Method and system for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor

Abstract

The present invention belongs to the field of phosphorus halides and discloses a method and system for preparing phosphorus pentafluoride through a continuous reaction using a tubular reactor. The method comprises the following steps: Step 1: adding phosphorus oxytrifluoride, hydrogen fluoride, and an inert carrier gas to a tubular reactor and reacting them at 30-70°C to obtain a reaction product; wherein the molar amount of the hydrogen fluoride is at least twice the molar amount of the phosphorus oxytrifluoride; Step 2: continuously introducing the reaction product from Step 1 into a gas-liquid separator for gas-liquid separation to obtain a liquid phase and a gas phase, and separating phosphorus pentafluoride from the gas phase; Step 3: continuously introducing the liquid phase into a pyrolysis unit for dehydration and pyrolysis to produce phosphorus pentafluoride. This method is a continuous reaction, does not require high temperature or high pressure, has a mild reaction temperature, and produces phosphorus pentafluoride with high purity and yield.

Description

Technical Field

[0001] The present invention relates to the field of phosphorus halides, and in particular to a method and system for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor. Background Art

[0002] Phosphorus pentafluoride (PF5) production processes primarily include direct and indirect methods. Direct methods (such as the reaction of phosphorus pentachloride with hydrofluoric acid) are widely used in industrial production due to their simplicity, but require strict control of reaction conditions. Indirect methods (such as the decomposition of hexafluorophosphoric acid) offer higher yields and purity.

[0003] The reaction of phosphorus pentachloride with hydrofluoric acid to produce phosphorus pentafluoride (PCl5 + 5HF → PF5 + 5HCl) is a common method used in industrial production. This method offers advantages such as readily available raw materials, a simple process, and ease of control. However, the reaction is highly exothermic, requiring strict control of reaction conditions. Direct reaction of elemental phosphorus (such as red or yellow phosphorus) with fluorine gas to produce phosphorus pentafluoride can yield a high-purity product, but the reaction is difficult to control and carries high production costs.

[0004] The preparation of phosphorus pentafluoride by the reaction of phosphorus oxytrifluoride and hydrogen fluoride is a new technology that has emerged in the past two years. For details, see:

[0005] Publication number CN115784181A is a continuous reactive distillation system for preparing phosphorus pentafluoride and its preparation. The system uses a continuous reactive distillation tower and multi-stage pressurized distillation technology to produce phosphorus pentafluoride by liquid-liquid reaction with phosphorus oxytrifluoride and hydrogen fluoride.

[0006] This solution can directly produce phosphorus pentafluoride through phosphorus oxytrifluoride. However, since the liquefaction temperature of phosphorus oxytrifluoride at normal pressure is -39.4°C, this solution has to adopt a pressurized production method. In order to ensure the production rate, it also needs to maintain a high temperature under pressurization.

[0007] Therefore, the technical problem that needs to be solved in this case is: how to reduce the process difficulty when producing phosphorus pentafluoride using phosphorus oxytrifluoride as raw material. Summary of the Invention

[0008] The present invention aims to provide a method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor. The method first adopts a tubular reactor to carry out a gas-gas reaction at normal pressure to obtain a gaseous product of phosphorus pentafluoride and a liquid product of hydrated hexafluorophosphoric acid. Then, hexafluorophosphoric acid hydrate is obtained after gas-liquid separation. The hexafluorophosphoric acid hydrate is dehydrated and pyrolyzed to obtain phosphorus pentafluoride. The entire reaction system is a continuous reaction, does not require high temperature and high pressure, and has a mild reaction. The obtained phosphorus pentafluoride has high purity and high yield.

[0009] At the same time, the invention also discloses a system for realizing the method.

[0010] The specific scheme of the present invention is:

[0011] A method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the method comprising the following steps:

[0012] Step 1: adding phosphorus oxytrifluoride, hydrogen fluoride, and an inert carrier gas into a tubular reactor and reacting them at 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 oxytrifluoride;

[0013] Step 2: continuously introducing 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 separating phosphorus pentafluoride from the gas phase;

[0014] Step 3: continuously introducing the liquid phase into a pyrolysis unit for dehydration pyrolysis to produce phosphorus pentafluoride.

