Method for reducing chlorine content of sodium hexafluorophosphate

Abstract

The invention relates to a method for reducing the chlorine content of sodium hexafluorophosphate, which comprises the following steps: introducing PF5 / HCl mixed gas into a mixed solution of sodium fluoride and an organic solvent, and reacting to generate a sodium hexafluorophosphate synthetic solution; purifying the sodium hexafluorophosphate synthetic liquid to obtain sodium hexafluorophosphate of which the chlorine content is less than 1ppm; the organic solvent is a first organic solvent or a second organic solvent, and the first organic solvent is a hydrocarbon organic solvent; the second organic solvent is a carbonic ester organic solvent. The sodium hexafluorophosphate obtained by the method is high in purity and low in chloride ion content, and meets the application requirements of sodium ion batteries; the method has the advantages of few three wastes, low energy consumption and high yield, and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, and in particular to a method for reducing the chlorine content of sodium hexafluorophosphate. Background Art

[0002] Sodium hexafluorophosphate has the advantages of high conductivity and stable solid electrolyte interface, and has gradually become the focus of sodium ion battery research. At present, the mainstream preparation process of sodium hexafluorophosphate is the hydrogen fluoride method, that is, hydrogen fluoride is used as the reaction solvent, and crystallization is carried out in hydrogen fluoride after the reaction is completed to obtain sodium hexafluorophosphate crystals.

[0003] Patent CN108946769A discloses a method for preparing sodium salt for sodium battery, wherein polyvinyl alcohol and sodium fluoride are mixed evenly, deionized water is added, and the mixture is dried and calcined to obtain porous sodium fluoride; phosphorus pentafluoride gas is introduced into a mixture of porous sodium fluoride and hydrogen fluoride liquid to react to obtain a sodium hexafluorophosphate solution; the sodium hexafluorophosphate solution is crystallized, filtered, and dried to obtain sodium hexafluorophosphate. Patent CN115285965A discloses a method for preparing sodium hexafluorophosphate from a mixed gas of sodium fluoride, high-purity hydrofluoric acid, and high-purity phosphorus pentafluoride, wherein the obtained reaction solution is filtered through a resin adsorbent, crystallized, precipitated, filtered, and dried under reduced pressure to obtain sodium hexafluorophosphate.

[0004] The main defects of preparing sodium hexafluorophosphate by hydrogen fluoride method are as follows: (1) the requirements for equipment materials are high and the risk is relatively high; (2) the purification process, whether it adopts dynamic crystallization or static crystallization, requires deep cooling process and consumes a lot of energy.

[0005] Therefore, research on the preparation of sodium hexafluorophosphate using other solvents such as carbonates has gradually emerged.

[0006] CN114890402A discloses a method for preparing hexafluorophosphate, which comprises dissolving hydrogen fluoride salt in a carbonate solvent, adding phosphorus pentachloride in batches under reduced pressure, and stirring the reaction at a temperature of 30 to 60°C; filtering after the stirring reaction, concentrating the obtained filtrate, cooling, crystallizing, and filtering again to obtain hexafluorophosphate crystals. The byproduct hydrogen chloride in this method is not easy to remove, resulting in excessive chloride ions and acidity of the hexafluorophosphate product. In addition, solid phosphorus pentachloride easily causes pipeline blockage and has problems such as difficulty in feeding.

[0007] CN115504448A discloses a method for preparing a phosphorus pentafluoride carbonate complex and co-producing sodium hexafluorophosphate, wherein phosphorus pentafluoride gas is prepared using phosphorus pentoxide and anhydrous hydrogen fluoride as raw materials and SO3 as a dehydrating agent, and a phosphorus pentafluoride carbonate complex is prepared, and the complex is further mixed with a carbonate solution of sodium fluoride to prepare sodium hexafluorophosphate, and a liquid salt of sodium hexafluorophosphate is obtained after deacidification. However, this method requires a large amount of carbonate for adsorbing phosphorus pentafluoride gas, and is not suitable for industrial production.

