JP2018002602A - Process for separating 2,3,3,3-tetrafluoropropene and hexafluoropropene, and process for producing 2,3,3,3-tetrafluoropropene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently separating 1234yf and HFP from a mixture containing 2,3,3,3-tetrafluoropropene (1234yf) and hexafluoropropene (HFP), and a method for efficiently producing 1234yf thereby. .. SOLUTION: A mixture containing 1234yf and HFP, saturated hydrocarbons having 5 to 12 carbon atoms, aromatic hydrocarbons having 6 to 9 carbon atoms, alcohols, ketones, amides, ethers and esters. A step of mixing an extraction solvent containing at least one selected from varieties, nitriles, chlorocarbons, hydrochlorocarbons, hydrofluoroethers, and hydrochlorofluorocarbons to obtain an extraction mixture, and the above-mentioned extraction. A method for separating 1234yf and HFP, comprising an extraction distillation step of distilling a mixture to obtain a distillate containing HFP as a main component and a canned product containing 1234yf as a main component of the extraction solvent. [Selection diagram] Fig. 1

Description

  The present invention relates to a method for separating 2,3,3,3-tetrafluoropropene and hexafluoropropene from a mixture comprising 2,3,3,3-tetrafluoropropene and hexafluoropropene, and 2,3 from said mixture. , 3,3-tetrafluoropropene relates to a method for producing separately. In the present specification, for halogenated hydrocarbons, the abbreviations of the compounds are shown in parentheses after the compound names. In the present specification, the abbreviations are used in place of the compound names as necessary.

  In recent years, 2,3,3,3-tetrafluoropropene (HFO-1234yf) has been highly expected as a new refrigerant to replace 1,1,1,2-tetrafluoroethane (HFC-134a), which is a greenhouse gas. It has been.

  As a method for producing HFO-1234yf, a method for producing HFO-1234yf from a raw material containing chlorofluorocarbons by a single reaction involving thermal decomposition has been proposed. As such a method, for example, Patent Document 1 presents a method of obtaining HFO-1234yf by thermally decomposing a mixture of chloromethane (R40) and chlorodifluoromethane (R22) in the presence of a heat medium. ing.

  In the reaction involving thermal decomposition, it is known that various compounds are produced as by-products in addition to the target substance HFO-1234yf. According to the study by the present inventors, when HFO-1234yf is produced by the above method, in the obtained reaction product, tetrafluoroethylene (TFE), fluoride other than the target substance HFO-1234yf and unreacted raw materials are included. Many types of by-products such as vinylidene (VdF), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), octafluorocyclobutane (RC318), and trifluoromethane (R23) are included.

  Usually, removal of by-products from the reaction product is carried out by distillation using a difference in boiling point. However, both HFO-1234yf and HFP have a boiling point of −29 ° C. and form an azeotropic composition. The separation of the two by distillation is not easy. That is, when a high-concentration HFO-1234yf is obtained from a mixture containing HFO-1234yf and HFP by an ordinary distillation method, a distillation apparatus having a very large number of stages is required, so that separation by distillation is generally difficult. Met.

Conventionally, an extractive distillation method is known as a method for separating one component from a mixture containing two components having very close boiling points or an azeotropic or azeotrope-like composition composed of two components (for example, patent literature). 2).
However, what kind of extraction solvent can be used from a mixture containing HFO-1234yf and HFP efficiently, for example, in a distillation column with a small number of stages, to separate the two to obtain a high concentration HFO-1234yf. The current situation is not known.

Japanese Patent No. 5201284 Japanese Patent No. 2827912

  The present invention has been made from the above viewpoint, and a method for efficiently separating 1234yf and HFP from a mixture containing HFO-1234yf (hereinafter also referred to as 1234yf) and HFP, and a method for efficiently producing 1234yf thereby. The purpose is to provide.

  The present invention relates to a mixture containing 1234yf and HFP, saturated hydrocarbons having 5 to 12 carbon atoms, aromatic hydrocarbons having 6 to 9 carbon atoms, alcohols, ketones, amides, ethers and esters. An extraction solvent containing at least one selected from nitriles, nitriles, chlorocarbons, hydrochlorocarbons, hydrofluoroethers, and hydrochlorofluorocarbons, and obtaining the extraction mixture, A method for separating 1234yf and HFP, comprising: distilling a mixture to obtain a distillate containing HFP as a main component; and an extractive distillation step for obtaining a bottom product containing the extraction solvent as a main component and containing 1234yf. I will provide a.

  The present invention also provides a method for producing 1234yf, comprising the step of separating 1234yf and HFP by the separation method of the present invention.

