CN112694387A - Difluoromethane purification method - Google Patents
Difluoromethane purification method Download PDFInfo
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- CN112694387A CN112694387A CN202011629668.4A CN202011629668A CN112694387A CN 112694387 A CN112694387 A CN 112694387A CN 202011629668 A CN202011629668 A CN 202011629668A CN 112694387 A CN112694387 A CN 112694387A
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- RWRIWBAIICGTTQ-UHFFFAOYSA-N difluoromethane Chemical compound FCF RWRIWBAIICGTTQ-UHFFFAOYSA-N 0.000 title claims abstract description 212
- 238000000746 purification Methods 0.000 title claims abstract description 49
- 238000000034 method Methods 0.000 title claims abstract description 24
- 239000012535 impurity Substances 0.000 claims abstract description 80
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 claims abstract description 34
- 238000001179 sorption measurement Methods 0.000 claims abstract description 20
- 239000003463 adsorbent Substances 0.000 claims abstract description 18
- RFCAUADVODFSLZ-UHFFFAOYSA-N 1-Chloro-1,1,2,2,2-pentafluoroethane Chemical compound FC(F)(F)C(F)(F)Cl RFCAUADVODFSLZ-UHFFFAOYSA-N 0.000 claims abstract description 16
- 239000002808 molecular sieve Substances 0.000 claims description 21
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims description 21
- XPDWGBQVDMORPB-UHFFFAOYSA-N Fluoroform Chemical compound FC(F)F XPDWGBQVDMORPB-UHFFFAOYSA-N 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 14
- 239000007788 liquid Substances 0.000 claims description 13
- 238000007599 discharging Methods 0.000 claims description 11
- 238000007689 inspection Methods 0.000 claims description 8
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 4
- 239000000047 product Substances 0.000 abstract description 29
- 238000009835 boiling Methods 0.000 abstract description 10
- 239000012264 purified product Substances 0.000 abstract description 3
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 12
- 239000007789 gas Substances 0.000 description 10
- 239000012071 phase Substances 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 6
- 239000012043 crude product Substances 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 238000011084 recovery Methods 0.000 description 4
- 238000005070 sampling Methods 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- SYNPRNNJJLRHTI-UHFFFAOYSA-N 2-(hydroxymethyl)butane-1,4-diol Chemical compound OCCC(CO)CO SYNPRNNJJLRHTI-UHFFFAOYSA-N 0.000 description 1
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- PRPAGESBURMWTI-UHFFFAOYSA-N [C].[F] Chemical compound [C].[F] PRPAGESBURMWTI-UHFFFAOYSA-N 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910000040 hydrogen fluoride Inorganic materials 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000000992 sputter etching Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/38—Separation; Purification; Stabilisation; Use of additives
- C07C17/389—Separation; Purification; Stabilisation; Use of additives by adsorption on solids
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/38—Separation; Purification; Stabilisation; Use of additives
- C07C17/383—Separation; Purification; Stabilisation; Use of additives by distillation
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a difluoromethane purification method, which comprises the steps of primary adsorption, primary rectification, primary impurity discharge and secondary rectification. The purification method of the difluoromethane removes moisture of a crude difluoromethane product by an adsorbent, and removes fluorocarbon impurities with lower boiling points, such as CF, by a primary rectification step4、CO2And CHF3Finally, removing the fluorocarbon impurities with higher boiling point, such as CHF, by a secondary rectification step3、CF3CF2Cl and C2HF5. The purification can remove fluorocarbon impurities in difluoromethane, ensure the stability of purification and obtain products with stable purity. Meanwhile, the second-stage rectification step can further remove fluorocarbon impurities with lower boiling points which cannot be removed in the first-stage rectification step, so that the quality of the purified product is kept stable.
Description
Technical Field
The invention relates to the technical field of gas purification, in particular to a difluoromethane purification method.
Background
High-purity difluoromethane is mainly used for ion etching of silicon layers, and with the rapid development of the semiconductor industry, the demand of high-purity difluoromethane is increasing. The purity of the high-purity difluoromethane used in the semiconductor industry is generally 99.999 percent, the purification of the difluoromethane relates to a deep removal technology of various impurities, and the difluoromethane raw material generally contains a large amount of O2、N2、CO2And R115, R125, R23 and R22. Due to the relatively reactive nature of difluoromethane, more fluorocarbon impurities are often produced when difluoromethane is subjected to molecular sieve dehydration. In the existing data, the impurities of the fluorocarbon impurities are rarely removed specially.
