JPH10310542A - Separation of pentafluoroethane and 1,1,1-trifluoroethane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently separating each component from the subject mixture, by subjecting a difficult-to-separate azeotrope-like mixed fluid to extractive distillation using a specific extraction agent. SOLUTION: This method comprises using 50-90 wt.% of at least one kind of ester (preferably, ethyl formate, methyl acetate or ethyl acetate) or ketone (prefeably, acetone, methyl ethyl ketone), easily available as an extractive reagent and having the standard boiling point of -10 to 100 deg.C, preferably, having a boiling point difference of >=40 deg.C from that of the mixed fluid and subjecting the mixed fluid composed of pentafluoroethane (hereinafter, referred to as HFC-125) and 1,1,1-trifluoroethane (hereinafter referred to as HFC-143a) or composed of HFC-125, HFC-143a and chloropentafluoro-ethane, all of which are difficult to separate from one another, to extractive distillation at a pressure of >= about 5 kg/cm<2> abs in a precision distillation tower, such as a packed tower or plate tower so as to efficiently separate the objective compounds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to pentafluoroethane (hereinafter referred to as "HFC-125") and 1,1,1-
A mixed fluid composed of trifluoroethane (hereinafter, referred to as “HFC-143a”), or HFC-125 and H
The present invention relates to a method for efficiently separating a mixed fluid composed of FC-143a and chloropentafluoroethane (hereinafter, referred to as “CFC-115”) into respective components.

[0002]

BACKGROUND OF THE INVENTION Distillation is the most common method of separating a fluid mixture into its constituent components. However, HFC-125 and HFC-143a have standard boiling points close to -48.5 ° C and -47.2 ° C.
The specific volatility of HFC-143a with respect to 125 is close to 1, and it is known that a mixed fluid composed of HFC-125 and HFC-143a has an azeotropic composition, and it is very difficult to separate the mixed fluid only by a general distillation method. Difficult.

Further, CFC- having a standard boiling point of -38.7 ° C.
115 also has a specific volatility relative to HFC-125 of 1
It is known that a mixed fluid composed of HFC-125 and CFC-115 has an azeotropic composition, and it is very difficult to separate this mixed fluid by a general distillation method. Therefore, an extractive distillation method in which a third component different from the standard boiling point of the constituent component is added to a fluid mixture having an azeotropic composition as an extractant and distillation is performed.

[0004] US Pat. No. 3,732,150 proposes a method for separating a mixed fluid having an azeotropic composition consisting of HFC-125 and HFC-143a. HFC by adding
-143a forms an azeotrope of ammonia with HFC-1
An azeotropic distillation method for separating 25 is disclosed. In addition, the present inventors have disclosed in JP-A-09-12487,
An extractive distillation method using at least one selected from carbon chlorides or hydrocarbons having 1 or 2 carbon atoms as an extractant is disclosed.

On the other hand, with respect to the separation of an azeotropic mixture fluid having an azeotropic composition consisting of HFC-125 and CFC-115, US Pat. No. 5,087,
No. 329 discloses an extractive distillation method in which a fluorocarbon having 1 to 4 carbon atoms or hydrogen and / or chlorine added thereto is used as an extractant. In addition, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 07-133240 that paraffin-based hydrocarbons, alcohols, ethers, esters, or ketones having a standard boiling point in the range of −10 ° C. to 100 ° C. Japanese Patent Application Laid-Open No. 08-143486 discloses an extractive distillation method in which a selected one is used as an extractant, and one selected from carbon chlorides or hydrocarbons having 1 or 2 carbon atoms is used as an extractant. ing.

[0006]

However, the effect of the extractant shown in the prior art used in the disclosed method for separating a mixed fluid comprising HFC-125 and HFC-143a is not so large, Ammonia used as an azeotropic agent is toxic and dangerous.
In addition, HFC-125, HFC-143a and CFC
The technology relating to the separation of the mixed fluid consisting of -115 is not described in the literature.

The present inventors have developed HFC-125 and HFC-125.
143a for the separation of the mixed fluid, or
HFC-125 and HFC-143a and CFC-11
The present invention has been achieved as a result of searching for an extractant for separation of a mixed fluid consisting of 5 and therefore, the present invention provides a mixed fluid of HFC-125 and HFC-143a using a practical extractant, or HFC-125 and HFC-143
It is an object of the present invention to provide a method for efficiently separating a mixed fluid consisting of a and CFC-115.

