Theoretical\nStudy on the Oxidation Reaction Mechanism\nof Three Working Fluids

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