Disclosure of Invention
The invention aims to provide a difluoromethane purification method to solve the problem that fluorocarbon impurities cannot be effectively removed in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention discloses a difluoromethane purification method, which comprises the following steps:
primary adsorption: removing water from the crude difluoromethane product;
primary rectification: when the water content in the difluoromethane crude product at the outlet of the adsorber is detected to be 1-5 ppm, introducing the difluoromethane crude product subjected to the primary adsorption step into a primary rectifying tower, and carrying out primary rectification, wherein the rectification temperature is 0-30 ℃, the rectification pressure is 0.5-0.8 Mpa, and the rectification time is 1-2 h;
first-stage impurity discharge: reducing the rectification pressure to 0.2-0.3 Mpa, and discharging light component impurities to the outside, wherein the discharge flow rate of the light component impurities is 1.5Nm3The discharge time is 1-2 h;
secondary rectification: the crude difluoromethane product after the first impurity discharge step is discharged in 30Nm3And introducing the flow velocity of the flow velocity/h into a secondary rectifying tower, and carrying out secondary rectification at the rectifying temperature of 0-30 ℃ and the rectifying pressure of 0.5-0.8 Mpa to obtain the purified difluoromethane.
In the difluoromethane purification method, in the primary adsorption step, an adsorbent is used for removing water, wherein the adsorbent comprises one or more of a 3A molecular sieve, a 4A molecular sieve, a ZSM molecular sieve and an X-11 molecular sieve.
In the purification method of the difluoromethane, in the primary adsorption step, a crude difluoromethane product is introduced into an adsorber filled with an adsorbent, and the flow rate of the crude difluoromethane product is 75 kg/h-150 kg/h.
In the difluoromethane purification method, in the primary rectification step, difluoromethane which is subjected to the primary adsorption step enters a primary rectification tower, and feeding is stopped when the liquid level of the primary rectification tower is 50-90%.
In the method for purifying difluoromethane, in the secondary rectification step, when the liquid level of the primary rectification tower is 10-15%, stopping introducing difluoromethane subjected to the primary impurity discharging step into the secondary rectification tower.
In the purification method of difluoromethane, after the step of discharging the said first class impurity, also include the step of purifying repeatedly; the repeated purification step comprises:
detecting the content of light component impurities in the first-stage rectifying tower;
if the content of the light component impurities is detected to be qualified, performing the secondary rectification step;
if the content of the light component impurities is unqualified, the primary rectification step is repeated until the content of the light component impurities is qualified.
In the difluoromethane purification process, the light component impurities include N2、O2、CF4、CO2And CHF3。
In the difluoromethane purification method, the difluoromethane purification method further comprises a check-before-filling step; said pre-filling inspection step is performed after completion of said secondary rectification step, said pre-filling inspection step comprising detecting N2、O2、CF4、CO2And the content of fluorocarbon impurities; wherein the fluorocarbon impurity comprises CHF3、CF3CF2Cl and C2HF5；
When N is present2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5When the content of the difluoromethane is qualified, introducing the difluoromethane subjected to the secondary rectification step into a product for filling;
when N is present2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5When the content of (B) is not qualified, repeating the second-stage rectification step until N is reached2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5The content of (A) is qualified.
The method for purifying difluoromethane of the present invention has the following beneficial effects:
(1) the method for purifying the difluoromethane removes the water content of the crude difluoromethane product by the adsorbent, and removes fluorocarbon impurities with lower boiling points, such as CF (fluorine carbon) by a primary rectification step4、CO2And CHF3Finally, removing the fluorocarbon impurities with higher boiling point, such as CHF, by a secondary rectification step3、CF3CF2Cl and C2HF5. The purification can remove fluorocarbon impurities in difluoromethane, ensure the stability of purification and obtain products with stable purity. Meanwhile, the second-stage rectification step can further remove light-weight fluorocarbon impurities which cannot be removed in the first-stage rectification step, so that the quality of the purified product is kept stable.
