A method for preparing phosphorus pentafluoride and co-producing difluorochloromethane

Abstract

This invention discloses a method for preparing phosphorus pentafluoride and co-producing difluorochloromethane. The method includes the following steps: 1) vaporizing PCl and reacting it with CHF3 and Cl2 in a reaction tube equipped with a supported catalyst to undergo a fluorine-chlorine exchange reaction, yielding a mixed gas containing products such as PF5 and CHClF2; 2) fractionating the mixed gas in a distillation column, collecting the product PF5 and unreacted CHF3 mixture from the top of the condenser. This mixture is then directly reacted with a LiF carbonate solution to convert it into a high-value-added lithium hexafluorophosphate solution; another product, CHClF2, is collected from the body of the distillation column. This invention utilizes CHF3, a high-temperature-effect, long-life fluorine chemical byproduct, as a fluorine source and PCl3 as a phosphorus source. Through the fluorine-chlorine exchange reaction of CF3H, PCl3, and Cl2, it converts into high-value-added PF5 gas, which is further converted into LiPF6, while simultaneously co-producing CHClF2, thus realizing the resource utilization of fluorine and possessing significant economic and social benefits.

Description

Technical Field

[0001] This invention relates to a method for preparing phosphorus pentafluoride (PF5) and co-producing difluorochloromethane (CHClF2), specifically a method for producing high-value-added PF5 and co-producing CHClF2 by reacting phosphorus trichloride (PCl3), trifluoromethane (CHF3), and chlorine (Cl2) as raw materials in the presence of a catalyst. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is used because of the small atomic radius of fluorine, low electronegativity, and PF6. - With its appropriate radius, good ionic conductivity, and electrochemical stability, lithium hexafluorophosphate is currently the most widely used electrolyte salt in commercially available lithium-ion batteries. Over the past decade, the lithium battery industry has developed rapidly, driving the rapid growth of upstream industries and continuously increasing the demand for lithium hexafluorophosphate.

[0003] Phosphorus pentafluoride, with the molecular formula PF5 and a molecular weight of 126.0, has a melting point of -93.8°C and a boiling point of -84.6°C under standard conditions. It is a non-flammable, colorless, and toxic gas that is highly irritating to the skin, eyes, and mucous membranes. Currently, phosphorus pentafluoride is a key raw material for the production of lithium hexafluorophosphate. The main methods for synthesizing phosphorus pentafluoride include: 1) phosphorus halide method; 2) phosphorus pentoxide and phosphoric acid method; and 3) elemental phosphorus method.

[0004] 1) Phosphorus halide process

[0005] The phosphorus halide process is the most studied, technologically mature, and widely used process for preparing phosphorus pentafluoride, including the phosphorus pentachloride process (PCl5) and the phosphorus trichloride process (PCl3).

[0006] Chinese patents CN101570327 and CN102502565 report methods for manufacturing PF5 using PCl5 as raw material and anhydrous hydrogen fluoride as solvent. This method is currently the most widely used process in industrial plants, but it still has some shortcomings: for example, in addition to being highly hygroscopic, PCl5 is also easily hydrolyzed and reacts readily with moisture in the air to produce corrosive hydrogen chloride gas. As a result, the purity of PCl5 decreases, which may affect the purity of LiPF6.

[0007] Japanese Patent JP2017-047045 discloses a method for preparing PF5 using PCl3, Cl2, and HF as raw materials via a continuous process. This method involves mixing and reacting PCl3 and Cl2 with a significantly excess of anhydrous HF liquid to produce PF5. The latent heat of vaporization of HF is used to remove the heat of reaction generated during the formation of PF5.

[0008] Although the process for preparing PF5 using phosphorus halides and anhydrous HF as raw materials has been industrialized, and this method is widely used in the commercial production of PF5 in China, the reaction is strongly exothermic, requiring strict temperature control. Furthermore, the PF5 produced by this method is a mixture of HF and HCl, making purification extremely difficult.

