Method and system for comprehensively utilizing tail gas in production of liquid lithium hexafluorophosphate

Abstract

The invention discloses a method and system for comprehensive utilization of liquid lithium hexafluorophosphate production tail gas, and the method comprises the following steps: compression and condensation: pressurizing the liquid lithium hexafluorophosphate production tail gas to 1-2 Mpa, and condensing the compressed tail gas at 10-20 DEG C to respectively obtain a first condensate and a first uncondensed gas; fluorine recovery: the first uncondensed gas is rectified in a rectifying tower, the kettle bottom temperature of the rectifying tower is 80-95 DEG C, gas at the top of the rectifying tower is condensed at 30-40 DEG C after being extracted, and second condensate and second uncondensed gas are obtained through separation; and hydrogen chloride recovery: contacting the second uncondensed gas with a defluorination agent in a defluorination tower for defluorination, and carrying out multi-stage absorption of hydrochloric acid on the defluorinated gas to obtain a high-purity hydrochloric acid product. The method has the advantages of low energy consumption, high quality of by-product hydrochloric acid and recyclability of fluorine resources.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tail gas utilization, in particular to a method and system for comprehensive utilization of tail gas in production of liquid lithium hexafluorophosphate. BACKGROUND

[0002] The production process of liquid lithium hexafluorophosphate concentrated solution is as follows: first, lithium fluoride and phosphorus pentachloride are reacted in a solvent to produce lithium monofluorophosphate pentachloride intermediate, and then substitution reaction is performed using hydrofluoric acid to obtain lithium hexafluorophosphate solution. A large amount of hydrogen chloride gas, a small amount of inert protective gas nitrogen, a small excess of hydrogen fluoride and a small amount of phosphorus pentafluoride gas overflow together to become process tail gas. The tail gas contains about 80-90% HCl, 0.1-0.4% PF5, 0.5-1% HF, 2-4% solvent, and the rest is nitrogen.

[0003] At present, the treatment method for lithium hexafluorophosphate production process tail gas mostly adopts the method of first condensing to remove most of the hydrogen fluoride gas, then water absorption of hydrogen chloride containing hydrogen fluoride and phosphorus pentafluoride, and by-product of fluorine-containing dilute hydrochloric acid. However, this process has the problems of high process energy consumption, incomplete condensation of hydrogen fluoride, low fluorine-chlorine separation efficiency, and the like. Moreover, the reaction of phosphorus pentafluoride gas in the tail gas with water produces phosphoric acid, and the by-product hydrochloric acid is fluorine-containing and phosphorus-containing acid, which has low quality and is difficult to reuse, resulting in resource waste. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defects of high process energy consumption of the existing tail gas treatment method, and low quality and difficult to reuse of the by-product, so as to provide a method and system for comprehensive utilization of lithium hexafluorophosphate production tail gas to solve the above problems.

[0005] The method for comprehensive utilization of lithium hexafluorophosphate production tail gas comprises the following steps:

[0006] Compressed condensation: the lithium hexafluorophosphate production tail gas is pressurized to 1-2 MPa, and the compressed tail gas is condensed at 10-20℃ to obtain a first condensate and a first non-condensed gas;

[0007] Fluorine recovery: the first non-condensed gas is subjected to rectification in a rectification column, the kettle bottom temperature of the rectification column is 80-95℃, and the gas collected from the top of the rectification column is condensed at 30-40℃ and separated to obtain a second condensate and a second non-condensed gas;

[0008] Hydrogen chloride recovery: the second non-condensed gas is contacted with a defluorination agent in a defluorination column for defluorination, and the gas after defluorination is subjected to multi-stage absorption of hydrochloric acid to obtain a high-purity hydrochloric acid product.

[0009] The reflux ratio of the second condensate in the rectification column is controlled to be between 0.8 and 2.

[0010] The number of theoretical plates of the rectification tower is 35-40, and the first non-condensed gas is fed between the 20th-25th plate of the rectification tower.

[0011] The content of HF in the second non-condensed gas is between 500-600 ppm.

[0012] The temperature in the tower of the defluorination tower is 20-30℃.

[0013] The defluorination agent is a saturated solution of chlorinated salt, and the chlorinated salt is preferably one or more of calcium chloride, aluminum chloride, iron chloride, magnesium chloride, sodium chloride and lithium chloride.

[0014] When the concentration of the chlorinated salt in the saturated solution of the chlorinated salt is less than 50 g / L, the saturated solution is filtered, and the filtrate is supplemented with chlorinated salt and then recycled.

[0015] The number of theoretical plates of the defluorination tower is 25-30.

[0016] The content of HF in the defluorinated gas discharged from the defluorination tower is between 30-60 ppm.

[0017] The defluorinated gas from the defluorination tower is subjected to multi-stage falling film absorption with water to obtain a high-purity hydrochloric acid product; preferably, the temperature of the water is 5-15℃, the concentration of the hydrochloric acid in the obtained high-purity hydrochloric acid product is 30-32%, and the content of HF in the high-purity hydrochloric acid product is between 10-50 ppm.

