Low-temperature plasma assisted VDF preparation device and method

Abstract

The invention discloses a low-temperature plasma assisted VDF clean preparation device and method, and belongs to the technical field of fluorine-containing compound preparation. The device comprises a plasma reaction cavity, a corrosion-resistant electrode arranged in the cavity, a gas flow stabilizing system and a multiple safety interlocking system. And the safety interlocking system comprises a voltage overload protection module, a gas leakage detection sensor, an induced draft fan and a PLC (Programmable Logic Controller) to form an automatic safety protection network. The preparation method comprises the following steps: introducing raw material gas into a reaction cavity through a gas flow stabilizing system; exciting low-temperature plasma, and carrying out activation reaction at 80-150 DEG C; and collecting and purifying the product. According to the method, the reaction temperature is reduced to 80-150 DEG C from traditional 600-800 DEG C, the VDF monomer selectivity is improved to 85% or above, the product purity reaches 99.8%, perfect safety guarantee is achieved, and clean, efficient and safe production of VDF is achieved.

Description

Technical Field

[0001] This invention relates to the field of fluorine compound preparation technology, specifically to a low-temperature plasma-assisted VDF (vinylidene fluoride) preparation apparatus and method. Background Technology

[0002] Vinylidene fluoride (VDF), a crucial fluorinated monomer, is an indispensable raw material for the synthesis of high-performance fluoropolymers such as polyvinylidene fluoride (PVDF) and fluororubber. These polymers, due to their excellent chemical resistance, weather resistance, dielectric properties, and mechanical strength, are widely used in cutting-edge fields such as chemical engineering, lithium-ion batteries, new energy, and building coatings.

[0003] Currently, the mainstream industrial process for large-scale VDF production is the high-temperature pyrolysis of 1,1-difluoroethane (R152a). While this technology is mature, its inherent flaws severely restrict the industry's green, safe, and high-quality development. 1. Extremely high energy consumption and severe side reactions: The thermal pyrolysis reaction needs to be carried out at a high temperature of 600~800℃, resulting in huge energy consumption. At this extreme temperature, the reaction selectivity is difficult to control precisely, leading to frequent side reactions such as deep pyrolysis, polymerization, and coking of raw materials, generating a large number of low-value by-products and polymers. This not only reduces the yield and selectivity of the target product VDF, but also makes the subsequent product separation and purification process extremely complicated, increasing production costs and environmental burden.

[0004] 2. Significant safety hazards exist: Traditional pyrolysis units lack real-time, interconnected safety monitoring for electrical systems and hazardous gas media. There is no rapid-response automatic protection and emergency response mechanism for the risks of voltage overload caused by high-voltage discharge (if applicable) or grid fluctuations, as well as leaks of highly toxic or explosive fluorine-containing raw materials or intermediates, posing potential threats to continuous production and the safety of operators.

[0005] 3. Insufficient precision in process control: Traditional reactors have limited precision in controlling key process parameters, such as gas flow rate and reaction atmosphere. Problems such as uneven gas distribution and flow rate fluctuations directly affect the contact efficiency of reactants and the stability of the reaction process, making it difficult to achieve optimal control of the reaction process. As a result, the purity and batch consistency of the product cannot meet the stringent requirements of high-end PVDF synthesis for VDF monomers (such as requiring a purity of >99.8% and alkyne impurities <0.03%).

[0006] To overcome the aforementioned bottlenecks, the industry urgently needs to develop a novel preparation technology capable of achieving efficient and highly selective synthesis of VDF under mild conditions. Low-temperature plasma technology, with its unique advantage of generating high-energy reactive species (such as electrons, ions, and free radicals) to significantly reduce reaction activation energy, offers a possibility for achieving this goal. However, successfully applying this technology to the industrial synthesis of VDF still requires solving a series of complex engineering and technical challenges, such as ensuring stable and uniform plasma generation, precise control of the reaction process, and system safety and reliability under high-pressure and high-risk environments.