  In this specification, “extraction distillation” means a mixture of two components having a very close boiling point and difficult to separate by ordinary distillation, and a relative volatility close to 1, or two components having an azeotropic or azeotrope-like composition. This means a distillation operation that facilitates separation by adding a solvent to the mixture of the above and separating the relative volatility of the original two components from 1. A solvent that separates the relative volatility from 1 in addition to the mixture is referred to as “extraction solvent”. The extraction solvent refers to a liquid that is liquid at normal temperature and pressure, but even if it is a gas at normal temperature and pressure, it can be treated as an extraction solvent if it exists as a liquid under the reaction conditions in the distillation column.

In the present specification, as the relative volatility, the relative volatility of 1234yf and HFP represented by the following formula (hereinafter sometimes referred to as “Rv”) is used.
Rv =
(Mole fraction of 1234yf in the gas phase portion / Mole fraction of HFP in the gas phase portion) / (Mole fraction of 1234yf in the liquid phase portion / Mole fraction of HFP in the liquid phase portion) (I)

  The present inventors have found that if Rv becomes considerably smaller than 1 by adding a solvent, HFP can be easily removed as a distillate component and 1234yf can be easily removed as a bottom component together with a solvent by extractive distillation. I found it.

  In the present specification, the “distillate” means a substance distilled from the top side of the distillation column, and the “bottom” means a substance distilled from the bottom side of the distillation column. .

  In the present specification, the term “main component” means that the amount of components other than the component is relatively small. The amount of “main component” is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol% or more, and most preferably 80 mol% or more.

  According to the present invention, 1234yf and HFP can be efficiently separated from a mixture containing 1234yf and HFP. Further, according to the present invention, a high concentration of 1234yf can be obtained efficiently.

It is a figure which shows the flow of the substance in embodiment of the separation method of this invention.

Embodiments of the present invention will be described below.
The separation method of the embodiment of the present invention includes the following steps (1) and (2).
(1) 1234yf, HFP, saturated hydrocarbons having 5 to 12 carbon atoms, aromatic hydrocarbons having 6 to 9 carbon atoms, alcohols, ketones, amides, ethers, esters, nitriles, Step of obtaining an extraction mixture by mixing at least one extraction solvent selected from chlorocarbons, hydrochlorocarbons, hydrofluoroethers and hydrochlorofluorocarbons (2) Distilling the extraction mixture Extractive distillation step for obtaining a distillate mainly composed of HFP and a bottoms mainly composed of the extraction solvent and containing 1234yf

In the embodiment, the method may further include (3) a step of distilling the bottom product obtained in the extractive distillation step and recovering the extraction solvent (hereinafter also referred to as a “bottom product distillation step”). it can. And it is preferable to reuse the said extraction solvent collect | recovered at the distillation process of the bottoms in the said extractive distillation process.
Hereinafter, each process of the embodiment will be described.

  In the following description, a mixture containing 1234yf and HFP before adding the extraction solvent may be referred to as a mixture A. Although the mixture A is described as a mixture composed of two components, 1234yf and HFP, the mixture A may contain a third component other than 1234yf and HFP. When the mixture includes a third component, the third component is a component that differs in behavior from 1234yf and / or HFP depending on its boiling point and affinity for the extraction solvent. Even when the third component is included, 1234yf and HFP can be efficiently separated by performing the separation method of the embodiment.

<(1) Step of obtaining a mixture for extraction>
In this step, an extraction solvent is added to the mixture A containing 1234yf and HFP to obtain an extraction mixture. Addition of the extraction solvent to the mixture A is not particularly limited as long as it is before distillation (extraction distillation), and the extraction mixture obtained by adding the extraction solvent to the mixture A is supplied to the extraction distillation column. Also good. However, from the viewpoint of the efficiency of the distillation operation, the extraction mixture is prepared in the extractive distillation tower by a method such as supplying the extraction solvent to the extractive distillation tower supplied with the mixture A, and the distillation is performed simultaneously with the preparation. It is preferable to make it.

The mixture A is, for example, a mixture composed of 1234yf and HFP. The composition (molar ratio) of 1234yf and HFP in the mixture A is not particularly limited.
As described above, 1234yf and HFP have the same boiling point, and a mixture of both forms an azeotropic or azeotrope-like composition, so that Rv is close to 1.

Here, the azeotropic composition of 1234yf and HFP is a composition having a “relative volatility Rv between 1234yf and HFP” represented by the formula (I) of 1.00. An azeotropic composition has the advantage that when the composition is repeatedly evaporated and condensed, there is no change in composition, and there is an advantage that performance can be obtained very stably when used in applications such as refrigerants. Cannot be separated by ordinary distillation operations.
The azeotrope-like composition of 1234yf and HFP is a composition in which the relative volatility Rv represented by the formula (I) is in the range of 1.00 ± 0.20.

As a specific example of Rv of the mixture A, Table 1 shows the results of measuring Rv by the following method at a pressure of 1.011 × 10 ⁶ Pa for a plurality of mixtures having different compositions of 1234yf and HFP.
From Table 1, it can be seen that the mixture of 1234yf and HFP has Rv within a range that is not significantly different from 1 in any composition.

