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Патент USA US2407407

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2,407,405
Patented Sept. 10, 1946
UNITED STATES PATENT OFFICE
2,407,405
STABILIZATION OF TETRAFLUORO
ETHYLENE
Melvin ‘Adam > Dietrich, Claymont, and Robert
Michael Joyce, Jr., Marshallton, Del., assign
ors to E. I. du Pont de Nemours & ‘Company,
Wilmington, Del., a corporation of Delaware
No Drawing.
Application February 15, 1943,
Serial No. 476,028
'7 Claims.
(Cl. 260-6525)
1
This invention relates to a method for prevent
ing the polymerization of tetra?uoroethylene and
to compositions of matter comprising tetra?uoro
ethylene.
'
ered that by removing this oxygen completely
or essentially so, namely, to a concentration of
not more than 40 parts of oxygen in a million
parts of tetra?uoroethylene, it is possible to store
the tetra?uoroethylene at 25° C. under superate
mospheric pressure for several months without
'
Tetrafluoroethylene, being a gas boiling at
—'l6° C. with a critical temperature of 333° C.,
would be stored desirably in the normal manner
by placing the material under pressure in a steel
container and allowing it to stand at room tem
perature. This method of storage is, however, not
possible because, in accordance with the teaching
of U. S. Patent 2,230,654, polymerization takes
place when tetra?uoroethylene is subjected to
2
atmospheric pressure. We have further discov
appreciable polymerization.
It is a surprising and hitherto unsuspected fact
10 that so small a quantity of oxygen as 0.1% by
volume should be responsible for the polymeriza
tion of tetra?uoroethylene under such mild con
ditions as room temperature and superatmos
pheric pressure. The importance of this discove
superatmospheric pressure ‘at 20° to 25° C. for a
ery is emphasized by the fact that we have found
few days. Prior to this invention it has been the 15 it impossible to handle ordinary liquid tetra
practice to store tetra?uoroethylene at the tem
'fluoroethylene under superatmospheric pressure
perature of solid carbon dioxide since only in this
and room temperature in piping systems consist
way could the spontaneous polymerization be pre
ing of small bore high pressure steel tubing and
vented during storage for any substantial length
needle valves because polymerization quickly pro
of time. The tendency to spontaneous polymeri 20 duces a plug in the lines or in the valves. On the
zation is less at low pressures, for example, tetra
other hand, tetra?uoroethylene of which the oxy
?uoroethylene at one atmosphere at room tem
gen content has been reduced to 20 parts per mil
perature would undergo very little polymeriza
lion is stable under these conditions and can be
tion over a period of weeks or months. The stor
handled satisfactorily in such lines and valves
age, and especially the handling of tetra?uoro 25 without plugging, This discovery has, therefore,
ethylene at atmospheric pressure is, however, ex
made possible the handling of liquid tetra?uoro
tremely impractical and for some purposes (as in
ethylene in room temperature piping systems.
compression systems for the controlled polymeri
The desired reduction in the oxygen content
zation of tetra?uoroethylene) impossible.
can be accomplished either by the mechanical
30
This invention has as an object the production
removal of the oxygen from the tetra?uoroethyl
of stable tetra?uoroethylene which can be stored
ene or by adding to the tetra?uoroethylene small
at normal temperature and superatmospheric
amounts of oxygen-reactive materials. Illustra
pressure for an inde?nite period of time without
tive of the ?rst mentioned method is removal by
undergoing spontaneous polymerization. A fur
fractional distillation, preferably at low tempera
therobject is a method for treating tetra?uoro 35 ture and superatmospheric pressure; by scrub
ethylene whereby this material can be handled at
bing the tetra?uoroethylene with an oxygen-re='
room temperature and superatmospheric pressure
in piping systems without clogging the tubing and
valves because of . spontaneous polymerization.
Other objects will appear hereinafter’.
