Lithium hexafluorophosphate synthesis tail gas comprehensive utilization system and method

Abstract

The invention discloses a lithium hexafluorophosphate synthesis tail gas comprehensive utilization system and method. The system comprises a tail gas compressor, a tail gas precooler, a gas-liquid separator, a 1 # tower, a partial condenser, a 1 # tower reflux tank, a reboiler, a 2 # tower, an HCl absorption device and a drying device. The tail gas is separated through a gas-liquid separator after being compressed and precooled, a liquid phase enters a 1 # tower for separation, an anhydrous hydrogen fluoride finished product is obtained in a tower kettle, a gas phase at the top of the 1 # tower is subjected to partial condensation, then gas reflux is performed, liquid is sent to the 1 # tower and a 2 # tower respectively, and the gas phase separated by the gas-liquid separator enters the 2 # tower to be in contact with liquid extracted from the top of the 1 # tower in the 2 # tower to recover residual hydrogen fluoride; recycled tail gas is introduced into an HCl absorption device to prepare hydrochloric acid, and nitrogen-containing tail gas is introduced into a drying device to obtain qualified nitrogen which is recycled to a lithium hexafluorophosphate production section. Compared with conventional pressurized rectification, the system has the advantages that the equipment operation pressure and energy consumption are lower, the HF content in the terminal HCl tail gas is lower, a large amount of nitrogen is recycled, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of tail gas treatment, and in particular relates to a system and method for comprehensive utilization of tail gas from lithium hexafluorophosphate synthesis. Background Art

[0002] Lithium hexafluorophosphate is the main electrolyte lithium salt used in commercial lithium-ion batteries, and has achieved large-scale industrial production. At present, the industrial production process of lithium hexafluorophosphate is mainly the hydrogen fluoride solvent method. The raw materials of this process are easy to obtain, the reaction time is short, the reaction process is easy to control, and the raw material conversion rate is high. The general steps are: dissolve lithium fluoride in anhydrous hydrogen fluoride to form LiF•HF solution, pass phosphorus pentachloride and hydrogen fluoride to react to obtain high-purity phosphorus pentafluoride to react to generate lithium hexafluorophosphate crystals, and separate and dry to obtain lithium hexafluorophosphate products.

[0003] During the production process, excess hydrogen fluoride, phosphorus pentafluoride, a large amount of hydrogen chloride produced by the reaction, and nitrogen used for purging will be discharged from the reaction system as production tail gas. At present, the methods for recovering hydrogen fluoride in the tail gas mainly include condensation method and compression distillation method. Due to the presence of low-boiling point substances such as hydrogen chloride and nitrogen in the tail gas, the hydrogen fluoride condensation in the condensation method is incomplete, the recovery rate is low, and the purity is not high. The compression distillation method has a high operating pressure. In addition, due to the large fluctuations in the components of the tail gas from the synthesis of lithium hexafluorophosphate, the traditional compression distillation method cannot adapt to this fluctuation well, and it is easy to cause the HF in the tail gas after treatment to exceed the standard, resulting in a partial waste of fluorine resources. In addition, the traditional treatment process does not consider nitrogen recovery. In fact, after nitrogen recovery, it not only reduces the nitrogen consumption in the plant area, but also greatly reduces the emission of harmful gases, which is more in line with environmental protection policy requirements. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide a system and method for comprehensive utilization of lithium hexafluorophosphate synthesis tail gas.

[0005] The specific technical solutions are as follows: A lithium hexafluorophosphate synthesis tail gas comprehensive utilization system, comprising a tail gas compressor, a tail gas precooler, a gas-liquid separator, a No. 1 tower, a partial condenser, a No. 1 tower reflux tank, a reboiler, a No. 2 tower, an HCl absorption device and a drying device; The outlet pipeline of the tail gas compressor is connected to the tail gas precooler and the gas-liquid separator in sequence, the gas outlet pipeline of the gas-liquid separator is connected to the bottom of the 2# tower, the liquid outlet pipeline of the gas-liquid separator is connected to the 1# tower, the top outlet pipeline of the 1# tower is connected to the partial condenser, the outlet pipeline of the partial condenser is divided into two pipelines, one pipeline is refluxed and connected to the outlet pipeline of the tail gas compressor, and the other pipeline is connected to the reflux tank of the 1# tower and then divided into two pipelines to connect the tops of the 1# tower and the 2# tower respectively, the bottom outlet pipeline of the 1# tower is connected to the reboiler reflux, the bottom outlet pipeline of the 2# tower is divided into two pipelines, which are respectively connected to the 1# tower and the middle of the 2# tower, and the top pipeline of the 2# tower is connected to the HCl absorption device and the drying device in sequence.