(Measurement method of Rv)
A measurement sample is put into a 500 mL autoclave with a pressure gauge, and is gradually heated by an external heater so as to be a predetermined pressure (1.011 × 10 ⁶ Pa). After the pressure reaches a predetermined value, a certain time (2 Time) to stabilize the composition in the autoclave. Next, samples were taken from the gas phase and the liquid phase, respectively, and analyzed by gas chromatography (manufactured by Agilent Technologies, instrument name: 6850) to measure the molar ratio of 1234yf and HFP. And Rv was calculated | required from molar ratio of both.

  The separation method of the embodiment of the present invention is a method of taking out HFP as a distillate component by extractive distillation. By adding the extraction solvent described below, Rv is made considerably smaller than 1, in other words, 1234yf is hardly volatilized, so that 1234yf and HFP are efficiently separated.

The extraction solvent to be added to the mixture A has a high boiling point per se and hardly volatilizes, and has an affinity only for 1234yf out of 1234yf and HFP, and makes 1234yf difficult to volatilize. Is a solvent that makes the value considerably smaller than 1. The extraction solvent is preferably a solvent that makes Rv less than 0.91, and more preferably a solvent that makes Rv less than 0.8.
The difference in Rv depending on the type of extraction solvent will be described later.

The boiling point of the extraction solvent needs to have a large boiling point difference from 1234yf from the viewpoint of efficient distillation / separation in the later-described (3) bottoms distillation step. However, it is preferable that the boiling point of the extraction solvent is not too high from the viewpoint of productivity in the distillation process of (3) bottoms. The boiling point of the extraction solvent is preferably in the range of 40 to 250 ° C. In addition, the boiling point of the substance in this specification shall show the boiling point (standard boiling point) in a normal pressure (1.013 * 10 < ⁵ > Pa) unless there is particular notice.

  Extraction solvents include saturated hydrocarbons having 5 to 12 carbon atoms, aromatic hydrocarbons having 6 to 9 carbon atoms, alcohols, ketones, amides, ethers, esters, nitriles, chlorocarbons, hydrocarbons It contains at least one selected from chlorocarbons, hydrofluoroethers, and hydrochlorofluorocarbons.

  Here, the saturated hydrocarbons are hydrocarbon compounds that do not have an unsaturated bond and do not have a halogen element. The saturated hydrocarbons having 5 to 12 carbon atoms are preferably straight-chain saturated hydrocarbon compounds having 5 to 12 carbon atoms from the viewpoint of efficiently performing distillation and separation in the distillation process of the bottoms described later. A linear saturated hydrocarbon compound of several 6 to 10 is more preferable. Specifically, pentane, hexane, heptane, octane, nonane and decane are preferred, and hexane, heptane, octane, nonane and decane are more preferred.

  As aromatic hydrocarbons having 6 to 9 carbon atoms, from the viewpoint of efficiently performing distillation / separation in the distillation process of the bottom product described later, a straight chain as a substituent having an aromatic ring and bonded to the aromatic ring is used. A compound having a straight or branched saturated hydrocarbon group is preferred. Specifically, benzene, toluene, xylene, and trimethylbenzene are preferable, and toluene is most preferable.

  Alcohols are compounds having at least one alcoholic hydroxyl group. As the alcohols, aliphatic alcohols having 1 to 4 carbon atoms in the main chain are preferable from the viewpoint of efficiently performing distillation and separation in the later-described distillation process of the bottoms. Specific examples include methanol, ethanol, propanol, and butanol.

Ketones are compounds represented by the general formula: R ¹ —C (═O) —R ² (R ¹ and R ² represent the same or different unsubstituted aliphatic hydrocarbon groups). is there. As ketones, from the viewpoint of efficiently performing distillation / separation in the distillation process of the bottom product described later, in the above general formula, R ¹ and R ² each have 1 to ² carbon atoms, and R ¹ and R ² Ketones having 2 to 4 carbon atoms in total are preferred. Specific examples of ketones include acetone, diethyl ketone, and methyl ethyl ketone.

  Examples of amides include chain amides having 3 to 5 carbon atoms or aliphatic cyclic amides. As the amides, tertiary amides in which all of the hydrogen atoms of the amino group are substituted with alkyl groups are preferred from the viewpoint of efficiently performing distillation and separation in the distillation step of the bottom product described later. Specifically, N-methylpyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc) are preferable.

  As ethers, from the viewpoint of efficiently performing distillation and separation in the bottoms distillation process described later, a chain ether having 2 to 4 carbon atoms in which two hydrocarbon groups are bonded to an oxygen atom, and a ring. Examples of the constituent atoms include cyclic ethers having an oxygen atom. Cyclic ethers having 3 to 4 carbon atoms are preferred. Specific examples include dimethyl ether, diethyl ether, ethyl methyl ether, tetrahydrofuran, and 1,3-dioxolane, with 1,3-dioxolane being preferred.

