Perfluoropivalonitrile as a Promising Eco-Friendly Dielectric Compound to Replace the Most Potent Greenhouse Gas SF 6

Identification of a novel dielectric gas to replace the most potent greenhouse gas SF6 is highly desired for the environmentally sustainable development of high-voltage power transmission and distribution. On the basis of the extensive ab initio calculations and molecular simulations, we present perfluoropivalonitrile (C5F9N) as a promising alternative eco-friendly insulation gas that shows competitive performance than the well-known heptafluoroisobutyronitrile (C4F7N). As the dangling C–F bond in C4F7N is substituted by the CF3 group, various properties of symmetrical C5F9N have been tuned precisely. The dielectric strength of C5F9N is predicted to be 2.5-fold of SF6, and an about 20% improvement is gained with respect to C4F7N. The boiling point of C5F9N is almost identical to that of C4F7N as the electrostatic and long-range dispersion can be compensated completely by the enhanced exchange repulsions in the intermolecular interaction. In terms of mechanisms and kinetic analysis for the atmospheric degradation of C5F9N by OH and Criegee (CH2OO) radicals, the energetic reaction routes of C5F9N have been simplified because of the C3-symmetrical configuration and the reactivity has been reduced to some extent with the additional electron-withdrawing CF3 groups. The atmospheric lifetime is estimated to be 40 years, and the global warming potential of 2979 is only one-eighth of SF6. Thermodynamically, C5F9N can be stable up to 875 K upon overheating. Characteristic decomposition products of C5F9N include C2F6 and CF3CN as initialized by the simple C–CF3 bond cleavage. For the sake of practical use, it is shown that the 8% C5/92% CO2 gaseous mixture constitutes a good compromise and a viable formulation for insulation.