151
Trifuoroacetic Acid from CFC Replacements
many additional sources of TFA. Most chemicals that have a trifuoromethyl
functional group (-CF 3 ) attached to a carbon are now suspected of potentially
forming TFA. Not all chemicals with a trifuoromethyl group will form TFA
since there are some other products that can be formed, such as trifuoromethanol that can eventually be converted to CO 2 and HF (Franklin, 1993).
The degree to which a -CF 3 containing molecules will form TFA is dependent
on the particular chemical, but most of them have the potential to form TFA
to some degree. Some of these additional chemicals that can form TFA have
the potential to create localized increases in TFA concentrations.
The frst, and probably largest source of TFA, is the atmospheric oxidation of HFC compounds as discussed above. These HFCs and HCFCs have
many applications. For example, HFC-134a is the main replacement for
CFC-12 and it is used extensively in small refrigeration units in cars and
domestic situations. Since this compound is not fammable, it is used as a
propellent in aerosol cans and “canned air” for removing dust from electronics. HFC-134a has a high GWP of 1,200 compared to CO 2 which has
a GWP of 1.0 by defnition. Due to this high GWP, HFC-134a is currently
being phased out in favor of compounds like HFO-1234yf that have considerably lower GWP values due to their short half-life in the atmosphere.
Some HCFCs, such as HCFC-123 and HCFC-124, have likewise been used
as transitional substitutes for the CFCs. These compounds, like HFC-134a,
also form TFA when they degrade in the atmosphere (Kotamarthi et al.,
1998). These compounds also have high GWP, so they are scheduled to be
phased out of new products in 2020 in developed countries and 2030 in
developing countries although they can be used to service existing equipment for an additional ten years. It is worth noting that not all transitional
HFCs and HCFCs form TFA. For example, HCFC-22 (CHClF 2 ) was the most
used refrigerant in the 2010s (Booten et al., 2020), but it does not form TFA
simply because it is a single carbon with two fuorines, one chlorine and
a hydrogen on it. HCFC-141b (CH 3 CCl 2 F) and HCFC-142b (CH 3 CClF 2 ) are
other examples. HFCs and HCFCs that have the potential to form TFA must
have a trifuoro group in the molecule.
The atmospheric concentrations of these compounds, and HFC-134a in
particular, have increased as their usage has increased (Figure 9.3). The
global consumption of HFC-134a was estimated to be between 260,000 and
310,000 t/yr, which makes it the most abundant currently used refrigerant
second only to HCFC-22 (CHClF 2 ) (Booten et al., 2020). It is expected that
TFA generation in the atmosphere will increase alongside the increased
atmospheric concentrations of HFC-134a. While HFC-134a is still a major
refrigerant, its phaseout has already begun and its most probable replacement is HFO-1234yf (Figure 9.1), which has a low GWP due to its very short
atmospheric half-life. By 2021, all new vehicles in the United States will have
HFO-1234yf as the refrigerant instead of HFC-134a. HFO-1234yf has solved
both the ozone-depleting problem and the global warming problem, but it
still forms TFA in the process (Henne et al., 2012; Luecken et al., 2010).
Trifuoroacetic Acid from CFC Replacements
many additional sources of TFA. Most chemicals that have a trifuoromethyl
functional group (-CF 3 ) attached to a carbon are now suspected of potentially
forming TFA. Not all chemicals with a trifuoromethyl group will form TFA
since there are some other products that can be formed, such as trifuoromethanol that can eventually be converted to CO 2 and HF (Franklin, 1993).
The degree to which a -CF 3 containing molecules will form TFA is dependent
on the particular chemical, but most of them have the potential to form TFA
to some degree. Some of these additional chemicals that can form TFA have
the potential to create localized increases in TFA concentrations.
The frst, and probably largest source of TFA, is the atmospheric oxidation of HFC compounds as discussed above. These HFCs and HCFCs have
many applications. For example, HFC-134a is the main replacement for
CFC-12 and it is used extensively in small refrigeration units in cars and
domestic situations. Since this compound is not fammable, it is used as a
propellent in aerosol cans and “canned air” for removing dust from electronics. HFC-134a has a high GWP of 1,200 compared to CO 2 which has
a GWP of 1.0 by defnition. Due to this high GWP, HFC-134a is currently
being phased out in favor of compounds like HFO-1234yf that have considerably lower GWP values due to their short half-life in the atmosphere.
Some HCFCs, such as HCFC-123 and HCFC-124, have likewise been used
as transitional substitutes for the CFCs. These compounds, like HFC-134a,
also form TFA when they degrade in the atmosphere (Kotamarthi et al.,
1998). These compounds also have high GWP, so they are scheduled to be
phased out of new products in 2020 in developed countries and 2030 in
developing countries although they can be used to service existing equipment for an additional ten years. It is worth noting that not all transitional
HFCs and HCFCs form TFA. For example, HCFC-22 (CHClF 2 ) was the most
used refrigerant in the 2010s (Booten et al., 2020), but it does not form TFA
simply because it is a single carbon with two fuorines, one chlorine and
a hydrogen on it. HCFC-141b (CH 3 CCl 2 F) and HCFC-142b (CH 3 CClF 2 ) are
other examples. HFCs and HCFCs that have the potential to form TFA must
have a trifuoro group in the molecule.
The atmospheric concentrations of these compounds, and HFC-134a in
particular, have increased as their usage has increased (Figure 9.3). The
global consumption of HFC-134a was estimated to be between 260,000 and
310,000 t/yr, which makes it the most abundant currently used refrigerant
second only to HCFC-22 (CHClF 2 ) (Booten et al., 2020). It is expected that
TFA generation in the atmosphere will increase alongside the increased
atmospheric concentrations of HFC-134a. While HFC-134a is still a major
refrigerant, its phaseout has already begun and its most probable replacement is HFO-1234yf (Figure 9.1), which has a low GWP due to its very short
atmospheric half-life. By 2021, all new vehicles in the United States will have
HFO-1234yf as the refrigerant instead of HFC-134a. HFO-1234yf has solved
both the ozone-depleting problem and the global warming problem, but it
still forms TFA in the process (Henne et al., 2012; Luecken et al., 2010).