A process for the continuous production of food grade anhydrous dibasic potassium phosphate

Abstract

The present application relates to the technical field of dipotassium hydrogen phosphate production, and discloses a process method for continuously producing food-grade anhydrous dipotassium hydrogen phosphate, which aims to obtain food-grade anhydrous dipotassium hydrogen phosphate product through one-step drying reaction in a rotary polymerization furnace, effectively solves the problems of many control processes, complicated process control and high production cost, and greatly reduces the coke content under the condition of ensuring the content of dipotassium hydrogen phosphate.

Description

Technical Field

[0001] This invention relates to the field of dipotassium hydrogen phosphate production technology, and in particular to a process for the continuous production of food-grade anhydrous dipotassium hydrogen phosphate. Background Technology

[0002] Existing methods for producing food-grade anhydrous dipotassium hydrogen phosphate typically involve crystallization and drying. Both methods have the following problems: (1) Crystallization process: This method utilizes a high concentration of food-grade thermal phosphoric acid to neutralize potassium hydroxide or potassium carbonate to produce dipotassium hydrogen phosphate. The process involves preparing a solution of potassium hydroxide or potassium carbonate with a mass fraction of approximately 30%, and gradually adding thermal phosphoric acid with a mass fraction of approximately 85% while continuously stirring. The reaction temperature is controlled at 80~100℃ and the pH of the reaction solution is controlled at 8.5~9.0. After the reaction is complete, the solution is filtered, heated and concentrated, cooled and crystallized, centrifuged, and dried to obtain dipotassium hydrogen phosphate. The mother liquor from the crystallization process is returned to the concentration process for reuse. The disadvantage of this method is that there are many control steps, the process control is cumbersome, and the production cost is high.

[0003] (2) Drying process: Currently, there are two drying processes: two-step drying with high tower and horizontal furnace and one-step drying with high tower. The two-step drying process with high tower and horizontal furnace has a long process, high energy consumption, and high production cost, which is not conducive to the large-scale production of orthophosphate. In addition, the one-step drying process with high tower produces products with low density and less loading capacity for the same volume, which cannot meet the needs of high-end customers. Summary of the Invention

[0004] This invention provides a continuous process for producing food-grade anhydrous dipotassium hydrogen phosphate. By controlling parameters such as furnace head temperature, furnace tail temperature, nozzle diameter, spray range angle, flow rate, and pressure, it eliminates the need for high-tower drying and uses a rotary polymerization furnace for one-step production of fixed dipotassium hydrogen phosphate. This solves the problems of numerous control steps, cumbersome process control, and high production costs in the crystallization method, and the long, energy-intensive, and costly two-step drying process using high towers and horizontal furnaces in the drying method, which is not conducive to the large-scale production of orthophosphates. In addition, the one-step high-tower drying process produces products with lower density, resulting in a smaller loading capacity for the same volume.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate includes the following steps: Neutralization: Food-grade refined wet-process phosphoric acid and liquid ion-exchange membrane potassium hydroxide are added to the neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. During the reaction, the temperature is controlled at 100~150℃. At the end of the neutralization reaction, the pH is controlled at 8.5~8.9 and the specific gravity is 1.50~1.62g / mL. After passing the test, the solution is transferred to a storage tank for later use. Polymerization: A direct-fired burner is installed in the rotary polymerization furnace, using hydrogen as fuel. The furnace is equipped with longitudinally arranged lifting plates that are evenly distributed. After controlling the furnace head temperature to 150~160℃ and the furnace tail temperature to 125~135℃, feeding begins. A high-pressure pump is used to spray the neutralization liquid into the rotary polymerization furnace through an atomizing spray gun for polymerization reaction. The material is atomized and fully contacts the flame, instantly evaporating the moisture. The solid material falls into the furnace in granular form and polymerizes into dipotassium hydrogen phosphate under a negative pressure maintained at -0.25MPa. Solid handling: After cooling and crushing, dipotassium hydrogen phosphate is transported to the packaging area by a conveyor.

[0006] Preferably, in the neutralization step, the raw materials used are food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide.

[0007] Preferably, in the neutralization step, the final reaction point of the neutralization solution is controlled at pH 8.8-8.9 and specific gravity 1.58-1.62 g / mL.

