Method for preparing sodium hexafluorophosphate by gas-solid process, and use of same

Abstract

A method for preparing sodium hexafluorophosphate by a gas-solid process, and the use of same. The method comprises the following steps: introducing gaseous phosphorus pentafluoride into a sodium monofluorophosphate solid to perform a gas-solid reaction, so as to generate a solid mixture of sodium hexafluorophosphate and phosphate; then adding a polar solvent to the solid mixture for dissolving same, so as to obtain a sodium hexafluorophosphate solution and a solid filter residue; concentrating the sodium hexafluorophosphate solution, and then adding an organic solvent so as to precipitate sodium hexafluorophosphate to obtain a crude product; then adding a polar solvent for dissolving same to obtain a sodium hexafluorophosphate solution, concentrating same, adding an organic solvent for precipitating sodium hexafluorophosphate, and performing vacuum drying to obtain high-purity sodium hexafluorophosphate, the polar solvent being one of dimethyl carbonate and diethyl carbonate, and the organic solvent being one of benzene or toluene. The method uses the gas-solid process to synthesize sodium hexafluorophosphate, and involves simple technological processes, and the product after multi-stage purification has high purity, can be used as an electrolyte for sodium ion batteries for use in the fields of new energy electric vehicles, energy storage and the like, thus achieving wide application prospects.

Description

A method for preparing sodium hexafluorophosphate by gas-solid method and its application Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a method for preparing sodium hexafluorophosphate by a gas-solid process and an application thereof. Background Art

[0002] In recent years, with the rapid development of the lithium battery industry, upstream lithium ore raw material prices have remained high. The high cost of lithium battery materials has gradually become a barrier to the transformation of the new energy industry. Therefore, the development of new secondary battery technologies that can complement lithium-ion batteries is crucial. Sodium batteries are abundant, inexpensive, and environmentally friendly, making them a promising alternative to lithium-ion batteries and offering broad market prospects and applications.

[0003] Compared with lithium-ion batteries, sodium-ion batteries have higher safety performance, abundant sodium resource reserves, easily available raw materials, and lower costs. However, the energy density, capacity, and charge and discharge frequency of sodium-ion batteries are not as good as those of lithium-ion batteries. Therefore, sodium-ion batteries are generally used in small energy storage fields such as energy storage cabinets, electric motorcycles, electric tricycles, or mobile phones and computers. In large energy storage fields, they are generally used in combination with lithium-ion batteries.

[0004] Sodium hexafluorophosphate, as the main power source of sodium-ion batteries and electrolyte, has also become the focus of research and layout of current new energy companies. How to prepare high-purity sodium hexafluorophosphate at low cost will help promote the healthy and rapid development of the sodium-ion battery industry and achieve "overtaking on curves" in the field of new energy batteries.

[0005] A Chinese invention patent application with publication number CN114772614A discloses a method for preparing sodium hexafluorophosphate: sodium hexafluorophosphate is prepared using sodium fluoride and phosphorus pentafluoride as raw materials. The organic solvent used, Freon, is a major greenhouse gas that can cause irreversible damage to the natural environment.

[0006] Chinese invention patent application publication number CN114873577A discloses a method for preparing sodium hexafluorophosphate: phosphorus pentoxide, hydrogen fluoride, and a sodium source are used as raw materials to prepare sodium hexafluorophosphate. The reaction conditions are harsh, and the sodium hexafluorophosphate solution is heated, concentrated, and crystallized, which causes partial decomposition of the sodium hexafluorophosphate and a high impurity content.

[0007] In summary, the current methods for preparing sodium hexafluorophosphate have disadvantages such as harsh process conditions, highly polluting raw materials used, and low product purity. Therefore, finding an efficient and environmentally friendly method to prepare high-purity sodium hexafluorophosphate is of epoch-making significance for the development of new energy batteries.

[0008] Summary of the Invention

[0009] In view of the shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing sodium hexafluorophosphate by a gas-solid process and its application. The process flow is simple, the product has high purity and good particle size, can be used as an electrolyte for sodium ion batteries, and is applied in fields such as new energy electric vehicles, and has a broad application market and prospects.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for preparing sodium hexafluorophosphate by a gas-solid process is provided, comprising the following steps:

[0012] S1: passing phosphorus pentafluoride gas into sodium monofluorophosphate solid to carry out gas-solid reaction to generate a solid mixture of sodium hexafluorophosphate and phosphate;

[0013] S2: adding a polar solvent to the solid mixture produced in S1 to fully dissolve it, filtering it, washing the resulting filter residue with a polar solvent, and combining the filtrate and the washing liquid to obtain a sodium hexafluorophosphate solution;

[0014] S3: The sodium hexafluorophosphate solution obtained in S2 is concentrated and then an organic solvent is added to crystallize the sodium hexafluorophosphate, which is filtered and the resulting filter residue is washed with an organic solvent to obtain a crude sodium hexafluorophosphate product. The filtrate and the washing solution are combined to obtain a mixed mother liquor 1;

