Method and device for preparing octafluoropropane through plasma cracking

Abstract

The invention belongs to the technical field of fluorine-containing fine chemical synthesis, and particularly relates to a method and device for preparing octafluoropropane through plasma cracking. The method comprises the following steps: S1, introducing nitrogen trifluoride and hexafluoropropylene into a reactor according to a flow ratio of (0.2-3.2): 1, after electrifying, cracking the nitrogen trifluoride, and reacting with the hexafluoropropylene to generate reaction products octafluoropropane and nitrogen; and S2, condensing and separating the reaction product octafluoropropane from nitrogen, and finally collecting the octafluoropropane in a liquid form. The device comprises a plasma reactor, a cold trap and an octafluoropropane storage tank which are arranged in the material flow direction, the cold trap is further communicated with a vacuum pump, and a hexafluoropropylene gas inlet is formed in the plasma reactor. According to the method, hexafluoropropylene and NF3 directly react, NF3 is cracked into free fluorine ions in a plasma reactor, and the free fluorine ions and hexafluoropropylene react to generate octafluoropropane. The reaction process is mild, and continuous production can be realized.

Description

Technical Field

[0001] This application belongs to the field of fluorine-containing fine chemical synthesis technology, specifically relating to a method and apparatus for preparing octafluoropropane by plasma pyrolysis. Background Technology

[0002] High-purity octafluoropropane (C3F8, also known as FC-218 or perfluoropropane) offers significant advantages in certain critical processes of etching and chemical vapor deposition (CVD) chamber cleaning in ultra-high-precision integrated circuit manufacturing. These advantages include minimal lateral edge erosion, high etching rates, and excellent process precision, effectively meeting the stringent requirements of low linewidth and high-precision patterns in advanced semiconductor manufacturing. As the global semiconductor industry rapidly advances towards smaller process nodes, the market demand for octafluoropropane, as an important chip etching gas, continues to grow.

[0003] Currently, there are various processes for preparing octafluoropropane, but all have limitations to varying degrees. One common method reported in China involves extracting octafluoropropane as a byproduct generated during the production of carbon tetrafluoride (CF4) or hexafluoropropylene (C3F6). However, octafluoropropane extracted as a byproduct typically contains various fluorocarbon impurities at very high levels, making its quality indicators difficult to control and unable to directly meet the high purity requirements of semiconductor manufacturing.

[0004] Another mainstream process reported in China involves the synthesis of octafluoropropane (CN107098790B) through the reaction of cobalt trifluoride (CoF3) catalyzed hexafluoropropylene (C3F6) or heptafluoropropane with fluorine (F2). The challenge of this method lies in the fact that the direct reaction between fluorine and hexafluoropropylene is violently exothermic, posing uncontrollable risks and significant safety hazards. While using cobalt trifluoride as a catalyst results in a relatively milder reaction and improved safety, and produces octafluoropropane with higher purity that is easier to further purify, the process has significant shortcomings: the reaction is discontinuous, the overall process is complex, and the cobalt trifluoride catalyst is prone to coking, clogging, and pulverization during the reaction, affecting production efficiency and stability.

[0005] Internationally, several patented technologies for preparing octafluoropropane from hexafluoropropylene have been disclosed for some time. However, these technologies generally face challenges such as numerous byproducts, unsatisfactory selectivity, and the difficulty in obtaining extremely high-purity products (especially removing chloride impurities) economically and efficiently. Furthermore, the extraction and subsequent purification of fluorocarbon gaseous byproducts are themselves industry challenges. Traditional purification methods (such as distillation, extractive distillation, membrane separation, and adsorption) suffer from high equipment costs, complex processes, and low purity. This has prompted the industry to continuously develop new purification technologies.

