System and method for comprehensive utilization of lithium hexafluorophosphate synthesis tail gas

Abstract

The application discloses a lithium hexafluorophosphate tail gas comprehensive utilization system and method, which comprises a tail gas compressor, a tail gas pre-cooler, 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; after pre-cooling, the tail gas is separated by the gas-liquid separator, the liquid phase enters the 1# tower for separation, the anhydrous hydrogen fluoride product is obtained from the tower kettle, the gas phase at the top of the 1# tower is refluxed after partial condensation, the liquid is sent to the 1# tower and the 2# tower respectively, the gas phase obtained by the gas-liquid separator is sent into the 2# tower to contact with the liquid taken out from the top of the 1# tower to recover the remaining hydrogen fluoride, the recovered tail gas is introduced into the HCl absorption device to prepare hydrochloric acid, the nitrogen-containing tail gas is introduced into the drying device to obtain qualified nitrogen gas which is reused to the lithium hexafluorophosphate production section. Compared with the conventional pressurized rectification, the system has lower operating pressure, energy consumption and HF content in the terminal HCl tail gas, and a large amount of nitrogen gas is recycled and utilized, thereby reducing the production cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tail gas treatment, and particularly relates to a lithium hexafluorophosphate synthesis tail gas comprehensive utilization system and method. BACKGROUND

[0002] Lithium hexafluorophosphate is the most main electrolyte lithium salt used in the current commercialized lithium ion battery, and has realized large-scale industrial production. At present, the industrialized production process of lithium hexafluorophosphate is mainly hydrogen fluoride solvent method, the reaction raw material of which is easy to obtain, the reaction time is short, the reaction process is easy to control, and the raw material conversion rate is high. The rough steps are as follows: lithium fluoride is dissolved in anhydrous hydrogen fluoride to form a LiF•HF solution, phosphorus pentachloride and hydrogen fluoride are introduced to react to obtain high-purity phosphorus pentafluoride to generate lithium hexafluorophosphate crystals, and lithium hexafluorophosphate products are obtained after separation and drying.

[0003] Excessive hydrogen fluoride, phosphorus pentafluoride and hydrogen chloride generated in the production process and nitrogen gas used for purging are 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. Since there are low-boiling-point substances such as hydrogen chloride and nitrogen in the tail gas, the condensation of hydrogen fluoride is not complete, the recovery rate is low, and the purity is not high. The operation pressure of the compression distillation method is high, and since the composition of lithium hexafluorophosphate synthesis tail gas fluctuates greatly, the traditional compression distillation method cannot well adapt to such fluctuations, which easily causes the HF in the treated tail gas to exceed the standard, resulting in waste of part of fluorine resources. Moreover, the traditional treatment process does not consider the recovery of nitrogen, and in fact, after the recovery of nitrogen, not only the nitrogen consumption of the plant is reduced, but also the emission of harmful gases is greatly reduced, which is more in line with the requirements of environmental protection policy. SUMMARY

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

[0005] The specific technical solutions are as follows:

[0006] A lithium hexafluorophosphate synthesis tail gas comprehensive utilization system, comprising a tail gas compressor, a tail gas pre-cooler, a gas-liquid separator, a 1# column, a partial condenser, a 1# column reflux tank, a reboiler, a 2# column, an HCl absorption device and a drying device.

[0007] The outlet pipeline of the tail gas compressor is connected with the tail gas pre-cooler and the gas-liquid separator in sequence, the gas outlet pipeline of the gas-liquid separator is connected with the bottom of the 2# tower, the liquid outlet pipeline of the gas-liquid separator is connected with the 1# tower, the top outlet pipeline of the 1# tower is connected with the partial condenser, the outlet pipeline of the partial condenser is divided into two pipelines, one pipeline is connected with the outlet pipeline of the tail gas compressor in reflux, the other pipeline is connected with the 1# tower and the 2# tower in reflux after the 1# tower reflux tank, the bottom outlet pipeline of the 1# tower is connected with the reboiler in reflux, the bottom outlet pipeline of the 2# tower is divided into two pipelines and connected with the 1# tower and the 2# tower in the middle, and the top pipeline of the 2# tower is connected with the HCl absorption device and the drying device in sequence.

[0008] Further, the pipeline connected with the 1# tower of the gas-liquid separator is provided with a condensate delivery pump, and the outlet pipeline of the 1# tower reflux tank is provided with a 1# tower reflux pump; the bottom outlet pipeline of the 2# tower is provided with an absorption liquid delivery pump.

