Method for preparing phosphorus pentafluoride by taking phosphorus trioxide as raw material

Abstract

The invention belongs to the technical field of chemical material preparation, and discloses a method for preparing phosphorus pentafluoride by taking phosphorus trioxide as a raw material, and the method comprises the following steps: step 1, spraying phosphorus trioxide in a gaseous form into a first tubular reactor and reacting with oxygen in the first tubular reactor, by controlling the ratio of phosphorus trioxide to oxygen, part of phosphorus trioxide is converted into phosphorus pentoxide, and the reaction product is a mixture of phosphorus trioxide and phosphorus pentoxide; 2, the mixture and fluorine gas are introduced into a second tubular reactor, so that phosphorus pentoxide and part of unreacted phosphorus trioxide react with fluorine gas to generate phosphorus pentafluoride. The preparation process disclosed by the invention completely overcomes the defects that the traditional process is violent in reaction and cannot realize industrial mass production, and has the advantages of mild reaction and capability of realizing mass production.

Description

Technical Field

[0001] The invention relates to the technical field of chemical material preparation, and in particular to a method for preparing phosphorus pentafluoride by using phosphorus trioxide as a raw material. Background Art

[0002] Phosphorus pentafluoride (PF 5 ) is an important inorganic compound, widely used in the electronics industry, organic synthesis, lithium battery electrolytes and other fields.

[0003] In the prior art, the synthesis of phosphorus pentafluoride can be roughly divided into a direct method and an indirect method. The indirect method is: synthesizing hexafluorophosphoric acid through various pathways, and then obtaining phosphorus pentafluoride by thermal decomposition of hexafluorophosphoric acid. For example, the patent application with publication number CN117361458A, which is a subject of a continuous production method of phosphorus pentafluoride, first generates hexafluorophosphoric acid by reacting phosphorus pentoxide and HF, and then dehydrates to form phosphorus pentoxide.

[0004] The direct method can be divided into the following according to the source of phosphorus: direct synthesis of phosphorus pentafluoride from elemental phosphorus, direct synthesis of phosphorus pentafluoride from phosphorus pentachloride, and direct synthesis of phosphorus pentafluoride from phosphoric acid. For details, please refer to the following information: Direct synthesis of phosphorus pentafluoride from elemental phosphorus: Patent application with publication number CN109052350A, which is about a continuous production method of phosphorus pentafluoride, and patent application with publication number CN102372264A, which is about a method for purifying phosphorus pentafluoride, and patent application with publication number CN102421702A, which is about a method for manufacturing phosphorus pentafluoride and a reactor design, both disclose the use of white phosphorus, red phosphorus or yellow phosphorus as a phosphorus source to react with fluorine gas to prepare phosphorus pentafluoride; Among them, CN109052350A describes that the reaction between fluorine and phosphorus is violent and will release a large amount of heat. In the previous experiments of the applicant, it was also found that the reaction is a violent exothermic reaction and needs to be carried out in a specific safety reactor.

[0005] At the same time, in the prior art, the reactions of phosphorus and fluorine gases are all carried out under conditions of relatively low concentrations, the purpose of which is to effectively control heat dissipation and avoid excessive heat accumulation.

[0006] Methods such as direct synthesis of phosphorus pentafluoride from phosphorus pentachloride and direct synthesis of phosphorus pentafluoride from phosphoric acid all involve reacting with fluoride to obtain phosphorus pentafluoride through fluorine replacement.

[0007] From the above analysis, it can be seen that in the art, a method for preparing phosphorus pentafluoride by direct reaction of phosphorus oxide and fluorine gas has not yet been reported.

[0008] The reason is that the melting point of white phosphorus (yellow phosphorus) is 44°C, and the melting point of red phosphorus is 590°C; therefore, in the prior art, white phosphorus is liquefied and then sprayed and reacted with fluorine gas to form a gas-liquid mixed system, and the reaction is very easy to start.

[0009] However, the melting point of phosphorus pentoxide is as high as 340°C. If phosphorus pentoxide and fluorine gas are simply mixed, it will be difficult to react due to the difficulty of solid-gas reaction.

[0010] Although phosphorus trioxide has a low melting point, it has high chemical energy, and its direct reaction with fluorine gas is still violent and difficult to control.