[0015] The present invention uses phosphorus oxytrifluoride and hydrogen fluoride to react to generate phosphorus pentafluoride and hydrated hexafluorophosphoric acid. The reaction product also contains an inert carrier gas, unreacted HF and phosphorus oxytrifluoride. The chemical reaction equation is:

[0016] POF3+2HF→PF5+H2O;

[0017] POF3+3HF+H2O→HPF6·2H2O;

[0018] By adopting the above-mentioned continuous reaction method, the following advantages are achieved:

[0019] 1. The reaction conditions become milder. By using a tubular reactor for gas-gas reaction, no pressure or high temperature is required, and the process is controllable.

[0020] 2. After gas-liquid separation, the liquid phase is continuously pumped into the pyrolysis unit for dehydration and pyrolysis, which can achieve a truly continuous reaction of the entire process;

[0021] In production, the condensate obtained during the gas-liquid separation and the condensation of phosphorus pentafluoride is directly recycled to step 1 without purification, thereby reducing production costs.

[0022] 3. The overall yield reached over 90%, and the purity of phosphorus pentafluoride reached over 99.5% without purification.

[0023] In the above-mentioned method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the molar ratio of phosphorus oxytrifluoride to hydrogen fluoride is 1:3-5.

[0024] 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 its peak, and most of the lost yield occurs in the pyrolysis part.

[0025] In the above-mentioned method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the inert carrier gas is nitrogen or argon; and the molar ratio of the inert carrier gas to hydrogen fluoride is 3-5:1.

[0026] In the above-mentioned method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the gas-liquid separator includes a feed port, an exhaust port, and a liquid discharge port; the feed port is connected to the outlet of the tubular reactor; the exhaust port 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; and the condensation temperature of the first cold trap is -96 to -110°C;

[0027] In step 2, the gas phase is sequentially processed through 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; and the liquid phase continuously enters step 3;

[0028] The liquid hydrogen fluoride collected by the first condenser is heated and vaporized and then used as the raw material of step 1.

[0029] In the above-mentioned method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the gas after pyrolysis in the pyrolysis unit is subjected to primary condensation, secondary condensation, and tertiary condensation to obtain phosphorus pentafluoride;

[0030] The temperature of the primary condensation is -10 to -30°C; the temperature of the secondary condensation is -40 to -50°C; and the temperature of the tertiary condensation is -96 to -110°C.

[0031] In the above-mentioned method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the temperature of the dehydration pyrolysis in step 3 is 130-150°C.

[0032] In addition, the present invention also discloses a continuous reaction system for implementing the above-mentioned method, comprising 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.

[0033] In the above-mentioned continuous reaction system, the gas-liquid separation unit includes a gas-liquid separator; the gas-liquid separator includes a feed port, an exhaust port and a liquid discharge port; the feed port is connected to the outlet of the tubular reactor; the exhaust port is connected to a first condenser, a second condenser, a first cold trap and a first tail gas absorption device;

[0034] The pyrolysis unit includes a pyrolysis kettle; the upper part of the pyrolysis kettle is connected to a gas outlet; the gas outlet is sequentially connected to a third condenser, a fourth condenser, a second cold trap, and a second tail gas absorption device; the pyrolysis kettle is also provided with a feed pipe and a sulfur trioxide filling pipe; the bottom of the pyrolysis kettle is provided with a waste liquid discharge pipe; the feed pipe is connected to the discharge port of the gas-liquid separator.

[0035] In the above continuous reaction system, the length of the tubular reactor is 120 m and the diameter is 20 mm.

[0036] In the above-mentioned continuous reaction system, the condensing temperature of the first condenser is -10~-30°C; the condensing temperature of the second condenser is -40~-50°C; the condensing temperature of the first cold trap is -96~-110°C; the condensing temperature of the third condenser is -10~-30°C; the condensing temperature of the fourth condenser is -40~-50°C; and the condensing temperature of the second cold trap is -96~-110°C.