[0007] Therefore, developing a low-temperature plasma-assisted VDF clean preparation process that integrates high-efficiency activation, precise control, and intrinsic safety has become an urgent need and an important direction for technological development in this field. Summary of the Invention

[0008] Based on the background art, the present invention aims to solve the following core problems existing in the current VDF preparation process, especially the high-temperature pyrolysis method: Excessively high reaction temperatures (600~800℃) result in huge energy consumption, numerous side reactions, low product selectivity, and difficulties in subsequent separation and purification. The production safety assurance system is inadequate, lacking a rapid response and linkage protection mechanism for abnormal voltage and dangerous gas leaks; Insufficient process control precision and unstable gas flow affect reaction efficiency and product purity, making it difficult to meet the quality requirements of high-end applications for VDF monomers.

[0009] To overcome the above-mentioned technical difficulties, the present invention provides a low-temperature plasma-assisted VDF cleaning preparation process and system.

[0010] On one hand, the present invention provides a low-temperature plasma-assisted VDF cleaning preparation system, characterized in that it comprises: Plasma reaction unit: includes a specially designed sealed plasma reaction chamber, which contains electrodes made of high-temperature and corrosion-resistant materials. The electrodes are arranged in an optimized array to ensure uniform plasma distribution.

[0011] Precision gas control unit: including a gas flow stabilization system connected to the gas inlet and outlet of the reaction chamber. This system uses a high-precision mass flow controller to achieve precise and stable control of the reaction gas flow.

[0012] Multiple safety interlocking units include: A voltage overload protection module is used to monitor and protect the plasma generation circuit in real time. At least one high-precision gas leak detection sensor is deployed at key points in the reaction system; The exhaust fan has its intake port located inside the reaction environment, and its exhaust pipe leads to the outside. The PLC controller, as the control center, is connected to the voltage protection module, leakage sensor and induced draft fan signal to form an automated safety response network.

[0013] On the other hand, the present invention provides a low-temperature plasma-assisted VDF cleaning preparation process using the above-mentioned system, characterized by comprising the following steps: S1. System preparation and feeding: Start the system, accurately introduce raw material gas into the plasma reaction chamber through the gas flow stabilization system, and activate multiple safety interlock units; S2. Plasma activation reaction: The excitation electrode generates low-temperature plasma, which, under mild temperature conditions of 80℃~150℃, enables the plasma to undergo a highly efficient activation and conversion reaction with the raw material gas molecules. S3. Product collection and purification: After the reaction is completed, the gaseous products discharged from the outlet are collected by condensation and purified by distillation to obtain high-purity VDF monomer.

[0014] Compared with the prior art, the present invention has the following significant advantages: 1. Energy-saving and highly efficient with significantly improved selectivity: By efficiently activating the reactant molecules through low-temperature plasma, the reaction temperature is significantly reduced from the traditional 600-800℃ to 80-150℃, resulting in a substantial reduction in energy consumption. Simultaneously, through precise control of plasma parameters, the selectivity of VDF monomers is increased by more than 10% compared to traditional thermal decomposition processes, effectively suppressing the formation of byproducts.

[0015] 2. Extremely high product purity, meeting high-end demands: Thanks to mild reaction conditions and optimized reaction pathways, the content of key impurities such as alkynes in the product is successfully suppressed to below 0.03%, and the final VDF monomer purity is stably above 99.8%, which fully meets the stringent standards for raw materials in the synthesis of high-performance PVDF resin.

[0016] 3. Intrinsically safe and highly reliable: A multi-layered safety interlocking system integrating voltage protection, gas leak monitoring, and automatic ventilation has been constructed, enabling real-time perception and rapid automatic handling of potential risks, which greatly improves the intrinsic safety level and operational reliability of the production process.

[0017] 4. Stable process and easy to control: The combination of a specially designed electrode structure and a high-precision gas flow stabilization system ensures the uniformity of plasma distribution and the stability of the reaction atmosphere, providing a solid guarantee for the repeatability of the process and the consistency of the product, and making it easier to achieve precise industrial control. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the overall structure of the low-temperature plasma-assisted VDF preparation device of the present invention.

[0019] In the diagram: 1-Plasma reaction chamber; 2-Electrode; 3-Air inlet; 4-Air outlet; 5-Gas flow stabilization system; 6-Voltage overload protection module; 7-Signal transmission route; 8-PLC controller; 9-Exhaust fan; 9.1-Fan intake port; 9.2-Fan exhaust pipe; X1, X2-Gas leak detection sensors. Detailed Implementation

[0020] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0021] Example 1 This embodiment provides a low-temperature plasma-assisted system for the clean preparation of VDF and details its workflow.

