Method and system for preparing phosphorus pentafluoride through continuous reaction by adopting tubular reactor

Abstract

The invention belongs to the field of phosphorus halides, and discloses a method and a system for preparing phosphorus pentafluoride through continuous reaction by adopting a tubular reactor, the method comprises the following steps: step 1, adding phosphorus oxyfluoride, hydrogen fluoride and inert carrier gas into the tubular reactor, and reacting at 30-70 DEG C to obtain a reaction product; wherein the molar weight of the hydrogen fluoride is more than two times of the molar weight of the phosphorus oxyfluoride; 2, continuously introducing the reaction product in the step 1 into a gas-liquid separator for gas-liquid separation to obtain a liquid phase and a gas phase, and separating the gas phase to obtain phosphorus pentafluoride; and 3, continuously introducing the liquid phase into a pyrolysis unit, and carrying out dehydration pyrolysis to generate phosphorus pentafluoride. The method is a continuous reaction, high temperature and high pressure are not needed, the reaction is mild, and the purity and the yield of the obtained phosphorus pentafluoride are relatively high.

Description

Technical Field

[0001] The present invention relates to the field of phosphorus halides, and particularly to a method and system for continuously preparing phosphorus pentafluoride using a tubular reactor. Background Art

[0002] The production processes of phosphorus pentafluoride (PF5) mainly include the direct method and the indirect method. The direct method (such as the reaction of phosphorus pentachloride with hydrofluoric acid) is widely used in industrial production because of its simplicity and feasibility, but the reaction conditions need to be strictly controlled. The indirect method (such as decomposition through hexafluorophosphoric acid) has a higher yield and purity.

[0003] The reaction of phosphorus pentachloride with hydrofluoric acid to produce phosphorus pentafluoride (PCl5 + 5HF → PF5 + 5HCl) is a commonly used method in industrial production. The advantages of this method are easily available raw materials, simple process and easy control, but the reaction is highly exothermic and the reaction conditions need to be strictly controlled. The direct reaction of elemental phosphorus (such as red phosphorus or yellow phosphorus) with fluorine gas to produce phosphorus pentafluoride can obtain high-purity products, but the reaction is difficult to control and the production cost is relatively high.

[0004] Using phosphorus oxyfluoride and hydrogen fluoride to react to prepare phosphorus pentafluoride is a new technology that has emerged in the past two years. Specifically, it can be seen in: Publication No. CN115784181A, with the theme of a continuous reaction rectification preparation system for phosphorus pentafluoride and its preparation; this solution uses a continuous reaction rectification column and multi-stage pressurized rectification technology to carry out a liquid-liquid reaction between phosphorus oxyfluoride and hydrogen fluoride to prepare phosphorus pentafluoride.

[0005] This solution can directly produce phosphorus pentafluoride from phosphorus oxyfluoride. However, since the liquefaction temperature of phosphorus oxyfluoride under normal pressure is -39.4°C, this solution has to be produced under pressure. In order to ensure the production rate, it also needs to maintain a high temperature under pressure.

[0006] Therefore, the technical problem to be solved in this case is: how to reduce the process difficulty when using phosphorus oxyfluoride as a raw material to produce phosphorus pentafluoride. Summary of the Invention

[0007] The object of the present invention is to provide a method for continuously preparing phosphorus pentafluoride using a tubular reactor. In this method, a tubular reactor is first used to carry out a gas-gas reaction under normal pressure to obtain a gas product of phosphorus pentafluoride and a liquid product of hydrated hexafluorophosphoric acid. Then, after gas-liquid separation, hexafluorophosphoric acid hydrate is obtained. The hexafluorophosphoric acid hydrate undergoes dehydration pyrolysis to obtain phosphorus pentafluoride. The entire reaction system is a continuous reaction, without the need for high temperature and high pressure, the reaction is mild, and the obtained phosphorus pentafluoride has a high purity and yield.