[0008] Preferably, the feed flow rate of the spray gun in the polymerization step is controlled at 1.8~2.5m³. 3 / h, pressure controlled at 2.0~3.0MPa.

[0009] Preferably, the spray gun used in the polymerization step has a nozzle with an orifice diameter of 3.0~3.5mm and an atomization angle of 45°.

[0010] More preferably, the spray gun in the polymerization step uses a nozzle with an orifice diameter of 3.0 mm and an atomization angle of 45°.

[0011] Preferably, the furnace head temperature is controlled at 138~148℃ and the furnace tail temperature is controlled at 115~120℃ in the polymerization step.

[0012] Preferably, the method further includes a gas treatment step: the induced draft fan draws the hot air and dust in the rotary polymerization furnace to the spray washing tower for washing and dust removal before venting; the circulating liquid in the spray washing tower is filtered and then reused in the neutralization slurry.

[0013] More preferably, the gas treatment step also includes an induced draft fan drawing the hot air and dust from the cooling device in the solid treatment step into a spray washing tower for washing and dust removal before venting. The circulating liquid in the spray washing tower is filtered and then reused in the neutralization slurry.

[0014] Preferably, the dipotassium hydrogen phosphate product contains 98% or more of dipotassium hydrogen phosphate and less than 10% of pyrophosphate.

[0015] The beneficial effects of this invention are: 1. Food-grade anhydrous dipotassium hydrogen phosphate is obtained by drying and reacting in a rotary polymerization furnace in one step, which effectively solves the problems of multiple control steps, complicated process control and high production costs. 2. There are relatively few process control parameters, mainly the feed pressure, atomization angle, atomization nozzle diameter, and the temperature of the furnace head and tail during drying; 3. Reduce the pyrophosphate content in the product, making the coke content much lower than that produced by other processes; 4. Using water washing dust removal can effectively separate and reuse dust in exhaust gas through hydrolysis; 5. Replacing thermal phosphoric acid with wet phosphoric acid can effectively reduce production costs. Detailed Implementation

[0016] As a preferred embodiment 1, a process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate includes the following steps: Neutralization: Food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide are added to the neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. During the reaction, the temperature is controlled at 100~150℃. At the end of the neutralization reaction, the pH is controlled at 8.5~8.9 and the specific gravity is 1.50~1.62g / mL. After passing the test, it is transferred to the storage tank for later use. Polymerization: A direct-fired burner is installed inside the rotary polymerization furnace, using hydrogen as fuel. The furnace is equipped with equidistantly distributed longitudinal lifters. Feeding begins after the furnace head temperature is controlled at 150~160℃ and the furnace tail temperature at 125~135℃. A high-pressure pump injects the neutralization liquid into the rotary polymerization furnace through an atomizing spray gun for polymerization. The feed flow rate is controlled at 1.8~2.5 m³ / h. 3 / h, pressure controlled at 2.0~3.0MPa, spray gun uses nozzle with 3.0~3.5mm orifice diameter and 45° atomization angle, the material is fully atomized and comes into contact with the flame, the moisture is evaporated instantly, the solid material falls into the furnace in granular form, and polymerizes into dipotassium hydrogen phosphate product under negative pressure maintained at -0.25MPa; Solid processing: After cooling and crushing, dipotassium hydrogen phosphate is conveyed to the packaging area by a conveyor. Gas handling: The induced draft fan draws the hot air and dust from the rotary polymerization furnace and the hot air and dust from the cooling device in the processing steps into the spray washing tower for washing and dust removal before being discharged. The circulating liquid in the spray washing tower is filtered and then reused in the neutralization slurry.

