New research progress on synthesis and properities of eco-friendly insulating gas heptafluoroisobutyronitrile((i-C4F7N))

摘要

As global climate change intensifies, higher requirements are imposed on the insulation and environmental performance of eco-friendly gases for electrical insulation. Although SF6 gas has excellent insulating properties and arc-quenching capabilities, it has been classified as one of the greenhouse gases in the Kyoto protocol. At present, SF6 emissions have been restricted. Many researchers and academic institutions are committed to the research and development of SF6 replacement gas in order to achieve the development of green energy. The GWP of heptafluoroisobutyronitrile($i-C_{4}F_{7}N$) is only 2210, which is far lower than that of SF6. The gas $i-C_{4}F_{7}N$ as a potential and alternative gas for SF6 has attracted academics’ attention. Recently, GE has built a 420 kV $i-C_{4}F_{7}N/CO_{2}$ GIL. In the first part, this review briefly introduced the background of insulating gases and the discovery of $i-C_{4}F_{7}N$. Then it broadly covers the new progress on the preparation of $i-C_{4}F_{7}N$ in the second part. Methylperfluoroisobutyrate, perfluoroisobutyryl acid, tetrafluoroethylene, hexafluoropro-pylene and perfluoro(4-methylpent-2-ene) can be used as the initial starting material to synthesize $i-C_{4}F_{7}N$. In the third part, the review presented the new research progresses on dielectric properties of $i-C_{4}F_{7}N$ and $i-C_{4}F_{7}N/CO_{2}$ gas mixture. The pure $i-C_{4}F_{7}N$ shows a dielectric strength which is approximately twice that of SF6. In addition, experimental study indicates that the dielectric strength of the $i-C_{4}F_{7}N$ gas mixture with 18–20% $i-C_{4}F_{7}N$ can be achieved similar to that of pure SF6. Further, it reviews the research progress on the insulation properties of the $i-C_{4}F_{7}N$ gas mixture over the past 3 years. They have a great influence on reducing greenhouse gas emissions from the electrical industry and the application of $i-C_{4}F_{7}N$ in industry. In the last part, the research progress on dissociative ionization dynamics of dielectric gas $i-C_{4}F_{7}N$ was described. Furthermore, the decomposition products and mechanism of the environmentally friendly insulating gas $i-C_{4}F_{7}N$, $i-C_{4}F_{7}N/CO_{2}$ or $i-C_{4}F_{7}N/N_{2}$ gas mixture under different experimental conditions (temperature or discharge) are reviewed. Besides, the achievements on the main decomposition pathways of $i-C_{4}F_{7}N$ and the enthalpy of each path at different temperatures were described.