[0015] S4: adding the crude sodium hexafluorophosphate obtained in S3 to a polar solution for dissolution, and filtering the dissolved crude sodium hexafluorophosphate solution through precise filtration to remove insoluble impurities to obtain a sodium hexafluorophosphate solution;

[0016] S5: concentrating the sodium hexafluorophosphate solution obtained in S4 and adding an organic solvent to crystallize the sodium hexafluorophosphate, filtering the resulting filter residue and washing it with an organic solvent to obtain a wet product of sodium hexafluorophosphate. Combining the filtrate and the washing solution to obtain a mixed mother liquor 2;

[0017] S6: vacuum drying the wet sodium hexafluorophosphate obtained in S5 to obtain a high-purity sodium hexafluorophosphate product, wherein phosphorus pentafluoride is first periodically introduced during the vacuum drying process, and then nitrogen is periodically introduced; wherein:

[0018] In S2 and S4, the polar solvent is one of dimethyl carbonate (DMC) and diethyl carbonate (DEC);

[0019] In S3 and S5, the organic solvent is benzene or toluene.

[0020] According to the above scheme, in S1, the phosphorus pentafluoride gas is derived from the thermal decomposition and purification of hexafluorophosphate.

[0021] According to the above scheme, in S1, the gas-solid reaction temperature is 110-140°C.

[0022] According to the above scheme, in S1, the gas-solid reaction time is 11 to 13 hours.

[0023] According to the above scheme, in S1, the molar ratio of sodium monofluorophosphate and phosphorus pentafluoride in the gas-solid reaction is 1:(1.15-1.25).

[0024] According to the above scheme, in S1, the gas-solid reactor is connected in two stages in series, and the material is selected from stainless steel, Hastelloy alloy or Monel alloy.

[0025] According to the above scheme, in S2, the amount of polar solvent added for dissolution is 3 to 5 times the amount of the solid mixture, and the amount of polar solvent added for washing is 0.5 to 1 times the amount of the solid mixture; in S4, the amount of polar solvent added is 5 to 8 times the amount of crude sodium hexafluorophosphate.

[0026] According to the above scheme, in S3 and S5, the concentration temperature is 40 to 50°C and the pressure is -0.04 to -0.06 MPa.

[0027] According to the above scheme, in S3, the sodium hexafluorophosphate solution is concentrated to 28-33%; in S5, the sodium hexafluorophosphate solution is concentrated to 28-33%. This can avoid the precipitation of sodium hexafluorophosphate during the concentration process. If sodium hexafluorophosphate precipitates during the concentration process, it will be mixed with impurities and the crystal grains will be poor.

[0028] According to the above scheme, in S3 and S5, the amount of the organic solvent added after concentration is 3 to 5 times the amount of the sodium hexafluorophosphate concentrate, and the amount of the organic solvent added for washing is 2 to 3 times the amount of the sodium hexafluorophosphate concentrate.

[0029] According to the above scheme, in S6, the vacuum drying conditions of the wet sodium hexafluorophosphate product are: drying temperature: 85-95°C, drying time: 12-15h, and drying negative pressure: -0.085--0.090MPa.

[0030] According to the above scheme, in S6, during the vacuum drying process, phosphorus pentafluoride is first introduced periodically, and then nitrogen is introduced periodically.

[0031] According to the above scheme, in S6, the purity of the high-purity sodium hexafluorophosphate obtained is above 99.95%.

[0032] According to the above scheme, the metal impurity ions (including but not limited to Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, and As) in the above sodium hexafluorophosphate are reduced to below 5 ppm.

[0033] According to the above scheme, the recovered polar solvent generated by concentration in S3 is applied to the dissolution process of S2; the mixed solvent generated by filtration and washing in S3 is concentrated and separated to obtain a polar solvent and an organic solvent, the polar solvent is reused in the dissolution and filtration and washing processes of S2, and the organic solvent is reused in the concentration and crystallization process of S3; the recovered polar solvent generated by concentration in S5 is applied to the dissolution process of S2 or S4; the mixed solvent generated by filtration, washing and washing in S5 is concentrated and separated to obtain a polar solvent and an organic solvent, the polar solvent is reused in the dissolution process of S2 or S4, and the organic solvent is reused in the concentration and crystallization process of S3.

[0034] This proposal provides a method for preparing sodium hexafluorophosphate by a gas-solid method, and the obtained high-purity sodium hexafluorophosphate is used as an electrolyte in sodium ion batteries in new energy batteries.

