Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02197171 2002-03-26
1
PROCESS FOR PRODUCING PENTAFLUOROETHANE
Technical Field
The present invention relates to a process of producing
pentafluoroethane by separating pentafiuoroethane out of a mixture
comprising at least pentafluoroethane (which is sometimes referred
to as HFC-125) and chloropentafluoroethane (which is sometimes
referred to as CFC-115) using extractive distillation in which a
specific compound is used as an extractant (or solvent). Such a
mixture may be for example a reaction .product from a production
process of pentafluoroethane by fluorinating tetrachloroethylene.
Background Art
HFC-125 is a useful compound which can be a substitute
for FreonT"" which does not contain chlorine, and it is used as a
refrigeration medium, a forming agent, a propellant and so on.
Fluorination of tetrachloroethylene is employed as a process of
producing HFC-125. In such a process, dichlorotetrafluoroethane,
dichlorotrifluoroethane, hexafluoroethane, CFC-115 and so on are
produced as by-products.
Among those, CFC-115 has a boiling point of -38.7 °C
which is considerably close to the boiling point of HFC-125 (-48.5°C)
2 5 as a desired product. Further, the relative volatility of these
two compounds is near one. Particularly when a mixture contains
HFC-125 at a concentration of not less than 95 mol % (thus, CFC-
115 is not more than 5 mol %), the relative volatility is about 1.04.
CA 02197171 2002-03-26
2
Therefore, it requires a distillation apparatus having many plates to
separate HFC-125 in its higher concentration out of such a mixture
using a conventional distillation operation, which generally means
that the separation using distillation is extremely difficult.
In the present specification, the relative volatility (a) is
defined as follows when a solution consisting essentially of at
least two components A and B in question (a boiling point of
component A < a boiling point of component B) is in a vapor-liquid
equilibrium state:
1 0 a = (Ya/xA ) / {YB/x B )
wherein xA is a molar fraction of lower boiling component A in the
liquid phase, xB is a molar fraction of higher boiling component B in
the liquid phase, yA is a molar fraction of lower boiling component A
in the vapor phase which is equilibrated with the liquid phase and yB
1 5 is a molar fraction of the higher boiling component B in such a
phase.
Extractive distillation has been employed as a process of
separating one component from a mixture of a system of which
relative volatility is close to one. With regard to separation of a
20 mixture of HFC-125 and CFC-115, for example U. S. Patent No.
5,087,329 discloses an extractive distillation process which uses a
fluorocarbon containing 1 to 4 carbon atoms as an extractant.
In the process disclosed in U. S. Patent No. 5,087,329, a
relative volatility between HFC-125 and CFC-115 is about 1.2 based
2 5 on calculation using figures shown in Example 1 thereof. Thus, in
order that the concentration of HFC-125 is increased from HFC-125 /
CFC-115 = 7/93 (mol % / mol %) to HFC-125 / CFC-115 = 99.7/0.3
{mol % / mol %) using distillation, about 40 theoretical plates are
CA 02197171 2002-03-26
3
required. The number of the theoretical plates were calculated as
explained below.
Disclosure of Invention
The present inventors have searched for a process in
which HFC-125 is further effectively separated out of a mixture
comprising HFC-125 and CFC-115 using extractive distillation, and
found that when a mixture comprising at least HFC-125 and CFC-
115 is subjected to extractive distillation, HFC-125 is effectively
(for example, using a distillation column having a very small number
of theoretical plates) separated from the mixture by using, as an
extractant (or a solvent), at least one compound (thus, as a single
compound or a mixture of the compounds) selected from an alcohol
containing 1 to 4 carbon atoms, a ketone containing 3 to 7 carbon
1 5 atoms, an ether containing 2 to 6 carbon atoms and nitromethane or
at least one selected from a hydrocarbon containing 3 to 8 carbon
atoms, trichloroethylene and carbon tetrachloride.
