A process for the preparation of phosphorus trifluoride

Abstract

The application provides a preparation method of phosphorus trifluoride, which comprises the following steps: (1) heating an organic fluorine salt in an oxygen-free environment, and then mixing a phosphorus source to obtain a mixed gas through a temperature control reaction; and (2) performing secondary condensation separation on the mixed gas obtained in the step (1) to obtain the phosphorus trifluoride. The preparation method provided by the application has a wide source of raw materials and low cost. By selecting a suitable fluorination reagent, the requirement for the material of the equipment is relatively low, the corrosiveness of the reaction process to the reaction equipment is small, and the phosphorus trifluoride product with high purity, stable quality, less impurities and less metal content can be obtained. The preparation method has an industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology and relates to a method for preparing fluorides, particularly a method for preparing phosphorus trifluoride. Background Technology

[0002] Phosphorus trifluoride is an inorganic compound with the chemical formula PF3. At room temperature and pressure, it is a colorless and odorless toxic gas; in its liquid state, it is a colorless and transparent liquid. It produces little smoke in air and is quite stable. When heated, it reacts with hydrogen to form PH3, and it reacts with water to form phosphorous acid and hydrogen fluoride. Furthermore, phosphorus trifluoride decomposes in alkalis and is soluble in ethanol.

[0003] Currently, there are few publicly disclosed production processes for phosphorus trifluoride. Chinese patent CN 101955173A discloses a technique for preparing phosphorus trifluoride by reacting phosphorus trichloride and zinc fluoride, and CN105776168A discloses a method for preparing hexafluorophosphate. Both of these patents employ a technique involving the reaction of phosphorus trichloride and zinc fluoride to prepare phosphorus trifluoride. These two methods easily form the byproduct phosphorus fluorochloride, making impurity removal difficult and resulting in low-purity phosphorus trifluoride.

[0004] Chinese patent CN 117228643A discloses a method for preparing electronic-grade phosphorus trifluoride. The method includes: first, adding phosphorus trichloride to a reactor under an inert atmosphere and heating it at 40–60°C for 20–50 minutes; then, slowly introducing anhydrous hydrogen fluoride from the bottom of the reactor to ensure sufficient contact and reaction, generating phosphorus trifluoride, which is then directly condensed and collected; finally, purification by distillation to obtain electronic-grade phosphorus trifluoride. This method suffers from drawbacks such as high equipment corrosion and low reaction conversion rate.

[0005] Chinese patent CN 117163925A discloses a method for preparing phosphorus trifluoride, which includes: reacting phosphorus with iodine, and then reacting the resulting phosphorus triiodide with a fluoride salt to prepare phosphorus trifluoride. This method involves many experimental steps and uses iodine reagents, resulting in high costs. Alternatively, a recycling step can be used to reduce the cost of iodine reagents, but this still adds processing steps and further increases the process cost.

[0006] Therefore, in view of the shortcomings of the existing technology, there is a need to provide a method for preparing phosphorus trifluoride that is simple in production process, has cheap and readily available raw materials, high reaction conversion rate, few gaseous by-products and low corrosivity to equipment, and can reduce production safety risks. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing phosphorus trifluoride. This method yields phosphorus trifluoride with high purity and high yield, while also having lower production costs and lower production safety risks, making it suitable for industrial-scale production of high-purity phosphorus trifluoride products. To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing phosphorus trifluoride, the method comprising the following steps:

[0009] (1) Heating an organic fluorine salt in an anaerobic environment, and then mixing it with a phosphorus source to carry out a temperature-controlled reaction to obtain a mixed gas;

[0010] (2) The mixed gas obtained in step (1) is subjected to secondary condensation separation to obtain the phosphorus trifluoride.

[0011] In this invention, a mixed gas with byproducts is obtained through a simple reaction of an organic fluoride salt and a phosphorus source. The byproducts are then separated by simple condensation, yielding high-purity, stable phosphorus trifluoride gas. The preparation method provided by this invention significantly reduces the pollution and production safety risks associated with cleaning the reaction vessel, which involves highly toxic trihalides, and effectively avoids contamination by metal elements.