[0008] The above carbonate solvent method has the disadvantages of low reaction selectivity, difficult feeding, low product purity and high chloride ion content. Summary of the invention

[0009] In order to solve the above technical problems, the present invention proposes a method for reducing the chlorine content of sodium hexafluorophosphate. The obtained sodium hexafluorophosphate has high purity and low chloride ion content, which meets the application requirements of sodium ion batteries; the amount of solvent used is small, the three wastes are small, the energy consumption is low, the yield is high, and it is suitable for industrial production.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] A method for reducing the chlorine content of sodium hexafluorophosphate, the method comprising: passing a PF5 / HCl mixed gas into a mixed liquid of sodium fluoride and an organic solvent to react and generate a sodium hexafluorophosphate synthetic liquid; purifying the sodium hexafluorophosphate synthetic liquid to obtain sodium hexafluorophosphate with a chlorine content of less than 1 ppm; the organic solvent is a first organic solvent or a second organic solvent, the first organic solvent is a hydrocarbon organic solvent; the second organic solvent is a carbonate organic solvent.

[0012] Specifically, the hydrocarbon organic solvent is selected from an alkane organic solvent or an aromatic organic solvent; the alkane organic solvent is selected from C5 to C 10 Alkanes or C1~C 10 Halogenated alkane; the aromatic organic solvent is benzene, halogenated benzene, a derivative of benzene or a derivative of halogenated benzene, and the general formula I of the aromatic organic solvent is:

[0013]

[0014] Wherein, R1, R2, R3, R4, R5, and R6 are independently selected from H, halogen, C1-C 10 A straight chain, branched chain or cyclic alkyl group.

[0015] The carbonate organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

[0016] Specifically, the method of the present invention comprises the following steps:

[0017] Step A: adding an organic solvent and sodium fluoride in a mass ratio of 10:1 to 30:1 into a reaction container, and mixing under the protection of an inert gas to obtain a mixed solution of sodium fluoride and the organic solvent;

[0018] Step B: introducing PF5 / HCl mixed gas into a reaction container, wherein the mass ratio of PF5 to sodium fluoride is 3:1 to 9:1, and reacting at a reaction temperature of 0 to 50° C. for 0.5 to 24 hours to obtain a sodium hexafluorophosphate synthetic liquid.

[0019] The organic solvent in the above steps is a reaction solvent.

[0020] The molecular weight of sodium fluoride is 42, and the molecular weight of sodium hexafluorophosphate is 168. Theoretically, 1g of sodium fluoride can generate 4g of sodium hexafluorophosphate after complete reaction; the solubility of sodium hexafluorophosphate in organic solvents is fixed, so it is only necessary to set the mass ratio of sodium fluoride and organic solvent. If sodium fluoride is completely converted during the reaction and the organic solvent is not volatilized, the obtained sodium hexafluorophosphate synthetic liquid is just a saturated solution of sodium hexafluorophosphate. In the subsequent purification process, the amount of the first organic solvent can be reduced as much as possible. Specifically, the mass ratio of the organic solvent to sodium fluoride is preferably 10:1 to 20:1, and more preferably 10:1 to 12:1.

[0021] The organic solvent and sodium fluoride are mixed while stirring at a rotation speed of 300 to 1500 rpm, preferably 500 to 1000 rpm, and more preferably 600 to 800 rpm.

[0022] In the preparation process of the method of the present invention, the flow rate of the PF5 / HCl mixed gas into the mixed solution of sodium fluoride and the organic solvent is 0.1-1.0 g / min, preferably 0.1-0.5 g / min, and more preferably 0.15-0.20 g / min.

[0023] The mass ratio of PF5 to sodium fluoride is preferably 3:1 to 9:1, more preferably 4.5:1 to 6:1.

[0024] The reaction temperature is 0 to 50° C., preferably 10 to 30° C., more preferably 20 to 30° C.; the reaction time is 0.5 to 24 h, preferably 1 to 6 h, more preferably 1.5 to 3 h.

[0025] The method can react under normal pressure.