[0008] At the same time, the present invention also discloses a system for realizing this method.

[0009] The specific solution of the present invention is as follows: A method for continuously preparing phosphorus pentafluoride by using a tubular reactor, the method comprising the following steps: Step 1: Add phosphorus oxyfluoride, hydrogen fluoride and an inert carrier gas into the tubular reactor, and react under the condition of 30-70 °C to obtain a reaction product; wherein, the molar amount of the hydrogen fluoride is more than twice the molar amount of the phosphorus oxyfluoride; Step 2: Continuously introduce the reaction product of Step 1 into a gas-liquid separator for gas-liquid separation to obtain a liquid phase and a gas phase, and separate phosphorus pentafluoride from the gas phase; Step 3: Continuously introduce the liquid phase into a pyrolysis unit for dehydration pyrolysis to produce phosphorus pentafluoride.

[0010] The present invention uses phosphorus oxyfluoride and hydrogen fluoride to react to generate phosphorus pentafluoride and hexafluorophosphoric acid hydrate. At the same time, the reaction product also contains an inert carrier gas, unreacted HF and phosphorus oxyfluoride. The chemical reaction equation is as follows: POF3 + 2HF → PF5 + H2O; POF3 + 3HF + H2O → HPF6·2H2O; By adopting the above continuous reaction method, the following advantages are obtained: 1. The reaction conditions become mild. By using a tubular reactor for gas-gas reaction, there is no need for pressurization or high temperature, and the process is controllable; 2. After gas-liquid separation, the liquid phase is continuously pumped into the pyrolysis unit for dehydration pyrolysis, and a truly continuous reaction of the whole process can be realized; In production, the condensate obtained from the gas phase of gas-liquid separation before condensing phosphorus pentafluoride can be directly recycled to Step 1 without purification treatment, reducing production costs; 3. The overall yield reaches more than 90%. Without purification, the purity of phosphorus pentafluoride reaches more than 99.5%.

[0011] In the above method for continuously preparing phosphorus pentafluoride by using a tubular reactor, the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:3-5.

[0012] In actual production, the amount of hydrogen fluoride can be further increased, but it will not bring any economic benefits or reaction results. After testing, when the molar ratio is 1:3.5-5, the yield can reach the peak, and most of the lost yield is generated in the pyrolysis part.

[0013] In the above method for continuously preparing phosphorus pentafluoride by using a tubular reactor, the inert carrier gas is nitrogen or argon; the molar ratio of the inert carrier gas to hydrogen fluoride is 3-5:1.

[0014] In the above method for continuously preparing phosphorus pentafluoride by using a tubular reactor, the gas-liquid separator includes a feed inlet, an exhaust outlet, and a liquid discharge outlet; the feed inlet is connected to the outlet of the tubular reactor; the exhaust outlet is connected to a first condenser, a second condenser, a first cold trap, and a first tail gas absorption device; the condensation temperature of the first condenser is -10 to -30 °C; the condensation temperature of the second condenser is -40 to -50 °C; the condensation temperature of the first cold trap is -96 to -110 °C; In step 2, the gas phase is sequentially treated by the first condenser, the second condenser, and the first cold trap; unreacted liquid hydrogen fluoride is separated from the first condenser; phosphorus pentafluoride is separated from the first cold trap; the liquid phase continuously enters step 3; The liquid hydrogen fluoride collected by the first condenser is used as the raw material for step 1 after being heated and vaporized.

[0015] In the above method for continuously preparing phosphorus pentafluoride by using a tubular reactor, the gas pyrolyzed by the pyrolysis unit is condensed once, twice, and three times to obtain phosphorus pentafluoride; The temperature of the first condensation is -10 to -30 °C; the temperature of the second condensation is -40 to -50 °C, and the temperature of the third condensation is -96 to -110 °C.