[0011] Therefore, it is inherently difficult to directly prepare phosphorus pentafluoride using fluorine gas. There is an irreconcilable contradiction between reaction controllability, mildness and industrial mass production. Summary of the invention

[0012] The object of the present invention is to provide a method for preparing phosphorus pentafluoride using phosphorus trioxide as a raw material. The method adopts a tubular reactor for continuous reaction. In the first tubular reactor, phosphorus trioxide (P 2 O 3 , P 4 O 6 For the convenience of measurement, all molar quantities in the following text are expressed as P 2 O 3 The method comprises the following steps: reacting phosphorus pentoxide with fluorine gas in a second tubular reactor to obtain phosphorus pentafluoride with a small amount of phosphorus trioxide, and then reacting the phosphorus pentoxide with fluorine gas in a second tubular reactor to obtain phosphorus pentafluoride with a high yield. The preparation process of the present invention completely overcomes the defects of the traditional process of violent reaction and inability to industrialize mass production, and has the advantages of mild reaction and ability to mass produce.

[0013] The specific scheme of the present invention is: A method for preparing phosphorus pentafluoride using phosphorus trioxide as a raw material, the method comprising the following steps: Step 1: spraying gaseous phosphorus trioxide into a first tubular reactor and reacting with oxygen in the first tubular reactor, and controlling the ratio of phosphorus trioxide to oxygen so that part of the phosphorus trioxide is converted into phosphorus pentoxide, and the reaction product is a mixture of phosphorus trioxide and phosphorus pentoxide; Step 2: introducing the mixture and fluorine gas into a second tubular reactor to react phosphorus pentoxide and part of unreacted phosphorus trioxide with fluorine gas to generate phosphorus pentafluoride; The outlet temperature of the first tubular reactor is lower than the gasification temperature of phosphorus trioxide and higher than the melting point of phosphorus trioxide.

[0014] Through the above process, we found that in the second tubular reactor, the mixture can react with fluorine gas relatively easily to obtain phosphorus pentafluoride with a relatively considerable yield. The reaction conditions of the entire reaction process are mild and the reaction has low requirements on equipment. In preliminary experiments, we verified that fluorine gas is difficult to react with solid phosphorus pentoxide. The present invention overcomes the barrier of the difficulty of solid-gas reaction by controlling the conversion of phosphorus pentoxide in step 1.

[0015] We speculate that the possible reason is that: in step 1, a portion of phosphorus trioxide is reserved and does not react, and the outlet temperature of the first tubular reactor is lower than the gasification temperature of phosphorus trioxide, so that phosphorus trioxide can condense on the periphery of the core with solid phosphorus pentoxide as the core to form a mist-like mixture; in the second tubular reactor, the fluorine gas and the phosphorus trioxide on the surface of the core react violently, and a large amount of heat is instantly generated, so that the phosphorus pentoxide as the core absorbs and makes the phosphorus pentoxide in the outermost layer of the core close to and at the gasification temperature, thereby making the fluorine gas and phosphorus pentoxide react more easily, and part of the reaction heat generated by the reaction is absorbed by the temperature control jacket of the second tubular reactor and the other part is continuously provided to the phosphorus pentoxide inside the core to maintain the continuous progress of the reaction. At the same time, through the reaction of step 1, phosphorus trioxide can be converted into phosphorus pentoxide, reducing the chemical energy of the raw materials, so that the reaction in the second tubular reactor is relatively stable and the temperature is controllable.

[0016] In addition, this project has also studied a technical route that uses phosphorus pentoxide as a raw material, heats it to its sublimation temperature and reacts it with fluorine gas. This technical route has many problems, such as difficulty in heating and difficulty in controlling the reaction at high ambient temperatures. At the same time, this route also needs to overcome the risk that phosphorus pentoxide easily absorbs water, causing the raw material to carry water, and the reaction between water and fluorine gas is too violent and easy to explode.

[0017] At the same time, compared with the scheme of using white phosphorus or yellow phosphorus as raw materials and directly reacting with fluorine gas, this scheme can achieve the purpose of high output and low equipment investment, completely overcoming the problem that this technical route cannot achieve large-scale production.

