JPH083082A - Production of pentafluoroethane - Google Patents

Abstract

PURPOSE:To efficiently separate pentafluoroethane (HFC-125) from a mixture of HFC-125 and chloropentafluoroethane (CFC-115). CONSTITUTION:HFC-125 is produced in high concentration by the extractive distillation of a mixture 2 containing HFC-125 and CFC-115. The extractive distillation is carried out by using methanol, ethanol, butanol, propyl alcohol, pentafluoropropanol, tetrafluoropropanol or acetone as the extractant 3 to obtain CFC-115 as the distillate 4 and a mixture of HFC-125 and the extractant as the bottom product 5, separating the extractant 3 from HFC-125 in the mixture by distillation and reusing the separated extractant 3 for the extractive distillation.

Description

Detailed Description of the Invention

[0001]

This invention relates to the fluorination of a mixture comprising at least pentafluoroethane (hereinafter also referred to as HFC-125) and chloropentafluoroethane (hereinafter also referred to as CFC-115), for example tetrachloroethylene. The present invention relates to a method for separating pentafluoroethane from a reaction product of a pentafluoroethane production process by an extractive distillation method using a specific compound as an extractant (solvent).

[0002]

2. Description of the Related Art HFC-125 is a compound useful as an alternative CFC compound containing no chlorine, and is used as a refrigerant, a foaming agent, a propellant, or the like. This HFC-12
As the manufacturing method of No. 5, a method of fluorinating tetrachloroethylene is adopted. In this manufacturing method,
Dichlorotetrafluoroethane, dichlorotrifluoroethane, hexafluoroethane, CFC-115 and the like are produced as by-products.

Among these by-products, CFC-115 has a boiling point of -38.7 ° C., which is the target product, HFC.
It is very close to the boiling point of −125, −48.5 ° C., and
The relative volatility of these two compounds is close to 1, especially HF
In the case of a mixture containing 95 mol% or more of C-125 (5 mol% or less of CFC-115), the specific volatility is about 1.0.
It becomes 4. Therefore, when a high concentration HFC-125 is to be separated by subjecting such a mixture to a conventional distillation treatment, a distillation apparatus having a large number of stages is required, and the separation is generally very difficult. Is.

In this specification, the specific volatility (α) is
When the solution containing at least the target component A and the target component B (boiling point of component A <boiling point of component B) is in a gas-liquid equilibrium state, the molar fraction of the low boiling point component A in the liquid phase is x _A
And the molar fraction of the high boiling point component B is x _B , the molar fraction of the low boiling point component A in the vapor phase when in equilibrium with the liquid phase is y _A, and the molar fraction of the high boiling point component B is When y _B is defined, α = (y _A / x _A ) / (y _B / x _B ).

[0005]

The extractive distillation method is adopted as a method for separating one component from a mixture of a system having a relative volatility close to 1 as described above. HFC-125 and C
Regarding the extractive distillation method for separating the mixture of FC-115, for example, US Pat. No. 5,087,329 discloses an extractive distillation method using a fluorocarbon having 1 to 4 carbon atoms as an extractant. .

However, US Pat. No. 5,087,32
In the method disclosed in No. 9, HFC-125 and CFC are calculated when calculated based on the numerical values described in Example 1 thereof.
The specific volatility of -115 is about 1.2, so
For example, from a mixture of HFC-125 / CFC-115 = 7/93 (mol% / mol%), HFC-125 / CFC-
HFC up to 115 = 99.7 / 0.3 (mol% / mol%)
About 40 theoretical plates are required to increase the concentration of -125 by distillation. The method described later was used to calculate the theoretical plate number.

[0007]

The inventors of the present invention have made extensive studies on a method for more efficiently separating HFC-125 from a mixture containing HFC-125 and CFC-115 by an extractive distillation method, and as a result, at least HF
Upon extractive distillation from a mixture comprising C-125 and CFC-115, selected from alcohols having 1 to 4 carbon atoms, ketones having 3 to 7 carbon atoms, ethers having 2 to 6 carbon atoms and nitromethane. Use of at least one compound or at least one compound selected from hydrocarbons having 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride as an extracting agent (or solvent) (thus, alone or as a mixture) By doing so, it was found that HFC-125 can be separated efficiently by using, for example, a distillation column having a very small number of theoretical plates.