[0006] In summary, although there are various technical solutions for the preparation and purification of octafluoropropane, developing a synthesis process that can balance high safety, high selectivity, high purity, continuous production, and ease of operation remains a direction for continuous efforts by those skilled in the art. Summary of the Invention

[0007] To address the problems of high equipment cost, complex processes, and low purity in the preparation and purification of octafluoropropane in existing technologies, this application proposes a method and apparatus for preparing octafluoropropane by plasma pyrolysis that can achieve high safety, high selectivity, high purity, continuous production, and simple operation.

[0008] The proposed solution is as follows:

[0009] On the one hand, this application provides a method for preparing octafluoropropane by plasma pyrolysis, comprising the following steps:

[0010] Step S1. Nitrogen trifluoride and hexafluoropropylene are introduced into the reactor at a flow rate ratio of 0.2 to 3.2:1. After being energized, the nitrogen trifluoride is decomposed and reacts with hexafluoropropylene to produce the reaction products octafluoropropane and nitrogen gas.

[0011] Step S2. The reaction product octafluoropropane and nitrogen are condensed and separated, and finally the octafluoropropane is collected in liquid form.

[0012] Preferably, the purity of the nitrogen trifluoride is ≥99.95%; and the purity of the hexafluoropropylene is ≥99%.

[0013] Preferably, the voltage after energization is 1000-7500V and the ionized gas pressure is -0.1-0.05MPa.

[0014] Preferably, the flow rate of the nitrogen trifluoride gas is 100-2000 L / min.

[0015] Preferably, the pressure of the reactor is -0.1 to 0 MPa, and the temperature is 20 to 100°C.

[0016] Preferably, the condensation separation temperature is -160 to -30°C.

[0017] On the other hand, this application provides an apparatus for preparing octafluoropropane by plasma pyrolysis, including a plasma reactor, a cold trap and an octafluoropropane storage tank arranged in the direction of material flow, wherein the cold trap is also connected to a vacuum pump and the plasma reactor is provided with a hexafluoropropylene inlet.

[0018] Preferably, the plasma reactor has a porous distribution ring arranged along the axial direction of the plasma reaction chamber inside, which divides the plasma reactor into a hexafluoropropylene inlet chamber and a reaction mixing chamber. The plasma reactor also has a central quartz tube inside, and electrodes with a spiral coil structure are arranged outside the central quartz tube. The central quartz tube passes through the hexafluoropropylene inlet chamber and is connected to the reaction mixing chamber. A nitrogen trifluoride inlet is also provided at one end of the central quartz tube.

[0019] Preferably, the porous distribution ring is uniformly provided with a plurality of circular holes for hexafluoropropylene to uniformly enter the reaction mixing chamber.

[0020] The beneficial effects of this application are as follows:

[0021] The method for preparing octafluoropropane by plasma pyrolysis proposed in this application offers advantages over existing technologies in terms of reaction safety, product selectivity, process simplicity, equipment requirements, and environmental friendliness. This application uses nitrogen trifluoride as the fluorine source, instead of the highly toxic, corrosive, and uncontrollable fluorine gas used in traditional methods. This fundamentally avoids the violent exothermic reaction and potential explosion risks that may occur when fluorine gas directly fluorinates hexafluoropropene.

[0022] The reaction in this application is carried out in a low-temperature plasma environment, with the reaction temperature controlled within a low range of 20 to 100°C, far lower than the high temperatures required by some catalytic fluorination methods, further improving the intrinsic safety level of the process. The plasma causes nitrogen trifluoride to crack, generating active fluorine radicals (F·). These radicals undergo an addition reaction with hexafluoropropylene to produce octafluoropropane and nitrogen gas. The reaction pathway is relatively simple, with very few byproducts. The byproduct nitrogen gas is easily separated from the target product octafluoropropane, avoiding the cumbersome and costly purification steps caused by complex fluorocarbon impurities generated in traditional methods. Subsequent efficient separation of octafluoropropane (liquid) and nitrogen (gaseous) can be achieved simply through low-temperature condensation, simplifying the process.