[0018] In the above method, the inlet temperature of the first tubular reactor is 180-200°C, and the outlet temperature of the first tubular reactor is 90-110°C; the first tubular reactor is provided with a temperature-control jacket, and the insulation temperature from the inlet to the outlet of the first tubular reactor gradually decreases.

[0019] In the above method, the insulation temperature of the second tubular reactor is -20°C to 0°C.

[0020] In some preferred embodiments of the present invention, the insulation temperature of the second tubular reactor is -20°C, -15°C, -10°C, -5°C or 0°C.

[0021] In the first tubular reactor, the temperature is maintained at a higher level in the early stage of the reaction to increase the reaction rate of phosphorus trioxide so that most of the phosphorus trioxide can react quickly with oxygen. In the later stage of the reaction, the temperature is lowered to about 100°C to allow the unreacted phosphorus trioxide and phosphorus pentoxide to be fully mixed.

[0022] Insulating the first tubular reactor at a relatively high temperature can ensure that phosphorus trioxide reacts in gaseous form; although the insulation temperature of the second tubular reactor is below 0°C, the gas discharged from the first tubular reactor is at a relatively high temperature and will not suddenly drop to 0°C; this is conducive to a relatively mild reaction of phosphorus trioxide with fluorine gas at a suitable temperature under controllable temperature conditions.

[0023] In some preferred embodiments of the present invention, the inlet temperature of the first tubular reactor is 180°C, 185°C, 190°C or 200°C; the outlet temperature of the first tubular reactor is 90°C, 95°C, 100°C, 105°C or 110°C.

[0024] In the above method, in step 1, the molar ratio of phosphorus trioxide to oxygen is 1:0.85~0.95.

[0025] In the preferred embodiment of the present invention, phosphorus trioxide is preferably reacted by 85% to 95%. During the implementation of this project, we found a more peculiar phenomenon, that is, the more phosphorus trioxide is retained, the better. The more phosphorus trioxide is retained, the lower the yield of phosphorus pentafluoride is when the yield is finally calculated, and the more violent the reaction is. After analysis, we believe that the heat released when too much phosphorus trioxide remains in the periphery of the core will cause phosphorus trioxide and fluorine gas to react, and the remaining phosphorus trioxide in the periphery of the core layer will be quickly gasified, causing the heat generated by the reaction to be unable to be absorbed by the core, and ultimately causing solid phosphorus pentoxide to be unable to be fully reacted. Of course, too little phosphorus trioxide is retained, which is also not conducive to the conversion of phosphorus pentafluoride, because the phosphorus trioxide coated on the periphery of the core is too little, and the heat generated during the reaction is not enough to heat phosphorus pentoxide to a sufficient temperature.

[0026] In the above method, the diameter of the first tubular reactor is 15-25 cm; the length of the first tubular reactor is 80-120 m; preferably, the diameter of the first tubular reactor is 20 cm; the length of the first tubular reactor is 100 m; The diameter of the second tubular reactor is 15-25 cm; the length of the second tubular reactor is 150-200 m.

[0027] In the above method, oxygen can be added together with an inert gas carrier gas into the first tubular reactor. Generally speaking, the preferred carrier gas is nitrogen, and the volume of the carrier gas and the volume of oxygen can be selected to be 1:0.5~2.

[0028] In the above method, the fluorine gas is introduced into the second tubular reactor in the form of a mixed gas of an inert gas and fluorine gas; in the mixed gas, the volume ratio of the inert gas to the fluorine gas is 6 to 3:1; The amount of fluorine gas used is excessive, and too much fluorine gas will not affect the reaction. From the perspective of cost saving, taking 1L oxygen flow rate as an example, the mixed gas introduction speed is 50~70L / min.

[0029] In the above method, the outlet of the second tubular reactor is connected to a condenser and a cold trap; the condenser is used to separate impurities with a boiling point higher than that of phosphorus pentafluoride, and the cold trap is used to collect phosphorus pentafluoride; the gas discharged from the cold trap is filtered and dried and enters a gas storage tank or is washed with liquid to absorb unreacted fluorine gas before being discharged.

[0030] In the above method, the condenser is a multi-stage condenser connected in series, and the temperature of the condenser gradually decreases from -30°C to -50°C; the temperature of the cold trap is -96~-110°C.

[0031] In the above method, the gaseous phosphorus trioxide is obtained by an incomplete reaction of elemental phosphorus and oxygen.