Accordingly, the present invention is at least HFC-1.
25 and CFC-115 were subjected to extractive distillation to obtain HF having a relatively reduced concentration of CFC-115.
To obtain a high concentration of C-125, preferably substantially free of CFC-115, HFC-125 has 1 carbon atom.
~ 4 alcohols, C3-7 ketones, C2-6 ethers and at least one compound selected from nitromethane, or C3-8 hydrocarbons, trichloroethylene and carbon tetrachloride There is provided a method for separating HFC-125 from said mixture, characterized in that at least one compound selected from the above is used as an extractant.

That is, according to the present invention, a mixture containing at least pentafluoroethane and chloropentafluoroethane as main components is extractively distilled to contain pentafluoroethane substantially free of chloropentafluoroethane as main component. A process for producing pentafluoroethane by separating pentafluoroethane from the mixture to obtain a mixture consisting of alcohols having 1 to 4 carbon atoms, ketones having 3 to 7 carbon atoms, and ethers having 2 to 6 carbon atoms. At least one compound selected from the group consisting of nitromethane and nitromethane, or at least one compound selected from a hydrocarbon having 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride is used as an extractant, and Alcohols, C3-7 ketones, C2-6
When at least one compound selected from ethers and nitromethane is used as the extractant, a mixture containing pentafluoroethane and the extractant as main components is obtained as a bottom product, or a mixture containing 3 to 8 carbon atoms. When using at least one compound selected from the hydrocarbons, trichlorethylene and carbon tetrachloride as an extractant, a mixture comprising pentafluoroethane as a distillate as a main component is obtained. Provide a way.

As used herein, the term "main component" means that the amount of components other than that component is relatively small. Specifically, it is sufficient if the amount of the "main component" is 50% or more, and specifically 60% or more, for example 80%.
That is all. Further, in the present specification, the term “substantially” means a mixture containing pentafluoroethane as a main component, for example, a mixture having a concentration of pentafluoroethane of 90% by weight or more, preferably a mixture of 99.9% by weight or more, More preferably, it means finally obtaining a mixture of 99.99% by weight or more.

In the method of the present invention, at least one selected from alcohols having 1 to 4 carbon atoms, ketones having 3 to 7 carbon atoms, ethers having 2 to 6 carbon atoms and nitromethane.
When a compound of one kind is used as an extractant, a mixture containing pentafluoroethane as a bottom product and an extractant as main components as described above, preferably, the concentration of chloropentafluoroethane is 0.1% by weight or less. , More preferably 0.01% by weight or less of a mixture is obtained. In this case, if the ratio of chloropentafluoroethane to pentafluoroethane in the bottom product is at least less than the ratio in the original mixture, preferably 1/10 or less, more preferably 1 The composition of the distillate from the extractive distillation step is not particularly limited as long as it is reduced to 100/100 or less. Even if the distillate contains chloropentafluoroethane as a main component, pentafluoroethane is mainly contained. It may be contained as a component, or may be a mixture containing chloropentafluoroethane and pentafluoroethane as main components.

In the method of the present invention, when at least one compound selected from hydrocarbons having 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride is used as the extractant, the pentadistillate is used as the distillate as described above. A mixture containing fluoroethane as the main component, preferably having a pentafluoroethane concentration of 99.9% by weight or more, is obtained.
In this case, if the ratio of pentafluoroethane to chloropentafluoroethane in the distillate is at least increased from the ratio of the original mixture, preferably 10 times or more, more preferably 100 times. The composition of the bottom product is not particularly limited as long as it is increased above, and even if it contains chloropentafluoroethane and the extractant as the main components, it does not contain chloropentafluoroethane, pentafluoroethane and the extractant as the main components. It may be a mixture comprising

In one aspect of the invention, the mixture is a binary system consisting essentially of HFC-125 and CFC-115. In another aspect of the present invention, the resulting bottom product, for example, a bottom product containing an extractant and pentafluoroethane as a main component, or a bottom product containing chloropentafluoroethane and an extractant as a main component. By distilling the output, pentafluoroethane or chloropentafluoroethane is separated from the extractant, whereby the extractant is recovered, and the extractant may be supplied to the extractive distillation step for reuse.

