A process for separating a mixture of tetrafluoropropene and tetrafluoroethane

Abstract

The application discloses a separation method of tetrafluoropropylene and tetrafluoroethane mixture, mainly comprising the following steps: taking the tetrafluoropropylene and tetrafluoroethane mixture as raw materials, adding ionic liquid in an extractive rectification tower, and performing extractive rectification on the raw materials, wherein the cation of the ionic liquid has the structure of formula (I), and the anion is one of perchlorate ion [ClO4] or fluorosulfonylimide [FSI] ion. In formula (I), R and R' are respectively selected from C1-C4 alkyl. The specified ionic liquid is added in the extractive rectification tower, high-efficiency separation of the tetrafluoropropylene and tetrafluoroethane mixture is realized, high-purity tetrafluoropropylene and tetrafluoroethane can be obtained, the mass purity of the tetrafluoropropylene and tetrafluoroethane products can be as high as 99.6%, and compared with other ionic liquids, the ionic liquid used in the application has smaller energy consumption in the extractive rectification separation process under the condition of obtaining products with the same purity, and the annual economic cost is lower.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refrigerant recovery and separation, and particularly relates to a separation method of a tetrafluoropropene and tetrafluoroethane mixture. BACKGROUND

[0002] A refrigerant is a medium substance used to complete energy conversion in an air conditioner. Tetrafluoropropene and tetrafluoroethane are commonly used refrigerants in the refrigeration and air conditioning industry. They can be mixed in a mass ratio of 0.56:0.44 to prepare a mixed refrigerant R513A commonly used in household air conditioners. R513A refrigerant has zero ozone depletion potential (ODP) and low global warming potential (GWP), and is used to replace R134a refrigerant in air conditioning or medium-temperature commercial refrigeration systems (including direct expansion and centrifugal machines). Whether it is a new system installation or an existing system modification, the R513A refrigerant has the same energy efficiency as the R134a refrigerant, and can achieve the best balance of high energy efficiency and environmental sustainability. As the use of R513A increases year by year, the R513A contained in the equipment needs to be recovered in a timely manner due to leakage or when the equipment reaches the end of its service life, to avoid direct discharge into the atmosphere, further exacerbating the trend of global warming or causing resource waste. Part of the recovered R513A can meet the charging requirements of the same refrigeration equipment refrigerant, and the remaining part needs to be separated into corresponding pure components, i.e., tetrafluoropropene and tetrafluoroethane, and then respectively put into different fields for continued use.

[0003] However, since the tetrafluoropropene and tetrafluoroethane system is a completely miscible binary azeotropic system, it is difficult to separate and obtain high-purity tetrafluoroethane and tetrafluoropropene by conventional rectification means, and therefore it is necessary to use an extractive distillation method to separate the mixture of the two. There are extractive distillation methods in the prior art that use organic solvents as extractants to separate azeotropic mixtures, for example: Patent Document 1 (US6156161A) discloses an "extractive distillation process for separating difluoromethane and pentafluoroethane with dichloromethane"; Patent Document 2 (JP2007091762A) discloses a "method for separating HFC-32 and HFC-125"; which uses an extractant containing dichloromethane to separate difluoromethane (HFC-32) and pentafluoroethane (HFC-125) from a mixture containing the two. There are also extractive distillation methods that use inorganic salts as extractants to separate azeotropic mixtures. However, organic solvents as extractants have the disadvantages of being volatile, using a large amount, and high energy consumption; inorganic salts as extractants can damage the equipment.

[0004] As a new type of extractant, ionic liquid has stable chemical properties, good solubility, high boiling point, low volatility, and strong designability, and is a green solvent, so it is widely used and studied. The related researches of the prior art also show that it can be used for extractive distillation of azeotropic mixture, for example: patent document 3 (WO2021076480A1) discloses a method for separating components of an azeotropic mixture using ionic liquid. However, at present, there are still technical problems such as how to use to further improve the extraction separation efficiency, the purity of the separated product, and how to further reduce the amount of ionic liquid and improve the recovery rate of ionic liquid. SUMMARY

[0005] Therefore, the present application provides a separation method of tetrafluoropropylene and tetrafluoroethane mixture, which uses ionic liquid as an extractant for extractive distillation of tetrafluoropropylene and tetrafluoroethane near-azeotrope system. Compared with the traditional extractive distillation method, it has low volatility, no pollution, small amount, low energy consumption, and avoids damage to the equipment.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A separation method of tetrafluoropropylene and tetrafluoroethane mixture, using tetrafluoropropylene and tetrafluoroethane mixture as raw material, adding ionic liquid in the extractive distillation column, and carrying out extractive distillation on the raw material, wherein,

[0008] The cation of the ionic liquid has the structure of formula (I), and the anion is one of perchlorate ion [ClO4] or fluorosulfonylimide [FSI] ion;

[0009]

[0010] In formula (I), R and R' are respectively selected from alkyl with 1-4 carbon atoms in the alkyl chain.