[0032] The method of preparing a mixture mixed with phosphorus pentoxide can refer to the prior art: Patent application with publication number CN108975294A, the subject of which is a device and method for producing electronic-grade phosphorus pentoxide. In order to prepare electronic-grade phosphorus pentoxide, it first obtains a mixture of phosphorus trioxide and phosphorus pentoxide by gasifying yellow phosphorus and not completely burning it, and then continues to react this mixture with pure oxygen to avoid direct combustion of phosphorus trioxide entrained in the product.

[0033] In the present invention, phosphorus trioxide can be prepared by precisely controlling the phosphorus-oxygen ratio to produce phosphorus trioxide with relatively high purity, or it can be prepared by using the above-mentioned prior art method to prepare a mixture of phosphorus trioxide and phosphorus pentoxide.

[0034] In addition, the present invention also discloses a system for implementing the above method, comprising a first tubular reactor, a second tubular reactor, a condenser and a cold trap connected in sequence; The first tubular reactor is used to supply gaseous phosphorus trioxide and oxygen for reaction, and the reaction product is a mixture of phosphorus trioxide and phosphorus pentoxide; The second tubular reactor is used for reacting the mixture with fluorine gas, so that phosphorus pentoxide and part of unreacted phosphorus trioxide and fluorine gas react to generate phosphorus pentafluoride; The condenser is used to separate impurities with a boiling point higher than phosphorus pentafluoride from the product output from the second tubular reactor; The cold trap is used to collect phosphorus pentafluoride in the gas output from the condenser.

[0035] In the above system, the first tubular reactor and the second tubular reactor are both provided with temperature-control jackets; the first tubular reactor is provided with multiple temperature-control jackets, and the temperature at different positions of the first tubular reactor is independently controlled in the form of multi-stage temperature control; a pump for pumping gas is arranged between the first tubular reactor and the second tubular reactor; the condenser is a multi-stage condenser connected in series, and the temperature of the condenser gradually decreases from -30°C to -50°C; a filter is arranged between the condenser and the cold trap; the outlet of the cold trap is connected to a tail gas absorption tank.

[0036] The beneficial effects of this application are: The invention adopts a tubular reactor to carry out a continuous reaction. In a first tubular reactor, phosphorus trioxide and oxygen react to obtain phosphorus pentoxide, while retaining a small amount of phosphorus trioxide, and then react with fluorine gas in a second tubular reactor to obtain phosphorus pentafluoride with a high yield. The preparation process of the invention completely overcomes the defects of violent reaction and inability to industrialize mass production of traditional processes, and has the advantages of mild reaction and ability to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of the equipment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. In the description of the present invention, it should be noted that, if no specific conditions are specified in the embodiments, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0039] Before describing the method of the present invention, the system involved in the present invention is first introduced. The following embodiments are all produced using this system: refer to Figure 1 , a system for producing phosphorus pentafluoride, comprising a first tubular reactor 1, a second tubular reactor 2, a first condenser 3, a second condenser 4, a third condenser 5, a filter 6, a cold trap 7, and a tail gas absorption tank 8 connected in sequence; The first tubular reactor 1 and the second tubular reactor 2 are both provided with temperature-control jackets. The inlet temperature of the first tubular reactor 1 is controlled at 180-200°C, preferably 190-200°C, and the outlet temperature is controlled at 90-110°C, preferably 100-110°C. The temperature gradually decreases from front to back, so the first tubular reactor 1 has multiple temperature-control jackets, which are controlled in the form of multi-stage temperature control; the temperature of the temperature-control jacket of the second tubular reactor 2 is controlled at 0°C to -20°C, and the temperature cannot be too low. If the temperature is too low, the phosphorus trioxide in the mixed gas entering will quickly reach the liquefaction temperature point (23.8°C). A pump 9 for pumping gas is provided between the first tubular reactor 1 and the second tubular reactor 2, so that a positive airflow can be formed in the first tubular reactor 1; The diameter of the first tubular reactor 1 is 20 cm; the length of the first tubular reactor 1 is 100 m; The diameter of the second tubular reactor 2 is 20 cm; the length of the second tubular reactor 2 is 200 m; It should be noted that: in actual production, the specifications and length of the tubular reactor can be flexibly adjusted according to actual production conditions. For example, the length can be shortened or extended according to the reactants, processing volume, etc., as long as the purpose of the reaction process is achieved.