[0006] Furthermore, a condensate delivery pump is provided on the pipeline connecting the gas-liquid separator and the 1# tower, a 1# tower reflux pump is provided on the outlet pipeline of the 1# tower reflux tank, and an absorption liquid delivery pump is provided on the outlet pipeline at the bottom of the 2# tower.

[0007] Furthermore, the HCl absorption device includes a multi-stage falling film absorber or a multi-stage packed tower, and is equipped with a water washing tower and an alkali washing tower; the drying device includes a heat exchanger, a cold dryer and a molecular sieve dryer, the bottom of the multi-stage falling film absorber or the top of the multi-stage packed tower is connected to the bottom of the water washing tower through a pipeline, the top of the water washing tower is connected to the bottom of the alkali washing tower through a pipeline, the top of the alkali washing tower is connected to the inlet of the heat exchanger tube side, the outlet of the heat exchanger tube side is connected to the inlet of the cold dryer, the outlet pipeline of the cold dryer is connected to the shell side inlet of the heat exchanger, the shell side outlet pipeline is connected to the inlet of the dryer, and the outlet pipeline of the dryer goes to the nitrogen use point in the plant.

[0008] A method for comprehensively utilizing lithium hexafluorophosphate synthesis tail gas using the above system comprises the following steps: 1) Compressing the tail gas of lithium hexafluorophosphate synthesis by a tail gas compressor, condensing the compressed tail gas by a tail gas precooler, and separating it into uncondensed gas and condensed liquid by a gas-liquid separator; 2) The condensate is transported to the 1# tower through the condensate delivery pump for separation and purification to obtain high-purity anhydrous hydrogen fluoride; 3) The gas produced from the top of the 1# tower is partially condensed into liquid through a partial condenser. The liquid passes through the 1# tower reflux tank and enters the 1# tower and the 2# tower respectively. The uncondensed gas phase refluxes to the tail gas precooler; 4) The uncondensed gas in step 1) is contacted with the liquid produced from the top of tower 1# in tower 2# to recover the remaining hydrogen fluoride; 5) The recovered tail gas is passed into the HCl absorption device to prepare hydrochloric acid, and the nitrogen-containing tail gas is passed into the drying device to obtain qualified nitrogen gas to be reused in the lithium hexafluorophosphate production section.

[0009] Furthermore, in step 1), the lithium hexafluorophosphate synthesis tail gas is compressed to 0.5~1.5MPa by a tail gas compressor, a cooler is provided in the tail gas compressor, and the exhaust temperature of the compressed tail gas is controlled to 10~70°C, and the compressed tail gas is condensed to -20~-45°C by a tail gas precooler.

[0010] Furthermore, in step 2), the operating pressure of tower 1# is 0.5-2.0 MPa, the tower top temperature is controlled at -20--45°C, the tower bottom temperature is controlled at 60-115°C, and the reflux ratio is controlled at 0.5-3.

[0011] Furthermore, the operating pressure of the 2# tower in step 4) is 0.5-1.5 MPa, the hydrogen fluoride content in the tail gas recovered by the 2# tower is less than 50 ppm, the 2# tower contains multiple sections of fillers, and the absorption process is gas-liquid countercurrent contact.

[0012] Furthermore, in step 5), the operating pressure of the HCl absorption device is 0.3-1.0 MPa, and the operating pressure of the drying device is 0.3-1.0 MPa.

[0013] The beneficial effects of the present invention are: Under the same composition of tail gas feed conditions, the tail gas compression pressure is lower, the hydrogen fluoride recovery rate is higher, the hydrogen fluoride content in the terminal exhaust gas and the overall energy consumption are lower, and the operation of the tail gas condensate liquid phase entering the 1# tower can also ensure that in the case of fluctuations in the synthetic tail gas feed, the buffer tank can be used for adjustment, which greatly reduces the operating difficulty of the recovery and distillation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the process of the present invention; In the figure: 1. tail gas compressor; 2. tail gas precooler; 3. gas-liquid separator; 4. condensate delivery pump; 5. 1# tower; 6. partial condenser; 7. 1# tower reflux tank; 8. 1# tower reflux pump; 9. reboiler; 10. 2# tower; 11. absorption liquid delivery pump; 12. HCl absorption device; 13. drying device. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited thereto.

