Kinetics of CF3CH2OCH3 (HFE-263fb2), CHF2CF2CH2OCH3 (HFE-374pcf), and CF3CF2CH2OCH3 (HFE-365mcf3) with OH radicals, IR absorption cross sections, and global warming potentials.

ABSTRACT

Hydrofluoroethers (HFEs), such as CF3CH2OCH3 (HFE-263fb2), CHF2CF2CH2OCH3 (HFE-374pcf), and CF3CF2CH2OCH3 (HFE-365mcf3), have been proposed in the last few decades as the third-generation replacements for perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs) because of their zero stratospheric ozone depletion potentials and relatively low global warming potentials (GWPs). These GWPs depend on the radiative efficiency (RE) and the atmospheric lifetime (τOH) of HFEs due to the reaction with hydroxyl (OH) radicals. The temperature and pressure dependencies of the OH-rate coefficient (kOH(T)) for HFE-263fb2, HFE-374pcf, and HFE-365mcf3 are not known. Therefore, in this paper, we present the first study on the temperature (263-353 K) and pressure (50-500 torr of helium) dependence of kOH(T) for the titled HFEs. No pressure dependence of kOH(T) was observed in the investigated range. From kOH(298 K), estimated τOH are 17 days (for HFE-263fb2), 12 days (for HFE-374pcf), and 13 days (for HFE-365mcf3). The observed T-dependencies of kOH(T) (in cm3 molecule-1 s-1) are well described by (3.88 ± 0.89) × 10-12 exp[-(508 ± 69)/T] for HFE-263fb2, (2.81 ± 0.33) × 10-12 exp[-(312 ± 35)/T] for HFE-374pcf, and (2.60 ± 0.31) × 10-12 exp[-(319 ± 35)/T] for HFE-365mcf3. A correlation between log kOH(298 K) and the activation energy (Ea) of the process is presented, allowing the prediction of Ea for OH-reactions with other HFEs, exclusively investigated at room temperature. In addition to the kinetic measurements, the infrared absorption cross sections of HFE-263fb2, HFE-374pcf, and HFE-365mcf3 were determined between 520 and 3100 cm-1. Lifetime corrected REs and GWPs relative to CO2 at 100 years' time horizon were reexamined. The impact of the investigated HFEs on the radiative forcing of climate change would be negligible.