A method for preparing phosphorus pentafluoride gas

Abstract

The present invention discloses a method for preparing phosphorus pentafluoride gas, comprising the following steps: (1) reacting a phosphorus-containing compound with hydrogen fluoride and an organic acid anhydride dehydrating agent to generate a hexafluorophosphoric acid solution; and (2) heating the hexafluorophosphoric acid solution to decompose it into gaseous hydrogen fluoride and phosphorus pentafluoride. The method has high water removal efficiency, simple process, and is easy to be continuously produced.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for preparing phosphorus pentafluoride gas. Background Art

[0002] Phosphorus pentafluoride (PF5) is a colorless, odorless gas under normal conditions, with a melting point of -93.78°C and a boiling point of -84.5°C. As a fluorinating agent, PF5 can transfer ions and is widely used in the electronics industry, battery manufacturing, polymer materials, and catalysts. Currently, lithium hexafluorophosphate (LiPF6) has become the mainstream electrolyte salt for lithium-ion batteries. Using PF5 as a raw material allows the production of high-performance LiPF6.

[0003] The preparation methods of PF5 are divided into direct method and indirect method. The direct method generally uses toxic and highly corrosive raw materials such as hydrogen fluoride (HF) and fluorine (F2). Among them, the method of preparing PF5 by reacting HF and phosphorus pentachloride (PCl5) has been industrialized. Due to the strong exothermic reaction, the reaction temperature must be strictly controlled, otherwise it will cause an explosion. In addition, PCl5 is easy to volatilize and cause pipeline blockage, and the by-product hydrogen chloride (HCl) and PF5 have similar boiling points, so the separation energy consumption is large. The indirect method first generates intermediate products such as phosphorus oxyfluoride (POF3) and hexafluorophosphoric acid (HPF6) and then prepares PF5. Patent CN101570328B A method for preparing LiPF6 was developed, which first reacts anhydrous hydrogen fluoride (AHF) with phosphorus pentoxide (P2O5) to produce HPF6, then adds fuming sulfuric acid to the HPF6 solution under cooling and stirring to produce PF5, and finally reacts with lithium fluoride (LiF) to produce LiPF6. This method avoids the disadvantage of the direct method for producing PF5, which is difficult to control at high temperature, but still has the following problems: (1) The reaction between phosphorus pentoxide and HF is highly exothermic, and the temperature of the reaction system needs to be maintained at around 0°C, so HF needs to be added slowly to avoid the reaction being highly exothermic, which also results in a long reaction time of 3-5 hours; (2 ) Fuming sulfuric acid is used as a dehydrating agent in the dehydration stage. In order to maintain the moderate viscosity of fuming sulfuric acid for easy operation, fuming sulfuric acid above 25°C is often added, which will cause the excess HF in the system to boil locally and the generated hexafluorophosphoric acid to decompose prematurely to produce phosphorus pentafluoride, resulting in a decrease in the yield of phosphorus pentafluoride; (3) Fuming sulfuric acid will react with HF to produce stable fluorosulfonic acid (FHO3S). Therefore, SO3 must be added after most of HF reacts with P2O5 to produce HPF6 to remove water and minimize the loss of F element. This also results in an increase in the number of reaction steps and a corresponding extension of the reaction time; (4) FHO3S and HF are both strongly corrosive acids. The strong decomposition of hexafluorophosphate will produce a small amount of SO3 when it decomposes hexafluorophosphate at high temperature to produce PF5. The subsequent SO3 will crystallize in the pipeline and block the pipeline during the condensation operation. Patent CN101570326B discloses a preparation method of lithium hexafluorophosphate. Its preparation process is similar to that of the above-mentioned patent CN101570328B, except that the raw material phosphorus pentoxide is replaced by concentrated phosphoric acid. Since the heat release of the reaction between concentrated phosphoric acid and HF is less than that of the reaction between phosphorus pentoxide and HF, the reaction time is shortened to 2h. However, fuming sulfuric acid is still required for subsequent treatment, which has similar problems to the above-mentioned patent CN101570328B.