[0012] It is worth noting that the preparation method described in this invention is carried out in a sealed, heatable reactor equipped with a stirring device and a condenser reflux device.

[0013] As a preferred technical solution of the present invention, the protective atmosphere used in the oxygen-free environment in step (1) includes nitrogen and / or inert gas.

[0014] Preferably, the inert gas includes any one or a combination of at least two of helium, neon, or argon. Typical but non-limiting combinations include: a combination of helium and neon, a combination of helium and argon, a combination of neon and argon, or a combination of helium, neon, and argon.

[0015] As a preferred technical solution of the present invention, the organic fluoride salt in step (1) includes triethylamine trihydrofluoride and / or triethylamine tetrahydrofluoride.

[0016] The reaction principle of the preparation method described in this invention is as follows: organic fluoride salts react with phosphorus trichloride to generate triethylamine hydrochloride and / or tetraamine hydrochloride, hydrogen chloride and phosphorus trifluoride; thus achieving the preparation of crude phosphorus trifluoride.

[0017] Preferably, the heating temperature in step (1) is 10 to 70°C, for example, it can be 10°C, 20°C, 30°C, 40°C, 50°C, 60°C or 70°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, step (1) further includes condensation reflux temperature control after heating.

[0019] Preferably, the temperature for condensation reflux control is 10 to 50°C, for example, it can be 10°C, 20°C, 30°C, 40°C or 50°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, the condensation reflux temperature control time is 10 to 20 minutes, for example, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes or 20 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] The condensation reflux temperature control process described in this invention is carried out after heating the organic fluorine salt and before the temperature-controlled reaction of the mixed phosphorus source.

[0022] In this invention, the purpose of heating the organofluorine salt is to control the temperature range of the reaction. Too low or too high a reaction temperature is not conducive to the reaction. If the heating temperature is too high, more raw materials will volatilize, the reaction will be incomplete and the conversion rate will be reduced. If the heating temperature is too low, the reaction rate will be reduced. In addition, the purpose of the condensation reflux temperature control is to reflux most of the organofluorine salt and phosphorus source, so that the two reactants can react fully.

[0023] As a preferred technical solution of the present invention, the phosphorus source in step (1) includes any one of phosphorus trichloride, phosphorus tribromide or phosphorus triiodide, preferably phosphorus trichloride.

[0024] Preferably, the purity of the phosphorus trichloride is greater than 99%, for example, it can be 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8% or 99.9%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] It is worth noting that compared to phosphorus tribromide and phosphorus triiodide, phosphorus trichloride has the advantages of being inexpensive and widely available, so phosphorus trichloride is the preferred choice as a reaction raw material.

[0026] Preferably, the mixing method in step (1) includes dropwise mixing.

[0027] Preferably, the dropping rate of the mixture is 0.3 to 0.8 g / min, for example, 0.3 g / min, 0.4 g / min, 0.5 g / min, 0.6 g / min, 0.7 g / min or 0.8 g / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] As a preferred technical solution of the present invention, the molar ratio of phosphorus in the phosphorus source in step (1) to fluorine in the organic fluoride salt is 1:3 to 3.5, for example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4 or 1:3.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] As a preferred technical solution of the present invention, the temperature-controlled reaction in step (1) includes an initiation reaction and a stabilization reaction carried out sequentially.

[0030] Preferably, the temperature for initiating the reaction is 120–160°C, for example, 120°C, 130°C, 140°C, 150°C or 160°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the time for initiating the reaction is 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the temperature of the stable reaction is 70 to 100°C, for example, 70°C, 80°C, 90°C or 100°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the stabilization reaction time is 2.2 to 2.8 hours, for example, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours or 2.8 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the phosphorus source used for the initiating reaction accounts for 18 to 22 wt% of the mass of the phosphorus source used for the temperature-controlled reaction. For example, it can be 18 wt%, 19 wt%, 20 wt%, 21 wt%, or 22 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] As a preferred embodiment of the present invention, the mixed gas includes phosphorus trifluoride, a phosphorus source, an organic fluoride salt, and impurity gases.