[0026] In a specific embodiment, the purification process of the present invention is achieved by the following steps:

[0027] When the organic solvent (reaction solvent) is the first organic solvent, the sodium hexafluorophosphate synthesis liquid is directly filtered to obtain a crude sodium hexafluorophosphate product, and then the crude sodium hexafluorophosphate product is washed with the first organic solvent (washing solvent), and after drying, sodium hexafluorophosphate having a chlorine content of less than 1 ppm is obtained; the mass ratio of the first organic solvent (washing solvent) for washing to the first organic solvent (reaction solvent) in the mixed solution of sodium fluoride and the organic solvent is 1:5 to 1:1, preferably 1:2 to 1:1.

[0028] The first organic solvent can be recycled. Specifically, at room temperature, the solution obtained after washing is pre-distilled under reduced pressure to remove hydrogen chloride, the tail gas is absorbed by alkali solution, and then heated to 35-40° C. to collect the first organic solvent. According to the test, the water content of the first organic solvent is less than 10 ppm, and the recovery rate of the first organic solvent is greater than 90%, and the first organic solvent can continue to be recycled.

[0029] In another specific embodiment, the purification process of the present invention is achieved by the following steps:

[0030] When the organic solvent (reaction solvent) is the second organic solvent, a first organic solvent is added to the sodium hexafluorophosphate synthesis liquid, and the mass ratio of the first organic solvent to the second organic solvent is 5:1 to 1:1, preferably 2:1 to 1.5:1; after the sodium hexafluorophosphate is precipitated, the sodium hexafluorophosphate is filtered to obtain a crude sodium hexafluorophosphate, and the crude sodium hexafluorophosphate is washed with the first organic solvent, and after drying, sodium hexafluorophosphate having a chlorine content of less than 1 ppm is obtained; the mass ratio of the first organic solvent (washing solvent) for washing to the second organic solvent (reaction solvent) in the mixed solution of sodium fluoride and the organic solvent is 1:5 to 1:1, preferably 1:2 to 1:1.

[0031] The first organic solvent and the second organic solvent can be recycled. Specifically, the following steps are included: first, the filtrate obtained by suction filtration (a mixture of the first organic solvent and the second organic solvent) is mixed with the solution obtained after washing (the first organic solvent), and then pre-reduced pressure distillation is performed at room temperature to remove hydrogen chloride, and the tail gas is absorbed by alkali solution, and the first organic solvent is collected at 30-35°C. After no solvent is evaporated, it is heated to 50-60°C to collect the second organic solvent. According to the test, the water content of the first organic solvent and the second organic solvent is less than 10ppm, and the recovery rate of the first organic solvent and the second organic solvent is greater than 90%, and they can continue to be used.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The sodium hexafluorophosphate obtained by the method of the present invention has high purity and low chloride ion content, which meets the application requirements of sodium ion batteries;

[0034] 2. The method of the present invention has less three wastes, low energy consumption, high yield, low carbon and environmental protection, and is suitable for industrial production. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0036] Example 1

[0037] Step A: Add 1 g of sodium fluoride (24 mmol) and 10 g of dimethyl carbonate (a second organic solvent) into a reaction bottle made of PFA, start stirring, and replace with nitrogen to obtain a mixed solution of the sodium fluoride and the second organic solvent;

[0038] Step B: Pass the PF5 / HCl mixed gas (PF5 content of 4.5 g, 36 mmol) from the PF5 synthesis reactor into the reaction bottle at a flow rate of 0.20 g / min, and react at 20° C. for 1.5 h to obtain a sodium hexafluorophosphate synthesis liquid;

[0039] Step C: adding 15 g of dichloromethane to the sodium hexafluorophosphate synthesis liquid to precipitate the sodium hexafluorophosphate; filtering the precipitated sodium hexafluorophosphate and washing with 5 g of dichloromethane (the first organic solvent) to obtain a crude sodium hexafluorophosphate; fully drying the crude sodium hexafluorophosphate at 80° C. to obtain 3.82 g of pure sodium hexafluorophosphate with a yield of 95.5%.

[0040] Ion chromatography showed that the chloride ion content of pure sodium hexafluorophosphate was 0.91 ppm.