Thus, the present invention provides a process of
separating HFC-125 out of a mixture comprising at least HFC-125
and CFC-115 by subjecting the mixture to extractive distillation so
as to obtain HFC-125 in which a CFC-115 concentration is relatively
reduced, and preferably highly concentrated HFC-125 which does not
substantially contain CFC-115 characterized in that at least one
compound selected from an alcohol containing 1 to 4 carbon atoms, a
ketone containing 3 to 7 carbon atoms, an ether containing 2 to 6
carbon atoms and nitromethane, or at least one compound selected
from a hydrocarbon containing 3 to 8 carbon atoms,
trichloroethylene and carbon tetrachloride is used as an extractant.
21~~~11
4
That is, the present invention provides a process of
producing pentafluoroethane in which pentafluoroethane is
separated out of a mixture comprising at least pentafluoroethane
and chloropentafluoroethane which together constitute a main
component of the mixture by subjecting the mixture to extract ~e
distillation so as to obtain a mixture which contains
pentafluoroethane as a main component and which does not
substantially contain chloropentafluoroethane, which process is
characterized in that
at least one compound selected from an alcohol
containing 1 to 4 carbon atoms, a ketone containing 3 to 7 carb.sn
atoms, an ether containing 2 to 6 carbon atoms and nitromethar~e, or
at least one compound selected from a hydrocarbon containing ;t to 8
carbon atoms, trichloroethylene and carbon tetrachloride is ust~ J as
an extractant of the extractive distillation, and
a mixture comprising pentafluoroethane and the
extractant which together constitute a main component of the
mixture is obtained as a bottom product provided that at least one
compound selected from the alcohol containing 1 to 4 carbon atoms,
the ketone containing 3 to 7 carbon atoms, the ether containing 2 to
6 carbon atoms and nitromethane is used as the extractant, or
a mixture comprising pentafluoroethane as main
component is obtained as a distillate product provided that at least
one compound selected from the hydrocarbon containing 3 to 8
2 5 carbon atoms, trichloroethylene and carbon tetrachloride is used as
the extractant.
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4a
In a preferred embodiment there is provided a process of
producing pentafluoroethane by subjecting a mixture comprising at least
pentafluoroethane and chloropentafluoroethane to an extractive distillation
step so as to obtain pentafluoroethane which does not substantially
contain chloropentafluoroethane, which process is characterized by
supplying the mixture to the extractive distillation step, supplying, as an
extractant to the extractive distillation step, at least one compound
selected from an alcohol containing 1 to 4 carbon atoms, a ketone
containing 3 to 7 carbon atoms, an ether containing 2 to 6 carbon atoms
and nitromethane, or at least one compound selected from a hydrocarbon
containing 3 to 8 carbon atoms, trichloroethylene and carbon
tetrachloride, and obtaining a mixture comprising pentafluoroethane and
the extractant which together constitute a main component of the mixture
as a bottom product from the extractive distillation step, or a mixture
comprising pentafluoroethane as a main component of the mixture as a
distillate product from the extractive distillation step.
2197171
Brief Description of Drawings
Fig. 1 shows a flow sheet of one embodiment of a
separation process in which the process according to the present
invention is carried out; and
5 Fig. 2 shows a flow sheet of another embodiment of a
separation process in which the process according to the present
invention is carried out.
In the drawings, reference numbers denote the following
elements, respectively:
1. extractive distillation apparatus
2. mixture which contains HFC-125 and CFC-115
3. extractant
4. distillate product
5. bottom product
6. distillate product
7. bottom product
8. heat exchanger
9. distillation apparatus for HFC-125 separation
11. extractive distillation apparatus
12, mixture which contains HFC-125 and CFC-115
13. extractant
14. distillate product
15. bottom product
16. distillate product
17. bottom product
18. heat exchanger
19. distillation apparatus for extractant recovery
z~g~~~~
6
Detailed Description of Invention
In the present specification, the term "main component"
is intended to mean that an amount of the other component rather
than the main component is relatively small. It is sufficient that an
amount of the main component i~ concretely not less than 50 %,
more concretely not less than 60 %, and for example not less than
80 %. Further, in the present specification, the term
"substantially" is intended to mean that a mixture is ultimately
obtained in which pentafluoroethane is a main component, for
example a mixture in which a concentration of pentafluoroethar~e is
not Less than 90 % by weight, preferably not less than 99.9 % by
weight and more preferably not less than 99.99 % by weight.