[0018] An apparatus for implementing the above method comprises:

[0019] The compression condensation system comprises a compressor, a condensation assembly and a solvent recovery tank connected in sequence;

[0020] The rectification system comprises a rectification tower connected to the gas outlet of the solvent recovery tank, a condenser arranged at the top of the rectification tower, a reflux intermediate tank connected to the condenser, and an HF recovery assembly arranged at the bottom of the rectification tower;

[0021] The defluorination tower is connected to the gas outlet of the reflux intermediate tank.

[0022] The hydrogen chloride absorption system is formed by connecting multi-stage falling film absorption towers in series and is connected to the gas outlet at the top of the defluorination tower.

[0023] The present application firstly uses a compressor to pressurize, and the pressurized tail gas is cooled by a condensing assembly to recover the organic solvent in the tail gas into a solvent recovery tank for storage and recycling. The tail gas after pressurization and cooling is a first uncondensed gas, which enters a rectifying tower to realize separation of HCl and HF. The HCl in the tail gas comes out of the top of the rectifying tower, is condensed by a condenser at the top of the rectifying tower, and then enters a reflux intermediate tank. The HCl in gas phase form comes out of the top of the reflux intermediate tank to obtain a second uncondensed gas, which enters a next step of a defluorination tower for defluorination. The liquid phase at the bottom of the reflux intermediate tank is a second condensate, part of which is used as reflux of the rectifying tower to ensure that the content of HF in the second uncondensed gas is between 500-600 ppm. The tower kettle of the rectifying tower is an HF product, which is cooled by an HF pre-cooler, pumped into an HF recovery tank for storage and recycling. The second uncondensed gas coming out of the top of the rectifying tower enters the bottom of the defluorination tower, and from bottom to top, contacts with a defluorination agent in the defluorination tower. The purified HCl product flows out of the top of the defluorination tower, and is absorbed by a hydrochloric acid absorption system to be a high-purity hydrochloric acid product through multi-stage absorption.

[0024] The technical scheme of the present application has the following advantages:

[0025] The method for comprehensive utilization of the tail gas in production of liquid lithium hexafluorophosphate provided by the present application comprises compression and condensation, fluorine recovery, and hydrogen chloride recovery. The method solves the problems of difficult recovery of solvent in the conventional tail gas treatment process in production of liquid lithium hexafluorophosphate, and incomplete separation of hydrogen fluoride and hydrogen chloride gas in the process tail gas, which leads to waste of fluorine resources and poor quality of by-product hydrochloric acid. The entire treatment process of the present application has no three wastes emission, and industrial-grade concentrated hydrochloric acid is prepared. The quality of the by-product hydrochloric acid is high, fluorine resources can be recycled, resource utilization is efficient, energy consumption is extremely low, and production cost is further reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the present application or the technical scheme in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0027] Figure 1 It is a structural schematic diagram of the system of the present application.

[0028] Explanation of reference signs:

[0029] 1- compressor; 2- condensation assembly; 3- solvent recovery tank; 4- distillation tower; 5- condenser; 6- reflux intermediate tank; 7- HF precooler; 8- HF recovery tank; 9- defluorination tower. DETAILED DESCRIPTION

[0030] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be noted that the terms "side," "upper," "lower," "top," "bottom," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical connections; direct connections or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0033] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] A system for realizing comprehensive utilization of tail gas from the production of liquid lithium hexafluorophosphate, such as Figure 1As shown, it includes a compressor 1, a condensing component 2, a solvent recovery tank 3, a distillation tower 4, a condenser 5, a reflux intermediate tank 6, and a defluorination tower 9 connected by pipelines; the compressor 1 is respectively provided with an exhaust gas inlet and outlet, the condensing component 2 includes a raw material precooler and a raw material cooler, and the raw material precooler and the raw material cooler are both provided with a cooling water inlet and outlet, the exhaust gas outlet on the compressor 1 is connected to the exhaust gas inlet of the condensing component 2, the cooling outlet of the condensing component 2 is connected to the inlet of the solvent recovery tank 3, the solvent recovery tank 3 is provided with a gas outlet and a liquid outlet, the distillation tower 4 is respectively provided with a process exhaust gas inlet, a tower top HCl gas outlet, a reflux liquid inlet, and a tower bottom recovered HF outlet, and the gas outlet of the solvent recovery tank 3 is connected to the distillation tower 4, the process tail gas inlet is connected, the top HCl gas outlet is connected to the condenser 5, the reflux intermediate tank 6, and the reflux liquid inlet to form a circulation loop, the reflux intermediate tank 6 is provided with a gas outlet, the bottom HF recovery outlet of the rectifying tower 4 is connected to the HF precooler 7, the cooled HF solution enters the HF recovery tank 8 for recycling, and the bottom of the rectifying tower 4 is also provided with a reboiler to maintain the bottom temperature of the rectifying tower 4; the defluorination tower 9 is respectively provided with an HCl gas inlet, a defluorination liquid outlet and a tail gas outlet after defluorination, the gas outlet of the reflux intermediate tank 6 is connected to the HCl gas inlet of the defluorination tower 9, the defluorination liquid outlet is connected through a pipeline pump, and the tail gas outlet after defluorination is connected to the hydrochloric acid absorption device through a pipeline. The absorption device is composed of a multi-stage falling film absorption tower in series, and the absorption method is gas-liquid countercurrent contact.