[0041] Example 2

[0042] The operation of Example 2 is the same as that of Example 1, except that the second organic solvent in the mixed solution of sodium fluoride and the second organic solvent is ethyl methyl carbonate, and the other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0043] Example 3

[0044] The operation of Example 3 is the same as that of Example 1, except that the second organic solvent in the mixed solution of sodium fluoride and the second organic solvent is diethyl carbonate, and the other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0045] Example 4

[0046] The operation of Example 4 is the same as that of Example 1, except that the ventilation rate of the PF5 / HCl mixed gas is 0.10 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0047] Example 5

[0048] The operation of Example 5 is the same as that of Example 1, except that the ventilation rate of the PF5 / HCl mixed gas is 0.15 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0049] Example 6

[0050] The operation of Example 6 is the same as that of Example 1, except that the ventilation rate of the PF5 / HCl mixed gas is 0.50 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0051] Example 7

[0052] The operation of Example 7 is the same as that of Example 1, except that the ventilation rate of the PF5 / HCl mixed gas is 1.00 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0053] Example 8

[0054] The operation of Example 8 is the same as that of Example 1, except that the mass ratio of PF5 to sodium fluoride is 3:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0055] Example 9

[0056] The operation of Example 9 is the same as that of Example 1, except that the mass ratio of PF5 to sodium fluoride is 6:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0057] Example 10

[0058] The operation of Example 10 is the same as that of Example 1, except that the mass ratio of PF5 to sodium fluoride is 9:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0059] Embodiment 11

[0060] The operation of Example 11 is the same as that of Example 1, except that the reaction temperature is 0° C., and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0061] Example 12

[0062] The operation of Example 12 is the same as that of Example 1, except that the reaction temperature is 30° C., and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0063] Embodiment 13

[0064] The operation of Example 13 is the same as that of Example 1, except that the reaction temperature is 50° C., and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0065] Embodiment 14

[0066] The operation of Example 14 is the same as that of Example 1, except that the reaction time is 3 hours, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0067] Embodiment 15

[0068] The operation of Example 15 is the same as that of Example 1, except that the first organic solvent used for washing is n-hexane, and the other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0069] Example 16

[0070] The operation of Example 16 is the same as that of Example 1, except that the first organic solvent used for washing is toluene, and the other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0071] Embodiment 17

[0072] The operation of Example 17 is the same as that of Example 1, except that the mass ratio of the first organic solvent to the second organic solvent used for precipitation is 2.0:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0073] Embodiment 18

[0074] The operation of Example 18 is the same as that of Example 1, except that the mass ratio of the first organic solvent to the second organic solvent used for precipitation is 5.0:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0075] Embodiment 19

[0076] The operation of Example 19 is the same as that of Example 1, except that the mass ratio of the first organic solvent to the second organic solvent used for washing is 1:5, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0077] Embodiment 20

[0078] The operation of Example 20 is the same as that of Example 1, except that the mass ratio of the first organic solvent to the second organic solvent used for washing is 1:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0079] Embodiment 21

[0080] The operation of Example 21 is the same as that of Example 1, except that the first organic solvent and the second organic solvent are recycled and reused as those in Example 1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 1 below.

[0081] Comparative Example 1

[0082] The operations of step A and step B of comparative example 1 are the same as those of example 1;

[0083] Step C: Concentrate the sodium hexafluorophosphate synthesis solution, remove the solvent to obtain a crude sodium hexafluorophosphate; fully dry the crude sodium hexafluorophosphate at 80° C. to obtain a pure sodium hexafluorophosphate. The yield and chloride ion content of the pure sodium hexafluorophosphate are shown in Table 1 below.

[0084] Comparative Example 2

[0085] The operations of step A and step B of comparative example 2 are the same as those of example 1;

[0086] Step C: The sodium hexafluorophosphate synthesis solution is concentrated, the solvent is removed, and the solution is washed with 5 g of dichloromethane (the first organic solvent) to obtain a crude sodium hexafluorophosphate product; the crude sodium hexafluorophosphate product is fully dried at 80° C. to obtain a pure sodium hexafluorophosphate product. The yield and chloride ion content of the pure sodium hexafluorophosphate product are shown in Table 1 below.

