JP3262454B2 - Method for purifying pentafluoroethane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the purification of pentafluoroethane, and more particularly, to the purification of pentafluoroethane having a standard boiling point of -10.
Paraffinic hydrocarbons in the range of 100 ° C to 100 ° C,
The present invention relates to a method for purifying pentafluoroethane by extractive distillation using an extractant selected from alcohols, ethers, esters, or ketones.

[0002]

2. Description of the Related Art Monochlorodifluoromethane (hereinafter referred to as HCFC-22), which has been widely used in refrigerants such as air conditioners and refrigerators, is a substance that destroys the ozone layer existing in the stratosphere, that is, as a specific CFC. It is subject to regulations. So, HCFC
Pentafluoroethane (hereinafter, referred to as HFC-125) having the same properties as -22 has attracted attention as one of the alternatives to HCFC-22. This HFC-125
Is usually produced by reacting hydrogen fluoride with perchloroethylene as a raw material, and therefore, monochloropentafluoroethane (hereinafter, CFC) is used as a reaction by-product.
-115). However, this CFC-115 is also regulated worldwide as a specific CFC, and must be separated.

[0003] Distillation is one of the most common methods of separating a fluid mixture into its constituents, but the inventors have studied that the relative volatility of CFC-115 to HFC-125 is close to 1, For example, when the pressure is around 5 kg / cm ² G, it is 1.01 to 1.02, and it is extremely difficult to separate by only a simple distillation method. Therefore, an extractive distillation method in which a third component having a different boiling point from that of the component is added to the fluid mixture as an extractant and distillation is performed. For example, U.S. Pat. No. 5,082,329 discloses that C.P.
HFC-125 to HFC-1 containing FC-115
A method for separating 25 is disclosed.

[0004]

However, in the separation method disclosed in U.S. Pat. No. 5,082,329, 1,2-dichlorotetrafluoroethane or the like is used as a fluorocarbon compound as an extractant. However, there is a problem that the extractant itself is regulated as a specific CFC. The present invention relates to HFC-125 and its reaction by-product, CFC-
It is an object of the present invention to provide a method for purifying HFC-125 without using specific freon as an extractant when separating HFC-115 by extractive distillation.

[0005]

Means for Solving the Problems In order to solve the above problems, a method for purifying HFC-125 according to the present invention comprises the steps of:
When the extractive distillation of HFC-125 containing 15 is carried out, the standard boiling point (that is, the boiling point under atmospheric pressure) is -10 as an extractant.
Paraffinic hydrocarbons in the range of 100 ° C to 100 ° C,
It is characterized by using an extractant selected from alcohols, ethers, esters or ketones.

[0006] By adding the above extractant, HFC-1
Increasing or decreasing the relative volatility of CFC-115 to 25 from 1 allows for separation of both.
Here, the relative volatility is defined as the ratio of the equilibrium coefficients of the components of the fluid mixture, wherein the components are HFC-125 and CFC
Assuming −115, it is expressed by the following equation (1).

[0007]

(Equation 1)

As is apparent from the equation (1), when the relative volatility is 1, the composition of both gas and liquid phases becomes the same, and separation by distillation becomes impossible. When the relative volatility is greater than 1, the mole fraction of CFC-115 in the gas phase becomes larger than the mole fraction of CFC-115 in the liquid phase, and CFC-115 is concentrated in the gas phase, so that separation by distillation is difficult. It becomes possible. On the other hand, when it is smaller than 1, the molar fraction of CFC-115 in the liquid phase becomes larger than the molar fraction of CFC-115 in the gas phase, and C
Since FC-115 is concentrated to a liquid phase, it can be separated by distillation.

[0009] Conditions that can be used as an extractant include: high selectivity; high solubility; and a standard boiling point within an appropriate range. It is easy to recover the extractant, that is, a raw material having a large difference in boiling point from HFC-125. Do not react. The greater the value obtained by dividing the specific volatility when the extractant is present by the specific volatility when the extractant is not present, the higher the selectivity of the extractant.

[0010] The range of the standard boiling point of the extractant is different from the standard boiling point of HFC-125 and CFC-115 in consideration of the ease of distillation separation between the extractant and the target substances HFC-125 and CFC-115. It is necessary that the boiling point is higher than a certain level. Specifically, the difference in boiling point between the target substance and the extractant is preferably about 30 ° C. or more, more preferably 40 ° C. or more. Therefore, HFC-125 and CFC-115
Are −48.5 ° C. and −38.7 ° C., respectively. Therefore, it is preferable to select an extractant having a standard boiling point of −10 ° C. or higher. In addition, it is necessary that the boiling point is not too high so that a special heating source is not required and the temperature distribution in the distillation column is not extremely increased. Specifically, HFC-125 and CFC-115
Is preferably about 140 ° C. or less, more preferably 120 ° C. or less, and it is therefore preferable to select an extractant having a standard boiling point of 100 ° C. or less.