(2) The method for purifying the difluoromethane adopts an operation mode of repeatedly increasing and decreasing pressure, so that impurities can be better separated from the difluoromethane, and the loss of the difluoromethane in the purification process is reduced by reducing the pressure and discharging the impurities.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. In order to facilitate an understanding of the present invention, a more complete description of the present invention is provided below. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The invention discloses a difluoromethane purification method, which comprises the following steps:
primary adsorption: removing water from the crude difluoromethane product;
primary rectification: when the water content in the crude difluoromethane product is 1-5 ppm, introducing the crude difluoromethane product subjected to the primary adsorption step into a primary rectifying tower, and carrying out primary rectification at the rectifying temperature of 0-30 ℃, under the rectifying pressure of 0.5-0.8 MPa for 1-2 h;
first-stage impurity discharge: reducing the rectification pressure to 0.2-0.3 Mpa, and discharging light component impurities to the outside, wherein the discharge flow rate of the light component impurities is 1.5Nm3The discharge time is 1-2 h;
secondary rectification: the crude difluoromethane product after the first impurity discharge step is discharged in 30Nm3And introducing the flow velocity of the flow velocity/h into a secondary rectifying tower, and carrying out secondary rectification at the rectifying temperature of 0-30 ℃ and the rectifying pressure of 0.5-0.8 Mpa to obtain the purified difluoromethane.
The method for purifying the difluoromethane removes moisture of a crude difluoromethane product by an adsorbent, and discharges fluorocarbon impurities with lower boiling points to the outside in a gas phase form by a primary rectification step to achieve the aim of removing the fluorocarbon impurities with lower boiling points, wherein the fluorocarbon impurities with lower boiling points comprise CF4、CO2And CHF3Etc.; then, after primary rectificationIntroducing the difluoromethane into a secondary rectifying tower in a liquid phase form; finally, collecting the gaseous difluoromethane at the gas phase outlet of the secondary rectifying tower through the secondary rectifying step, and reserving the fluorocarbon impurities with higher boiling points in the secondary rectifying tower, wherein the fluorocarbon impurities with higher boiling points comprise CHF3、CF3CF2Cl and C2HF5And the like. The purification can remove fluorocarbon impurities in difluoromethane, ensure the stability of purification and obtain products with stable purity. Meanwhile, the second-stage rectification step can further remove light-weight fluorocarbon impurities which cannot be removed in the first-stage rectification step, so that the quality of the purified product is kept stable.
In addition, the difluoromethane purification method disclosed by the invention adopts an operation mode of repeatedly increasing and decreasing pressure, so that impurities can be better separated from difluoromethane, and the loss of difluoromethane in the purification process is reduced by reducing pressure and discharging the impurities.
In the primary adsorption step, the adsorbent is filled in an adsorber, and the crude difluoromethane product passes through the adsorber and is discharged from the outlet of the adsorber. When the difluoromethane crude product enters primary rectification at the outlet of the adsorber, moisture detection is required, and the moisture content is 1-5 ppm. The primary adsorption step removes partial water firstly, reduces the purification pressure of the rectifying tower, and enables the purification pressure of the rectifying tower to be more suitable for removing fluorocarbon impurities.
Specifically, in the primary adsorption step, an adsorbent is used for moisture removal, and the adsorbent comprises one or more of a 3A molecular sieve, a 4A molecular sieve, a ZSM molecular sieve and an X-11 molecular sieve.
Difluoromethane has certain activity, when contacting with various conventional adsorbents, the reaction is easy to occur, the adsorption temperature is increased, and difluoromethane is easy to decompose under high temperature conditions, such as carbonyl fluoride, hydrogen fluoride and the like, so that the difficulty of purifying difluoromethane is increased, and impurities are increased. The 3A molecular sieve, the 4A molecular sieve, the ZSM molecular sieve and the X-11 molecular sieve have stable chemical properties, and the condition that difluoromethane reacts in the primary adsorption step to generate more new impurities can be effectively reduced.
Specifically, in the primary adsorption step, the crude difluoromethane product is introduced into a pipeline containing an adsorbent, and the flow rate of the crude difluoromethane product is 75 kg/h-150 kg/h.