[0011] Preferably, the cation of the ionic liquid is selected from alkyl imidazole cation.

[0012] Preferably, the alkyl of the cation of the ionic liquid is selected from methyl or ethyl.

[0013] Preferably, the ionic liquid is 1-ethyl-3-methyl imidazole perchlorate ([EMIM][ClO4]) or 1-ethyl-3-methyl imidazole fluorosulfonylimide salt ([EMIM][FSI]).

[0014] Preferably, the mass ratio of the ionic liquid to the raw material is 5-8.

[0015] Preferably, the reflux ratio of the extractive distillation column is 0.5-3.

[0016] Preferably, the column bottom temperature of the extractive rectification column is 30-100℃, and the operating pressure of the extractive rectification column is 0.5-1MPa.

[0017] Preferably, the mass content of tetrafluoroethane in the mixture of tetrafluoroethane and tetrafluoropropene is 40-70%.

[0018] Preferably, the separation method further comprises:

[0019] tetrafluoropropene is taken from the top line of the extractive rectification column;

[0020] the extractive rectification column bottom stream is introduced into a solvent flash tank for flashing;

[0021] tetrafluoroethane is led out from the top stream of the solvent flash tank;

[0022] the ionic liquid is introduced into the extractive rectification column from the bottom of the solvent flash tank.

[0023] Preferably, the operating pressure of the solvent flash tank is 1-2kPa, and the operating temperature is 160℃.

[0024] The separation method of the mixture of tetrafluoroethane and tetrafluoropropene according to the present application has the following beneficial effects compared to the prior art:

[0025] The present application adds a specified ionic liquid in the extractive rectification column, realizes the efficient separation of the mixture of tetrafluoroethane and tetrafluoropropene, and can obtain high-purity tetrafluoroethane and tetrafluoropropene, wherein the mass purity of the tetrafluoroethane and tetrafluoropropene products can be as high as 99.6%; and compared to other ionic liquids, under the condition of obtaining products with the same purity, the ionic liquid used in the present application has lower energy consumption in the process of extractive rectification separation, and lower annual economic cost.

[0026] The ionic liquid used in the present application has low volatility, no pollution, and is more environmentally friendly; in the process of separating the mixture of tetrafluoroethane and tetrafluoropropene, the ionic liquid has good stability, less loss, can be recycled, and the recovery rate is as high as 99.9%. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The figure is a flow diagram of the separation system of the mixture of tetrafluoroethane and tetrafluoropropene according to the present application;

[0028] Among them:

[0029] IL-ionic liquid supplement; MIX-mixer; T1-extractive rectification column; T2-solvent flash tank; S1-extractive rectification column extractant feed; F-extractive rectification column raw material feed; F2-solvent recovery tank feed; P1-circulating pump; C1-heat exchanger; Q C -condenser load; QR - reboiler duty. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. The described embodiments are only possible technical implementations of the present application, and not all possible implementations. Those skilled in the art can obtain other embodiments by combining the embodiments of the present application without creative effort, and these embodiments are also within the protection scope of the present application.

[0031] A separation method of a tetrafluoropropene and tetrafluoroethane mixture, comprising adding an ionic liquid in an extractive rectification column to carry out extractive rectification on a tetrafluoropropene and tetrafluoroethane mixture as raw material. The cation of the ionic liquid has a structure of formula (I); and the anion is one of perchlorate ions [ClO4] or fluorosulfonylimide ions [FSI].

[0032]

[0033] In formula (I), R and R' are respectively selected from C1-C4 alkyl, preferably methyl and ethyl.

[0034] On the thermodynamic level, the selectivity is used as an index to evaluate the separation performance of the ionic liquid for R513A, that is, the greater the difference between the amounts of R134a and R1234yf dissolved in the same ionic liquid, the higher the selectivity of the ionic liquid for them. In the present application, a method based on the conductor-like screening model for relativistic quantum systems (COSMO-RS) is used to calculate and screen the selectivity of the ionic liquid. Although EMIMN(CF3)2 has the highest selectivity, its melting point is higher than 100℃, which cannot meet the requirement that the extractant be in a liquid state in the actual separation process. In summary, EMIMFSI and EMIMClO4 have the highest R513A selectivity, and they can exist in a liquid state at room temperature. In the present application, these two ionic liquids are used to simulate the process flow of separating R513A.