In addition to the above consideration of the standard boiling point, HFC-1
As a result of examination in consideration of solubility and reactivity to 25 and CFC-115, the substance contained in any of paraffinic hydrocarbons, alcohols, ethers, esters, and ketones as an extractant, Moreover, it has been found that a substance having a standard boiling point in the range of -10 ° C to 100 ° C is preferable.

In the above description, the relative volatility was measured by using a pressurized Osmer type gas-liquid equilibrium measuring apparatus by measuring CFC-115 by about 3 m.
ol% of crude HFC-125, and various extractants were added thereto to equilibrate at a temperature of 20 ° C. Then, the liquid phase and gas phase were sampled, and the composition of each phase was analyzed by gas chromatography. The relative volatility was determined from the above equation (1) based on the analysis value. Table 1 shows the results of measuring the relative volatility by changing the extractant.

[0013]

[Table 1]

As apparent from Table 1, when extractive distillation is performed using a paraffinic hydrocarbon having a standard boiling point in the range of -10 ° C to 100 ° C as an extractant, HFC-
The specific volatility of CFC-115 with respect to 125 is reduced to 0.6 or less, especially when n-pentane is used as the extractant.
4 was found to decrease. From this, CFC-115 can be separated from HFC-125 as a high boiling component by performing extractive distillation using a substance having a standard boiling point in the range of -10 ° C to 100 ° C in paraffinic hydrocarbons as an extractant. Becomes possible.

Alcohols having a standard boiling point of -10 ° C to 1
When extractive distillation was performed using a substance in the range of 00 ° C. as an extractant, the relative volatility of CFC-115 relative to HFC-125 increased to 1.9 or more, especially when methyl alcohol was used as the extractant. Found to increase to 4.5.
From this fact, CFC-115 can be converted to HF as a low boiling component by performing extractive distillation using an alcohol having a standard boiling point in the range of -10 ° C to 100 ° C as an extractant.
It becomes possible to separate from C-125.

Ethers having a standard boiling point of -10 ° C to 10
It has been found that when extractive distillation is performed using a substance in the range of 0 ° C. as an extractant, the relative volatility of CFC-115 relative to HFC-125 increases to 1.7 or more. Particularly, diethyl ether is preferable. From this, CFC-1 was obtained by performing extractive distillation using ethers having a standard boiling point in the range of −10 ° C. to 100 ° C. as an extractant.
15 can be separated from HFC-125 as a low boiling component.

Esters having a standard boiling point of -10 ° C to 10
When extractive distillation was performed using a substance in the range of 0 ° C. as an extractant, the relative volatility of CFC-115 with respect to HFC-125 increased to 2.3 or more, especially when methyl acetate was used as the extractant. Found to increase to 4.7. From this, CFC-115 can be converted to HFC-125 as a low boiling component by performing extractive distillation using a substance having a standard boiling point in the range of −10 ° C. to 100 ° C. as an extractant.
Can be separated.

Ketones having a standard boiling point of -10 ° C to 100
When extractive distillation using a substance in the range of ° C as an extractant was performed, the relative volatility of CFC-115 relative to HFC-125 increased to 3.2 or more. .4. From this, CFC-115 can be separated from HFC-125 as a low-boiling component by performing extractive distillation using a ketone having a standard boiling point in the range of −10 ° C. to 100 ° C. as an extractant. Becomes

As described above, when the HFC-125 containing CFC-115 is separated by distillation, the above-mentioned extractant is used as the third component, whereby HFC-125 can be converted to HFC-125 with respect to HFC-125.
15 has a specific volatility less than 1, preferably 0.6
HFC-125 and CFC-115 can be separated by extractive distillation to obtain a high-purity HFC- 125 can be obtained.

In the above extractant, particularly preferred extractants include n-pentane and acetone. In general, the higher the extractant concentration, the more the specific volatility between the substances to be separated is 1
In the case of acetone, for example, the concentration of the extractant in the present invention is 30% by weight or more, preferably 50% by weight to 90% by weight. In addition, the above-mentioned extractants may be used alone or in combination of two or more. In this case, it is possible to mix extractants that make the specific volatility of CFC-115 with respect to HFC-125 smaller than 1, or to mix extractors that make the volatility larger than 1, but make the extractant smaller than 1 and larger than 1. Mixing with an extractant is not preferred.
Specifically, chloropen to pentafluoroethane
Paraffin that reduces the specific volatility of tafluoroethane to less than 1
A mixture of two or more selected from quinone hydrocarbons
Extractant or chlorope for pentafluoroethane
To increase the specific volatility of nantafluoroethane to greater than 1.
Select from coals, ethers, esters and ketones
Extractive distillation using an extractant made by mixing two or more types
It can be carried out.

