Document nkN9om5veMjjwz5RNwMz2E768

7p. Telomer Research Program AR226-1943 Report Title: Extended Laboratory Study of the Atmospheric Degradation of Fluorinated Alcohols Author(s): Professor Georges Le Bras, Geraldine Solignac and Dr. Abdelwahid Mellouki. Contractor: Centre National De La Recherche Scientifique - Laboratoire de Combustion et Systemes Reactifs (CNRS - LCSR) Study Dates: July 2004 - December 2004 Study Objective The project goal was the determination of the photolysis rate of perfluorinated aldehydes, C6F13CHO and C8F17CHO, produced in the OH-initiated oxidation of the corresponding Telomer B Alcohols, C6F13CH2CH2OH and C8F17CH2CH2OH. These data are important since atmospheric photolysis of these aldehydes may compete with reaction with OH radicals, thereby reducing or even eliminating production of the corresponding perfluorocarboxylic acids, in low NOx conditions. Materials and Methods All the photolysis experiments using solar radiation were performed at the outdoor European reactor EUPHORE in Valencia, Spain. The EUPHORE facility consists of two independent hemispherical outdoor simulation chambers, made of FEP foil, with a volume of 200 m3 each (http://www.gva.es./ceam). EUPHORE has a variety of instruments (including FTIR, GC-FID, HPLC) available for in-situ analysis or off-line sampling and the high FTIR detection sensitivity allows use of VOC and NOX concentration ranges close to those present in the atmosphere. Since the perfluorinated aldehydes were not (and are not) available, the experimental design was to produce perfluorinated aldehydes indirectly in the EUPHORE chamber via the OH-initiated oxidation of the corresponding Telomer B Alcohols. This approach met with difficulties and additional experiments were also carried out at EUPHORE using Cl-initiated oxidation of C6F13CH2OH in air to directly produce C6F13CHO. In addition, experiments have been carried out on the Cl-initiated oxidation of C6F13CH2OH in air using the 480L glass photoreactor at the University of Wuppertal. Research grade samples of the Telomer B Alcohols and C6F13CH2OH are readily available. OH radicals were produced in-situ by photolysis of HONO or H2O2. Cl atoms were produced by photolysis of ClC(O)C(O)Cl at EUPHORE and by photolysis of molecular Chlorine at Wuppertal. All chemicals used were lab grade reagents. Does not contain TSCA CBI 1 TRP (March 30, 2005) At EUPHORE, molecular species concentrations and product analysis were monitored by longpath length FTIR and GC-MS and photolysis experiments were performed used natural light. At Wuppertal, experiments were performed in a 480L duran glass reactor interfaced to an in-situ FTIR spectrometer (Nicolet Magna 520) with a pathlength of 51.6 m and a resolution of 1 cm-1. The reactor was surrounded with 20 superactinic lamps (Philips TLA 40W/05, 300 < < 450 nm, max = 360 nm) used to photochemically initiate the experiments. Findings OH-initiated oxidation of C6F13CH2CH2OH (June 28th at EUPHORE) The experiment was performed using the photolysis of HONO as OH radical source and the initial concentration of C6F13CH2CH2OH was 250 ppbv. The loss of C6F13CH2CH2OH in absence of light was found to be comparable to that due to dilution (corresponding to the loss of SF6) indicating that the wall loss of C6F13CH2CH2OH is negligible in our experimental conditions. During the experiment, the consumption of C6F13CH2CH2OH due to its reaction with OH radicals was estimated to be around 16 %. GC-MS analysis showed two main products of the reaction. These products could not be not positively identified, however, one of them may be the Telomer aldehyde (C6F13CH2CHO). The FTIR analysis was rapidly complicated following the formation of the reaction products and the overlap of the fluorinated compounds with similar IR spectra. However, the IR spectra obtained during the experiments showed the presence of an unidentified band 1194-1264 cm-1 which could not be attributed to CF2O nor to C6F13C(O)H (see Figure 1). Absorbance 1100 1150 residual spectrum CF2O 1200 1250 Wavenumber (cm-1) 1300 1350 Figure 1: Residual spectrum after subtraction of C6F13CH2CH2OH and CF2O Does not contain TSCA CBI 2 TRP (March 30, 2005) OH-initiated