[0016] like Figure 1As shown, a lithium hexafluorophosphate synthesis tail gas comprehensive utilization system comprises a tail gas compressor 1, a tail gas precooler 2, a gas-liquid separator 3, a condensate delivery pump 4, a 1# tower 5, a partial condenser 6, a 1# tower reflux tank 7, a 1# tower reflux pump 8, a reboiler 9, a 2# tower 10, an absorption liquid delivery pump 11, an HCl absorption device 12 and a drying device 13, the outlet pipeline of the tail gas compressor 1 is connected to the tail gas precooler 2 and the gas-liquid separator 3 in sequence, the gas outlet pipeline of the gas-liquid separator 3 is connected to the bottom of the 2# tower 10, the liquid outlet pipeline of the gas-liquid separator 3 is connected to the 1# tower 5 through the condensate delivery pump 4, and the top of the 1# tower 5 is connected to the 2# tower 10. The outlet pipeline of the partial condenser 6 is connected to the partial condenser 6, and the outlet pipeline of the partial condenser 6 is divided into two pipelines. One pipeline is refluxed and connected to the outlet pipeline of the tail gas compressor 1, and the other pipeline is connected to the reflux tank 7 of the 1# tower and the 1# reflux pump 8 and then divided into two pipelines to connect the top of the 1# tower 5 and the 2# tower 10 respectively. The bottom outlet pipeline of the 1# tower 5 is refluxed and connected to the reboiler 9. An absorption liquid delivery pump 11 is arranged on the bottom outlet pipeline of the 2# tower 10. The outlet pipeline of the absorption liquid delivery pump 11 is divided into two pipelines, which are respectively connected to the middle of the 1# tower 5 and the 2# tower 10. The top pipeline of the 2# tower 10 is connected to the HCl absorption device 12 and the drying device 13 in sequence.

[0017] The main equipment of the HCl absorption device 12 is a multi-stage falling film absorber or a multi-stage packed tower, and a water washing tower and an alkali washing tower are configured to remove and recover the acidic components in the tail gas. The main equipment of the drying device 13 is a heat exchanger, a cold dryer and a molecular sieve dryer. The bottom of the multi-stage falling film absorber or the top of the multi-stage packed tower is connected to the bottom of the water washing tower through a pipeline, the top of the water washing tower is connected to the bottom of the alkali washing tower through a pipeline, the top of the alkali washing tower is connected to the heat exchanger tube inlet, the heat exchanger tube outlet is connected to the cold dryer inlet, the cold dryer outlet pipeline is connected to the heat exchanger shell inlet, the shell outlet pipeline is connected to the dryer inlet, and the dryer outlet pipeline goes to the nitrogen use point in the plant.

[0018] Example 1

[0019] In a lithium hexafluorophosphate production project, the composition (mass fraction) of the synthetic tail gas (including the tail gas from the reaction section and the tail gas from the drying section) on the production line is 53% HCl, 12% HF, 2% PF5, and 33% N2. Liquid nitrogen condensation is used to recover hydrogen fluoride with a purity of 92% at -80°C, with a recovery rate of 90%. Uncondensed tail gas water is absorbed to obtain about 2t / h of mixed acid (containing 2.5% phosphoric acid, 4% hydrofluoric acid, and 30% hydrochloric acid), and the mixed acid is entrusted to external treatment, resulting in a waste of fluorine resources.

