Method for the degradation of sulfur hexafluoride gas under electrochemical conditions

Abstract

This invention discloses a method for the electrochemical degradation of sulfur hexafluoride gas, belonging to the field of organic electrochemical technology. In this method, at room temperature, triphenylphosphine and sulfur hexafluoride degrade sulfur hexafluoride through an electrochemical reaction under the action of electrodes, an electrolyte, and a base. The positive electrode is zinc (Zn), the negative electrode is tin (Sn), the electrolyte is tetrabutylammonium tetrafluoroborate, and the base is triethylamine. The advantages are: the method uses mild conditions, readily available and inexpensive raw materials, and is simple to operate, making it highly valuable for application.

Description

Technical Field

[0001] This invention relates to the field of organic electrochemical technology, and in particular to a method for the degradation of sulfur hexafluoride gas under electrochemical conditions. Background Technology

[0002] Sulfur hexafluoride (SF6) is a highly stable and persistent greenhouse gas with a Global Warming Potential (GWP) of 24,300 and an atmospheric lifetime of approximately 3,200 years. It directly impacts the natural environment, contributing to global warming. One kilogram of SF6 released into the atmosphere is equivalent to about 24.3 tons of CO2. Global SF6 emissions accumulate annually, exerting a continuous environmental impact. Currently, the global atmospheric concentration of SF6 has risen from 3.67 ppt (ng / L) in 1994 to 10.5 ppt in 2020, and this concentration continues to rise. Many countries and regions worldwide have recognized the severity of the SF6 greenhouse effect and have implemented measures to control the equivalent carbon emissions from SF6. Since 2011, the permissible emission limit for SF6 has been set at 10% of the capacity of gas-insulated equipment, with this limit decreasing by 1% annually until 2020, when the SF6 emission limit remained at 1%.

[0003] Currently, existing methods for degrading SF6 include gas recovery and recycling, adsorption, pyrolysis, photodegradation, catalytic degradation, and plasma methods. Most of these methods have limitations in practical application. For example, gas recovery and recycling equipment alone costs approximately 500,000 RMB, making it very expensive. Adsorption can only purify small amounts of SF6 gas and is ineffective for high concentrations and large quantities. Pyrolysis requires extremely high temperatures, places high demands on equipment, and is difficult to operate. Photodegradation takes a long time to degrade SF6 and has low efficiency. Catalytic degradation catalysts are prone to poisoning and loss of activity during use, and only exhibit high catalytic activity at high temperatures, resulting in significant energy consumption. Plasma is currently the best method for degrading SF6, but plasma treatment devices require additional equipment, greatly increasing the cost. Examples of specific SF6 degradation methods are provided below.

[0004] Method 1: Heating at 250°C for 24 hours in a sealed glass bottle will convert some SF6 into sulfonyl fluoride (identified by infrared spectroscopy); trace amounts of silicon tetrafluoride are the only other product.

[0005]

[0006] The drawback of this method is that the reaction needs to be carried out at high temperatures, which not only consumes a lot of energy and is difficult to operate, but also places extremely high demands on the degradation equipment. In industrial degradation, this directly leads to an increase in process costs and is not economically friendly.

[0007] Method 2: Using ultraviolet light as the light source, SF6, an electron-rich nitrogen heterocyclic carbene activation gas, is used at 80 degrees Celsius to obtain 2,2-difluoroimidazoline or 2,2-difluoroimidazoline and thio derivatives of the carbene precursor.

[0008]

[0009] The drawbacks of this method are that although photodegradation of SF6 can produce non-toxic products, the degradation time is long and the degradation efficiency is low, which does not meet the requirements of industrial applications. An additional light source is required during the degradation process. The light source is expensive and has a short effective life. The degradation products are adsorbed on the reactor wall, affecting the light transmission, which leads to low degradation efficiency. In addition, the reaction requires the use of nitrogen heterocyclic carbene, which is expensive. Summary of the Invention

[0010] The technical problem to be solved by this invention is how to solve the problems of difficult degradation, complicated operation and high degradation cost of existing SF6.

[0011] The present invention solves the above-mentioned technical problems through the following technical means:

[0012] A method for degrading sulfur hexafluoride gas under electrochemical conditions includes the following steps: placing triphenylphosphine, electrolyte, alkali and solvent into a reaction vessel, filling it with sulfur hexafluoride gas, and connecting it to a power source with a zinc rod as the positive electrode and a tin rod as the negative electrode to carry out an electrolytic reaction.

[0013] Note: Under electrochemical conditions, sulfur hexafluoride gas reacts with triphenylphosphine via electrolysis to produce triphenylphosphine sulfur and triphenylphosphine difluoride. Triphenylphosphine difluoride readily hydrolyzes to triphenylphosphine oxychloride. The reaction equation is as follows:

[0014]

[0015] The alkali is used to protect the positive electrode, which is zinc (Zn) and tin (Sn). The product contains triphenylphosphine difluoride, which is easily hydrolyzed to become triphenylphosphine oxide.

