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 (τ_OH) of HFEs due to the reaction with hydroxyl (OH) radicals. The temperature and pressure dependencies of the OH-rate coefficient (k_OH(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 k_OH(T) for the titled HFEs. No pressure dependence of k_OH(T) was observed in the investigated range. From k_OH(298 K), estimated τ_OH are 17 days (for HFE-263fb2), 12 days (for HFE-374pcf), and 13 days (for HFE-365mcf3). The observed T-dependencies of k_OH(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 k_OH(298 K) and the activation energy (E_a) of the process is presented, allowing the prediction of E_a 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.