[0035] Specifically, the separation method of the mixture adopts Figure 1 The extractive rectification separation cycle shown in the figure comprises the following steps:

[0036] S1: adding a tetrafluoropropene and tetrafluoroethane mixture as raw material from a middle lower part of the extractive rectification column;

[0037] The mixture of tetrafluoropropene and tetrafluoroethane is added as raw material in the extractive rectification column T1, and the mass content of tetrafluoroethane is 40-70%, preferably 44%.

[0038] The extractive distillation column used in the extractive distillation operation can be a plate column or a packed column;

[0039] The plate column can be selected from a bubble cap column, sieve plate column and float valve column; the packing used in the packed column can be selected from bulk packing and structured packing, and the preferred packing is Pall ring packing or wire mesh structured packing.

[0040] S2: adding the ionic liquid as an extractant from the top of the extractive distillation column to perform extractive distillation;

[0041] In the extraction process, the mass ratio of the extractant to the raw material is 5-8, and the ionic liquid is added in the extractive distillation column, wherein the reflux ratio of the extractive distillation column is 0.5-3, the column bottom temperature of the extractive distillation column is 30-100℃, and the operating pressure of the extractive distillation column is 0.5-1 MPa.

[0042] S3: collecting the high-purity tetrafluoropropylene product from the top line of the extractive distillation column;

[0043] S4: introducing the extractive distillation column bottom stream from the bottom of the extractive distillation column into a solvent flash tank T2 for flashing;

[0044] The solvent flash tank for flashing the stream T2 is operated under reduced pressure, and the operating pressure of the solvent flash tank is 1-2 kPa, and the operating temperature is 160℃.

[0045] S5: introducing the high-purity byproduct tetrafluoroethane from the top stream of the solvent flash tank through a pipeline;

[0046] S6: introducing the ionic liquid from the bottom of the solvent flash tank into the extractive distillation column to realize the recycling of the ionic liquid.

[0047] To further verify the superiority of the separation method of the tetrafluoropropylene and tetrafluoroethane mixture according to the present application, the present application gives the following Examples 1-4 and Comparative Examples 5 and 6, which are all for separating 1000 kg / h of the tetrafluoropropylene and tetrafluoroethane mixture in the extractive distillation cycle as shown in Figure 1 .

[0048] Among them, Examples 1 and 2 use 1-ethyl-3-methylimidazolium perchlorate ([EMIM][ClO4]) ionic liquid as the extractant; Examples 3 and 4 use 1-ethyl-3-methylimidazolium fluorosulfonimide salt ([EMIM][FSI]) ionic liquid as the extractant; and Comparative Examples 5 and 6 use 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) ionic liquid as the extractant.

[0049] Example 1:

[0050] The extractive distillation column T1 has 26 theoretical plates (number of plates counted from top to bottom), 1-ethyl-3-methylimidazolium perchlorate ([EMIM][ClO4]) extractant S1 is fed from the 2nd plate at a flow rate of 11500 kg / h, tetrafluoroethane and tetrafluoropropene mixture (44 wt% tetrafluoroethane + 56 wt% tetrafluoropropene) F is fed from the 13th theoretical plate at a flow rate of 1000 kg / h. The extractive distillation column T1 is operated at a pressure of 0.5 MPa, with a reflux ratio of 2 at the top, a top draw of 560 kg / h, a temperature at the top of the extractive distillation column of 14.4479 °C, and a temperature at the bottom of the extractive distillation column of 49.913 °C, resulting in a mass fraction of greater than 99.6% tetrafluoropropene product at the top.

[0051] The extractive distillation column T1 bottom product tetrafluoroethane and ionic liquid mixture enters the solvent flash drum T2, which is operated at a pressure of 1 kPa, a flash temperature of 160 °C, a mass fraction of greater than 99.6% tetrafluoroethane product at the top, and a mass fraction of greater than 99.999% ionic liquid extractant at the bottom, which is recycled back to the extractive distillation column T1 for reuse. The reboiler heat duty consumed is 191.904 kW, the condenser duty is 50.278 kW, and the total power consumed is 242.182 kW.