In the present process, when at least one compound
se'ected from the alcohol containing 1 to 4 carbon atoms, the ketone
1 5 containing 3 to 7 carbon atoms, the ether containing 2 to 6 carUon
atoms and nitromethane is used as the extractant, a mixture is
obtained as a bottom product which contains pentafluoroetha~e and
the extractant together constituting a main component of the
mixture as described above, preferably a mixture in which a
concentration of chloropentafluoroethane is not more than 0.1 % by
weight, and more preferably a mixture in which a concentration of
chloropentafluoroethane is not more than 0.01 % by weight. In this
case, there is no limitation on a composition of a .distillate product
provided that a ratio of chloropentafluoroethane to
pentafluoroethane in the bottom product is reduced from an original
ratio thereof, preferably reduced to not more than 1/10 of the
original ratio, and mare preferably reduced to not more than 1/100
of the original ratio.. The distillate product may contain
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chloropentafluoroethane as a main component thereof, may contain
pentafluoroethane as a main component thereof or may contain
chloropentafluoroethane and pentafluoroethane which together
constitute a main component thereof with the proviso described
just above.
In the present process, when at least one compound
selected from the hydrocarbon containing 8 to 8 carbon atoms,
trichloroethylene and carbon tetrachloride is used as the extractant,
a mixture is obtained as a distillate product which contains
pentafluoroethane as a main component thereof as described above,
preferably a mixture in which a concentration of pentafluoroethane
is not less than 99.9 % by weight. In this case, there is no
limitation on a composition of a bottom product provided that a
ratio of pentafluoroethane to chloropentafluoroethane in the
distillate product is increased from an original ratio thereof,
preferably increased to not less than 10 times the original ratio, and
more preferably increased to not less than 100 times the
original ratio. The bottom product may contain
chloropentafluoroethane and the extractant which together
2 0 constitute a main component of the bottom product, or may contain
chloropentafluoroethane pentafluoroethane and the extractant which
together constitute a main component of the bottom product with
the proviso described just above.
In one embodiment of the present invention, the mixture
2 5 is of a binary system which consists substantially of HFC-125 and
CFC-115.
In another embodiment of the present invention, the
bottom product thus obtained, for example one which contains the
CA 02197171 2002-03-26
extractant and pentafluoroethane which together constitute a main
component of the bottom product or one which contains
chloropentafluoroethane and the extractant which together
constitute a main component of the bottom product is subjected to
distillation so as to separate into the extractant and
pentafluoroethane or chloropentafluoroethane, whereby the
extractant is recovered, which may be supplied to and re-used in the
extractive distillation step.
In the present specification, the term extractive
distillation has the meaning which is generally used in the field, in
particular the field of chemical engineering; for example, it means a
distillation operation which is characterized in that addition of a
third component to a mixture of a binary system facilitates
separation of the mixture due to the relative volatility being
considerably deviated from one by means of the third component,
otherwise the separation would be difficult when using
conventional distillation.
In the present invention, the alcohol containing 1 to 4
carbon atoms is intended to mean a compound having 1 to 4 carbon
2 0 atoms which form a main chain and which contains at least one
hydroxyl group, such as an aliphatic alcohol having 1 to 4 carbon
atoms. Concretely, methanol, ethanol, butanol, propanol,
pentafluoropropanol (C2F5CH20H), tetrafluoropropanol
(HCF2CF2CH20H), ethylene glycol, propanediol and trifluoroethanol
2 5 can be exemplified.
In the present invention, the ketone containing 3 to 7
carbon atoms is intended to mean a ketone which is represented by a
general formula: R~-CO-R2 (wherein R1 and R2 are aliphatic
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hydrocarbon groups which may be the same or different from each
other, respectively). Concretely, acetone, diethyl ketone and methyl
ethyl ketone can be exemplified.
In the present invention, the ether containing 2 to 6
carbon atoms is intended to mean an ether which is of a general
formula: R1-O-R2 (wherein R1 and R2 are aliphatic hydrocarbon
groups which may be the same or different from each other,
respectively). Concretely, diethyl ether, dimethyl ether, methyl
ethyl ether and dipropyl ether can be exemplified.
