United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-97/065 August 1997
&EPA Project Summary
New Chemical Alternative for
Ozone-Depleting Substances:
HFC-236fa
N. Dean Smith, Theodore G. Brna, Cynthia L. Gage, and Robert V. Hendriks
Hydrofluorocarbons (MFCs) form a
class of chemicals having the potential
to replace stratospheric ozone deplet-
ing substances such as chlorofluoro-
carbons (CFCs) and hydrochlorofluoro-
carbons (HCFCs). The report gives re-
sults of a preliminary evaluation of a
new HFC (HFC-236fa or 1,1,1,3,3,3-
hexafluoropropane) as a possible al-
ternative for CFC-114 (1,2-dichloro-
1,1,2,2-tetrafluoroethane) refrigerant for
chillers and as a possible fire suppres-
sant replacement for halon-1301
(bromotrifluoromethane). Evaluation
tests included examinations of flam-
mability, stability, atmospheric lifetime,
thermophysical properties, lubricant
miscibility and solubility, materials com-
patibility, inhalation toxicity, refrigera-
tion performance, heat transfer charac-
teristics, and flame suppression. Re-
sults of these examinations indicate
that HFC-236fa is a viable alternative
for CFC-114 refrigerant and for halon-
1301 or -1211 fire extinguishing agent.
Its relatively long atmospheric lifetime
may be a concern from a global warm-
ing perspective.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory's Air Pollution
Prevention and Control Division, Re-
search Triangle Park, NC, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Fully halogenated CFCs and their bro-
mine-containing relatives (halons) are rec-
ognized as primary contributors to deple-
tion of Earth's stratospheric ozone layer.
As early as 1978, the U. S. Environmen-
tal Protection Agency (EPA) promulgated
regulations banning the use of CFCs as
aerosol propellents in all but a few ex-
empted applications. In the mid-1980's,
the EPA began considering additional
regulatory restrictions on the use of CFCs
and halons. In the course of this consid-
eration, it became apparent that few, if
any, alternative chemicals were readily
available or had been proven applicable
to the numerous CFC and halon uses
which had grown dramatically in the time
following the 1978 CFC aerosol ban.
Following the advice of an expert panel
convened by the EPA, the Agency's Of-
fice of Research and Development un-
dertook a program to systematically
search for additional alternative chemi-
cals to serve as backups if the few chemi-
cals proposed by industry fell short of
expectations. Over a 3-year period, 37
new compounds were prepared of suffi-
cient stability and in sufficient yield and
purity to obtain a limited set of relevant
property measurements. All of these com-
pounds were partially fluorinated hydro-
carbons or ethers. Based on the thermo-
physical properties obtained for these
compounds, EPA selected 12 chemicals
(including HFC-236fa) for more extensive
evaluation.
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Evaluation Tests and Results
HFC-236fa contains no chlorine or bro-
mine atoms and therefore has zero po-
tential to deplete stratospheric ozone. Its
reaction rate at 298 K with hydroxyl (OH)
radical is 0.034 x 10'14 cm3 molecule'1
sec1. This reaction rate translates into an
atmospheric lifetime of approximately 192
years and a 100-year horizon global
warming potential (GWP) of 6300 (rela-
tive to GWP for CO2 = 1).
Theoretical analysis and experimental
evaluations in a semihermetic compres-
sor confirm that HFC-236fa can be con-
sidered as a replacement for CFC-114 in
chillers. HFC-236fa was found to have a
higher refrigerating capacity and coeffi-
cient of performance (COP) than CFC-
114 at operating conditions typical of CFC-
114 chillers. The experimental COP was
higher than or equal to that of CFC-114 at
condensing temperatures up to 70°C and
declined somewhat at higher condensing
temperatures.
HFC-236fa was included in a matrix of
four MFCs and one hydrofluoroether ex-
amined for thermal and hydrolytic stability
and materials compatibility. These tests
showed that, with and without a polyolester
(POE) lubricant present, several common
elastomers gave acceptable overall per-
formance in terms of change in weight,
volume, linear swell, and hardness. Con-
versely, fluoropolymers such as Viton®,
Kalrez®, and Teflon® were especially sus-
ceptible to absorption of MFCs, including
HFC-236fa, resulting in unacceptable
swelling. Hydrogenated nitrile butyl rubber
and natural rubber showed excessive
swelling when the POE oil was added to
the refrigerants. Neoprene was deemed
unsuitable due to shrinkage and
embrittlement, with and without the lubri-
cant present. Aluminum, steel, cast iron,
copper, brass, and bronze were compat-
ible with HFC-236fa and the POE lubri-
cant. Of four molecular sieve bead desic-
cants tested, three were of three Ang-
strom average pore diameter and exhib-
ited no apparent reactivity with HFC-236fa.
The fourth desiccant had an average pore
diameter of four Angstroms and showed
some evidence of degradation of HFC-
236fa based on an increase in the fluoride
ion content of the desiccant after the ag-
ing test.
HFC-236fa was found to be completely
miscible with ISO-68 POE oil over the
temperature range of -30 to +125°C. Lu-
bricity tests indicated that the chemical
was compatible with this type of lubricant
and that the refrigerant/lubricant mixture
provided good wear resistance.
Heat transfer coefficients of HFC-236fa
were determined in test rigs configured to
investigate refrigerant-side coefficients in
centrifugal chillers. Coefficients were mea-
sured for two conventional finned tubes
and three performance-enhanced tubes
during shell-side condensation and pool
boiling on the outside of a single horizon-
tal tube. For pool boiling tests, a miscible
POE lubricant was added to the HFC-236fa
up to a lubricant concentration of 3 wt %. A
comparison of shell-side heat transfer co-
efficients obtained for HFC-236fa with
those obtained for CFC-114 under identi-
cal conditions showed HFC-236fa to have
better heat transfer during condensation
with a maximum increase of 40% relative
to CFC-114. For pool boiling, HFC-236fa
provided a maximum heat transfer increase
of 80% relative to CFC-114.
HFC-236fa was found to be nonflam-
mable by standards set by the American
Society of Testing and Materials (ASTM).
In laboratory cup-burner tests, a concen-
tration of 5.6 volume % HFC-236fa in air
was found to extinguish an n-heptane
flame. This extinguishing concentration is
equivalent (within experimental error) to
that of a commercially available fire ex-
tinguishing agent; i.e., HFC-227ea
(1,1,1,2,3,3,3-heptafluoropropane).
Considerable toxicity testing was per-
formed for HFC-236fa due in large part to
the U. S. Navy's interest in retrofitting its
shipboard CFC-114 chillers with HFC-
236fa. Toxicity tests included acute inha-
lation, cardiac sensitization, genetic toxic-
ity, developmental toxicity, and 90-day
subchronic inhalation. The maximum con-
centration of HFC-236fa administered to
rats and rabbits for the inhalation toxicity
evaluations was 50,000 ppm. The only
notable compound-related effect was a
diminished response or lack of response
by the test animals to an alerting stimulus
during exposure. Although rats exposed
to 50,000 ppm were generally non-
responsive and rats exposed to 20,000
ppm had a diminished response during
the first week of exposure of a 2-week
study, most animals exhibited normal alert-
ing responses during the second week.
Any diminished response effect was com-
pletely reversible upon cessation of expo-
sure.
A maximum concentration of 200,000
ppm of HFC-236fa in air was used for the
cardiac sensitization tests using six male
beagle dogs as the subjects. Adverse ef-
fects, including two fatalities, were ob-
served at concentrations at or above
150,000 ppm (15%). There were no ad-
verse cardiac effects observed at or be-
low 100,000 ppm (10%). Based on all
toxicity tests performed, HFC-236fa should
pose no significant toxicity problems at
concentrations up to 100,000 ppm in air.
Conclusions
Performance testing under simulated
chiller operating conditions indicates that
HFC-236fa is as good as or superior to
CFC-114. Preliminary material compatibil-
ity tests reveal that certain elastomers may
not be suitable for use with HFC-236fa
and/or POE-type lubricants. However, sev-
eral elastomers exhibited good behavior,
and no thermal or chemical instability prob-
lems were uncovered with the refrigerant.
HFC-236fa is considered "safe" to use in
refrigeration systems based on its con-
firmed nonflammability and low toxicity.
While its high chemical stability is advan-
tageous from an engineering standpoint,
it renders the compound resistant to re-
moval from the atmosphere, thereby im-
parting a long atmospheric lifetime to the
chemical. This, coupled with a relatively
high infrared absorptivity, yields a rela-
tively high global warming potential for the
compound.
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N. Dean Smith (also the EPA Project Officer, see below), Theodore G. Brna,
Cynthia L. Gage, and Robert V. Hendriks are with EPA's AirPollution Prevention
and Control Division, Research Triangle Park, NC 27711.
The complete report, entitled "New Chemical Alternative for Ozone-Depleting
Substances: HFC-236fa," (Order No. PB97-186 308; Cost: $21.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
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POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
EPA/600/SR-97/065
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