[0037] The beneficial effects of this application are:

[0038] The production process of the present invention has relatively mild reaction conditions and can realize continuous production. The phosphorus pentafluoride obtained by separation has high purity and the yield of phosphorus pentafluoride generally reaches more than 90%. An industrial production method is proposed for the production of phosphorus pentafluoride. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Flowchart of the system of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be described clearly and completely below in conjunction with the examples of the present invention. In the description of the present invention, it should be noted that, where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer were used. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0041] Before describing the method of the present invention, the system involved in the present invention is first introduced. The subsequent embodiments and comparative examples are all produced using this system:

[0042] refer to Figure 1, a continuous reaction system for implementing the above method, comprising a tubular reactor 1, a gas-liquid separation unit 2, and a pyrolysis unit 3;

[0043] The mixture obtained from the tubular reactor 1 is subjected to gas-liquid separation in the gas-liquid separation unit 2 to obtain a gas phase and a liquid phase. The liquid phase is dehydrated and pyrolyzed in the pyrolysis unit 3 to obtain phosphorus pentafluoride, and phosphorus pentafluoride is separated from the gas phase.

[0044] Specifically, the tubular reactor 1 is 120 meters long and 20 mm in diameter. It is equipped with inlets for phosphorus oxyfluoride gas, hydrogen fluoride gas, and an inlet for an inert carrier. A temperature-controlled jacket is installed on the outside of the tubular reactor to maintain a relatively stable temperature. Generally, the permissible gas flow rate of the tubular reactor is 0.5 to 2 L / min.

[0045] The gas-liquid separation unit 2 includes a gas-liquid separator 21; the gas-liquid separator 21 includes a feed port 22, an exhaust port 23, and a drain port 24; the feed port 22 is connected to the outlet of the tubular reactor 1; the exhaust port 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; and the condensation temperature of the first cold trap 27 is -96 to -110°C.

[0046] The reaction products of the tubular reactor 1 include: hydrated hexafluorophosphoric acid, phosphorus pentafluoride, inert carrier gas, unreacted hydrogen fluoride, trace amounts of phosphorus oxytrifluoride, etc. After gas-liquid separation, the hydrated hexafluorophosphoric acid is separated, and the other gas components enter the first condenser 25. The substance condensed in the first condenser 25 is liquid hydrogen fluoride, and the trace amounts of phosphorus oxytrifluoride are separated in the second condenser 26. Finally, the material entered the cold trap and condensed to obtain phosphorus pentafluoride. The other gases are absorbed by the first tail gas absorption device 28 and then discharged.

[0047] The pyrolysis unit 3 includes a pyrolysis kettle 31; since hexafluorophosphoric acid is highly corrosive, a corrosion-resistant bushing is required; a gas outlet is connected to the top of the pyrolysis kettle 31; the gas outlet is sequentially connected to a third condenser 32, a fourth condenser 33, a second cold trap 34, and a second tail gas absorption device 35; a feed pipe 38 and a sulfur trioxide filling pipe 36 are also provided on the pyrolysis kettle 31; a waste liquid discharge pipe 37 is provided at the bottom of the pyrolysis kettle 31; the feed pipe 38 is connected to the discharge port 24 of the gas-liquid separator 21; the condensation temperature of the third condenser 32 is -10~-30°C; the condensation temperature of the fourth condenser 33 is -40~-50°C; and the condensation temperature of the second cold trap 34 is -96~-110°C.

[0048] The third condenser 32 is used to condense hydrogen fluoride, and the condensed hydrogen fluoride needs to be purified before it can be reused in step 1; in the fourth condenser 33, other impurities except phosphorus pentafluoride and non-condensable gases are condensed; the second cold trap 34 is used to recover phosphorus pentafluoride, and the remaining gas is absorbed by the second tail gas absorption device 35 and then discharged.