In the present invention, the hydrocarbon containing 3 to
8 carbon atoms includes both a cyclic hydrocarbon and a chain
hydrocarbon. The cyclic hydrocarbon is intended to mean one which
contains at least one cyclic structure. Concretely, cyclohexane,
cyclopentane, cyclopropane and cyclobutane can be exemplified as a
saturated cyclic hydrocarbon. As an unsaturated cyclic hydrocarbon,
an aromatic hydrocarbon such as benzene can be exemplified. The
chain hydrocarbon also includes both a saturated one and an
unsaturated one, and normal octane and normal hexene
can be exemplified. As a mixture thereof, using petroleum ether or
2 0 petroleum benzine may be particularly preferred.
The present inventors have ;>tudied the extractants as
described above which are used in the process of separating HFC-
125 from the mixture comprising HFC-125 and CFC-115 by
extractive distillation, and obtained measurements of the relative
volatilities between HFC-125 and CFC-115 which are shown in
Table 1 below:
2197111
,o
Table 1
Extractant Extractant Relative
Ratio*) Volatility (x)
(1 j Dichlorotrifluoroethane**0.85 1.2
j
(2) Dichloropentafluoropropane0.67 1.2
(3 ) Tetrachloroethylene 1.33 1.2
(4~ Dichloromethane 2.12 0.9
(5) Methanol 1.60 0.4
(6) Ethanol 1.5 0.5
(7) Propanol 1.2 0.76
(8) Butanol 1.4 0.86
(9) Pentafluoropropanol 1.2 0.88
(1 J) Tetrafluoropropanol 1.6 0:65
(1 1 Acetone 0.5 0.4
)
(12) Cyclohexane 1.6 1.7
(13) Cyclopentane 1.5 1.9
(14) Trichloroethylene 2.0 1.4
(15) Carbon Tetrachloride 1.6 1.5
(16} Normal Octane 1.4 1.8
(17) Petroleum Benzine 4.7 2.1
(18) Petroleum Ether 4.0 2.,
(19) Diethyl Ether 1.4 0.7
(20) Nitromethane 1.4 0.4 ,
*} Extractant Ratio = / weight of (NFC-
weight of extractant
2 125 + CFC-115)
5
**) Extractant describedU.S. Patent 5,087,329
in No.
When the measurements of Table 1 were obtained, the
following manner was employed: After a sealed vessel was
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evacuated to an almost vacuum pressure, predetermined amounts of
HFC-125, CFC-115 and the extractant were charged into the vessel,
which was allowed to reach a vapor-liquid equilibrium state at a
temperature of 20 °C. Then, the liquid phase and the vapor phase
were analyzed using gas chromatography to obtain compositions of
both phases as molar fractions. The relative volatility a was
calculated using the above equation a = (yA/xA) / (ye/xB).
As clearly seen from Table 1, when the alcohol having 1
to 4 carbon atoms, the ketone having 3 to 7 carbon atoms, the ether
1 0 having 2 to 6 carbon atoms or nitromethane which is represented by
compound (5) to (11), (19) or (20) in Table 1 is used as the
extractant, the relative volatility is considerably smaller than one.
In addition, when the hydrocarbon having 3 to 8 carbon
atoms, trichloroethylene or carbon tetrachloride which is
1 5 represented by compounds (12) to (18) in Table 1 is used as the
extractant, the relative volatilities are considerably larger than
one. Therefore, when HFC-125 is to be :>eparated out of the mixture
of HFC-125 and CFC-115 by the extractive distillation using a
compound (5) to (20) in Table 1 as the extractant, it is expected
20 that the separation would be carried out using a distillation
apparatus which includes a much smaller number of theoretical plates
than a conventional apparatus.
Generally, when a mixture comprising HFC-125 and CFC-
115 is subjected to a distillation operation, HFC-125 is
2 5 concentrated into an enriching section (a top side of a column) since
its boiling point is lower than that of CFC-115. However, when the
relative volatility is smaller than 1, for example when one or more
compounds from (5) to (11 ) and (19) and (20) are used as the
219?~~1
12
extractant, CFC-115 is concentrated into the top side of the column.