[0040] The shell side temperature of the first condenser 3 is -30°C, the shell side temperature of the second condenser 4 is -40°C, and the shell side temperature of the third condenser 5 is -50°C. Through the step-by-step condensation of the three condensers, all substances except non-condensable gases and phosphorus pentafluoride will become solid; after being filtered by the filter 6, the remaining gas is composed of phosphorus pentafluoride, oxygen, fluorine gas and possible inert gas, and is deep-cooled by the cold trap 7, the phosphorus pentafluoride is condensed, and the non-condensable gas enters the tail gas absorption tank 8 for absorption, and the liquid in the tail gas absorption tank 8 is water.

[0041] The phosphorus trioxide used in the following examples is all refined phosphorus trioxide (CAS: 1314-24-5, purity ≥99wt%).

[0042] Example 1 A method for preparing phosphorus pentafluoride using phosphorus trioxide as a raw material, the method comprising the following steps: Step 1: spraying gaseous phosphorus trioxide (heating phosphorus trioxide to a temperature above the gasification temperature in a light-proof environment under nitrogen protection to produce gaseous phosphorus trioxide) into a first tubular reactor and reacting with oxygen in the first tubular reactor, and converting part of the phosphorus trioxide into phosphorus pentoxide by controlling the ratio of phosphorus trioxide to oxygen; the inlet temperature of the first tubular reactor is 200° C., and the outlet temperature is controlled at 100° C., which includes incompletely reacted oxygen, incompletely reacted gaseous phosphorus trioxide, solid phosphorus pentoxide, liquid phosphorus trioxide and nitrogen, and the product is in the form of smoke; in this step 1, oxygen is supplied in the form of nitrogen and oxygen; the volume ratio of oxygen to nitrogen is 1:1; the total flow rate is 2L / min (standard state), and the oxygen flow rate is 1L / min (standard state); the molar flow rate of oxygen is 0.045mol / min, and that of phosphorus trioxide is 0.053mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.85; The gas volumes described in this article are all under standard conditions and will not be repeated later.

[0043] The reaction equation of this step is: 2 O 3 +O 2 →P 2 O 5 ; Step 2: introducing the mixed gas and the fluorine-nitrogen gas into a second tubular reactor, so that phosphorus pentoxide and part of the unreacted phosphorus trioxide react with the fluorine gas in the fluorine-nitrogen gas to generate phosphorus pentafluoride; The composition of the fluorine-nitrogen gas is 85 vol% nitrogen and 15 vol% fluorine. In this embodiment, in order to completely convert phosphorus pentafluoride, an excess of fluorine is used. The supply rate of the fluorine-nitrogen gas is 50 L / min. The control temperature of the temperature-controlled jacket of the second tubular reactor is 0°C.

[0044] The reaction equation involved in this step is: 2P 2 O 3 +10F 2 →4PF 5 +3O 2 ; 2P 2 O 5 +10F 2 →4PF 5 +5O 2 ; Step 3: The gas discharged from the second tubular reactor is condensed step by step through the first condenser, the second condenser, and the third condenser, and then filtered through the filter, and then enters the cold trap for condensation, and the non-condensable gas enters the tail gas absorption tank; the phosphorus pentafluoride in the cold trap is collected, and its yield and purity are tested.

[0045] Example 2 The method is substantially the same as Example 1, except that the phosphorus trioxide is 0.053 mol / min, the molar flow rate of oxygen is 0.048 mol / min, and the molar ratio of phosphorus trioxide to oxygen is 1:0.9.

[0046] Example 3 The method is substantially the same as Example 1, except that the phosphorus trioxide is 0.053 mol / min, the molar flow rate of oxygen is 0.050 mol / min, and the molar ratio of phosphorus trioxide to oxygen is 1:0.95.

[0047] Example 4 The method is substantially the same as Example 1, except that the phosphorus trioxide is 0.053 mol / min, the molar flow rate of oxygen is 0.042 mol / min, and the molar ratio of phosphorus trioxide to oxygen is 1:0.8.