[0036] Preferably, the impurity gas includes hydrogen fluoride and / or hydrogen chloride.

[0037] As a preferred technical solution of the present invention, the secondary condensation separation in step (2) includes a first-stage condensation and a second-stage condensation performed sequentially.

[0038] Preferably, the temperature of the first stage of condensation is 10 to 40°C, for example, it can be 10°C, 20°C, 30°C or 40°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the first-stage condensation time is 3 to 4 hours, for example, it can be 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the temperature of the second-stage condensation is -20 to 0°C, for example, it can be -20°C, -16°C, -12°C, -8°C, -4°C or 0°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the second-stage condensation time is 3 to 4 hours, for example, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] As a preferred embodiment of the present invention, the first stage of condensation is used to condense and recover phosphorus sources and / or organic fluoride salts.

[0043] Preferably, the second stage of condensation is used to condense and recover impurity gases.

[0044] Furthermore, this invention separates and condenses the volatilized phosphorus trichloride and triethylamine trihydrofluoride through a first-stage condensation process, which can be returned to step (1) for direct use as raw materials; the second-stage condensation process separates and condenses any impurities such as hydrogen fluoride and hydrogen chloride that may be generated, with the remaining gas being crude phosphorus trifluoride. The generated triethylamine hydrochloride is dissolved in ethanol and then disposed of.

[0045] As a preferred embodiment of the present invention, the method for preparing phosphorus trifluoride provided by the present invention includes the following steps:

[0046] (1) Heating the organic fluoride salt to 10-70°C in an oxygen-free environment, condensing and refluxing to control the temperature to 10-50°C and holding for 10-20 min, and then adding a mixed phosphorus source dropwise at a rate of 0.3-0.8 g / min to carry out a temperature-controlled reaction to obtain a mixed gas;

[0047] The phosphorus in the phosphorus source has a molar ratio of phosphorus to fluorine in the organic fluoride salt of 1:3 to 3.5; the temperature-controlled reaction includes an initiation reaction and a stabilization reaction carried out sequentially; the initiation reaction is carried out at a temperature of 120 to 160°C for 20 to 40 minutes; the stabilization reaction is carried out at a temperature of 70 to 100°C for 2.2 to 2.8 hours.

[0048] (2) The mixed gas obtained in step (1) is subjected to first-stage condensation and second-stage condensation to obtain the phosphorus trifluoride;

[0049] The temperature of the first-stage condensation is 10–40℃, and the time is 3–4 hours; the temperature of the second-stage condensation is -20–0℃, and the time is 3–4 hours.

[0050] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The preparation method provided by the present invention has a simple reaction process, the generated by-products are easy to handle, and the continuous operation of the reaction device is guaranteed.

[0053] (2) The preparation method provided by the present invention greatly reduces the pollution and production safety risks of highly toxic trihalides caused by cleaning the reaction vessel, avoids the pollution of metal elements, and can obtain phosphorus trifluoride products with high purity and stable quality.

[0054] (3) The preparation method provided by the present invention has a high yield of phosphorus trichloride and has prospects for industrial application. Detailed Implementation

[0055] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0056] Example 1

[0057] This embodiment provides a method for preparing phosphorus trifluoride, the method comprising the following steps:

[0058] (1) 17.2 g of triethylamine trihydrofluoride was heated to 50 °C in a helium atmosphere, refluxed and controlled to 40 °C and held for 15 min, and then mixed phosphorus trichloride was added dropwise at a rate of 0.5 g / min to carry out the temperature-controlled reaction to obtain a mixed gas.

[0059] The molar ratio of phosphorus in the phosphorus source to fluorine in triethylamine trihydrofluoride is 1:3.2; the temperature-controlled reaction includes an initiation reaction and a stabilization reaction carried out sequentially; the amount of phosphorus trichloride added in the initiation reaction is 2.7 g, the temperature is 140 °C, and the time is 30 min; the amount of phosphorus trichloride added in the stabilization reaction is 11 g, the temperature is 85 °C, and the time is 2.5 h.