[0023] This application utilizes a continuous feedstock of nitrogen trifluoride and hexafluoropropylene into a reactor, resulting in a continuous product output. This overcomes the problems of low production efficiency and catalyst pulverization inherent in batch processes such as the cobalt trifluoride catalytic method. The porous distribution rings ensure uniform entry of hexafluoropropylene into the reaction zone, contributing to the stability and efficiency of the reaction.

[0024] This method boasts high reaction selectivity, minimal byproducts, and requires high purity (≥99.95% and ≥99%) for both nitrogen trifluoride and hexafluoropropylene, resulting in high initial product purity. Combined with an efficient condensation separation step, it facilitates further purity enhancement, making it easier to meet the electronic-grade standards required by the semiconductor industry. Attached Figure Description

[0025] Appendix Figure 1A diagram of the apparatus for preparing octafluoropropane by plasma pyrolysis according to this application.

[0026] Attached image labels:

[0027] 1. Plasma reactor; 2. Cold trap; 3. Vacuum pump; 4. Octafluoropropane storage tank; 101. Electrode with spiral coil structure; 102. Central quartz tube; 103. Porous distribution ring; 104. Nitrogen trifluoride inlet; 105. Hexafluoropropylene inlet. Detailed Implementation

[0028] To further illustrate the technical means and effects adopted by this application in order to achieve the intended purpose of the invention, the following detailed description of the specific implementation methods, structures, features and effects of this application is provided in conjunction with the accompanying drawings and preferred embodiments.

[0029] Device Examples

[0030] This embodiment provides an apparatus for preparing octafluoropropane by plasma pyrolysis, see [link to apparatus]. Figure 1 It includes a plasma reactor 1, a cold trap 2 and an octafluoropropane storage tank 4 arranged along the material flow direction. The cold trap 2 is also connected to a vacuum pump 3. The plasma reactor 1 is equipped with a hexafluoropropylene inlet 105.

[0031] The plasma reactor 1 has a porous distribution ring 103 arranged along the axial direction of the plasma reaction chamber inside. The porous distribution ring 103 divides the plasma reactor 1 into a hexafluoropropylene inlet chamber and a reaction mixing chamber. The plasma reactor 1 also has a central quartz tube 102 inside. The central quartz tube 102 has an electrode 101 with a spiral coil structure outside. The central quartz tube 102 passes through the hexafluoropropylene inlet chamber and is connected to the reaction mixing chamber. One end of the central quartz tube 102 is also provided with a nitrogen trifluoride inlet 104.

[0032] Implementation principle of the device:

[0033] Before starting the reaction, the airtightness of the system consisting of plasma reactor 1, cold trap 2, octafluoropropane storage tank 4, and vacuum pump 3 must be checked. Then, the operating parameters are set: the control temperature of cold trap 2 is preset to the range of -160℃ to -30℃, the reactor system pressure is adjusted to -0.1MPa to 0MPa, and the reactor temperature is maintained between 20℃ and 100℃. The purity of nitrogen trifluoride must be ≥99.95%, and the purity of hexafluoropropylene must be ≥99%. Ensure the reaction is carried out in a controlled and safe environment to avoid leakage or abnormal pressure.

[0034] Nitrogen trifluoride and hexafluoropropylene are introduced into plasma reactor 1 at a flow ratio of 0.2:1 to 3.2:1. Nitrogen trifluoride enters through the nitrogen trifluoride inlet 104 on the central quartz tube 102, with a flow rate controlled between 100 L / min and 2000 L / min; hexafluoropropylene enters through the hexafluoropropylene inlet 105 on plasma reactor 1 and is evenly distributed into the reaction mixing chamber through the circular holes on the porous distribution ring 103. The porous distribution ring 103 ensures that hexafluoropropylene is evenly dispersed in the reaction chamber, avoiding excessively high local concentrations.