In the present specification, extractive distillation is used in the meaning generally used in the field concerned, particularly in the field of chemical engineering, and the addition of a third component to a binary component mixture which is difficult to separate by distillation. The relative volatility of the original two-component system to 1
It means a distillation operation characterized by facilitating the distillation separation by separating it considerably from.

In the present invention, the alcohol having 1 to 4 carbon atoms means that the main chain carbon number is 1 to 4 and at least 1.
The above-mentioned compound having a hydroxyl group is meant, for example, alcohols such as aliphatic alcohols having 1 to 4 carbon atoms, and specifically, methanol, ethanol, butanol, propanol, pentafluoropropanol (C
₂ F ₅ CH ₂ OH), tetrafluoropropanol (HC
F ₂ CF ₂ CH ₂ OH), ethylene glycol, propanediol and trifluoroethanol can be mentioned. Further, in the present invention, the ketone having 3 to 7 carbon atoms is represented by the general formula R ₁ —CO—R ₂ (R ₁ and R ₂ are the same or different aliphatic hydrocarbon groups). Ketones, and specific examples thereof include acetone, diethyl ketone, and methyl ethyl ketone. In the present invention, ethers having 2 to 6 carbon atoms mean the general formula R ₁
Ethers represented by —O—R ₂ (R ₁ and R ₂ are the same or different aliphatic hydrocarbon groups), specifically, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether, etc. Can be mentioned. Further, in the present invention, the hydrocarbon having 3 to 8 carbon atoms includes both cyclic hydrocarbon and chain hydrocarbon,
The cyclic hydrocarbon means a hydrocarbon having at least one or more cyclic structures, and specific examples of the cyclic saturated hydrocarbon include cyclic saturated hydrocarbons such as cyclohexane, cyclopentane, cyclopropane and cyclobutane. Examples of the cyclic unsaturated hydrocarbon include aromatic hydrocarbons such as benzene.
The chain hydrocarbon includes both saturated and unsaturated hydrocarbons, and specific examples thereof include normal octane and normal hexene. It may be particularly preferred to use petroleum ethers and petroleum benzines as mixtures of these.

The inventors have found that HFC-125 and CFC-1
Regarding the method for separating HFC-125 from the mixture containing 15 by the extractive distillation method, various investigations were conducted on the above-mentioned extractants, and some of the extractants were HFC as shown in Table 1 below. -125 and CFC-11
A specific volatility measurement result of 5 was obtained:

Table 1 Extractant Extractant ratio *) Specific volatility (α) (1) Dichlorotrifluoroethane *) 0.85 1.2 (2) Dichloropentafluoropropane 0.67 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 (10) Tetrafluoropropanol 1.6 0.65 (11) 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 (1 ) Petroleum ether 4.0 2.1 (19) Diethyl ether 1.4 0.7 (20) Nitromethane 1.4 0.4 *) Extractant ratio = Extractant weight / (HFC-125 + CFC-115) weight ** ) Extractants disclosed in US Pat. No. 5,087,329

To obtain the values in Table 1 above, after degassing the sealed container to a substantially vacuum, HFC-125, CFC
-115, the extractant was added in a predetermined amount and left at 20 ° C. to be in a gas-liquid equilibrium state, and the liquid phase composition and the gas phase composition in that state were each analyzed by a gas chromatograph to obtain a mole fraction, The measurement method of calculating the relative volatility α by the above formula α = (y _A / x _A ) / (y _B / x _B ) was used.