[0008]

Means for Solving the Problems The present inventors have developed HFC-125 and HFC which are very difficult to separate by a general distillation method.
-143a mixed fluid or HFC-125 and HFC
A practical and highly effective extractant has been found in an extractive distillation method as a method for separating an azeotropic mixture fluid composed of -143a and CFC-115. The extractant has a standard boiling point of-
HFC-125 and HFC-125 are obtained by extractive distillation using this extractant, comprising at least one of esters or ketones in the range of 10 ° C to 100 ° C.
A mixed fluid composed of FC-143a or HFC-
The present invention provides a method for separating a mixed fluid consisting of H.125 and HFC-143a and CFC-115.

Using at least one of esters or ketones having a standard boiling point in the range of -10 ° C. to 100 ° C. as an extractant, HFC-125 and HFC-14 are used.
3a, or HFC-125 and H
It was found that the extraction fluid of the mixed fluid consisting of FC-143a and CFC-115 can be separated very efficiently.

In particular, the extractant is preferably selected from the group consisting of ethyl formate, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone and the like.

This is an effect brought about by changing the specific volatility of HFC-143a or CFC-115 with respect to HFC-125 to be larger than 1 due to the presence of the extractant in the extractive distillation system. That is, in general, when the relative volatility is 1, the composition of both gas and liquid phases becomes the same, so that separation by distillation is impossible. For example,
If the specific volatility of HFC-143a with respect to HFC-125 is greater than 1, the mole fraction of HFC-143a in the gas phase will be greater than the mole fraction in the liquid phase,
a is concentrated in the gas phase and can be separated by distillation.

The standard boiling points of preferred extractants used in the present invention are shown below. Ethyl formate 54 ° C Methyl acetate 57 ° C Ethyl acetate 77 ° C Acetone 56 ° C Ethyl methyl ketone 79 ° C

As described above, the boiling points of the preferred extractants used in the present invention are HFC-125, HFC-143a, CFC-
It is sufficiently higher than the boiling point of 115. Generally, it is desired that the difference in boiling point between the fluid mixture fluid and the extractant is about 30 ° C. or more, preferably 40 ° C. or more in consideration of recovering the extractant. Esters and ketones used as the extractant of the present invention have a relatively high boiling point and satisfy the above requirements. All of these extractants are inexpensive and readily available on the market, and can be said to be highly practical extractants.

A preferred extractive distillation method used in the present invention is a method in which an extractant is supplied to a distillation column above a supply stage of a feedstock and distillation is performed. Any distillation column can be used as long as it has a function necessary for ordinary distillation, but it is preferable to use a precision distillation column such as a packed column or a tray column. The operation conditions of distillation can be various modes depending on the utility and the degree of separation, and are not limited. The operating pressure is preferably at least about 5 kg / cm ² abs so that the overhead temperature of the distillation column does not become too low. In this case, the tower top temperature is about -10 ° C or higher.

In the distillation, the extractant of the present invention is HFC-125.
In order to make the specific volatility of HFC-143a with respect to
A mixed fluid with HFC-125 containing more HFC-125 is distilled out, and HFC- containing more HFC-125 from the bottom of the column.
A mixed fluid of 143a and the extractant is obtained. By changing the conditions of the distillation operation, for example, the supply amount of the mixed fluid and the extractant, the operation temperature, the operation pressure, the reflux ratio, the distillate amount, the bottom amount, etc., HFC-125 is substantially contained from the top of the column. Distilling off HFC-143a which is not
A mixed fluid of HFC-125 and the extractant substantially containing no FC-143a can be discharged.

Furthermore, if economical efficiency is achieved, the mixed fluid consisting of HFC-125 and HFC-143a distilled or canned is subjected to separate extraction distillation or ordinary or precision distillation to obtain high purity. HFC-1
25 or HFC-143a can be obtained. still,
The extractant for separately performing the extractive distillation may be the same as the extractant for the first extractive distillation. A mixed fluid consisting of HFC-125 and an extractant discharged from the bottom of the distillation column, or H
The mixed fluid composed of FC-125, HFC-143a and the extractant has a higher standard boiling point of the extractant than that of HFC-125 or HFC-143a.
And only HFC-143a can be easily isolated from the mixed fluid by ordinary distillation.