[0016] Preferably, the molar ratio of the alkali to triphenylphosphine is 3-8:1.

[0017] Preferably, the molar ratio of the base to triphenylphosphine is 5:1.

[0018] Preferably, the base is triethylamine.

[0019] Preferably, the molar ratio of the electrolyte to triphenylphosphine is 1 to 2.5:1, more preferably 2:1. When the molar ratio of the electrolyte to triphenylphosphine is 2:1, the yield of the final product is high.

[0020] Preferably, the electrolyte is one or more of tetrabutylammonium tetrafluoroborate and tetrabutylammonium hexafluorophosphonate, more preferably tetrabutylammonium tetrafluoroborate. When the electrolyte is tetrabutylammonium tetrafluoroborate, the yield of the final product is high.

[0021] Preferably, the current during the electrolysis process is 5 to 15 mA, and more preferably 10 mA. When the current is 10 mA, the yield of the final product is high.

[0022] Preferably, the reaction temperature is room temperature, preferably 25°C; the reaction time is 4 to 8 hours, preferably 6 hours. When the reaction time is 6 hours, the yield of the final product is high.

[0023] Preferably, the solvent is one of tetrahydrofuran, dichloromethane, and dichloroethane, with tetrahydrofuran being more preferred. When the solvent is tetrahydrofuran, the yield of the final product is high. The molar concentration of triphenylphosphine in the solvent is 0.1 mmol / mL.

[0024] This invention is carried out in a system with a single organic solvent; other organic solvents may also be present in the system if necessary, but from the perspective of reaction yield and simplicity of operation, it is preferable not to add other organic solvents, that is, to use a single organic solvent as the reaction solvent.

[0025] The advantages of this invention are:

[0026] 1. The reaction temperature of this invention is room temperature, and the inexpensive and readily available triphenylphosphine compound is used as the reaction substrate. The commercial price of triphenylphosphine is 115 yuan / kg. Compared with other degradation methods, the cost is greatly reduced. Under electrochemical conditions, sulfur hexafluoride gas is degraded in a short time and with a high conversion rate, which not only saves time but also has economic advantages.

[0027] 2. The reaction conditions of this invention are mild, the reaction raw materials used (including triphenylphosphine alcohol and triethylamine) are inexpensive and readily available, no metal catalyst is required, the reaction conversion rate is extremely high, the reaction time is fast, and the degradation products are non-toxic and pollution-free, and are usable organic synthesis raw materials. It has the characteristics of being environmentally friendly and industrially scalable, and has significant advantages compared with other degradation methods.

[0028] 3. The present invention provides a process for degrading SF6 gas using the method described above. After the reaction is completed, the reaction solution is hydrolyzed for 2 hours, and then extracted with saturated ammonium chloride solution and ethyl acetate. The organic layer is dried with anhydrous NaSO4, and the solvent is removed by vacuum. After rotary evaporation and concentration, column chromatography is performed to obtain triphenylphosphine sulfur and hydrolyzed triphenylphosphine difluoride, i.e., triphenylphosphine oxide. Attached Figure Description

[0029] Figure 1 The 1H NMR spectrum of triphenyloxyphosphine described in Example 1;

[0030] Figure 2 The carbon NMR spectrum of triphenyloxyphosphine described in Example 1;

[0031] Figure 3 The phosphorus NMR spectrum of triphenyloxyphosphine described in Example 1;

[0032] Figure 4 The 1H NMR spectrum of triphenylphosphine sulfide described in Example 1;

[0033] Figure 5 The carbon NMR spectrum of triphenylphosphine sulfide described in Example 1;

[0034] Figure 6 The NMR phosphorus spectrum of triphenylphosphine sulfide described in Example 1. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] 1 H NMR, 13 C NMR and 31 P NMR measurements were performed using a Bruker Avance 400 spectrometer. The test temperature was room temperature, and the solvent was deuterated chloroform. (Reference selection follows.) 1 ¹H NMR: CHCl₃ was 7.260 ppm; 13 CNMR: CHCl3 was 77,000 ppm.