On the other hand, when one or more compounds from
(12) to (18) are used as the exiractant, HFC-125 is concentrated
into the top side of the column as the distillation apparatus as usual
since the relative volatility is larger than 1.
Using the same manner as in the case when the data of
Table 1 were obtained, the present inventors further studied effects
of a composition of the mixture of HFC-125 and CFC-115 and an
extractant ratio on the relative volatility for the case in which the
mixture of HFC-125 and CFC-115 is subjected to the extractive:
distillation using methanol as the extractant, and obtained results
shown in Table 2 below:
Table 2 (in case using methanol as extractant)
Weight Ratio of Extractant Relative
HFC-125 / CFC-115 Ratio*) Volatility
99.98 / 0.017 1.5 0.47
99.84 / 0.164 2.1 0.48
97.8 / 2.2 3.0 0.26
97.8/ 2.2 1.6 0.39
97.8 / 2.2 0.8 0.57
97.8 / 2.2 0.2 0.77
80.9 / 19.1 1.2 0.48
38.3 / 61.7 1.2 0.48
*) Extractant Ratio = weight of methanol / weight of {HFC-125
+ CFC-115)
It has been confirmed from the results of Table 2 that
the alpha {a) is considerably smaller than one in all the weight
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ratios, so that the addition of methanol into the mixture of HFC-125
and CFC-115 at various extractant ratios leads to effective
separation of CFC-115 as a volatile component, namely methanol is
preferable as the extractant when separation of the HFC-125/CFC-
115 mixture is carried out using the extractive distillation.
Then, the separation process of the present invention
will be hereinafter compared with Example described in U.S. Patent
No. 5,087,329 as to the number of theoretical plates of an
extractive distillation column which is required for example when
concentrated HFC-125 (e.g. a mixture of HFC-125 (99.9 mol %) /
CFC-115 (0.1 mol %)) is to be obtained from a mixture of HFC-125
(90 mol %) / CFC-115 (10 mol %).
The process described in the above U.S. Patent requires
about 26 theoretical plates in order to produce a top distillate
product of concentrated HFC-125 (e.g. concentrated to a mixture of
HFC-125 (99.9 mol %) / CFC-115 (0.1 mol %)). In this case,
calculation was carried out assuming the relative volatility to be
1.2. To the contrary, when according to the present process the
extractant such as those (12) to (18) is used which makes the
relative volatility larger than ane, the required number of
theoretical plates is about eight. In this case, calculation was
carried out assuming the relative volatility to be 1.9.
When according to the present process the extractant
such as those (5) to (11 ) and (19) and (20) which is used makes the
relative volatility smaller than one, CFC-115 is concentrated into
the top side of the column as a low boiling component. When the
column has about six theoretical plates, a mixture of the extractant
and HFC-125 which is concentrated to a ratio of HFC-125 (99.9 mol
CA 02197171 2002-03-26
14
%) / CFC-115 (0.1 mol %) as a distillate product is produced as a
bottom product while a mixture is produced in which a
concentration of CFC-115 is increased from its original
concentration to a ratio of HFC-125 (80 mol %) / CFC-115 (20 mol
%). In this case, calculation was carried out assuming the relative
volatility to be 0.4.
The required number (N) of the theoretical plates
referred to in the above was calculated according to the following
equation:
1 0 aN = (Yw/xw) / (YD/xD)
wherein a is a relative volatility, xp is a molar fraction of HFC-125
in a top distillate product, xw is a molar fraction of HFC-125 in a
bottom (or still) product, yo is a molar fraction of CFC-115 in a top
distillate product and yw is a molar fraction of CFC-115 in a bottom
(or still) product.
When the extractant which is used makes the relative
volatility smaller than one, HFC-125 should be separated from the
extractant so as to finally obtain HFC-125 alone since the bottom
product from the extractive distillation step contains the
2 0 extractant as described above. This separation is easily carried out
with a conventional distillation operation using a plate column or a
packed column since a boiling point difference is large between
HFC-125 and the extractant. Thus, HFC-125 is effectively separated
out of the mixture comprising at least HFC-125 and CFC-115 by
using combination of the extractive distillation operation with the
distillation operation thereafter which separates the extractant.