On the other hand, the inventors have found that the extractant of the present invention is HF
The effect of the present invention on the mixed fluid comprising C-125, HFC-143a and CFC-115 is
-125 and HFC-143a, and the same effect on the mixed fluid consisting of HFC-125 and CFC-115 described in JP-A-7-133240 by the present inventors. HFC-1
The specific volatility of HFC-143a and CFC-115 to 25 was found to be greater than 1.

When extractive distillation is carried out using a mixed fluid consisting of HFC-125, HFC-143a and CFC-115 as a feedstock, HFC-125 is compared with the feedstock from the top of the column due to the relative volatility of each component. Low HFC-
A mixed fluid of 143a and CFC-115 distills out, and HFC-143 containing more HFC-125 from the bottom of the column.
a, A mixed fluid of CFC-115 and the extractant is obtained. The conditions of the distillation operation, for example, the supply of the mixed fluid and the extractant
By changing the operating temperature, operating pressure, reflux ratio, distillate amount, bottom amount, etc., it is possible to distill HFC-143a and CFC-115 substantially free of HFC-125 from the top of the column, HFC-143a and CFC-11 from the bottom
It is possible to take out a mixed fluid of HFC-125 and the extractant substantially containing no 5.

Furthermore, if economical efficiency can be achieved, the extractive fluid or the mixed fluid consisting of HFC-143a and CFC-115 distilled or canned is subjected to separate extractive distillation or ordinary or precision distillation. Thereby, high-purity HFC-125 or HFC-143a can be obtained. Note that the extractant for separately performing the extractive distillation may be the same as the extractant for the first extractive distillation. The extractant in the mixed fluid discharged from the bottom of the distillation column can be easily isolated from the mixed fluid by ordinary distillation as described above. The isolated extractant can be recycled as it is as the extractant for extractive distillation. In general, the higher the extractant concentration, the more advantageous it is to separate the relative volatility between the substances to be separated from one, and the extractant in the present invention has a concentration of 20% by weight.
As described above, the content is more preferably in the range of 50 to 90% by weight.
Further, each of the above-mentioned extractants may be used alone,
It is also possible to use a mixture of more than one species.

[0020]

EXAMPLES The present invention will be specifically described with reference to examples. (Example 1) HFC-12 containing 5% by weight of HFC-143a was added to an Osmer type vapor-liquid equilibrium measuring device made of stainless steel.
5 was charged as a feed material, and ethyl formate, methyl acetate, ethyl acetate, acetone, or methyl ethyl ketone was added thereto as an extractant, and the gas-liquid equilibrium relationship was measured. Table 1 shows a series of test results.

[0021]

[Table 1]

The relative volatility of HFC-143a with respect to HFC-125 increased from 1 in any of the extractants.

(Example 2) A stainless steel Osmer type vapor-liquid equilibrium measuring apparatus was charged with HFC-125 containing 5% by weight of HFC-143a as a feed material, and acetone was used as an extractant so as to have a predetermined concentration. Was added to measure the gas-liquid equilibrium relationship. Table 2 shows the test results.

[0024]

[Table 2]

From these results, it was found that HFC-125
It can be seen that the specific volatility of FC-143a increases as the concentration of the extractant in the liquid phase increases, and the separation ability is improved.

Example 3 A precision distillation column made of stainless steel having a diameter of 65 mm and a theoretical stage of 24 was used, and the pressure was 6 kg / cm.
HFC containing 1% by weight of HFC-143a at ² abs
-125 as a feedstock, 21k from the top of the tower at 2k
g / h, and acetone was used as an extractant and fed at a position of 5 kg from the top of the tower at 4 kg / h. Extractive distillation was performed at a reflux ratio of 2, and a distillate was distilled off at the top of the column at a rate of 0.12 kg / h, and a bottom product of 5.88 kg / h was obtained from the bottom of the column. Table 3 shows the results. In the table, "nd" indicates that no detection was performed.

[0027]

[Table 3]

The detection limit of HFC-143a in this experiment is 1 wtppm. From this result, a mixture of HFC-125 and acetone substantially free of HFC-143a was obtained as a bottom product by extractive distillation of HFC-125 having a purity of 99% by weight. Further, the bottom product is subjected to ordinary distillation in a second distillation column, so that H
High purity HFC-125 with FC-143a of 1 ppm or less
Could be obtained. The recovery rate of HFC-125 was about 95%.