[0009] 2) Phosphorus pentoxide process and phosphoric acid process

[0010] Chinese patent CN101570328 reports the preparation of the intermediate product hexafluorophosphoric acid (HPF6) using phosphorus pentoxide (P2O5) and anhydrous HF as raw materials. The intermediate product is then treated with fuming sulfuric acid, followed by heating to decompose it and produce phosphorus pentafluoride gas. The reaction equation is as follows:

[0011] P₂O₅ + 12HF → 2HPF₆ + 5H₂O

[0012] HPF6 + SO3 → PF5 + FSO3H

[0013] Chinese patent CN102502544 discloses a method for preparing phosphorus pentafluoride, using calcium fluoride (CaF2) instead of HF to generate phosphorus pentafluoride gas. US patent (application number: US2001041158A1) discloses a method for preparing phosphorus pentafluoride using polyphosphoric acid, anhydrous HF, and fuming sulfuric acid. The final product is a mixture of PF5, POF3, and HF; obtaining high-purity PF5 remains quite difficult.

[0014] This type of method involves anhydrous HF and fuming sulfuric acid, and water is generated during the process, resulting in aqueous acid. In addition, the reaction temperature of this process is above 100°C, which makes the materials extremely corrosive to the equipment. Even with equipment lined with fluoroplastics, there are still problems with the sealing, heat transfer, and heat resistance of the equipment, resulting in short equipment life and high equipment investment.

[0015] 3) Elemental phosphorus method

[0016] Japanese patent document JP2001-122605 discloses a process for preparing phosphorus pentafluoride by reacting a mixture of metal fluoride powder and red phosphorus with fluorine gas (F2). The reaction formula is: 2P + 5F2 → 2PF5. The preferred metal fluorides are NaF, CaF2, and FeF3, with a product selectivity >99% and purity close to 100%. The advantages of this method are extremely high product selectivity and purity, and low water content; the disadvantages are the need for expensive F2, high requirements for reaction equipment materials and production safety measures. Furthermore, because it is a gas-solid reaction, temperature control is difficult, making industrialization very challenging.

[0017] Therefore, a better method for the preparation of PF5 is needed. This invention, through in-depth research, selects inexpensive and stable PCl3 as the phosphorus source and strong greenhouse gas CF3H (GMP) as the phosphorus source. 100 Using 14800 ppm as the fluorine source and Cl2 as the oxidant / chlorinating agent, the three undergo a fluorine-chlorine exchange reaction in the presence of a supported catalyst to obtain high-value-added PF5 and CF2ClH, realizing the resource utilization of fluorine resources. The phosphorus pentafluoride prepared by this invention is free of impurities such as POF3 and HCl, and features low cost and high purity. It can be directly used in the synthesis of LiPF6, demonstrating significant economic and social benefits. Summary of the Invention

[0018] The purpose of this invention is to provide a method for preparing PF5 and co-producing CHClF2 using PCl3, CHF3 and Cl2 as raw materials, in order to address the shortcomings of existing technologies.

[0019] The following reactions occur in a reaction system using PCl3, CHF3, and Cl2 as raw materials, with the target reaction as follows:

[0020] PCl3 + 5CHF3 + Cl2 → PF5 + 5CHClF2

[0021] The following side reactions may also occur:

[0022] CHF3 + Cl2 → CCl2F2 + HF

[0023] CHF3 + Cl2 → CClF3 + HCl

[0024] To reduce the occurrence of side reactions and improve the conversion rate of raw materials and the selectivity of target products, this invention achieves this through the following technical solution:

[0025] A method for preparing phosphorus pentafluoride and co-producing difluorochloromethane, characterized by comprising the following steps:

[0026] Step 1) After vaporization, PCl3 is reacted with CHF3 and Cl2 in a reaction tube containing a supported catalyst to carry out a fluorine-chlorine exchange reaction, resulting in a mixed gas containing PF5 and CHClF2.

[0027] Step 2) The mixed gas generated in the above steps is fed into a distillation column for fractionation. The light component product PF5 and the unreacted CHF3 mixture are collected from the top of the distillation column; another product, difluorochloromethane (CHClF2), is collected from the body of the distillation column. The unreacted PCl3 is collected in the bottom of the column and can be recycled.

[0028] The light component product PF5 and unreacted CHF3 mixed gas collected from the top of the distillation column can be directly reacted with LiF carbonate solutions to obtain LiPF6 solution.

[0029] In step 1), PCl3 is first vaporized in a vaporizer and then enters the reactor. The temperature range of the vaporizer is between 100°C and 300°C.

[0030] Preferably, the temperature range of the vaporizer is between 150°C and 250°C. In the catalytic system provided by this invention, the ratio of the support, active component, and auxiliary agent is sufficient to enable it to promote the breaking of the CF bond and the chloro-fluorine exchange reaction in trifluoromethane.