[0035] A voltage of 1000V to 7500V is applied to the spiral coil electrode outside the central quartz tube 102, causing nitrogen trifluoride gas to ionize and crack within the plasma reaction chamber. The cracked active fluorine species contact and react with hexafluoropropylene in the reaction mixing chamber to produce octafluoropropane and nitrogen gas. Utilizing plasma energy to directly crack nitrogen trifluoride eliminates the need for an additional catalyst, lowering the reaction activation energy and allowing the reaction to proceed efficiently at lower temperatures (20℃~100℃). The high-voltage electric field causes the nitrogen trifluoride molecules to crack, generating active fluorine radicals (F·). These radicals undergo an addition reaction with hexafluoropropylene molecules, ultimately producing octafluoropropane. The byproduct nitrogen gas is easily separated due to its high chemical stability.

[0036] This design achieves physical separation of reactants. First, in the central region where plasma energy is most concentrated, the chemically more stable NF3 is forcibly decomposed into highly reactive fluorine radicals. These activated fluorine radicals then diffuse into the peripheral reaction mixing chamber, where they encounter hexafluoropropylene molecules that enter uniformly through porous rings. This approach avoids directly exposing hexafluoropropylene to the strongest plasma region, thus reducing the possibility of excessive decomposition or polymerization of hexafluoropropylene as a side reaction. The porous ring distribution ensures that hexafluoropropylene enters the reaction zone in a large-area, uniform manner, increasing the contact area and collision probability with fluorine radicals. Uniform material distribution prevents excessively high or low reactant concentrations in localized areas, resulting in a stable reaction rate, high product selectivity, and facilitating the formation of the single target product, octafluoropropane. Physically isolating the two reactants before they enter the core reaction zone and activating one reactant before mixing with the other enhances the controllability and safety of the entire chemical process.

[0037] The reaction mixture (containing octafluoropropane and nitrogen) flows out of the plasma reactor and into the cold trap unit. At the low temperature (-160°C to -30°C) set in the cold trap, the octafluoropropane gas is condensed and liquefied, while non-condensable gases such as nitrogen remain in a gaseous state and flow out. Gas-liquid separation is achieved through low-temperature condensation, and octafluoropropane is initially enriched in a high-purity liquid form. The boiling point difference between octafluoropropane and nitrogen allows for selective liquefaction at low temperatures, thus efficiently separating the target product.

[0038] The liquefied octafluoropropane is collected in an octafluoropropane storage tank, while uncondensed gases such as nitrogen are discharged from the system, achieving continuous collection of the product and safe treatment of the tail gas. The liquid octafluoropropane in the octafluoropropane storage tank can be directly used as the crude product.

[0039] The entire operation process utilizes plasma technology to achieve continuous preparation of octafluoropropane, which has the advantages of mild conditions, no need for catalysts, and high efficiency.

[0040] Examples 1-3 and Comparative Examples 1-3 are based on the devices provided in the device embodiments, and their specific operations are as follows:

[0041] Example 1

[0042] A method for preparing octafluoropropane by plasma pyrolysis involves the following steps: NF3 stored in a gas cylinder is depressurized to 0.1 MPa by a pressure reducer and then introduced into a plasma reactor at a certain flow rate. The ionization voltage is controlled at 1000 V. Subsequently, C3F6 stored in a gas cylinder is depressurized to 0.5 MPa by a pressure reducer and then introduced into the reactor at a certain flow rate. The flow-volume ratio of NF3 to C3F6 is controlled at 0.2:1, the flow rate of NF3 is 700 L / min, the ionization gas pressure is -0.1 to 0.05 MPa, the pressure of the plasma reactor is -0.1 to 0 MPa, and the temperature is 20 °C.

[0043] When the pressure in the plasma reactor reaches the predetermined value of 0.02 MPa, the cold trap is opened and the temperature of the cold trap is controlled at -160℃. The byproduct nitrogen is transported to the tail gas absorption tower. Octafluoropropane is stored in the cold trap in liquid form and collected in the octafluoropropane storage tank. The purity of the obtained octafluoropropane is 99.6% and the yield is 45.6%.

