A mixed acid treatment device

Abstract

The application relates to the tail gas treatment technical field in the lithium hexafluorophosphate production process, and specifically discloses a mixed acid treatment device, a reaction kettle in communication with a mixed acid storage tank, a neutralization tank, a plate-and-frame filter press, a calcium liquid collecting tank, a fluorine removal tank, a filter, a calcium chloride storage tank, a thickening evaporator, a steam heater and a granulator are sequentially communicated with the reaction kettle through pipelines; conveying pumps are connected between the reaction kettle and the neutralization tank, the calcium liquid collecting tank and the fluorine removal tank, the fluorine removal tank and the filter, the filter and the thickening evaporator, and the thickening evaporator and the calcium chloride storage tank. The device converts the mixed acid into calcium fluoride and calcium chloride solid matters, and then sells the solid matters, so that the mixed acid does not need to be transported to an external factory for treatment, transportation cost is saved, transportation risks of the mixed acid are avoided, and the calcium fluoride and the calcium chloride can bring a large amount of economic value to the factory.

Description

Technical Field

[0001] This utility model relates to the field of tail gas treatment technology in the production process of lithium hexafluorophosphate, and specifically to a mixed acid treatment device. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is the main raw material for manufacturing electrolytes for lithium-ion batteries. Due to its good ionic conductivity and electrochemical stability, it is currently the most commonly used lithium salt electrolyte and is mainly used to prepare lithium-ion battery electrolytes. With the rise of the new energy market, the demand for lithium hexafluorophosphate is increasing.

[0003] Currently, the main production method for lithium hexafluorophosphate (LiPF6) is the HF solvent method. This method involves dissolving LiF in hydrofluoric acid and then reacting it with phosphorus pentafluoride (PF5). The reaction equation is: PCl5 + 5HF + LiF → LiPF6 + 5HCl, yielding the LiPF6 product. However, this method produces a large amount of the byproduct HCl-HF mixed acid gas. Hydrogen fluoride (HF) gas is highly corrosive, irritating the respiratory tract, damaging the lungs, and causing bone damage with long-term exposure at low concentrations; it also pollutes the air and corrodes equipment. Hydrogen chloride (HCl) is a gas with an irritating odor, highly soluble in water, and forms hydrochloric acid mist when it encounters water vapor in the atmosphere. This hydrochloric acid mist falls to the ground with precipitation, forming acid rain that causes widespread damage to soil, water bodies, buildings, and plants. Furthermore, hydrogen chloride gas is highly corrosive. It corrodes metallic materials such as steel structures and copper wires, shortening their service life. Hydrogen chloride can also react chemically with materials such as marble and limestone on buildings, causing erosion and peeling of the material surface, damaging the building's appearance and structural integrity. Therefore, the byproduct HCl-HF mixed acid gas must be recovered and treated during the preparation of lithium hexafluorophosphate.

[0004] Chinese utility model patent CN210206374U discloses a tail gas treatment device in the production process of lithium hexafluorophosphate. This device includes a two-stage water washing tower and a two-stage alkaline washing tower. These towers absorb the large amounts of hydrogen chloride and hydrogen fluoride gases generated during lithium hexafluorophosphate production to prepare mixed acid for subsequent by-product production, effectively reducing the amount of alkaline absorbent used in the subsequent alkaline washing process. However, this device can only recover hydrogen chloride and hydrogen fluoride gases and convert them into mixed acid; it cannot further convert the mixed acid into safe products. Due to the high processing cost of the mixed acid itself, the factory has to sell it to fluorochemical companies for processing. Given the high risk associated with mixed acid, the factory incurs high transportation costs and bears significant transportation risks. Therefore, the mixed acid converted from the recovered hydrogen chloride and hydrogen fluoride gases by this device is unlikely to generate economic value for the factory. Utility Model Content

[0005] The purpose of this invention is to provide a mixed acid treatment device to solve the problem that existing devices are not capable of converting mixed acid into safe products, which forces factories to sell mixed acid to fluorochemical manufacturers for processing, resulting in high transportation costs and risks for the factories, and making it difficult for mixed acid to generate economic value for the factories.

