A method for preparing phosphorus pentafluoride using phosphorus trioxide as a raw material

Abstract

The present invention belongs to the technical field of chemical material preparation, and discloses a method for preparing phosphorus pentafluoride using phosphorus trioxide as a raw material. The method comprises the following steps: Step 1: Spraying gaseous phosphorus trioxide into a first tubular reactor and reacting it with oxygen in the first tubular reactor. By controlling the ratio of phosphorus trioxide to oxygen, 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 so that phosphorus pentoxide and part of the unreacted phosphorus trioxide react with fluorine gas to generate phosphorus pentafluoride. The preparation process of the present invention completely overcomes the defects of violent reaction and inability to be industrially mass-produced in the traditional process, and has the advantages of mild reaction and ability to produce in batches.

Description

Technical Field

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

[0002] Phosphorus pentafluoride (PF5) is an important inorganic compound, which is widely used in the fields of electronics industry, organic synthesis, lithium battery electrolyte, etc.

[0003] In the prior art, the synthesis of phosphorus pentafluoride can generally be divided into a direct method and an indirect method. The indirect method is as follows: synthesize hexafluorophosphoric acid through various means, and then obtain phosphorus pentafluoride through the pyrolysis of hexafluorophosphoric acid. For example, in the patent application with the publication number CN117361458A and the theme of a continuous production method of phosphorus pentafluoride, it first reacts phosphorus pentoxide with HF to generate hexafluorophosphoric acid, and then dehydrates to form phosphorus pentoxide.

[0004] The direct method can be divided 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; specifically, the following information can be seen:

[0005] Direct synthesis of phosphorus pentafluoride from elemental phosphorus: The patent applications with the publication numbers CN109052350A (theme: continuous production method of phosphorus pentafluoride), CN102372264A (theme: a method for purifying phosphorus pentafluoride), and CN102421702A (theme: method and reactor design for manufacturing phosphorus pentafluoride) all disclose the use of white phosphorus, red phosphorus or yellow phosphorus as a phosphorus source to react with fluorine gas to prepare phosphorus pentafluoride;

[0006] Among them, it is described in CN109052350A that the reaction between fluorine gas and phosphorus is violent, and a large amount of heat will be released during the reaction. In the previous experiments of the applicant, it was also found that this reaction is a violent exothermic reaction and needs to be carried out in a specific safety reactor.

[0007] At the same time, in the prior art, the reaction between phosphorus and fluorine gas is carried out at a relatively low concentration, and the purpose is to effectively control the heat dissipation and avoid excessive heat accumulation.

[0008] Methods such as direct synthesis of phosphorus pentafluoride from phosphorus pentachloride and direct synthesis of phosphorus pentafluoride from phosphoric acid all react with fluorides and obtain phosphorus pentafluoride through fluorine substitution.

[0009] Through the above analysis, it can be seen that in this field, the method of directly reacting phosphorus oxides with fluorine gas to prepare phosphorus pentafluoride has not been reported for the time being.

[0010] The reason is as follows: 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 mixing system, and the reaction can be easily initiated.

[0011] However, the melting point temperature of phosphorus pentoxide is as high as 340°C. If phosphorus pentoxide and fluorine gas are simply mixed, due to the reaction difficulty of the solid-gas reaction, it is very difficult to carry out the reaction.

[0012] Although the melting point of phosphorus trioxide is relatively low, it has relatively high chemical energy, and its direct reaction with fluorine gas is still violent and difficult to control.

[0013] Therefore, there are natural difficulties in directly preparing phosphorus pentafluoride with fluorine gas, and there are irreconcilable contradictions among reaction controllability, mildness, and industrial batch production. Summary of the Invention

[0014] The object of the present invention is to provide a method for preparing phosphorus pentafluoride with phosphorus trioxide as a raw material. This method uses a tubular reactor for continuous reaction. In the first tubular reactor, phosphorus trioxide (P2O3, P4O6, for the convenience of measurement, all molar amounts hereinafter are measured with P2O3 as the measurement object) reacts with oxygen to obtain phosphorus pentoxide, while retaining a small amount of phosphorus trioxide, and then reacts with fluorine gas in the second tubular reactor to obtain phosphorus pentafluoride with a higher yield. The preparation process of the present invention completely overcomes the defects of violent reaction and inability to mass-produce industrially in the traditional process, and has the advantages of mild reaction and ability to produce in batches.