[0031] An active component is added to the supported catalyst. As a preferred embodiment, the mass ratio of the support, active component, and auxiliary agent is 100:(1-20):(0.1-5). More preferably, the mass ratio of the catalyst support, active component, and auxiliary agent is 100:(3-10):(0.5-2). In step 1), the active component of the supported catalyst is one, two, or a combination of three or more of the oxides, chlorides, fluorides, nitrates, or sulfates of Cr, Sb, Ru, Ti, Fe, Mg, and Al. Chlorides, nitrates, or sulfates of Cr, Sb, Ru, and Fe are preferred.

[0032] In step 1), the promoter for the supported catalyst is an oxide, chloride, sulfate, or nitrate of La, Sm, Bi, Ce, Zr, V, or Zn. Preferably, the promoter is an oxide, chloride, or nitrate of La, Sm, Bi, or Zr.

[0033] As a further preferred option, the catalyst supporter is La2O3, Sm2O3, Bi2O3 and ZrCl4.

[0034] In step 1), the support for the catalyst is Al2O3 or AlF3.

[0035] In step 1), to avoid the generation of the byproduct HCl, the molar ratio of PCl3, CHF3, and Cl2 is also an important factor affecting the product composition. Controlling the Cl2 feed ratio can effectively suppress the generation of HCl. Therefore, the molar ratio of PCl3, CF3H, and Cl2 is (1:1:0.1) to (1:15:1).

[0036] Preferably, the molar ratio of PCl3, CF3H and Cl2 is (1:5:0.5) to (1:10:0.8).

[0037] In step 1), the reaction temperature is 200–400°C.

[0038] Preferably, the reaction temperature is 250–300°C.

[0039] In step 1), the contact time between the PCl3, CF3H and Cl2 mixture and the chlorofluorination catalyst is 1.5s to 15s.

[0040] Preferably, the residence time of the PCl3, CF3H and Cl2 mixture with the chlorofluorination catalyst is 3s to 10s.

[0041] In step 2), in order to collect the mixture of PF5 and unreacted CF3H from the top of the distillation column and collect another product CF2ClH in the column body, the temperature of the distillation column condenser is controlled at (-20 to -50°C) and the pressure at the top of the column is controlled at (0.5MPa to 2.0MPa).

[0042] Preferably, the temperature of the distillation column condenser is controlled at (-30 to -40℃), and the pressure at the top of the column is controlled at (0.8MPa to 1.0MPa).

[0043] In step 2), the PF5 obtained by distillation and the unreacted CF3H mixed gas are passed into a LiF carbonate solution to obtain a LiPF6 solution. The solvent can be one of dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (EMC).

[0044] Compared with the prior art, the technical features and beneficial effects of the present invention are as follows:

[0045] (1) Using CHF3, a strong greenhouse gas, as a fluorine source and PCl3 as a phosphorus source, in the presence of Cl2, the fluorine-chlorine exchange reaction is transformed into PF5 gas with high added value, while simultaneously producing difluorochloromethane (CHClF2), realizing the resource utilization of fluorine element, which has important economic and social benefits.

[0046] (2) Compared with other PF5 preparation methods, this invention effectively promotes the fluorine-chlorine exchange reaction of PCl3, CHF3 and Cl2 by introducing a chlorofluorination supported catalyst. The PF5 gas and a small amount of unreacted CHF3 mixture obtained are almost free of HF, HCl and POF3 impurities, and can be directly used for the preparation of LiPF6 carbonate solutions without the need for crystallization and purification, which has a significant cost advantage.

[0047] (3) The present invention can not only achieve the aforementioned technical effects by using a tubular reaction device and a distillation separation tower in series, but also directly prepare LiPF6, realize continuous production, improve efficiency, and have industrialization value. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the process for preparing phosphorus pentafluoride (PF5) and co-producing difluorochloromethane (CF2ClH) according to an embodiment of the present invention. The above figure includes the following reference numerals:

[0049] P-1: PCl3 storage tank; P-2: Cl2 storage tank; P-3: CF3H storage tank; P-4: PCl3 vaporizer; P-5: reaction product buffer tank; P-6: distillation column; P-7: PF5 buffer tank; P-8: CHClF2 collection tank; R-1: reactor; E-1: PCl3 transfer pump; E-2: compressor.