[0060] (2) The mixed gas obtained in step (1) is subjected to first-stage condensation and second-stage condensation to obtain the phosphorus trifluoride;

[0061] The first stage of condensation is at a temperature of 25°C for 3.5 hours; the second stage of condensation is at a temperature of -10°C for 3.5 hours.

[0062] Example 2

[0063] This embodiment provides a method for preparing phosphorus trifluoride, the method comprising the following steps:

[0064] (1) 16.1 g of triethylamine trihydrofluoride was heated to 70 °C under a nitrogen atmosphere, refluxed and controlled to 50 °C and held for 10 min. Then, a mixed phosphorus source was added dropwise at a rate of 0.8 g / min to carry out the temperature-controlled reaction and obtain a mixed gas.

[0065] The molar ratio of phosphorus in the phosphorus source to fluorine in triethylamine trihydrofluoride is 1:3; the temperature-controlled reaction includes an initiation reaction and a stabilization reaction carried out sequentially; the amount of phosphorus trichloride added in the initiation reaction is 2.7g, the temperature is 160℃, and the time is 20min; the amount of phosphorus trichloride added in the stabilization reaction is 11g, the temperature is 100℃, and the time is 2.2h.

[0066] (2) The mixed gas obtained in step (1) is subjected to first-stage condensation and second-stage condensation to obtain the phosphorus trifluoride;

[0067] The temperature of the first-stage condensation is 40℃ and the time is 3 hours; the temperature of the second-stage condensation is -20℃ and the time is 3 hours.

[0068] Example 3

[0069] This embodiment provides a method for preparing phosphorus trifluoride, the method comprising the following steps:

[0070] (1) 18.8 g of triethylamine trihydrofluoride was heated to 10 °C in a neon atmosphere, refluxed and kept at 10 °C for 20 min, and then mixed phosphorus source was added dropwise at a rate of 0.3 g / min to carry out temperature control reaction to obtain mixed gas;

[0071] The molar ratio of phosphorus in the phosphorus source to fluorine in triethylamine trihydrofluoride is 1:3.5; the temperature-controlled reaction includes an initiation reaction and a stabilization reaction carried out sequentially; the amount of phosphorus trichloride added in the initiation reaction is 2.7g, the temperature is 120℃, and the time is 40min; the amount of phosphorus trichloride added in the stabilization reaction is 11g, the temperature is 70℃, and the time is 2.8h.

[0072] (2) The mixed gas obtained in step (1) is subjected to first-stage condensation and second-stage condensation to obtain the phosphorus trifluoride;

[0073] The temperature of the first stage of condensation is 10℃ and the time is 4 hours; the temperature of the second stage of condensation is 0℃ and the time is 4 hours.

[0074] Example 4

[0075] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0076] In this embodiment, the temperature for initiating the reaction in step (1) is adjusted to 120°C, and the temperature for stabilizing the reaction is adjusted to 70°C.

[0077] Example 5

[0078] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0079] In this embodiment, the temperature for initiating the reaction in step (1) is adjusted to 110°C, and the temperature for stabilizing the reaction is adjusted to 60°C.

[0080] Example 6

[0081] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0082] In this embodiment, the temperature for initiating the reaction in step (1) is adjusted to 160°C, and the temperature for stabilizing the reaction is adjusted to 100°C.

[0083] Example 7

[0084] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0085] In this embodiment, the temperature for initiating the reaction in step (1) is adjusted to 170°C, and the temperature for stabilizing the reaction is adjusted to 110°C.

[0086] Example 8

[0087] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0088] In this embodiment, the molar ratio of phosphorus in the phosphorus source to fluorine in triethylamine trihydrofluoride is adjusted to 1:2.7, that is, the amount of triethylamine trihydrofluoride added is 14.5g.

[0089] Example 9

[0090] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0091] In this embodiment, the molar ratio of phosphorus in the phosphorus source to fluorine in triethylamine trihydrofluoride is adjusted to 1:3.9, that is, the amount of triethylamine trihydrofluoride added is 20.96g.

