CN112979499B - Separation method of mixed gas of heptafluoroisobutyronitrile and carbon dioxide - Google Patents
Separation method of mixed gas of heptafluoroisobutyronitrile and carbon dioxide Download PDFInfo
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Abstract
The invention discloses a method for separating a mixed gas of heptafluoroisobutyronitrile and carbon dioxide, which adopts a means of combining adsorption and rectification and modifies a core adsorbent to efficiently remove organic and inorganic impurities in the mixed gas of heptafluoroisobutyronitrile and carbon dioxide, thereby realizing efficient recycling of heptafluoroisobutyronitrile, having simple separation process and safe operation and realizing continuous and stable operation.
Description
Technical Field
The invention belongs to the technical field of gas separation and purification, and particularly relates to a method for separating heptafluoroisobutyronitrile from a mixed gas of heptafluoroisobutyronitrile and carbon dioxide.
Background
Heptafluoroisobutyronitrile (hereinafter referred to as "C 4 F 7 N') is sulfur hexafluoride (hereinafter referred to as "SF") under the same condition 6 ") 2.2 times higher, the greenhouse effect capacity is much lower than that of SF 6 Is considered to be a new generation of environmentally friendly SF 6 Instead of an insulating medium. But C is 4 F 7 Liquefaction temperature ratio SF of N 6 Significantly higher at-4.7 ℃ atThe problem of liquefaction exists in the practical application process. C 4 F 7 N must be used in admixture with other low boiling point gases. Wherein g3 gas from GE company, C 4 F 7 N and CO 2 After mixing, the insulating material is used for electrical equipment, and the insulating property reaches SF 6 More than 80% of the total weight of the fertilizer, and the greenhouse effect is less than SF 6 5 percent of the total amount of the components, and discharge decomposition products are nontoxic, environment-friendly and safe, and have been applied to electric equipment such as 145kV Gas Insulated Switches (GIS) and 420kV Gas Insulated Lines (GIL), thereby attracting hot attention at home and abroad.
When C is present 4 F 7 N and CO 2 The mixed gas of (2) is applied to electrical equipment, and as the equipment operates, partial discharge and other phenomena may exist, so that the mixed gas is subjected to discharge decomposition. The research shows that C 4 F 7 N and CO 2 When the mixed gas of (2) is decomposed by discharge, CF is generated 3 Free radical, CF 2 Free radical, CF radical, etc., mainly to form CF 3 CF 2 CN、CF 3 Nitriles such as CN and CNCN and CF 4 、C 2 F 6 、C 3 F 8 And the like, and thus the insulating performance of the mixed gas is affected, so that the mixed gas in the electrical equipment needs to be periodically refreshed. For C to reach service life 4 F 7 N and CO 2 If the mixed gas is directly discharged, not only the environment is polluted, but also huge resource waste is caused. Therefore, for C in the mixed gas 4 F 7 N is separated and purified, thereby realizing C 4 F 7 The cyclic utilization of N has very important practical significance.
At present, for C 4 F 7 N and CO 2 The separation and purification of the mixed gas has not been reported yet, and C in the mixed gas is realized 4 F 7 The high-efficiency separation of N has certain technical difficulty.
Disclosure of Invention
The invention aims to solve the technical blank in the background and provides a method for separating a mixed gas of heptafluoroisobutyronitrile and carbon dioxide, so as to realize high-efficiency recovery of heptafluoroisobutyronitrile.
A separation method of a mixed gas of heptafluoroisobutyronitrile and carbon dioxide comprises the following sequential steps:
(1) introducing mixed gas of heptafluoroisobutyronitrile and carbon dioxide into an adsorption tower, and performing adsorption treatment in the presence of an adsorbent to control the content of organic impurities to be less than 0.3%; the adsorbent is a modified porous carrier, and is prepared by mixing the porous carrier with a metal soluble salt aqueous solution, soaking at room temperature, filtering, and drying, wherein the metal soluble salt is at least one or more of chlorides or nitrates of K, Na, Mg, Al, Cr, Fe, Co, Ni, and Zn;
(2) the mixed gas after adsorption treatment enters a separation tower, carbon dioxide flows out from the top of the tower, and the tower kettle liquid phase material enters a drying tower;
(3) the liquid phase material at the bottom of the tower is treated by a drying agent in a drying tower to remove inorganic impurities, wherein the inorganic impurities comprise water and acid;
(4) the dried material enters a rectifying tower, and the heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, so that the purity can reach over 99.5 percent.
The porous carrier is one or more of activated alumina, activated carbon, molecular sieve and silica gel.
The preparation method of the adsorbent comprises the following steps: dissolving metal soluble salt in water to prepare metal salt solution, adding one or more of activated alumina, activated carbon, molecular sieve and silica gel to mix with the metal salt solution, soaking at room temperature for 12-48 hours, filtering, drying in an oven at 60 ℃ for 12-48 hours, and then drying at 120 ℃ and 180 ℃ for 5-20 hours under the protection of nitrogen; wherein the concentration of the metal salt solution is 0.1-2mol/L, and the solid-liquid mass ratio during mixing is 2/1-1/10.
The preparation method of the adsorbent comprises the following steps: dissolving metal soluble salt in water to prepare metal salt solution, adding one of activated alumina and activated carbon to be mixed with the metal salt solution, soaking for 12-24 hours at room temperature, filtering, drying in an oven at 60 ℃ for 12-48 hours, and then drying at 130-160 ℃ for 5-20 hours under the protection of nitrogen; wherein the concentration of the metal salt solution is 0.1-1mol/L, and the solid-to-liquid ratio is 1/1-1/5 during mixing.
In the step (1), the operating pressure of the adsorption tower is 0.3-0.5MPa, and the operating temperature is 0-20 ℃.
In the step (2), the operation pressure of the separation tower is 0.2-0.4MPa, the tower top temperature is 0-20 ℃, and the tower kettle temperature is-20 to-5 ℃.
The packing of the separation tower is a metal pall ring, a metal Raschig ring, a metal theta ring or a metal regular packing.
The operating pressure of the rectifying tower in the step (4) is 0.1-0.2MPa, the tower top temperature is-10-0 ℃, and the tower kettle temperature is 40-60 ℃.
The rectifying tower packing is a metal pall ring, a metal step ring or a metal theta ring.
The method for separating the mixed gas of the heptafluoroisobutyronitrile and the carbon dioxide can efficiently remove organic impurities such as perfluoronitriles, perfluorohydrocarbons and the like and inorganic impurities such as water, acid, carbon dioxide and the like in the mixed gas of the heptafluoroisobutyronitrile and the carbon dioxide, realize the efficient recovery of the heptafluoroisobutyronitrile, obtain the heptafluoroisobutyronitrile product with the purity of more than 99.3 percent, the moisture content of less than 10ppm, the hydrogen ion content (acidity) of less than 1ppm and the noncondensable gas content of less than 0.3 percent, and ensure that the recovery rate of the heptafluoroisobutyronitrile can reach more than 95 percent.
Drawings
FIG. 1 is a flow chart of a process for separating a mixed gas of heptafluoroisobutyronitrile and carbon dioxide.
The arrows in the figure indicate the material flow direction.
Detailed Description
The invention will be further described in the following with reference to the accompanying drawings and examples, which are not intended to limit the invention, but which may be modified and varied by those skilled in the art in accordance with the spirit of the invention, the scope and spirit of the invention being indicated by the appended claims.
The adsorbent is obtained by modifying commercially available activated alumina, activated carbon, molecular sieve and silica gel.
The desiccant is A-type molecular sieve, activated alumina or silica gel, which are all commercially available products.
As shown in fig. 1, a method for separating a mixed gas of heptafluoroisobutyronitrile and carbon dioxide comprises the following sequential steps:
(1) introducing the mixed gas of heptafluoroisobutyronitrile and carbon dioxide into an adsorption tower 1, and controlling the content of organic impurities to be less than 0.3% by adsorption treatment in the presence of an adsorbent;
(2) the mixed gas after adsorption treatment enters a separation tower 2, carbon dioxide flows out from the top of the tower, and the liquid-phase material in the bottom of the tower enters a drying tower;
(3) the liquid phase material at the bottom of the tower is treated by a drying agent in a drying tower 3 to remove inorganic impurities, wherein the inorganic impurities comprise water and acid;
(4) the dried material enters a rectifying tower 4, and the heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, so that the purity can reach over 99.5 percent.
Example 1
Mixing the gas (C) 4 F 7 N：9.2％、CO 2 : 90.1 percent and the content of organic impurities is 0.5 percent) is fed into an adsorption tower, and the adsorbent is MgCl 2 The operating pressure of the adsorption tower is 0.30MPa, and the operating temperature is 5 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal pall ring, the operation pressure of the separation tower is 0.25MPa, the temperature of the top of the tower is 0 ℃, the temperature of a tower kettle is-15 ℃, carbon dioxide flows out from the top of the tower, the material in the tower kettle enters a drying tower for treatment, a drying agent is a 3A molecular sieve, and inorganic impurities such as water, acid and the like in the material are removed; the dried material enters a rectifying tower, the filler is a metal pall ring, the operating pressure of the rectifying tower is 0.12MPa, the temperature of the top of the rectifying tower is minus 5 ℃, the temperature of the bottom of the rectifying tower is 55 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.5%, the moisture content is 5.6ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.1%, and the recovery rate of the heptafluoroisobutyronitrile is 97.1%.
Example 2
Mixing the gas (C) 4 F 7 N：9.2％、CO 2 : 90.1 percent and the content of organic impurities is 0.5 percent) is introduced into an adsorption tower, and the adsorbent is Mg (NO) 3 ) 2 The operating pressure of the adsorption tower is 0.33MPa, and the operating temperature is 7 ℃; the mixed gas after adsorption treatment enters a separation tower, and gold is used as a fillerThe method belongs to pall rings, the operating pressure of a separation tower is 0.25MPa, the temperature of the top of the tower is 10 ℃, the temperature of a tower kettle is-15 ℃, carbon dioxide flows out from the top of the tower, materials in the tower kettle enter a drying tower for treatment, a drying agent is a 3A molecular sieve, and inorganic impurities such as water, acid and the like in the materials are removed; the dried material enters a rectifying tower, the filler is a metal pall ring, the operating pressure of the rectifying tower is 0.12MPa, the temperature of the top of the tower is-5 ℃, the temperature of a tower kettle is 55 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.7%, the moisture content is 6.2ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.2%, and the recovery rate of the heptafluoroisobutyronitrile is 96.5%.
Example 3
Mixing the gas (C) 4 F 7 N：9.2％、CO 2 : 90.1 percent and the content of organic impurities is 0.5 percent) is introduced into an adsorption tower, the adsorbent is KCl modified activated alumina, the operating pressure of the adsorption tower is 0.40MPa, and the operating temperature is 12 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal pall ring, the operating pressure of the separation tower is 0.30MPa, the temperature of the top of the tower is 0 ℃, the temperature of a tower kettle is-8 ℃, carbon dioxide flows out from the top of the tower, the material in the tower kettle enters a drying tower for treatment, a drying agent is a 3A molecular sieve, and inorganic impurities such as water, acid and the like in the drying tower are removed; the dried material enters a rectifying tower, the filler is a metal pall ring, the operating pressure of the rectifying tower is 0.18MPa, the temperature of the top of the rectifying tower is-5 ℃, the temperature of a tower kettle is 60 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.3%, the moisture content is 7.7ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.2%, and the recovery rate of the heptafluoroisobutyronitrile is 95.3%.
Example 4
Mixing the gas (C) 4 F 7 N：8.8％、CO 2 : 90.1 percent and the content of organic impurities is 0.9 percent) is introduced into an adsorption tower, and the adsorbent is ZnCl 2 The operating pressure of the adsorption tower is 0.40MPa, and the operating temperature is 12 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal pall ring, the operation pressure of the separation tower is 0.30MPa, the temperature of the top of the tower is 0 ℃, the temperature of a tower kettle is-8 ℃, carbon dioxide flows out from the top of the tower, the materials in the tower kettle enter a drying tower for treatment, a drying agent is a 3A molecular sieve, and the drying agent is removedInorganic impurities such as water and acid; the dried material enters a rectifying tower, the filler is a metal theta ring, the operating pressure of the rectifying tower is 0.18MPa, the temperature of the top of the rectifying tower is-5 ℃, the temperature of a tower kettle is 60 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.3%, the moisture content is 7.1ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.2%, and the recovery rate of the heptafluoroisobutyronitrile is 96.9%.
Example 5
Mixing the gas (C) 4 F 7 N：8.8％、CO 2 : 90.1 percent and the content of organic impurities is 0.9 percent) is introduced into an adsorption tower, and the adsorbent is Zn (NO) 3 ) 2 The operating pressure of the adsorption tower is 0.34MPa, and the operating temperature is 7 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal Raschig ring, the operation pressure of the separation tower is 0.22MPa, the temperature of the top of the tower is 10 ℃, the temperature of a tower kettle is-15 ℃, carbon dioxide flows out from the top of the tower, the material in the tower kettle enters a drying tower for treatment, a drying agent is a 3A molecular sieve, and inorganic impurities such as water, acid and the like in the material are removed; the dried material enters a rectifying tower, the filler is a metal theta ring, the operating pressure of the rectifying tower is 0.10MPa, the temperature of the top of the rectifying tower is-5 ℃, the temperature of a tower kettle is 50 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.5%, the moisture content is 6.3ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.2%, and the recovery rate of the heptafluoroisobutyronitrile is 97.7%.
Example 6
Mixing the gas (C) 4 F 7 N：4.5％、CO 2 : 94.0 percent of organic impurities with the content of 1.1 percent) is fed into an adsorption tower, and the adsorbent is NiCl 2 The operating pressure of the adsorption tower is 0.31MPa, and the operating temperature is 7 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal Raschig ring, the operation pressure of the separation tower is 0.27MPa, the temperature of the top of the tower is 0 ℃, the temperature of a tower kettle is-10 ℃, carbon dioxide flows out from the top of the tower, the material in the tower kettle enters a drying tower for treatment, and a drying agent is activated alumina to remove inorganic impurities such as water, acid and the like; the dried material enters a rectifying tower, the filler is a metal theta ring, the operating pressure of the rectifying tower is 0.12MPa, the temperature at the top of the tower is minus 5 ℃, the temperature at the bottom of the tower is 50 ℃,heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.7 percent, the water content is 3.7ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.1 percent, and the recovery rate of the heptafluoroisobutyronitrile is 97.7 percent.
Example 7
Mixing the gas (C) 4 F 7 N：4.5％、CO 2 : 94.0 percent of organic impurities with the content of 1.1 percent) is fed into an adsorption tower, and the adsorbent is CrCl 3 The operating pressure of the adsorption tower is 0.33MPa, and the operating temperature of the modified activated carbon is 7 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal pall ring, the operation pressure of the separation tower is 0.25MPa, the temperature of the top of the tower is 10 ℃, the temperature of a tower kettle is-15 ℃, carbon dioxide flows out from the top of the tower, the material in the tower kettle enters a drying tower for treatment, a drying agent is activated alumina, and inorganic impurities such as water, acid and the like in the drying tower are removed; the dried material enters a rectifying tower, the filler is a metal theta ring, the operating pressure of the rectifying tower is 0.12MPa, the temperature of the top of the rectifying tower is-5 ℃, the temperature of the bottom of the rectifying tower is 55 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.5%, the moisture content is 4.4ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.1%, and the recovery rate of the heptafluoroisobutyronitrile is 95.8%.
Example 8
Mixing the gas (C) 4 F 7 N：8.8％、CO 2 : 90.1 percent and the content of organic impurities is 0.9 percent) are introduced into an adsorption tower, and the adsorbent is Cr (NO) 3 ) 3 The operating pressure of the adsorption tower is 0.40MPa, and the operating temperature is 12 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal pall ring, the operation pressure of the separation tower is 0.30MPa, the temperature of the top of the tower is 0 ℃, the temperature of a tower kettle is-8 ℃, carbon dioxide flows out from the top of the tower, the material at the tower kettle enters a drying tower for treatment, and a drying agent is activated alumina to remove inorganic impurities such as water, acid and the like; the dried material enters a rectifying tower, the filler is a metal theta ring, the operating pressure of the rectifying tower is 0.18MPa, the temperature of the top of the tower is-5 ℃, the temperature of a tower kettle is 60 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.4 percent, the moisture content is 3.9ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.2 percent, and the recovery rate of the heptafluoroisobutyronitrile is 95.5 percent。
Example 9
Mixing the gas (C) 4 F 7 N：8.8％、CO 2 : 90.1 percent and the content of organic impurities is 0.9 percent) is fed into an adsorption tower, and the adsorbent is CoCl 2 The modified molecular sieve has the adsorption tower operating pressure of 0.44MPa and the operating temperature of 20 ℃; the mixed gas after adsorption treatment enters a separation tower, a filler is a metal theta ring, the operation pressure of the separation tower is 0.32MPa, the temperature of the top of the tower is 5 ℃, the temperature of a tower kettle is-5 ℃, carbon dioxide flows out from the top of the tower, the material at the tower kettle enters a drying tower for treatment, a drying agent is activated alumina, and inorganic impurities such as water, acid and the like in the drying tower are removed; the dried material enters a rectifying tower, the filler is a metal theta ring, the operating pressure of the rectifying tower is 0.20MPa, the temperature of the top of the rectifying tower is 0 ℃, the temperature of a tower bottom is 60 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.5 percent, the moisture content is 5.1ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.1 percent, and the recovery rate of the heptafluoroisobutyronitrile is 97.9 percent.
Example 10
Mixing the gas (C) 4 F 7 N：4.5％、CO 2 : 94.0 percent of organic impurities with the content of 1.1 percent) is fed into an adsorption tower, and the adsorbent is NiCl 2 The modified molecular sieve has the adsorption tower operating pressure of 0.33MPa and the operating temperature of 10 ℃; the mixed gas after adsorption treatment enters a separation tower, the filler is a metal regular filler, the operating pressure of the separation tower is 0.25MPa, the temperature of the top of the tower is 0 ℃, the temperature of a tower kettle is-10 ℃, carbon dioxide flows out from the top of the tower, the material in the tower kettle enters a drying tower for treatment, and a drying agent is silica gel to remove inorganic impurities such as water, acid and the like in the material; the dried material enters a rectifying tower, the filler is a metal stepped ring, the operating pressure of the rectifying tower is 0.15MPa, the temperature of the top of the rectifying tower is-7 ℃, the temperature of the bottom of the rectifying tower is 55 ℃, heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, the purity is 99.6%, the moisture content is 7.1ppm, the hydrogen ion content (acidity) is 0.1ppm, the non-condensable gas content is 0.1%, and the recovery rate of the heptafluoroisobutyronitrile is 95.6%.
Claims (3)
1. A method for separating heptafluoroisobutyronitrile from a mixed gas of heptafluoroisobutyronitrile and carbon dioxide comprises the following sequential steps:
(1) introducing mixed gas of heptafluoroisobutyronitrile and carbon dioxide into an adsorption tower, and performing adsorption treatment in the presence of an adsorbent to control the content of organic impurities to be less than 0.3%; the adsorbent is a modified porous carrier, and is prepared by mixing the porous carrier with a metal soluble salt aqueous solution, soaking at room temperature, filtering, and drying, wherein the metal soluble salt is at least one or more of chlorides or nitrates of K, Na, Mg, Al, Cr, Fe, Co, Ni, and Zn;
(2) the mixed gas after adsorption treatment enters a separation tower, carbon dioxide flows out from the top of the tower, and the tower kettle liquid phase material enters a drying tower;
(3) the liquid phase material at the bottom of the tower is treated by a drying agent in a drying tower to remove inorganic impurities, wherein the inorganic impurities comprise water and acid;
(4) the dried material enters a rectifying tower, and the heptafluoroisobutyronitrile is extracted from the top of the rectifying tower, so that the purity can reach over 99.5 percent;
the porous carrier is one or more of activated alumina, activated carbon, molecular sieve and silica gel;
in the step (1), the operation pressure of the adsorption tower is 0.3-0.5MPa, the operation temperature is 0-20 ℃,
in the step (2), the operation pressure of the separation tower is 0.2-0.4MPa, the temperature at the top of the tower is 0-20 ℃, the temperature at the bottom of the tower is-20 ℃ to-5 ℃,
the packing of the separation tower is a metal pall ring, a metal Raschig ring, a metal theta ring or a metal regular packing,
in the step (4), the operating pressure of the rectifying tower is 0.1-0.2MPa, the temperature at the top of the tower is-10-0 ℃, the temperature at the bottom of the tower is 40-60 ℃,
the rectifying tower packing is a metal pall ring, a metal stepped ring or a metal theta ring.
2. The method of claim 1, wherein the adsorbent is prepared by: dissolving metal soluble salt in water to prepare metal salt solution, adding one or more of activated alumina, activated carbon, molecular sieve and silica gel to mix with the metal salt solution, soaking at room temperature for 12-48 hours, filtering, drying in an oven at 60 ℃ for 12-48 hours, and then drying at 120 ℃ and 180 ℃ for 5-20 hours under the protection of nitrogen; wherein the concentration of the metal salt solution is 0.1-2mol/L, and the solid-liquid mass ratio during mixing is 2/1-1/10.
3. The method of claim 2, wherein the adsorbent is prepared by: dissolving metal soluble salt in water to prepare metal salt solution, adding one of activated alumina and activated carbon to be mixed with the metal salt solution, soaking for 12-24 hours at room temperature, filtering, drying in an oven at 60 ℃ for 12-48 hours, and then drying at 130-160 ℃ for 5-20 hours under the protection of nitrogen; wherein the concentration of the metal salt solution is 0.1-1mol/L, and the solid-to-liquid ratio is 1/1-1/5 during mixing.
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