_
Tetra?uoroethylene, in common with most
other gases for which precautions to the contrary
have not been taken, contains a small amount of
oxygen, generally from about 0.1% to 0.2% ‘by
volume. In other gases, such as hydrogen, nitro
active solution, such as a solution of a 'chromous
salt, “silver salt” (an alkaline solution containing.
sodium hydrosul?te and sodium beta-anthra-s»
quinone sulfonate); or by passing the gas over" "
a metallic catalyst, such as copper or nickel at
elevated temperatures. The most valuable of the
oxygen-reactive materials which can be added to
the tetra?uoroethylene to bring about the desired
stabilization against polymerization are those
compounds which are capable of reacting with
oxygen at atmospheric pressure and normal tem
perature. An example of a material of this kind
is “Terpene B” hydrocarbon mixture which is a
gen, ethylene, and carbon dioxide, this small
amount of- oxygen is‘ inconsequential and is gen
erally ignored since this oxygen is without e?ect
on the gas itself and can be left in the gaswith
out bringing about any change in the gas. ‘We :50 terpene fraction consisting principally of dipen
have now discovered that tetra?uoroethylene dif
tene and terpinolene boiling at 176° to 196° C.,
fers from other gases in that the small amount
having an 'nD2o of 1.470-1.478, and a density of
of normally contained oxygen causes the poly
0.855-0J870 at 15.5° C. Oxygen-containing tetra
merization, previously referredlto,1which takes
?uoroethylene to which has been added about
place on storing at room temperatureand super, 5,5
3
2,407,405
‘0.5% of this hydrocarbon mixture undergoes no
merization after standing for about a month in a
polymerization whatever on storage at room tem
perature and superatmospheric pressure, condi
tions under which the unstabilized tetra?uoro
ethylene polymerizes appreciably in a few days.
The invention is further illustrated by the fol
lowing examples:
steel cylinder in the absence of its liquid phase
under 200 lbs/sq. in. pressure at room tempera
ture. This polymerization is a serious matter in
Cl
the storage of gaseous tetrafluoroethylene since
the polymer often forms near the valve in the
cylinder and prevents the removal of the unpoly
Example I
merized monomer. This terta?uoroethylene is
stabilized against such polymerization by the ad
Tetra?uoroethylene is subjected to fractional 10 dition of 0.5% by weight of “Terpene B” hydro
distillation in a steel still at —19° C. and 123
carbon mixture to the storage container. This
lbs/sq. in. pressure, the oxygen-rich foreshot be
stable tetra?uoroethylene can be stored for sev
ing topped off and discarded. The remaining
eral months without any polymerization taking
tetra?uoroethylene, after distillation, contains
place.
only 7 parts per million of oxygen. Three glass
' '
Example IV
tubes, to one of which is added 0.1,cc.'of “Terpene 1,5
Ordinary oxygen-containing tetra?uoroethyL
B” hydrocarbon mixture, are flushed with low-'
one‘ is stabilized against polymerization with
oxygen nitrogen (15-20 parts per million of
about 0.5% by weight of the following compounds‘,
oxygen) and then cooled in solid carbon dioxide
methanol. Each of the tubes is ?lled about half 20 employing the method described in Example II.
The stabilizers employed are tetrahydronaphtha
full of liquid tetra?uoroethylene containing '7
lene, benzaldehyde, octene-l, methyl methacry
parts per million of oxygen by passing the gaseous
late, cobalt naph'thenate (3% solution in mineral
tetra?uoroethylene into the tube under slight
spirits), and a1pha~pinene. None of these stable
positive pressure which is maintained by a mer
tetra?uoroethylenes undergoes any polymeriza
cury column thereby condensing the gas. Tube
tion in three months at roomtemperature under
#1 is then transferred to a bath of liquid nitrogen
its own vapor pressure. The control experiment
to freeze the tetra?uoroethylene; the free space
with unstable tetra?uoroethylene undergoes con
in the upper part of the tube is displaced with
siderable polymerization in two weeks, and in one
air, and the tube is sealed with a torch. Tube
#2, to which the “Terpene B” hydrocarbon mix 30 month tetra?uoroethylene polymer forms a solid
block in the glass tube.