[0048] Example 5 The method is substantially the same as Example 1, except that the phosphorus trioxide is 0.053 mol / min, the molar flow rate of oxygen is 0.040 mol / min, and the molar ratio of phosphorus trioxide to oxygen is 1:0.75.

[0049] Example 6 The method is substantially the same as Example 1, except that the phosphorus trioxide is 0.053 mol / min, the molar flow rate of oxygen is 0.052 mol / min, and the molar ratio of phosphorus trioxide to oxygen is 1:0.98.

[0050] Example 7 The process is substantially the same as in Example 1, except that the supply rate of fluorine and nitrogen gas is 60 L / min.

[0051] Example 8 The process is substantially the same as in Example 1, except that the supply rate of fluorine and nitrogen gas is 70 L / min.

[0052] Example 9 The method is substantially the same as Example 1, except that the inlet temperature of the first tubular reactor is 180°C, and the outlet temperature is controlled at 90°C; and the temperature of the temperature-controlled jacket of the second tubular reactor is controlled at -10°C.

[0053] Example 10 The method is substantially the same as Example 1, except that the inlet temperature of the first tubular reactor is 190°C, and the outlet temperature is controlled at 110°C; and the temperature of the temperature-controlled jacket of the second tubular reactor is controlled at -20°C.

[0054] Embodiment 11 The method is substantially the same as Example 1, except that the temperature of the temperature-control jacket of the second tubular reactor is controlled at 10°C.

[0055] Example 12 The method is substantially the same as Example 1, except that the temperature of the temperature-control jacket of the second tubular reactor is controlled at 20°C.

[0056] Performance Testing The purity test method of phosphorus pentafluoride is: Infrared spectroscopy Principle: Phosphorus pentafluoride molecules have a specific infrared absorption spectrum. By measuring its infrared spectrum and comparing it with the standard spectrum, its purity can be qualitatively determined.

[0057] Operation steps: Place the phosphorus pentafluoride sample in the gas pool, scan the sample using an infrared spectrometer, and record its infrared spectrum. Compare the measured spectrum with the infrared spectrum of standard phosphorus pentafluoride, analyze the position and intensity of its absorption peak, determine whether there is an impurity absorption peak, and thus evaluate the purity.

[0058] Note: When preparing samples, be careful to avoid sample contamination or decomposition, and ensure that the light source, detector and other components of the spectrometer work properly to obtain accurate spectral data.

[0059] The purity and yield of phosphorus pentafluoride can be seen in Table 1 below; Table 1 Purity and yield Yield % Purity wt% Example 1 83.1 99.5 Example 2 82.9 99.5 Example 3 82.5 99.4 Example 4 75.4 99.5 Example 5 72.1 99.6 Example 6 35.8 99.5 Example 7 83.6 99.5 Example 8 83.7 99.5 Example 9 82.3 99.4 Example 10 83.8 99.5 Embodiment 11 82.5 99.6 Example 12 82.1 99.5 Result analysis: 1. It can be seen from Examples 1 to 6 that when the molar ratio of phosphorus trioxide to oxygen is 1:0.85 to 0.95, it is the highest. The yields of Examples 4 and 5 gradually decrease. The possible reason is that in the second tubular reactor, the phosphorus trioxide formed in the outer layer of phosphorus pentoxide is too much and a small amount of gaseous phosphorus trioxide remains in the mixed gas. Under the action of fluorine gas, the phosphorus trioxide in the outer layer of phosphorus pentoxide reacts with the fluorine gas to release heat, but the heat generated rapidly gasifies the phosphorus trioxide outside the core, resulting in the inability of phosphorus pentoxide to obtain enough heat, thereby causing a sharp decrease in yield. At the same time, the excessive phosphorus trioxide makes the temperature of the second tubular reactor more and more difficult to control.

[0060] It can be seen from Example 6 that when the molar ratio reaches 1:0.98, the yield of phosphorus pentafluoride also decreases sharply because some cores cannot be coated. Therefore, it can be seen from Examples 1 to 6 that the ratio of phosphorus trioxide to oxygen is a very critical parameter in the present invention, and the ratio of the two should be accurately controlled during the production process.

[0061] 2. It can be seen from Examples 7 and 8 that the results are similar to those of Example 1, indicating that excess fluorine gas has no significant effect on the reaction process.