[0015] The specific solution of the present invention is as follows:

[0016] A method for preparing phosphorus pentafluoride with phosphorus trioxide as a raw material, the method comprising the following steps:

[0017] Step 1: Spray gaseous phosphorus trioxide into the first tubular reactor and react with the oxygen in the first tubular reactor. By controlling the ratio of phosphorus trioxide and oxygen, part of the phosphorus trioxide is converted into phosphorus pentoxide, and the reaction product is a mixture of phosphorus trioxide and phosphorus pentoxide;

[0018] Step 2: Feed the mixture and fluorine gas into the second tubular reactor so that phosphorus pentoxide and part of the unreacted phosphorus trioxide react with fluorine gas to generate phosphorus pentafluoride;

[0019] The outlet temperature of the first tubular reactor is lower than the vaporization temperature of phosphorus trioxide and higher than the melting point temperature of phosphorus trioxide.

[0020] 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 considerable yield. The reaction conditions throughout the reaction process are mild, and the requirements for equipment are relatively low. In the preliminary experiment, we verified that it is very difficult for fluorine gas to react with solid phosphorus pentoxide. Through the conversion control of phosphorus pentoxide in step 1 of the present invention, the barrier that is difficult to carry out the solid-gas reaction is overcome.

[0021] We speculate that the possible reasons are as follows: In step 1, a part of phosphorus trioxide is reserved without reaction, and the outlet temperature of the first tubular reactor is lower than the vaporization temperature of phosphorus trioxide, so that phosphorus trioxide can condense on the periphery of the core of solid phosphorus pentoxide to form a misty mixture; in the second tubular reactor, fluorine gas reacts violently with phosphorus trioxide on the surface of the core, instantaneously generating a large amount of heat, causing the phosphorus pentoxide serving as the core to absorb and making the outermost layer of the core of phosphorus pentoxide close to and at the vaporization temperature, thereby making it easier for fluorine gas to react with phosphorus pentoxide. A 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 supplied to the phosphorus pentoxide inside the core to maintain the continuous progress of the reaction. At the same time, through the reaction in step 1, phosphorus trioxide can be converted into phosphorus pentoxide, reducing the chemical energy of the raw materials and making the reaction in the second tubular reactor proceed more smoothly and the temperature controllable.

[0022] In addition, this project has also studied the technical route of using phosphorus pentoxide as a raw material and reacting with fluorine gas after heating to its sublimation temperature. This technical route has many problems such as difficult heating and difficult control of the reaction at high ambient temperatures. At the same time, this route also needs to overcome the risks that phosphorus pentoxide is easy to absorb water, resulting in water in the raw materials, and the reaction between water and fluorine gas is too violent and prone to explosion.

[0023] At the same time, compared with the scheme of directly reacting white phosphorus or yellow phosphorus with fluorine gas as raw materials, this scheme can achieve the purpose of high yield and less equipment investment, and completely overcomes the problem that large-scale production cannot be achieved by this technical route.

[0024] 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; a temperature control jacket is provided outside the first tubular reactor, and the insulation temperature from the inlet to the outlet of the first tubular reactor gradually decreases.

[0025] In the above method, the insulation temperature of the second tubular reactor is -20 °C to 0 °C.

[0026] 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.

[0027] In the first tubular reactor, maintain a relatively high temperature in the early stage of the reaction to increase the reaction rate of phosphorus trioxide, so that most of the phosphorus trioxide can quickly react with oxygen. In the later stage of the reaction, by cooling to about 100 °C, the unreacted phosphorus trioxide and phosphorus pentoxide can be fully mixed.