[0017] As a preferred embodiment 2, a process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate includes the following steps: Neutralization: Food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide are added to the neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. During the reaction, the temperature is controlled at 100~150℃. At the end of the neutralization reaction, the pH is controlled at 8.8~8.9 and the specific gravity is 1.58~1.62g / mL. After passing the test, it is transferred to the storage tank for later use. Polymerization: A direct-fired burner is installed inside the rotary polymerization furnace, using hydrogen as fuel. The furnace is equipped with equidistantly distributed longitudinal lifters. Feeding begins after the furnace head temperature is controlled at 150~160℃ and the furnace tail temperature at 125~135℃. A high-pressure pump injects the neutralization liquid into the rotary polymerization furnace through an atomizing spray gun for polymerization. The feed flow rate is controlled at 1.8~2.5 m³ / h. 3 / h, pressure controlled at 2.0~3.0MPa, the spray gun uses a nozzle with a 3.0mm orifice and a 45° atomization angle, the material is fully atomized and comes into contact with the flame, the moisture is evaporated instantly, the solid material falls into the furnace in granular form, and polymerizes into dipotassium hydrogen phosphate product under a negative pressure maintained at -0.25MPa; Solid processing: After cooling and crushing, dipotassium hydrogen phosphate is conveyed to the packaging area by a conveyor. Gas handling: The induced draft fan draws the hot air and dust from the rotary polymerization furnace and the hot air and dust from the cooling device in the processing steps into the spray washing tower for washing and dust removal before being discharged. The circulating liquid in the spray washing tower is filtered and then reused in the neutralization slurry.

[0018] As a preferred embodiment 3, food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide were added to a neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. The reaction temperature was controlled at 100-150℃. At the end of the neutralization reaction, the pH was controlled at 8.96 and the specific gravity at 1.60 g / mL. After passing the tests, the solution was stored in a tank for later use. Polymerization was then carried out using a spray gun with a 3.5mm orifice diameter and a 45° atomization angle, under the conditions shown in Table 1. Table 1

[0019] The results are shown in Table 2: Table 2

[0020] The test data from Examples 3-1 to 3-4 show that after cooling down the product during the first polymerization, the coke content decreased from 45.62% at startup to 11.69%, a significant decrease, failing to meet the predetermined target of a coke content below 10%.

[0021] Problems found: When the furnace head temperature is above 180℃ and the furnace tail temperature is above 135℃, the coke content is above 12% and the pH is above 9.3; when the temperature is below 135℃, the amount of agglomerated material at the polymerization furnace tail increases, and the coke content and pH do not decrease significantly.

[0022] As a preferred embodiment 4, food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide were added to a neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. During the reaction, the temperature was controlled at 100-150℃. At the end of the neutralization reaction, the pH was controlled at 8.86-8.89, and the specific gravity at 1.60 g / mL. After passing the tests, the solution was stored in a tank for later use. Polymerization was then carried out using a spray gun with a 3.0 mm orifice diameter and a 45° atomization angle, under the conditions shown in Table 3. Table 3

[0023] The results are shown in Table 4: Table 4

[0024] The test data from Examples 4-1 to 4-4 show that after adjusting the pH of the slurry, the temperature of the primary polymerization furnace head and tail continued to decrease, and the coke content of the product decreased from 11.78% to 9%, with a significant decrease in coke content. The pH stabilized at around 9.15, achieving the predetermined target of coke content below 10%.

[0025] Problems: When the furnace head temperature is below 150℃ and the furnace tail temperature is below 130℃, the coke content remains stable below 10%. There is more agglomerated material than powder at the furnace tail of the polymerization furnace, and the furnace tail feed pipe is frequently blocked, making it impossible to maintain stable and normal production.

[0026] As a preferred embodiment 5, food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide were added to a neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. During the reaction, the temperature was controlled at 100-150℃. At the end of the neutralization reaction, the pH was controlled at 8.85-8.88, and the specific gravity at 1.60 g / mL. After passing the tests, the solution was transferred to a storage tank for later use. Polymerization was then carried out using a spray gun with a 3.0 mm orifice diameter and a 45° atomization angle, under the conditions shown in Table 5. Table 5

[0027] The results are shown in Table 6: Table 6

[0028] The test data from Examples 5-1 to 5-4 show that continued cooling of the primary polymerization furnace head and tail reduced the product coke content from 10.31% to 5.95%, a significant decrease. The pH stabilized at around 9.05, achieving the predetermined target of a coke content below 10%, and the flow rate stabilized at 2.45~2.5m³. 3 At a rate of / h, more than 30 tons of dipotassium phosphate can be produced per day, achieving both quality and quantity targets. The coke content of the product produced by this process is superior to that of products from competitors.

