close

Вход

Забыли?

вход по аккаунту

?

Патент USA US2406153

код для вставки
Aug- 20, 1946-
E. E. LEWIS
'
2,406,153
DEPOLYMERIZATION OF POLYMERIC TETRAFLUOBOETHYLENE
Filed June 23, 1944
TICETRA
PRESSURE
VS
PRODUCT COMPOSITiON
MPERCENT
II)
15
20
25 30
40 50 50 70 80 90100
I50 200 250 300
PRESSURE 'MILLIMETERS OF MERCURY
400 500 S00 100,800,90111
jzl
III-nest £-Lew
j‘s
BY
INVENTOR.
ihmlmmf
2,406,153
Patented Aug. 20, 1946
UNITED STATES PATENT OFFICE
’
2.406.153
DEPOLYMERIZATION or rotmaic
rn'ramuoaoarmana
Ernest a. Lewis. Lyndhurst, N. 3., asslgnor to a. L
du Pont de Nemours & Company, Wilmington,
DeL, a corporation of Delaware
Application June 23, 1944, Serial No. 541,.821
scams. (Cl. 260-4853)
1
This invention relates to the depolymerization
of polymeric tetra?uoroethylene and, more par
ticularly, to a process of depolymerizing poly
merie tetra?uoroethylene under conditions to
yield a high proportion of monomeric tetra?uoro
ethylene.
Polymeric tetra?uoroethylene has been sub
jected heretofore to pyrolysis under varying con
ditions whereby a number of products have been
tetra?uoroethylene based on weight of the poly
mer treated.
.
The decomposition of the polymeric tetra
?uoroethylene may be conveniently carried out
in a reaction tube of iron or other material sub
stantlally inert to the reaction and the reaction
products. The tube may be heated conveniently
by means of electric coils although other means
may be employed. The products of decomposi
obtained including monomeric tetra?uoroethyl 10 tion are then passed ?rst through a trap for
ene, hexa?uorocyclopropane having the formula
C3Fs, octa?uorocyclobutane having the formula
C4Fa, and certain polymeric products having
solids and the gases are then led into a receiver
maintained at a low temperature by a dry ice
methanoi bath or the like where the gases may
be condensed. A considerable amount of the
relatively low melting points. The proporticnof
monomeric tetra?uoroethylene recovered has 15 polymer charged into the reaction tube tends to
collect in the cool part of the exit end of the tube
been relatively low, usually considerably less than
but this may be conveniently prevented by plac
50% by weight of the polymer pyrolyzed and,
ing one or more 2- or 3-inch rolled up cylinders
hence, the heretofore known procedures have not
been satisfactory for commercial recovery of
monomeric tetra?uoroethylene from scrap poly
of galvanized iron window screening or similar
20 inert material which, preferably, is a good con
ductor for heat, in the reaction tube toward the
exit end thereof and heating the tube at that
point to above the decomposition point of the poly
vide an economical process for the recovery of
mer. This also tends to prevent the formation
monomeric tetra?uoroethylene from polymeric
tetra?uoroethylene. A further object is to pro 25 of a white sublimate of undetermined composi
tion although at the reduced pressures of the
vide a process of depolymerizing polymeric tetra
present invention, the tendency to form this sub
?uoroethylene to obtain a high yield of mono- limate is greatly reduced in any event.
meric tetra?uoroethyiene. Other objects will be
The decomposition point of the polymeric
apparent from the description of the invention
30 tetra?uoroethylene may vary somewhat with dif
given hereinafter.
1
ferent samples but in general the polymer com
The above objects are accomplished according
mences decomposing at about 550° C. and heat
to the present invention by heating polymeric
ing the decomposition tube or chamber to a tem
tetrai‘luoroethylene at a temperature above its
perature of 600° C.-700° C. is preferred. There
decomposition point under a reduced pressure not
exceeding about 150 millimeters of mercury and 35 is no great di?erence in the proportion of mono
collecting the monomeric tetra?uoroethylene
meric tetra?uoroethylene recovered through the
mer.