  Examples of the esters include chain esters or aliphatic cyclic esters having 3 to 6 carbon atoms from the viewpoint of efficiently performing distillation / separation in the distillation process of the bottoms described later, and those having 4 to 6 carbon atoms. Cyclic esters are preferred. Specifically, γ-butyrolactone is preferable.

Nitriles are compounds represented by the general formula: R ³ —CN (R ³ represents an unsubstituted aliphatic hydrocarbon group). As the nitriles, nitriles having 1 to 5 carbon atoms in R ³ in the above general formula are preferable from the viewpoint of efficiently performing distillation and separation in the distillation step of the bottoms described later. Specifically, acetonitrile is preferable.

  Chlorocarbons are compounds in which the atoms constituting the molecule are carbon and chlorine. Specific examples of chlorocarbons include carbon tetrachloride and tetrachloroethylene from the viewpoint of efficiently performing distillation / separation in the distillation process of the bottoms described later.

  Hydrochlorocarbons are compounds in which the atoms constituting the molecule are carbon, chlorine and hydrogen. Specific examples of hydrochlorocarbons include dichloromethane, chloroform, and dichloropropane from the viewpoint of efficiently performing distillation and separation in the distillation process of the bottoms described later.

As hydrofluoroethers, from the viewpoint of efficiently performing distillation / separation in the later-described distillation process of the bottoms, the general formula: R ^f1 —O—R ^f2 (R ^f1 and R ^f2 are the same or different carbons from each other). indicates the number 1-3 fluoroalkyl group. fluoroalkyl group may be a perfluoroalkyl group. provided ^that at least one of ^{R f1} and ^{R f2} have the hydrogen ^atom, the number of carbon atoms of ^{R f1} and ^{R f2} Is preferably 2 to 4.) is preferable. Specifically, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (asa commercially available product, Asahi Clin AE-3000 (trade name, manufactured by Asahi Glass Co., Ltd.)) can be mentioned. it can.

Hydrochlorofluorocarbons are compounds in which the atoms constituting the molecule are carbon, fluorine, chlorine and hydrogen. As hydrochlorofluorocarbons, from the viewpoint of efficiently performing distillation and separation in the distillation process of the bottom product described later, specifically, 1,3-dichloro-1,1,2,2,3-pentafluoropropane ( As a commercially available product, Asahi Clin AK225cb (trade name, manufactured by Asahi Glass Co., Ltd.) can be mentioned.
From the viewpoint of efficiently performing distillation / separation in the after-product distillation step described later, the extraction solvent is pentane, hexane, heptane, octane, nonane, decane, benzene, toluene, xylene, trimethylbenzene, methanol, ethanol, propanol. , Butanol, acetone, methyl ethyl ketone, diethyl ketone, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, 1,3-dioxolane, γ-butyllactone, acetonitrile, carbon tetrachloride, tetrachloroethylene, dichloromethane, chloroform, dichloropropane, 1,1 , 2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, preferably containing at least one selected from the group consisting of dichloropentafluoropropane.

As a specific example of the Rv value when the extraction solvent is added to the mixture A, the extraction solvent is added to the 3: 1 (molar ratio) mixture of 1234yf and HFP, and the solvent: 1234yf: HFP = 60: 30: 10 (molar ratio). The values of Rv when added so as to be) are shown in Table 2 together with the boiling point of the solvent. Rv was measured by the same method as described above under the same pressure of 1.011 × 10 ⁶ Pa.

For comparison, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane (a commercially available product of Asahi) Table 2 shows the Rv measured under the same conditions for Klin AC-2000 (trade name, manufactured by Asahi Glass Co., Ltd.).
In addition, as shown in Table 1, Rv of a 3: 1 (molar ratio) mixture of 1234yf and HFP is 0.924.

  As can be seen from Table 2, any solvent other than AC-2000 specifically listed above is a solvent that makes Rv smaller than 0.91. By adding these solvents to a mixture of 1234yf and HFP, the vapor-liquid equilibrium of 1234yf and HFP was changed, and Rv was less than 0.91. Therefore, by using these solvents as extraction solvents, 1234yf and HFP can be separated by making it difficult to volatilize 1234yf. Specifically, high concentration HFP can be obtained as a distillate.

  When AC-2000 is used as the solvent, Rv does not become 0.91 or less. Addition of such a solvent hardly changes the vapor-liquid equilibrium between 1234yf and HFP, and the effect of adding the solvent cannot be obtained.