Also, when the extractant is used which makes the
relative volatility larger than one, the bottom product of the
CA 02197171 2002-03-26
extractive distillation step contains the extractant as described
above. In this case, objective HFC-125 is produced as the distillate
product of the extractive distillation step, and thus, any treatment
of the bottom product is possible. Preferably, the extractant is
5 recovered from the bottom product using for example distillation
and re-used in the extractive distillation step.
If the mixture to be separated contains a third component
in addition to HFC-125 and CFC-115, the only difference is
that the third component behaves together with HFC-125 and/or
10 CFC-115 depending on a boiling point of the third component. Thus,
even if the third component is contained in the mixture, HFC-125 is
separated from CFC-115 by carrying out the extractive distillation
using the extractant according to the present invention.
Further, with respect to the re-use of the extractant in
15 the extractive distillation step, when the extractant disclosed in
U.S. Patent No. 5,087,329 is used, CFC-115 is concentrated into the
bottom product and the extractant is also recovered from the
distillation bottom. This means that the extractant contains a large
amount of CFC-115, which necessitates complete separation of
CFC-115 for the re-use of the extractant. If only a small amount of
CFC-115 remains in the extractant, CFC~-115 may be ultimately
added to the extractive distillation step, whereby extraction
efficiency may deteriorate and the required number of
theoretical plates may increase. In fact, it is estimated that the
2 5 required number of theoretical plates of a distillation apparatus
would be about 10 to 20 in order to separate CFC-115 while the
extraction efficiency does not deteriorate. This is
also applicable when the cyclic hydrocarbon is used as the
CA 02197171 2002-03-26
16
extractant in the process of the present invention.
On the other hand, in the process according to the present
invention in which the extract such as the compound (5) to (11 ) and
(19) or (20) is used which makes the relative volatility smaller than
one, for example, the bottom product from the extractive
distillation step does not substantially contain CFC-115 so that it
is sufficient to separate only HFC-125 from the extractant.
Therefore, even though HFC-125 remains in the extractant at a
concentration of a few percent and such extractant is re-used in
the extractive distillation step, almost no effect is observed on the
extraction efficiency. Thus, the number of theoretical plates of the
distillation apparatus required for the recovery of the extractant is
only about 2 to 5. From this view point, it is preferable in the
process of the present invention to use at least one selected from
the alcohol containing 1 to 4 carbon atoms, the ketone containing 3
to 7 carbon atoms, the ether containing 2 to 6 carbon atoms and
nitromethane as the extractant.
The extractive distillation process using the compound as
the extractant according to the present invention can be carried out with
2 0 any distillation apparatus which is conventionally used such as a
plate column, a packed column and so on. There are no specific
limitations on the various conditions of the distillation apparatus
(such as operation temperature, operation pressure, reflux ratio,
total plate number of the distillation apparatus, plate levels of
2 5 mixture feed and extractant feed and so on), and proper conditions
are selected depending on the desired separation. Since HFC-125 and
CFC-115 have considerably low boili~~g points, it is generally
preferable to carry out the extractive distillation under a
CA 02197171 2002-03-26
17
pressurized condition. The operation pressure may be for example in
the range between 0 and 30 Kg/cm2-G (gauge pressure), and
preferably in the range between 10 and 20 Kg/cm2-G. Temperatures
at the top and the bottom of the distillation apparatus are
determined depending on the operation pressure and compositions of
the distillate product and the bottom product. In order to carry out
the distillation operation economically considering operation
temperatures of a condenser and a reboiler, the temperature at the
top of the distillation apparatus is preferably in the range between
-40 and 50 °C, and the temperature at the bottom of the distillation
apparatus is preferably in the range between -20 and 70 °C.
The process of the present invention may be carried out
in a batch mode or a continuous mode. Although in some cases, the
process may be carried out in a semi-continuous mode wherein
withdrawal and/or feed is carried out intermittently, the extractant
should be continuously supplied to the distillation apparatus.