[0036] Specifically, the present invention first uses a compressor 1 to pressurize the exhaust gas, and the pressurized exhaust gas is cooled by a condensation component 2. The condensation component 2 includes a raw material pre-cooler and a raw material cooler. The exhaust gas cooled by the condensation component 2 enters the solvent recovery tank 3. The organic solvent in the exhaust gas is recovered by the solvent recovery tank 3 for recycling, storage and utilization. The exhaust gas separated in the solvent recovery tank 3 is the first uncondensed gas. The first uncondensed gas enters the distillation tower 4, and the separation of HCl and HF is achieved in the distillation tower 4. The HCl in the exhaust gas comes out from the top of the distillation tower, is condensed by the condenser 5 at the top of the distillation tower, and enters the reflux intermediate tank 6. The HCl comes out from the top of the reflux intermediate tank 6 in the form of a gas phase to obtain a second uncondensed gas. The second uncondensed gas enters the next step of the defluorination tower 9 for defluorination. The liquid phase at the bottom of the reflux intermediate tank 6 is the second condensate. Part of the second condensate is used as the reflux of the distillation tower 4 to ensure that the HF content in the second uncondensed gas is between 500 and 600 ppm. The HF product in the distillation column kettle is cooled in an HF precooler 7 and then pumped into an HF recovery tank 8 for storage and recycling. The second uncondensed gas from the top of distillation column 4 enters the bottom of defluorination column 9, where it comes into contact with the defluorinating agent inside. The purified HCl product then flows out of the top of the defluorination column and is absorbed by the hydrochloric acid absorption system through multi-stage absorption to produce a high-purity hydrochloric acid product. The hydrochloric acid absorption system consists of multiple falling-film absorption towers connected in series, using a gas-liquid countercurrent absorption method.

[0037] The method for realizing comprehensive utilization of tail gas from the production of liquid lithium hexafluorophosphate using the above system comprises:

[0038] (1) The tail gas from the production process of liquid lithium hexafluorophosphate is passed into compressor 1. The composition of the tail gas from the production process of liquid lithium hexafluorophosphate is: 86% HCl, 0.14% PF5, 0.9% HF, 6% solvent, and the rest is nitrogen. The flow rate of compressor 1 is 500m 3 / hr, the outlet pressure of the compressor 1 is 1.3Mpa; the material of the compressor 1 is 316L, C276 or Monel alloy, the compressed tail gas enters the condensation component 2, passes through the raw material precooler and the raw material cooler in sequence and is cooled to 10-15°C before entering the solvent recovery tank 3, the condensate is collected by the solvent recovery tank 3, the condensate is the solvent ethyl methyl carbonate, and is stored and recycled in the solvent recovery tank 3, the uncondensed gas is the first uncondensed gas, and the first uncondensed gas is a mixed gas of HCl, HF, N2, and PF5. The first uncondensed gas enters the subsequent distillation tower 4 for fluorine recovery;

[0039] (2) The first uncondensed gas obtained after the pressurized condensation in step (1) is introduced into the feed port of the distillation tower 4 to separate HCl and HF in the distillation tower. The distillation tower has a diameter of 0.5m and a height of 15m. It uses a wire mesh filler (made of S316L, C276 or Monel alloy) with a filler height of 12m. The low-boiling-point component HCl comes out from the top of the distillation tower, is condensed to 30-35°C by the condenser 5 at the top of the distillation tower, and then enters the reflux intermediate tank 6. The liquid component at the bottom of the reflux intermediate tank 6 partially refluxes into the top of the distillation tower, and the reflux liquid flow rate is controlled to be 0.6-0.8m 3 / hr, a liquid distributor is installed inside the tower for uniform distribution, and the reflux ratio is controlled at approximately 0.8 to 1. Uncondensed HCl, N2, and PF5 emerge from the top of the reflux intermediate tank 6 in the gaseous form to obtain the second uncondensed gas, which enters the next step.

[0040] The bottom of the distillation tower 4 is connected to the reboiler, which is made of 316L, C276 or Monel alloy. The heat exchange area of ​​the reboiler is 15m 2 ; Use steam heating to control the bottom temperature of the kettle at 85-90℃. The output of the distillation tower kettle is HF product, which is cooled by HF precooler 7 and then pumped into HF recovery tank 8 for storage and recycling. The heat exchange area of ​​the condenser is 10m 2 , made of 316L, C276 or Monel alloy.