An object of the present invention is to pro
thereby produced.
temperature range of 600° C. to 700° C. or even at
as high as 800° C., a slight tendency toward de
The present invention resides in large part in
creased yields being noted as the temperature
the discovery that the pressure at which the de
composition of the polymeric tetra?uoroethylene 40 is advanced. It the section 01' the reaction tube
in which the rolled up screening is placed, is
is carried out, profoundly in?uences the com
position of the depolymerizatlon products ob
heated to as high as 800° C. the formation of the
sublimate is substantially completely stopped but
tained and, unexpectedly, that the proportion
of monomeric tetra?uoroethylene in the recov
even at a temperature of 600° C. the amount of
ered gases is exceedingly high when the depoly 45 sublimate formed is no appreciable factor.
merization is carried out at pressures less than
about 150 millimeters of mercury although the
proportion 01 monomeric tetra?uoroethylene
While neither substantial variations in the
temperature to which the reaction tube is heated
nor the temperature to which the screening is
heated within the reaction tubeI materially af
beyond about 150 millimeters. It has further 50 fects the proportion of tetra?uoroethylene re
been found that other conditions may be varied
covered. reducing the pressure in the decomposi
widely without e?ecting any radical change in
rapidly decreases as the pressure is increased
the composition or the recovered gases but cer
tion chamber does affect the composition oi’ the
recovered gases greatly. The drawing forming
tain steps may be taken to improve the e?iciency
or the process with respect to yield of monomeric 55 ‘a part of this application shows in the single ?g
2,406, 158
3
4
ure thereof a curve which illustrates this clearly.
In Fig 1. the curve shown is laid out on log.‘
Percent
C2F4 ___________________________________ __ 85.7
arithmic graph paper and indicates the relation
between the composition of the gases recovered
in the depolymerization of polymeric tetra
?uoroethylene and the pressure employed. The
pressure in millimeters of mercury is given along
the abscissa and the percent of monomeric tetra
C3Fc ___________________________________ __ 14.3
A second run was carried out as above but a
temperature of ‘700° C. was maintained in the
sections of the reaction tube heated by the ?rst
two resistance coils. The collected gases showed
the following analysis:
?uoroethylene, by weight of the total recovered
gases, is given along the ordinate. At points a, 10
CzFs
b, and c where the pressure in the reaction tube
varied from 40 to 70 millimeters of mercury, the
Percent
____ ....
__..
82.1
CzFc ____________________________________ __
17.9
Example I]
monomeric tetra?uoroethylene in the recovered
gases is well above 80% and even at point (I, 150
Three runs were carried out substantialhl as
millimeters of mercury pressure, the yield is up 15 in the first run of Example I except that pres
proximately 80%. But when the pressure is in
sures of 55 millimeters, 70 millimeters, and 150
creased to 250 millimeters of mercury, point e,
millimeters of mercury were maintained, with
there is a sharp break in the composition with
the following results:
'
the monomeric tetra?uoroetnvlene dropping to
below 60% and continuing to drop at about the 20
Analysis of collected gases
same rate at pressures of 350 millimeters. point
Pressure. millimeters of mercury
‘
J‘. and 760 millimeters. point g. which is atmos
csFl
CaFl
ClFl
pheric pressure. The recovered gases show only
aproximately 15% monomeric tetrailuoroethylene
at atmospheric pressure.
25
The sharp break in the curve in Fig. 1 beyond
the point d corresponds with a distinct change
Percent
Percent
Percent
55 ________________________________ . .
84. 1
l5. 3
________ i ,
70 _______________________________ __
83.0
17.0
________ H
150 ............................... _.