[0035] The present invention has the following beneficial effects:

[0036] 1. The present invention adopts a gas-solid method for preparing sodium hexafluorophosphate for the first time, wherein phosphorus pentafluoride and sodium monofluorophosphate are used as raw materials to react to obtain sodium hexafluorophosphate. The impurities in the obtained product mainly include sodium phosphate, sodium monofluorophosphate, sodium difluorophosphate, etc., as well as various metal impurities. The impurities are complex and difficult to be purified to trace levels by conventional purification methods. The present invention adopts the synergistic effect of two different solvents, a polar solvent and an organic solvent. By dissolving the product with a polar solvent and the impurities with an organic solvent, and performing a two-way dissolution, washing and filtration of the product and impurities, the insoluble matter and metal ion impurities in the sodium hexafluorophosphate can be effectively removed, and the impurities in the electronic-grade target product can be removed to trace levels. The product has a high purity of over 99.95%, and the indicators meet the standards of electronic-grade products. It can be applied to industries such as new energy batteries and energy storage.

[0037] 2. Vacuum drying is used in the drying process of wet sodium hexafluorophosphate, and phosphorus pentafluoride gas protection and nitrogen purging are periodically used to displace and remove solvent residues to ensure the quality indicators of sodium hexafluorophosphate products.

[0038] 3. Furthermore, the filtrate, washing liquid and concentrated recovery liquid generated in the purification process of the present invention can be recycled, and precision filtration can effectively discharge the impurities enriched in the process out of the system, avoiding the enrichment of impurities caused by the recycling of the mother liquor; the present invention combines the purification process with solvent recovery and reuse, reduces the consumption of solvent, generates less "three wastes", is green and environmentally friendly, low in cost, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a flow chart of the gas-solid method for preparing sodium hexafluorophosphate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0041] The embodiment of the present invention provides a method for preparing sodium hexafluorophosphate by a gas-solid process, comprising the following steps:

[0042] S1: passing phosphorus pentafluoride gas into sodium monofluorophosphate solid to carry out gas-solid reaction to generate a solid mixture of sodium hexafluorophosphate and phosphate;

[0043] S2: adding a polar solvent to the solid mixture produced in S1 to fully dissolve it, filtering it, washing the resulting filter residue with a polar solvent, and combining the filtrate and the washing liquid to obtain a sodium hexafluorophosphate solution;

[0044] S3: The sodium hexafluorophosphate solution obtained in S2 is concentrated and then an organic solvent is added to crystallize the sodium hexafluorophosphate, which is filtered and the resulting filter residue is washed with an organic solvent to obtain a crude sodium hexafluorophosphate product. The filtrate and the washing solution are combined to obtain a mixed mother liquor 1;

[0045] S4: adding the crude sodium hexafluorophosphate obtained in S3 to a polar solution for dissolution, and filtering the dissolved crude sodium hexafluorophosphate solution through precise filtration to remove insoluble impurities to obtain a sodium hexafluorophosphate solution;

[0046] S5: concentrating the sodium hexafluorophosphate solution obtained in S4 and adding an organic solvent to crystallize the sodium hexafluorophosphate, filtering the resulting filter residue and washing it with an organic solvent to obtain a wet product of sodium hexafluorophosphate. Combining the filtrate and the washing solution to obtain a mixed mother liquor 2;

[0047] S6: vacuum drying the wet sodium hexafluorophosphate obtained in S5 to obtain a high-purity sodium hexafluorophosphate product, wherein phosphorus pentafluoride is first periodically introduced during the vacuum drying process, and then nitrogen is periodically introduced; wherein:

[0048] In steps S2 and S4, the polar solvent is one of dimethyl carbonate (DMC) and diethyl carbonate (DEC);

[0049] In steps S3 and S5, the organic solvent is benzene or toluene.

[0050] In one embodiment, in step S1, phosphorus pentafluoride gas is derived from the thermal decomposition and purification of hexafluorophosphate.

[0051] In one embodiment, in step S1, the gas-solid reaction temperature is 110-140° C., and the reaction time is 11-13 hours.

[0052] In one embodiment, in step S1, the molar ratio of sodium monofluorophosphate to phosphorus pentafluoride in the gas-solid reaction is 1:(1.15-1.25).

[0053] In one embodiment, in step S1, the gas-solid reactor is connected in two stages in series, and the material is selected from stainless steel, Hastelloy alloy or Monel alloy.

[0054] In one embodiment, in step S2, the amount of polar solvent added for dissolution is 3 to 5 times the amount of the solid mixture, and the amount of polar solvent added for washing is 0.5 to 1 times the amount of the solid mixture; in step S4, the amount of polar solvent added is 5 to 8 times the amount of crude sodium hexafluorophosphate.

[0055] In one embodiment, in steps S3 and S5, the concentration temperature is 40 to 50° C., and the pressure is -0.04 to -0.06 MPa.

[0056] In one embodiment, in step S3, the sodium hexafluorophosphate solution is concentrated to 28-33%; in step S5, the sodium hexafluorophosphate solution is concentrated to 28-33%.

[0057] In one embodiment, in steps S3 and S5, the amount of organic solvent added is 3 to 5 times the amount of the sodium hexafluorophosphate concentrate, and the amount of washing organic solvent added is 2 to 3 times the amount of the sodium hexafluorophosphate concentrate.

