evaporating and dehydrating the molten disodium hydrogen phosphate dodecahydrate to obtain a slurry material containing disodium hydrogen phosphate dihydrate; (3) The slurry material of step (2) is heated to make the disodium hydrogen phosphate dihydrate molten, and then the material is transferred to a flake forming machine for flake forming to obtain flake disodium hydrogen phosphate dihydrate.

2. The preparation method according to claim 1, characterized in that: In step (1), the temperature of disodium hydrogen phosphate dodecahydrate is controlled at 40-80° C. to keep it in a molten state.

3. The preparation method according to claim 1, characterized in that: Step (2) includes at least one of the following conditions: a. The temperature of evaporation and dehydration is 45~85℃; b. Evaporation removes 35% to 42% of the total mass of disodium hydrogen phosphate dodecahydrate; c. Evaporation and dehydration adopt single-effect evaporation, multiple-effect evaporation or MVR evaporation; d. Evaporative dehydration is evaporation at normal pressure or evaporation at reduced pressure.

4. The preparation method according to claim 3, characterized in that: In step (2), during the reduced pressure evaporation, the vacuum degree is 0.05-0.09 MPa and the evaporation temperature is 45-85°C.

5. The preparation method according to claim 1, characterized in that: In step (3), disodium hydrogen phosphate dihydrate becomes molten at 90-100°C.

6. The preparation method according to claim 1 or 5, characterized in that: In step (3), during the melting process of disodium hydrogen phosphate dihydrate, the water vapor formed is converted back into water by condensation and reflux, thereby preventing the disodium hydrogen phosphate dihydrate from being dehydrated and precipitated.

7. The preparation method according to claim 1 or 5, characterized in that: In step (3), the material forms a liquid film with a thickness of 0.5 to 1.5 mm in a flake machine. The liquid film is blown with hot air to remove free water, and then cooled and solidified by cold air blowing. After slicing, flaky disodium hydrogen phosphate dihydrate is obtained.

8. The preparation method according to claim 7, characterized in that: In step (3), the hot air temperature is 90-120°C, and the material is purged until the moisture content is ≤5%.

9. The preparation method according to claim 7, characterized in that: In step (3), the cold air temperature is 2~15℃.

10. The preparation method according to any one of claims 1 to 5, characterized in that: In step (1), the disodium hydrogen phosphate dodecahydrate is a by-product produced during the production of glyphosate.

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