Method for removing HCFC-1122 in HFC-134a

Abstract

The invention relates to the technical field of fluorine chemical industry, in particular to a method for removing HCFC-1122 in HFC-134a. The method comprises the following specific steps: adding an aprotic polar solvent, trifluoroethanol and potassium fluoride into a stainless steel reaction kettle, and mixing and stirring; heating the uniformly stirred materials in the stainless steel reaction kettle to a reaction temperature; the method comprises the following steps: introducing HFC-134a gas rich in HCFC-1122 at the top of an HFC-134a rectifying tower into a stainless steel reaction kettle for reaction; the reacted gas is condensed by a reflux condenser on the stainless steel reaction kettle, components with higher boiling points flow back to the reaction kettle, and the gas which cannot be condensed enters a compressor to be compressed and pressurized; rectifying the pressurized gas in a special rectifying tower, returning the tower top gas of the special rectifying tower to the HFC-134a rectifying tower, and returning the tower kettle material to the stainless steel reaction kettle; and the qualified HFC-134a is continuously produced from the tower kettle of the HFC-134a rectifying tower. According to the method, the problem of impurities in the product in production is solved, the production cost of the product is reduced, the economic benefit is improved, and the method has wide market requirements.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine chemical industry, in particular to a method for removing HCFC-1122 from HFC-134a. Background Art

[0002] 1,1,1,2-Tetrafluoroethane (HFC-134a) has a normal pressure boiling point of -26.5°C, an ODP value (ozone depletion potential) of 0, and a GWP value (greenhouse effect potential) of 0.26. It is currently mainly used as a refrigerant for automotive air conditioners in the market, and is also partially used in medical aerosols.

[0003] There are two mature synthetic routes for HFC-134a, both of which use trichloroethylene as raw material. The difference is: one is a two-step synthesis in gas phase, and the other is a two-step synthesis in liquid phase. In both synthetic methods, while the main reaction is taking place, the reaction of 2-chloro-1,1,1-trifluoroethane (HCFC-133a) removing HF to generate 2-chloro-1,1-difluoroethylene (HCFC-1122) will also occur. The reaction principle is: CF3-CH2Cl → CF2=CHCl(HCFC-1122)+HF HCFC-1122 is a toxic substance with a boiling point of -17.7℃. It can form an azeotrope with HFC-134a and cannot be separated by conventional methods. At present, the common practices for removing HCFC-1122 from HFC-134a are: 1. Use special molecular sieves for adsorption removal. After the molecular sieve is saturated with adsorption, it is regenerated by hot nitrogen or air analysis and reused. The disadvantage of this method is that HCFC-1122 still exists after the molecular sieve is analyzed and cannot be eliminated. In addition, the adsorbed HFC-134a during the analysis process is difficult to recover due to the presence of a large amount of non-condensable gas, resulting in losses. 2. Use chlorine, hydrogen fluoride, and hydrogen to react with HCFC-1122 to form saturated alkanes and then distill and separate. During the reaction of chlorine and HCFC-1122, HFC-134a is also chlorinated by chlorine, resulting in loss. The chlorinated material needs to be washed with alkali and water before distillation and separation, which is cumbersome. The addition reaction of hydrogen fluoride and HCFC-1122 also has the problem that the material needs to be washed with alkali and water to remove the acidity and then distilled and separated. When hydrogen and HCFC-1122 undergo addition reaction under the catalysis of hydrogenation catalyst, part of HFC-134a will also be reduced and replaced by hydrogen, resulting in material loss. In addition, the safety risk in the hydrogenation process is high. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for removing HCFC-1122 from HFC-134a to solve the above problems. In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for removing HCFC-1122 from HFC-134a, using trifluoroethanol and HCFC-1122 (2-chloro-1,1-difluoroethylene) in a non-protonic polar solvent to react under the catalysis of potassium fluoride to generate 1,1-difluoro-2-chloroethyl-2,2,2-trifluoroethyl ether, thereby removing HCFC-1122 from HFC-134a, so that the volume fraction of HCFC-1122 in HFC-134a is less than 10×10 -6 ; The specific steps are as follows: Step 1, adding aprotic polar solvent, trifluoroethanol and potassium fluoride into a stainless steel reactor and mixing and stirring; Step 2, heating the materials stirred evenly in the stainless steel reactor to the reaction temperature; Step 3, introducing the HFC-134a gas rich in HCFC-1122 from the top of the HFC-134a distillation tower into a stainless steel reactor for reaction; Step 4: The reacted gas is condensed by a reflux condenser on a stainless steel reactor, and the components with higher boiling points are refluxed back to the reactor, while the gas that cannot be condensed is compressed and pressurized by a compressor; Step 5, the pressurized gas is distilled in a dedicated distillation tower, the top gas of the dedicated distillation tower returns to the HFC-134a distillation tower, and the bottom material returns to the stainless steel reactor; Step six, the HFC-134a distillation tower kettle continuously produces qualified HFC-134a.