As is clear from the results shown in Table 1, alcohols having 1 to 4 carbon atoms represented by the compounds (5) to (11) and (19) and (20) in Table 1, and 3 to 3 carbon atoms. When using ketones having 7 carbon atoms, ethers having 2 to 6 carbon atoms and nitromethane as extractants, the relative volatility is 1
Much smaller. In addition, (12) to (18) in Table 1
When a hydrocarbon having a carbon number of 3 to 8, represented by the above compound, trichloroethylene and carbon tetrachloride is used as an extractant, the specific volatility becomes considerably larger than 1. Therefore, Table 1
HFC-1 from a mixture comprising at least HFC-125 and CFC-115 by extractive distillation using the compounds of (5) to (20) as an extractant.
When 25 is separated, it is expected that it can be carried out by a distillation apparatus having a number of theoretical plates far smaller than the conventional one.

Generally, HFC-125 and CFC-
When distilling a mixture with 115, H having a low boiling point
FC-125 is usually concentrated on the top side of the extractive distillation apparatus, but when the specific volatility is less than 1, for example, the compounds of (5) to (11) and (19) and (20) If one or more is used as the extractant, CFC-115 will be concentrated at the top of the column.
However, when one or more of (12) to (18) in Table 1 is used as an extractant, the relative volatility is reversed to 1
As it becomes larger, HFC-125 is concentrated on the top side of the extractive distillation apparatus as usual. In addition, the inventors have used HFC-
In the case of extractive distillation of a mixture of 125 and CFC-115, the influence of the mixture composition of HFC-125 / CFC-115 and the ratio of the extractant on the specific volatility,
A more detailed examination was made by measuring the relative volatility using the same measurement method as in Table 1 and the results in Table 2 below were obtained:

Table 2 (When Methanol is Used as Extractant) HFC-125 / CFC-115 Weight Ratio Extractant Ratio *) Specific 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 = methanol weight / (HFC-125 + CFC-) 115) Weight

From the results in Table 2, α is 1 in each case.
Considerably smaller, HFC-125 / with various extractant ratios
CFC-115 can be efficiently separated as a volatile component by adding methanol to the CFC-115 mixture, that is, methanol is used as an extractant when the HFC-125 / CFC-115 mixture is separated by extractive distillation. It has been confirmed that is preferable.

Next, for example, HFC-125 / CFC-1
15 (mol% / mol%) = 90/10 from mixture HF
C-125 / CFC-115 (mol% / mol%) = 9
Regarding the theoretical plate number of the extractive distillation column required to obtain HFC-125 concentrated to 9.9 / 0.1, the separation method of the present invention and the example disclosed in US Pat. No. 5,087,329 are used. Compare with. In the process disclosed in the U.S. Patent, the theory required to obtain HFC-125 / CFC-115 (mol% / mol%) = 99.9 / 0.1 concentrated HFC-125 as overhead distillate. The number of stages is about 26 (in this case, the specific volatility is calculated as 1.2). In contrast, in the method of the present invention, the extractant (1
When an extractant having a relative volatility greater than 1 is used as in 2) to (18), the required theoretical plate number is about 8 (in this case, the relative volatility was calculated as 1.9).

Further, in the method of the present invention, CFC-115 is obtained by the method using an extractant having a specific volatility of less than 1 as in the extractants (5) to (11) and (19) and (20). Since it is concentrated at the top of the column as a low-boiling component, a mixture of HFC-125 and extractant concentrated to HFC-125 / CFC-115 (mol% / mol%) = 99.9 / 0.1 from the bottom of the column. As a canned product,
HFC-125 / CFC-115 (mol% / mol%) =
It was found that obtaining a mixture having a concentration of CFC-115 increased to 80/20 as a distillate can be achieved with a theoretical plate number of about 6 (in this case, the specific volatility was calculated as 0.4). did).