In the process of the present invention, a ratio (S/F) of
an amount (S) of the extractant to an amount (F) of the feed mixture
(namely, HFC-125 and CFC-115) has an effect on the extent of
2 0 separation. Generally, the ratio may be properly selected depending
on a composition of HFC-125/CFC-115 of the mixture to be
subjected to the extractive distillation, an allowable concentration
of CFC-115 which remains in the separated HFC-125 and so on. The
required number of theoretical plates of the extractive distillation
apparatus may be properly selected in combination with the
selection of the ratio (S/F).
Preferred separation may usually be achieved with the
ratio based on weight in the range between about 0.1 and 20, and
CA 02197171 2002-03-26
18
preferably in the range between about 1 and 10. For example, the
following example can be shown: A mixture of CFC-115 (1 mol %)
and HFC-125 (99 mol %) is subjected to the extractive distillation
using the extractant selected from the compounds (5) to (11 ) and
(19) and (20), whereby CFC-115 is distilled in a concentration
increased to 10 mol % (thus, 90 mol % of HFC-125) and also an HFC-
125 stream is finally obtained of which CFC-115 concentration is
not more than 0.1 mol % (thus, more than 99.9 mol % of HFC-125)
after the separation from the extractant. In order to achieve this
separation, it is sufficient that the required number of theoretical
plates in the extractive distillation is in the range of, for example,
about 5 to 30 and the weight ratio of the extractant to the mixture
consisting of HFC-125 and CFC-115 is in the range of, for example,
about 1 to 10.
Best Mode for Carrying Out the Invention
The present invention will be explained in detail with
reference to Fig. 1 by way of an example in which methanol is used
as the extractant which makes the relative volatility between HFC-
125 and CFC-115 smaller than 1.
A mixture 2 comprising HFC-125 and CFC-115 (for
example HFC-i25 l CFC-115 = 90 mol % / 10 mol %) is supplied to
an extractive distillation apparatus 1 which is operated under a
pressurized condition (for example 15 Kg/cm2-G). For example, an
apparatus having the number of theoretical plate of about ten is
used as the distillation apparatus 1. Methanol 3 is supplied to the
distillation apparatus 1 (for example, onto the first theoretical
plate from the top). The amount of methanol is, for example, about
CA 02197171 2002-03-26
19
five times by weight that of the mixture 2. When, under those
conditions, the mixture is supplied, for example, onto the fifth
theoretical plate from the top and a reflux ratio is set for ten,
whereby a mixture of HFC-125 / CFC-115 (for example 10 mol % /
90 mol %) is withdrawn from the top as a distillate product 4.
In addition, a mixture containing methanol and HFC-125 /
CFC-115 (for example 99.9 mol % / 0.1 mol %) is withdrawn from
the bottom as a bottom product 5 (methanol concentration is 85 %).
Then, the bottom product is supplied to a distillation apparatus 9
which is operated under a pressurized condition (for example 12
Kg/cm2-G), and HFC-125 is obtained as a distillate product 6 from
the top which contains substantially neither methanol nor CFC-115.
Methanol which does not substantially contain HFC-125 is recovered
from the bottom of the distillation apparatus 9 as a bottom product
7, which is supplied to the extractive distillation apparatus 1 to re-
use as the extractant. Methanol to be re-used may be supplied to the
distillation apparatus 1 optionally after it is heated or cooled as
required through a heat exchanger 8.
In the process of the present invention, the level of the
plate onto which the extractant is supplied is preferably above a
plate onto which the mixture is supplied in any of the extractants
used. Thus, the plate onto which a reflux is returned and the plate
onto which the extractant is supplied may be the same. Optionally,
the plate onto which the mixture is fed and the plate onto which the
extractant is supplied may be the same. Alternatively, before the
mixture is fed to the distillation apparatus, it may be mixed with
the extractant and then the resulting mixture may be supplied to the
distillation apparatus.
CA 02197171 2002-03-26
Concretely, when methanol is used as the extractant, it
is more preferable to supply methanol onto a plate which is located
about 3 to 5 theoretical plates above a plate onto which the mixture
is supplied.
5 Employing the apparatus and the operation conditions as
described above, HFC-125 which does not substantially contain CFC-
115 can be separated out of the mixture which contains HFC-125
and CFC-115.
Next, the present invention will be explained in detail
1 0 with reference to Fig. 2 by way of another example in which
cyclopentane is used as the extractant which makes the relative
volatility between HFC-125 and CFC-115 larger than 1 as in the
cases of the compounds (12) to (18).