oxidation of C8F17CH2CH2OH (June 29th and 30th at EUPHORE) Two runs were performed: in the first one the photolysis of HONO was used as the OH source while H2O2 was used in the second one. The C8F17CH2CH2OH initial concentrations were 130 ppbv and 180 ppbv, respectively. In both experiments the consumption of C8F17CH2CH2OH was estimated to be 20 %. GC-MS analysis showed two main products, one of them may be the "first" aldehyde C8F17CH2CHO which was supported by HPLC-MS analysis that indicated the formation of a carbonyl compound. Figure 2 shows the concentration-time profile of C8F17CH2CH2OH. Similarly to what was observed for C6F13CH2CH2OH, the FTIR analysis was rapidly complicated by the overlapping IR bands of different fluorinated compounds present in the system (reactant and reaction products). Hence, in absence of IR spectra of pure product samples and reference spectra, it is still difficult to conclusively identify the reaction products. 144 [C8F17CH2CH2OH] 140 ppbV 136 132 C8F17CH2CH2OH + HONO 29 06 04 EUPHORE 128 -4000 0 time (s) (t = 0: chamber opened) Figure 2 4000 Cl-Initiated oxidation of C6F13CH2OH at EUPHORE (July 1st and 2nd) The aim of these experiments was to generate C6F13CHO directly and check for its photolysis under sunlight conditions. Chlorine atoms were produced using the photolysis of ClC(O)C(O)Cl. Initial concentrations of C6F13CH2OH were 180 ppbv and 220 ppbv, respectively on July 1st and 2nd. The initial concentrations of ClC(O)C(O)Cl were chosen in order to obtain different consumption of C6F13CH2OH in both experiments (85 % and 15 % in the first and second run, respectively). In both experiments, CF2O was the major product observed by FTIR analysis (see Figure 3). Does not contain TSCA CBI 3 TRP (March 30, 2005) 6.2E+012 6E+012 C6F13CH2OH CF2O 3.0E+011 [C6F13CH2OH] molecule cm-3 [CF2O] molecule cm-3 5.8E+012 5.6E+012 2.0E+011 5.4E+012 5.2E+012 1.0E+011 5E+012 0 4000 time (s) t=0 chamber opened 8000 0.0E+000 Figure 3: Concentration-time profiles of C6F13CH2OH and CF2O. The expected mechanism of the Cl-initiated oxidation of C6F13CH2OH leading to the aldehyde C6F13CHO is: Cl + C6F13CH2OH HCl + C6F13CHOH C6F13CHOH + O2 C6F13CHO + HO2 C6F13CHO then reacts with Cl and could also be photolysed: C6F13CHO + Cl C6F13CO + HCl C6F13CHO + h C6F13CO + H C6F13CHO + h C6F13 + HCO C6F13CO and C6F13 radicals will ultimately lead to CF2O. The rate constants obtained at Wuppertal for (k(Cl + C6F13CH2OH) and k(Cl + C6F13CHO)) (see next section) were used to fit the EUPHORE experimental profiles to tentatively assess the importance of the photolysis of the aldehyde. Again, no definitive conclusion could be drawn because the FTIR analysis was rapidly complicated following the formation of the reaction products and the overlapping of the fluorinated compounds with similar IR spectra. Does not contain TSCA CBI 4 TRP (March 30, 2005) Kinetics & mechanism of the Cl reaction with C6F13CH2OH studied at Wuppertal The relative rate technique was used to measure the rate constant of the reaction of Cl with C6F13CH2OH relative to that of Cl with CH3Cl. The relevant reactions in the system were: Cl + C6F13CH2OH products (1) Cl + CH3Cl products (2) Assuming that the fluoroalcohol and the CH3Cl are consumed only by Cl, it can be shown that: ln([C6F13CH2OH]o/([C6F13CH2OH]t)/ = k1/k2 ln([CH3Cl]o/([CH3Cl]t) where the subscripts 0 and t indicate concentrations before irradiation and at time t, respectively. Reactants concentrations were monitored using the IR absorption features 3550-3650 cm-1 and 2820-3150 cm-1 for C6F13CH2OH and CH3Cl, respectively. Infrared spectra were derived from 32 co-added interferograms. Control experiments showed that side reactions such as photolysis of C6F13CH2OH and CH3Cl, as well as heterogenous and dark reactions were negligible in our experimental conditions. Using the value of k(Cl+CH3Cl) = 4.8x10-13 cm3 molecule-1 s-1 for the reference reaction, we have derived the reaction rate constant of Cl with C6F13CH2OH: k (Cl + C6F13CH2OH) = (6.5 0.4) x10-13 cm3 molecule-1 s-1 In Table 1, we have compared this rate constant with the data reported previously for the reactions of Cl with shorter fluorinated alcohols with the formula