[0004] Sulfur trioxide is an inorganic anhydride that reacts with water as follows: SO3( l ) + H2O( l ) = H2SO4( l) + 90.21 kJ, and this reaction is commonly used to prepare sulfuric acid. Organic anhydrides can also react with water to form the corresponding carboxylic acids. This reaction proceeds easily under the catalysis of a base or acid. Lower anhydrides can be hydrolyzed smoothly without acid or base catalysis, and the addition of an acid or base can increase the hydrolysis rate. The hydrolysis equation for symmetrical anhydrides is as follows: (RCO)2O + H2O → 2RCO2H. For example, the hydrolysis equation for acetic anhydride is: H3COOOCCH3 + H2O = 2CH3COOH + 39.9 kJ; the hydrolysis equation for propionic anhydride is: (C2H5CO)2O + H2O = 2C2H5COOH + 37.3 kJ. It can be seen that, on the one hand, the thermal effect of the reaction between organic anhydrides and water is smaller than that of the reaction between SO3 and water, making the reaction easier to control. On the other hand, organic anhydrides do not react with HF and can therefore be added with HF. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems of complex production process and poor reaction control of the existing indirect method for producing phosphorus pentafluoride, and to provide a method for preparing phosphorus pentafluoride with simple reaction and easy control.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the present invention provides a method for preparing phosphorus pentafluoride gas, comprising the following steps: (1) reacting a phosphorus-containing compound with hydrogen fluoride and an organic anhydride dehydrating agent to generate a hexafluorophosphoric acid solution; in this process, the organic anhydride dehydrating agent not only acts as a dehydrating agent to remove water generated by the reaction of the phosphorus-containing compound and hydrogen fluoride, but also can "dilute" the concentration of the phosphorus-containing compound when added before the reaction of the phosphorus-containing compound and hydrogen fluoride, making the phosphorus-containing compound more fluid. While diluting the concentration of the phosphorus-containing compound, it also undoubtedly increases the volume of the reaction solution, so that the reaction heat generated when hydrogen fluoride is subsequently added for reaction can be removed more quickly; at the same time, since the addition of hydrogen fluoride makes the entire solution system acidic, it is also conducive to accelerating the hydrolysis rate of the organic anhydride dehydrating agent and shortening the dehydration reaction time; (2) heating the hexafluorophosphoric acid solution to decompose it into gaseous hydrogen fluoride and phosphorus pentafluoride; in the decomposition process, the HF, organic anhydride, organic acid, etc. contained in the system are high-boiling-point substances, which are easily separated from the generated PF5, reducing the subsequent separation energy consumption.

[0007] Compared with the prior art, the present invention has the following advantages: (1) the use of an organic acid anhydride dehydrating agent results in a smaller heat effect than SO3, making the reaction easier to control; (2) the organic acid anhydride dehydrating agent can be added before the reaction of the phosphorus-containing compound with hydrogen fluoride, thereby achieving simultaneous dehydration during the reaction and improving production efficiency; (3) the addition of the organic acid anhydride dehydrating agent regulates the fluidity of the phosphorus-containing compound, thereby improving the thermal conductivity of the system; (4) the organic acid anhydride dehydrating agent generates corresponding organic acid after dehydration, which can be easily recovered from the system; BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0009] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0011] Example 1:

[0012] This specific embodiment provides a method for preparing phosphorus pentafluoride gas, comprising the following steps: adding phosphorus pentoxide powder to a hexafluorophosphoric acid reactor under inert gas protection, then adding acetic anhydride, stirring and mixing until uniform, maintaining the temperature of the reactor between -5 and 5°C, slowly adding anhydrous hydrogen fluoride, maintaining the temperature of the reaction system at no more than 10°C, and the entire reaction process lasting 3 hours, wherein the molar ratio of the acetic anhydride input to the phosphorus pentoxide is 10:1, and the ratio of the final molar amount of the anhydrous hydrogen fluoride added to the molar amount of the phosphorus pentoxide is 12.5 to 13:1; transferring the hexafluorophosphoric acid solution to a hexafluorophosphoric acid decomposition reactor, heating and decomposing to generate phosphorus pentafluoride gas, and passing the generated gas into a condenser to preliminarily remove high-boiling-point gases such as organic anhydride, organic acid, and hydrogen fluoride to obtain crude gas rich in phosphorus pentafluoride; wherein the decomposition temperature of the hexafluorophosphoric acid decomposition reactor is controlled between 140°C and 160°C.

[0013] Example 2:

[0014] This specific embodiment provides a method for preparing phosphorus pentafluoride gas, comprising the following steps: adding 90% phosphoric acid to a hexafluorophosphoric acid reactor under inert gas protection, then adding acetic anhydride, stirring and mixing until uniform, slowly adding anhydrous hydrogen fluoride while maintaining the temperature of the hexafluorophosphoric acid reactor between 0° C. and 10° C., maintaining the temperature of the reaction system at no more than 15° C., and the entire reaction process lasting 3 hours, wherein the mass ratio of the acetic anhydride input to the 90% phosphoric acid is 8:1, and the ratio of the final mass of the anhydrous hydrogen fluoride added to the mass of the 90% phosphoric acid is 1.2-1.4:1; transferring the hexafluorophosphoric acid solution to a hexafluorophosphoric acid decomposition reactor, heating and decomposing to generate phosphorus pentafluoride gas, and passing the generated gas into a condenser to preliminarily remove high-boiling-point gases such as organic anhydride, organic acid, and hydrogen fluoride to obtain crude gas rich in phosphorus pentafluoride; wherein the decomposition temperature of the decomposition reactor is controlled between 140° C. and 160° C.

[0015] Although the embodiments of the present invention have been described above, it will be apparent to those skilled in the art that modifications and substitutions made without departing from the principles and spirit of the present invention are intended to fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing phosphorus pentafluoride gas, characterized in that: The following steps are involved: (1) a phosphorus-containing compound reacts with hydrogen fluoride to generate a hexafluorophosphoric acid solution, and an organic acid anhydride dehydrating agent is added before the phosphorus-containing compound reacts with hydrogen fluoride; and (2) the hexafluorophosphoric acid solution is heated and decomposed into gaseous hydrogen fluoride and phosphorus pentafluoride.

2. The method for preparing phosphorus pentafluoride gas according to claim 1, wherein: The phosphorus-containing compound is selected from one or more of phosphorus pentoxide, orthophosphoric acid, metaphosphoric acid, polyphosphoric acid or pyrophosphoric acid.

3. The method for preparing phosphorus pentafluoride gas according to claim 1, wherein: The organic acid anhydride dehydrating agent is selected from one or more organic acid anhydrides, and the general chemical formula of the organic acid anhydride is R1C(O)OC(O)R2.

4. The method for preparing phosphorus pentafluoride gas according to claim 1, wherein: The mass concentration of the hydrogen fluoride is 5% to 100%; the ratio of the molar amount of the hydrogen fluoride to the molar amount of the phosphorus element in the phosphorus-containing compound is 6 to 12:

1.

5. The method for preparing phosphorus pentafluoride gas according to claim 4, characterized in that: The mass concentration of hydrogen fluoride is 100%.

6. The method for preparing phosphorus pentafluoride gas according to claim 1, wherein: The ratio of the molar amount of the organic acid anhydride dehydrating agent to the molar amount of the oxygen element in the phosphorus-containing compound is 1 to 10:

1.

7. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The reaction temperature of the phosphorus-containing compound and the hydrogen fluoride or the dehydration temperature of the organic acid anhydride dehydrating agent is controlled at -10 to 30°C.

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