[0049] In the present invention, phosphorus loss primarily occurs during the dehydration pyrolysis process. This is a continuous reaction system, with the pyrolysis kettle 31 continuously feeding and discharging waste liquid. During this process, a small amount of the phosphorus source, namely hexafluorophosphoric acid, is discharged with the waste liquid. From a production economics perspective, this small amount of material loss is completely acceptable compared to the production benefits brought about by continuous production.

[0050] Example 1

[0051] A method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, the method comprising the following steps:

[0052] Step 1: adding phosphorus oxytrifluoride, excess hydrogen fluoride and an inert carrier gas into a tubular reactor and reacting at 50°C;

[0053] The molar ratio of phosphorus oxyfluoride 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 oxyfluoride, hydrogen fluoride and inert carrier gas is 1 L / min.

[0054] Step 2: The reaction product of step 1 is continuously introduced into a gas-liquid separator for gas-liquid separation to obtain a liquid phase and a gas phase. The gas phase is sequentially processed through 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; and the liquid phase continuously enters step 3.

[0055] Step 3: continuously introducing the liquid phase into a pyrolysis unit for dehydration pyrolysis to produce phosphorus pentafluoride;

[0056] The pyrolysis temperature is 130°C; sulfur trioxide is kept fed, and its molar amount is kept at 1:1 with the molar amount of phosphorus oxyfluoride in step 1, and the bottom of the pyrolysis kettle is continuously drained to keep the liquid level in the pyrolysis kettle at a height of about 30%;

[0057] The following products are produced by thermal decomposition: sulfur trioxide and water form sulfuric acid, and the kettle remains in the state of fuming sulfuric acid. Hydrated hexafluorophosphoric acid decomposes under the action of sulfur trioxide to produce hydrogen fluoride and phosphorus pentafluoride.

[0058] The third condenser mainly condenses to produce liquid hydrogen fluoride, which needs to be purified before it can be reused in step 1; the second cold trap recovers phosphorus pentafluoride.

[0059] Example 2

[0060] The process is substantially the same as in Example 1, except that: in step 1, the reaction temperature of the tubular reactor is 30° C.; the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:4; the molar ratio of nitrogen to hydrogen fluoride is 3:1; and the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride, and inert carrier gas in the tubular reactor is 1.06 L / min.

[0061] In step 3, the heating temperature of the reactor is 140°C.

[0062] Example 3

[0063] The process is substantially the same as in Example 1, except that: 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; and the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride, and inert carrier gas in the tubular reactor is 0.94 L / min.

[0064] In step 3, the heating temperature of the reactor is 150°C.

[0065] Example 4

[0066] The process is substantially the same as Example 1, except that the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:5; and the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride and inert carrier gas in the tubular reactor is 0.98 L / min.

[0067] Example 5

[0068] The process is substantially the same as Example 1, except that the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:2; and the flow rate of the mixed gas composed of phosphorus oxyfluoride, hydrogen fluoride and inert carrier gas in the tubular reactor is 1.03 L / min.

[0069] Performance testing

[0070] The purity test methods for phosphorus pentafluoride are: infrared spectroscopy;

[0071] 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.

[0072] Steps:

[0073] A phosphorus pentafluoride sample gas cell is scanned using an infrared spectrometer and its infrared spectrum is recorded. The measured spectrum is compared with the infrared spectrum of standard phosphorus pentafluoride to analyze the position and intensity of the absorption peaks to determine whether there are impurity absorption peaks, thereby evaluating the purity.

[0074] The purity of the phosphorus pentoxide in the above embodiments exceeds 99.5%.

[0075] The calculation method of the yield of phosphorus pentafluoride is:

[0076] Yield of step 2 = M1*100% / M;

[0077] Yield of step 3 = M2*100% / M;

[0078] M1 is the molar amount of phosphorus pentafluoride collected by the first cold trap in step 2;

[0079] M2 is the molar amount of phosphorus pentafluoride collected by the second cold trap in step 3;

[0080] M is the molar amount of phosphorus oxytrifluoride, M=1 mol.

