Kinetics and products formation of the gas-phase reactions of tetrafluoroethylene with OH and NO3 radicals and ozone

Article abstract of DOI:10.1016/S0009-2614(99)00698-3

Fourier-transformed infrared spectroscopy (FT-IR) was used to determine the rate constants and products for the reactions of tetrafluoroethylene (C₂F₄) with OH, NO₃ and O₃ at 298±4 K and 740±5 Torr. The rate constants (k) measured were: k_CF2CF2+OH=(1.13±0.33)×10^-11, k_CF2CF2+NO3<3×10^-15 and k_CF2CF2+O3=(4.80±0.62)×10^-21 (in cm³ molecule^-1 s^-1 and all values are with 2σ overall uncertainties). CF₂O was the only oxidation end-product identified from the above reactions. The results obtained indicate a chemical lifetime of tetrafluoroethylene of about 1 day in the troposphere.

Full text of DOI:10.1016/S0009-2614(99)00698-3

2
0 August 1999
Chemical Physics Letters 309 Ž1999. 364–368
www.elsevier.nlrlocatercplett
Kinetics and products formation of the gas-phase reactions of
tetrafluoroethylene with OH and NO radicals and ozone
3
a
a,)
b
a
Gloria Acerboni , Niels R. Jensen , Bruno Rindone , Jens Hjorth
a
European Commission, Joint Research Centre, EnÕironment Institute, TP 272, I-21020 Ispra (VA), Italy
Department of EnÕironmental Science, UniÕersity of Milan, Via L. Emanueli 15, I-20126 Milan, Italy
b
Received 1 March 1999; in final form 5 June 1999
Abstract
Fourier-transformed infrared spectroscopy ŽFT-IR. was used to determine the rate constants and products for the
reactions of tetrafluoroethylene ŽC F . with OH, NO and O3 at 298"4 K and 740"5 Torr. The rate constants Žk.
2
4
3
y
11
y15
y21
measured were: k
sŽ1.13"0.33.=10 , k
-3=10
and k
sŽ4.80"0.62.=10
CF2CF2qO3
CF2CF2qOH
y1 y1
CF2CF2qNO3
3
Žin cm molecule
s
and all values are with 2s overall uncertainties.. CF O was the only oxidation end-product
2
identified from the above reactions. The results obtained indicate a chemical lifetime of tetrafluoroethylene of about 1 day in
the troposphere. q 1999 Elsevier Science B.V. All rights reserved.
1
. Introduction
emitted into the atmosphere is unknown. This could
be compared, for example, with the global annual
production and emissions of saturated perfluoro
compounds like CF , C F and SF , which have
The kinetics of saturated perfluoro compounds
like CF , C F and SF have been investigated and it
is well understood that they are very stable with
atmospheric lifetimes of more than 3000 years w1x.
Only very limited kinetic information is available
about unsaturated perfluoro compounds, like C F ,
and their atmospheric lifetimes are not known. In
this investigation, we have determined the rate coef-
ficients and the products for the reactions of C F4
with the radicals OH and NO and with O in order
to estimate the chemical lifetime and the fate of this
compound in the atmosphere.
4
2
6
6
4
2
6
6
9
9
been estimated to be about 27=10 , 27=10 and
9
y1
5
1
=10 g year , respectively, by the end of the
980s and the early 1990s Žassuming that all is
2
4
emitted to the atmosphere. w3,4x.
Three previous studies dealing with the gas-phase
degradation of C F have been published: Heicklen
2
4
2
w5x used infrared spectroscopy to study the gas-phase
3
3
reaction between C F and O at room temperature
2
4
3
and at 1–24 Torr total pressure. He measured the
rate constant for the reaction between C F and O
2
4
3
For unsaturated perfluoro compounds like C F ,
2
4
y19
3
y1 y1
to be 4.98=10
cm molecule
s
and he found
global annual production has been estimated to be
around 50=10 g year in 1998 w2x, but the amount
carbonyl fluoride, CF O, as the only product. Toby
9
y1
2
and Toby w6x also studied the gas-phase reaction
between C F and O in the temperature range from
2
4
3
)
Corresponding author
273 to 383 K and in the pressure range from 0.3 to
0
009-2614r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
PII: S0009-2614Ž99.00698-3

G. Acerboni et al.rChemical Physics Letters 309 (1999) 364–368
365
1
5 Torr by using gas chromatography. They obtained
y20
3
y1 y1
a value of 2.84=10
cm molecule
s
for the
rate constant of this reaction. Because of the above
discrepancy, we decided to investigate this reaction.