[0005] As a further embodiment of the present invention, the aprotic polar solvent in step 1 includes but is not limited to acetonitrile, N , N -Dimethylformamide, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, N-methylpyrrolidone, hexamethylphosphoric triamide.

[0006] As a further solution of the present invention, the catalyst used in step 1 is potassium fluoride, and the added amount is 1% to 5% of the amount of the solvent.

[0007] As a further embodiment of the present invention, the reaction raw material used in step 1 is trifluoroethanol.

[0008] As a further solution of the present invention, the reaction temperature of the stainless steel reactor in step 2 is 30°C to 90°C.

[0009] As a further solution of the present invention, the reaction pressure of the stainless steel reactor in step 2 is normal pressure.

[0010] As a further solution of the present invention, the reaction process in step three is a continuous reaction.

[0011] As a further embodiment of the present invention, the volume fraction of HCFC-1122 in step 6 is less than 10×10 -6 , and the HFC-134a content is greater than 99.9%.

[0012] Since the present invention adopts the above technical solution, the present invention has the following advantages and positive effects: 1. The present invention can continuously and conveniently remove HCFC-1122 from HFC-134a under relatively low temperature and normal pressure conditions. Trifluoroethanol and HCFC-1122 can react when in contact in the presence of a catalyst. A single reactor can process more than 1 ton of HFC-134a rich in HCFC-1122 per hour. The reaction speed is fast, and conventional reaction equipment can meet production needs. 2. The present invention can not only remove HCFC-1122 from HFC-134a, but also the by-product 1,1-difluoro-2-chloroethyl-2,2,2-trifluoroethyl ether produced by the reaction can be used as the raw material of patent CN202211151832, and trifluoroethanol and potassium hydroxyacetate can be produced by a separate reaction. Potassium hydroxyacetate can be sold and trifluoroethanol can be reused; 3. This method not only solves the impurity problem of products in production, but also reduces the production cost of products, improves economic benefits, and has broad market demand. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] Example 1 2 tons of N-methylpyrrolidone (NMP) were added to a 5 cubic stainless steel reactor, and 1 ton of trifluoroethanol and 20 kg of potassium fluoride were added under stirring. After the addition, the mixture was stirred for 1 hour and the temperature was raised to 90°C. The HFC-134a gas rich in HCFC-1122 at the top of the HFC-134a distillation tower was continuously introduced into the reactor from the bottom of the stainless steel reactor. The air intake speed was controlled to be no less than 1 ton of HFC-134a per hour, and the volume fraction of HCFC-1122 in the HFC-134a gas discharged from the stainless steel reactor was less than 50×10 -6The exhaust HFC-134a gas is condensed by the reflux condenser on the reactor and then pressurized to above 0.5MPa by the gas compressor before entering the dedicated distillation tower for distillation. The HFC-134a gas at the top of the dedicated distillation tower enters the middle of the HFC-134a distillation tower for further distillation, keeping the volume fraction of HCFC-1122 in HFC-134a in the reactor of the HFC-134a distillation tower below 10×10 -6 , continuously producing HFC-134a. The materials in the dedicated distillation tower kettle are returned to the stainless steel reactor. The pressure of the gas compressor booster is linked to the pressure of the HFC-134a distillation tower, and the pressure of the gas compressor booster is higher than the pressure of the HFC-134a distillation tower by more than 0.1MPa.

