INVESTIGADORES
ARANGUREN ABRATE Juan Pablo
congresos y reuniones científicas
Título:
Photooxidation of CF3CCl=CCl2, CF3CCl=CClCF3 and CF3CF=CFCF3 by OH radicals at 298 K and atmospheric pressure. Atmospheric lifetimes, Ozone Depletion Potentials (ODPs), Radiative Forcings and Global Warming Potentials (GWPs)
Autor/es:
PEIRONE, SILVINA A.; ARANGUREN, JUAN P.; COMETTO. PABLO M.; TACCONE, RAÚL A.; NIETO, JORGE.; LANE, SILVIA I.
Lugar:
La Serena, Chile
Reunión:
Encuentro; X Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2010
Resumen:
Perhaloalkenes are extensively used to synthesize fluoropolymers. A series of hydrocarbons containing both chlorine and fluorine, have been used as refrigerants, blowing agents, cleaning fluids, solvents, and as fire extinguishing agents. Fluorinated alkenes are the most likely reactive impurities in HCFCs, being present as residual starting material from production or as decomposition products. They have been shown to cause stratospheric ozone depletion and have been banned for many uses. It is widely known that, the main gas phase removal process of the volatile organic compounds (VOCs) in the troposphere is photooxidation by OH radicals.
In this work, we present the first experimental determination of the relative rate constants for the reactions of CF3CCl=CCl2, CF3CCl=CClCF3 and CF3CF=CFCF3 with OH at 298 K and atmospheric pressure. The experimental set up used consisted of an 80 L collapsible Teflon film chamber, simulating atmospheric conditions, surrounded by germicidal lamps, providing UV radiation with a ë maximum around 254 nm. These lamps were used to produce OH radicals by the UV photolysis of H2O2. The depletion of the organics (perhaloalkenes and reference compounds), by the reaction with OH, was monitored using a gas chromatograph coupled to a flame ionization detector (GC-FID).
The obtained rate constants were: k(OH + CF3CCl=CCl2) = (9,0 ± 1,1) x 10-13, k(OH + CF3CCl=CClCF3) = (2,1 ± 0,2) x 10-13, k(OH + CF3CF=CFCF3) = (3,7 ± 0,2) x 10-13, in units of cm3 molecule-1 s-1. The reference compounds were propane and methanol for CF3CCl=CCl2, acetone and ethane for CF3CCl=CClCF3, and propane and ethane for CF3CF=CFCF3.
Taking into account an OH radical concentration (12 hours daytime average) of 2 x 106 molecules cm-3 and the relationship ô = 1/k [OH], the lifetimes of the studied haloalkenes were calculated, obtaining values of 11, 28 and 31 days for CF3CCl=CCl2, CF3CCl=CClCF3 and CF3CF=CFCF3, respectively.
Integrating the absorption cross sections between 500 and 1500 cm-1, radiative forcings for the three compounds were calculated and their GWPs were estimated. ODPs were also calculated.
The obtained ODP values are small, therefore, their impact on the stratospheric O3 depletion is negligible. On the other hand, The GWP values suggest that these compounds contribute to the greenhouse effect, mainly caused by the strong absorption of the C-F bond in the IR spectral region mentioned above.