[0020] The tail gas is treated by the method of the present invention, and the process is as follows: 1) Compressing the tail gas of lithium hexafluorophosphate synthesis to 1.5MPa through tail gas compressor 1, and introducing circulating water into the cooler of tail gas compressor 1 to cool the compressed tail gas to 50°C; 2) The compressed tail gas enters the tail gas precooler 2, and a -45~-50℃ refrigerant is introduced to cool the compressed tail gas to -35℃. The condensed compressed tail gas is separated in the gas-liquid separator 3, and the condensate is transported to the 1# tower 5 for rectification through the condensate delivery pump 4. The operating pressure of the 1# tower 5 is 1.5MPa, the top temperature is -33℃, the bottom temperature is 114℃, and the reflux ratio is 1.5. The partial condenser 6 at the top of the 1# tower 5 produces 99.6% pure hydrogen chloride liquid as the reflux liquid of the 1# tower 5 itself and the spray liquid of the 2# tower 10. The small amount of gas produced returns to the inlet of the tail gas precooler 2, and the bottom of the tower produces 99.9% pure hydrogen fluoride, which is sent to the tank area for storage after cooling; 3) The uncondensed gas separated by the gas-liquid separator 3 is led to the inlet of the bottom of the 2# tower 10. The operating pressure of the 2# tower 10 is 1.0MPa, the top temperature is -48°C, and the bottom temperature is -47°C. The top gas of the 2# tower 10 is mainly hydrogen chloride, nitrogen, phosphorus pentafluoride and 41ppm hydrogen fluoride. The spray liquid absorbs the hydrogen fluoride in the tail gas and is sent to the 1# tower 5 from the absorption liquid delivery pump 11 to recover the absorbed hydrogen fluoride.

[0021] Comparative Example 1 For comparison, the synthetic tail gas in Example 1 was treated by a conventional single-tower distillation method. After being compressed and cooled, the synthetic tail gas was directly introduced into the 1# tower 5, and the top gas phase was extracted. Under the condition of ensuring that the refrigerant specifications (controlling the top temperature of the 1# tower 5) and the reflux ratio were the same, the operating pressure of the tail gas compressor 1 and the 1# tower 5 was 2.1 MPa, the top temperature was -33°C, the bottom temperature was 124°C, the reflux ratio was 1.5, and the bottom of the 1# tower (5) extracted hydrogen fluoride with a purity of 99.6%, and the top gas phase extracted hydrogen chloride, nitrogen, phosphorus pentafluoride and 398 ppm hydrogen fluoride.

[0022] Example 2

[0023] In a lithium hexafluorophosphate production project, the synthetic tail gas on the production line also includes the tail gas of the reaction section and the tail gas of the drying section. Only the hydrogen fluoride in the tail gas of the reaction section is considered to be recovered, and the tail gas composition (mass fraction) is: 81% HCl, 16% HF, 1% PF5, 2% N2. The tail gas is treated by the method of the present invention, and the operation process is the same as that of Example 1. The operating parameters, energy consumption and product indicators are shown in Table 1.

[0024] Comparative Example 2 For comparison, the synthetic tail gas in Example 2 was treated by conventional single-tower distillation method, and the operation process was the same as that of Comparative Example 1. The operating parameters, energy consumption and product indicators are shown in Table 1.

[0025] Table 1 Summary of parameters in the embodiments and comparative examples

[0026] By utilizing the method and system of the present invention, high-purity hydrogen fluoride and hydrogen chloride tail gas with extremely low hydrogen fluoride content can be obtained when treating lithium hexafluorophosphate synthetic tail gas with different compositions, and the system operating pressure is significantly lower than that of the ordinary single-tower distillation method, and the operating energy consumption is also reduced. The operation of feeding the condensed liquid phase into the No. 1 tower 5 can also ensure that the buffer tank is used for adjustment in the case of fluctuations in the synthetic tail gas feed, which greatly reduces the operating difficulty of the recovery distillation system and greatly reduces the operating cost of the enterprise.

[0027] The above describes the implementation modes of the present invention. For those skilled in the art, various improvements and modifications may be made to the present invention without departing from the principles of the present invention. These improvements and modifications shall be deemed to be within the protection scope of the present invention.