[0016] In the above method for continuously preparing phosphorus pentafluoride by using a tubular reactor, the temperature of the dehydration pyrolysis in step 3 is 130 to 150 °C.

[0017] In addition, the present invention also discloses a continuous reaction system for implementing the above method, including the tubular reactor, the gas-liquid separation unit, and the pyrolysis unit; the gas-liquid separation unit is used to perform gas-liquid separation on the reaction product obtained in the tubular reactor to obtain the gas phase and the liquid phase; the pyrolysis unit is used to dehydrate and pyrolyze the liquid phase to obtain phosphorus pentafluoride.

[0018] In the above continuous reaction system, the gas-liquid separation unit includes a gas-liquid separator; the gas-liquid separator includes a feed inlet, an exhaust outlet, and a liquid discharge outlet; the feed inlet is connected to the outlet of the tubular reactor; the exhaust outlet is connected to a first condenser, a second condenser, a first cold trap, and a first tail gas absorption device; The pyrolysis unit includes a pyrolysis kettle; a gas outlet is connected to the upper part of the pyrolysis kettle; the gas outlet is sequentially connected to a third condenser, a fourth condenser, a second cold trap, and a second tail gas absorption device; a feed pipe and a sulfur trioxide injection pipe are further provided on the pyrolysis kettle; a waste liquid discharge pipe is provided at the bottom of the pyrolysis kettle; the feed pipe is connected to the liquid discharge port of the gas-liquid separator.

[0019] In the above continuous reaction system, the length of the tubular reactor is 120 m and the pipe diameter is 20 mm.

[0020] In the above continuous reaction system, the condensation temperature of the first condenser is -10~-30°C; the condensation temperature of the second condenser is -40~-50°C; the condensation temperature of the first cold trap is -96~-110°C; the condensation temperature of the third condenser is -10~-30°C; the condensation temperature of the fourth condenser is -40~-50°C; the condensation temperature of the second cold trap is -96~-110°C.

[0021] The beneficial effects of this application are: The reaction conditions of the production process of the present invention are relatively mild, continuous production can be achieved, the purity of the phosphorus pentafluoride obtained by separation is relatively high, and the yield of phosphorus pentafluoride generally reaches more than 90%, providing an industrial production method for the production of phosphorus pentafluoride. Description of the Drawings

[0022] Figure 1 It is a flow chart of the system of the present invention. Detailed Embodiments

[0023] 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 not specifying specific conditions, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specifying the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0024] Before elaborating on the method of the present invention, the system involved in the present invention will be introduced first, and the subsequent examples and comparative examples will all use this system for production: Refer to Figure 1 , a continuous reaction system for implementing the above method, including a tubular reactor 1, a gas-liquid separation unit 2, and a pyrolysis unit 3; The mixture obtained from the tubular reactor 1 is subjected to gas-liquid separation through the gas-liquid separation unit 2 to obtain a gas phase and a liquid phase. The liquid phase is dehydrated and pyrolyzed through the pyrolysis unit 3 to obtain phosphorus pentafluoride, and phosphorus pentafluoride is separated from the gas phase.