Example 4 The same distillation column as in Example 3 was used, and at a pressure of 6 kg / cm ² abs, 1 HFC-125 was added.
HFC-143a containing weight% was supplied as a feed material to the 21st position from the top at 2 kg / h, and acetone was supplied as an extractant to the 5th position from the top at 8 kg / h. Extractive distillation was performed at a reflux ratio of 5, and a distillate of 1.84 k
g / h, and 8.16 kg / h of bottom product was obtained from the bottom of the column. Table 4 shows the results. In the table, "nd" indicates that no detection was performed.

[0030]

[Table 4]

The detection limit of HFC-125 in this experiment is 1 wtppm. From these results, the purity was 99% by weight.
The extractive distillation of HFC-143a yielded HFC-143a substantially free of HFC-125 as a distillate. The recovery rate of HFC-143a is about 9
It was 3%.

Example 5 Using the same distillation column as in Example 3, HFC-1 containing 5% by weight of HFC-143a and 1% by weight of CFC-115 at a pressure of 6 kg / cm ² abs.
25 kg as a feed material at a position 21 stages from the top of the tower at 2 kg /
h, and acetone was used as an extractant at a position of 5 kg from the top of the tower at 8 kg / h. Perform extractive distillation at a reflux ratio of 3,
A distillate was distilled at a rate of 0.31 kg / h from the top of the column, and a bottom of 9.68 kg / h was obtained from the bottom of the column. Table 5 shows the results. In the table, "nd" indicates that no detection was performed.

[0033]

[Table 5]

The detection limit of CFC-115 in this experiment is 1 wtppm. From this result, the purity was 94% by weight.
Of HFC-125 by extractive distillation
HFC without FC-143a and CFC-115
A mixture of -125 and acetone was obtained as bottoms.
CFC-115 is HFC-1 like HFC-143a.
It is a substance that forms an azeotropic mixed fluid with 25 and is known to be difficult to separate by ordinary distillation operations. However, the present results confirmed that the presence of CFC-115 had no effect on extractive distillation and could be separated from HFC-125 simultaneously with HFC-143a. Furthermore, by subjecting the bottom product to normal distillation in the second distillation column, high-purity HFC-125 with HFC-143a and CFC-115 of 1 ppm or less could be obtained from the top of the column. Also, H
The recovery of FC-125 was about 90%.

[0035]

As described above, the present invention relates to a mixed fluid of pentafluoroethane and 1,1,1-trifluoroethane, which is difficult to separate by ordinary distillation, or pentafluoroethane and 1 Having a azeotropic composition, such as a mixed fluid comprising 1,1,1-trifluoroethane and chloropentafluoroethane, is obtained by converting an easily available ester or ketone having a standard boiling point in the range of -10 ° C to 100 ° C. This is an epoch-making method that can be separated into each component by extractive distillation using at least one of the compounds as an extractant.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Reiji Takahashi 5-1 Okawacho, Kawasaki-ku, Kawasaki-shi, Kawasaki Prefecture Showa Denko KK Production Technology Center

Claims (6)

[Claims] 1. A mixed fluid containing pentafluoroethane and 1,1,1-trifluoroethane has a standard boiling point of -10.
A method for separating pentafluoroethane and 1,1,1-trifluoroethane, comprising extracting and distilling at least one of esters or ketones having a temperature in the range of from 100 ° C. to 100 ° C. as an extractant. 2. A mixed fluid comprising pentafluoroethane, 1,1,1-trifluoroethane and chloropentafluoroethane is prepared by mixing at least one of esters or ketones having a standard boiling point in the range of -10 ° C. to 100 ° C. A method for separating pentafluoroethane, 1,1,1-trifluoroethane and chloropentafluoroethane, wherein the extractant is subjected to extractive distillation using one as an extractant. 3. The method according to claim 1, wherein the extractant is at least one selected from ethyl formate, methyl acetate, ethyl acetate, acetone, and methyl ethyl ketone. 4. The method according to claim 1, wherein 1,1,1-trifluoroethane is separated from a mixed fluid composed of pentafluoroethane and 1,1,1-trifluoroethane to obtain high-purity pentafluoroethane. Separation method. 5. The method according to claim 1, wherein pentafluoroethane is separated from a mixed fluid comprising pentafluoroethane and 1,1,1-trifluoroethane to obtain high-purity 1,1,1-trifluoroethane. Separation method. 6. A high-purity pentane by separating 1,1,1-trifluoroethane and chloropentafluoroethane from a mixed fluid comprising pentafluoroethane and 1,1,1-trifluoroethane and chloropentafluoroethane. 3. The method according to claim 2, wherein fluoroethane is obtained.