  From the viewpoint of efficiently separating 1234yf and HFP by extractive distillation, the addition amount of the extraction solvent (hereinafter also referred to as extraction solvent ratio) is 0.1 / 1 to 1000/1000 in terms of the molar ratio of the extraction solvent to 1234yf. 1 is preferable, 1/1 to 100/1 is more preferable, and 1.5 / 1 to 50/1 is further preferable. By setting it within this range, Rv in the extraction mixture can be made smaller than 0.91, and 1234yf and HFP can be efficiently separated.

When methanol is used as the extraction solvent, the influence of the extraction solvent ratio on Rv is as shown in Table 3.
Extraction solvent ratio = Mole fraction of extraction solvent / 1mol fraction of 1234yf

  From Table 3, it can be seen that when methanol is used as the extraction solvent, the relative volatility Rv of 1234yf and HFP is smaller than 0.91 in a wide range of the extraction solvent ratio of 2-11.

  In the following extractive distillation, the ratio of the extraction solvent affects the degree of separation. Therefore, the composition of the mixture A to be extracted and distilled (molar ratio of 1234yf / HFP) and one of the separated components are allowed to remain. The extraction solvent ratio can be appropriately selected according to the concentration of the other component. It is also possible to select the required number of extractive distillation columns in relation to the extraction solvent ratio.

<(2) Extractive distillation step>
In this step, the extraction mixture obtained in the step (1) is distilled. This distillation is extractive distillation. The extraction solvent used in the embodiment is such that Rv when a solvent is added to a mixture of 1234yf and HFP is a value considerably smaller than 1 (for example, less than 0.91). Therefore, by distillation of the extraction mixture, a distillate containing HFP as a main component is obtained from the top of the distillation column, and a bottom containing 1234yf is obtained from the bottom of the column.

  In the following description, the distillate obtained from the top side of the distillation column in the extractive distillation step is referred to as the first distillate, and the bottom product obtained from the bottom side of the distillation column is referred to as the first distillate. Shown as canned food. In addition, a distillate obtained from the top of the distillation column in the distillation step of the bottom product (first bottom product) is indicated as a second distillate, and the distillation column of the bottom product is shown in the distillation step of the bottom product. The bottom product obtained from the tower bottom side is referred to as a second bottom product.

  In an embodiment, the extractive distillation can be performed using a commonly used distillation apparatus such as a plate column or a packed column. Various conditions for extractive distillation, such as operating temperature, operating pressure, reflux ratio, the total number of distillation columns, the position of the charging stage, the position of the extraction solvent supply stage, etc. are not particularly limited, and are intended separations. Can be selected as appropriate to achieve the above. Since both 1234yf and HFP have a low boiling point, the pressure is preferably 0 to 5 MPaG (gauge pressure), and extractive distillation is preferably performed under pressure.

  Furthermore, the temperature at the top and bottom of the distillation column depends on the operating pressure and the composition of the distillate (first distillate) and bottoms (first bottoms). In consideration of the temperature of the condenser and reheater provided at the top and bottom of the column, in order to carry out the distillation operation economically, the temperature at the top of the column is -60 to 100 ° C., and the temperature at the bottom of the column is 50 to 200 ° C. is preferable. Extractive distillation can be carried out either batchwise or continuously, or in some cases, semi-continuous where distillate and bottoms are withdrawn intermittently or charged intermittently. Need to supply.

  The extraction solvent having affinity with 1234yf makes Rv smaller than 0.91, as represented by the solvents shown in Table 2. Therefore, by performing extractive distillation of the extraction mixture containing 1234yf, HFP, and the extraction solvent, a mixture containing HFP as a main component as the first distillate is obtained from the top of the extractive distillation column. The composition of the first distillate is not limited as long as it contains HFP as a main component, but the molar fraction of HFP is preferably 90% (90 mol%) or more, preferably 99 mol% or more. More preferably.

  Moreover, the 1st bottom product containing 1234yf which has an extraction solvent as a main component and has affinity with this extraction solvent is obtained from the tower bottom side of an extractive distillation tower. This first bottom product contains HFP, but the molar fraction of HFP relative to the sum of 1234yf and HFP is greatly reduced compared to the molar fraction in mixture A. The molar fraction of HFP with respect to the sum of 1234yf and HFP in the first bottom product is preferably reduced to 1/10 or less of the molar fraction in the mixture A. Thus, HFP is separated by extractive distillation and contained in the first distillate at a very high concentration. It is preferable that the first bottom product is further sent to a distillation step and distilled (re-distilled).

<(3) Distillation process of bottoms>
In this step, the first bottom product obtained in the extractive distillation step is distilled (re-distilled). Since the extraction solvent contained in the first bottom product and its affinity component 1234yf have a large difference in boiling point, this distillation can be easily carried out by a normal distillation separation operation. The extraction solvent and 1234yf are separated by distillation of the first bottom product. And a second distillate containing 1234yf and having a mole fraction of 1234yf relative to the sum of 1234yf and HFP increased relative to the mole fraction in mixture A, i.e., 1234yf is enriched compared to mixture A. Obtained from the top of the distillation column.