[0022] The system structure is as follows: Figure 1 As shown, the main components and parameters are as follows: Plasma reaction chamber 1: The main body is made of 316L stainless steel, and it is a cylindrical, sealed structure with a designed volume of 10 liters. The chamber is designed to withstand a pressure of 0.5 MPa and a temperature of 200℃. Its inner wall is mirror-polished (surface roughness Ra≤0.4μm) to facilitate stable plasma distribution and reduce wall effects.

[0023] Electrode 2: Two sets of parallel plate electrodes arranged in an array, with the electrode plates made of Hastelloy C-276. The electrode plate spacing is optimized to 15mm, and they are fixed to the cavity by insulating ceramic components. The electrodes are connected to an external radio frequency (RF) power supply via a coaxial cable. The RF power supply has a rated power of 2kW and a frequency of 13.56MHz.

[0024] Gas flow stabilization system 5: This system includes a feed gas (R152a) mass flow controller (MFC, range 0-500 sccm, accuracy ±1% FS), a carrier gas (argon) MFC (range 0-1000 sccm, accuracy ±1% FS), and a back pressure valve. The mass flow controller is connected to the inlet 3 via a 1 / 4-inch stainless steel pipe, and the outlet 4 is connected to the back pressure valve and the product collection system via a pipe.

[0025] Multiple safety interlocking units: Voltage overload protection module 6: Integrated inside the RF power supply, with an action threshold set to 120% of the rated voltage.

[0026] Gas leak detection sensors (X1, X2): Hydrogen fluoride (HF) specific sensors using laser spectroscopy principle. X1 is installed after the raw material gas inlet valve assembly, and X2 is installed near the flange interface of the reaction chamber. Detection resolution ≤ 1 ppm.

[0027] Exhaust fan 9: Explosion-proof centrifugal fan, rated air volume 300 m³ / h 3 / h, total pressure 800 Pa. The fan intake 9.1 is connected to the gas collection hood on the top of the reaction cabinet through a PVC pipe, and the fan exhaust pipe 9.2 is led out to the outdoor high-altitude emission point.

[0028] PLC controller 8: adopts Siemens S7-1200 series, and is connected to all the above safety components through digital and analog modules.

[0029] The steps for preparing VDF using the above system are as follows: 1) System preparation and leak detection Close all valves and perform a comprehensive leak test on the system using a helium mass spectrometer to ensure a leakage rate of <1×10⁻⁶. - 9 mbar·L / s.

[0030] Turn on the circulating cooling water system and set the temperature to 25℃.

[0031] Start the PLC controller 8 and enter the self-test mode to confirm that the voltage overload protection module 6 and the gas leak sensors (X1, X2) have normal readings and that the start / stop function of the induced draft fan 9 is intact.

[0032] 2) Reactant feeding and atmosphere establishment Argon gas is introduced into the plasma reaction chamber 1 via the gas flow stabilization system 5 as a carrier gas, with the flow rate set at 500 sccm, maintaining the chamber pressure at 2000 Pa. Subsequently, R152a feed gas is introduced, with the flow rate set at 100 sccm. The external heating jacket of the chamber (not shown in the figure) is activated to preheat the reaction system to 80°C.

[0033] 3) Plasma activation reaction Turn on the RF power supply and apply 800W to excite and generate cryogenic plasma. Adjust the matching circuit to ensure the reflected power is less than 5W.

[0034] Under these conditions, the temperature of the reaction system stabilizes at 110℃ (monitored by a K-type thermocouple on the cavity wall).

[0035] The reaction lasted for 60 minutes. During this time, PLC controller 8 monitored various parameters in real time. Online gas chromatography (GC) analysis showed that the monomer selectivity of VDF was 87%.

[0036] 4) Safety monitoring and emergency response When the reaction was in progress for 30 minutes, a simulated gas leak was detected (achieved by slightly opening the sampling valve), and sensor X2 detected that the HF concentration exceeded the standard (>5 ppm) within 3 seconds.