[0092] Example 10

[0093] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0094] In this embodiment, the temperature of the first-stage condenser in step (2) is adjusted to 50°C.

[0095] Example 11

[0096] This embodiment provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0097] In this embodiment, the temperature of the second-stage condensation in step (2) is adjusted to 5°C.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0100] The first-stage condensation process is omitted in this comparative example.

[0101] Comparative Example 2

[0102] This comparative example provides a method for preparing phosphorus trifluoride, the only difference between this method and Example 1 is that:

[0103] The second-stage condensation process is omitted in this comparative example.

[0104] Comparative Example 3

[0105] This comparative example provides a method for preparing phosphorus trifluoride, the method comprising:

[0106] (1) 13.7 g of phosphorus trichloride was heated to 50 °C under a helium atmosphere; then hydrogen fluoride was introduced to obtain the reaction product; the molar ratio of phosphorus in the phosphorus source to fluorine in the hydrogen fluoride was 1:3.2.

[0107] (2) The reaction product obtained in step (1) is subjected to first-stage condensation and second-stage condensation. The temperature of the first-stage condensation is 25℃ and the time is 3.5h; the temperature of the second-stage condensation is -10℃ and the time is 3.5h.

[0108] The phosphorus trifluoride provided in the above embodiments and comparative examples was weighed, and the purity and yield of the obtained phosphorus trifluoride are shown in Table 1. The purity was measured by gas chromatography, and the yield was calculated based on the phosphorus source.

[0109] Table 1

[0110]

[0111]

[0112] The following points can be observed from Table 1:

[0113] (1) Based on the comprehensive analysis of Examples 1-3, it can be seen that the phosphorus trifluoride obtained by the preparation method provided by the present invention has a purity of >92wt% and a yield of >76%.

[0114] (2) Comprehensive analysis of Examples 1 and Examples 4-7 shows that the temperature control reaction in step (1) of this invention will affect the purity and yield of the product phosphorus trifluoride. When the reaction temperature is too high, more raw materials will volatilize, the reaction will be insufficient and the conversion rate will be reduced. When the reaction temperature is too low, the reaction rate will be reduced, the reaction will be insufficient and the conversion rate will be reduced.

[0115] (3) Comprehensive analysis of Examples 1 and 10-11 and Comparative Examples 1-2 shows that the secondary condensation separation in step (2) will affect the purity and yield of the product phosphorus trifluoride.

[0116] Omitting the first stage of condensation will prevent the raw materials from being recycled and will affect the purity of the product; if the temperature of the first stage of condensation is too high, it will result in the loss of raw materials and affect the purity of the product.

[0117] Omitting the second-stage condensation will result in an increased impurity content in the crude phosphorus trifluoride product, affecting product purity; when the temperature of the second-stage condensation is too high, it will also result in an increased impurity content in the crude phosphorus trifluoride product, affecting product purity.

[0118] (4) Comprehensive analysis of Example 1 and Comparative Example 3 shows that, compared with hydrogen fluoride, triethylamine trihydrofluoride has the advantages of better reaction efficiency and higher purity when triethylamine trihydrofluoride is selected as the fluorine source.

[0119] In summary, the preparation method provided by this invention has a wide range of raw material sources and low cost; by selecting a suitable fluorinating reagent, the requirements for equipment materials are relatively low, the reaction process has little corrosiveness to the reaction equipment, and it can obtain phosphorus trifluoride products with high purity, stable quality, few impurities, and especially low metal content; this preparation method has promising prospects for industrial application.