Necessary number of theoretical plates (N) used in the above comparison
Was calculated based on the formula α ^N = (y _W / x _W ) / (x _D / y _D ). In the above formula, α: relative volatility x _D : mole fraction of HFC-125 in the overhead distillate x _W : mole fraction of HFC-125 in bottom product (still) y _D : tower Molar fraction of CFC-115 in top distillate y _W : Molar fraction of CFC-115 in bottom product (still).

When an extractant having a relative volatility of less than 1 is used, as described above, the bottom product of the extractive distillation step contains the extractant, so that HFC-125 is finally obtained alone. Requires separation of HFC-125 from the extractant. Since this separation has a large boiling point difference between HFC-125 and the extractant, it can be easily carried out by an ordinary distillation separation operation using a plate column or a packed column. Therefore, by combining the extractive distillation operation and the subsequent distillation operation for separating the extractant, at least HFC-125 and CFC-
HFC-125 can be efficiently separated from the mixture comprising 115.

Even when an extractant having a relative volatility of more than 1 is used, the bottom product of the extractive distillation step contains the extractant as described above. In this case, the target HFC-12
5 is obtained as a distillate in the extractive distillation step, and the bottom product may be treated in any manner. Usually, however, the extractant is recovered from the bottom product by, for example, distillation, and then extracted in the extractive distillation step. It is preferably reused.

When the mixture to be separated contains a third component other than HFC-125 and CFC-115, it behaves together with HFC-125 and / or CFC-115 depending on the boiling point of the third component. The only difference is that
Even when the third component is included, the separation method by extractive distillation using the extractant of the present invention is performed to obtain HFC-125.
Can be separated from CFC-115.

Further, regarding reuse of the extractant in the extractive distillation step, when using the extractant disclosed in US Pat. No. 5,087,329, CFC-115 is concentrated at the bottom of the column and extracted. Since the agent is also collected from the bottom of the column, the extractant contains a large amount of CFC-115, and it is necessary to sufficiently separate and remove CFC-115 when reusing. In this case, even if a small amount of CFC-115 remains in the extractant, the result is that CFC-11 appears in the extractive distillation column.
Since 5 may be added, the extraction efficiency may be significantly reduced and the number of theoretical plates required for distillation may be increased. In fact, the number of theoretical plates required for the distillation apparatus to separate CFC-115 without significantly reducing the extraction efficiency is 10 to 2
It is estimated to be 0 stage. In this respect, the same applies when a cyclic hydrocarbon is used as an extractant in the method of the present invention.

On the other hand, in the method of the present invention, the extractant (5)
In the method using an extractant having a relative volatility of 1 or less as in (11) and (19) and (20), for example, the bottom product of the extractive distillation step does not substantially contain CFC-115. Therefore, only the extracted HFC-125 need be separated from the extractant. Therefore, even if HFC-125 remains in the extractant by several%, when it is reused as the extractant, the extraction efficiency is hardly affected. Therefore, the number of theoretical plates required for the distillation column for recovering the extractant is only about 2 to 5 plates. In this sense, in the method of the present invention, at least one selected from alcohols having 1 to 4 carbon atoms, ketones having 3 to 7 carbon atoms, ethers having 2 to 6 carbon atoms, and nitromethane is used as an extractant. More preferably.

The extractive distillation method using the extractant of the present invention can be carried out using a commonly used distillation apparatus such as a plate column or a packed column. Various conditions of the distillation apparatus (for example, operating temperature, operating pressure, reflux ratio, total number of distillation apparatus stages, position of charging stage, position of extractant supply stage, etc.) are not particularly limited and are intended. The choice can be made to achieve the separation. HFC-12
5 and CFC-115 have significantly lower boiling points,
Extractive distillation under pressure is generally preferred, eg 0.
-30Kg / cm ² -G (gauge pressure), preferably 10-2
An operating pressure of 0 Kg / cm ² -G can be adopted. Further, the temperature at the top and bottom of the distillation apparatus depends on the operating pressure and the composition of the distillate and the bottom product. In order to carry out the distillation operation economically in consideration of the temperature of the condenser and the temperature of the reboiler, the temperature at the top of the column is preferably about -40 to 50 ° C, and the temperature at the bottom of the column is preferably about -20 to 70 ° C. .