[0087] Comparative Example 3

[0088] The operations of step A and step B of comparative example 3 are the same as those of example 1;

[0089] Step C: 15 g of dichloromethane is added to the sodium hexafluorophosphate synthesis liquid to precipitate sodium hexafluorophosphate; the precipitated sodium hexafluorophosphate is filtered, and the crude sodium hexafluorophosphate is fully dried at 80° C. to obtain pure sodium hexafluorophosphate. The yield and chloride ion content of the pure sodium hexafluorophosphate are shown in Table 1 below.

[0090]

[0091]

[0092]

[0093] Embodiment 22

[0094] Step A: Add 1 g of sodium fluoride (24 mmol) and 10 g of dichloromethane to a PFA reaction bottle, start stirring, and replace with nitrogen;

[0095] Step B: Pass the PF5 / HCl mixed gas (PF5 content of 4.5 g, 36 mmol) from the PF5 synthesis reactor into the reaction bottle at a flow rate of 0.15 g / min, and react at 20° C. for 1.5 h to obtain a sodium hexafluorophosphate synthesis solution;

[0096] Step C: directly filter the sodium hexafluorophosphate reaction solution and wash it with dichloromethane (5 g); fully dry the filter residue at 80° C. to obtain 3.44 g of pure sodium hexafluorophosphate with a yield of 85.3%.

[0097] Ion chromatography showed that the chloride ion content of pure sodium hexafluorophosphate was 0.13 ppm.

[0098] Embodiment 23

[0099] The operation of Example 23 is the same as that of Example 22, except that the first organic solvent in the mixed solution of sodium fluoride and the first organic solvent is n-hexane, and the other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0100] Embodiment 24

[0101] The operation of Example 24 is the same as that of Example 22, except that the first organic solvent in the mixed solution of sodium fluoride and the first organic solvent is toluene, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0102] Embodiment 25

[0103] The operation of Example 25 is the same as that of Example 22, except that the ventilation rate of the PF5 / HCl mixed gas is 0.10 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0104] Embodiment 26

[0105] The operation of Example 26 is the same as that of Example 22, except that the ventilation rate of the PF5 / HCl mixed gas is 0.15 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0106] Embodiment 27

[0107] The operation of Example 27 is the same as that of Example 22, except that the ventilation rate of the PF5 / HCl mixed gas is 0.50 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0108] Embodiment 28

[0109] The operation of Example 28 is the same as that of Example 22, except that the ventilation rate of the PF5 / HCl mixed gas is 1.00 g / min, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0110] Embodiment 29

[0111] The operation of Example 29 is the same as that of Example 22, except that the mass ratio of PF5 to sodium fluoride is 3:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0112] Embodiment 30

[0113] The operation of Example 30 is the same as that of Example 22, except that the mass ratio of PF5 to sodium fluoride is 6:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0114] Embodiment 31

[0115] The operation of Example 31 is the same as that of Example 22, except that the mass ratio of PF5 to sodium fluoride is 9:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0116] Embodiment 32

[0117] The operation of Example 32 is the same as that of Example 22, except that the reaction temperature is 0° C., and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0118] Embodiment 33

[0119] The operation of Example 33 is the same as that of Example 22, except that the reaction temperature is 30° C., and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0120] Embodiment 34

[0121] The operation of Example 32 is the same as that of Example 22, except that the reaction temperature is 50° C., and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0122] Embodiment 35

[0123] The operation of Example 35 is the same as that of Example 22, except that the reaction time is different, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0124] Embodiment 36

[0125] The operation of Example 36 is the same as that of Example 22, except that the mass ratio of the first organic solvent for washing to the first organic solvent for reaction is 1:5, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0126] Embodiment 37

[0127] The operation of Example 37 is the same as that of Example 22, except that the mass ratio of the first organic solvent for washing to the first organic solvent for reaction is 1:1, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0128] Embodiment 38

[0129] The operation of Example 38 is the same as that of Example 22, except that the first organic solvent is recycled and reused as in Example 22, and other operations remain unchanged. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0130] Comparative Example 4

[0131] The operations of step A and step B of comparative example 5 are the same as those of example 22;

[0132] Step C: Filter the sodium hexafluorophosphate reaction solution directly, and fully dry the filter residue at 80° C. to obtain pure sodium hexafluorophosphate. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0133] Comparative Example 5

[0134] The operation of Comparative Example 5 is the same as that of Example 22, except that: the first organic solvent in the mixed solution of sodium fluoride and the first organic solvent in step A is chlorodifluoromethane; in step C, the sodium hexafluorophosphate reaction solution is concentrated, and the solvent is removed to obtain pure sodium hexafluorophosphate. The yield and chloride ion content of pure sodium hexafluorophosphate are shown in Table 2 below.