[0029] Problem: Flow rate 2.3m 3 At a flow rate of 1.45 m³ / h, with a furnace head temperature of 160-180℃ and a furnace tail temperature of 120-130℃, the pH was 9.08. The amount of agglomerated material at the furnace tail decreased significantly, while the coke content increased to approximately 10%. Increasing the furnace speed and flow rate did not significantly reduce the coke content. 3 When the furnace head temperature is 138~148℃ and the furnace tail temperature is 115~120℃, the coke content can be stabilized at a minimum of about 5.5%. However, the material at the furnace tail tends to clump together and wet material appears intermittently, causing frequent blockages in the system and making it impossible to maintain stable and normal production.

[0030] In summary, through Examples 3 to 5, the feasibility of one-step production of dipotassium hydrogen phosphate was initially verified through pilot-scale process. No furnace wall slagging occurred after 48 hours of continuous operation, and production was continuous and stable. Secondly, the control parameters for dipotassium phosphate production were determined through trial and error. The neutralized slurry pH was 8.8-8.9, the specific gravity was 1.58-1.62 g / mL, and production was relatively stable within the range of 150-160℃ at the furnace head and 125-135℃ at the furnace tail, with the coke content meeting requirements. The optimal coke content was achieved within the range of 138-148℃ at the furnace head and 115-120℃ at the furnace tail. Below 125℃ at the furnace tail, there was a significant amount of agglomerated material, and below 120℃, intermittent wet material appeared at the furnace tail.

[0031] As a preferred embodiment 6, a trial production of embodiments 5-3 was carried out, and the batches of products were analyzed. The test results are shown in Table 7. Table 7

[0032] It meets the requirements for the product.

Claims

1. A process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate, characterized in that, Includes the following steps: Neutralization: Food-grade refined wet-process phosphoric acid and liquid ion-exchange membrane potassium hydroxide are added to the neutralization vessel at an acid-to-base ratio of 1:2 to generate dipotassium hydrogen phosphate neutralization solution. During the reaction, the temperature is controlled at 100~150℃. At the end of the neutralization reaction, the pH is controlled at 8.5~8.9 and the specific gravity is 1.50~1.62g / mL. After passing the test, the solution is transferred to a storage tank for later use. Polymerization: A direct-fired burner is installed inside the rotary polymerization furnace, using hydrogen as fuel. The furnace is equipped with equidistantly distributed longitudinal lifters. Feeding begins after the furnace head temperature is controlled at 150~160℃ and the furnace tail temperature at 125~135℃. A high-pressure pump injects the neutralized liquid into the rotary polymerization furnace through an atomizing spray gun for polymerization. The feed flow rate of the spray gun is controlled at 1.8~2.5 m³ / h. 3 / h, pressure controlled at 2.0~3.0Mpa, spray gun uses nozzle with 3.0~3.5mm orifice diameter and 45° atomization angle, the material is fully atomized and comes into contact with the flame, the moisture is evaporated instantly, the solid material falls into the furnace in granular form, and polymerizes into dipotassium hydrogen phosphate product under negative pressure maintained at -0.25MPa; Solid handling: After cooling and crushing, dipotassium hydrogen phosphate is transported to the packaging area by a conveyor.

2. The process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate according to claim 1, characterized in that, In the neutralization step, the raw materials used are food-grade refined 85% wet-process phosphoric acid and liquid ion-exchange membrane 48% potassium hydroxide.

3. The process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate according to claim 1, characterized in that, In the neutralization step, the final reaction point of the neutralization solution is controlled at pH 8.8-8.9 and specific gravity 1.58-1.62 g / mL.

4. The process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate according to claim 1, characterized in that, In the polymerization step, the spray gun uses a nozzle with an orifice diameter of 3.0 mm and an atomization angle of 45°.

5. The process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate according to claim 1, characterized in that, The method also includes a gas treatment step: the induced draft fan draws the hot air and dust in the rotary polymerization furnace to the spray washing tower for washing and dust removal before venting. The circulating liquid in the spray washing tower is filtered and then reused in the neutralization slurry.

6. The process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate according to claim 5, characterized in that, The gas treatment step also includes an induced draft fan drawing the hot air and dust from the cooling device in the solid treatment step into a spray washing tower for washing and dust removal before being discharged. The circulating liquid in the spray washing tower is filtered and then reused in the neutralization slurry.

7. The process for continuous production of food-grade anhydrous dipotassium hydrogen phosphate according to claim 1, characterized in that, The dipotassium hydrogen phosphate product contains 98% or more of dipotassium hydrogen phosphate and less than 10% of pyrophosphate.

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