Gas-phase advanced oxidation as an integrated air pollution control technique

Gas-phase advanced oxidation (GPAO) is an emerging air cleaning technology based on the natural self-cleaning processes that occur in the Earth’s atmosphere. The technology uses ozone, UV-C lamps and water vapor to generate gas-phase hydroxyl radicals that initiate oxidation of a wide range of pollutants. In this study four types of GPAO systems are presented: a laboratory scale prototype, a shipping container prototype, a modular prototype, and commercial scale GPAO installations. The GPAO systems treat volatile organic compounds, reduced sulfur compounds, amines, ozone, nitrogen oxides, particles and odor. While the method covers a wide range of pollutants, effective treatment becomes difficult when temperature is outside the range of 0 to 80 °C, for anoxic gas streams and for pollution loads exceeding ca. 1000 ppm. Air residence time in the system and the rate of reaction of a given pollutant with hydroxyl radicals determine the removal efficiency of GPAO. For gas phase compounds and odors including VOCs (e.g. C6H6 and C3H8) and reduced sulfur compounds (e.g. H2S and CH3SH), removal efficiencies exceed 80%. The method is energy efficient relative to many established technologies and is applicable to pollutants emitted from diverse sources including food processing, foundries, water treatment, biofuel generation, and petrochemical industries

Atmospheric Chemistry of (CF₃)₂CF–CN: A Replacement Compound for the Most Potent Industrial Greenhouse Gas, SF₆

FTIR/smog chamber experiments and ab initio quantum calculations were performed to investigate the atmospheric chemistry of (CF₃)₂CFCN, a proposed replacement compound for the industrially important sulfur hexafluoride, SF₆. The present study determined <i>k</i>(Cl + (CF₃)₂CFCN) = (2.33 ± 0.87) × 10^–17, <i>k</i>(OH + (CF₃)₂CFCN) = (1.45 ± 0.25) × 10^–15, and <i>k</i>(O₃ + (CF₃)₂CFCN) ≤ 6 × 10^–24 cm³ molecule^–1 s^–1, respectively, in 700 Torr of N₂ or air diluent at 296 ± 2 K. The main atmospheric sink for (CF₃)₂CFCN was determined to be reaction with OH radicals. Quantum chemistry calculations, supported by experimental evidence, shows that the (CF₃)₂CFCN + OH reaction proceeds via OH addition to −C­(N), followed by O₂ addition to −C­(OH)N·, internal H-shift, and OH regeneration. The sole atmospheric degradation products of (CF₃)₂CFCN appear to be NO, COF₂, and CF₃C­(O)­F. The atmospheric lifetime of (CF₃)₂CFCN is approximately 22 years. The integrated cross section (650–1500 cm^–1) for (CF₃)₂CFCN is (2.22 ± 0.11) × 10^–16 cm² molecule^–1 cm^–1 which results in a radiative efficiency of 0.217 W m^–2 ppb^–1. The 100-year Global Warming Potential (GWP) for (CF₃)₂CFCN was calculated as 1490, a factor of 15 less than that of SF₆