[0006] To solve the above-mentioned technical problems, the following technical solution is provided:

[0007] A mixed acid treatment device includes a reaction vessel connected to a mixed acid storage tank. After the reaction vessel, a neutralization tank, a plate and frame filter press, a calcium solution collection tank, a defluorination tank, a filter, a calcium chloride storage tank, a thickening evaporator, a steam heater, and a granulator are connected in sequence via pipelines. A transfer pump is connected between the reaction vessel and the neutralization tank, the calcium solution collection tank and the defluorination tank, the defluorination tank and the filter, and the calcium chloride storage tank and the thickening evaporator.

[0008] The basic principle of the above technical solution is as follows: mixed acid and crushed calcium carbonate are added together to a reaction vessel to generate a mixed solution containing calcium chloride and calcium fluoride. The mixed solution is then pumped into a neutralization tank via a transfer pump to adjust the pH to a weakly alkaline state to avoid residual mixed acid. The neutralized liquid is then pumped into a plate and frame filter press for filtration. The filter cake is calcium fluoride. The filtrate flows into a calcium solution collection tank and is then pumped into a defluorination tank. After defluorination by a defluorinating agent in the defluorination tank, the solution is pumped into a filter for filtration. The resulting calcium chloride solution is stored in a calcium chloride storage tank. The calcium chloride solution in the storage tank is then pumped sequentially into a thickening evaporator and a steam heater for thickening and concentration. When the calcium chloride concentration reaches approximately 20% to 45%, it is sent to a granulator to prepare calcium chloride granules.

[0009] The beneficial effects of the above technical solution are as follows: Compared with the existing mixed acid solution that can only collect and convert the waste gas generated during the lithium hexafluorophosphate production process into hydrogen chloride and hydrogen fluoride without subsequent mixed acid treatment equipment, this technical solution sets up mixed acid treatment equipment to convert the mixed acid into calcium fluoride and calcium chloride solids before selling it. There is no need to transport the mixed acid to an external factory for processing, saving transportation costs and avoiding the transportation risks of mixed acid. Moreover, the sale of calcium fluoride and calcium chloride can bring a lot of economic value to the factory.

[0010] Furthermore, the reactor is equipped with a jacket, and the jacket contains circulating cooling water for temperature control.

[0011] Furthermore, the reactor is connected to a screw conveyor via a pipeline, and the screw conveyor's feed inlet is connected to a crusher, which is connected to a calcium carbonate bucket elevator. Solid calcium carbonate blocks are fed into the crusher via the bucket elevator for crushing, and then fed into the reactor via the screw conveyor to react with the mixed acid.

[0012] Furthermore, the crushing particle size of the crusher is controlled at D50 between 20 and 35 mm. Calcium carbonate with a crushed particle size of 20-35 mm can react better with mixed acid, improving the efficiency of mixed acid treatment.

[0013] Furthermore, the stirring rate of the reactor is controlled at 20~30Hz, the reaction time is 3~5h, and the reaction temperature is less than 60℃.

[0014] Furthermore, the neutralization tank is connected to a lime mixing tank, into which production water and calcium oxide are added to produce lime water. The lime water and calcium hydroxide are used to adjust the pH of the mixed solution containing calcium chloride and calcium fluoride generated in the reactor, controlling the pH value between 7.5 and 9 to make the solution weakly alkaline and avoid residual mixed acid. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of an embodiment of the present utility model.

[0016] The reference numerals in the accompanying drawings of the instruction manual include: 1. Reactor; 2. Screw conveyor; 3. Crusher; 4. Calcium carbonate bucket elevator; 5. Neutralization tank; 6. Plate and frame filter press; 7. Calcium solution collection tank; 8. Defluorination tank; 9. Calcium chloride storage tank; 10. Thickening evaporator; 11. Steam heater; 12. Granulator; 13. Conveying pump; 14. Lime mixing tank; 15. Chain conveyor; 16. Detailed Implementation

[0017] The following detailed description illustrates the specific implementation method:

[0018] The basic implementation examples are as follows: Figure 1 As shown:

[0019] A mixed acid treatment device, such as Figure 1As shown, the reactor includes a reaction vessel 1 connected to a mixed acid storage tank. The reaction vessel 1 is equipped with a jacket containing circulating cooling water for temperature control. A chain conveyor 16 is connected to the feed inlet of the reaction vessel 1 via a pipe. A screw conveyor 2 is connected to the feed inlet of the chain conveyor 16. The screw conveyor 2 is equipped with a weight sensor for measuring the weight of calcium carbonate. A crusher 3 is connected to the feed inlet of the screw conveyor 2. The crushing particle size of the crusher 3 is controlled at D50 between 20 and 35 mm. A calcium carbonate bucket elevator 4 is connected to the outlet of the reactor 1, and via pipelines, a neutralization tank 5, a plate and frame filter press 6, a calcium solution collection tank 7, a defluorination tank 8, a filter 9, a calcium chloride storage tank 10, a thickening evaporator 11, a steam heater 12, and a granulator 13 are sequentially connected. Transfer pumps 14 are connected between the reactor 1 and the neutralization tank 5, between the neutralization tank 5 and the plate and frame filter press 6, between the calcium solution collection tank 7 and the defluorination tank 8, between the defluorination tank 8 and the filter 9, and between the calcium chloride storage tank 10 and the thickening evaporator 11. Above the inlet of the neutralization tank 5, a lime mixing tank 15 is connected via a pipeline. Production water and calcium oxide are added to the lime mixing tank 15 to produce lime water. The lime water and calcium hydroxide are then introduced into the neutralization tank 5 for pH adjustment.

[0020] The specific implementation process is as follows:

[0021] The mixed acid and crushed calcium carbonate are added together to reactor 1. The stirring speed in reactor 1 is controlled at 20~30Hz, and the reaction temperature is kept below 60℃. When the reaction temperature exceeds 60℃, it can be cooled by cooling water in the jacket. The reaction is carried out for 5 hours to generate a mixed solution containing calcium chloride and calcium fluoride. The mixed solution is then transferred to neutralization tank 5 via transfer pump 14 to adjust the pH to 7.5~9, making the mixed solution weakly alkaline and avoiding residual mixed acid. The pH-adjusted mixed solution is then pumped into... The filter press 6 performs filtration, producing calcium fluoride as the filter cake. The filtrate flows into the calcium solution collection tank 7 and is then pumped into the defluorination tank 8. After defluorination with a defluorinating agent in the defluorination tank 8, the filtrate is pumped into the filter 9 for filtration. The resulting calcium chloride solution is stored in the calcium chloride storage tank 10. The calcium chloride solution in the storage tank 10 is then pumped sequentially into the thickening evaporator 11 and the steam heater 12 for thickening and concentration. When the calcium chloride concentration reaches approximately 20% to 45%, it is sent to the granulator 13 to prepare calcium chloride granules. This device includes equipment for processing mixed acid, converting it into calcium fluoride and calcium chloride solids for sale. This eliminates the need to transport the mixed acid to an external factory for processing, saving transportation costs and avoiding the risks associated with transporting mixed acid. Furthermore, the sale of calcium fluoride and calcium chloride brings significant economic value to the factory.

[0022] The above descriptions are merely embodiments of this utility model, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of this utility model, and these should also be considered within the scope of protection of this utility model. These modifications will not affect the effectiveness of the implementation of this utility model or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A mixed acid treatment apparatus, comprising a reaction vessel connected to a mixed acid storage tank, characterized in that: The reactor is connected in sequence via pipelines to a neutralization tank, a plate and frame filter press, a calcium solution collection tank, a defluorination tank, a filter, a calcium chloride storage tank, a thickening evaporator, a steam heater, and a granulator; a transfer pump is connected between the reactor and the neutralization tank, the calcium solution collection tank and the defluorination tank, the defluorination tank and the filter, and the calcium chloride storage tank and the thickening evaporator.

2. The mixed acid treatment device according to claim 1, characterized in that: The reactor is equipped with a jacket, and the jacket contains circulating cooling water for temperature control.

3. The mixed acid treatment device according to claim 2, characterized in that: The reactor is connected to a screw conveyor via a pipeline. The screw conveyor's feed inlet is connected to a crusher, and the crusher is connected to a calcium carbonate bucket elevator.

4. The mixed acid treatment device according to claim 3, characterized in that: The crushing particle size of the crusher is controlled at D50 of 20~35mm.

5. The mixed acid treatment device according to claim 4, characterized in that: The stirring rate of the reactor is controlled at 20~30Hz, the reaction time is 3~5h, and the reaction temperature is less than 60℃.

6. The mixed acid treatment device according to claim 5, characterized in that: The neutralization box is connected to a lime mixing box, into which production water and calcium oxide are added to produce lime water.

Images