CN111170888A

CN111170888A - A kind of method of purifying heptafluoroisobutyronitrile

Info

Publication number: CN111170888A
Application number: CN202010029268.3A
Authority: CN
Inventors: 任章顺; 袁胜芳; 鲍金强; 牛鹏飞; 张金彪
Original assignee: Liming Research Institute of Chemical Industry Co Ltd
Current assignee: Haohua Gas Co Ltd
Priority date: 2020-01-02
Filing date: 2020-01-02
Publication date: 2020-05-19

Abstract

The invention discloses a method for purifying heptafluoroisobutyronitrile. The heptafluoroisobutyronitrile product is obtained after the crude gas of heptafluoroisobutyronitrile is adsorbed, rectified and deeply adsorbed. Isobutyronitrile crude gas is passed into the first-level adsorption column to remove water and some organic impurities; (2) the heptafluoroisobutyronitrile after adsorption enters into the delighting rectifying tower to carry out continuous rectification to remove light component impurities, and after delighting The gas enters the deweighting distillation tower to remove heavy component impurities; (3) the deweighted heptafluoroisobutyronitrile gas passes through the secondary adsorption column, and the remaining isomer heptafluoro-n-butyronitrile is removed by deep adsorption, and the heptafluoroisobutyronitrile is collected. Nitrile products. The method is simple in process, continuous in operation and easy to realize industrialization.

Description

Method for purifying heptafluoroisobutyronitrile

Technical Field

The invention relates to a method for purifying heptafluoroisobutyronitrile.

Background

The heptafluoroisobutyronitrile is a novel environment-friendly insulating gas material, has the characteristics of low boiling point, high volatility, excellent electrical insulating property, good environment-friendly performance and the like, and can be used as a dielectric composition of an insulator of electrical equipment. The greenhouse effect index (GWP) of heptafluoroisobutyronitrile is only 2210 and is far lower than that of sulfur hexafluoride (GWP is 23500), so that the heptafluoroisobutyronitrile can be used for replacing the traditional sulfur hexafluoride insulating gas, and the problem of the atmospheric greenhouse effect is greatly reduced. Heptafluoroisobutyronitrile has received much attention from the global electrical industry and is beginning to find application.

US2015/0083979a1 discloses a preparation process by an electrolytic fluorination method: the method comprises the steps of taking isobutyric anhydride as a starting material, carrying out electrolytic fluorination on isobutyric anhydride and hydrogen fluoride in an electrochemical reactor to obtain heptafluoro isobutyryl fluoride, carrying out rectification, separation and purification on the heptafluoro isobutyryl fluoride, carrying out esterification on the heptafluoro isobutyric acid methyl ester and methanol to obtain heptafluoro isobutyronitrile, and then preparing heptafluoro isobutyronitrile. The method has the key steps that a certain amount of isomerization by-product heptafluoro-n-butyryl fluoride is inevitably generated in the preparation of heptafluoro isobutyryl fluoride through electrolytic fluorination, so that impurities such as isomer heptafluoro-n-butyronitrile, heptafluoro-acetonitrile, heptafluoro-propionitrile and the like are introduced into heptafluoro isobutyronitrile. Patent documents CN 108395382A, CN 108424375A, CN 108863847 a and the like report a process for preparing heptafluoroisobutyronitrile by acylation and addition using hexafluoropropylene as a raw material, and a small amount of impurities such as hexafluoropropylene and the isomer heptafluoron-butyronitrile are introduced in the preparation process.

The heptafluoro-n-butyronitrile and heptafluoro-isobutyronitrile have similar boiling points and properties, the separation difficulty is high, the 50% lethal concentration (LC-50) absorbed in 4 hours is 2.5 times of that of the heptafluoro-isobutyronitrile, the toxicity is high, and in addition, the existence of impurities such as nitrogen, oxygen, carbon dioxide, hexafluoropropylene, moisture and the like introduced in the preparation process of the heptafluoro-isobutyronitrile has important influence on electrical insulation and safe use. The method for removing the above impurities in heptafluoroisobutyronitrile has not been reported.

Disclosure of Invention

The invention aims to provide a method for purifying heptafluoroisobutyronitrile.

In order to achieve the purpose, the technical scheme of the invention is as follows: a method for purifying heptafluoroisobutyronitrile is to obtain a heptafluoroisobutyronitrile product by adsorbing, rectifying and deeply adsorbing crude heptafluoroisobutyronitrile gas, and comprises the following steps:

(1) introducing the crude gas of the heptafluoroisobutyronitrile into a first-stage adsorption column to remove water and part of organic impurities.