[0058] In one embodiment, in steps S3 to S5, the multi-stage purification can effectively reduce the metal impurity ions (including but not limited to Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, and As) in sodium hexafluorophosphate to below 5 ppm.

[0059] In one embodiment, in step S6, the drying temperature of the wet sodium hexafluorophosphate product is 85-95° C., the drying time is 12-15 h, and the drying negative pressure is -0.085-0.090 MPa; the drying method is to first periodically introduce phosphorus pentafluoride and then periodically introduce nitrogen during the vacuum drying process.

[0060] In one embodiment, in step S6, the purity of the obtained sodium hexafluorophosphate is above 99.95%.

[0061] In one embodiment, the recovered polar solvent generated by the concentration in step S3 is applied to the dissolution process of S2; the mixed solvent generated by filtration and washing in S3 is concentrated and separated to obtain a polar solvent and an organic solvent, the polar solvent is reused in the dissolution and filtration and washing process of S2, and the organic solvent is reused in the concentration and crystallization process of S3; the recovered polar solvent generated by the concentration in S5 is applied to the dissolution process of S2 or S4; the mixed solvent generated by filtration, washing and washing in S5 is concentrated and separated to obtain a polar solvent and an organic solvent, the polar solvent is reused in the dissolution process of S2 or S4, and the organic solvent is reused in the concentration and crystallization process of S3.

[0062] The following are specific examples.

[0063] Example 1:

[0064] A method for preparing sodium hexafluorophosphate by a gas-solid process is provided, comprising the following steps:

[0065] S1: Weigh 923.52g of sodium monofluorophosphate solid into 1# and 2# gas-solid reactors, mix them evenly, heat to 130°C, and rotate the gas-solid reactor at a rate of 4-5r / min. Pass 1000.00g of phosphorus pentafluoride produced by thermal decomposition and purification of hexafluorophosphate into the 1# gas-solid reactor through the axial side to react with the solid. The reaction time is 13h. Excess phosphorus pentafluoride gas continues to enter the 2# gas-solid reactor for reaction. The waste gas is absorbed by the tail gas and discharged in compliance with the emission standards.

[0066] S2: After cooling 1365.68 g of the solid mixture produced by the gas-solid reaction in S1, 5640.26 g of DEC solvent was added to fully dissolve the mixture. Filtering yielded 903.94 g of filter cake, which was washed with 723.15 g of DEC solvent. The washing liquid and the filtered mother liquor were mixed to obtain a sodium hexafluorophosphate solution.

[0067] S3: The sodium hexafluorophosphate solution obtained in S2 is concentrated at 50°C and -0.06 MPa to a sodium hexafluorophosphate concentration of approximately 30%. The resulting 4867.19 g of DEC is recovered as solvent and reused in the solid mixture dissolution step. 2470.27 g of benzene is added to the resulting 1964.76 g of sodium hexafluorophosphate concentrate and mixed thoroughly. Based on the solubility curve of sodium hexafluorophosphate in benzene, sodium hexafluorophosphate solid is precipitated. Filtering yields 615.63 g of sodium hexafluorophosphate solid and 3819.41 g of mixed solvent 1. The sodium hexafluorophosphate solid is washed with 1119.32 g of benzene to obtain crude sodium hexafluorophosphate. The washings and mixed solvent are mixed to obtain a mixed mother liquor 1. The polar solvent and organic solvent are recovered from the mixed mother liquor 1 and reused separately for dissolution in S2 and concentration in S3.

[0068] S4: The crude sodium hexafluorophosphate obtained in S3 was added to 3376.95 g of DEC solvent and dissolved and mixed evenly. After precise filtration to remove insoluble impurities, a sodium hexafluorophosphate solution was obtained.

[0069] S5: The sodium hexafluorophosphate solution obtained in S4 is concentrated at a temperature of 50° C. and a pressure of −0.06 MPa to a sodium hexafluorophosphate concentration of about 30%. The generated 2145.69 g of DEC solvent is reused in the dissolution step. 2316.48 g of fresh benzene is added to 1846.88 g of the sodium hexafluorophosphate concentrate and mixed thoroughly. According to the solubility curve of sodium hexafluorophosphate in benzene solvent, sodium hexafluorophosphate solid is precipitated. After filtration, 578.69 g of sodium hexafluorophosphate solid and 3584.67 g of mixed solvent 2 are obtained. The sodium hexafluorophosphate solid is washed with 1115.29 g of benzene to obtain a wet sodium hexafluorophosphate product. The washing liquid and the mixed solvent are mixed to obtain a mixed mother liquor 2. The mixed mother liquor 2 is used to recover the polar solvent and the organic solvent, and then reused in the dissolution in S4 and the concentration in S3.

