Hexafluoropropene, oxidized, oligomers, reduced, fluorinated

Phototransformation in air

Administrative data

Endpoint:

phototransformation in air

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Details on test method are given. Method and results are scientifically valid.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2006

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

By the mean of smog chamber/FTIR techniques and by analogy to other long-lived perfluorinated compounds, the following parameters have been determined:

(i) the kinetics of reactions with chlorine atoms and hydroxyl radicals,
(ii) the infrared spectrum,
(iii) the atmospheric lifetime, and
(iv) the global warming potential.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Hexafluoropropene, oxidized, oligomers, reduced, fluorinated

EC Number:

500-537-5

EC Name:

Hexafluoropropene, oxidized, oligomers, reduced, fluorinated

Cas Number:

161075-00-9

Molecular formula:

R-O(C3F6O)m-R with R= - CF3, - C2F5, -CF2H

IUPAC Name:

1,1,1,2,3,3-hexafluoro-2,3-bis(1,1,2,2,2-pentafluoroethoxy)propane; 1,1,1,2,3,3-hexafluoro-2-(1,1,2,2,2-pentafluoroethoxy)-3-(trifluoromethoxy)propane; 1,1,1,2,3,3-hexafluoro-3-(1,1,2,2,2-pentafluoroethoxy)-2-(trifluoromethoxy)propane; 1,1,1,2,3,3-hexafluoro-3-{[1,1,1,2,3,3-hexafluoro-3-(trifluoromethoxy)propan-2-yl]oxy}-2-(trifluoromethoxy)propane; 1,1,1,3,3,4,6,6,7,9,9,10,12,12,12-pentadecafluoro-4,7,10-tris(trifluoromethyl)-2,5,8,11-tetraoxadodecane; 1-(difluoromethoxy)-1,1,2,3,3,3-hexafluoro-2-(1,1,2,2,2-pentafluoroethoxy)propane; 2,2,3,5,5,6-hexafluoro-3,6-bis(trifluoromethyl)-1,4-dioxane; 2-(difluoromethoxy)-1,1,1,2,3,3-hexafluoro-3-(1,1,2,2,2-pentafluoroethoxy)propane

Details on test material:

- Name of test material (as cited in study report): GALDEN HT 70, PFPMIPE (Perfluoropolymethylisopropyl ether)
- Substance type: Reaction mass
- Physical state: liquid
- Composition of test material, percentage of components: The fraction of GALDEN LMW selected for the experiment boils at 70°C, has an average molecular weight of 410 and is composed primarily of CF3OCF(CF3)CF2OCF2-OCF3 (molecular weight = 386), with smaller amounts of CF3OCF(CF3)CF2OCF2OCF2OCF3 (molecular weight = 452) and longer-chain PFPMIEs.

Study design

Details on test conditions:

The atmospheric chemistry of PFPMIE was investigated.
Specifically, the following information was determined using smog chamber/FTIR techniques and by analogy to other long-lived perfluorinated compounds:
(i) the kinetics of reactions with chlorine atoms and hydroxyl radicals,
(ii) the infrared spectrum,
(iii) the atmospheric lifetime, and
(iv) the global warming potential.


Experiments were performed in a 140 L Pyrex reactor interfaced to a Mattson Sirus 100 FTIR spectrometer.
The reactor was surrounded by 22 fluorescent blacklamps (GE F15T8-BL), which were used to photochemically initiate the experiments. Chlorine atoms were produced by the photolysis of molecular chlorine:

Cl2 + hv --> Cl + Cl

OH radicals were produced by the photolysis of CH3ONO in air:

CH3ONO + hv --> CH3O(°) + NO
CH3O(°) + O2 --> HO2 + HCHO
HO2 + NO --> OH + NO2

In relative rate experiments, the following reactions take place:
OH/Cl + reactant --> products


All experiments were performed at 296 +-1 K.

Concentrations of reactants and products were monitored by FTIR spectroscopy. IR spectra were derived from 32 coadded interferograms with a spectral resolution of 0.25 cm-1 and an analytical path length of 27.1 m. To check for the unwanted loss of compounds via heterogeneous reactions, reaction mixtures were left to stand in the chamber for 60 min without irradiation; there was no observable (<1%) loss of the reactants.

Results and discussion

% Degradation

% Degr.:

100

Sampling time:

800 yr

Test condition:

estimate

Any other information on results incl. tables

Kinetics

The kinetics of reaction 1 were measured relative to those of reaction 2:

Cl+PFPMIE--> products (1)

Cl+CF2ClH--> products (2)

UV irradiation of the gas mixture for 4 min led to a 94% consumption of CF2ClH but no observable loss (<2%) of

PFPMIE. Usingk2)1.7_10-15 cm3 molecule-1 s-1 (6), we derive an upper limit ofk1<2_10-17 cm3 molecule-1 s-1.

The loss of PFPMIE via reaction with Cl atoms is not of atmospheric significance.

The kinetics of reaction 3 were measured relative to those of reaction 4:

OH+PFPMIE -- > products (3)

OH+C2H2 -- > products (4)

UV irradiation of the gas mixture led to a loss of C2H2 but no discernible loss of PFPMIE. By analogy to the substantial existing database for fluorinated compounds, if PFPMIE were to be oxidized by reaction with OH radicals, it would be expected to result in conversion of PFPMIE into COF2 via an “unzipping” mechanism (Wallington T.J. et al, 1997)). IR product features attributable to COF2 were sought but not found, and an upper limit of 0.0565 mTorr was established for the formation of this compound.