[0028] Insulating at a relatively high temperature in the first tubular reactor can ensure that phosphorus trioxide reacts in a gaseous state; 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 immediately; this is conducive to the reaction of phosphorus trioxide with fluorine gas at a suitable temperature under controlled temperature conditions in a relatively mild manner.

[0029] 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.

[0030] In the above method, in step 1, the molar ratio of phosphorus trioxide to oxygen is 1:0.85 - 0.95.

[0031] In a preferred embodiment of the present invention, preferably 85% to 95% of the phosphorus trioxide is reacted. During the implementation of this project, we found a rather peculiar phenomenon. It is not that the more phosphorus trioxide is retained, the better. The more phosphorus trioxide is retained, the lower the yield of phosphorus pentafluoride and the more violent the reaction during the final yield calculation. After analysis, we believe that the excessive residual phosphorus trioxide on the periphery of the core will cause the heat released when phosphorus trioxide reacts with fluorine gas to quickly vaporize the remaining phosphorus trioxide on the periphery of the core layer, resulting in the heat generated by the reaction not being absorbed by the core, and ultimately resulting in insufficient reaction of solid phosphorus pentoxide. Of course, too little retention of phosphorus trioxide is also not conducive to the conversion of phosphorus pentafluoride because too little phosphorus trioxide coated on the periphery of the core will not generate enough heat during the reaction to raise the temperature of phosphorus pentoxide to a sufficient level.

[0032] In the above method, the inner diameter of the first tubular reactor is 15 - 25 cm; the length of the first tubular reactor is 80 - 120 m; preferably, the inner diameter of the first tubular reactor is 20 cm; the length of the first tubular reactor is 100 m;

[0033] The inner diameter of the second tubular reactor is 15 - 25 cm; the length of the second tubular reactor is 150 - 200 m.

[0034] In the above method, in the first tubular reactor, oxygen can be introduced together with an inert gas carrier. Generally, the preferred carrier gas is nitrogen, and the volume ratio of the carrier gas to oxygen can be selected from 1:0.5 to 2.

[0035] In the above method, in the second tubular reactor, fluorine gas is introduced 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 fluorine gas is 6 to 3:1;

[0036] The amount of fluorine gas used is in excess. Excessive fluorine gas will not affect the reaction. From the perspective of cost savings, taking a 1L oxygen flow rate as an example, the feeding rate of the above-mentioned mixed gas is 50 to 70L / min.

[0037] In the above method, the outlet of the second tubular reactor is connected with 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, dried and then enters a gas storage tank or is discharged after being washed with liquid to absorb unreacted fluorine gas.

[0038] In the above method, the condenser is a multi-stage series condenser, and the temperature of the condenser gradually decreases from -30°C to -50°C; the temperature of the cold trap is -96 to -110°C.

[0039] In the above method, the gaseous form of phosphorus trioxide is obtained by the incomplete reaction of elemental phosphorus and oxygen.

[0040] The method for the mixture mixed with phosphorus pentoxide can refer to the prior art: a patent application with the publication number CN108975294A and the theme of a production device and method for 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 incomplete combustion, and then continues to react this mixture with pure oxygen to avoid the phosphorus trioxide entrained in the product due to direct combustion.

[0041] In the present invention, phosphorus trioxide with relatively high purity can be produced by precisely controlling the ratio of phosphorus to oxygen, or the method of the prior art for the mixture of phosphorus trioxide and phosphorus pentoxide can be used for preparation.

[0042] In addition, the present invention also discloses a system for implementing the above method, including a first tubular reactor, a second tubular reactor, a condenser and a cold trap connected in sequence;

[0043] The first tubular reactor is used for the reaction of gaseous phosphorus trioxide and oxygen, and the reaction product is a mixture of phosphorus trioxide and phosphorus pentoxide;

[0044] The second tubular reactor is used for the reaction of the mixture and fluorine gas, so that phosphorus pentoxide and part of the unreacted phosphorus trioxide and fluorine gas react to generate phosphorus pentafluoride;

[0045] The condenser is used to separate impurities with boiling points higher than that of phosphorus pentafluoride in the products output from the second tubular reactor;

[0046] The cold trap is used to collect phosphorus pentafluoride in the gas output from the condenser.