[0070] S6: The wet sodium hexafluorophosphate obtained in S5 is vacuum dried at 90°C and -0.088MPa for 14 hours, wherein phosphorus pentafluoride is periodically introduced during the vacuum drying process, and then nitrogen is periodically introduced. Specifically, the process is as follows: phosphorus pentafluoride gas protection is used for the first 8 hours, phosphorus pentafluoride gas is periodically introduced for 10 minutes every 2 hours, and vacuum drying is performed for 1 hour and 50 minutes; nitrogen gas is periodically replaced for 6 hours, nitrogen gas is periodically introduced for 10 minutes every 1 hour, and vacuum drying is performed for 50 minutes. After drying, the product is cooled to room temperature to obtain 521.08g of sodium hexafluorophosphate product with a purity of 99.95%. The metal impurity ions (such as Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, As, etc.) in the sodium hexafluorophosphate can be reduced to below 5ppm.

[0071] Example 2:

[0072] A method for preparing sodium hexafluorophosphate by a gas-solid process is provided, comprising the following steps:

[0073] S1: Weigh 1847.04g of sodium monofluorophosphate solid into 1# and 2# gas-solid reactors, mix them evenly, heat to 130°C, and rotate the gas-solid reactor at a rate of 4-5r / min. Pass 2000.00g of phosphorus pentafluoride produced by thermal decomposition and purification of hexafluorophosphate into the 1# gas-solid reactor through the axial side to react with the solid. The reaction time is 13h. Excess phosphorus pentafluoride gas continues to enter the 2# gas-solid reactor for reaction. The waste gas is absorbed by the tail gas and discharged in compliance with the emission standards.

[0074] S2: After cooling 2714.24 g of the solid mixture produced by the gas-solid reaction in S1, 11508.39 g of DEC solvent was added to fully dissolve the mixture. Filtering yielded 1814.11 g of filter cake, which was washed with 1451.29 g of DEC solvent. The washing liquid and the filtered mother liquor were mixed to obtain a sodium hexafluorophosphate solution.

[0075] S3: The sodium hexafluorophosphate solution obtained in S2 is concentrated at 50°C and -0.06 MPa to a sodium hexafluorophosphate concentration of approximately 30%. The resulting 10019.69 g of DEC is recovered as solvent and reused in the solid mixture dissolution step. 4995.93 g of benzene is added to the resulting 3853.45 g of sodium hexafluorophosphate concentrate and mixed thoroughly. Based on the solubility curve of sodium hexafluorophosphate in benzene, sodium hexafluorophosphate solid is precipitated. Filtering yields 1207.41 g of sodium hexafluorophosphate solid and 7641.97 g of mixed solvent 1. The sodium hexafluorophosphate solid is washed with 2337.99 g of benzene to obtain crude sodium hexafluorophosphate. The washings and mixed solvent are mixed to obtain a mixed mother liquor 1. The polar solvent and organic solvent are recovered from the mixed mother liquor 1 and reused separately for dissolution in S2 and concentration in S3.

[0076] S4: The crude sodium hexafluorophosphate obtained in S3 was added to 6721.02 g of DEC solvent and dissolved and mixed evenly. After precise filtration to remove insoluble impurities, a sodium hexafluorophosphate solution was obtained.

[0077] S5: The sodium hexafluorophosphate solution obtained in S4 is concentrated at a temperature of 50° C. and a pressure of −0.06 MPa to a sodium hexafluorophosphate concentration of about 30%. The generated 4306.19 g of DEC solvent is reused in the dissolution step. 3622.24 g of the sodium hexafluorophosphate concentrate is added with 4630.65 g of fresh benzene and thoroughly mixed. According to the solubility curve of sodium hexafluorophosphate in benzene solvent, sodium hexafluorophosphate solid is precipitated. After filtration, 1134.97 g of sodium hexafluorophosphate solid and 7117.92 g of mixed solvent 2 are obtained. The sodium hexafluorophosphate solid is washed with 2208.03 g of benzene to obtain a wet sodium hexafluorophosphate product. The washing liquid and the mixed solvent are mixed to obtain a mixed mother liquor 2. The mixed mother liquor 2 is used to recover the polar solvent and the organic solvent, and then reused in the dissolution in S4 and the concentration in S3.

[0078] S6: The wet sodium hexafluorophosphate obtained in S5 is vacuum dried at 90°C and -0.088MPa for 14 hours, wherein phosphorus pentafluoride is periodically introduced during the vacuum drying process, and then nitrogen is periodically introduced. Specifically, the process is as follows: phosphorus pentafluoride gas protection is performed for the first 8 hours, phosphorus pentafluoride gas is periodically introduced for 10 minutes every 2 hours, and vacuum drying is performed for 1 hour and 50 minutes; nitrogen gas is periodically replaced for the next 6 hours, nitrogen gas is periodically introduced for 10 minutes every 1 hour, and vacuum drying is performed for 50 minutes. After drying, the product is cooled to room temperature to obtain 1021.98g of sodium hexafluorophosphate product with a purity of 99.95%. The metal impurity ions (such as Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, As, etc.) in the sodium hexafluorophosphate can be reduced to below 5ppm.