Claims

1. A lithium hexafluorophosphate synthesis tail gas comprehensive utilization system, characterized in that: It comprises an exhaust gas compressor (1), an exhaust gas precooler (2), a gas-liquid separator (3), a No. 1 tower (5), a partial condenser (6), a No. 1 tower reflux tank (7), a reboiler (9), a No. 2 tower (10), an HCl absorption device (12) and a drying device (13); The outlet pipeline of the tail gas compressor (1) is connected to the tail gas precooler (2) and the gas-liquid separator (3) in sequence, the gas outlet pipeline of the gas-liquid separator (3) is connected to the bottom of the second tower (10), the liquid outlet pipeline of the gas-liquid separator (3) is connected to the first tower (5), the top outlet pipeline of the first tower (5) is connected to the partial condenser (6), the outlet pipeline of the partial condenser (6) is divided into two pipelines, one pipeline is refluxed and connected to the outlet pipeline of the tail gas compressor (1), the other pipeline is connected to the first tower reflux tank (7) and then divided into two pipelines and respectively connected to the top of the first tower (5) and the second tower (10), the bottom outlet pipeline of the first tower (5) is refluxed and connected to the reboiler (9), the bottom outlet pipeline of the second tower (10) is divided into two pipelines and respectively connected to the middle of the first tower (5) and the second tower (10), and the top pipeline of the second tower (10) is sequentially connected to the HCl absorption device (12) and the drying device (13).

2. A lithium hexafluorophosphate synthesis tail gas comprehensive utilization system as claimed in claim 1, characterized in that: A condensate delivery pump (4) is provided on the pipeline connecting the gas-liquid separator (3) and the No. 1 tower (5); a No. 1 tower reflux pump (8) is provided on the outlet pipeline of the No. 1 tower reflux tank (7); and an absorption liquid delivery pump (11) is provided on the bottom outlet pipeline of the No. 2 tower (10).

3. A lithium hexafluorophosphate synthesis tail gas comprehensive utilization system as claimed in claim 2, characterized in that: The HCl absorption device (12) comprises a multi-stage falling film absorber or a multi-stage packed tower, and is equipped with a water scrubber and an alkali scrubber; the drying device (13) comprises a heat exchanger, a cold dryer and a molecular sieve dryer, the multi-stage falling film absorber or the multi-stage packed tower is connected to the water scrubber, the alkali scrubber and the heat exchanger in sequence, the tube side outlet of the heat exchanger is connected to the cold dryer inlet, the cold dryer outlet pipeline is connected to the heat exchanger shell side inlet, and the shell side outlet pipeline is connected to the molecular sieve dryer.

4. A method for comprehensive utilization of lithium hexafluorophosphate synthesis tail gas using the system as claimed in claim 3, characterized in that: The steps include: 1) Compressing lithium hexafluorophosphate synthesis tail gas through a tail gas compressor (1), condensing the compressed tail gas through a tail gas precooler (2), and separating it into uncondensed gas and condensed liquid through a gas-liquid separator (3); 2) The condensate is transported to the No. 1 tower (5) through the condensate transport pump (4) for separation and purification to obtain high-purity anhydrous hydrogen fluoride; 3) The gas produced from the top of the 1# tower (5) is partially condensed into liquid through a partial condenser (6), and the liquid passes through the 1# tower reflux tank (7) and enters the 1# tower (5) and the 2# tower (10) respectively, and the uncondensed gas phase is refluxed to the tail gas precooler (2); 4) the uncondensed gas from step 1) is brought into contact with the liquid produced from the top of tower 1 (5) in tower 2 (10) to recover the remaining hydrogen fluoride; 5) The recovered tail gas is passed into an HCl absorption device (12) to prepare hydrochloric acid, and the nitrogen-containing tail gas is passed into a drying device (13) to obtain qualified nitrogen gas to be recycled to the lithium hexafluorophosphate production section.

5. The method according to claim 3, characterized in that In step 1), the lithium hexafluorophosphate synthesis tail gas is compressed to 0.5-1.5 MPa by a tail gas compressor (1). A cooler is provided in the tail gas compressor (1) to control the exhaust temperature of the compressed tail gas to 10-70° C. The compressed tail gas is condensed to -20--45° C. by a tail gas precooler (2).

6. The method according to claim 3, characterized in that The operating pressure of the 1# tower (5) in step 2) is 0.5~2.0MPa, the tower top temperature is controlled at -20~-45°C, the tower bottom temperature is controlled at 60~115°C, and the reflux ratio is controlled at 0.5~3.

7. The method according to claim 3, characterized in that The operating pressure of the 2# tower (10) in step 4) is 0.5-1.5 MPa, and the hydrogen fluoride content in the tail gas recovered from the 2# tower (10) is less than 50 ppm.

8. The method according to claim 3, characterized in that In step 5), the operating pressure of the HCl absorption device (12) is 0.3-1.0 MPa, and the operating pressure of the drying device (13) is 0.3-1.0 MPa.

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