80. 3
l4. 5
5. .l
in the composition of the recovered gases in that.
at pressures below 150 millimeters of mercury
The proportion of monomeric tetra?uoroethyl
one in the collected gases remained above 80% in
the recovered gases consisted of monomeric 80 each
instance but no octafiuorocyclobutane was
tetrafiuoroethylene and hexa?uorocyclopropane
detected
except in the run at 150 millimeters
as far as analyses show, no octailuorocyclobutane
pressure where 52% was found by analysis.
being found although it might have been pres
A run under substantially identical conditions
ent in traces. On the other hand, employing
but at a pressure 0! 250 millimeters of mercury
35
pressures about 150 millimeters of mercury, octa
showed the following analysis of the collected
?uorocyclobutane was found in the recovered
gases:
gases in all runs and rapidly increased as the
Percent
pressure increased above 150 millimeters. Since
the composition of the recovered gases was ana
CiFi ___________________________________ __ 57.3
CaFs ___________________________________ -- 19.0
lyzed in each instance by distillation and there 40 CM _
___
_
____ _- 23.7
was some doubt about the last 4% of the prod
Further
runs
at
still
higher
pressures
showed
uct to be distilled, it is recognized that there is
a rapid decline in the proportion of monomeric
the possibility of an error. not exceeding 3.3%
tetrailuoroethylene, a typical run at atmospheric
total error. whichrhowever. would not materially
pressure showed the following analysis of col
affect the validity of the ?ndings above.
lected gases:
The following examples. in which all propor
.
Percent
tions are given by weight unless otherwise noted.
CiiFi
14.2
illustrate speci?c embodiments of the invention:
CaFs26.0
Example I
59.8
50 64F: __- '
Example III
Polymeric tetra?uoroethylene subdivided to
pass through a 1P; in. screen, was introduced into
Two runs were carried out under conditions
a reaction chamber consisting of a 27% in. sec
similar to those in the first run of Example I
tion of 3/4 in. pipe provided with three electrical 5." but temperatures of 700° C. and 800° C. were
resistance coils for heating, the pipe extending
maintained in the section of the reaction tube
about 1 it. beyond the coils at both ends and a
in which the cylinder of wire screening was po
cylinder of rolled up galvanized iron window
sitioned. The collected gases showed upon anal
screening of 30-mesh being positioned in the sec
ysis, 86.8% of CzF4 and 82.8% of C3F4, respectively.
tion of the pipe heated by the third resistance 60 indicating that no improvement in the percent
coil. The cylinder of wire screening‘was ap
age of monomeric tetra?uoroethylene in the col
proximately 2%- in. long and the cylinder walls
lected gases results from heating the section
consisted of double thicknesses of the screening
with the wire screening to the high temperature
while one end of the cylinder was closed with a
although formation of the white sublimate is
single thickness of the screening. The pipe form
65
eliminated substantially entirely.
ing the reaction tube was heated to about 600°
It will be understood that the above examples
C. by each resistance coil and the products 01'
are merely illustrative and that the present in
depolymerization were ?rst passed through two
ventlon broadly comprises heating polymeric tet
vacuum ?asks ?lled‘with glass wool to trap solids
ra?uoroethylene at a temperature above its de
and the gases were then collected in cylinders 70 composition point under a reduced pressure not
cooled by a dry ice-methanol mixture.
exceeding about 150 millimeters of mercury and
During the run a uniform pressure of 41 milli
collecting the monomeric tetraiiuoroethylene thus
meters of mercury was maintained in the reac
tion tube and the collected gases showed the fol
lowing analysis:
formed.
‘
'
Those skilled in the art will appreciate that
75 the apparatus for carrying out the present in
.
8,406,108
5
6
vention may be varied widely and that the proc
ess may be run continuously. semi-continuously,
to be understood that the invention is not lim
ited to the speci?c embodiments thereof except
or batch-wise. Although the use 01' a. cylinder of
wire screening heated to a temperature above
as de?ned in the appended claims.
the decomposition point of the polymer and placed
in the path 01' travel of the decomposition prod
ucts is advantageous in favoring the complete
depolymerization of the polymer and preventing
"
I claim:
1. Method of producing monomeric tetra?uoro
ethylene which comprises heating polymeric
tetraiiuoroethylene at a temperature above its
decomposition point under a reduced pressure
not exceeding about 150 millimeters of mercury
the formation of a sublimate, thus contributing
to increased efficiency of the process and also fore 10 and collecting the resulting monomeric tetra
stalling dimculties due to solid condensates in
?uoroethylene gas formed.
teriering with or cutting oil the ?ow of gases
2. Method of producing monomeric tetrailuoro
through the apparatus, this expedient does not
ethylene which comprises heating polymeric
in?uence appreciably the proportion of tetra?uo
tetra?uoroethylene at a temperature of at least
roethylene in, the collected gases.