(2) And (3) the adsorbed heptafluoroisobutyronitrile enters a light component removing rectifying tower to be continuously rectified to remove light component impurities, and the gas after light component removal enters a heavy component removing rectifying tower to remove heavy component impurities. Impurities such as nitrogen, oxygen, carbon dioxide, hexafluoropropylene, C1-C3 subfluoride and the like are removed from the top of the light rectifying tower; the heavy component removed by the heavy component removing rectifying tower is most of heavy components such as heptafluoro-n-butyronitrile and methyl trifluoroacetate.

(3) And (3) the removed heptafluoroisobutyronitrile gas passes through a secondary adsorption column, the residual isomer heptafluoron-butyronitrile is removed by deep adsorption, and a heptafluoroisobutyronitrile product is collected.

The volume content of the heptafluoroisobutyronitrile in the crude heptafluoroisobutyronitrile gas is generally not less than 80 percent, preferably more than 90 percent, wherein the impurities mainly comprise: (a) o is₂、N₂、CO₂Light components such as perfluoroacetonitrile, perfluoropropionitrile, hexafluoropropylene and the like; (b) heptafluoro-n-butyronitrile, methyl trifluoroacetate and other heavy components; (c) h₂O。

The adsorbent in the first-stage adsorption column in the step (1) is preferably silica gel, activated alumina and an A-type molecular sieve, and is preferably a 3A-type molecular sieve.

The adsorption process conditions in the step (1) are generally as follows: the temperature is 40-100 ℃, preferably 40-70 ℃, and the crude gas can be ensured to enter the rectifying tower in a continuous airflow mode; the pressure is 0.3-0.6 MPa, preferably 0.4 MPa; the gas flow is 0.1-10 kg/h, and the airspeed is 10-1000 h^-1Preferably, the gas flow is 0.1-2 kg/h, and the space velocity is 10-500 h^-1。

In the step (2), the light component removal rectifying tower has the tower pressure of 0.15-0.3 MPa, the tower kettle temperature of 20-30 ℃ and the tower top temperature of 15-25 ℃. And (4) introducing the light components at the top of the tower into a tail gas catcher, and transferring the liquid phase at the bottom of the tower to a heavy component removal rectifying tower when the content of the light components in the tower kettle is less than 0.2%.

In the heavy component removing rectifying tower in the step (2), the tower pressure is 0.05-0.15 MPa, the temperature of a tower kettle is 10-20 ℃, the temperature of a tower top is 5-15 ℃, high boiling point impurities such as heptafluoro-n-butyronitrile, methyl trifluoroacetate and the like are rich and discharged from the kettle bottom, the content of heavy components at the tower top is analyzed, and when the content is less than 0.2%, the gas phase of the components at the tower top enters a secondary adsorption column.

And (4) in the step (3), the secondary adsorption column is used, wherein the adsorbent is active carbon, a molecular sieve and the like. Coconut shell activated carbon and F03 molecular sieve are preferred. The adsorption temperature is 20-30 ℃, the pressure is 0-0.15 MPa, and the gas flow is 10-1000g/h, and the airspeed of 10-300 h^-1And when the content of the isomer heptafluoro-n-butyronitrile in the outlet of the secondary adsorption column is monitored to be less than 0.1 percent, collecting a finished product. The temperature of the heptafluoro-n-butyronitrile low-temperature storage tank is generally-10 to-30 ℃.

The gas components in each process of the method can be monitored and analyzed on line by a gas chromatograph. The method provided by the invention can prepare a heptafluoroisobutyronitrile product with the purity of more than 99.5 percent (area percentage content), the water content is lower than 10ppmv, and the fluorine n-butyronitrile content of the isomer is not higher than 0.05 percent (area percentage content).

The method provided by the invention has the advantages of simple process, continuous operation and easy realization of industrialization.

Drawings

FIG. 1 is a process flow diagram for purifying heptafluoroisobutyronitrile.

Wherein: 1. first grade adsorption column, 2. light-removing rectifying tower, 3. heavy-removing rectifying tower, 4. second grade adsorption column, 5. low-temp. storage tank, 6. tail gas collector

Detailed Description

The present invention will be described in further detail with reference to examples, but the present invention is not limited to the following examples. The following percentage contents are all area percentage contents.