[0025] Specifically, the specifications of the tubular reactor 1 are a length of 120 m and a pipe diameter of 20 mm; it is provided with an inlet for introducing phosphorus oxyfluoride gas, an inlet for introducing hydrogen fluoride gas, and an inlet for an inert carrier; the outside of the tubular reactor is provided with a temperature control jacket for controlling the temperature inside the tubular reactor to be in a relatively stable state. Generally, the allowable gas flow rate of this tubular reactor is 0.5 - 2 L / min; The gas-liquid separation unit 2 includes a gas-liquid separator 21; the gas-liquid separator 21 includes a feed inlet 22, an exhaust outlet 23, and a liquid discharge outlet 24; the feed inlet 22 is connected to the outlet of the tubular reactor 1; the exhaust outlet 23 is connected to a first condenser 25, a second condenser 26, a first cold trap 27, and a first tail gas absorption device 28; the condensation temperature of the first condenser 25 is -10 to -30 °C; the condensation temperature of the second condenser 26 is -40 to -50 °C; the condensation temperature of the first cold trap 27 is -96 to -110 °C; The reaction products of the tubular reactor 1 include: hydrated hexafluorophosphoric acid, phosphorus pentafluoride, inert carrier gas, unreacted hydrogen fluoride, trace amounts of phosphorus oxyfluoride, etc.; after gas-liquid separation, the hydrated hexafluorophosphoric acid is separated out, and other gas components will enter the first condenser 25; the substance condensed in the first condenser 25 is liquid hydrogen fluoride, trace amounts of phosphorus oxyfluoride will be separated out in the second condenser 26, and finally the material condensed in the cold trap is phosphorus pentafluoride; other gases are discharged after being absorbed by the first tail gas absorption device 28; The pyrolysis unit 3 includes a pyrolysis kettle 31; since hexafluorophosphoric acid has strong corrosiveness, a corrosion-resistant lining needs to be used; the upper part of the pyrolysis kettle 31 is connected with a gas outlet; the gas outlet is successively connected with a third condenser 32, a fourth condenser 33, a second cold trap 34, and a second tail gas absorption device 35; the pyrolysis kettle 31 is also provided with a feed pipe 38 and a sulfur trioxide injection pipe 36; the bottom of the pyrolysis kettle 31 is provided with a waste liquid discharge pipe 37; the feed pipe 38 is connected to the liquid discharge outlet 24 of the gas-liquid separator 21; the condensation temperature of the third condenser 32 is -10 to -30 °C; the condensation temperature of the fourth condenser 33 is -40 to -50 °C; the condensation temperature of the second cold trap 34 is -96 to -110 °C.

[0026] The third condenser 32 is used to condense hydrogen fluoride, and the condensed hydrogen fluoride needs to be purified before being recycled to step 1; other impurities except phosphorus pentafluoride and non-condensable gases are condensed in the fourth condenser 33; the second cold trap 34 is used to recover phosphorus pentafluoride, and the remaining gases are discharged after being absorbed by the second tail gas absorption device 35.

[0027] In the present invention, the loss of phosphorus mainly occurs during the dehydration pyrolysis process. The present invention is a continuous reaction system, and the pyrolysis kettle 31 is produced by maintaining a method of feeding while discharging waste liquid. During this process, a small amount of phosphorus source, that is, a small amount of hexafluorophosphoric acid, will be discharged with the waste liquid. From the perspective of production economy, the loss of a small amount of materials is completely acceptable compared to the production benefits brought by continuous production.

[0028] Example 1 A method for continuously preparing phosphorus pentafluoride using a tubular reactor, the method comprising the following steps: Step 1: Add phosphorus oxytetrafluoride, excessive hydrogen fluoride, and an inert carrier gas into the tubular reactor and react under the condition of 50°C; The molar ratio of phosphorus oxytetrafluoride to hydrogen fluoride is 1:3; the inert carrier gas is nitrogen, and the molar ratio of nitrogen to hydrogen fluoride is 4:1; in the tubular reactor, the flow rate of the mixed gas composed of phosphorus oxytetrafluoride, hydrogen fluoride, and the inert carrier gas is 1 L / min.

[0029] Step 2: Continuously introduce the reaction product of Step 1 into a gas-liquid separator for gas-liquid separation to obtain a liquid phase and a gas phase. The gas phase is sequentially treated by a first condenser, a second condenser, and a first cold trap. Unreacted liquid hydrogen fluoride is separated from the first condenser; phosphorus pentafluoride is separated from the first cold trap; the liquid phase continuously enters Step 3; Step 3: Continuously introduce the liquid phase into a pyrolysis unit for dehydration pyrolysis to produce phosphorus pentafluoride; The pyrolysis temperature is 130°C; sulfur trioxide is continuously fed, and its molar amount and the molar amount of phosphorus oxytetrafluoride in Step 1 are maintained at 1:1. The bottom of the pyrolysis kettle continuously discharges liquid to keep the liquid level in the pyrolysis kettle at a height of about 30%; The pyrolysis produces the following products: sulfur trioxide and water form sulfuric acid, and the kettle maintains a state of fuming sulfuric acid. Hydrated hexafluorophosphoric acid decomposes under the action of sulfur trioxide to produce hydrogen fluoride and phosphorus pentafluoride.