Gozzo and Camaggi w7x used gas chromatography to
study the products of the reaction between C F and
2
4
ozone at 273 K and at 1 atm. They observed CF O
2
and tetrafluoroethylene epoxide, CF CF O, as prod-
2
2
ucts. To our knowledge, kinetics or products of the
reactions of C F with OH and NO have not been
determined.
2
4
3
Fig. 1. Plot of lnÄwCF CF x rwCF CF x 4 corrected for wall losses
2
2
0
2
2 t
and photolysis versus lnwcyclohexanex rwÄwcyclohexanex 4 for the
0
t
decay of CF CF and cyclohexane during the photolysis of meth-
2
2
ylnitrite producing OH radicals. kw slosses on the wall andror
photolysis.
2
. Experimental
All the experiments were performed in purified
air at 740"5 Torr total pressure and at 298"4 K in
a 480 l Teflon-coated reaction chamber. The cham-
ber is surrounded by UVrVIS lamps Žblack lamps,
l0300 nm. and equipped with a multiple reflection
mirror system for on-line Fourier transform infrared
spectroscopy ŽFT-IR. with a total optical pathlength
NO radicals were produced by mixing O with an
3
3
excess of NO , to establish equilibrium between
2
NO , NO and N O . Ozone was prepared by silent
3
2
2
5
discharge of pure oxygen. CH ONO was synthesized
3
by adding H SO Ž50 wt% aqueous solution. to
2
4
sodium nitrite dissolved in a methanolrwater mix-
of 81.23 m. A detailed description of the experimen-
ture as described in detail elsewhere w9x.
tal system has been published previously w8x. The
The OH and NO3 reaction rate constants were
determined with the ‘relative rate’ method and the
O3 reaction rate constant was measured under
‘pseudo-first-order’ conditions on C F . Both meth-
spectra were obtained with a Bruker IFS 113 v at a
y1
nominal resolution of 1 cm
scans.
by co-adding 20–50
2
4
Hydroxyl radicals were generated from in-situ
ods have been previously described in detail w10x.
Reference compounds used in the ‘relative rate’
method were propene and cyclohexane. The refer-
ence compounds used for each reaction are listed in
the footnote of Table 1. By the ‘relative rate’ method,
the ratio of the rate constants k rk is found as the
photolysis of methylnitrite ŽCH ONO. in the pres-
3
ence of NO by using UVrVIS lamps Žl0300 nm..
Table 1
Rate constants k determined in this and other investigations at
room temperature. All k values from this investigation are given
A
B
slope of a plot of lnŽ A rA .yk t versus lnŽB rB .
0
t
w
0
t
3
y1 y1
in units of cm molecule
s
and with 2s overall uncertainty
yk t, where A and B are the initial concentra-
w
0
0
Compound
CF CF
Reference
tions, A and B are the concentrations at time t and
t t
2
2
y11
a
c
kw t is an additional first-order loss process, if any
additional loss process is present, described by the
rate constant kw for A and B, respectively Žsee, e.g.,
Fig. 1.. The pseudo-first-order method has also been
described elsewhere w10x. Loss of C F in an excess
OH
NO3
O3
1.13"0.33=10
-3=10
This work.
This work.
This work.