The crude gas of heptafluoroisobutyric acid is analyzed by gas chromatography, wherein the purity of heptafluoroisobutyronitrile is 92.2%, the total amount of oxygen and nitrogen is 2.7%, the content of carbon dioxide is 0.1%, the content of perfluoroacetonitrile is 0.3%, the content of perfluoropropionitrile is 0.6%, the content of hexafluoropropylene is 1.3%, the content of perfluoro-n-butyronitrile is 2.5%, and the content of methyl trifluoroacetate is 0.3%.

Example 1

Heating crude gas of heptafluoro isobutyl to 40 ℃, the pressure is 0.5MPa, the gas flow is 1kg/h, and the space velocity is 300h^-1And the gas enters a first-stage adsorption column (active alumina is used as a filler), the adsorbed heptafluoroisobutyronitrile gas enters a light component removal rectifying tower, the pressure in the light component removal rectifying tower is 0.21MPa, the temperature of a tower kettle is 27.5 ℃, and the temperature of a tower top is 22.5 ℃. And (3) sampling and analyzing the content of low-boiling-point impurities in the tower kettle, wherein the total content of oxygen and nitrogen is 0.1%, the content of hexafluoropropylene is 0.04%, and other low-boiling-point impurities are not detected. The product extracted from the tower bottom enters a heavy component removing rectifying towerThe pressure in the heavy component removing rectifying tower is 0.12MPa, the temperature of the tower bottom is 19.0 ℃, and the temperature of the tower top is 13.5 ℃. And (3) sampling and analyzing the content of high-boiling-point impurities at the top of the tower, wherein the content of the heptafluoro n-butyronitrile is 0.15%, and other high-boiling-point impurities are not detected, extracting a gas phase at the top of the tower into a secondary adsorption column (an adsorbent is coconut shell activated carbon), detecting the content of the heptafluoro n-butyronitrile at the outlet of the sampling and analyzing adsorption column, and cooling and storing the product extracted from the outlet of the adsorption column into a low-temperature storage tank at the temperature of-10 ℃ to finish product filling. The product analysis results are shown in Table 1.

Example 2

In the same manner as in example 1, the crude gas pressure of the crude heptafluoroisobutyl gas was 0.3MPa, the gas flow rate was 2kg/h, and the space velocity was 500h^-1And the gas enters a first-stage adsorption column (silica gel is used as a filler), the adsorbed heptafluoroisobutyronitrile gas enters a light component removing rectifying tower, the pressure in the light component removing rectifying tower is 0.17MPa, the temperature of a tower kettle is 25.5 ℃, and the temperature of a tower top is 21.0 ℃. The low boiling point impurity content in the bottom of the tower is sampled and analyzed, wherein the total content of oxygen and nitrogen is 0.16 percent, the content of hexafluoropropylene is 0.22 percent, and CO is₂The content is 0.03 percent, and other low boiling point impurities are not detected. The product extracted from the tower bottom enters a weight removal tower, the pressure in the weight removal rectifying tower is 0.10MPa, the temperature of the tower bottom is 17.0 ℃, and the temperature of the tower top is 12.5 ℃. And (3) sampling and analyzing the content of high-boiling-point impurities at the top of the tower, wherein the content of the heptafluoro-n-butyronitrile is 0.13%, and other high-boiling-point impurities are not detected, extracting a gas phase at the top of the tower into a secondary adsorption column (an adsorbent is an F03 molecular sieve), wherein the content of the heptafluoro-n-butyronitrile at the outlet of the adsorption column is 0.05%, and extracting a product at the outlet of the adsorption column, cooling and storing the product in a low-temperature storage tank at the temperature of-. The product analysis results are shown in Table 1.

Example 3

In the same manner as in example 1, the crude gas pressure of the crude heptafluoroisobutyl gas was 0.4MPa, the gas flow rate was 0.5kg/h, and the space velocity was 100h^-1And the gas enters a first-stage adsorption column (the filler is a 3A molecular sieve), the adsorbed heptafluoroisobutyronitrile gas enters a light component removal rectifying tower, the pressure in the light component removal rectifying tower is 0.11MPa, the temperature of a tower kettle is 20.8 ℃, and the temperature of a tower top is 18.5 ℃. The low boiling point impurity content in the tower kettle is sampled and analyzed, wherein the total content of oxygen and nitrogen is 0.02 percent, and the content of hexafluoropropylene is 0.06 percent. The product extracted from the tower bottom enters a heavy component removing rectifying tower, the pressure in the heavy component removing rectifying tower is 0.08MPa, and the tower bottomThe temperature was 17.3 ℃ and the overhead temperature was 13.5 ℃. And (3) sampling and analyzing the content of high-boiling-point impurities at the top of the tower, wherein the content of the heptafluoro n-butyronitrile is 0.10 percent, detecting other high-boiling-point impurities, extracting a gas phase at the top of the tower, allowing the gas phase to enter a secondary adsorption column (an adsorbent is coconut shell activated carbon), not detecting the content of the heptafluoro n-butyronitrile at the outlet of the sampling and analyzing adsorption column, cooling and storing a product extracted from the outlet of the adsorption column by a low-temperature storage tank at the temperature of-20 ℃. The product analysis results are shown in Table 1.

TABLE 1 test results of products

Detecting items	Example 1	Example 2	Example 3
				Content of heptafluoroisobutyronitrile/%)	99.8	99.6	99.9
Oxygen + nitrogen/%)	0.10	0.16	0.02
				CO₂/％	0.01	0.03	Not detected out
Hexafluoropropylene/%)	0.04	0.12	0.06
				Heptafluoro-n-butyronitrile/%)	Not detected out	0.05	Not detected out
H₂O/ppmv	3.6	4.2	3.2

Claims

1. a method for purifying heptafluoroisobutyronitrile, the heptafluoroisobutyronitrile crude gas is obtained after adsorption, rectification, deep adsorption, heptafluoroisobutyronitrile product, comprises the following steps:

(1) pass heptafluoroisobutyronitrile crude gas into the first-level adsorption column to remove water and some organic impurities;

(2) the heptafluoroisobutyronitrile after the adsorption enters into the light removal rectifying tower and carries out continuous rectification to remove the light component impurities, and after the light removal, the gas enters the weight removal rectification tower to remove the heavy component impurities;

(3) The heptafluoroisobutyronitrile gas after deweighting passes through the secondary adsorption column, and the remaining isomer heptafluoro-n-butyronitrile is removed by deep adsorption, and the heptafluoroisobutyronitrile product is collected.

2. The method according to claim 1, the heptafluoroisobutyronitrile volume content in the heptafluoroisobutyronitrile crude gas is not less than 80%, and wherein impurities are mainly: (a) O ₂ , N ₂ , CO ₂ , perfluoroacetonitrile, perfluoropropionitrile, hexafluoropropylene and other light components; (b) heptafluoro-n-butyronitrile, methyl trifluoroacetate and other heavy components; (c) H ₂ O.

3. method according to claim 1, what removes at the top of the light rectifying tower is nitrogen, oxygen, carbon dioxide, hexafluoropropylene, C1-C The impurities such as low fluoride; what removes the heavy rectifying tower is most of Isomers of heptafluoro-n-butyronitrile, methyl trifluoroacetate and other heavy components.

4. The method according to claim 1, wherein the adsorbent in the primary adsorption column is silica gel, activated alumina, and A-type molecular sieve.

5. The method according to claim 1, the adsorption process conditions in step (1) are: temperature is 40～100 ℃, pressure is 0.3～0.6MPa, gas flow is 0.1～10kg/h, and space velocity is 10～1000h ^-1 .

6. The method according to claim 1, wherein in the step (2), a light rectifying tower is removed, the tower pressure is 0.15～0.3MPa, the tower still temperature is 20～30°C, and the tower top temperature is 15～25°C.

7. The method according to claim 1, in step (2), the liquid phase at the bottom of the still is transferred to the deweighting rectifying tower when the light components content in the tower still of the delighting rectification tower is less than 0.2%.

8. The method according to claim 1, wherein in the step (2), the deweighting rectification tower has a tower pressure of 0.05 to 0.15 MPa, a tower still temperature of 10 to 20 °C, and a tower top temperature of 5 to 15 °C.

9. The method according to claim 1, wherein in step (2), when the content of heavy components at the top of the deweighting rectification tower is <0.2%, the gas phase of the top components enters the secondary adsorption column.

10. The method according to claim 1, wherein the adsorbent in the secondary adsorption column is activated carbon and molecular sieve; the adsorption temperature is 20～30°C, the pressure is 0～0.15MPa, the gas flow is 10～1000g/h, and the space velocity is 10～300h ^-1 .