[0135]

[0136]

Claims

1. A method for reducing the chlorine content of sodium hexafluorophosphate, characterized in that: The method comprises the following steps: introducing a PF5 / HCl mixed gas into a mixed liquid of sodium fluoride and an organic solvent to react and generate a sodium hexafluorophosphate synthetic liquid; the sodium hexafluorophosphate synthetic liquid is purified to obtain sodium hexafluorophosphate with a chlorine content of less than 1 ppm; the organic solvent is a first organic solvent or a second organic solvent, the first organic solvent is a hydrocarbon organic solvent; the second organic solvent is a carbonate organic solvent.

2. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 1, characterized in that: The hydrocarbon organic solvent is selected from an alkane organic solvent or an aromatic organic solvent; the alkane organic solvent is selected from C5~C 10 Alkanes or C1~C 10 Halogenated alkane; the aromatic organic solvent is benzene, halogenated benzene, a derivative of benzene or a derivative of halogenated benzene, and the general formula I of the aromatic organic solvent is: Wherein, R1, R2, R3, R4, R5, and R6 are independently selected from H, halogen, C1-C 10 A straight chain, branched chain or cyclic alkyl group.

3. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 1, characterized in that: The carbonate organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

4. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 1, characterized in that: The method comprises the following steps: Step A: adding an organic solvent and sodium fluoride in a mass ratio of 10:1 to 30:1 into a reaction container, and mixing under the protection of an inert gas to obtain a mixed solution of sodium fluoride and the organic solvent; Step B: introducing PF5 / HCl mixed gas into a reaction container, wherein the mass ratio of PF5 to sodium fluoride is 3:1 to 9:1, and reacting at a reaction temperature of 0 to 50° C. for 0.5 to 24 hours to obtain a sodium hexafluorophosphate synthetic liquid.

5. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 4, characterized in that: The introduction rate of the PF5 / HCl mixed gas is 0.1-1.0 g / min.

6. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 4, characterized in that: The reaction is carried out under stirring at a stirring speed of 300 to 1500 rpm.

7. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 1, characterized in that: The purification treatment comprises the following steps: when the organic solvent is the first organic solvent, the sodium hexafluorophosphate synthesis liquid is directly filtered to obtain a crude sodium hexafluorophosphate product, the crude sodium hexafluorophosphate product is then washed with the first organic solvent, and after drying, sodium hexafluorophosphate having a chlorine content of less than 1 ppm is obtained; the mass ratio of the first organic solvent used for washing to the first organic solvent in the mixed solution of sodium fluoride and the organic solvent is 1:5 to 1:

1.

8. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 1, characterized in that: The purification treatment comprises the following steps: when the organic solvent is the second organic solvent, a first organic solvent is added to a sodium hexafluorophosphate synthesis liquid, wherein the mass ratio of the first organic solvent to the second organic solvent is 1:1 to 5:1; after the sodium hexafluorophosphate is precipitated, the sodium hexafluorophosphate is filtered to obtain a crude sodium hexafluorophosphate product, and the crude sodium hexafluorophosphate product is washed with the first organic solvent, and after drying, sodium hexafluorophosphate having a chlorine content of less than 1 ppm is obtained; and the mass ratio of the first organic solvent used for washing to the second organic solvent in the mixed solution of sodium fluoride and the organic solvent is 1:5 to 1:

1.

9. The method for reducing the chlorine content of sodium hexafluorophosphate according to claim 1, characterized in that: The first organic solvent and the second organic solvent can be recycled.

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