[0079] Example 3:

[0080] A method for preparing sodium hexafluorophosphate by a gas-solid process is provided, comprising the following steps:

[0081] S1: Weigh 4617.60g of sodium monofluorophosphate solid into 1# and 2# gas-solid reactors, mix them evenly, heat to 130℃, and rotate the gas-solid reactor at a rate of 4-5r / min. Pass 5000.00g of phosphorus pentafluoride produced by thermal decomposition and purification of hexafluorophosphate into the 1# gas-solid reactor through the axial side to react with the solid. The reaction time is 13h. Excess phosphorus pentafluoride gas continues to enter the 2# gas-solid reactor for reaction. The waste gas is absorbed by the tail gas and discharged in compliance with the emission standards.

[0082] S2: After cooling 6870.00 g of the solid mixture produced by the gas-solid reaction in S1, 27823.52 g of DEC solvent was added to fully dissolve the mixture. Filtering yielded 4504.55 g of filter cake, which was washed with 3603.64 g of DEC solvent. The washing liquid and the filtered mother liquor were mixed to obtain a sodium hexafluorophosphate solution.

[0083] S3: The sodium hexafluorophosphate solution obtained in S2 is concentrated at 50°C and -0.06 MPa to a sodium hexafluorophosphate concentration of approximately 30%. The resulting 23818.57 g of DEC is recovered as solvent and reused in the solid mixture dissolution step. 10008.66 g of the sodium hexafluorophosphate concentrate is added to 12221.64 g of benzene and thoroughly mixed. Based on the solubility curve of sodium hexafluorophosphate in benzene, sodium hexafluorophosphate solid is precipitated. Filtering yields 3136.05 g of sodium hexafluorophosphate solid and 19094.25 g of mixed solvent 1. The sodium hexafluorophosphate solid is washed with 5701.91 g of benzene to obtain crude sodium hexafluorophosphate. The washings and mixed solvent are mixed to obtain a mixed mother liquor 1. The polar solvent and organic solvent are recovered from the mixed mother liquor 1 and reused separately for dissolution in S2 and concentration in S3.

[0084] S4: The crude sodium hexafluorophosphate obtained in S3 is added to 17004.71 g of DEC solvent and dissolved and mixed evenly. After precise filtration to remove insoluble impurities, a sodium hexafluorophosphate solution is obtained.

[0085] S5: The sodium hexafluorophosphate solution obtained in S4 is concentrated at a temperature of 50° C. and a pressure of −0.06 MPa to a sodium hexafluorophosphate concentration of about 30%. The resulting 10,732.62 g of DEC solvent is reused in the dissolution step. 9,408.14 g of the sodium hexafluorophosphate concentrate is added with 11,516.70 g of fresh benzene and thoroughly mixed. According to the solubility curve of sodium hexafluorophosphate in benzene solvent, sodium hexafluorophosphate solid is precipitated. After filtration, 2,947.89 g of sodium hexafluorophosphate solid and 17,976.96 g of mixed solvent 2 are obtained. The sodium hexafluorophosphate solid is washed with 5,895.77 g of benzene to obtain a wet sodium hexafluorophosphate product. The washing liquid and the mixed solvent are mixed to obtain a mixed mother liquor 2. The mixed mother liquor 2 is used to recover the polar solvent and the organic solvent, and then reused in the dissolution in S4 and the concentration in S3.

[0086] S6: The wet sodium hexafluorophosphate obtained in S5 is vacuum dried at 90°C and -0.088MPa for 14 hours, wherein phosphorus pentafluoride is periodically introduced during the vacuum drying process, and then nitrogen is periodically introduced. Specifically, the process is as follows: phosphorus pentafluoride gas protection is used for the first 8 hours, phosphorus pentafluoride gas is periodically introduced for 10 minutes every 2 hours, and vacuum drying is performed for 1 hour and 50 minutes; nitrogen gas is periodically replaced for 6 hours, nitrogen gas is periodically introduced for 10 minutes every 1 hour, and vacuum drying is performed for 50 minutes. After drying, the product is cooled to room temperature to obtain 2654.16g of sodium hexafluorophosphate product with a purity of 99.96%. The metal impurity ions (such as Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, As, etc.) in the sodium hexafluorophosphate can be reduced to below 5ppm.

[0087] Comparative Example 1:

[0088] S1: Weigh 1385.28g of sodium monofluorophosphate solid into 1# and 2# gas-solid reactors, mix them evenly, heat to 130°C, and rotate the gas-solid reactor at a rate of 4-5r / min. Pass 1500.00g of phosphorus pentafluoride produced by thermal decomposition and purification of hexafluorophosphate into the 1# gas-solid reactor through the axial side to react with the solid. The reaction time is 13h. Excess phosphorus pentafluoride gas continues to enter the 2# gas-solid reactor for reaction. The waste gas is absorbed by the tail gas and discharged in compliance with the emission standards.