[0030] The third condenser mainly condenses to produce liquid hydrogen fluoride, and this part of hydrogen fluoride needs to be purified before being recycled to Step 1; the second cold trap recovers phosphorus pentafluoride.

[0031] Example 2 Generally the same as Example 1, the difference is that: in Step 1, the reaction temperature of the tubular reactor is 30°C; the molar ratio of phosphorus oxytetrafluoride to hydrogen fluoride is 1:4; the molar ratio of nitrogen to hydrogen fluoride is 3:1; in the tubular reactor, the flow rate of the mixed gas composed of phosphorus oxytetrafluoride, hydrogen fluoride, and the inert carrier gas is 1.06 L / min.

[0032] In Step 3, the heating temperature of the reaction kettle is 140°C.

[0033] Example 3 Generally the same as Example 1, the differences are as follows: In step 1, the reaction temperature of the tubular reactor is 70 °C; the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:3.5; the molar ratio of nitrogen to hydrogen fluoride is 5:1; in the tubular reactor, the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride, and inert carrier gas is 0.94 L / min.

[0034] In step 3, the heating temperature of the reaction kettle is 150 °C.

[0035] Example 4 Generally the same as Example 1, the differences are that the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:5; in the tubular reactor, the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride, and inert carrier gas is 0.98 L / min.

[0036] Example 5 Generally the same as Example 1, the differences are that the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:2; in the tubular reactor, the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride, and inert carrier gas is 1.03 L / min.

[0037] Performance Detection The purity detection 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, the purity can be qualitatively judged.

[0038] Operation steps: Place the phosphorus pentafluoride sample in the gas cell sample, 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 peaks, and determine whether there are impurity absorption peaks to evaluate the purity.

[0039] The purity of phosphorus pentoxide in each of the above examples exceeds 99.5%.

[0040] The calculation method of the yield of phosphorus pentafluoride is: The yield of step 2 = M1 * 100% / M; The yield of step 3 = M2 * 100% / M; M1 is the molar amount of phosphorus pentafluoride collected by the first cold trap in step 2; M2 is the molar amount of phosphorus pentafluoride collected by the second cold trap in step 3; M is the molar amount of phosphorus oxyfluoride, M = 1 mol.

[0041] The yield of phosphorus pentafluoride can be seen in Table 1 below; Table 1 Yield Table

[0042] Result analysis:

[0043] 1. As can be seen from Examples 1 to 4, when the molar ratio of HF to phosphorus oxyfluoride reaches 3:1 or more, its overall yield has little fluctuation; when the molar ratio reaches 2 or less, the overall yield decreases significantly; too little HF cannot achieve the complete reaction of phosphorus oxyfluoride.

[0044] 2. The purity of phosphorus pentafluoride of the present invention is relatively high. The main reason is that the reaction raw materials of the present invention are relatively single, the reaction process is mild, no by-products are generated, and the condensation temperatures of other impurities of phosphorus pentafluoride vary greatly, and the purity of the separated product is relatively high.

[0045] 3. By using a tubular reactor, the present invention combines phosphorus oxyfluoride and gaseous hydrogen fluoride, and combines liquid separation and dehydration pyrolysis operations to increase the overall yield of phosphorus pentafluoride to more than 95%.

[0046] The reaction of the present invention realizes a fully continuous reaction for directly producing phosphorus pentafluoride, the reaction conditions are mild, and both the yield and purity are relatively high.