[0041] (3) The second uncondensed gas in step (2) is introduced into the bottom of the defluorination tower 9, which has a diameter of 0.5 m and a height of 5 m, and uses wire mesh packing (S316L, C276 or Monel) with a packing height of 3 m. The flow rate of the second uncondensed gas in the defluorination tower 9 is controlled at 1 m / s, and the defluorination agent is 20% calcium chloride aqueous solution, which is sprayed at a rate of 0.5 m 3 / hr to defluorinate the second uncondensed gas, and the temperature in the defluorination tower 9 is controlled at 20-30°C. When the phosphorus pentafluoride in the tail gas contacts the calcium chloride aqueous solution in the defluorination tower from bottom to top, the purified HCl product flows out from the top of the defluorination tower and is absorbed as a hydrochloric acid product in the hydrochloric acid absorption system. Water is used in the hydrochloric acid absorption system to absorb hydrochloric acid, and the temperature of the water is 5-15°C. The concentration of hydrochloric acid in the high-purity hydrochloric acid product obtained by absorption is 30-32%, and the HF content in the high-purity hydrochloric acid product is between 10-50 ppm.

[0042] The sampling analysis results of the hydrochloric acid product are as follows: hydrochloric acid content 30.65%, fluoride ion 13 ppm, and phosphorus content (as P2O5) 2.6 ppm.

[0043] The analysis results of the hydrogen fluoride stored in the HF recovery tank 8 are as follows: HF content 89.24%, solvent content 10.22%, chloride ion 2300 ppm, and phosphorus content (as P2O5) 219 ppm.

[0044] The energy consumption of the system used in this embodiment is about 0.05 degrees of electricity per 1 kg of hydrochloric acid product produced.

[0045] Example 2

[0046] The difference between this example and Example 1 is that the parameter conditions in the above method are different, and the others are the same as those in Example 1, which specifically includes:

[0047] The method for realizing comprehensive utilization of liquid lithium hexafluorophosphate production tail gas includes:

[0048] (1) The liquid lithium hexafluorophosphate production process tail gas is introduced into the compressor 1, and the composition of the liquid lithium hexafluorophosphate production process tail gas is: 87% HCl, 0.4% PF5, 1% HF, 3% solvent, and the rest is nitrogen.

[0049] The flow rate of the compressor 1 is 300 m 3 / hr, the compressor 1 outlet pressure is 1.3 Mpa; the compressor 1 material is 316L, C276 or Monel alloy, the compressed tail gas enters the condensing assembly 2, sequentially passes through the raw material pre-cooler, the raw material cooler and is cooled to 10-15℃, and then enters the solvent recovery tank 3, the condensate is collected through the solvent recovery tank 3, the condensate is solvent methyl ethyl carbonate, is stored and recycled in the solvent recovery tank 3, and the uncondensed gas is the first uncondensed gas; the first uncondensed gas is a mixed gas of HCl, HF, N2 and PF5; the first uncondensed gas enters the subsequent rectifying column 4 for fluorine recovery.

[0050] (2) The first uncondensed gas obtained after pressurized condensation in step (1) is introduced into the feed inlet of the rectifying column 4, and the separation of HCl and HF is realized in the rectifying column. The rectifying column is 0.4 m in diameter, 13 m in height, uses metal wire mesh packing (material is S316L, C276 or Monel alloy), the packing is 10 m high, the low-boiling-point component HCl comes out from the top of the rectifying column, is condensed to 30-35℃ through the condenser 5 at the top of the rectifying column, and then enters the reflux intermediate tank 6; the liquid component at the bottom of the reflux intermediate tank 6 partially returns to the top of the rectifying column as reflux, the reflux liquid flow is controlled to be 0.3-0.5 m 3 / hr, a liquid distributor is arranged in the column to uniformly distribute, and the reflux ratio is controlled to be about 0.8-1. The uncondensed HCl, N2 and PF5 come out from the top of the reflux intermediate tank 6 in the form of gas phase to obtain the second uncondensed gas, which enters the next step.

[0051] The column kettle of the rectifying column 4 is connected with a reboiler, the reboiler is made of 316L, C276 or Monel alloy, the reboiler heat exchange area is 10 m 2 ; steam heating is used, and the kettle bottom temperature is controlled to be 85-90℃. The HF product is taken out from the column kettle of the rectifying column, is cooled through the HF pre-cooler 7, is pumped into the HF recovery tank 8 for storage and recycling, the condenser heat exchange area is 8 m 2 , and the material is 316L, C276 or Monel alloy.

[0052] (3) The second uncondensed gas in step (2) is introduced into the bottom of the defluorination column 9, the defluorination column is 0.4 m in diameter and 5 m in height, uses metal wire mesh packing (material is S316L, C276 or Monel alloy), the packing is 3 m high, the second uncondensed gas flow rate in the defluorination column 9 is controlled to be 0.8 m / s, the defluorination agent is 5% sodium chloride aqueous solution, the defluorination of the second uncondensed gas is carried out at a spraying amount of 0.4 m 3 / hr, and the defluorination column 9 temperature is controlled to be 20-30℃. When the phosphorus pentafluoride in the tail gas contacts the defluorination agent sodium chloride aqueous solution in the defluorination column from bottom to top, the purified HCl product flows out from the top of the defluorination column and is absorbed into the hydrochloric acid absorption system to become a hydrochloric acid product.