ture had been added, is treated similarly. Tube
Tetra?uoroethylene is stabilized with com
#3 is transferred to the liquid nitrogen to freeze
pounds which react with oxygen on standing in
the tetrafiuoroethylene, a current of nitrogen
air at ordinary temperature and pressure. By
containing 15 to 20 parts per million of oxygen
being passed into the tube to prevent access of 35 this is meant not only those compounds which
are essentially quantitatively reacted on standing
air, and the tube is then sealed. The three tubes
in air for a brief period, but also those compounds
are removed from the liquid nitrogen and allowed
which react more slowly with oxygen on being
to stand at room temperature under the vapor
agitated in an oxygen atmosphere at ordinary
pressure of tetra?uoroethylene (about 27 atm.).
temperature and pressure.‘ ' Of these the organic
In less than 17 hours the tetra?uoroethylene in
are preferred over the inorganic compounds.
tube #1, which contained air and no stabilizing
Organic compounds which are suitable for the
agent, forms a solid piece of polymer in the tube.
stabilization of tetra?uoroethylene include those
Tubes #2 and #3 are free of polymer. After
containing a multiple bonded carbon atom as is
standing 4 months under these conditions tube
present in ‘compounds containing ethylenic,
#2 contains no polymer whatever. At the end of
acetylenic and aldehydic linkages. Examples of
this period tube #3 contains only a trace of poly
mer which is formed as the result of the oxygen
compounds containing the ethylenic linkage in
content of the nitrogen with which the tube was
clude the ethylenic hydrocarbons such as hexenes
?ushed before sealing.
Example II
and octenes, terpene hydrocarbons, vinyl cyclo
hexene, and cyclohexene; the unsaturated acids,
such as naphthenic acids, methacrylic acid,
crotonic acid, undecylenic acid, as well as their
ployed in Example I is added 0.1 cc. of “Terpene
esters, amides, and salts; the unsaturated nitriles,
such as allyl cyanide; the unsaturated amines,
B” hydrocarbon mixture. Both tubes are then
cooled in liquid ethylene and half ?lled with 55 such as crotylamine; the unsaturated alcohols,
such as allyl alcohol and cinnamyl alcohol; the
liquid tetra?uoroethylene by condensation of the
unsaturated aldehydes; such as acrolein, and the
gas. The tetra?uoroethylene employed for these
corresponding unsaturated acetals; and the un
experiments had not been subjected to any special
To one of two glass tubes similar to those em
treatment and contains approximately 0.2%
oxygen by volume. The tubes are then trans
ferred to a bath of liquid nitrogen and sealed.
The tubes are then removed from the cold bath
and allowed to stand at room temperature under
the vapor pressure of tetra?uoroethylene. The
saturated ethers such as dioxene.
.
,
Examples of operable compounds which con
tain the acetylenic linkage are l-pentine, propi
olic acid, and its derivatives, for example, esters,
amides and salts, and mono- and divinyl acet
ylenes.
-
'
-
unstable tetra?uoroethylene in the tube to Which 65
Particularly useful are those compounds in
no “Terpene B” had been added polymerizes to a
which there is no hydrogen atom on at least
solid white block in less than one week. On the
one multiple bonded carbon atom. These com
other hand, the stable tetra?uoroethylene con
pounds are particularly susceptible to reaction
taining the “Terpene B” does not polymerize at
with atmospheric oxygen, and are of great utility
all after standing 5 months at room temperature 70 as stabilizers for tetra?uoroethylene. For exam
and superatmospheric pressure.
ple, among such hydrocarbons are many terpenes,
such as alpha-pinene, dipentene, and terpinolene,
Example III
and also such compounds as tetrahydronaph
thalene. Likewise, methacrylicacid and its func
0.2% oxygen by volume) undergoes some poly 75 tional derivatives, for' example,‘ esters, amides
Ordinary tetra?uoroethylene (containing about
2,407,405
and salts, are illustrative of unsaturated acids of
this class.
tetra?uoroethylene, but also from the fact that
'the stabilized tetra?uoroethylene can be trans
‘
Other oxygen-reactive compounds include ali
mitted satisfactorily, particularly inthe liquid
phatic and aromatic aldehydes, such as formalde
hyde, acetaldehyde, and benzaldehyde; aliphatic
and aromatic amines, such as dibutylamine, tri
butylamine, aniline, and diphenylamine; and
aliphatic and aromatic mercaptans, such as butyl
mercaptan, octyl mercaptan, thiophenol, and
thio-beta-naphthol.