[0050] Figure 2 The image shows the phosphorus NMR spectrum of the synthesized LiPF6 solution. Detailed Implementation

[0051] The technical solution and its effects of the present invention will be further described below through specific embodiments. The following embodiments are for illustrative purposes only, and the invention is not limited to the described embodiments or examples. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0052] I. Catalyst Preparation

[0053] Example 1: Catalyst Preparation

[0054] The main catalyst was prepared by impregnation method: First, Al2O3 was calcined at 800℃ and 1000℃ for 4h respectively and then ground into powder for later use; then, 10mL of Cr(NO3)3 solution with a Cr mass fraction of 3% was added to 15g of the above-mentioned high-temperature calcined Al2O3 powder, and impregnated at 50℃ for 6h. After filtration, the filter cake was dried in an oven at 120℃ for 12h. Finally, the powder was calcined at 200℃ under a nitrogen atmosphere for 4h to obtain the catalyst parent material.

[0055] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the Sm2O3 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0056] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0057] Example 2: Catalyst Preparation

[0058] The main catalyst was prepared by impregnation method: First, Al2O3 was calcined at 800℃ and 1000℃ for 4h respectively and then ground into powder for later use; then, 10mL of hydrochloric acid solution of SbCl3 with a mass fraction of 3% was added to 15g of the above-mentioned high-temperature calcined Al2O3 powder, and impregnated at 50℃ for 6h. After filtration, the filter cake was dried in an oven at 120℃ for 12h. Finally, the powder was calcined at 200℃ under a nitrogen atmosphere for 4h to obtain the catalyst parent material.

[0059] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the Sm2O3 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0060] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0061] Example 3: Catalyst Preparation

[0062] The main catalyst was prepared by impregnation method: First, AlF3 was calcined at 600℃ and 800℃ for 4h respectively and then ground into powder for later use; then 10mL of a methanol solution of RuCl3 with a Ru mass fraction of 3% was added to 15g of the above-mentioned high-temperature calcined AlF3 powder, and impregnated at 50℃ for 6h, then dried in an oven at 120℃ for 12h, and finally calcined at 200℃ under a nitrogen atmosphere for 4h to obtain the catalyst parent material.

[0063] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the Sm2O3 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0064] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0065] Example 4: Catalyst Preparation

[0066] The main catalyst was prepared by impregnation method: First, AlF3 was calcined at 600℃ and 800℃ for 4h respectively and then ground into powder for later use; then 10mL of FeCl3 aqueous solution with Fe mass fraction of 3% was added to 15g of the above-mentioned high-temperature calcined AlF3 powder, impregnated at 50℃ for 6h, then dried in an oven at 120℃ for 12h, and finally calcined at 200℃ under nitrogen atmosphere for 4h to obtain the catalyst parent material.

[0067] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the catalyst matrix with the auxiliary agent through physical grinding, and finally compress it into tablets at 20 MPa and then crush it to 10-20 mesh for later use.

[0068] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0069] Example 5: Catalyst Preparation

[0070] The main catalyst was prepared by impregnation method: First, AlF3 was calcined at 600℃ and 800℃ for 4h respectively and then ground into powder for later use; then 10mL of CoCl2 aqueous solution with a Co mass fraction of 3% was added to 15g of the above-mentioned high-temperature calcined AlF3 powder, impregnated at 50℃ for 6h, then dried in an oven at 120℃ for 12h, and finally calcined at 200℃ under nitrogen atmosphere for 4h to obtain the catalyst parent material.

[0071] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the catalyst matrix with the auxiliary agent through physical grinding, and finally compress it into tablets at 20 MPa and then crush it to 10-20 mesh for later use.

[0072] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0073] Comparative Example 1: Catalyst Preparation

[0074] The catalyst precursor was prepared in the same manner as in Example 1.

[0075] Add 5 wt% La2O3 to the catalyst matrix as an auxiliary component, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the catalyst matrix with the auxiliary component through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0076] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0077] Comparative Example 2: Catalyst Preparation

[0078] The catalyst precursor was prepared in the same manner as in Example 1.

[0079] Add 5 wt% Bi₂O₃ as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the catalyst matrix mass. Mix the catalyst matrix with the auxiliary agent through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0080] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0081] Comparative Example 3: Catalyst Preparation

[0082] The catalyst precursor was prepared in the same manner as in Example 1.