[0053] The sampling analysis result of the hydrochloric acid product is: hydrochloric acid content 31.12%, fluorine ion 32ppm, phosphorus content (as P2O5) 1.9ppm.

[0054] The analysis result of the hydrogen fluoride stored in the hydrogen fluoride recovery tank 8 is: HF content 90.64%, solvent content 8.78%, chlorine ion 900ppm, phosphorus content (as P2O5) 143ppm.

[0055] The energy consumption of the system used in this embodiment is about 0.06 degree of electricity per 1kg of hydrochloric acid product.

[0056] Example 3

[0057] The difference from Example 1 is that the parameter conditions in the method are different, and the others are the same as Example 1, which specifically includes:

[0058] (1) The liquid lithium hexafluorophosphate production process tail gas is introduced into the compressor 1, and the composition of the liquid lithium hexafluorophosphate production process tail gas is: 90% HCl, 0.3% PF5, 0.5% HF, 2% solvent, and the rest is nitrogen.

[0059] The flow rate of the compressor 1 is 500m 3 / hr, and the outlet pressure of the compressor 1 is 1Mpa; the material of the compressor 1 is 316L, C276 or Monel alloy, and the compressed tail gas enters the condensing assembly 2, and is cooled to 15-18℃ in turn through the raw material pre-cooler and the raw material cooler, and then enters the solvent recovery tank 3, and the condensate is collected through the solvent recovery tank 3, and the condensate is the solvent methyl ethyl carbonate, which is stored and recycled in the solvent recovery tank 3, and the uncondensed gas is the first uncondensed gas, which is a mixture of HCl, HF, N2 and PF5, and the first uncondensed gas enters the subsequent rectifying column 4 for fluorine recovery;

[0060] (2) The first uncondensed gas obtained after pressurized condensation in step (1) is introduced into the feed inlet of the rectifying column 4, and the separation of HCl and HF is realized in the rectifying column. The rectifying column is 0.5m in diameter and 15m in height, and uses metal wire mesh packing (material S316L, C276 or Monel alloy), and the packing is 12m high. The low-boiling-point component HCl comes out from the top of the rectifying column, is condensed to 35-40℃ by the condenser 5 at the top of the rectifying column, and then enters the reflux intermediate tank 6. The liquid component at the bottom of the reflux intermediate tank 6 partially refluxes into the top of the rectifying column, and the flow rate of the reflux liquid is controlled at 0.6-0.8m 3 / hr, and a liquid distributor is arranged in the column for uniform distribution, and the reflux ratio is controlled at about 1.2-1.5. The uncondensed HCl, N2 and PF5 come out from the top of the reflux intermediate tank 6 in the form of gas phase to obtain the second uncondensed gas, which enters the next step.

[0061] The kettle of the rectification tower 4 is connected with a reboiler, the reboiler is made of 316L, C276 or Monel, the heat exchange area of the reboiler is 15 m 2 ; steam is used for heating, and the kettle bottom temperature is controlled to be 80-85°C. The product taken out from the kettle of the rectification tower is HF product, the HF product is cooled by the HF pre-cooler 7 and then pumped into the HF recovery tank 8 for storage and recycling, the heat exchange area of the condenser is 10 m 2 , and the material is 316L, C276 or Monel.

[0062] (3) The second uncondensed gas in step (2) is introduced into the bottom of the defluorination tower 9, the diameter of the defluorination tower is 0.5 m, the height of the tower is 5 m, wire mesh packing (made of S316L, C276 or Monel) is used, the packing height is 3 m, the flow rate of the second uncondensed gas in the defluorination tower 9 is controlled to be 1 m / s, the defluorination agent is 20% calcium chloride aqueous solution, and the spray amount is 0.5 m 3 / hr to defluorinate the second uncondensed gas, and the temperature in the defluorination tower 9 is controlled to be 20-30°C. When the phosphorus pentafluoride in the tail gas contacts with the defluorination agent calcium chloride aqueous solution in the defluorination tower from bottom to top, the purified HCl product flows out from the top of the defluorination tower and is absorbed by the hydrochloric acid absorption system to become a hydrochloric acid product.

[0063] The sampling analysis result of the hydrochloric acid product is that the hydrochloric acid content is 31.2%, the fluorine ion content is 21 ppm, and the phosphorus content (calculated as P2O5) is 2 ppm.

[0064] The analysis result of the hydrogen fluoride stored in the HF recovery tank 8 is that the HF content is 88%, the solvent content is 11%, the chlorine ion content is 1320 ppm, and the phosphorus content (calculated as P2O5) is 580 ppm.

[0065] The energy consumption of the system used in this embodiment is about 0.05 degrees of electricity per 1 kg of hydrochloric acid product.

[0066] Example 4

[0067] The difference between this example and example 1 is that the parameter conditions in the method are different, and the others are the same as those in example 1, which specifically includes:

[0068] (1) The liquid lithium hexafluorophosphate production process tail gas is introduced into the compressor 1, and the composition of the liquid lithium hexafluorophosphate production process tail gas is 87% HCl, 0.1% PF5, 1.9% HF, 5% solvent, and the rest is nitrogen.