,
,g
6
the commercially obtained oxygen-containing
‘phase. through high pressure tubes and valves,
Without any stoppages due to the formation of
polymer plugs. Such handling is impossible with
unstable tetra?uoroethylene. Chemical stabiliz
ers can be removed if desired either by fractional
10 distillation or by scrubbing with a liquid which
The amount of such stabilizer to be employed
naturally depends on the oxygen content of the
adsorbs or reacts with the stabilizer.
As many apparently widely different embodi
ments of this invention may be made without de
ltetrafluoroethylene which is to be stabilized.
parting from the spirit and scope thereof, it is
Broadly speaking, stabilizers are employed in
to be understood that we do not limit ourselves
15
amounts ranging from about 0.01% to 5% or
to the speci?c embodiments thereof except as de
10%, based on the amount of tetra?uoroethylene.
?ned in the appended claims.
In most cases the stabilizer is employed in the
We claim:
.
amount of about 0.01% to about 1% by weight
l. Tetra?uoroethylene stabilized with sufficient
based on the amount of tetra?uoroethylene.
ethylenically unsaturated hydrocarbon to prevent
Tetra?uoroethylene containing less than 20
polymerization of the tetrafluoroethylene at 25° C.
parts per million of oxygen can be stored or han
and superatmospheric pressure.
dled at room temperature and superatmospheric
‘2. Tetra?uoroethylene stabilized with su?cient
pressure, either as a gas or as a liquid, for several
amount of a terpene hydrocarbon to prevent poly
weeks without undergoing any polymerization.
Tetra?uoroethylene containing 20 to 40 parts per 25 merization of the tetrafluoroethylene at 25° C.
and superatmospheric pressure.
million of oxygen can be handled under such con
3. A process for treating tetra?uoroethylene
ditions for short periods of time, for example, 1-2
which substantially reduces its tendency to spon
days without any polymerization taking place.
taneous polymerization at 25° C. and superat
At some inconvenience, tetra?uoroethylene con
mospheric pressure, said process comprising in
taining 20 to 40 parts per million of oxygen can
corporating into the tetrafluoroethylene a small
be stored at 0° C. for longer periods of time, for
amount
of an ethylenically unsaturated hydro
example, a few weeks, without any spontaneous
polymerization. The stabilization of rtetra?u
4. The process set forth in claim 3 in which said
oroethylene by the removal of oxygen can be ac
unsaturated
hydrocarbon is a terpene hydro
35
complished as previously mentioned by fractional
carbon.
distillation to remove the oxygen in a foreshot,
‘5. The process set forth in claim 3 in which
preferably at low temperature and superatmos
said ethylenically unsaturated hydrocarbon is
pheric pressure, or by scrubbing the rtetraflu
added in amount of from 0.01% to 10% by weight '
oroethylene with oxygen-reactive liquids, such as
of the tetro?uoroethylene.
solutions of chromous salts, cuprous salts, par
carbon.
ticularly lcuprous ammonium salts, or “silver sal ”
(an alkaline solution of sodium hydrosulfite con
taining sodium beta-anthraquinone sulfonate as
the catalyst, J. Am. Chem. Soc. 46, 2639 (1924) ) .
'
I
6. Tetrafluoroethylene stabilized with ethyleni
cally unsaturated hydrocarbon in amount of from
0.01 % to 10% by weight of the tetra?uoroeth
ylene.
~
'7. Tetrafluoroethylene stabilized with a terpene
The present invention presents a valuable eco 45
hydrocarbon
in amount of from 0.01% to 10% by
nomic advantage not only from the fact that
weight of the tetra‘?uoroethylene.
tetrafluoroethylene stabilized by the process of
MELVIN ADAM DIETRICI-I.
this invention can be stored for long periods of
ROBERT MICHAEL JOYCE, JR.
time without the polymerization which occurs in
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