[0089] S2: After cooling, 2030.28g of solid mixture generated by gas-solid reaction was fully dissolved in 8324.15g of DEC solvent. After filtration, 1362.55g of filter cake was obtained, and 1090.04g of DEC solvent was added for washing. The washing liquid and the filtered mother liquor were mixed and evenly mixed, and concentrated to a sodium hexafluorophosphate concentration of about 30% under the temperature conditions of 50°C and the pressure conditions of -0.06MPa. The generated 8383.91g of DEC solvent was reused in the solid mixture dissolution process. 2866.09g of sodium hexafluorophosphate concentrate was added to 3543.01g of benzene and mixed evenly. According to the solubility curve of sodium hexafluorophosphate in benzene solvent, sodium hexafluorophosphate solid was precipitated. After filtration, 898.04g of sodium hexafluorophosphate solid and 5511.06g of mixed solvent were obtained. The sodium solid was washed with 1714.44g of benzene, and the washing liquid and mixed solvent were mixed and reused. The sodium hexafluorophosphate solid was vacuum dried at 90°C and -0.088MPa for 14 hours. Phosphorus pentafluoride and then nitrogen were periodically introduced during the vacuum drying process. Specifically, the vacuum drying process was performed under phosphorus pentafluoride gas protection for the first 8 hours, followed by periodic introduction of phosphorus pentafluoride gas for 10 minutes every 2 hours, and vacuum drying for 1 hour and 50 minutes. The vacuum was then periodically replaced with nitrogen for 6 hours, followed by periodic introduction of nitrogen gas for 10 minutes every 1 hour, and vacuum drying for 50 minutes. After drying, the solid was cooled to room temperature to obtain 762.80g of finished sodium hexafluorophosphate with a purity of 99.60%, which does not meet the quality standards for sodium battery applications.

[0090] Comparative Example 2:

[0091] S1: Weigh 2770.56g of sodium monofluorophosphate solid into 1# and 2# gas-solid reactors, mix them evenly, heat to 130°C, and rotate the gas-solid reactor at a rate of 4-5r / min. Pass 3000.00g of phosphorus pentafluoride produced by thermal decomposition and purification of hexafluorophosphate into the 1# gas-solid reactor through the axial side to react with the solid. The reaction time is 13h. Excess phosphorus pentafluoride gas continues to enter the 2# gas-solid reactor for reaction. The waste gas is absorbed by the tail gas and discharged in compliance with the emission standards.

[0092] S2: After cooling, the 4060.56 g solid mixture produced by the gas-solid reaction was fully dissolved in 16688.91 g of acetonitrile solvent. Filtering yielded a 2834.72 g filter cake, which was washed with 2267.78 g of acetonitrile solvent. The washings and filtered mother liquor were mixed and concentrated at 50°C and -0.06 MPa to a sodium hexafluorophosphate concentration of approximately 30%. The resulting 17068.48 g of acetonitrile solvent was reused in the solid mixture dissolution step.

[0093] S3: 5721.87 g of the obtained sodium hexafluorophosphate concentrate was added to 7073.26 g of dichloromethane and mixed thoroughly. According to the solubility curve of sodium hexafluorophosphate in dichloromethane solvent, sodium hexafluorophosphate solid was precipitated, and 1621.20 g of sodium hexafluorophosphate solid and 11173.93 g of mixed solvent 1 were obtained by filtration. The sodium hexafluorophosphate solid was washed with 2947.63 g of dichloromethane, and the washing liquid and the mixed solvent were mixed to obtain a mixed mother liquor 1. The mixed mother liquor 1 was used to recover the polar solvent and the organic solvent and then reused to dissolve in S2 and concentrate in S3.

[0094] S4: Add 8907.49 g of acetonitrile solvent to the obtained sodium hexafluorophosphate solid and dissolve and mix evenly. After filtering out insoluble impurities through precise filtration, a sodium hexafluorophosphate solution is obtained.

[0095] S5: The sodium hexafluorophosphate solution obtained in S4 is concentrated under a temperature condition of 50° C. and a pressure condition of −0.06 MPa to a sodium hexafluorophosphate concentration of about 30%. The generated 5665.10 g of acetonitrile solvent is reused in the dissolution step. 4863.59 g of the sodium hexafluorophosphate concentrate is added with 6012.27 g of fresh dichloromethane and mixed thoroughly to precipitate sodium hexafluorophosphate solid. After filtration, 1378.02 g of sodium hexafluorophosphate solid and 9497.84 g of mixed solvent 2 are obtained. The sodium hexafluorophosphate solid is washed with 2505.48 g of dichloromethane. The washing liquid and the mixed solvent are mixed and reused to obtain a mixed mother liquor 2. The polar solvent and the organic solvent are recovered from the mixed mother liquor 2 and reused separately for dissolution in S4 and concentration in S3.