[0069] The flow rate of the compressor 1 is 500 m 3 / hr, the outlet pressure of the compressor 1 is 2 MPa; the material of the compressor 1 is 316L, C276 or Monel alloy, the compressed tail gas enters the condensation component 2, passes through the raw material precooler and the raw material cooler in sequence and is cooled to 18-20°C before entering the solvent recovery tank 3, the condensate is collected by the solvent recovery tank 3, the condensate is the solvent ethyl methyl carbonate, and is stored and recycled in the solvent recovery tank 3, the uncondensed gas is the first uncondensed gas, and the first uncondensed gas is a mixed gas of HCl, HF, N2, and PF5, and the first uncondensed gas enters the subsequent distillation tower 4 for fluorine recovery;

[0070] (2) The first uncondensed gas obtained after the pressurized condensation in step (1) is introduced into the feed port of the distillation tower 4 to separate HCl and HF in the distillation tower. The distillation tower has a diameter of 0.5m and a height of 15m. It uses a wire mesh filler (made of S316L, C276 or Monel alloy) with a filler height of 12m. The low-boiling-point component HCl comes out from the top of the distillation tower, is condensed to 30-35°C by the condenser 5 at the top of the distillation tower, and then enters the reflux intermediate tank 6. The liquid component at the bottom of the reflux intermediate tank 6 partially refluxes into the top of the distillation tower, and the reflux liquid flow rate is controlled to be 0.6-0.8m 3 / hr, with a liquid distributor installed inside the tower for uniform distribution. The reflux ratio is controlled at approximately 1.8 to 2.0. Uncondensed HCl, N2, and PF5 emerge as a gas from the top of the reflux intermediate tank 6 as a second uncondensed gas, which is then fed to the next step.

[0071] The bottom of the distillation tower 4 is connected to the reboiler, which is made of 316L, C276 or Monel alloy. The heat exchange area of ​​the reboiler is 15m 2 ; Use steam heating to control the bottom temperature of the kettle at 90-95℃. The output of the distillation tower kettle is HF product, which is cooled by HF precooler 7 and then pumped into HF recovery tank 8 for storage and recycling. The heat exchange area of ​​the condenser is 10m 2 , made of 316L, C276 or Monel alloy.

[0072] (3) The second uncondensed gas in step (2) enters the bottom of the defluorination tower 9, the defluorination tower has a diameter of 0.5m and a tower height of 5m, and uses a metal mesh filler (made of S316L, C276 or Monel alloy) with a filler height of 3m. The flow rate of the second uncondensed gas in the defluorination tower 9 is controlled to be 1m / s, and the defluorination agent is a 20% calcium chloride aqueous solution with a 0.5m 3 The second uncondensed gas is defluorinated at a spray rate of 1000 rpm / hr, and the temperature in the defluorination tower 9 is controlled at 20-30°C. As phosphorus pentafluoride in the tail gas contacts the defluorinating calcium chloride aqueous solution in the defluorination tower from bottom to top, the purified HCl product flows out of the top of the defluorination tower and is absorbed by the hydrochloric acid absorption system as hydrochloric acid product.

[0073] The hydrochloric acid product sampling analysis results are: hydrochloric acid content 31.5%, fluorine ion 11 ppm, phosphorus content (as P2O5) 4 ppm.

[0074] The hydrogen fluoride analysis results of the hydrogen fluoride recovery tank 8 storage are: HF content 84%, solvent content 15%, chloride ion 421 ppm, phosphorus content (as P2O5) 314 ppm.

[0075] The system used in this embodiment consumes about 0.07 degrees of electricity per 1 kg of hydrochloric acid product produced.

[0076] Comparative Example 1

[0077] The method for realizing comprehensive utilization of liquid lithium hexafluorophosphate production tail gas by using the compression condensation system + rectification system in Example 1, comprising:

[0078] (1) The liquid lithium hexafluorophosphate production process tail gas is introduced into the compressor 1, and the composition of the liquid lithium hexafluorophosphate production process tail gas is: 87% HCl, 0.4% PF5, 1% HF, 4% solvent, and the rest is nitrogen.

[0079] The flow rate of the compressor 1 is 500 m 3 / hr, and the outlet pressure of the compressor 1 is 1.3 Mpa; the material of the compressor 1 is 316L, C276 or Monel alloy, and the compressed tail gas enters the condensation assembly 2, and is cooled to 10-15°C in turn through the raw material pre-cooler and the raw material cooler, and then enters the solvent recovery tank 3, and the condensate is collected through the solvent recovery tank 3, and the condensate is the solvent methyl ethyl carbonate, which is stored and recovered in the solvent recovery tank 3, and the uncondensed gas is the first uncondensed gas, which is a mixed gas of HCl, HF, N2 and PF5, and the first uncondensed gas enters the subsequent rectification tower 4 for fluorine recovery;