[0037] Example 1:

[0038] A method for degrading sulfur hexafluoride gas under electrochemical conditions includes the following steps:

[0039] In an 8 mL sample vial equipped with a magnetic stirrer, triphenylphosphine (131.0 mg, 0.5 mol), tetrabutylammonium tetrafluoroborate electrolyte (329.3 mg, 2.0 equiv, 1.0 mol), triethylamine (728 μL, 5.0 equiv, 2.5 mol), and tetrahydrofuran (THF) (5.0 mL) were added to dissolve and form a solution of triphenylphosphine and tetrabutylammonium tetrafluoroborate. The sample vial was capped, and a tin rod and a lead rod, each approximately 12 cm long, were inserted into the vial through the cap gasket. The solution was bubbled with a balloon filled with SF6 gas for 5 minutes. Then, a power supply was connected with the zinc rod as the positive electrode and the tin rod as the negative electrode. The current was controlled at 10 mA using an ammeter, and the electrolysis reaction was carried out at room temperature for 8 hours. The reaction was monitored using TLC during the process. After the reaction was completed, the reaction solution was hydrolyzed for 2 hours, and then extracted with saturated ammonium chloride solution and ethyl acetate. The organic layer was dried with anhydrous NaSO4, and the solvent was removed under vacuum. After rotary evaporation and concentration, column chromatography was performed to obtain 73.7 mg of triphenylphosphine oxide (conversion rate of 53%) and 41.2 mg of triphenylphosphine sulfide (conversion rate of 28%). The two were added together to obtain a conversion rate of 81% for triphenylphosphine.

[0040] Product: Triphenylphosphine oxide 1 H NMR (400MHz, CDCl3) δ7.70-7.60(m,6H),7.54-7.48(m,3H),7.47-7.40(m,6H)ppm. 13 C NMR (101MHz, CDCl3) δ132.9,132.0,131.9,131.8,128.5,128.3ppm. 31 P NMR (162MHz, CDCl3) δ29.18ppm.

[0041] Product: Triphenylphosphine Sulfate 1 H NMR (400MHz, CDCl3) δ7.78-7.67(m,6H),7.55-7.46(m,3H),7.46-7.38(m,6H)ppm. 13 C NMR (101MHz, CDCl3) δ133.2,132.3,132.2,132.0,131.5,131.4,128.5,128.3ppm. 31 P NMR (162MHz, CDCl3) δ43.33ppm.

[0042]

[0043] As can be seen from Example 1, the method of the present invention starts with inexpensive and readily available triphenylphosphine compounds, uses inexpensive and readily available triphenylphosphine compounds as reaction substrates, and degrades sulfur hexafluoride gas in a short time and with a high conversion rate under electrochemical conditions.

[0044] Table 1. Conversion rate of sulfur hexafluoride gas degradation under different conditions

[0045]

[0046] Standard condition: 1 0.5mmol (1.0eq.), base 2.5mmol (5.0eq.), solvent5.0mL, 25℃. Isolated yields were given. fluoride; n-Bu4NPF6=Tetrabutylammoniumhexafluorophosphate; n-Bu4NBF4=Tetrabutylammonium Tetrafluoroborate.

[0047] The word "trace" means a very small amount that cannot be separated by column chromatography.

[0048] Example 2:

[0049] The difference between this embodiment and Example 1 is that the amount of triethylamine is 1.5 mol, while the other steps are the same as in Example 1.

[0050] Example 3:

[0051] The difference between this embodiment and Example 1 is that the amount of triethylamine is 4 mol, while the remaining steps are the same as in Example 1.

[0052] Example 4:

[0053] The difference between this embodiment and Embodiment 1 is that the electrolyte is 0.5 mol of tetrabutyltetrafluoroborate ammonium, and the remaining steps are the same as in Embodiment 1.

[0054] Example 5:

[0055] The difference between this embodiment and Embodiment 1 is that the electrolyte is 1.25 mol of tetrabutyltetrafluoroborate ammonium, while the other steps are the same as in Embodiment 1.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for degrading sulfur hexafluoride gas under electrochemical conditions, characterized in that, The process includes the following steps: placing triphenylphosphine, electrolyte, alkali and solvent into a reaction vessel, filling it with sulfur hexafluoride gas, and connecting it to a power source with a zinc rod as the positive electrode and a tin rod as the negative electrode to carry out an electrolytic reaction; The electrolyte is tetrabutylammonium tetrafluoroborate; the solvent is tetrahydrofuran; and the base is triethylamine. The current during the electrolysis process is 5~15 mA.

2. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The molar ratio of the alkali to triphenylphosphine is 3-8:

1.

3. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 2, characterized in that, The molar ratio of the base to triphenylphosphine is 5:

1.

4. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The molar ratio of the electrolyte to triphenylphosphine is 1~2.5 :

1.

5. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 4, characterized in that, The molar ratio of the electrolyte to triphenylphosphine is 2:

1.

6. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The current during the electrolysis process is 10 mA.

7. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The current during the electrolysis process is 5mA.

8. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The current during the electrolysis process is 15mA.

9. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The reaction temperature is room temperature, and the reaction time is 4 to 8 hours.

10. The method for degrading sulfur hexafluoride gas under electrochemical conditions according to claim 1, characterized in that, The molar concentration of the triphenylphosphine in the solvent is 0.1 mmol / mL.

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