Document MJZpOQ0EzjVvEZxO2Jxw6dKZz

RECYCLED I-pV*) AR226-2702 AR226-2702 TORONTO WORKSHOP MATERIALS Septem ber 13-14,2004 _ Atmospheric Chemistry of Fluorotelomer Alcohols (Part 2) Robert Waterland DuPont Engineering Research & Technology, Wilmington, DE Outline What do we know for certain? initial gas phase reaction kinetics photolysis of FTOHs What do we know a little about? role of HOx and NOx photolysis of fluoroaldehydes What's missing that we must know? heterogeneous chemistry competition between HOx and NOx hydrates & fluorotelomer olefins The miracles o f science] 2 What we know for certain FTOH, CnF2n+1CH2CH2OH (n=l,10) are sufficiently volatile to be present in the atmosphere. [Stock etal,, 2004; Krusic etal., 2004 (submitted)] They do not photodissociate in the gas phase. [S. Mello etal., in preparation] The sole gas phase oxidation product is CnF2n+1CH2CHO. FTOH lifetime is approx. 11 days: expect long-range gas-phase transport. [Hurley eta!., 2004; Le Bras eta/., 577SC2004] CnF2n+1CH2CHO oxidises primarily to CnF2n+1CHO. [Hurley etal., 2004; Le Bras etal., 5F77IC2004] mm The miracles o f science'] What we know a little about L100%^^ C,,F,n+1CH2CHO (FTAL) most C,,F2ntlCHO (PFAL) What? A. It depends on what else is around: NOx and HOx. A'. It depends on where you are: urban/suburban or remote. IamThe miracles o f science What we know a little about A. What else is around: NOx. A'. Where you are: urban/suburban. CnF2nH.iC (0)02N 02(FPAN) and mostly CF20 B u t.... V; ; . ;V ;o ; This Is based on n=l,2,3,4. For the higher aldehydes (n>4), yields to FPAN and CF20 are unknown. 5 What we know a little about A. What else is around: HOx. A'. Where you are: remote regions. Qi^n+lCHO Will likely give some CnF2n+1C(0)0H and 0 ; B u t.... This is based on n = l,2,3,4 in smog chamber. For the higher aldehydes (n>4), yields to PFCA and 0 3 are unknown. _______ What we know a little about FTOH has to run a gauntlet of NOx dominant air before reaching region where acid can be made. The miracles o f science \/ What we know a little about Competition from photolysis. Do the fluoroaldehydes photolyze? Competition with chemical pathways? Q iF2n+lCH O + h v -- *CnF 2m 1 + ' C H 0 C nF2n+lH + C 0 What is known: The fluoroaldehydes absorb in the solar UV. They absorb a little more strongly than the normal aldehydes. The normal aldehydes photodissociate readily (hours/days). The miracles o f science] What we know a little about Hashikawa eta!., 1 Fluor. Chem. (in press). What is known: Solar UV absorption increases with chain length. Absorption peak shifted to higher % vs. normal aldehydes. Solar flux 1000X higher at peak of C4F9CHO vs. CH3CHO. What is unknown: -r... .......................................im.i.. . Quantum yields for photodissociation. For CF3CHO, photolysis quantum yield at 290-400 nm is 0.02. For CH3CHO, at 300nm the quantum yield is ~0.4. For the higher aldehydes no data exist. Figure I DuPont sponsoring an experimental quantum yield study I< 3 RThemiracles o f science What's missing that we must know? Heterogeneous physical chemistry Does FTOH sorb to atmospheric aerosol? If so, what happens to sorbed FTOH? water phase (condense/surfactant/separated phase) organic phase (condense/surfactant/separated phases) graphitic soot & mineral fraction Virtually nothing known about FTOH sorbing Strong indication of tight binding to soils Chemistry completely unknown I DuPont sponsoring an initial experimental investigation of FTOH s c .... ; What's missing that we must know? Heterogeneous reaction chemistry What is the chemistry on solid surfaces and liquids? e.g. Ellis eta/. [2004] reported ~5% PFCAs yield from FTOH + *C (no NOx) a suite of lower PFCAs were observed Proposed mechanism is HF elimination from perfluoroalcc)hols CF3(CF2)x.1CF2OH -- CF3(CF2)x.1CFO + HF We know this doesn't happen in gas phase So, it must be heterogeneous chemistry (but where?) Probably on quartz walls of small smog chamber The miracles o f science] 11 Smog Chamber at Ford Motor Co. KM B B B I Surface/Volume' ratio high;. 'Walls reactive. Reactant concentrations are ~100 ppm Photos are courtesy of T. Wallington, Ford. . -.. 0.14 m3 Pyrex chamber, 296 K, 700 7oirIrr ImmThe miracles o f science 12 EUPHORE Chamber in Valencia MR The miracles o f science] 13 What's missing that we must know? Perflnnrmktehvrie hydrates C,,F2n+1CHO -H20 = C,,F2n+1CH(OH)2 n=1-4 fluoroaldehydes are commercially available only as hydrates Do the n>4 fluoroaldehydes react with water droplets to give hydrates? If so, what is the chemistry of these hydrates? -, little study of hydrates to date 14 What's missing that we must know? Telomer B Olefin? CnF2n+1CH=CH2 (TBO) Residual levels of TBO and FTOH in polymers comparable Vapor pressures of TBO and FTOH are comparable 8-2 FTOH = 3 Pa at 21 C 8-2 TBO = 15 Pa at 25 C TBO much less water soluble (less in water phase?) 8-2 FTOH = 0.130 mg/L (Clariant) 8-2 TBO = 0.001 mg/L (Clariant) Little known about TBO chemistry Le Bras (2000) studied CnF2n+1CH=CH2 (n=4,6) with OH and Cl OH chemistry appears to be similar to FTOHs I Mre studyofTtelosrser 6 Olefin Atmospheric Chem needed Conclusions What we know for certain initial gas phase reaction kinetics What we know a little about - and need to know more about competition between HOx and NOx chemical fate of fluoroaldehydes photolysis of fluoroaldehydes What's missing that we must know? sorbing of FTOH to atmospheric aerosol heterogeneous chemistry hydrates & fluorotelomer olefins