When the flow rate of the crude difluoromethane product is lower than 75kg/h, the contact time of difluoromethane and the adsorbent is increased, and the opportunity that difluoromethane reacts with the adsorbent to generate new impurities is increased. When the flow rate of the crude difluoromethane product is more than 150kg/h, the contact time of difluoromethane and the adsorbent is too short, so that the effect of adsorbing moisture by the adsorbent is reduced, and the moisture content of difluoromethane is higher.
Specifically, in the primary rectification step, difluoromethane which passes through the primary adsorption step enters a primary rectification tower, and feeding is stopped when the liquid level of the primary rectification tower is 50-90%.
By increasing the rectification pressure, the fluorocarbon impurities can be better separated from the difluoromethane; and then, the rectification pressure is reduced, the fluorocarbon impurities are discharged by emptying, the discharge amount of dichloromethane can be reduced while the fluorocarbon impurities are discharged, and the purpose of reducing the loss of dichloromethane in the purification process is achieved.
Specifically, in the secondary rectification step, when the liquid level of the primary rectification tower is 10-15%, the difluoromethane subjected to the primary impurity discharging step is stopped from being introduced into the secondary rectification tower.
The material gets into the second grade rectifying column with liquid phase form in the one-level rectifying column, reduces light component impurity and gets into the second grade rectifying column, simultaneously through setting for the volume of surplus difluoromethane in the one-level rectifying column, avoids the problem in the heavy component impurity follows dichloromethane and gets into the second grade rectifying column to improve the purification precision. Heavy component impurity is CF3CF2Cl and C2HF5Equal mass of fluorocarbon impurities.
Further, after the step of discharging the first-stage impurities, the method also comprises a step of repeating purification; the repeated purification step comprises:
detecting the content of light component impurities in the first-stage rectifying tower;
if the content of the light component impurities is detected to be qualified, performing the secondary rectification step;
if the content of the light component impurities is unqualified, the primary rectification step is repeated until the content of the light component impurities is qualified.
The repeated purification steps can ensure that light component impurities in the difluoromethane to be purified can be discharged as much as possible, which is beneficial to improving the purity of the product.
Still further, the light fraction impurities include N2、O2、CF4、CO2And CHF3. Since the mass of the materials in the tower is distributed from light to heavy from top to bottom, the crude product containing light component impurities is discharged from the top of the rectifying tower A.
Preferably, the difluoromethane purification process further comprises a pre-filling inspection step; said pre-filling inspection step is performed after completion of said secondary rectification step, said pre-filling inspection step comprising detecting N2、O2、CF4、CO2And the content of fluorocarbon impurities; wherein the fluorocarbon impurity comprises CHF3、CF3CF2Cl and C2HF5；
When N is present2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5When the content of the difluoromethane is qualified, introducing the difluoromethane subjected to the secondary rectification step into a product for filling;
when N is present2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5When the content of (B) is not qualified, repeating the second-stage rectification step until N is reached2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5The content of (A) is qualified.
The inspection step before filling can further ensure that impurities in the difluoromethane are completely removed, so that the purified difluoromethane reaches the qualified quality, and the stability of the product purity is ensured.
Example 1
The crude difluoromethane product was passed through a tertiary molecular sieve at a flow rate of 150kg/hAnd detecting that the water content at a third-stage molecular sieve sampling port is 1ppm, feeding the water into a first-stage rectifying tower, and stopping feeding when the liquid level in the tower is 85%. Maintaining the rectification temperature of the primary rectifying tower at 25 ℃ and the rectification pressure of 0.7Mpa, and rectifying for 2 hours; reducing the pressure in the tower to 0.3Mpa, the temperature in the tower to 30 ℃ below zero, opening a discharge pipeline valve with the flow rate of 0.01Nm3H, starting to empty for 2 hours; after 6 buck-boost operations, the gas phase outlet, N, was detected2＜8ppm、O2＜2ppm、CO2Less than 1ppm and less than 10ppm of other fluorocarbon, and enters second-stage rectification.
At a flow rate of 30Nm3And feeding the material to the secondary rectifying tower at a flow speed of/h, closing a bottom communicating valve when 10% of the liquid level of the primary rectifying tower remains, and opening an inlet and outlet valve of a reboiler of the secondary rectifying tower for rectification. Controlling the pressure of the secondary rectifying tower to be 0.7Mpa, controlling the temperature in the tower to be 15 ℃, and detecting a gas phase outlet after 2 hours of rectification: n is a radical of2＜8ppm、O2＜2ppm、CO2Less than 1ppm, other fluorocarbons less than 10ppm, H2O is less than 3 ppm. And entering the product tank for filling.
The recovery of example 1 was 95%.
Example 2
The crude product of difluoromethane passes through the third-stage molecular sieve at the flow rate of 75kg/h, the water content detected by the sampling port of the third-stage molecular sieve is 5ppm, the crude product enters the first-stage rectifying tower, and the feeding is stopped when the liquid level in the tower is 50%. Maintaining the rectification temperature of the primary rectifying tower at 0 ℃ and the rectification pressure of 0.5Mpa, and rectifying for 1 hour; reducing the pressure in the tower to 0.2Mpa, the temperature in the tower to 0 ℃, opening a discharge pipeline valve, and controlling the flow rate to be 0.01Nm3H, starting to empty for 2 hours; after 6 buck-boost operations, the gas phase outlet, N, was detected2＜8ppm、O2＜2ppm、CO2Less than 1ppm and less than 10ppm of other fluorocarbon, and enters second-stage rectification.
At a flow rate of 30Nm3And feeding the material to the secondary rectifying tower at the flow speed of/h, closing the bottom communicating valve when the liquid level of the primary rectifying tower is remained by 15%, and opening an inlet and outlet valve of a reboiler of the secondary rectifying tower for rectifying. Controlling the pressure of the secondary rectifying tower to be 0.5Mpa, controlling the temperature in the tower to be 15 ℃, and detecting a gas phase outlet after 2 hours of rectification: n is a radical of2＜8ppm、O2＜2ppm、CO2Less than 1ppm of other fluorineCarbon less than 10ppm, H2O is less than 3 ppm. And entering the product tank for filling.
The recovery of example 2 was 94%.
Comparative example 1
Difluoromethane passes through the third-stage molecular sieve at the flow rate of 100kg/h, the water content detected by a third-stage molecular sieve sampling port is less than 5ppm, the difluoromethane enters a first-stage rectifying tower, and the feeding is stopped when the liquid level in the tower is 80%. Maintaining the rectification temperature of the primary rectifying tower at 25 ℃ and the rectification pressure of 0.7Mpa, and rectifying for 2 hours; opening the discharge line valve at a flow rate of 0.05Nm3H, starting to empty for 2 hours; detection of gas phase outlet, N2＜8ppm、O2＜2ppm、CO2Less than 1ppm and less than 10ppm of other fluorocarbon, and enters second-stage rectification.
At a flow rate of 30Nm3Feeding the material to the secondary rectifying tower at the flow speed of/h, closing a bottom communicating valve when the liquid level of the primary rectifying tower is 10-15% remained, and opening an inlet and outlet valve of a reboiler of the secondary rectifying tower for rectifying. Controlling the pressure of the secondary rectifying tower to be 0.7Mpa, controlling the temperature in the tower to be 15 ℃, and detecting a gas phase outlet after 2 hours of rectification: n is a radical of2＜8ppm、O2＜2ppm、CO2Less than 1ppm, less than 10ppm of other fluorocarbons, and less than 3ppm of H2O. And entering the product tank for filling.
The recovery of comparative example 1 was 88%.
As can be seen from comparison of comparative example 1, example 1 and example 2, the recovery rate of dichloromethane was significantly reduced when the purification was not performed by repeating the operation of raising and lowering the pressure.
Comparative example 2
Difluoromethane passes through the third-stage molecular sieve at the flow rate of 100kg/h, the water content detected by a third-stage molecular sieve sampling port is less than 5ppm, the difluoromethane enters a first-stage rectifying tower, and the feeding is stopped when the liquid level in the tower is 80%. Maintaining the rectification temperature of the primary rectifying tower at 20 ℃ and the rectification pressure of 0.3Mpa, and rectifying for 2 hours; opening a valve of a discharge pipeline, and starting emptying at the flow rate of 0.01Nm3/h for 2 hours; after 24h, N2: 15ppm, other fluorocarbons: 20ppm, gas phase outlet after 48h, N2: 8ppm, other fluorocarbons: 13ppm, and other fluorocarbon impurities such as trifluoromethane can not be separated in comparative example 2.