The method of the present invention can be carried out batchwise or continuously or, if necessary, semicontinuously with intermittent withdrawal and / or charging. It is necessary to supply continuously.

In the process of the invention, the feed mixture (F) to be separated which is fed with the extractant (S) fed during the extractive distillation (hence HFC-125 and CFC-).
The ratio (S / F) to 115) influences the degree of separation. Generally, this ratio is the composition of HFC-125 / CFC-115 of the extractive distillation mixture and the permissible CFC-11 remaining in the separated HFC-125.
5 It can be appropriately selected depending on the concentration and the like. At this time, the required theoretical plate number of the extractive distillation apparatus may be appropriately selected in relation to this ratio.

Generally, this proportion is 0,0 by weight.
A preferable separation is achieved by adjusting the amount to about 1 to 20, preferably about 1 to 10. For example, CFC-115
A mixture of (1 mol%) and HFC-125 (99 mol%) was added to extractants (5) to (11) and (1
9) and (20) are used for extractive distillation to evaporate CFC-115 up to a concentration of CFC-115 of 10 mol% (90 mol% of HFC-125), and then to distill it to 0.1. HFC-containing less than mol% CFC-115
125 (hence, 99.9 mol% or more of HFC-125) is finally obtained after separation from the extractant,
The required theoretical plate number in the extractive distillation is, for example, 5 to 30, and the weight ratio of the extractant to the mixture of HFC-125 and CFC-115 is, for example, 1 to 10 times.

Next, referring to the attached flow sheet of FIG. 1, as an example of the case where an extractant which makes the relative volatility of HFC-125 and CFC-115 less than 1 is used,
The method of the present invention, including the reuse when methanol is used, will be described in more detail. HFC-125 and CFC-
Mixture 2 comprising 115 (eg HFC-125 /
CFC-115 (mol% / mol%) = 90/10)
For example, it is supplied to the extractive distillation apparatus 1 operated under pressure (for example, 15 Kg / cm ² -G). As the distillation apparatus 1, one having a theoretical plate number of, for example, about 10 is used, and methanol 3 of, for example, about 5 times the weight of the mixture 2 is used for the distillation apparatus 1 (for example, 1
The tray of the theoretical stage of the first stage). Under such conditions, for example, when the mixture is supplied to the tray of the fifth theoretical plate from the top and operated at a reflux ratio of 10, for example, HFC-125 / CFC-115 (mol% / mol %) = 10/90 mixture can be withdrawn as distillate 4.

From the bottom of the tower, for example, HFC-125 /
A mixture containing methanol at a ratio of CFC-115 (mol% / mol%) = 99.9 / 0.1 was withdrawn as bottom product 5 (methanol concentration 85%), and this was pressurized (for example, 12 kg / cm 2). ² -G) to the distillation apparatus 9 operated,
From the top of the column, HFC-125 substantially free of methanol and CFC-115 is obtained as distillate 6. Methanol substantially free of HFC-125 is recovered as a bottom product 7 from the bottom of the distillation apparatus 9 and is supplied to the extractive distillation apparatus 1 to be reused as an extractant. The methanol to be reused is heated or cooled by the heat exchanger 8 if necessary, and then supplied to the distillation apparatus 1.

In the method of the present invention, the position of the tray of the extractive distillation apparatus for supplying the extractant is located above the position of the tray for supplying the mixture, whichever extractant is used. preferable. Therefore, the extractant may be supplied to the same tray as that for supplying the reflux. However, in some cases, the extraction agent may be fed to the same tray as the mixture, or the mixture may be mixed with the extraction agent before being fed to the distillation apparatus and then fed to the distillation apparatus. Specifically, when methanol is used as the extractant, it is more preferable to supply methanol to a tray which is 3 to 5 theoretical plates above the tray for supplying the mixture. With such a device and operation, CF
HFC-125 substantially free of CFC-115 can be separated from a mixture containing C-115 and HFC-125.