[0081] The yield of phosphorus pentafluoride can be seen in Table 1 below;

[0082] Table 1 Yield

[0083]

[0084] Result analysis:

[0085] 1. As can be seen from Examples 1 to 4, when the molar ratio of HF to phosphorus oxytrifluoride reaches 3:1 or above, the overall yield has little fluctuation; when the molar ratio reaches 2 or below, the overall yield is significantly reduced; too little HF cannot achieve complete reaction of phosphorus oxytrifluoride.

[0086] 2. The phosphorus pentafluoride of the present invention has a high purity. The main reasons are that the reaction raw materials of the present invention are relatively simple, the reaction process is mild, no by-products are generated, and the condensation temperatures of other impurities in phosphorus pentafluoride vary greatly, so the separated product has a high purity.

[0087] 3. The present invention uses a tubular reactor, phosphorus oxyfluoride and gaseous hydrogen fluoride, and combines liquid separation and dehydration pyrolysis operations to increase the comprehensive yield of phosphorus pentafluoride to over 95%.

[0088] The reaction of the invention realizes a fully continuous reaction for directly producing phosphorus pentafluoride, has mild reaction conditions, and has high yield and purity.

Claims

1. A method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor, characterized in that: The method comprises the following steps: Step 1: adding phosphorus oxyfluoride, hydrogen fluoride, and an inert carrier gas into a tubular reactor and reacting at 30-70° C. to obtain a reaction product; the molar ratio of phosphorus oxyfluoride to hydrogen fluoride is 1:3-5; the tubular reactor does not need to be pressurized; Step 2: continuously introducing 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 separating phosphorus pentafluoride from the gas phase; Step 3: continuously introducing the liquid phase into a pyrolysis unit for dehydration and pyrolysis to produce phosphorus pentafluoride; The gas-liquid separator includes a feed port, an exhaust port and a liquid discharge port; The feed port is connected to the outlet of the tubular reactor; the exhaust port 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; and the condensation temperature of the first cold trap is -96 to -110°C; In the step 2, the gas phase is sequentially processed through the first condenser, the second condenser, and the first cold trap; Separating unreacted liquid hydrogen fluoride 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 heated and vaporized and then used as the raw material of step 1.

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

1.

3. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 1, characterized in that: The gas produced by the pyrolysis unit is condensed once, twice, and three times to obtain phosphorus pentafluoride; The temperature of the primary condensation is -10 to -30°C; the temperature of the secondary condensation is -40 to -50°C; and the temperature of the tertiary condensation is -96 to -110°C.

4. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 3, characterized in that: The temperature of the dehydration pyrolysis in step 3 is 130-150°C.

5. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 1, characterized in that: The implementation of the method relies on a continuous reaction system, which includes the tubular reactor, the gas-liquid separation unit, and the pyrolysis unit; The gas-liquid separation unit is used to separate the reaction product obtained in the tubular reactor into gas and liquid 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.

6. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 5, characterized in that: The gas-liquid separation unit includes the gas-liquid separator; The pyrolysis unit includes a pyrolysis kettle; the upper part of the pyrolysis kettle is connected to a gas outlet; the gas outlet is sequentially connected to a third condenser, a fourth condenser, a second cold trap, and a second tail gas absorption device; the pyrolysis kettle is also provided with a feed pipe and a sulfur trioxide filling pipe; the bottom of the pyrolysis kettle is provided with a waste liquid discharge pipe; the feed pipe is connected to the discharge port of the gas-liquid separator.

7. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 6, characterized in that: The length of the tubular reactor is 120 m and the diameter is 20 mm.

8. The method for preparing phosphorus pentafluoride by continuous reaction using a tubular reactor according to claim 6, characterized in that: The condensation temperature of the third condenser is -10~-30°C; the condensation temperature of the fourth condenser is -40~-50°C; and the condensation temperature of the second cold trap is -96~-110°C.

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