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

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, SF
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emissions have been restricted. Many researchers and academic institutions are committed to the research and development of SF
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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 SF
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. The gas $i-C_{4}F_{7}N$ as a potential and alternative gas for SF
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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 SF
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. 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 SF
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. 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.