[0044] Example 2

[0045] A method for preparing octafluoropropane by plasma pyrolysis involves the following steps: NF3 stored in a gas cylinder is depressurized to 0.3 MPa by a pressure reducer and then introduced into a plasma reactor at a certain flow rate. The ionization voltage is controlled at 1500 V. Subsequently, C3F6 stored in a gas cylinder is depressurized to 0.3 MPa by a pressure reducer and then introduced into the reactor at a certain flow rate. The flow-to-volume ratio of NF3 to C3F6 is controlled at 1.8:1, the flow rate of NF3 is 1000 L / min, the ionization gas pressure is -0.1 to 0.05 MPa, the pressure of the plasma reactor is -0.1 to 0 MPa, and the temperature is 50 °C.

[0046] When the pressure in the plasma reactor reaches the predetermined value of 0.03 MPa, the cold trap is opened and the temperature of the cold trap is controlled at -100℃. The byproduct nitrogen is transported to the tail gas absorption tower. Octafluoropropane is stored in the cold trap in liquid form and collected in the octafluoropropane storage tank. The purity of the obtained octafluoropropane is 99.8%, and the yield is 52.1%.

[0047] Example 3

[0048] A method for preparing octafluoropropane by plasma pyrolysis involves the following steps: NF3 stored in a gas cylinder is depressurized to 0.5 MPa by a pressure reducer and then introduced into a plasma reactor at a certain flow rate. The ionization voltage is controlled at 7500 V. Subsequently, C3F6 stored in a gas cylinder is depressurized to 0.5 MPa by a pressure reducer and then introduced into the reactor at a certain flow rate. The flow-volume ratio of NF3 to C3F6 is controlled at 3.2:1, the flow rate of NF3 is 100 L / min, the ionization gas pressure is -0.1 to 0.05 MPa, the pressure of the plasma reactor is -0.1 to 0 MPa, and the temperature is 100 °C.

[0049] When the pressure in the plasma reactor reaches the predetermined value of 0.03 MPa, the cold trap is opened and the temperature of the cold trap is controlled at -30℃. The by-product nitrogen gas is transported to the tail gas absorption tower. Octafluoropropane is stored in the cold trap in liquid form and collected in the octafluoropropane storage tank. The purity of the obtained octafluoropropane is 99.9% and the yield is 49.8%.

[0050] Comparative Example 1

[0051] Compared to Example 1, the reaction temperature is adjusted in this example as follows:

[0052] A method for preparing octafluoropropane by plasma pyrolysis involves the following steps: NF3 stored in a gas cylinder is depressurized to 0.1 MPa and then introduced into a plasma reactor at a controlled flow rate. The ionization voltage is controlled at 1000 V. Subsequently, C3F6 stored in a gas cylinder is depressurized to 0.5 MPa and then introduced into the reactor at a controlled flow rate. The flow-to-volume ratio of NF3 to C3F6 is controlled at 0.2:1, the flow rate of NF3 is 700 L / min, the ionization gas pressure is -0.1 to 0.05 MPa, the pressure of the plasma reactor is -0.1 to 0 MPa, and the temperature is 130 °C. When the pressure of the plasma reactor reaches a predetermined value of 0.02 MPa, the cold trap is opened, and the cold trap temperature is controlled at -160 °C. The byproduct nitrogen is transported to a tail gas absorption tower, and the octafluoropropane is stored in the cold trap in liquid phase and collected in an octafluoropropane storage tank. The obtained octafluoropropane has a purity of 91.4% and a yield of 35.4%.