  Since the first bottom product contains HFP together with 1234yf, the second distillate obtained by distilling the first bottom product includes HFP. In the distillate, since the mole fraction of 1234yf is larger than that of the mixture A as described above, the mole fraction of HFP in the second distillate is considerably smaller than that of the mixture A. Therefore, high concentration 1234yf can be obtained as the second distillate.

  Furthermore, in the redistillation step, a second bottom product containing the extraction solvent at a very high concentration is obtained from the bottom side of the distillation column. The obtained second bottom product can be directly supplied to the extractive distillation step and reused as an extraction solvent. Further, the second bottom product can be further purified to recover the extraction solvent and reused in the extractive distillation step.

  Thus, according to the embodiment of the present invention, 1234yf and HFP in the mixture A are efficiently separated, and HFP is obtained at a high concentration as the main component of the first distillate in the extractive distillation step. Moreover, 1234yf concentrated from the mixture A can be obtained as the second distillate in the redistillation step.

  Next, the substance flow in the method for separating 1234yf and HFP of the present invention will be further described with reference to FIG.

  As shown in FIG. 1, a mixture 1 containing 1234yf and HFP at a predetermined ratio (for example, 1234yf / HFP = 75 mol% / 25 mol%) is supplied to an extractive distillation column 2 operated, for example, under pressure. . As the extractive distillation tower 2, one having 1 to 100 stages is used, and the mixture 1 is supplied to a stage below the central part of the extractive distillation tower 2. Then, the extraction solvent 3 (for example, methanol) having a molar fraction of 0.1 to 1000 times the molar fraction of 1234yf in the mixture 1 is supplied to the stage above the supply stage of the mixture 1 in the extractive distillation column 2. To do. Distillation is performed in this manner, and the first distillate 4 containing HFP, which is a component having no affinity for the extraction solvent 3, as the main component is extracted from the top of the extractive distillation column 2.

Further, from the bottom side of the extractive distillation column 2, as the first bottom product 5, a mixture containing the extraction solvent as a main component and containing 1234yf is extracted. Next, the first bottom product 5 is supplied to a solvent recovery column 6 which is another distillation column operated, for example, under pressure, and a second distillate 7 substantially free of extraction solvent is added to the column. Get from the top. In the second distillate 7 obtained, the mole fraction of 1234yf relative to the sum of 1234yf and HFP is increased compared to a similar mole fraction in mixture 1. In this way, as the second distillate 7, a mixture in which the molar fraction of 1234yf is increased as compared to the mixture 1, that is, a mixture in which the molar concentration of 1234yf is concentrated is obtained.
In the present specification, the term “substantially does not contain A” means that the A content is 0.1 mol% or less.

From the tower bottom side of the solvent recovery tower 6, a second product 8 having an extraction solvent as a main component is obtained. The extraction solvent is recovered in this way, and the recovered extraction solvent 3 is reused. The extraction solvent 3 to be reused is supplied to the extractive distillation column 1 after being heated or cooled by the heat exchanger 9 as necessary.
In addition, in FIG. 1, the code | symbol 10 shows a condenser and the code | symbol 11 shows a heater.

As described above, the position (stage) for supplying the extraction solvent 3 in the extractive distillation column 2 is preferably a stage located above the stage for supplying the mixture 1 and is extracted to the same stage as the stage for supplying reflux. The solvent 3 may be supplied. In some cases, the extraction solvent 3 may be supplied to the same stage as the mixture 1. Further, the mixture 1 may be supplied after being previously mixed with the extraction solvent 3 before being supplied to the extractive distillation column 2.
By such an apparatus and operation, 1234yf and HFP can be separated from the mixture 1 containing 1234yf and HFP, and 1234yf substantially free of HFP can be obtained.

  Using the results shown in Tables 2 to 3 obtained by measuring the relative volatility (Rv) of 1234yf and HFP described above, a calculation method based on a known thermodynamic property (Chemcad; Chemstations Chemical Engineering Process Simulator) The following extractive distillation and redistillation simulations were performed.

  The simulations of Examples 1 to 12 were conducted using extraction solvents with Rv of less than 0.91 in the ternary system to which the solvent was added. Moreover, the simulation of the comparative example 1 which distills the mixture of 1234yf and HFP without adding an extraction solvent, and the comparative example 2 which uses AC-2000 which is a solvent close to 1 with Rv 0.91 or more in a ternary system Each simulation was performed.