[0009] Further, the HCl absorption device comprises a multi-stage falling film absorber or a multi-stage packed tower, and is provided with a water washing tower and an alkali washing tower; the drying device comprises a heat exchanger, a cold dryer and a molecular sieve dryer, the bottom pipeline of the multi-stage falling film absorber or the top pipeline of the multi-stage packed tower is connected with the bottom of the water washing tower, the top pipeline of the water washing tower is connected with the bottom of the alkali washing tower, the top pipeline of the alkali washing tower is connected with the inlet of the tube side of the heat exchanger, the outlet of the tube side of the heat exchanger is connected with the inlet of the cold dryer, the outlet pipeline of the cold dryer is connected with the inlet of the shell side of the heat exchanger, the outlet pipeline of the shell side is connected with the inlet of the dryer, and the outlet pipeline of the dryer is connected with the nitrogen use point of the factory area.

[0010] A method for comprehensive utilization of lithium hexafluorophosphate synthesis tail gas by using the above system, comprising the following steps:

[0011] 1) The lithium hexafluorophosphate synthesis tail gas is compressed by the tail gas compressor, the compressed tail gas is condensed by the tail gas pre-cooler, and is separated into uncondensed gas and condensate by the gas-liquid separator;

[0012] 2) The condensate is delivered to the 1# tower by the condensate delivery pump to separate and purify to obtain high-purity anhydrous hydrogen fluoride;

[0013] 3) The gas collected from the top of the 1# tower is partially condensed into liquid by the partial condenser, the liquid enters the 1# tower and the 2# tower after the 1# tower reflux tank, and the uncondensed gas phase is refluxed to the tail gas pre-cooler;

[0014] 4) The uncondensed gas of step 1) and the liquid collected from the top of the 1# tower are contacted in the 2# tower to recover the remaining hydrogen fluoride;

[0015] 5) The recovered tail gas is introduced into the HCl absorption device to prepare hydrochloric acid, and the nitrogen-containing tail gas is introduced into the drying device to obtain qualified nitrogen gas which is reused to the lithium hexafluorophosphate production section.

[0016] Further, the lithium hexafluorophosphate synthesis tail gas in step 1) is compressed to 0.5-1.5 MPa by a tail gas compressor, a cooler is arranged in the tail gas compressor, the discharge temperature of the compressed tail gas is controlled to 10-70 DEG C, and the compressed tail gas is condensed to -20--45 DEG C by a tail gas pre-cooler.

[0017] Further, the operating pressure of the 1# column in step 2) is 0.5-2.0 MPa, the column top temperature is controlled to -20--45 DEG C, the column bottom temperature is controlled to 60-115 DEG C, and the reflux ratio is controlled to 0.5-3.

[0018] Further, the operating pressure of the 2# column in step 4) is 0.5-1.5 MPa, the hydrogen fluoride content in the 2# column recovered tail gas is less than 50 ppm, the 2# column contains multi-stage packing, and the absorption process is gas-liquid countercurrent contact.

[0019] Further, the operating pressure of the HCl absorption device in step 5) is 0.3-1.0 MPa, and the operating pressure of the drying device is 0.3-1.0 MPa.

[0020] The present application has the following beneficial effects:

[0021] Under the same 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 discharged tail gas is lower, the total energy consumption is lower, and under the condition that the synthesis tail gas feed fluctuates, the operation of the tail gas condensate phase into the 1# column can also be ensured, the buffer tank is used for adjustment, and the operation difficulty of the recovery rectification system is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The present application is a flow diagram;

[0023] In the figure: 1, tail gas compressor; 2, tail gas pre-cooler; 3, gas-liquid separator; 4, condensate delivery pump; 5, 1# column; 6, partial condenser; 7, 1# column reflux tank; 8, 1# column reflux pump; 9, reboiler; 10, 2# column; 11, absorption liquid delivery pump; 12, HCl absorption device; 13, drying device. DETAILED DESCRIPTION

[0024] The present application will be further described below in combination with the drawings and examples, but the protection scope of the present application is not limited thereto.

[0025] For example, Figure 1As shown, a lithium hexafluorophosphate synthesis tail gas comprehensive utilization system, including tail gas compressor 1, tail gas pre-cooler 2, gas-liquid separator 3, condensate delivery pump 4, 1# tower 5, partial condenser 6, 1# tower reflux tank 7, 1# tower reflux pump 8, reboiler 9, 2# tower 10, absorption liquid delivery pump 11, HCl absorption device 12 and drying device 13, the outlet pipeline of tail gas compressor 1 is connected with tail gas pre-cooler 2 and gas-liquid separator 3 in turn, the gas outlet pipeline of gas-liquid separator 3 is connected with the bottom of 2# tower 10, the liquid outlet pipeline of gas-liquid separator 3 is connected with 1# tower 5 through condensate delivery pump 4, the top outlet pipeline of 1# tower 5 is connected with partial condenser 6, the outlet pipeline of partial condenser 6 is divided into two pipelines, one pipeline is connected with the outlet pipeline of tail gas compressor 1 in reflux, the other pipeline is connected with 1# tower reflux tank 7 and 1# reflux pump 8 and then divided into two pipelines and connected with the top of 1# tower 5 and 2# tower 10 respectively, the bottom outlet pipeline of 1# tower 5 is connected with reboiler 9 in reflux, the bottom outlet pipeline of 2# tower 10 is provided with absorption liquid delivery pump 11, the outlet pipeline of absorption liquid delivery pump 11 is divided into two pipelines and connected with the middle of 1# tower 5 and 2# tower 10 respectively, the top pipeline of 2# tower 10 is connected with HCl absorption device 12 and drying device 13 in turn.