[0052] Example 2:

[0053] The extractive distillation column T1 has 32 theoretical plates (number of plates counted from top to bottom), 1-ethyl-3-methylimidazolium perchlorate ([EMIM][ClO4]) extractant S1 is fed from the 2nd plate at a flow rate of 11500 kg / h, tetrafluoroethane and tetrafluoropropene mixture (44 wt% tetrafluoroethane + 56 wt% tetrafluoropropene) F is fed from the 20th theoretical plate at a flow rate of 1000 kg / h. The extractive distillation column T1 is operated at a pressure of 0.5 MPa, with a reflux ratio of 2 at the top, a top draw of 560 kg / h, a temperature at the top of the extractive distillation column of 14.4479 °C, and a temperature at the bottom of the extractive distillation column of 50.635 °C, resulting in a mass fraction of greater than 99.6% tetrafluoropropene product at the top.

[0054] The extractive distillation column T1 bottom product tetrafluoroethane and ionic liquid mixture enters the solvent flash drum T2, which is operated at a pressure of 1 kPa, a flash temperature of 160 °C, a mass fraction of greater than 99.6% tetrafluoroethane product at the top, and a mass fraction of greater than 99.999% ionic liquid extractant at the bottom, which is recycled back to the extractive distillation column T1 for reuse. The reboiler heat duty consumed is 193.704 kW, the condenser duty is 50.278 kW, and the total power consumed is 243.982 kW.

[0055] Example 3:

[0056] The extractive distillation column T1 has 26 theoretical plates (number of plates counted from top to bottom), 1-ethyl-3-methylimidazolium fluorosulfonimide salt ([EMIM][FSI]) extractant S1 is fed from 2nd plate at a flow rate of 7800 kg / h, tetrafluoroethane and tetrafluoropropene mixture (44 wt% tetrafluoroethane + 56 wt% tetrafluoropropene) F is fed from 11th theoretical plate at a flow rate of 1000 kg / h. The extractive distillation column T1 is operated at a pressure of 0.5 MPa, with a reflux ratio of 2 at the top, a top draw of 560 kg / h, a temperature of 13.1154 °C at the top of the extractive distillation column and a temperature of 49.8927 °C at the bottom of the extractive distillation column, resulting in a mass fraction of greater than 99.7% tetrafluoropropene product at the top. The reboiler heat duty consumed is 141.491 kW, the condenser duty is 57.165 kW and the total power consumed is 198.656 kW.

[0057] The extractive distillation column T1 bottom product tetrafluoroethane and ionic liquid mixture enters the solvent flash drum T2 at a flash pressure of 1 kPa and a flash temperature of 160 °C, resulting in a mass fraction of greater than 99.7% tetrafluoroethane product at the top and a mass fraction of greater than 99.997% ionic liquid extractant at the bottom, which is recycled back to the extractive distillation column T1 for reuse.

[0058] Example 4:

[0059] The extractive distillation column T1 has 24 theoretical plates (number of plates counted from top to bottom), 1-ethyl-3-methylimidazolium fluorosulfonimide salt ([EMIM][FSI]) extractant S1 is fed from 2nd plate at a flow rate of 7800 kg / h, tetrafluoroethane and tetrafluoropropene mixture (44 wt% tetrafluoroethane + 56 wt% tetrafluoropropene) F is fed from 11th theoretical plate at a flow rate of 1000 kg / h. The extractive distillation column T1 is operated at a pressure of 0.5 MPa, with a reflux ratio of 2 at the top, a top draw of 560 kg / h, a temperature of 13.1154 °C at the top of the extractive distillation column and a temperature of 49.8927 °C at the bottom of the extractive distillation column, resulting in a mass fraction of greater than 99.7% tetrafluoropropene product at the top. The reboiler heat duty consumed is 141.491 kW, the condenser duty is 57.165 kW and the total power consumed is 198.656 kW.

[0060] The extractive distillation column T1 bottom product tetrafluoroethane and ionic liquid mixture enters the solvent flash drum T2 at a flash pressure of 1 kPa and a flash temperature of 160 °C, resulting in a mass fraction of greater than 99.7% tetrafluoroethane product at the top and a mass fraction of greater than 99.997% ionic liquid extractant at the bottom, which is recycled back to the extractive distillation column T1 for reuse.

[0061] Comparative Example 5:

[0062] The extractive distillation column T1 has 34 theoretical plates (number of plates counted from top to bottom), 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) extractant S1 is fed from 2nd plate at a flow rate of 17000 kg / h, tetrafluoroethane and tetrafluoropropene mixture (44 wt% tetrafluoroethane + 56 wt% tetrafluoropropene) F is fed from 22nd theoretical plate at a flow rate of 1000 kg / h. The extractive distillation column T1 is operated at a pressure of 0.5 MPa, with a reflux ratio of 2 at the top, a top draw of 560 kg / h, a temperature of 14.4415 °C at the top of the extractive distillation column and a temperature of 47.875 °C at the bottom of the extractive distillation column, resulting in a mass fraction of greater than 99.5% tetrafluoropropene product at the top. The reboiler heat duty consumed is 388.304 kW, the condenser duty is 98.107 kW and the total power consumed is 486.411 kW.