A mixture 12 comprising HFC-125 and CFC-115 (for
1 5 example HFC-125 / CFC-115 = 90 mol % / 10 mol %) is supplied to
an extractive distillation apparatus 11 which is operated under a
pressurized condition (for example 15 Kg/cm2-G). For example, an
apparatus having the number of theoretical plates of about twenty is
used as the distillation apparatus 11. Cyclopentane 13 is supplied
2 0 to the distillation apparatus 1 1 (for example, onto the fifth
theoretical plate from the top). The amount of cyclopentane is, for
example, about three times by weight that of the mixture 12.
When, under those conditions, the mixture 12 is supplied, for
example, onto the thirteenth theoretical plate from the top and a
reflux ratio is set for ten, whereby a mixture of HFC-125 / CFC-115
(for example 99.9 mol °~o / 0.01 mol %) is withdrawn from the top as
a distillate product 14.
In addition, a mixture containing cyclopentane and HFC-
2191111
21
125 / CFC-115 (for example 10 mol % / 90 mol %) is withdrawn
from the bottom as a bottom product 15 (cyclopentane concentration
is 70 %). Then, the bottom product is supplied to a distillation
apparatus 19 which is operated under a pressurized condition (for
example 12 Kg/cm2-G), and a mixture of HFC-125 and CFC-115 (10
mol % / 90 mol %) is obtained as a distillate product 16 from the
top which does not substantially contain cyclopentane.
Cyclopentane which contains substantially neither HFC-
125 nor CFC-115 is recovered from the bottom of the distillation
1 0 apparatus 19 as a bottom product 17, which is supplied to the
extractive distillation apparatus 11 to re-use as the extractant.
Cyclopentane to be re-used may be supplied to the distillation
apparatus 11 optionally after it is heated or cooled as required
through a heat exchanger 18.
The level of the plate onto which cyclopentane is
supplied is preferably above a plate onto which the mixture is
supplied as described above. It is 'more preferable to supply
cyclopentane onto a plate which is located about 7 to 10 theoretical
plates above a plate onto which the mixture is supplied.
Employing the apparatus and the operation conditions as
described above, HFC-125 which does not substantially contain CFC-
115 can be separated out of the mixture which contains HFC-125
and CFC-115.
Example
Using an extractive distillation column equipped with a
condenser at its top, a mixture of HFC-125 and CFC-115 (= 991
(wtlwt)) was treated. The distillation column had a diameter of
CA 02197171 2002-03-26
22
100 mm and 10 theoretical plates (actual plate number was 15), and
it was operated under a pressure of about 7 Kg/cm2-G (at the
column top). Methanol was supplied onto the second plate from the
top as the extractant, and the mixture to be distilled was fed at a
temperature of 38 °C onto the fifth plate fram the top.
Concentrated CFC-115 which contains HFC-125 was
withdrawn as a distillate product from the top. This operation was
carried out at a reflux ratio of 200. A mixture of HFC-125 and
methanol was withdrawn from the bottom at a temperature of 45 °C
which does not substantially contain CFC-115.
Mass balance of the above operation is shown Table 3
below:
Table 3
total flow HFC-125 CFC-115 methanol
rate (Kg/hr) {wt %) (wt %) (wt %)
(input)
Extractant (methanol) 50 100
HFC-125/CFC-115 mixture 10 99 1
(output)
Distillate product 1 89 9.9 1.1
Bottom product 5 9 14.9 0.01 8 5
The bottom product withdrawn from the bottom of the
distillation apparatus which contained HFC-125 and methanol and
small amount of CFC-115 was supplied to another distillation
apparatus having a diameter of 80 mm and 5 theoretical plates (the
number of actual plates was 7) which was operated under an
operation pressure of 5 Kg/cm2-G and a reflux ratio of 10, whereby
2~'~7171
23
HFC-125/CFC-115 {wt/wt) was obtained from the top and methanol
as a bottom product. The concentration of CFC-115 in the bot:om
product contained was not more than 0.01 % by weight. This
methanol can be re-used as the extractant of the extractive
distillation.