As can be seen from comparison of comparative example 2, example 1 and example 2, when purification was performed by low-pressure purification, other fluorocarbon impurities such as trifluoromethane could not be separated.
The technical principle of the present invention is described above in connection with specific embodiments. The description is made for the purpose of illustrating the principles of the invention and should not be construed in any way as limiting the scope of the invention. Other embodiments of the invention will occur to those skilled in the art without the exercise of inventive faculty based on the explanations herein, and such equivalent modifications or substitutions are intended to be included within the scope of the present invention as defined in the appended claims.
Claims (8)
1. A difluoromethane purification method, comprising the steps of:
primary adsorption: removing water from the crude difluoromethane product;
primary rectification: when the water content in the crude difluoromethane product is 1-5 ppm, introducing the crude difluoromethane product subjected to the primary adsorption step into a primary rectifying tower, and carrying out primary rectification at the rectifying temperature of 0-30 ℃, under the rectifying pressure of 0.5-0.8 MPa for 1-2 h;
first-stage impurity discharge: reducing the rectification pressure to 0.2-0.3 Mpa, and discharging light component impurities to the outside, wherein the discharge flow rate of the light component impurities is 1.5Nm3The discharge time is 1-2 h;
secondary rectification: the crude difluoromethane product after the first impurity discharge step is discharged in 30Nm3And introducing the flow velocity of the flow velocity/h into a secondary rectifying tower, and carrying out secondary rectification at the rectifying temperature of 0-30 ℃ and the rectifying pressure of 0.5-0.8 Mpa to obtain the purified difluoromethane.
2. A difluoromethane purification process according to claim 1, wherein: in the primary adsorption step, an adsorbent is used for moisture removal, and the adsorbent comprises one or more of a 3A molecular sieve, a 4A molecular sieve, a ZSM molecular sieve and an X-11 molecular sieve.
3. A difluoromethane purification process according to claim 1, wherein: in the primary adsorption step, the crude difluoromethane product is introduced into an adsorber filled with an adsorbent, and the flow rate of the crude difluoromethane product is 75 kg/h-150 kg/h.
4. A difluoromethane purification process according to claim 1, wherein: in the primary rectification step, difluoromethane which passes through the primary adsorption step enters a primary rectification tower, and feeding is stopped when the liquid level of the primary rectification tower is 50-90%.
5. A difluoromethane purification process according to claim 1, wherein: and in the secondary rectification step, stopping introducing the difluoromethane subjected to the primary impurity discharging step into the secondary rectification tower when the liquid level of the primary rectification tower is 10-15%.
6. A difluoromethane purification process according to claim 1, wherein: after the first-stage impurity discharging step, a repeated purification step is also included; the repeated purification step comprises:
detecting the content of light component impurities in the first-stage rectifying tower;
if the content of the light component impurities is detected to be qualified, performing the secondary rectification step;
if the content of the light component impurities is unqualified, the primary rectification step is repeated until the content of the light component impurities is qualified.
7. A difluoromethane purification process according to claim 6, wherein: the light component impurities comprise N2、O2、CF4、CO2And CHF3。
8. A difluoromethane purification process according to claim 1, wherein: the difluoromethane purification process further comprises a pre-filling inspection step; the pre-filling inspection step is performed after the completion of the secondary rectification stepSaid check-before-filling step comprising detecting N2、O2、CF4、CO2And the content of fluorocarbon impurities; wherein the fluorocarbon impurity comprises CHF3、CF3CF2Cl and C2HF5；
When N is present2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5When the content of the difluoromethane is qualified, introducing the difluoromethane subjected to the secondary rectification step into a product for filling;
when N is present2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5When the content of (B) is not qualified, repeating the second-stage rectification step until N is reached2、O2、CF4、CO2、CHF3、CF3CF2Cl and C2HF5The content of (A) is qualified.
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| CN202011629668.4A CN112694387A (en) | 2020-12-30 | 2020-12-30 | Difluoromethane purification method |
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