Heicklen w5x
Toby and Toby w6x
y15
b
y21
4.80"0.62=10
y19
O3
4.98=10
y20
O3
2.84=10
2
4
a
of O was measured to obtain a pseudo-first-order
Measured relative to propene and cyclohexane using k
3
OHqpropene
X
y11
3
y1 y1
sŽ3.0"0.8.=10
cm molecule
s
, where a rate constant
decay k ŽskwO x. from the plot of lnwCF CF x ver-
3
2
2 t
X
ratio of Ž0.375"0.118. was found, and k
sŽ7.2"
sus time t. A plot of measured k values versus O
x
w
OHqcyclohexane
3
y12
3
y1 y1
1
.5.=10
ratio of Ž1.566"0.226. was found.
cm molecule
s
w11,12x, where a rate constant
yielded the rate constant k as the slope Žsee, e.g.,
Fig. 3.. It should be mentioned that for the O3
reaction a large amount of cyclohexane Ž50–90
ppmV. was added to scavenge OH radicals and other
b
Measured relative to propene using k
sŽ9.4"5.5.=
NO3qC3H6
y15
3
y1 y1
1
0
cm molecule
s
w13x.
c
Determined by pseudo-first-order method.

3
66
G. Acerboni et al.rChemical Physics Letters 309 (1999) 364–368
radicals that may be formed by secondary chemistry
uncertainty is given as 2s , where s is the weighted
average of the standard deviation obtained in the two
1
3
y3
Ž1 ppmVs2.46=10 moleculescm
at 298 K
and 760 Torr..
series of experiments. The uncertainty of the O rate
3
In purified air, CF CF showed a first-order decay
constant was obtained by taking to 2s of the slope
shown in Fig. 3.
2
2
in our reaction chamber with the UVrVIS lamps
turned on Žl0300 nm., but without the presence of
The compounds used in this investigation had the
following purity: CF CF Ž)99.9% pure, Ausimont.,
CH ONO; this additional loss process was attributed
3
2
2
to wall loss and losses due to photolytical generation
propene ŽUcar, )99.5% pure., cyclohexane Ž99.5%
y6 y1
of radicals with k sŽ4.7"0.3.=10
s
. In the
pure, Carlo Erba., Ž99.9% pure, Ucar, CF O Ž97%
w
2
case of loss rate coefficients for the reference com-
pure, Matheson., synthetic air Ž80% N and 20% O :
2
2
y5
pound propene, a value of k sŽ1.1"0.2.=10
099.95% pure, SIO. and O Ž099.9% pure, SIO..
w
2
y1
s
was obtained. The reference compound cyclo-
hexane did not show any loss process, and a value of
y6 y1
-
2=10
s
were assumed for k , which means
3. Results and discussion
w
that no data adjustment is needed for this compound.
Without lamps on, none of the compounds showed
The reactions of CF CF with the radicals OH
2
2
y6
y1
any significant loss and a value -2=10
s
and NO , and with O have been investigated and
3
3
were assumed for k , which again means that no
w
the results from the kinetics study are summarised in
Table 1.
data adjustment is needed for the compounds in this
investigation. It should be mentioned that these addi-
tional losses are relatively small, because duration of
an experiment is normally between 10 and 60 min.
The additional loss process Žwall lossqphotolysis.
was always below 10% of the overall decay coeffi-
cients during an experiment for all of the experi-
ments performed in this investigation.
The reaction between CF CF and the OH radi-
2
2
cal:
CF CF qOH™products
1
Ž .
2
2
Fig. 1 shows the relative loss rates of CF CF and
2 2
cyclohexane in the presence of OH radicals. As
shown in Table 1, a value of k sŽ1.13"0.33.=
1
y11
3
y1 y1
The following IR bands were used for spectral
10
cm molecule
s
was determined. To our
y1
subtraction: 1163–1201 and 1265–1370 cm
for
knowledge, this rate constant has not been deter-
mined before, but one can compare it to the rate
coefficients of the reactions of CH CH , CH CF
y1
CF CF , 907–915 cm for propene and 2840–2895
2
2
y1
cm for cyclohexane.
