Stability Valorization of Hydrofluoroolefine HFO-1336mzzE and Its Mixtures under Arc Discharge Conditions

Abstract

Sulfur hexafluoride (SF6) has been conventionally used as an insulating gas in switchgear. However, owing to its high Global-warming Potential (GWP), the United Nations Framework Convention on Climate Change (UNFCCC) calls for its replacement with alternative gases. In this work, hydrofluoroolefine HFO-1336mzzE is analyzed as an alternative, due to its good dielectric strength and low GWP. For this purpose, the influence of electric discharges on the stability of this gas in mixtures with vector gases (air, CO2 and N2) at 20% (v/v) was studied, and the influence of humidity (0, 200, and 500 ppm) and temperature (25 °C, 60 and 120 °C) was determined. Electric arc discharge was conducted by a gas-insulated medium voltage switchgear prototype specifically designed for this work. Its main characteristic is the uniform distribution of the dissipated energy, facilitating better reproducibility of the results. The degradation of HFO-1336mzzE was monitored by gas chromatography coupled to mass spectrometry (GC/MS) sampling in addition to online measurement using Near-infrared spectroscopy (NIR). The degradation rate (DR) was measured by assessing the concentrations of the different degradation gases occurring in each experiment. The results were evaluated by using density functional theory (DFT) and transition state theory (TS). Finally, the DR analysis was completed with a study of coke formation for prolonged discharge periods. The gas mixture containing CO2 showed a higher stability compared to those containing air or N2, with temperature being the most decisive factor. A declining trend in the degradation rate tending toward stabilization was observed, rendering CO2 the preferred carrier gas.