HFCs and Their Final FateHFCs and Their Final Fate

Becky OtterBecky Otter

Chemistry 481Chemistry 481

February 3, 2005February 3, 2005

What are HFCs?What are HFCs? HFCs or HFCs or

hydrofluorocarbons are hydrofluorocarbons are made of H,F, & Cmade of H,F, & C

They are used as They are used as replacements for replacements for chlorofluorocarbons chlorofluorocarbons (CFCs) and (CFCs) and hydrochlorofluorocarbons hydrochlorofluorocarbons (HCFCs)(HCFCs)

HFCsHFCs 1,1,1,2-tetrafluoroethane or HFC-134a1,1,1,2-tetrafluoroethane or HFC-134a HFCs are used as replacements because have near-HFCs are used as replacements because have near-

zero ozone depletion potentials (ODP), short zero ozone depletion potentials (ODP), short atmospheric lifetimes, less or non-flammable, low global atmospheric lifetimes, less or non-flammable, low global warming potentials (GWPs), are cheap, high volatility, warming potentials (GWPs), are cheap, high volatility, and very low solubility in water.and very low solubility in water.

Most importantly the C-H bonds allow the HFCs to react Most importantly the C-H bonds allow the HFCs to react with OH radicals and breakdownwith OH radicals and breakdown

(Tsai, Chemosphere 61, 2005 p1539-1547)(Tsai, Chemosphere 61, 2005 p1539-1547)

C

F

F

F

C

F

H

H

HFC-134a CH2FCF3CH2FCF3

Oxidation of HFC-134aOxidation of HFC-134a

Pathway 1

Pathway 2

TFA

Rac

Rac

Rac

Rac

Rac

Rac

C

F

F

F

C

F

O

C

F

F

F

C

F

O

C

F

F

F

C

F

O

C

F

F

F

C

F

H

H

F

FF

H2O

F

FF

O2 OR NO OR H2O

O2

OH C

F

F

F

C

F

O

C O

F

F

C

F

F

F

C

O

OH

C

F

F

F

C

F

O

HF

CH

F

O

CO2

H2O

C

F

F

F

OH

+

++

+

+

+ + + +

H

H

H

H

H

HFC134-aCF3CFHO radical

CF3CFHO radical CF3COF

CF3CFHO radical

CF3COF

CF3 radical

CF3 radical

What happens to HFCs after they What happens to HFCs after they are released into the environment?are released into the environment?

HFCs remain in the lower HFCs remain in the lower atmosphereatmosphere

There are several products of There are several products of oxidation: TFA, HF, Coxidation: TFA, HF, C33FOF, FOF, COCO22, CF, CF33OH, HCOFOH, HCOF

Some HFCs (HFC-32, HFC-Some HFCs (HFC-32, HFC-143a, & HFC-152a) can form 143a, & HFC-152a) can form flammable mixtures with airflammable mixtures with air

Burning these compounds Burning these compounds produces more toxic produces more toxic compounds and other GHGs compounds and other GHGs adding to the Greenhouse adding to the Greenhouse EffectEffect

(Tsai, Chemosphere 61, 2005 p1539-1547)(Tsai, Chemosphere 61, 2005 p1539-1547)

HFCsAtmospheric lifetime (year) GWPa Flammability (%) log Kowd

      LFLb UFLc  

HFC-23 260 12 000 None 0.58 (0.64)

HFC-32 5 550 12.7–33.5 0.71 (0.21)

HFC-125 29 3400 None 0.84 (1.48)

HFC-134 9.6 1100 None 0.94

HFC-134a 13.8 1300 None 0.98 (1.06)

HFC-143a 52 4300 7.0–19.0 1.03

HFC-152a 1.4 120 4.2–20.2 1.13 (0.75)

HFC-227ea 33 3500 None 1.1

HFC-236ea 10 1200 None 1.2

HFC-236fa 220 9400 None 1.24

HFC-245ca 5.9 640 7.0–14.4 1.33

HFC-245fa 7.2 950 None 1.33 (1.35)

HFC-365mfc 9.9 890 3.8–13.3 1.79 (1.61)

HFC-43-10mee 15 1500 None 1.72

(Tsai, Chemosphere 61, 2005 p1539-1547)(Tsai, Chemosphere 61, 2005 p1539-1547)

So What Does This Mean?So What Does This Mean? Since HFCs have very low Since HFCs have very low

solubility in water they do solubility in water they do not stay in water very long not stay in water very long thus not serving a large riskthus not serving a large risk

COFCOF22 is a irritating gas and is a irritating gas and can be hydrolyzed to HF can be hydrolyzed to HF which is moderately toxic to which is moderately toxic to humans , however there humans , however there isn’t information on the isn’t information on the atmospheric concentration atmospheric concentration on the degradation product.on the degradation product.

TFA is also a skin/tissue TFA is also a skin/tissue irritant because it is a strong irritant because it is a strong carboxylic acid-it can be carboxylic acid-it can be acutely toxic to the acutely toxic to the biosystembiosystem

And Time Says?And Time Says? Culbertson and associates wanted Culbertson and associates wanted

to see how the relative amounts of to see how the relative amounts of CFCF33 containing compounds in containing compounds in

background air were changing background air were changing over the past two decades over the past two decades

The HFCs in question where CFThe HFCs in question where CF33H H

(HFC-23), CF(HFC-23), CF33CHCH33 (HFC-143a), (HFC-143a),

and CFand CF33CHCH22F (HFC-134a)F (HFC-134a)

Palmer Station, Antarctica

Cape Meares, OR

Point Barrow, AK

Table 1: Annual Average concentrations of CFTable 1: Annual Average concentrations of CF33--

containing trace gases in parts per trillion by containing trace gases in parts per trillion by volumevolume

( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

Fig. 4. OR emissions

( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

Fig. 5. AK and Antarctica emissions

Take home message: There has been a increase in the concentration of HFC in the atmosphere in OR, but only a slight difference has been seen in AK and Antarctica= Shows difference in where the emissions are coming from

Table 2. Average calculated emissions in Table 2. Average calculated emissions in

Greenhouse Gases yr−1 over five-year periodsGreenhouse Gases yr−1 over five-year periods

( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

What they concluded:What they concluded:

That over the past 2 decades, the That over the past 2 decades, the emission rates have increased thus the emission rates have increased thus the concentration of HFCs has increasedconcentration of HFCs has increased

There is a difference seen between the There is a difference seen between the two hemispheres most likely due to the two hemispheres most likely due to the fact that the Northern hemisphere emits fact that the Northern hemisphere emits more HFCsmore HFCs

CONCLUSIONSCONCLUSIONS HFCs are in fact GHGs HFCs are in fact GHGs

however I believe they however I believe they have much less have much less environmental impacts than environmental impacts than CFCs and HCFCsCFCs and HCFCs

The products of oxidation The products of oxidation are “rained out” and the are “rained out” and the atmospheric lifetime is atmospheric lifetime is relatively short for most relatively short for most HFCs-posing a much HFCs-posing a much smaller environment impact smaller environment impact than the alternatives than the alternatives

From experiments From experiments measuring concentrations measuring concentrations of HFCs, there is an of HFCs, there is an increase in the emission increase in the emission ratesrates