2
2
2
2
Typical initial experimental conditions: 2 ppmV
and CCl CCl with the OH radical: k
s
2
2
CH2CH2qOH
y1 y1
y12
3
-
wC F x-4 ppmV, 8 ppmV-wreference com-
Ž9.0 " 4.5. = 10
cm molecule
s
w11x,
2
4
y 12
3
poundx-50 ppmV, 10 ppmV-wCH ONOx-30
k
cule
10
s Ž4.0 " 2.0. = 10
cm mole-
3
CH2CF2q OH
y1 y1
ppmV, 8 ppmV-wNOx-15 ppmV, 10 ppmV-
wN O x-100 ppmV and 25 ppmV-wO x-600
s
w13x and k
sŽ1.7"0.3.=
CCl2CCl2qOH
y13
3
y1 y1
cm molecule
s
w14x. As can be seen, our
2
5
3
ppmV.
value is similar to the ethene and CH CF reactions
2 2
CF CF was calibrated by the normal monometric
but very different from the CCl CCl reaction. For
2 2
2
2
method.
reaction 1, carbonyl fluoride was the only end-prod-
uct identified with a product yield of 40–45% Žcarbon
in product compared to the reacted carbon.. Spectral
features at 793, 1302 and 1718 cm were observed
in the product spectrum indicating the presence of a
peroxynitrate compounds w15x. We have tentatively
attributed these bands to the compound CF2-
The value of the OH reaction rate constant and its
uncertainty were obtained as follows. First, rate con-
stants and s values were obtained from four indi-
vidual experiments for each of the reference com-
pounds, then the uncertainty of the rate constant of
the reference compound were incorporated by using
standard propagation of error, i.e., Ža qb . . Two
reference compounds were used, so the value of the
rate constant was calculated as the mean of the two
values weighted by their standard deviations. The
y1
2
2 0.5
ŽOH.CF O NO . This peroxynitrate compound is
2
2
2
not commercial available and therefore we do not
know how much of this compound is produced by
the reaction between C F and the OH radical, but
2
4

G. Acerboni et al.rChemical Physics Letters 309 (1999) 364–368
367
some of the missing carbon in the carbon balance is
within that product.
Fig. 2 shows the loss rates of CF CF due to its
2
2
reaction with NO3,
CF CF qNO ™products
2
Ž .
2
2
3
relative to that for propene in the presence of NO3
radicals. As shown in Table 1, a value of k -3=
2
y15
3
y1 y1
1
0
cm molecule
s
was determined. Due to
the relatively large random error on the individual
experiments and due to the large uncertainty for the
rate constant for the reference compound, we prefer
to present here the value as an upper limit. To our
knowledge, this parameter has not been determined
before, but it can be compared with the rate coeffi-
cient for reactions of CH CH with the NO radi-
X
Fig. 3. Plot of k versus wO x for the reaction between CF CF
3
2
2
and O3 in the presence of cyclohexane.
available in the literature, as shown in see Table 1. It
should be mentioned, that when we performed our
experiment in absence of cyclohexane added to
scavenge OH and other radicals , we obtained a
value about a factor of 10 larger, indicating that
secondary chemistry may have contributed to the
loss of C F reported in two previous investigations.
CF O was determined as the only identified oxida-
tion end-product and it had a product yield of 92–
2
2
3
y 16
Ž
cals:
cm molecule
k
s Ž2.09 " 0.40. = 10
CH 2CH 2q N O 3
y1 y1
3
.
s
w11x. As can be seen, both of
these reactions are relatively slow. For reaction 2,
carbonyl fluoride, CF O, was the only identified
2
product and it had a yield of 55-80% Žalso here on a
carbon basis.. In contrast to reaction 1, no spectral
2 4
2
features for either peroxynitrates or nitrates were
observed in the product spectrum, possibly indicating
that CF ŽONO .CF O NO is very unstable.
9
8% Žagain on a carbon basis.. Our yield of CF O
agrees with those reported previously w5,7x.
2
2
2
2
2
2
This rate constant, k , for the reaction between
3
CF CF and O :
2
2
3
4
. Atmospheric implications
CF CF qO ™products
3
Ž .