Next, like the extractants (12) to (18),
Referring to the flow sheet of FIG. 2, the method of the present invention, including the reuse with cyclopentane as an example of using an extractant that makes the relative volatility of HFC-125 and CFC-115 greater than 1. Will be described in more detail. HFC-
Mixture 12 comprising 125 and CFC-115
(For example, HFC-125 / CFC-115 (mol% / mol%) = 90/10) is, for example, pressurized (for example, 15 Kg / cm ²
-G) is supplied to the extractive distillation apparatus 11 operated. As the distillation apparatus 11, for example, one having a theoretical plate number of about 20 is used, and cyclopentane 13 having a weight of the mixture 12 of, for example, about 3 times is supplied to the distillation apparatus 11 (for example, an ideal tray 5th from the top). To do. Under such conditions, the mixture 12
Is fed to the ideal tray of the 13th tray from the top, and when operating at a reflux ratio of 10, for example, HFC
-125 / CFC-115 (mol% / mol%) = 99.
A 9 / 0.1 ratio of the mixture can be withdrawn as distillate 14.

From the bottom of the distillation apparatus 11, for example, H
A mixture comprising cyclopentane in which the ratio of FC-125 / CFC-115 (mol% / mol%) is 10/90 is withdrawn as bottom product 15 (cyclopentane concentration 70%), and this is pressurized under pressure, for example, 12 kg. HFC-125 / CFC-115 (mol% substantially free from cyclopentane) supplied to the distillation apparatus 19 operated at / cm ² -G.
/ Mole%) = 10/90 mixture can be withdrawn as distillate 16. Cyclopentane substantially free of HFC-125 and CFC-115 is recovered as bottom product 17 from the bottom of the distillation apparatus 19, and is supplied to the extractive distillation apparatus 11 to be reused as an extractant.
Cyclopentane to be reused may be used in the heat exchanger 1 if necessary.
After heating or cooling by 8, it is supplied to the distillation apparatus 11.
The position of the tray of the extractive distillation apparatus 11 for supplying cyclopentane is preferably located above the position of the tray for supplying the mixture 12 as described above, and more preferably 7 to 7 theoretical plates from the tray for supplying the mixture. Located about 10 above. With such a device and operation, CFC-
HFC-125 substantially free of CFC-115 can be separated from a mixture containing 115 and HFC-125.

[0040]

EXAMPLE An HF was extracted using an extractive distillation column equipped with a condenser at the top of the column and having a diameter of 100 mm and 10 theoretical plates (15 actual plates).
Mixture of C-125 and CFC-115 (HF
C-125 / CFC-115 (weight / weight) = 99 /
1) was treated by an extractive distillation column operating at an operating pressure of about 7 kg / cm ² -G (top). The methanol added as the extractant was supplied to the second tray from the top, and the mixture to be distilled was added to the fifth tray from the top at 38 ° C.

CFC-11 concentrated as overhead distillate
5 (including HFC-125) was extracted. In this distillation operation, the reflux ratio was 200. CFC from bottom
A mixture of HFC-125 and methanol substantially free of -115 was extracted at 45 ° C. The mass balance in this case is shown in Table 3 below:

Table 3 Total flow rate HFC-125 CFC-115 Methanol (Kg / hr) (wt%) (wt%) (wt%) (input) Extractant (methanol) 50 100 HFC-125 / CFC-115 mixture 10 99 1 (output) distillate 1 89 9.9 1.1 canned product 59 14.9 0.01 85

HFC-1 withdrawn from the bottom of the distillation apparatus
The bottom product containing 25, methanol and a small amount of CFC-115 has a diameter of 80 mm and has 5 theoretical plates (7 actual plates).
Was charged into another distillation apparatus of No. 3, and distilled at an operating pressure of 5 kg / cm ² -G and a reflux ratio of 10, and HFC-125 / C
A distillate of FC-115 (weight / weight) = 99.9 / 0.1 was obtained from the bottom of the column as a bottom product of methanol containing 1% by weight of HFC-125. In addition, CFC-11 in the canned product
5 was less than 0.01%. This methanol can be reused as an extractant for extractive distillation.