Example 1
From the 85th stage from the top of the 90-stage extractive distillation tower, a mixture of 1234yf and HFP (molar ratio 4: 1) is continuously fed at a rate of 606 g / hr, and from the 5th stage from the top, Methanol was continuously fed at a rate of 1281 g / hr. Then, the extractive distillation was continuously performed by setting the pressure in the extractive distillation tower to 0.2 MPaG (gauge pressure), the tower top temperature to −0.8 ° C., and the tower bottom temperature to 3.7 ° C. The first fraction as the first distillate was extracted from the column top side at a rate of 151 g / hr, and the second fraction as the first bottom product was extracted from the column bottom side at a rate of 1737 g / hr.

The composition of each of the extracted first and second fractions was analyzed. In the first fraction, HFP was 99 mol%, the extraction solvent was not detected, and the remainder was 1234yf.
On the other hand, 1234yf in the second fraction was 9.1 mol%, HFP was not detected, and the remainder was occupied by methanol as the extraction solvent.

  Next, the second fraction obtained from the extractive distillation tower is continuously supplied from the top of the 12th stage of the solvent recovery tower from the 7th stage at the same speed as the extraction speed of the second fraction. Distillation was continuously performed at a pressure of 0.2 MPaG, a tower top temperature of −0.7 ° C., and a tower bottom temperature of 94.6 ° C. The third fraction as the second distillate is withdrawn from the top of the solvent recovery tower at a rate of 455 g / hr, and the fourth fraction as the second bottom is taken out at a rate of 1282 g / hr from the bottom of the tower. Extracted.

  When the composition was analyzed for each of the extracted third fraction and fourth fraction, HFP was not detected in the third fraction, and 1234yf was 100.0 mol%. On the other hand, methanol in the fourth fraction was 100.0 mol%.

Examples 2-10
The simulation was carried out by changing the type of extraction solvent from Example 1. Specifically, the extraction solvent shown in Table 4 was used, and the molar ratio of 1234yf and HFP (shown as “1234yf / HFP” in Table 4. The same applies hereinafter), a mixture of 1234yf and HFP (mixed gas) ) Supply amount per hour (A), supply amount of extraction solvent per hour (B), molar ratio of extraction solvent to 1234yf (shown as “solvent / 1234yf” in Table 4, and so on). The molar ratio of the extraction solvent to HFP (shown as “solvent / HFP” in Table 4. The same applies hereinafter) and each condition were set as shown in Table 4, and the others were the same as in Example 1. Simulations of extractive distillation and redistillation were performed.

  And the result of having analyzed the composition of each 1st-4th fraction is shown in Table 4 with the result about the said Example 1. FIG. In this simulation, both the pressure in the extractive distillation column and the pressure in the solvent recovery column were set to 0.2 MPaG. These pressures were the same for the following Examples 11 to 12 and Comparative Examples 1 and 2.

Examples 11-12
As the extraction solvent, the same toluene as in Example 5 was used, and the simulation was performed by changing mainly the molar ratio of the extraction solvent to the affinity component.
Specifically, the extraction solvent shown in Table 5 was used, and the molar ratio of 1234yf and HFP (1234yf / HFP), the supply amount (A) of the mixture of 1234yf and HFP per hour, and the extraction solvent per hour Example 5: Supply amount (B), molar ratio of extraction solvent to 1234yf (solvent / 1234yf), molar ratio of extraction solvent to HFP (solvent / HFP), and conditions were set as shown in Table 5. Similarly, extraction distillation and redistillation were simulated. The results of analyzing the composition of each of the first to fourth fractions are shown in Table 5 together with that of Example 5.

Comparative Example 1
From the 85th stage from the top of the 90-stage distillation tower, a mixture of 1234yf and HFP (molar ratio 4: 1) was continuously fed at a rate of 606 g / h to carry out distillation, and the first fraction was taken from the top of the tower every hour. It extracted continuously at 307g, and the 2nd fraction was continuously extracted from the tower bottom side at 299g / h. During this time, the pressure in the distillation column was 0.2 MPaG, the column top temperature was -1.2 ° C, and the column bottom temperature was -1.1 ° C.

  Table 6 shows the results of analyzing the composition of each of the extracted first and second fractions. In the first fraction, 1234yf was 76 mol% and HFP was 24 mol%. On the other hand, 1234yf in the second fraction was 84 mol% and HFP was 16 mol%.

Comparative Example 2
From the 85th stage from the top of the 90-stage extractive distillation tower, a mixture of 1234yf and HFP (molar ratio 4: 1) is continuously fed at a rate of 606 g / hr, and from the 5th stage from the top of the tower. AC2000 was continuously fed at a rate of 12802 g / hr. Then, extractive distillation was continuously performed with the pressure in the extractive distillation column being 0.2 MPaG (gauge pressure), the tower top temperature being −1.5 ° C., and the tower bottom temperature being 47.3 ° C. The first fraction as the first distillate was extracted from the tower top side at a rate of 348 g / hr, and the second fraction as the first bottom product was extracted from the tower bottom side at a rate of 13060 g / hr.