Extractive distillation is carried out using a paraffinic hydrocarbon extractant that makes the specific volatility of CFC-115 relative to HFC-125 smaller than 1.
Almost all C-115 can be discharged from the bottom of the distillation column together with the extractant, and high-purity HFC-12
5 is obtained. Conversely, by performing extractive distillation using an extractant of alcohols, ethers, esters and ketones having a specific volatility of more than 1, almost all of the CFC-115 contained in the raw material is removed from the distillation column. HFC-125 which can be discharged from the distillate and contains almost no CFC-115 at the bottom can be obtained together with the extractant.

[0022]

【Example】

[Example 1] In a stainless steel rectification column having a diameter of 40φ and a theoretical number of 20 stages, CFC was conducted at a pressure of 5.9 kg / cm ² G.
Crude HFC-125 containing 2.9 mol% of -115 was supplied at a rate of 0.29 kg / h at a position 13 steps from the top of the tower, and acetone was supplied at a rate of 2.00 kg / h at a position of 3 steps from the top of the tower. At the top of the column at 0.05 kg / h. Table 2 shows the results. The bottom liquid was redistilled to completely separate acetone, so that the concentration of CFC-115 became 0.05%, and HFC-125 having a purity of 99.95% was used.
was gotten.

[0023]

[Table 2]

Example 2 In a stainless steel rectification tower having a diameter of 40φ and a theoretical plate number of 40, a pressure of 5.9 kg / cm.
Crude HFC containing 2.9 mol% of CFC-115 at ² G
125 at 30 kg from the top of the tower at 0.4 kg / h, n
-Place pentane at 10 columns from the top of the tower at 2.00 kg / h
And distilled out at a reflux ratio of 5 from the top of the tower at 0.32 kg / h. The results are as shown in Table 3, and CFC-115
Was 0.07%, and HFC-125 having a purity of 99.93% was obtained.

[0025]

[Table 3]

[0026]

As described above, the HF of the present invention is used.
The purification method of C-125 is based on CFC, which was conventionally difficult to remove.
Paraffinic hydrocarbons normal boiling point in the range of 100 ° C. from -10 ° C. to -115, alcohols, ethers, esters, or easily removable by extractive distillation using the extractant selected from ketones This is a revolutionary method.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-320077 (JP, A) JP-A-6-510980 (JP, A) Berg, Chem. Eng. Progress, 1969, Vol. 65, No. 9, p. 252-57 (58) Field surveyed (Int. Cl. ⁷ , DB name) C07C 19/08 C07B 63/00 C07C 17/386 C07C 19/12 CA (STN) REGISTRY (STN)

Claims (10)

(57) [Claims] 1. Paraffin-based hydrocarbons, alcohols, ethers, esters, or ketones having a standard boiling point in the range of -10 ° C. to 100 ° C., wherein chloropentafluoroethane which is an impurity in pentafluoroethane is used. A method for purifying pentafluoroethane, wherein the pentafluoroethane is removed by extractive distillation using an extractant selected from the group consisting of: 2. Extractive distillation is performed using an extractant obtained by mixing two or more kinds of paraffinic hydrocarbons that makes the relative volatility of chloropentafluoroethane to pentafluoroethane smaller than 1. The method for purifying pentafluoroethane according to claim 1, wherein 3. Extraction using an extractant obtained by mixing two or more selected from alcohols, ethers, esters and ketones, which makes the relative volatility of chloropentafluoroethane to pentafluoroethane greater than 1. The method for purifying pentafluoroethane according to claim 1, wherein distillation is performed. 4. Chloropentafluoroethane which is an impurity in pentafluoroethane is converted into n-pentane, i-pentane, n-hexane, methyl alcohol, i-propyl alcohol, ethyl alcohol, diethyl ether, ethyl formate, methyl acetate, A method for purifying pentafluoroethane, characterized in that the pentafluoroethane is removed by extractive distillation using an extractant selected from ethyl acetate, acetone or methyl ethyl ketone. 5. The method for purifying pentafluoroethane according to claim 4, wherein the extractant is n-pentane. 6. The method for purifying pentafluoroethane according to claim 4, wherein the extractant is a mixture of two or more selected from n-pentane, i-pentane and n-hexane. 7. The method for purifying pentafluoroethane according to claim 4, wherein the extractant is ethyl alcohol. 8. The method for purifying pentafluoroethane according to claim 4, wherein the extractant is diethyl ether. 9. The method for purifying pentafluoroethane according to claim 4, wherein the extractant is methyl acetate. 10. The method for purifying pentafluoroethane according to claim 4, wherein the extractant is acetone.