[0047] In the above system, both the first tubular reactor and the second tubular reactor are equipped with temperature control jackets; there are multiple temperature control jackets for the first tubular reactor to independently control the temperatures at different positions of the first tubular reactor in the form of multi-stage temperature control; a pump for sucking gas is arranged between the first tubular reactor and the second tubular reactor; the condenser is a multi-stage series condenser, 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 with a tail gas absorption tank.

[0048] The beneficial effects of this application are:

[0049] The present invention uses a tubular reactor for continuous reaction. In the first tubular reactor, phosphorus pentoxide is obtained by the reaction of phosphorus trioxide and oxygen, and a small amount of phosphorus trioxide is retained. Then, it reacts with fluorine gas in the second tubular reactor to obtain phosphorus pentafluoride with a higher yield; the preparation process of the present invention completely overcomes the defects of violent reaction and inability to industrialize mass production in the traditional process, and has the advantages of mild reaction and being able to produce in batches. Description of the Drawings

[0050] Figure 1 It is the equipment flow chart of the present invention. Detailed Embodiments

[0051] Next, the embodiments of the present invention will be used to clearly and completely describe the present invention. In the description of the present invention, it should be noted that for those without specific conditions indicated in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0052] Before elaborating on the method of the present invention, the system involved in the present invention will be introduced first, and the following embodiments will all use this system for production:

[0053] Refer to Figure 1 , a system for producing phosphorus pentafluoride, which includes 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;

[0054] Both the first tubular reactor 1 and the second tubular reactor 2 are equipped 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. From front to back, the temperature gradually decreases. Therefore, the temperature control jacket of the first tubular reactor 1 is multiple and is controlled in the form of multi-stage temperature control; the temperature control jacket of the second tubular reactor 2 controls its temperature at 0 °C to -20 °C. The temperature cannot be too low, otherwise the phosphorus trioxide in the incoming mixed gas will quickly reach the liquefaction temperature point (23.8 °C). A pump 9 for sucking gas is arranged between the first tubular reactor 1 and the second tubular reactor 2 to enable a forward air flow to be formed in the first tubular reactor 1;

[0055] The diameter of the first tubular reactor 1 is 20 cm; the length of the first tubular reactor 1 is 100 m;

[0056] The diameter of the second tubular reactor 2 is 20 cm; the length of the second tubular reactor 2 is 200 m;

[0057] It should be noted that: in actual production, the specifications and lengths of the tubular reactors can be adjusted more flexibly according to actual production conditions. For example, it is possible to shorten or extend the length according to reactants, throughput, etc., as long as the purpose of the reaction process is achieved.

[0058] 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 solids; after being filtered by the filter 6, the remaining gas consists of phosphorus pentafluoride, oxygen, fluorine, and possibly inert gases. After deep cooling by the cold trap 7, phosphorus pentafluoride is condensed, and the non-condensable gas enters the tail gas absorption tank 8 for absorption. The liquid in the tail gas absorption tank 8 is water.

[0059] The phosphorus trioxide used in the following examples is all refined phosphorus trioxide (CAS: 1314 - 24 - 5, purity ≥ 99 wt%).