The composition of each of the extracted first and second fractions was analyzed. In the first fraction, HFP was 23.2 mol%, the extraction solvent was 2.6 mol%, and the remainder was 1234yf.
On the other hand, 1234yf in the second fraction was 4.7 mol%, HFP was 0.9 mol%, and the balance was occupied by AC2000 as the extraction solvent.

  Next, the second fraction obtained from the extractive distillation tower is continuously fed from the top of the tenth stage of the solvent recovery tower from the sixth stage at the same speed as the extraction speed of the second fraction. Distillation was continuously performed at a pressure of 0.2 MPaG (gauge pressure), a column top temperature of -1.1 ° C, and a column bottom temperature of 106.9 ° C. The third fraction, which is the second distillate, is extracted from the top of the solvent recovery tower at a rate of 280 g / hr, and the fourth fraction, which is the second product, is extracted from the bottom of the tower at a rate of 12,780 g / hr. Extracted.

  Table 6 shows the results of analyzing the composition of each of the extracted third fraction and fourth fraction.

  From the results shown in Tables 4 to 5, in Examples 1 to 12 using the extraction solvent in which the Rv in the ternary system to which the extraction solvent is added is less than 0.91, all of them are 1234yf from the mixture of 1234yf and HFP. It can be seen that HFP and HFP can be efficiently separated, and a high concentration of 1234yf can be obtained.

  According to the present invention, 1234yf and HFP can be efficiently separated from a mixture containing 1234yf and HFP. In addition, according to the present invention, 1234yf useful as a refrigerant can be obtained at a high concentration because it has little influence on the ozone layer and has a low global warming potential.

  DESCRIPTION OF SYMBOLS 1 ... Mixture, 2 ... Extractive distillation tower, 3 ... Extraction solvent, 4 ... 1st distillate, 5 ... 1st bottom product, 6 ... Solvent recovery tower, 7 ... 2nd distillate, 8 ... 2nd canned goods.

Claims (8)

A mixture containing 2,3,3,3-tetrafluoropropene and hexafluoropropene, saturated hydrocarbons having 5 to 12 carbon atoms, aromatic hydrocarbons having 6 to 9 carbon atoms, alcohols, and ketones An extraction solvent containing at least one selected from amides, ethers, esters, nitriles, chlorocarbons, hydrochlorocarbons, hydrofluoroethers, and hydrochlorofluorocarbons Obtaining
The extractive distillation is obtained by distilling the extraction mixture to obtain a distillate containing hexafluoropropene as a main component and a distillate containing the extraction solvent as a main component and containing 2,3,3,3-tetrafluoropropene. And a process for separating 2,3,3,3-tetrafluoropropene and hexafluoropropene.   The method for separating 2,3,3,3-tetrafluoropropene and hexafluoropropene according to claim 1, wherein the extraction solvent has a boiling point of 40 to 250C.   The said extraction solvent is a solvent which makes the relative volatility of 2,3,3,3-tetrafluoropropene and hexafluoropropene smaller than 0.91, The 2,3,3 of Claim 1 or 2 A method for separating 3-tetrafluoropropene and hexafluoropropene.   The extraction solvent is pentane, hexane, heptane, octane, nonane, decane, benzene, toluene, xylene, trimethylbenzene, methanol, ethanol, propanol, butanol, acetone, methyl ethyl ketone, diethyl ketone, dimethylformamide, dimethylacetamide, N-methyl. Pyrrolidone, 1,3-dioxolane, γ-butyllactone, acetonitrile, carbon tetrachloride, tetrachloroethylene, dichloromethane, chloroform, dichloropropane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether The 2,3,3,3-tetrafluoropropene and hexafluoropropyl according to any one of claims 1 to 3, which is at least one selected from the group consisting of dichloropentafluoropropane and Pen method of separation.   The said extraction solvent is added in the range of 0.1 / 1-1000 / 1 by the molar ratio with respect to 2,3,3,3- tetrafluoro propene, 2,3 as described in any one of Claims 1-4. , 3,3-tetrafluoropropene and hexafluoropropene separation method.   The method for separating 2,3,3,3-tetrafluoropropene and hexafluoropropene according to any one of claims 1 to 5, wherein the extractive distillation step is performed under a pressure of 0 to 5 MPaG (gauge pressure).   The process according to any one of claims 1 to 6, further comprising a step of recovering the extraction solvent by distilling the bottom product, and reusing the recovered extraction solvent in the extraction distillation step. A method for separating 3,3,3-tetrafluoropropene and hexafluoropropene.   It has the process of isolate | separating 2,3,3,3- tetrafluoro propene and hexafluoro propene by the separation method as described in any one of Claims 1-7, 2, 3, 3, 3 characterized by the above-mentioned. -Method for producing tetrafluoropropene.

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