15 about 600° C, under a reduced pressure not ex
The speci?c temperature to which the reaction.
ceeding about 150 millimeters of mercury and
chamber is heated, may be varied widely, ‘pro
collecting the resulting monomeric tetra?uoro
viding it exceeds the decomposition point of the
ethylene gas formed.
polymer being processed. Higher temperatures
3. Method of producing monomeric tetra?uoro
i’avor more rapid depolymerization of the poly 20 ethylene which comprises heating polymeric
mer and, consequently, increased capacity for
tetra?uoroethylene at a temperature of 600° C.
any given apparatus but this advantage must be
7000 C. under a reduced pressure not exceeding
balanced against the slightly decreased produc
about 150 millimeters of mercury and collecting
tion of tetra?uoroethylene and the usual prob
the resulting monomeric tetrafiuoroethylene gas
lems involved in employing higher temperatures. 25 formed.
The examples show that there is a no great
4. Method of producing monomeric tetra?uoro
difference in product yield with variations in
ethylene which comprises heating polymeric ‘
pressure under 150 millimeters of mercury but a
tetra?uoroethylene at a temperature of 600' C.
pressure of 40 millimeters to 100 millimeters of
mercury ‘is preferred due to the slightly greater
yield of tetra?uoroethylene resulting therefrom.
The bene?ts of operating the system under a
very low pressure must, of course, be balanced
against the increased trouble of operating at such
pressures as compared to somewhat higher pres 35
sures under about 150 millimeters of mercury.
- An advantage of the present invention is that
it provides a practical and e?ioient means of re
covering monomeric tetra?uoroethylene from the
polymer. Speci?cally, the invention provides an 40
economical means of recovering monomeric tet
ra?uoroethylene from scrap polymer accumu
lated from molding operations and the like.
As many apparently widely different embodi
ments of this invention may be made without de 45
parting from the spirit and scope thereofI it is
700" C. under a reduced pressure of 40 millimeters
to 100 millimeters of mercury and collecting the
resulting monomeric tetra?uoroethyiene gas
formed.
5. Method of producing monomeric tetra?uoro
ethylene which comprises introducing ?nely
divided polymeric tetra?uoroethylene into a reac
tion tube maintained at a temperature of at
least about 600° C. and under a reduced pressure
not exceeding about 150 millimeters of mercury,
passing the decomposition products formed
through a screen of inert material maintained
at a temperature of at least about 600° C., and
thereafter collecting the gases resulting from the
depolymerization of said polymeric tetra?uoro
ethylene.
ERNEST E. LEWIS.
Certi?cate of Correction
Patent No; 2,406,153;
August 20, 1946.
ERNEST E. LEWIS
It is hereby certi?ed that errors appear in the printed speci?cation of the above
numbered patent requiring correction as follows: Column 4, line 33, for “52%”
read 5.2%; column 5, line 26, strike out the article “a”; and that the said Letters
Patent should be read with these corrections therein that the same may conform to
the record of the case in the Patent Of?ce.
Signed and sealed this 3rd day of December, A. D. 1946.
[ml
’
LESLIE FRAZER,
First Assistant Commissioner of Patents.
.