[0080] (2) The first uncondensed gas obtained after pressurized condensation in step (1) is introduced into the feed inlet of the rectification tower 4, and the separation of HCl and HF is realized in the rectification tower. The rectification tower is 0.5 m in diameter and 15 m in height, uses metal wire mesh packing (material S316L, C276 or Monel alloy), and the packing is 12 m high. The low-boiling-point component HCl comes out from the top of the rectification tower, is condensed to 30-35°C through the condenser 5 at the top of the rectification tower, and then enters the reflux intermediate tank 6. The liquid component at the bottom of the reflux intermediate tank 6 partially returns to the top of the rectification tower, and the flow rate of the reflux liquid is controlled at 0.6-0.8 m 3 / hr, and a liquid distributor is arranged in the tower for uniform distribution, and the reflux ratio is controlled at about 0.8-1. The uncondensed HCl, N2 and PF5 come out from the top of the reflux intermediate tank 6 in the form of gas phase to obtain the second uncondensed gas, which enters the next step.

[0081] The tower kettle of the rectification tower 4 is connected with a reboiler, the reboiler is made of 316L, C276 or Monel, and the heat exchange area of the reboiler is 15 m 2 ; steam is used for heating, and the kettle bottom temperature is controlled to be 85-90℃. The product taken out from the tower kettle of the rectification tower is HF product, the HF product is cooled by the HF pre-cooler 7, and then pumped into the HF recovery tank 8 for storage and recycling, the heat exchange area of the condenser is 10 m 2 , and the material is 316L, C276 or Monel.

[0082] (3) The second uncondensed gas is absorbed by the hydrochloric acid absorption system to obtain a hydrochloric acid product; water is used for hydrochloric acid absorption in the hydrochloric acid absorption system, the temperature of the water is 5-15℃, the concentration of the obtained hydrochloric acid product is 30-32%, and the HF content in the hydrochloric acid product is 100-300ppm.

[0083] The sampling analysis result of the hydrochloric acid product is that the hydrochloric acid content is 30.65%, the fluorine ion is 210ppm, and the phosphorus content (calculated according to P2O5) is 161ppm.

[0084] The analysis result of the second uncondensed gas is that the HCl content is 98.6%, the fluorine ion is 609ppm, and the phosphorus content (calculated according to P2O5) is 412ppm.

[0085] The energy consumption of the system used in the example is about 0.045 degrees of electricity per production of 1kg of hydrochloric acid product.

[0086] Comparative Example 2

[0087] The method for realizing comprehensive utilization of the tail gas in the production of liquid lithium hexafluorophosphate by using the compression condensation system + rectification system in the example 1, which comprises:

[0088] (1) The tail gas in the production of liquid lithium hexafluorophosphate is introduced into the compressor 1, and the composition of the tail gas is: 87% HCl, 0.4% PF5, 1% HF, 4% solvent, and the rest is nitrogen.

[0089] The flow rate of the compressor 1 is 500 m 3 / hr, and the outlet pressure of the compressor 1 is 3Mpa; the material of the compressor 1 is 316L, C276 or Monel, the compressed tail gas enters the condensation assembly 2, and then sequentially passes through the raw material pre-cooler and the raw material cooler to be cooled to 15-25℃, and then enters the solvent recovery tank 3, the condensate collected by the solvent recovery tank 3 is the solvent methyl ethyl carbonate, which is stored and recycled in the solvent recovery tank 3, and the uncondensed gas is the first uncondensed gas, which is a mixed gas of HCl, HF, N2 and PF5, and the first uncondensed gas enters the subsequent rectification tower 4 for fluorine recovery;

[0090] (2) The first uncondensed gas obtained after pressure condensation in step (1) is introduced into the feed inlet of the rectification tower 4, and separation of HCl and HF is achieved in the rectification tower. The rectification tower has a diameter of 0.5 m, a tower height of 15 m, uses wire mesh packing (material S316L, C276 or Monel), and the packing height is 12 m. The low-boiling-point component HCl comes out from the top of the rectification tower, is condensed to 30 to -35°C by the condenser 5 at the top of the rectification tower, and then enters the reflux intermediate tank 6. The liquid component at the bottom of the reflux intermediate tank 6 partially refluxes into the top of the rectification tower, and the reflux liquid flow is controlled at 0.6 to 0.8 m 3 / hr. A liquid distributor is arranged in the tower to uniformly distribute the liquid. The reflux ratio is controlled at about 0.8 to 1. The uncondensed HCl, N2 and PF5 come out from the top of the reflux intermediate tank 6 in the form of gas phase to obtain second uncondensed gas, which is introduced into the next step.

[0091] The tower kettle of the rectification tower 4 is connected to a reboiler. The reboiler has a material of 316L, C276 or Monel, and a heat exchange area of 15 m 2 . Steam is used for heating, and the kettle bottom temperature is controlled at 85 to 90°C. The product HF is taken out from the kettle of the rectification tower, is cooled by the HF pre-cooler 7, is pumped into the HF recovery tank 8 for storage, and is recycled. The condenser has a heat exchange area of 10 m 2 and a material of 316L, C276 or Monel.

[0092] (3) The second uncondensed gas in step (2) is introduced into the bottom of the defluorination tower 9. The defluorination tower has a diameter of 0.5 m, a tower height of 5 m, uses wire mesh packing (material S316L, C276 or Monel), and the packing height is 3 m. The flow rate of the second uncondensed gas in the defluorination tower 9 is controlled at 1 m / s. The defluorination agent is 20% calcium chloride aqueous solution, and the spraying amount is 0.5 m 3 / hr. The temperature in the defluorination tower 9 is controlled at 20 to 30°C. When the phosphorus pentafluoride in the tail gas contacts the calcium chloride aqueous solution in the defluorination tower from bottom to top, the purified HCl product flows out from the top of the defluorination tower, is absorbed by the hydrochloric acid absorption system, and is used as a hydrochloric acid product. Water is used in the hydrochloric acid absorption system for hydrochloric acid absorption, and the temperature of the water is 5 to 15°C. The high-purity hydrochloric acid product obtained by absorption has a hydrochloric acid concentration of 30 to 32%, and the HF content in the high-purity hydrochloric acid product is 10 to 50 ppm.

[0093] The sampling analysis results of the hydrochloric acid product are as follows: hydrochloric acid content 30.8%, fluorine ion 13 ppm, and phosphorus (calculated as P2O5) 17 ppm.

[0094] The analysis results of the hydrogen fluoride stored in the HF recovery tank 8 are as follows: HF content 90.56%, solvent content 9.14%, chlorine ion 1700 ppm, and phosphorus (calculated as P2O5) 189 ppm.

[0095] The system used in this embodiment consumes about 0.12 degree of electricity for producing 1 kg of hydrochloric acid product.

[0096] Obviously, the above embodiments are merely exemplary but not as limitation to the embodiments. Based on the above description, one of ordinary skill in the art can make other different forms of changes or variations. Here, it is not necessary and also impossible to enumerate all the embodiments. The obvious changes or variations derived from the above are still within the protection scope of the present application.

Claims

1. A method for comprehensive utilization of tail gas from the production of liquid lithium hexafluorophosphate, characterized in that: include: Compression and condensation: pressurizing the liquid lithium hexafluorophosphate production tail gas to 1-2 MPa, and condensing the compressed tail gas at 10-20°C to obtain a first condensate and a first uncondensed gas respectively; Fluorine recovery: The first uncondensed gas is distilled in a distillation tower with a bottom temperature of 80°C to 95°C. The gas at the top of the distillation tower is taken out and condensed at 30°C to -40°C, and separated to obtain a second condensate and a second uncondensed gas. Hydrogen chloride recovery: The second uncondensed gas is brought into contact with a defluorinating agent in a defluorination tower for defluorination. The defluorinated gas is subjected to multi-stage absorption of hydrochloric acid to obtain a high-purity hydrochloric acid product.

2. The method according to claim 1, characterized in that The reflux ratio of the second condensate in the distillation tower is controlled between 0.8 and 2.

3. The method according to claim 1 or 2, characterized in that The number of theoretical plates of the distillation tower is 35 to 40, and the first uncondensed gas is fed between the 20th to 25th plates of the distillation tower.

4. The method according to claim 3, characterized in that The HF content in the second uncondensed gas is between 500 and 600 ppm.

5. The method according to any one of claims 1 to 4, characterized in that The temperature inside the defluorination tower is 20-30°C.

6. The method according to claim 5, characterized in that The defluorinating agent is a saturated solution of a chloride salt, and the chloride salt is preferably one or more of calcium chloride, aluminum chloride, ferric chloride, magnesium chloride, sodium chloride and lithium chloride.

7. The method according to claim 6, characterized in that When the concentration of chloride salt in the saturated solution of chloride salt is lower than 50 g / L, the saturated solution is filtered, and chloride salt is added to the filtrate and then recycled.

8. The method according to any one of claims 1 to 7, characterized in that The defluorination tower has 25 to 30 theoretical plates.

9. The method according to any one of claims 1 to 8, characterized in that The HF content in the defluorinated gas discharged from the defluorination tower is between 30 and 60 ppm; The gas after defluorination in the defluorination tower is subjected to multi-stage falling film absorption with water to obtain a high-purity hydrochloric acid product; preferably, the water temperature is 5-15°C, the hydrochloric acid concentration in the high-purity hydrochloric acid product obtained by absorption is 30-32%, and the HF content in the high-purity hydrochloric acid product is between 10-50ppm.

10. A device for implementing the method according to any one of claims 1 to 9, characterized in that: include: A compression condensation system comprises a compressor (1), a condensation component (2) and a solvent recovery tank (3) which are connected in sequence; The distillation system comprises a distillation tower (4) connected to the gas outlet of the solvent recovery tank (3), a condenser (5) arranged at the top of the distillation tower (4), a reflux intermediate tank (6) connected to the condenser (5), and an HF recovery assembly arranged at the bottom of the distillation tower (4); a defluorination tower (9) connected to the gas outlet of the reflux intermediate tank (6); The hydrogen chloride absorption system is formed by connecting multiple falling film absorption towers in series and is connected to the gas outlet at the top of the defluorination tower (9).

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