[0053] Comparative Example 2

[0054] Compared to Example 1, this example adjusts the flow rate ratio of the reaction raw materials as follows:

[0055] A method for preparing octafluoropropane by plasma pyrolysis involves the following steps: NF3 stored in a gas cylinder is depressurized to 0.1 MPa and then introduced into a plasma reactor at a controlled flow rate. The ionization voltage is controlled at 1000 V. Subsequently, C3F6 stored in a gas cylinder is depressurized to 0.5 MPa and then introduced into the reactor at a controlled flow rate. The flow-to-volume ratio of NF3 to C3F6 is controlled at 4:1, the flow rate of NF3 is 700 L / min, the ionization gas pressure is -0.1 to 0.05 MPa, the pressure of the plasma reactor is -0.1 to 0 MPa, and the temperature is 130 °C. When the pressure of the plasma reactor reaches a predetermined value of 0.02 MPa, the cold trap is opened, and the cold trap temperature is controlled at -160 °C. The byproduct nitrogen is transported to the tail gas absorption tower, and the octafluoropropane is stored in the cold trap in liquid phase and collected in an octafluoropropane storage tank. The obtained octafluoropropane has a purity of 95.6% and a yield of 31.7%.

[0056] Comparative Example 3

[0057] Compared to Example 1, this example adjusts the reaction apparatus, that is, directly mixes and ionizes NF3 and C3F6 without dividing the reaction chamber, and the resulting octafluoropropane has a purity of 85.9% and a yield of 33.9%.

[0058] The above description is merely a preferred embodiment of this application and is not intended to limit this application in any way. Although this application has been disclosed above with reference to preferred embodiments, it is not intended to limit this application. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this application. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A method for the production of octafluoropropane by plasma cleavage, characterized in that, It comprises the following steps: Step S1. Nitrogen trifluoride and hexafluoropropylene are introduced into the reactor at a flow ratio of 0.2-3.2:

1. After electrification, the nitrogen trifluoride is cracked and reacts with the hexafluoropropylene to form reaction products octafluoropropane and nitrogen; Step S2. The reaction products octafluoropropane and nitrogen are condensed and separated, and finally the octafluoropropane is collected in liquid form.

2. The method of claim 1, wherein the method is characterized by, The purity of the nitrogen trifluoride is ≥99.95%; the purity of the hexafluoropropylene is ≥99%.

3. The method of claim 1, wherein the method is characterized by, The voltage after electrification is 1000-7500V, and the ionized gas pressure is -0.1-0.05MPa.

4. The method of claim 1, wherein the method is characterized by, The nitrogen trifluoride gas flow is 100-2000L / min.

5. The method of claim 1, wherein the method is characterized by: The pressure of the reactor is -0.1-0MPa, and the temperature is 20-100℃.

6. The method of claim 1, wherein the method is carried out in a plasma reactor. The condensation and separation temperature is -160--30℃.

7. An apparatus for use in a process for the production of octafluoropropane by plasma cleavage according to any one of claims 1 to 6, characterised in that, It comprises a plasma reactor (1), a cold trap (2) and an octafluoropropane storage tank (4) arranged along the material flow direction, the cold trap (2) is also connected with a vacuum pump (3), and the plasma reactor (1) is provided with a hexafluoropropylene gas inlet (105).

8. The apparatus for use in a process for the preparation of octafluoropropane by plasma cleavage according to claim 7, characterized in that A porous distribution ring (103) is arranged axially along the plasma reaction cavity in the plasma reactor (1), the porous distribution ring (103) divides the plasma reactor (1) into a hexafluoropropylene inlet cavity and a reaction mixing cavity, a center quartz tube (102) is further arranged in the plasma reactor (1), an electrode (101) with a spiral coil structure is arranged outside the center quartz tube (102), the center quartz tube (102) penetrates through the hexafluoropropylene inlet cavity and communicates with the reaction mixing cavity, and a nitrogen trifluoride gas inlet (104) is further arranged at one end of the center quartz tube (102).

9. The apparatus for use in a process for the preparation of octafluoropropane by plasma cleavage according to claim 8, characterized in that A plurality of circular holes for uniform entry of hexafluoropropylene into the reaction mixing cavity are uniformly arranged on the porous distribution ring (103).

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