[0026] The main equipment of HCl absorption device 12 is multi-stage falling film absorber or multi-stage packed tower, and water washing tower and alkali washing tower are configured to remove acidic components in the recovered tail gas, and the main equipment of drying device 13 is heat exchanger, cold dryer and molecular sieve dryer, the bottom pipeline of multi-stage falling film absorber or the top pipeline of multi-stage packed tower is connected with the bottom of water washing tower, the top pipeline of water washing tower is connected with the bottom of alkali washing tower, the top pipeline of alkali washing tower is connected with the inlet of tube side of heat exchanger, the outlet of tube side of heat exchanger is connected with the inlet of cold dryer, the outlet pipeline of cold dryer is connected with the inlet of shell side of heat exchanger, the outlet pipeline of shell side is connected with the inlet of dryer, and the outlet pipeline of dryer is connected with the nitrogen use point in factory area.

[0027] Example 1

[0028] The composition (mass fraction) of the synthesis tail gas (including reaction section tail gas and drying section tail gas) of a certain lithium hexafluorophosphate production project 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℃, and the recovery rate is 90%. Water absorption of the uncondensed tail gas obtains 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, causing waste of fluorine resources.

[0029] The tail gas is treated by the method of the application, and the process is as follows:

[0030] 1) The lithium hexafluorophosphate synthesis tail gas is compressed to 1.5MPa by tail gas compressor 1, and circulating water is introduced into the cooler of tail gas compressor 1 to cool the compressed tail gas to 50℃;

[0031] 2) The compressed tail gas enters the tail gas pre-cooler 2, and is cooled to -35℃ by -45~-50℃ coolant. The condensed compressed tail gas is separated in the gas-liquid separator 3, and the condensed liquid is sent to the 1# column 5 by the condensed liquid delivery pump 4 for rectification. The operating pressure of the 1# column 5 is 1.5 MPa, the overhead temperature is -33℃, the bottom temperature is 114℃, and the reflux ratio is 1.5. The 1# column 5 overhead takes 99.6% purity hydrogen chloride liquid as the 1# column 5 reflux liquid and the 2# column 10 spray liquid. A small amount of gas is returned to the tail gas pre-cooler 2 inlet. The 1# column 5 bottom takes 99.9% purity hydrogen fluoride, which is cooled and stored in the tank area.

[0032] 3) The uncondensed gas separated in the gas-liquid separator 3 is sent to the 2# column 10 bottom inlet. The operating pressure of the 2# column 10 is 1.0 MPa, the overhead temperature is -48℃, and the bottom temperature is -47℃. The 2# column 10 overhead gas mainly contains hydrogen chloride, nitrogen, phosphorus pentafluoride, and 41 ppm hydrogen fluoride. The spray liquid absorbs the hydrogen fluoride in the tail gas and is sent to the 1# column 5 by the absorption liquid delivery pump 11. The absorbed hydrogen fluoride is recovered.

[0033] Comparative Example 1

[0034] As a comparison, the synthetic tail gas in Example 1 is treated by the conventional single column rectification method. The compressed and cooled synthetic tail gas is directly sent to the 1# column 5. The operating pressure of the tail gas compressor 1 and the 1# column 5 is 2.1 MPa, the overhead temperature is -33℃, the bottom temperature is 124℃, and the reflux ratio is 1.5. The 1# column 5 bottom takes 99.6% purity hydrogen fluoride, and the overhead gas takes hydrogen chloride, nitrogen, phosphorus pentafluoride, and 398 ppm hydrogen fluoride.

[0035] Example 2

[0036] A lithium hexafluorophosphate production project, the synthetic tail gas on the production line also contains reaction section tail gas and drying section tail gas. Only the hydrogen fluoride in the reaction section tail gas is considered for recovery. The tail gas composition (mass fraction) is: 81% HCl, 16% HF, 1% PF5, and 2% N2. The tail gas is treated by the method of the present application, and the operating process is the same as Example 1. The operating parameters, energy consumption, and product indicators are shown in Table 1.

[0037] Comparative Example 2

[0038] As a comparison, the synthetic tail gas in Example 2 is treated by the conventional single column rectification method. The operating process is the same as Comparative Example 1. The operating parameters, energy consumption, and product indicators are shown in Table 1.