[0096] S6: Sodium hexafluorophosphate solid was vacuum dried at 90°C and -0.088MPa for 14 hours, during which phosphorus pentafluoride was periodically introduced and then nitrogen was periodically introduced. Specifically, phosphorus pentafluoride gas was used for protection for the first 8 hours, phosphorus pentafluoride gas was periodically introduced for 10 minutes every 2 hours, and vacuum drying was performed for 1 hour and 50 minutes; nitrogen was periodically replaced for 6 hours, nitrogen was periodically introduced for 10 minutes every 1 hour, and vacuum drying was performed for 50 minutes. After drying, it was cooled to room temperature to obtain 1240.71g of sodium hexafluorophosphate product with a purity of 98.90%, which does not meet the quality indicators for sodium battery application.

[0097] The above is only a preferred embodiment of the present invention. It should be pointed out that for the technical requirements of this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing sodium hexafluorophosphate by a gas-solid process, characterized in that: The following steps are involved: S1: Passing phosphorus pentafluoride gas into sodium monofluorophosphate solid to carry out gas-solid reaction to generate a solid mixture of sodium hexafluorophosphate and phosphate; S2: adding a polar solvent to the solid mixture produced in S1 to fully dissolve it, filtering it, washing the obtained filter residue with a polar solvent, and combining the filtrate and the washing liquid to obtain a sodium hexafluorophosphate solution; S3: the sodium hexafluorophosphate solution obtained in S2 is concentrated and then an organic solvent is added to crystallize the sodium hexafluorophosphate, which is filtered and the filter residue is washed with an organic solvent to obtain a crude sodium hexafluorophosphate product, and the filtrate and the washing liquid are combined to obtain a mixed mother liquor 1; S4: adding the crude sodium hexafluorophosphate obtained in S3 into a polar solution for dissolution, and filtering the dissolved crude sodium hexafluorophosphate solution through precise filtration to remove insoluble impurities to obtain a sodium hexafluorophosphate solution; S5: concentrating the sodium hexafluorophosphate solution obtained in S4, adding an organic solvent, crystallizing the sodium hexafluorophosphate, filtering, washing the obtained filter residue with an organic solvent to obtain a wet product of sodium hexafluorophosphate, and combining the filtrate and the washing liquid to obtain a mixed mother liquor 2; S6: vacuum drying the wet sodium hexafluorophosphate obtained in S5 to obtain a high-purity sodium hexafluorophosphate product. During the vacuum drying process, phosphorus pentafluoride is first introduced periodically, and then nitrogen is introduced periodically; wherein: In S2 and S4, the polar solvent is one of dimethyl carbonate and diethyl carbonate; in S3 and S5, the organic solvent is one of benzene and toluene.

2. The method according to claim 1, characterized in that In S1, the gas-solid reaction temperature is 110-140° C., the reaction time is 11-13 h; and the molar ratio of sodium monofluorophosphate to phosphorus pentafluoride in the gas-solid reaction is 1:(1.15-1.25).

3. The method according to claim 1, characterized in that In S2, the amount of polar solvent added for dissolution is 3 to 5 times that of the solid mixture, and the amount of polar solvent added for washing is 0.5 to 1 times that of the solid mixture; in S4, the amount of polar solvent added is 5 to 8 times that of the crude sodium hexafluorophosphate.

4. The method according to claim 1, characterized in that: In the above-mentioned S3 and S5, the concentration temperature is 40 to 50°C, and the pressure is -0.04 to -0.06 MPa.

5. The method according to claim 1, characterized in that In the S3, the sodium hexafluorophosphate solution is concentrated to 28-33%; in the S5, the sodium hexafluorophosphate solution is concentrated to 28-33%.

6. The method according to claim 1, characterized in that In the above-mentioned S3 and S5, the amount of the organic solvent added after concentration is 3 to 5 times of the concentrated sodium hexafluorophosphate solution, and the amount of the organic solvent added for washing is 2 to 3 times of the concentrated sodium hexafluorophosphate solution.

7. The method according to claim 1, characterized in that In S6, the vacuum drying temperature of the wet sodium hexafluorophosphate product is 85 to 95° C., the drying time is 12 to 15 hours, and the drying negative pressure is -0.085 to -0.090 MPa.

8. The method according to claim 1, characterized in that: In the S6, the purity of the obtained high-purity sodium hexafluorophosphate is above 99.95%.

9. The method according to claim 1, characterized in that: The recovered polar solvent generated by concentration in S3 is applied to the dissolution process of S2; the mixed solvent generated by filtration and washing in S3 is concentrated and separated to obtain a polar solvent and an organic solvent, the polar solvent is reused in the dissolution and filtration and washing processes of S2, and the organic solvent is reused after the concentration and crystallization process of S3; the recovered polar solvent generated by concentration in S5 is applied to the dissolution process of S2 or S4; the mixed solvent generated by filtration, washing and washing in S5 is concentrated and separated to obtain a polar solvent and an organic solvent, the polar solvent is reused in the dissolution process of S2 or S4, and the organic solvent is reused after the concentration and crystallization process of S3.

10. Use of the high-purity sodium hexafluorophosphate prepared by the method for preparing sodium hexafluorophosphate by a gas-solid method according to any one of claims 1 to 9 as an electrolyte for sodium ion batteries in new energy batteries.

Images