[0060] Example 1

[0061] A method for preparing phosphorus pentafluoride using phosphorus trioxide as a raw material, the method comprising the following steps:

[0062] Step 1: Phosphorus trioxide in gaseous form (under nitrogen protection, in a light-shielded environment, heating phosphorus trioxide to above its vaporization temperature to produce gaseous phosphorus trioxide) is sprayed into the first tubular reactor and reacts with oxygen in the first tubular reactor. By controlling the ratio of phosphorus trioxide to oxygen, part of the phosphorus trioxide is converted into phosphorus pentoxide; the inlet temperature of the first tubular reactor is 200 °C, and the outlet temperature is controlled at 100 °C. It includes unreacted oxygen, unreacted gaseous phosphorus trioxide, solid phosphorus pentoxide, liquid phosphorus trioxide, and nitrogen, and the product is in a smoky state; in this Step 1, oxygen is supplied in the form of nitrogen-oxygen mixture; the volume ratio of oxygen to nitrogen is 1:1; the total flow rate is 2 L / min (standard state), and the oxygen flow rate is 1 L / min (standard state); the molar flow rate of oxygen is 0.045 mol / min, and that of phosphorus trioxide is 0.053 mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.85;

[0063] The gas volumes described in this article are all volumes under standard conditions, and will not be repeated hereinafter.

[0064] The reaction equation for this step is: P2O3 + O2 → P2O5;

[0065] Step 2: The mixed gas and fluorine-nitrogen gas are introduced into the second tubular reactor so that phosphorus pentoxide and part of the unreacted phosphorus trioxide react with fluorine in the fluorine-nitrogen gas to produce phosphorus pentafluoride;

[0066] 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 excessive amount of fluorine is used; the supply amount of the fluorine-nitrogen gas is 50 L / min; the control temperature of the temperature control jacket of the second tubular reactor is 0 °C.

[0067] The reaction equations involved in this step are: 2P2O3 + 10F2 → 4PF5 + 3O2;

[0068] 2P2O5 + 10F2 → 4PF5 + 5O2;

[0069] 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, then filtered through a filter, and then enters a cold trap for condensation. 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.

[0070] Example 2

[0071] Generally the same as Example 1, the differences are as follows: The amount of phosphorus trioxide is 0.053 mol / min, and the molar flow rate of oxygen is 0.048 mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.9.

[0072] Example 3

[0073] Generally the same as Example 1, the differences are as follows: The amount of phosphorus trioxide is 0.053 mol / min, and the molar flow rate of oxygen is 0.050 mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.95.

[0074] Example 4

[0075] Generally the same as Example 1, the differences are as follows: The amount of phosphorus trioxide is 0.053 mol / min, and the molar flow rate of oxygen is 0.042 mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.8.

[0076] Example 5

[0077] Generally the same as Example 1, the differences are as follows: The amount of phosphorus trioxide is 0.053 mol / min, and the molar flow rate of oxygen is 0.040 mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.75.

[0078] Example 6

[0079] Generally the same as Example 1, the differences are as follows: The amount of phosphorus trioxide is 0.053 mol / min, and the molar flow rate of oxygen is 0.052 mol / min; the molar ratio of phosphorus trioxide to oxygen is 1:0.98.

[0080] Example 7

[0081] Generally the same as Example 1, the differences are as follows: The supply amount of fluorine nitrogen gas is 60 L / min.

[0082] Example 8

[0083] Generally the same as Example 1, the differences are as follows: The supply amount of fluorine nitrogen gas is 70 L / min.

[0084] Example 9

[0085] Generally the same as Example 1, the differences are as follows: The inlet temperature of the first tubular reactor is 180 °C, and the outlet temperature is controlled at 90 °C; the control temperature of the temperature control jacket of the second tubular reactor is -10 °C.

[0086] Example 10

[0087] Basically 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; the control temperature of the temperature control jacket of the second tubular reactor is -20 °C.

[0088] Example 11

[0089] Basically the same as Example 1, except that: the control temperature of the temperature control jacket of the second tubular reactor is 10 °C.

[0090] Example 12

[0091] Basically the same as Example 1, except that: the control temperature of the temperature control jacket of the second tubular reactor is 20 °C.

[0092] Performance detection

[0093] The purity detection method of phosphorus pentafluoride is as follows:

[0094] Infrared spectroscopy

[0095] Principle: Phosphorus pentafluoride molecules have a specific infrared absorption spectrum. By measuring its infrared spectrum and comparing it with the standard spectrum, the purity can be qualitatively judged.