[Brief description of drawings]

FIG. 1 shows a flow sheet of one specific example of a separation method for carrying out the method of the present invention.

FIG. 2 shows a flow sheet of another embodiment of a separation method for carrying out the method of the present invention.

[Explanation of symbols]

1 ... Extractive distillation apparatus, 2 ... HFC-125 and CFC-
Mixture containing 115, 3 ... Extractant, 4 ... Distillate, 5 ... Bottom product, 6 ... Distillate, 7 ... Bottom product, 8 ... Heat exchanger, 9 ... H
FC-125 separation distillation apparatus, 11 ... Extractive distillation apparatus, 12
... A mixture comprising HFC-125 and CFC-115,
13 ... Extractant, 14 ... Distillate, 15 ... Cans, 16 ... Distillates, 17 ... Cans, 18 ... Heat exchanger, 19 ... Extractant recovery distillation apparatus.

Claims (14)

[Claims] 1. A process for producing pentafluoroethane, wherein pentafluoroethane substantially free of chloropentafluoroethane is obtained by a step of subjecting a mixture comprising at least pentafluoroethane and chloropentafluoroethane to extractive distillation. Supplying the mixture to the extractive distillation step, at least one compound selected from alcohols having 1 to 4 carbon atoms, ketones having 3 to 7 carbon atoms, ethers having 2 to 6 carbon atoms and nitromethane, or carbon number 3-8
Of at least one compound selected from the hydrocarbons, trichlorethylene and carbon tetrachloride described above as an extractant to the extractive distillation step, and containing pentafluoroethane and the extractant as the bottom product of the extractive distillation step as main components. Or a mixture comprising pentafluoroethane as a main component as a distillate of the extractive distillation step is provided. 2. After mixing the mixture and the extractant,
The manufacturing method according to claim 1, wherein this is supplied to the extractive distillation step. 3. A weight-based ratio (S) to pentafluoroethane and chloropentafluoroethane (F) contained in the mixture of the extractant (S) used in the extractive distillation step.
/ F) is 0.1-10, The manufacturing method of Claim 1 or 2. 4. A mixture comprising pentafluoroethane separated by distilling a mixture comprising an extractant obtained as bottom product and pentafluoroethane as a main component, whereby a mixture comprising an extractant as a main component. Is recovered, and the recovered mixture is reused for extractive distillation. 4. The production method according to claim 1. 5. A mixture comprising pentafluoroethane as a main component is obtained as a distillate of the extractive distillation step, and an extractant and chloropentafluoroethane and optionally pentafluoroethane are contained as a main product as a bottom product. Chloropentafluoroethane and optionally pentafluoroethane are separated by distilling this mixture, whereby a mixture comprising an extractant as a main component is recovered and the recovered mixture is extracted. Reusable for distillation 1.
The manufacturing method according to any one of to 3. 6. The production method according to claim 1, wherein the extractant has a relative volatility (α) of pentafluoroethane and chloropentafluoroethane of 1 or less. 7. The extractant is methanol as claimed in claim 1.
The manufacturing method according to claim 4 or claim 6. 8. The extractant is acetone, as claimed in any one of claims 1 to 4.
And the manufacturing method according to claim 6. 9. The manufacturing method according to claim 1, wherein the extractant is cyclopentane. 10. The production method according to claim 1, wherein the extracting agent is diethyl ether. 11. The production method according to claim 1, wherein the extractant is nitromethane. 12. The manufacturing method according to claim 1, wherein the extractant is normal octane. 13. The production method according to claim 1, wherein the extractant is petroleum benzine. 14. The production method according to claim 1, wherein the extractant is petroleum ether.