[0015] Example 2 2 tons N , N -dimethylformamide (DMF) was added to a 5 cubic stainless steel reactor, and 1 ton of trifluoroethanol and 60 kg of potassium fluoride were added under stirring. After the addition, the mixture was stirred for 1 hour and the temperature was raised to 60°C. The HFC-134a gas rich in HCFC-1122 at the top of the HFC-134a distillation tower was continuously introduced into the reactor from the bottom of the stainless steel reactor. The air intake rate was controlled to be no less than 1 ton of HFC-134a per hour, and the volume fraction of HCFC-1122 in the HFC-134a gas discharged from the stainless steel reactor was less than 50×10 -6 If necessary, the air intake speed can be appropriately reduced or the reaction temperature can be increased. The discharged HFC-134a gas is condensed by the reflux condenser on the reactor and then pressurized to above 0.5MPa by the gas compressor before entering the dedicated distillation tower for distillation. The HFC-134a gas at the top of the dedicated distillation tower enters the middle of the HFC-134a distillation tower for further distillation, keeping the volume fraction of HCFC-1122 in the HFC-134a in the reactor of the HFC-134a distillation tower below 10×10 -6 , continuously producing HFC-134a. The materials in the dedicated distillation tower kettle are returned to the stainless steel reactor. The pressure of the gas compressor booster is linked to the pressure of the HFC-134a distillation tower, and the pressure of the gas compressor booster is higher than the pressure of the HFC-134a distillation tower by more than 0.1MPa.

[0016] Example 3 2 tons of 1,3-dimethyl-2-imidazolidinone (DMI) were added to a 5 cubic stainless steel reactor, and 1 ton of trifluoroethanol and 100 kg of potassium fluoride were added under stirring. After the addition, the mixture was stirred for 1 hour and the reaction temperature was maintained at 30°C. The HFC-134a gas rich in HCFC-1122 at the top of the HFC-134a distillation tower was continuously introduced into the reactor from the bottom of the stainless steel reactor, and the air intake rate was controlled to be no less than 1 ton of HFC-134a per hour, so that the volume fraction of HCFC-1122 in the HFC-134a gas discharged from the stainless steel reactor was less than 50×10 -6 The reaction temperature can be appropriately increased if necessary. The discharged HFC-134a gas is condensed by the reflux condenser on the reactor and then pressurized to above 0.5MPa by the gas compressor before entering the dedicated distillation tower for distillation. The HFC-134a gas at the top of the dedicated distillation tower enters the middle of the HFC-134a distillation tower for further distillation, keeping the volume fraction of HCFC-1122 in the HFC-134a in the reactor of the HFC-134a distillation tower below 10×10 -6 , continuously producing HFC-134a. The materials in the dedicated distillation tower kettle are returned to the stainless steel reactor. The pressure of the gas compressor booster is linked to the pressure of the HFC-134a distillation tower, and the pressure of the gas compressor booster is higher than the pressure of the HFC-134a distillation tower by more than 0.1MPa.

[0017] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for removing HCFC-1122 from HFC-134a, characterized in that: In an aprotic polar solvent, trifluoroethanol is used to react with HCFC-1122 (2-chloro-1,1-difluoroethylene) under the catalysis of potassium fluoride to generate 1,1-difluoro-2-chloroethyl-2,2,2-trifluoroethyl ether, thereby removing HCFC-1122 from HFC-134a and reducing the volume fraction of HCFC-1122 in HFC-134a to less than 10×10 -6 ; The specific steps are as follows: Step 1, adding aprotic polar solvent, trifluoroethanol and potassium fluoride into a stainless steel reactor and mixing and stirring; Step 2, heating the materials stirred evenly in the stainless steel reactor to the reaction temperature; Step 3, introducing the HFC-134a gas rich in HCFC-1122 from the top of the HFC-134a distillation tower into a stainless steel reactor for reaction; Step 4: The reacted gas is condensed by a reflux condenser on a stainless steel reactor, and the components with higher boiling points are refluxed back to the reactor, while the gas that cannot be condensed is compressed and pressurized by a compressor; Step 5, the pressurized gas is distilled in a dedicated distillation tower, the top gas of the dedicated distillation tower returns to the HFC-134a distillation tower, and the bottom material returns to the stainless steel reactor; Step six, the HFC-134a distillation tower kettle continuously produces qualified HFC-134a.

2. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The aprotic polar solvent in step 1 includes but is not limited to acetonitrile, N , N -Dimethylformamide, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, N-methylpyrrolidone, hexamethylphosphoric triamide.

3. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The catalyst used in step 1 is potassium fluoride, and the added amount is 1% to 5% of the solvent amount.

4. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The reaction raw material used in the step 1 is trifluoroethanol.

5. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The reaction temperature of the stainless steel reactor in step 2 is 30°C to 90°C.

6. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The reaction pressure of the stainless steel reactor in step 2 is normal pressure.

7. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The reaction process in step three is a continuous reaction.

8. The method for removing HCFC-1122 from HFC-134a according to claim 1, characterized in that: The volume fraction of HCFC-1122 in step 6 is less than 10×10 -6 , and the HFC-134a content is greater than 99.9%.