[0063] The extractive distillation column T1 bottom product tetrafluoroethane and ionic liquid mixture enters the solvent flash drum T2 at a flash pressure of 1 kPa and a flash temperature of 160 °C, resulting in a mass fraction of greater than 99.5% tetrafluoroethane product at the top and a mass fraction of greater than 99.997% ionic liquid extractant at the bottom, which is recycled back to the extractive distillation column T1 for reuse.

[0064] Comparative Example 6:

[0065] The extractive distillation column T1 has 26 theoretical plates (number of plates counted from top to bottom), 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) extractant S1 is fed from 2nd plate at a flow rate of 18000 kg / h, tetrafluoroethane and tetrafluoropropene mixture (44 wt% tetrafluoroethane + 56 wt% tetrafluoropropene) F is fed from 17th theoretical plate at a flow rate of 1000 kg / h. The extractive distillation column T1 is operated at a pressure of 0.5 MPa, with a reflux ratio of 2 at the top, a top draw of 560 kg / h, a temperature of 14.4404 °C at the top of the extractive distillation column and a temperature of 49.6588 °C at the bottom of the extractive distillation column, resulting in a mass fraction of greater than 99.5% tetrafluoropropene product at the top. The reboiler heat duty consumed is 427.05 kW, the condenser duty is 98.34 kW and the total power consumed is 525.39 kW.

[0066] The extractive distillation column T1 bottom product tetrafluoroethane and ionic liquid mixture enters the solvent flash drum T2 at a flash pressure of 1 kPa and a flash temperature of 160 °C, resulting in a mass fraction of greater than 99.5% tetrafluoroethane product at the top and a mass fraction of greater than 99.997% ionic liquid extractant at the bottom, which is recycled back to the extractive distillation column T1 for reuse.

[0067] The following table shows that in the working conditions of separating 1000 kg / h of mixed refrigerant, the two kinds of ionic liquids used in the application of examples 1-4 and comparative examples 5 and 6 have less dosage, the total load of the extractive distillation cycle is smaller, the economic cost is more optimal, the harm to the environment is smaller.

[0068] Comparison table of ionic liquid dosage and load of different ionic liquid extractive distillation separation processes

[0069]

[0070] The technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not contradict, they should be considered as the scope of the description. It should be noted that the "in an embodiment of the present application", "for example", "for example" and the like in the present application are intended to illustrate the present application, rather than to limit the present application. The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be considered as limiting the scope of the patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A process for separating a mixture of tetrafluoropropene and tetrafluoroethane, characterized by, The method comprises: using a mixture of tetrafluoropropene and tetrafluoroethane as raw material, adding an ionic liquid in an extractive distillation column to perform extractive distillation on the raw material, wherein the tetrafluoropropene is R1234yf and the tetrafluoroethane is R134a; The cation of the ionic liquid has a structure of formula (I), and the anion is a perchlorate ion [ClO4]; In formula (I), R and R' are respectively selected from alkyl with 1-4 carbon atoms in an alkyl chain.

2. The separation method of claim 1, wherein: The alkyl with 1-4 carbon atoms in the alkyl chain is selected from methyl or ethyl.

3. The separation method of claim 1, wherein: The ionic liquid is 1-ethyl-3-methyl imidazole perchlorate ([EMIM][ClO4]).

4. The separation method of claim 1, wherein: The mass ratio of the ionic liquid to the raw material is 5-8.

5. The separation method of claim 4, wherein: The reflux ratio of the extractive distillation column is 0.5-3.

6. The separation method of claim 5, wherein: The column bottom temperature of the extractive distillation column is 30-100 DEG C, and the operating pressure of the extractive distillation column is 0.5-1 MPa.

7. The separation method of claim 1, wherein: In the mixture of tetrafluoroethane and tetrafluoropropene, the mass content of tetrafluoroethane is 40-70%.

8. The separation method of claim 1, wherein: The separation method further comprises: tetrafluoropropene is taken from the top line of the extractive distillation column; the extractive distillation column bottom stream is introduced into a solvent flash tank for flashing; tetrafluoroethane is introduced from the top stream of the solvent flash tank; the ionic liquid is introduced from the bottom of the solvent flash tank into the extractive distillation column.

9. The separation method of claim 8, wherein: The operating pressure of the solvent flash tank is 1-2 kPa, and the operating temperature is 160 DEG C.

Images