8,406,108
5
6
vention may be varied widely and that the proc
ess may be run continuously. semi-continuously,
to be understood that the invention is not lim
ited to the speci?c embodiments thereof except
or batch-wise. Although the use 01' a. cylinder of
wire screening heated to a temperature above
as de?ned in the appended claims.
the decomposition point of the polymer and placed
in the path 01' travel of the decomposition prod
ucts is advantageous in favoring the complete
depolymerization of the polymer and preventing
"
I claim:
1. Method of producing monomeric tetra?uoro
ethylene which comprises heating polymeric
tetraiiuoroethylene at a temperature above its
decomposition point under a reduced pressure
not exceeding about 150 millimeters of mercury
the formation of a sublimate, thus contributing
to increased efficiency of the process and also fore 10 and collecting the resulting monomeric tetra
stalling dimculties due to solid condensates in
?uoroethylene gas formed.
teriering with or cutting oil the ?ow of gases
2. Method of producing monomeric tetrailuoro
through the apparatus, this expedient does not
ethylene which comprises heating polymeric
in?uence appreciably the proportion of tetra?uo
tetra?uoroethylene at a temperature of at least
roethylene in, the collected gases.
15 about 600° C, under a reduced pressure not ex
The speci?c temperature to which the reaction.
ceeding about 150 millimeters of mercury and
chamber is heated, may be varied widely, ‘pro
collecting the resulting monomeric tetra?uoro
viding it exceeds the decomposition point of the
ethylene gas formed.
polymer being processed. Higher temperatures
3. Method of producing monomeric tetra?uoro
i’avor more rapid depolymerization of the poly 20 ethylene which comprises heating polymeric
mer and, consequently, increased capacity for
tetra?uoroethylene at a temperature of 600° C.
any given apparatus but this advantage must be
7000 C. under a reduced pressure not exceeding
balanced against the slightly decreased produc
about 150 millimeters of mercury and collecting
tion of tetra?uoroethylene and the usual prob
the resulting monomeric tetrafiuoroethylene gas
lems involved in employing higher temperatures. 25 formed.
The examples show that there is a no great
4. Method of producing monomeric tetra?uoro
difference in product yield with variations in
ethylene which comprises heating polymeric ‘
pressure under 150 millimeters of mercury but a
tetra?uoroethylene at a temperature of 600' C.
pressure of 40 millimeters to 100 millimeters of
mercury ‘is preferred due to the slightly greater
yield of tetra?uoroethylene resulting therefrom.
The bene?ts of operating the system under a
very low pressure must, of course, be balanced
against the increased trouble of operating at such
pressures as compared to somewhat higher pres 35
sures under about 150 millimeters of mercury.
- An advantage of the present invention is that
it provides a practical and e?ioient means of re
covering monomeric tetra?uoroethylene from the
polymer. Speci?cally, the invention provides an 40
economical means of recovering monomeric tet
ra?uoroethylene from scrap polymer accumu
lated from molding operations and the like.
As many apparently widely different embodi
ments of this invention may be made without de 45
parting from the spirit and scope thereofI it is
700" C. under a reduced pressure of 40 millimeters
to 100 millimeters of mercury and collecting the
resulting monomeric tetra?uoroethyiene gas
formed.
5. Method of producing monomeric tetra?uoro
ethylene which comprises introducing ?nely
divided polymeric tetra?uoroethylene into a reac
tion tube maintained at a temperature of at
least about 600° C. and under a reduced pressure
not exceeding about 150 millimeters of mercury,
passing the decomposition products formed
through a screen of inert material maintained
at a temperature of at least about 600° C., and
thereafter collecting the gases resulting from the
depolymerization of said polymeric tetra?uoro
ethylene.
ERNEST E. LEWIS.
Certi?cate of Correction
Patent No; 2,406,153;
August 20, 1946.
ERNEST E. LEWIS
It is hereby certi?ed that errors appear in the printed speci?cation of the above
numbered patent requiring correction as follows: Column 4, line 33, for “52%”
read 5.2%; column 5, line 26, strike out the article “a”; and that the said Letters
Patent should be read with these corrections therein that the same may conform to
the record of the case in the Patent Of?ce.
Signed and sealed this 3rd day of December, A. D. 1946.
[ml
’
LESLIE FRAZER,
First Assistant Commissioner of Patents.
Документ
Категория
Без категории
Просмотров
0
Размер файла
580 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа