Theoretical Study on the Oxidation Reaction Mechanism of Three Working Fluids

Hydrofluoroolefins (HFOs), an environmentally-friendly working fluid, have attracted more and more attention. In order to evaluate the impacts of HFO-1225zc, HFO-1345mzz, and HFO-1438mzz(E) on global warming and other environmental changes, their photocatalytic oxidation reaction mechanisms and kinetics were investigated. First, the oxidation reaction mechanism of the three working fluids with •OH, •H, and :O radicals was calculated by density functional theory, which mainly included two pathways. Second, the reaction rate constants of three substances were calculated at different temperatures. The results indicated that the addition reactions with •OH, •H, and :O are exothermic processes and the extraction reactions with the three free radicals are endothermic processes. The addition reaction is the main pathway for the oxidation reaction. The reaction rates of HFO-1225zc and HFO-1345mzz are higher than those of HFO-1438mzz(E), and their lifetimes in the atmosphere are short, mainly because the number of F atoms in the first two is less than that of HFO-1438mzz(E), which will rapidly decompose in the atmosphere. From the perspective of global warming trends, due to the short residence time of HFOs in the atmosphere and low radiative forcing efficiency, the global warming potential of HFOs is much smaller than that of hydrofluorocarbons.