[0037] The PLC controller 8 immediately executes the interlocking actions: ① triggers the audible and visual alarm; ② closes the raw material gas inlet solenoid valve; ③ starts the induced draft fan 9 at full speed.

[0038] 5) Product collection and purification After the reaction is complete, turn off the RF power supply and the feed.

[0039] The reaction gas flowing out of outlet 4 is guided to a -40℃ cold trap for condensation, and the crude product is collected.

[0040] The crude product was transferred to a precision distillation unit for purification. The distillation conditions were: 30 theoretical plates, reflux ratio of 5:1, and collection of the fraction at 45-47°C.

[0041] Analysis of the final product: VDF purity was 99.82% and total alkyne impurities were 0.025% as determined by the GB / T 33917-2017 method.

[0042] Comparative example (traditional pyrolysis method): A comparative experiment was conducted in a tubular pyrolysis furnace using the same raw material (R152a). The reaction temperature was 650℃ and the space velocity was 100 h⁻¹. -1 The reaction time was 60 minutes. After purification by distillation under the same conditions, the crude product had a final VDF purity of 99.5%, an alkyne impurity content of 0.1%, and a VDF selectivity of 78%.

[0043] Example 2: In another embodiment, the electrode (2) structure of the reaction chamber (1) can be replaced with a dielectric barrier discharge (DBD) form, with the dielectric being 99% alumina ceramic and a discharge gap of 2 mm. Under reaction conditions of 90°C and 600W input power for 90 minutes, the VDF selectivity can reach 85%, and the final product purity is 99.79%, demonstrating the excellent effect of this invention.

[0044] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low temperature plasma assisted VDF cleaning preparation device, characterized in that, The application relates to a plasma reaction cavity (1) which is a closed structure and is provided with an air inlet (3) and an air outlet (4); an electrode (2) which is arranged in the plasma reaction cavity (1) and is made of a high-temperature-resistant and corrosion-resistant material; a gas flow stabilizing system (5) which is connected with the air inlet (3) and the air outlet (4) and is used for accurately controlling the gas flow in a reaction system; and a multiple safety interlocking system. The multiple safety interlocking system comprises: a voltage overload protection module (6) which is used for monitoring the voltage of a plasma generating circuit and cutting off the power supply when the voltage exceeds a safety threshold; at least one gas leakage detection sensor (X1, X2) which is arranged at the periphery of the reaction system and is used for detecting gas leakage; an air drafter (9) whose air suction port (9.1) is located in a reaction environment and whose air exhaust pipe (9.2) is connected with the outside; and a PLC controller (8) which is respectively connected with the voltage overload protection module (6), the gas leakage detection sensor (X1, X2) and the air drafter (9) in signal connection and is used for receiving an abnormal signal and executing a safety control instruction. The electrode (2) is arranged in an array in the plasma reaction cavity (1). The gas flow stabilizing system (5) adopts a high-precision mass flow controller. The number of the gas leakage detection sensors (X1, X2) is two, and the two sensors are respectively arranged at the air inlet end and the periphery of the reaction zone of the plasma reaction cavity (1). The application further discloses a preparation method of a high-purity vinylidene fluoride (VDF) monomer. The application further discloses a preparation method of a high-purity vinylidene fluoride (VDF) monomer. In step S2, when the gas leakage detection sensor (X1, X2) detects a leakage signal, the PLC controller (8) controls an alarm device to give an alarm and simultaneously starts the air drafter (9). In step S2, when the voltage overload protection module (6) detects that the voltage exceeds a safety threshold, the power supply of a plasma generating device is cut off. The purity of the VDF monomer after purification in step S3 is not lower than 99.8%, and the content of acetylene impurities is lower than 0.03%.

2. The apparatus of claim 1, wherein, ​ 3. The apparatus of claim 1, wherein, ​ 4. The apparatus of claim 1, wherein, ​ 5. A process for the low temperature plasma assisted VDF cleaning preparation using the system according to any one of claims 1 to 4, characterized in that, ​ ​ ​ ​ 6. The method of claim 5, wherein, ​ 7. The process of claim 5, wherein, ​ 8. The process of claim 5, wherein, ​

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