[0096] Operation steps: Put the phosphorus pentafluoride sample gas cell sample, use an infrared spectrometer to scan the sample, 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 peaks, and judge whether there are impurity absorption peaks, so as to evaluate the purity.

[0097] Precautions: Pay attention to avoiding contamination or decomposition of the sample during sample preparation, and ensure the normal operation of components such as the light source and detector of the spectrometer to obtain accurate spectral data.

[0098] The purity and yield of phosphorus pentafluoride can be seen in Table 1 below;

[0099] Table 1 Purity and yield table

[0100] 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 Example 11 82.5 99.6 Example 12 82.1 99.5

[0101] Result analysis:

[0102] 1. As can be seen from Examples 1 to 6, the yield is the highest when the molar ratio of phosphorus trioxide to oxygen is in the range of 1:0.85 to 0.95. The yields of Examples 4 and 5 gradually decrease. The possible reason is that in the second tubular reactor, too much phosphorus trioxide is formed on the outer layer of phosphorus pentoxide and there is a small amount of phosphorus trioxide remaining in the gaseous form in the mixed gas. Under the action of fluorine gas, the phosphorus trioxide on the outer layer of phosphorus pentoxide reacts with fluorine gas to release heat, but the heat generated quickly vaporizes the phosphorus trioxide outside the core, resulting in insufficient heat for phosphorus pentoxide to obtain, and then leading to a sharp decrease in the yield. At the same time, the excessive phosphorus trioxide makes it increasingly difficult to control the temperature of the second tubular reactor.

[0103] As can be seen from Example 6, when the molar ratio reaches 1:0.98, the yield of phosphorus pentafluoride also decreases sharply because part of the core cannot be coated. Therefore, as can be seen from Examples 1 to 6, the ratio of phosphorus trioxide to oxygen is a very critical parameter in the present invention. During the production process, the ratio of the two should be precisely controlled.

[0104] 2. As can be seen from Examples 7 and 8, the results are similar to those of Example 1, indicating that excessive fluorine gas has no obvious effect on the reaction process.

[0105] In some other embodiments of the present invention, the use of pure fluorine gas is verified, and it also produces a satisfactory yield, but the reaction is relatively violent and there will be a rapid temperature rise at the front end of the second tubular reactor, which has potential risks for production control.

[0106] 3. As can be seen from Examples 1, 9 to 12, the yields and purities of the five cases are satisfactory. During the experiment, we observed that the heating rates of Examples 11 and 12 are much faster than those of Examples 1, 9 and 10, and it is detected that the temperature at the front section of the second tubular reactor increases rapidly.

[0107] In summary, during the reaction process of the present invention, the heat release 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 a raw material, characterized in that, The method includes the following steps: Step 1: Inject phosphorus trioxide in gaseous form into the first tubular reactor and react it with oxygen in the first tubular reactor. By controlling the ratio of phosphorus trioxide to oxygen, 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: Feed the mixture and fluorine gas into the second tubular reactor so that phosphorus pentoxide and part of the unreacted phosphorus trioxide react with fluorine gas to form phosphorus pentafluoride; The outlet temperature of the first tubular reactor is lower than the vaporization temperature of phosphorus trioxide and higher than the melting point temperature of phosphorus trioxide; In Step 1, the molar ratio of phosphorus trioxide to oxygen is 1:0.85 - 0.

95.

2. The method according to claim 1, wherein 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; a temperature control jacket is provided outside the first tubular reactor, 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, wherein 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.

5. The method according to claim 4, wherein In the first tubular reactor, a first inert gas is input 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 fed in the form of a mixed gas of a 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.

6. The method according to claim 1, wherein The outlet of the second tubular reactor is connected with 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, dried and then enters a gas storage tank or is discharged after being washed with liquid to absorb unreacted fluorine gas; The condenser is a multi-stage series 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.

7. The method according to claim 1, wherein The gaseous form of phosphorus trioxide is obtained by the incomplete reaction of elemental phosphorus and oxygen.

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