[0062] In some other implementation cases of the present invention, the use of pure fluorine gas has been verified, which also produces a satisfactory yield, but its reaction is more violent and will encounter rapid temperature rise at the front end of the second tubular reactor, which poses a potential risk to production control.

[0063] 3. It can be seen from Examples 1, 9 to 12 that the yields and purities of the five cases are satisfactory. During the experiment, we observed that the heating rates of Examples 11 and 12 were much faster than those of Examples 1, 9 and 10, and it was detected that the temperature of the front section of the second tubular reactor increased rapidly.

[0064] In summary, the heat release in the reaction process of the present invention is controllable, the production efficiency is high, and the goal of directly producing phosphorus pentafluoride based on a phosphorus source and fluorine gas can be achieved.

Claims

1. A method for preparing phosphorus pentafluoride using phosphorus trioxide as raw material, characterized in that: The method comprises the following steps: Step 1: spraying gaseous phosphorus trioxide into a first tubular reactor and reacting with oxygen in the first tubular reactor, and controlling the ratio of phosphorus trioxide to oxygen so that part of the phosphorus trioxide is converted into phosphorus pentoxide, and the reaction product is a mixture of phosphorus trioxide and phosphorus pentoxide; Step 2: introducing the mixture and fluorine gas into a second tubular reactor to react phosphorus pentoxide and part of unreacted phosphorus trioxide with fluorine gas to generate phosphorus pentafluoride; The outlet temperature of the first tubular reactor is lower than the gasification temperature of phosphorus trioxide and higher than the melting point of phosphorus trioxide.

2. The method according to claim 1, characterized in that The inlet temperature of the first tubular reactor is 180-200° C., and the outlet temperature of the first tubular reactor is 90-110° C.; the first tubular reactor is externally provided with a temperature-controlling jacket, and the insulation temperature from the inlet to the outlet of the first tubular reactor gradually decreases.

3. The method according to claim 1, characterized in that The insulation temperature of the second tubular reactor is -20°C to 0°C.

4. The method according to claim 1, characterized in that: In the step 1, the molar ratio of phosphorus trioxide to oxygen is 1:0.85-0.

95.

5. The method according to claim 1, characterized in that The diameter of the first tubular reactor is 15-25 cm; the length of the first tubular reactor is 80-120 m; The diameter of the second tubular reactor is 15-25 cm; the length of the second tubular reactor is 150-200 m.

6. The method according to claim 5, characterized in that In the first tubular reactor, the first inert gas is introduced synchronously with oxygen, and the volume ratio of the first inert gas to oxygen is 1:0.5-2; in the second tubular reactor, fluorine gas is introduced in the form of a mixed gas of the second inert gas and fluorine gas; in the mixed gas, the volume ratio of the second inert gas to fluorine gas is 6-3:

1.

7. The method according to claim 1, characterized in that The outlet of the second tubular reactor is connected to a condenser and a cold trap; the condenser is used to separate impurities with a boiling point higher than that of phosphorus pentafluoride, and the cold trap is used to collect phosphorus pentafluoride; the gas discharged from the cold trap is filtered and dried and enters a gas storage tank or is washed with liquid to absorb unreacted fluorine gas before being discharged; The condenser is a multi-stage series-connected condenser, and the temperature of the condenser gradually decreases from -30°C to -50°C; the temperature of the cold trap is -96~-110°C.

8. The method according to claim 1, characterized in that The gaseous form of phosphorus trioxide is obtained by an incomplete reaction of elemental phosphorus and oxygen.

9. A system for implementing the method according to any one of claims 1 to 8, characterized in that: The invention comprises a first tubular reactor, a second tubular reactor, a condenser and a cold trap which are connected in sequence, wherein the first tubular reactor and the second tubular reactor are both provided with temperature-control jackets; the first tubular reactor is provided with a plurality of temperature-control jackets, and the temperature at different positions of the first tubular reactor is independently controlled in the form of multi-stage temperature control; a pump for pumping gas is arranged between the first tubular reactor and the second tubular reactor; the condenser is a multi-stage condenser connected in series, and the temperature of the condenser is gradually reduced from -30°C to -50°C; a filter is arranged between the condenser and the cold trap; and the outlet of the cold trap is connected with a tail gas absorption tank.

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