CF3OCF(CF3)CF2OCF2OCF3 is the main component of PFPMIE. Degradation initiated by C-C or C-O bond scission in the CF3OCF(CF3)-or-CF2OCF2OCF3 moieties will give either 2 or 4 molecules of COF2, respectively. Assuming formation of 2 molecules of COF2 the authors conclude that<0.028 mTorr of PFPMIE was consumed (i.e.,<0.032% of the initial PFPMIE concentration of 88.8 mTorr). In this experiment, C2H2 loss was 32.5%. We conclude thatk3/k4<8.1_10-4. Usingk4)8.45_10-13 cm3 molecule-1 s-1 (Sorensen M. et al, 2003), givesk3<6.8_10-16 cm3 molecule-1 s-1.

Using a global weighted-average OH concentration of 1.0_106 molecules cm-3 (Prinn R. G. et al., 2001) leads to a lifetime of PFPMIE withrespect to reaction with OH radicals of greater than 46 years.

Photolysis of PFPMIE

According to the authors, the main degradation pathway for PFPMIE is the upper atmosphere photolysis.

The authors assume that PFPMIE have the same absorption of perfluoroalkanes, which absorb strongly at 121.6 nm. Therefore, as the perfluoroalkanes is assumed that PFPMIE are photolyzed within few days at around 80 km.

However, the degradation of PFPMIE requires that it be present in the mesosphere before it can undergo photolysis. Only 2x10-5 of the atmosphere is found above a 75 km altitude. Consequently, air must cycle through the mesosphere many thousands of times before the entire atmospheric burden would be depleted. Although the absolute photolysis rate constant at 80 km is likely to be fast, the time taken for air to cycle through this altitude leads to a long lifetime. Compounds for which the main degradation pathway is upper-atmosphere photolysis have been estimated to have lifetimes of at least 800 years. This is the minimum lifetime for PFPMIE.

IR spectrum and Global Warning Potential.

IR spectra were recorded at 296 K using 0.9-2.4 mTorr of PFPMIE in 700 Torr of air diluent. Typical peak absorbances were in the range 0.05-0.7 and scaled linearly with the PFPMIE concentration. The absolute absorption spectrum is shown in the attached Figure.

The authors estimate the radiative forcing from IR absorption spectra, according to Pinnock S. et al. (1995) method. Assuming that lifetime of PFPMIE is 800 years, which was discussed above, and lifetime of CFC-11 is 45 years (Hounghton J.T. et al, 2001), the authors estimate that the HGWP of PFPMIE (relative to CFC-11) is 1.95 for a 100 year horizon and relative to CO2, the GWP of PFPMIE is 9000 for a 100 year time horizon (Relative to CO2, the GWP of CFC-11 on a 100 year time horizon is 4600).

 Basing on these results, the radiative forcing of PFPMIE is approximately 30% greater than that of the perfluoroalkane with the same number of C-F bonds,n-C6F14. This may reflect the fact that, in addition to the C-F bonds, PFPMIE has three C-O bonds that would be expected to absorb within the atmospheric window. Only a few compounds have been shown to have radiative forcings that exceed that of PFPMIE.

Applicant's summary and conclusion

Conclusions:

Galden LMW is estimated to have an atmospheric lifetime of 800 years.
For a 100 year horizon, the HGWP of GALDEN LMW is estimated to be 1.95 and the GWP to be 9000.

Executive summary:

The scope of the reported work was to provide information on the atmospheric fate of PFPEs. To provide these data the authors indagated the atmospheric chemistry of Perfluoropolymethylisopropyl ethers (PFPMIPEs), specifically the fraction of GALDEN LMW named GALDEN HT70 was analyzed. The analysed sample had an avarage molecular weight of 410 ant it was composed primarily of CF3OCF(CF3)CF2OCF2-OCF3 (molecular weight = 386), with smaller amounts of CF3OCF(CF3)CF2OCF2OCF2OCF3 (molecular weight = 452) and longer-chain PFPMIEs.

The following information was determined using smog chamber/FTIR techniques and by analogy to other long-lived perfluorinated compounds:

(i) the kinetics of reactions with chlorine atoms and hydroxyl radicals,

(ii) the infrared spectrum,

(iii) the atmospheric lifetime, and

(iv) the global warming potential.

As results, the loss of PFPMIE via reaction with Cl atoms is not of atmospheric significance and the lifetime of PFPMIE with respect to reaction with OH radicals was calculated to be greater than 46 years.

According to the authors, the main degradation pathway for PFPMIE is the upper atmosphere photolysis in which it is assumed that PFPMIEs are photolyzed within few days. Howerever, since the main degradation pathway is upper-atmosphere photolysis, PFPMIE have been estimated to have lifetimes of at least 800 years. The IR absorption spectrum is reported in the attached figure.

The authors estimated the radiative forcing from the IR absorption spectra, according to the Pinnock S. et al. (1995) method. Assuming that the lifetime of PFPMIE is 800 years the HGWP of PFPMIE (relative to CFC-11) was calculated to be 1.95 for a 100 year horizon and the GWP of PFPMIE was calculated to be 9000 for a 100 year time horizon (Relative to CO2, the GWP of CFC-11 on a 100 year time horizon is 4600).