[0083] Add 5 wt% ZrCl4 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the ZrCl4 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0084] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0085] Comparative Example 4: Catalyst Preparation

[0086] The main catalyst was prepared by impregnation method: First, Al2O3 was calcined at 800℃ and 1000℃ for 4h and then ground into powder for later use; then 20mL of Cr(NO3)3 solution with a mass fraction of 3% and 10mL of methanol solution of RuCl3 with a mass fraction of 3% were added to 15g of the above-mentioned high-temperature calcined Al2O3 powder, impregnated at 50℃ for 6h, and then dried in an oven at 120℃ for 12h. Finally, the powder was calcined at 200℃ under a nitrogen atmosphere for 4h to obtain the catalyst parent material.

[0087] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the Sm2O3 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0088] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0089] Comparative Example 5: Catalyst Preparation

[0090] The catalyst matrix was prepared in the same manner as in Example 1. No additives were added to the catalyst matrix, which was directly pressed into tablets at 20 MPa and then crushed to 10-20 mesh for later use.

[0091] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0092] Comparative Example 6: Catalyst Preparation

[0093] The catalyst precursor was prepared using the same method as in Example 1. The difference was that no active components were added to the precursor.

[0094] Add 5 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount based on 100% of the mass of the catalyst matrix. Mix the Sm2O3 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0095] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0096] Comparative Example 7: Catalyst Preparation

[0097] The catalyst precursor was prepared using the same method as in Example 1. The difference was that 1 mL of a 3% Cr(NO3)3 solution was added to 15 g of the above-mentioned high-temperature calcined Al2O3 powder.

[0098] Add 0.01 wt% Sm2O3 as an auxiliary agent to the catalyst matrix, with the addition amount being 100% of the mass of the catalyst matrix. Mix the Sm2O3 with the catalyst matrix through physical grinding, then compress it into tablets at 20 MPa, and finally crush it to 10-20 mesh for later use.

[0099] The supported catalyst is pretreated with fluorination before use. The specific pretreatment method is as follows: the supported catalyst is placed in the catalyst reaction tube, and a HF-N2 mixed gas with a molar ratio of 5:2 is introduced and fluorinated at 250-300°C for 180 minutes.

[0100] II. Preparation and purification of phosphorus pentafluoride and difluorochloromethane

[0101] Example 6

[0102] Step 1): Liquid PCl3 is vaporized in a vaporizer (P-4) and then fed into a reaction tube (R-1) containing the chlorofluorination catalyst prepared in Example 1, while CHF3 and Cl2 are added simultaneously. The temperature of the PCl3 vaporizer is 200°C, the temperature of the reaction tube is 300°C, the residence time is 6.3 s, and the feed molar ratio of PCl3, CF3H, and Cl2 is 1:8:1.

[0103] Step 2): The reaction gas obtained in Step 1) is fed into a buffer tank (P-5), compressed, and then fed into a distillation column (P-6) for separation. A mixture of PF5 and unreacted CHF3 is collected from the top of the column and fed into a buffer tank (P-7). Liquid CHClF2 is collected from the column body. The distillation column bottom temperature is 30℃, the top pressure is 0.6MPa, and the condenser temperature is -35℃.

[0104] Example 7

[0105] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Example 2 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0106] Example 8

[0107] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Example 3 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0108] Example 9

[0109] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Example 4 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0110] Example 10

[0111] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Example 5 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0112] Example 11

[0113] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 1 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0114] Example 12

[0115] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 2 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0116] Example 13

[0117] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 3 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0118] Example 14

[0119] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 4 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0120] Example 15

[0121] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 5 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0122] Example 16

[0123] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 6 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0124] Example 17

[0125] The method of Example 6 was followed, except that the chlorofluorination catalyst prepared in Comparative Example 7 was used instead of the chlorofluorination catalyst prepared in Example 1.

[0126] Example 18

[0127] The method is the same as in Example 6, except that the reaction temperature is 250°C.

[0128] Example 19

[0129] The method is the same as in Example 6, except that the molar ratio of PCl3, CF3H, and Cl2 is 1:10:1.