CnF2n+1CH2OH as shown. The length of CnF2n+1 group does not effect the reactivity of Cl atoms with CnF2n+1CH2OH (k(Cl+CnF2n+1CH2OH) 6.5x10-13 cm3 molecule-1 s-1 for n = 1 up to n = 6). Table 1: Rate constant values for the reaction of Cl with fluoroalcohols Fluoroalcohol CF3CH2OH CF3CF2CH2OH CF3(CF2)2CH2OH CF3(CF2)3CH2OH CF3(CF2)5CH2OH k(Cl) (6.5 0.5) x10-13 (6.5 0.5) x10-13 (6.5 0.5) x10-13 (6.5 0.5) x10-13 (6.5 0.4) x10-13 Does not contain TSCA CBI 5 TRP (March 30, 2005) Product Study of the Cl reaction with C6F13CH2OH: The Cl-initiated oxidation of C6F13CH2OH was investigated using the same system as that used for the kinetic study. The reaction of Cl with C6F13CH2OH proceeds by abstraction of H-atom from -CH2- group followed by reaction with O2 leading to the perfluorinated aldehyde C6F13CHO, as already mentioned : Cl + C6F13CH2OH C6F13CHOH + HCl C6F13CHOH + O2 C6F13CHO + HO2 The aldehyde may undergo further reaction with Cl atoms leading to other fluorinated compounds as end products. Figure 4 shows an example of the experimental concentration profile of C6F13CHO versus C6F13CH2OH. 0.16 22 11 04 0.12 [C6F13C(O)H] t /[C6F13CH2OH] 0 0.08 0.04 0 0 Fit 4: fit aldehyde Equation Y = (A/B)*X*(POW( X, B )-1) B = 3.340333806 A = -0.9801463796 Number of data points used = 60 Residual sum of squares = 0.000276506 Coef of determination, R-squared = 0.997656 Line/Symbol Plot 1 Fit 4: fit aldehyde 0.2 0.4 0.6 0.8 1 [C6F13CH2OH] t /[C6F13CH2OH]0 Figure 4: Formation of C6F13CHO versus loss of C6F13CH2OH The reaction rate constant of Cl with C6F13CHO was derived by fitting these profiles: k(Cl + C6F13CHO) = (2.8 0.7)x10-12 cm3 molecule-1 s-1 Conclusion The reaction of C6F13CH2CH2OH with OH radicals produces two main products. These products could not be not positively identified, however, one will likely be the Telomer aldehyde (C6F13CH2CHO). Similarly the reaction of C8F17CH2CH2OH with OH radicals produces two main products. GC-MS analysis showed two main products, one of them may be the "first" aldehyde C8F17CH2CHO which was supported by HPLC-MS analysis that indicated the formation of a carbonyl compound. Does not contain TSCA CBI 6 TRP (March 30, 2005) The Cl-Initiated oxidation of C6F13CH2OH was used to generate C6F13CHO directly and check for its photolysis under sunlight conditions. Large conversion of the alcohol (up to 85%) was observed and CF2O was the major product observed by FTIR analysis. Experimental rate constants obtained at Wuppertal were used to fit the EUPHORE experimental profiles to tentatively assess the importance of the photolysis of the aldehyde but no definitive conclusions could be drawn.. At Wuppertal, the rate constant of the reaction of Cl with C6F13CH2OH relative to that of Cl with CH3Cl was measured. Using the value of k(Cl+CH3Cl) = 4.8x10-13 cm3 molecule-1 s-1 for the reference reaction, we have derived the reaction rate constant of Cl with C6F13CH2OH: k (Cl + C6F13CH2OH) = (6.5 0.4) x10-13 cm3 molecule-1 s-1 In addition, the reaction rate constant of Cl with C6F13CHO was derived: k(Cl + C6F13CHO) = (2.8 0.7)x10-12 cm3 molecule-1 s-1 Unfortunately, the experiments performed at EUPHORE and in Wuppertal are inconclusive. Due to the absence of spectra of pure sample of C6F13CH2CHO and C6F13CHO, it was not possible to quantify the formation of these two aldehydes during the experiments. Other experiments are planned in the near future at EUPHORE to look directly at the photolysis of shorter aldehydes (C3F7CHO and C4F9CHO) which are available commercially through their corresponding hydrates. A few tests have been already conducted on C3F7CHO using an indoor smog chamber. Publications / Presentations T. KELLY, V. BOSSOUTROT, I. MAGNERON, K. WIRTZ, J. TREACY, A. MELLOUKI, H. SIDEBOTTOM, G. LE BRAS A kinetic and mechanistic study of the reactions of OH radicals and Cl atoms with 3,3,3trifluoropropanol under atmospheric conditions J. Phys. Chem. A (2005) 7, 334-341 A MELLOUKI, G. SOLIGNAC, G. LE BRAS, I. BARNES, R.L. WATERLAND The atmospheric chemistry of n-C6F13CH2OH To be presented at the SETAC Europe 15th Annual Meeting, Lille, 22-26 May 2005. (This work will also be submitted for publication) Does not contain TSCA CBI 7 TRP (March 30, 2005)