2
2
3
was determined using first-order conditions and a
Table 2 shows a rough estimate of the tropo-
X
plot of k versus wO x can be found in Fig. 3. As can
spheric chemical lifetime of CF CF with respect to
3
2 2
be seen in Table 1, a value of k sŽ4.80"0.62.=
reactions with OH, NO and ozone. As can be seen a
3
3
y21
3
y1 y1
1
0
cm molecule
s
was determined. This
very short atmospheric lifetime of about 1 day for
CF CF could be estimated with respect to its reac-
value is significantly lower than the other values
2
2
tion with the OH radical. Therefore the lifetime will
strongly depend on local and seasonal conditions, but
it does indicate a negligible global warming potential
ŽGWP. from this compound compared to GWP for
Table 2
Estimate of the tropospheric chemical lifetime t of tetrafluoro-
ethylene with respect to the reaction with OH, NO3 and ozone
a
b
c
Compound
C F
OH
1 day
NO3
)156 days
O3
9 years
2
4
a
Assuming an wOHx of 1=106 moleculescm w16x.
y3
Fig. 2. Plot of lnÄwCF CF x rwCF CF x 4 versus lnÄwpropenex r
2
2
0
2
2
t
0
b
c
7
y3
wÄwpropenex 4 for the decay of CF CF and propene during the
NO is assumed to be 2.5=10 moleculescm Ž1 pptV. w17,18x.
t
2
2
3
reaction with NO3 radicals.
The concentration given for O3 is a 24-h average w19x.

3
68
G. Acerboni et al.rChemical Physics Letters 309 (1999) 364–368
w5x J. Heicklen, J. Phys. Chem. 70 Ž1966. 477, qcorrection
CFC-11, which has been estimated to have an overall
atmospheric lifetime of about 50 years w20x. Com-
pared to atmospheric lifetimes of saturated perfluoro
sheet added by the author to page 480.
w6x F.S. Toby, S. Toby, J. Phys. Chem. 80 Ž1976. 2313.
w7x F. Gozzo, G. Camaggi, Chim. Ind. 50 Ž1968. 197.
w8x N.R. Jensen, J. Hjorth, C. Lohse, H. Skov, G. Restelli, Atm.
Environ. 25A Ž1991. 1897.
compounds like CF , CF CF and SF , which have
4
3
3
6
been estimated to be more than 3000 years w1x, the
w9x W.D. Taylor, T.D. Allston, M.J. Moscato, G.B. Fazekas, Int.
lifetime of C F of about 1 day is negligibly small.
2
4
J. Chem. Kinet. 12 Ž1980. 231.
The main atmospheric degradation product from
w10x M. Glasius, A. Calogirou, N.R. Jensen, J. Hjorth, C.J. Nielsen,
CF CF has been identified in this investigation to
2
2
Ž
.
Int. J. Chem. Kinet. 29 1997 527.
be CF O, which is rapidly Žwithin a few days.
2
w11x R. Atkinson, D.L. Baulch, R.A. Cox, R.F. Hampsom Jr., J.A.
Kerr, J. Troe, J. Phys. Chem. Ref. Data. 21 Ž1992. 1125.
w12x R. Atkinson, S.M. Aschmann, Int. J. Chem. Kinet. 24 Ž1992.
incorporated into raindropsraerosols w21x and even-
tually converted to HF and CO w22x.
2
9
83.
w13x R. Atkinson, D.L. Baulch, R.A. Cox, R.F. Hampsom Jr., J.A.
Kerr, J. Troe, J. Phys. Chem. Ref. Data. 18 Ž1989. 881.
w14x C.J. Howard, J. Chem. Phys. 65 Ž1976. 4771.
Acknowledgements
w15x H. Niki, P.D. Maker, C.M. Savage, L.P. Breitenbach, M.D.
Hurley, Int. J. Chem. Kinet. 18 Ž1986. 1235.
The authors gratefully acknowledge the help of G.
Ottobrini with the experimental work.
w16x R.G. Prinn, R.F. Weiss, B.R. Miller, J. Huang, F. Alyea, D.
Cunnold, P. Fraser, D. Hartley, P. Simmonds, Science 269
Ž1995. 187.
w17x U. Platt, F. Heintz, Isl. J. Chem. 34 Ž1994. 289.
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