Claims

1. A method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, characterized in that, The method includes the following steps: Step 1: Phosphorus oxyfluoride, hydrogen fluoride and an inert carrier gas are added into a tubular reactor and reacted under the condition of 30-70°C to obtain a reaction product; the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:3-5; Step 2: The reaction product obtained in Step 1 is continuously introduced into a gas-liquid separator for gas-liquid separation to obtain a liquid phase and a gas phase, and phosphorus pentafluoride is separated from the gas phase; Step 3: The liquid phase is continuously introduced into a pyrolysis unit for dehydration pyrolysis to produce phosphorus pentafluoride.

2. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 1, wherein The inert carrier gas is nitrogen or argon; the molar ratio of the inert carrier gas to hydrogen fluoride is 3-5:

1.

3. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 1, wherein The gas-liquid separator includes a feed inlet, an exhaust outlet and a drain outlet; the feed inlet is connected to the outlet of the tubular reactor; the exhaust outlet is connected with a first condenser, a second condenser, a first cold trap and a first tail gas absorption device; the condensation temperature of the first condenser is -10~-30°C; the condensation temperature of the second condenser is -40~-50°C; the condensation temperature of the first cold trap is -96~-110°C; In Step 2, the gas phase is sequentially treated by the first condenser, the second condenser and the first cold trap; Unreacted liquid hydrogen fluoride is separated from the first condenser; Phosphorus pentafluoride is separated from the first cold trap; the liquid phase continuously enters Step 3; The liquid hydrogen fluoride collected by the first condenser is used as the raw material for Step 1 after being heated and vaporized.

4. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 3, characterized in that, The gas after pyrolysis in the pyrolysis unit is condensed once, twice and three times to obtain phosphorus pentafluoride; The temperature of the first condensation is -10~-30°C; the temperature of the second condensation is -40~-50°C, and the temperature of the third condensation is -96~-110°C.

5. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 4, wherein The temperature of the dehydration pyrolysis in Step 3 is 130~150°C.

6. A continuous reaction system for implementing the method according to any one of claims 1 to 5, characterized in that, It includes the tubular reactor, the gas-liquid separation unit and the pyrolysis unit; The gas-liquid separation unit is used to perform gas-liquid separation on the reaction product obtained in the tubular reactor to obtain the gas phase and the liquid phase; the pyrolysis unit is used to obtain phosphorus pentafluoride after dehydrating and pyrolyzing the liquid phase.

7. The continuous reaction system according to claim 6, characterized in that, The gas-liquid separation unit includes a gas-liquid separator; the gas-liquid separator includes a feed inlet, an exhaust outlet and a drain outlet; the feed inlet is connected to the outlet of the tubular reactor; the exhaust outlet is connected with a first condenser, a second condenser, a first cold trap and a first tail gas absorption device; The pyrolysis unit includes a pyrolysis kettle; the upper part of the pyrolysis kettle is connected with a gas outlet; the gas outlet is sequentially connected with a third condenser, a fourth condenser, a second cold trap and a second tail gas absorption device; a feed pipe and a sulfur trioxide injection pipe are also provided on the pyrolysis kettle; a waste liquid discharge pipe is provided at the bottom of the pyrolysis kettle; the feed pipe is connected to the drain outlet of the gas-liquid separator.

8. The continuous reaction system according to claim 7, characterized in that, The length of the tubular reactor is 120m and the pipe diameter is 20mm.

9. The continuous reaction system according to claim 7, wherein The condensation temperature of the first condenser is -10~-30°C; the condensation temperature of the second condenser is -40~-50°C; the condensation temperature of the first cold trap is -96~-110°C; the condensation temperature of the third condenser is -10~-30°C; the condensation temperature of the fourth condenser is -40~-50°C; the condensation temperature of the second cold trap is -96~-110°C.

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