[0120] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing phosphorus trifluoride, characterized in that, The preparation method includes the following steps: (1) Heating an organic fluoride salt in an anaerobic environment, followed by mixing with a phosphorus source and carrying out a temperature-controlled reaction to obtain a mixed gas; the organic fluoride salt is triethylamine trihydrofluoride and / or triethylamine tetrahydrofluoride; the heating temperature is 10~70℃; The phosphorus source is any one of phosphorus trichloride, phosphorus tribromide, or phosphorus triiodide; the mixing method is dropwise mixing. The molar ratio of phosphorus in the phosphorus source to fluorine in the organic fluoride salt is 1:3~3.5; The temperature-controlled reaction comprises an initiation reaction and a stabilization reaction performed sequentially; the temperature of the initiation reaction is 120~160℃; the time of the initiation reaction is 20~40 min; the temperature of the stabilization reaction is 70~100℃; the time of the stabilization reaction is 2.2~2.8 h; the phosphorus source used in the initiation reaction accounts for 18~22 wt% of the mass of the phosphorus source used in the temperature-controlled reaction. (2) The mixed gas obtained in step (1) is subjected to secondary condensation separation to obtain the phosphorus trifluoride.

2. The method for preparing phosphorus trifluoride according to claim 1, characterized in that, The protective atmosphere used in the oxygen-free environment described in step (1) includes nitrogen and / or inert gases.

3. The method for preparing phosphorus trifluoride according to claim 2, characterized in that, The inert gas includes any one or a combination of at least two of helium, neon, or argon.

4. The method for preparing phosphorus trifluoride according to claim 1, characterized in that, Step (1) includes condensation reflux temperature control after heating.

5. The method for preparing phosphorus trifluoride according to claim 4, characterized in that, The temperature for the condensation reflux temperature control is 10~50℃.

6. The method for preparing phosphorus trifluoride according to claim 4, characterized in that, The condensation reflux temperature control time is 10~20 minutes.

7. The method for preparing phosphorus trifluoride according to claim 1, characterized in that, The dropping rate of the mixture in step (1) is 0.3~0.8 g / min.

8. The method for preparing phosphorus trifluoride according to claim 1, characterized in that, The mixed gas in step (1) includes phosphorus trifluoride, phosphorus source, organic fluoride salt and impurity gas.

9. The method for preparing phosphorus trifluoride according to claim 8, characterized in that, The impurity gases include hydrogen fluoride and / or hydrogen chloride.

10. The method for preparing phosphorus trifluoride according to claim 1, characterized in that, The secondary condensation separation in step (2) includes a first-stage condensation and a second-stage condensation performed sequentially.

11. The method for preparing phosphorus trifluoride according to claim 10, characterized in that, The temperature of the first stage of condensation is 10~40℃.

12. The method for preparing phosphorus trifluoride according to claim 10, characterized in that, The first-stage condensation time is 3-4 hours.

13. The method for preparing phosphorus trifluoride according to claim 10, characterized in that, The temperature of the second-stage condenser is -20~0℃.

14. The method for preparing phosphorus trifluoride according to claim 10, characterized in that, The second-stage condensation time is 3-4 hours.

15. The method for preparing phosphorus trifluoride according to claim 10, characterized in that, The first stage of condensation is used to condense and recover phosphorus sources and / or organic fluoride salts.

16. The method for preparing phosphorus trifluoride according to claim 10, characterized in that, The second-stage condenser is used to condense and recover impurity gases.

17. The method for preparing phosphorus trifluoride according to claim 1, characterized in that, The preparation method includes the following steps: (1) Heating the organic fluoride salt to 10~70℃ in an oxygen-free environment, then refluxing and controlling the temperature to 10~50℃ and holding for 10~20min, and then adding the mixed phosphorus source dropwise at a rate of 0.3~0.8g / min to carry out the temperature-controlled reaction to obtain the mixed gas; The phosphorus in the phosphorus source has a molar ratio of phosphorus to fluorine in the organic fluoride salt of 1:3 to 3.5; the temperature-controlled reaction includes an initiation reaction and a stabilization reaction carried out sequentially; the initiation reaction is carried out at a temperature of 120 to 160°C for 20 to 40 minutes; the stabilization reaction is carried out at a temperature of 70 to 100°C for 2.2 to 2.8 hours. (2) The mixed gas obtained in step (1) is subjected to first-stage condensation and second-stage condensation to obtain the phosphorus trifluoride; The temperature of the first stage of condensation is 10~40℃ and the time is 3~4h; the temperature of the second stage of condensation is -20~0℃ and the time is 3~4h.

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