[0039] Table 1 Summary of parameters in examples and comparative examples

[0040]

[0041] By using the method and system of the present application, 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, the system operating pressure is significantly lower than that of ordinary single-tower rectification method, the operation energy consumption is also reduced, the operation of the condensate phase into 1# tower 5 can also be ensured to be adjusted by using the buffer tank in the case of synthetic tail gas feed fluctuation, greatly reducing the operation difficulty of the recovery rectification system, and greatly reducing the enterprise operation cost.

[0042] The above describes the embodiments of the present application, and for those skilled in the art, various forms of improvement and refinement can be made to the present application without departing from the principles of the present application, and these improvements and refinements shall be considered as the protection scope of the present application.

Claims

1. A lithium hexafluorophosphate synthesis tail gas comprehensive utilization system, characterized in that, The tail gas compressor (1), the tail gas pre-cooler (2), the gas-liquid separator (3), the 1# column (5), the partial condenser (6), the 1# column reflux tank (7), the reboiler (9), the 2# column (10), the HCl absorption device (12) and the drying device (13) are included. The outlet pipeline of the tail gas compressor (1) is connected with the tail gas pre-cooler (2) and the gas-liquid separator (3) in sequence, the gas outlet pipeline of the gas-liquid separator (3) is connected with the bottom of the 2# column (10), the liquid outlet pipeline of the gas-liquid separator (3) is connected with the 1# column (5), the top outlet pipeline of the 1# column (5) is connected with the partial condenser (6), the outlet pipeline of the partial condenser (6) is divided into two pipelines, one pipeline is connected with the outlet pipeline of the tail gas compressor (1) in reflux, the other pipeline is connected with the 1# column reflux tank (7) and then is divided into two pipelines which are connected with the top of the 1# column (5) and the 2# column (10) respectively, the bottom outlet pipeline of the 1# column (5) is connected with the reboiler (9) in reflux, the bottom outlet pipeline of the 2# column (10) is divided into two pipelines which are connected with the middle of the 1# column (5) and the 2# column (10) respectively, the top pipeline of the 2# column (10) is connected with the HCl absorption device (12) and the drying device (13) in sequence.

2. The system for comprehensive utilization of lithium hexafluorophosphate synthesis tail gas according to claim 1, characterized in that, The condensate delivery pump (4) is arranged on the pipeline connected with the 1# column (5) of the gas-liquid separator (3), the 1# column reflux pump (8) is arranged on the outlet pipeline of the 1# column reflux tank (7); the absorption liquid delivery pump (11) is arranged on the bottom outlet pipeline of the 2# column (10).

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

4. A method for comprehensive utilization of lithium hexafluorophosphate synthesis tail gas by using the system according to claim 3, characterized in that, The method comprises the following steps: 1) the lithium hexafluorophosphate synthesis tail gas is compressed by the tail gas compressor (1), the compressed tail gas is condensed by the tail gas pre-cooler (2), and the tail gas is separated into uncondensed gas and condensate by the gas-liquid separator (3); 2) the condensate is delivered to the 1# column (5) by the condensate delivery pump (4) to separate and purify to obtain high-purity anhydrous hydrogen fluoride; 3) the gas collected from the top of the 1# column (5) is partially condensed into liquid by the partial condenser (6), the liquid enters the 1# column (5) and the 2# column (10) after the 1# column reflux tank (7), and the uncondensed gas phase is refluxed to the tail gas pre-cooler (2); 4) the uncondensed gas of step 1) and the liquid collected from the top of the 1# column (5) are contacted in the 2# column (10) to recover the remaining hydrogen fluoride; 5) the recovered tail gas is introduced into the HCl absorption device (12) to prepare hydrochloric acid, and the nitrogen-containing tail gas is introduced into the drying device (13) to obtain qualified nitrogen gas which is reused to the lithium hexafluorophosphate production section.

5. The method of claim 4, wherein, The lithium hexafluorophosphate synthesis tail gas in step 1) is compressed to 0.5-1.5 MPa by a tail gas compressor (1), a cooler is arranged in the tail gas compressor (1), the discharge temperature of the compressed tail gas is controlled to be 10-70 DEG C, and the compressed tail gas is condensed to -20--45 DEG C by a tail gas pre-cooler (2).

6. The method of claim 4, wherein, The operating pressure of the 1# column (5) in step 2) is 0.5-2.0 MPa, the overhead temperature is controlled to be -20--45 DEG C, the bottom temperature is controlled to be 60-115 DEG C, and the reflux ratio is controlled to be 0.5-3.

7. The method of claim 4, wherein, The operating pressure of the 2# column (10) in step 4) is 0.5-1.5 MPa, and the hydrogen fluoride content in the tail gas recovered by the 2# column (10) is less than 50 ppm.

8. The method of claim 4, wherein, The operating pressure of the HCl absorption device (12) in step 5) 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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