[0130] Results analysis:

[0131] The results of gaseous component sampling and analysis in buffer tank (P-5) during Examples 6-19 are shown in the table below:

[0132] Example <![CDATA[PF5(%)]]> <![CDATA[CHF3(%)]]> <![CDATA[CClF3(%)]]> <![CDATA[CHClF2(%)]]> <![CDATA[CFCl2H(%)]]> other 6 5.4 52.8 2.9 26.8 10.1 2.0 7 8.3 40.8 1.1 42.3 6 1.5 8 9.8 35.4 1.3 47.2 4.5 1.8 9 4.3 67.3 0.7 20.2 3.3 4.2 10 0.3 78.9 3.7 10.8 4.0 2.3 11 6.4 46.5 3.4 35.3 7.3 1.1 12 7.2 35.6 0.8 51.1 3.3 2.0 13 5.3 58.5 2.1 27.7 4.3 2.1 14 8.8 32.1 3.6 38.6 15.1 1.8 15 3.5 65.9 3.3 18.8 6.5 2.0 16 0 93.5 0.2 4.4 0.3 1.6 17 0.7 75.0 2.4 14.5 6.5 0.9 18 4.1 69.6 0.3 23.7 1.6 0.7 19 8.2 50.5 1.1 32.9 5.8 1.5

[0133] From Examples 6-19 in the table above, it can be seen that, except for #16, the raw materials PCl3, CHF3, and Cl2 can be converted into PF5 and CHClF2, and the reaction effect is good within the scope of the claims. In Example 14, the PF5 content in the reaction gas was 8.8%, theoretically 11.1%, and the yield was 79.3% (area normalization method). The active component in the catalyst is the key factor for reaction efficiency. Without the addition of the active component (Example 16), the chlorofluoride exchange reaction of CHF3 can hardly be promoted, no PF5 is produced, and the CHClF2 content is only 4.4%. After fractionation in a distillation vessel, the top gas of the distillation column is directly used for the synthesis of LiPF6 (Example 20).

[0134] III. Preparation of Dimethyl Carbonate Solution of LiPF6

[0135] Example 20

[0136] In Implementation 6, the mixed gas of PF5 and unreacted CHF3 collected from the top of the column was fed into a buffer tank (P-7) and then into a pre-prepared dimethyl carbonate (DMC) solution of LiF to obtain a dimethyl carbonate solution of LiPF6. Unreacted CF3H was discharged from the gas phase pipe of the reactor and recycled. The reaction temperature was 20℃, and the mass concentration of the LiF dimethyl carbonate solution was 10%. Samples of the LiPF6 dimethyl carbonate solution were taken for moisture, acidity, and NMR analysis. The results are shown in the table below.

[0137] Testing items Value / ppm Moisture 15.8 acidity 2.0

[0138] The NMR phosphorus spectrum analysis of the obtained LiPF6 solution is as follows: Figure 2 As shown.

Claims

1. A method for preparing phosphorus pentafluoride and co-producing difluorochloromethane, characterized in that... Includes the following steps: Step 1) After vaporization, PCl3 is reacted with CHF3 and Cl2 in a reaction tube containing a supported catalyst to carry out a fluorine-chlorine exchange reaction, resulting in a mixed gas containing PF5 and CHClF2. The supported catalyst comprises a support, an active component, and an auxiliary agent, with a mass ratio of 100:(1-20):(0.1-5); the active component of the supported catalyst is one, two, or three or more of the following: chlorides, fluorides, nitrates, or sulfates of Cr, Sb, Ru, and Fe; the auxiliary agent of the supported catalyst is one, two, or three or more of the following: oxides, chlorides, sulfates, or nitrates of La, Sm, Bi, and Zr; the support of the supported catalyst is alumina or aluminum fluoride. Step 2) The mixed gas generated in the above steps is fed into a distillation column for fractionation. The light component product PF5 and the unreacted CHF3 mixture are collected from the top of the distillation column; another product, difluorochloromethane (CHClF2), is collected from the body of the distillation column, and the unreacted PCl3 is collected in the bottom of the column.

2. The method according to claim 1, characterized in that... The molar ratio of PCl3, CHF3 and Cl2 is (1:1:0.1) to (1:15:1).

3. The method according to claim 1, characterized in that... The reaction temperature in step 1) is 200–400℃; the contact time between the PCl3, CHF3 and Cl2 mixture and the chlorofluorination catalyst is 1.5 s–15 s.

4. The method according to claim 1, characterized in that... In step 2), the temperature of the distillation column condenser is controlled at -20 to -50°C, and the pressure at the top of the column is controlled at 0.5 MPa to 2.0 MPa.

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