FIELD OF INVENTION

The invention relates to the separation of a mixture comprising 2-chloro-1, 1-difluoroethane (R142) and trans-dichloroethylene (TDCE) by extractive distillation, and more particularly to a separation process wherein the TDCE is selectively removed by extractive distillation, thus leading to 2-chloro-1, 1-difluoroethane purified.

TECHNICAL BACKGROUND

2-chloro-1, 1-difluoroethane (HCFC-142 or R142) is used as blowing agent in the manufacture of foams, or as a raw material in the manufacture of pharmaceuticals or agrochemicals.

2-chloro-1, 1-difluoroethane can be obtained by fluorination of 1, 1, 2-trichloroethane (T 1 12). This fluorination reaction generates a byproduct, trans-dichloroethylene (TDCE) in significant quantities. To ensure a satisfactory purity of the final product, it should eliminate the TDCE as completely as possible of the mixture obtained at the end of reaction.

WO 2013/053800 discloses a method of catalytic fluorination of 1, 1, 2-trichloroethane and / or 1, 2-dichloro-ethene in the presence of HF to obtain 1-chloro-2,2-difluoroethane. This document describes a step in which the 1, 2-dichloro-ethene and 1, 1, 2-trichloroethane are separated from 1-chloro-2,2-difluoroethane by distillation. This document does not describe the method according to the invention comprising an extractive distillation step.

The existence of an azeotrope or azeotrope-R142 / TDCE makes it difficult to complete separation of R142 and TDCE by simple distillation.

SUMMARY OF THE INVENTION

The invention relates firstly to a process for separating a mixture comprising 2-chloro-1, 1-difluoroethane and trans-dichloroethylene by extractive distillation.

The method of the invention is simple to implement, especially on an industrial scale.

The method according to the invention allows to get the 2-chloro-1, 1-difluoroethane with greater purity. Purities greater than or equal to 95%, or even greater than or equal to 98%, more preferably greater than or equal to 99% can thus be obtained.

According to one embodiment, it is implementing an extraction agent that selectively absorbs TDCE.

In another embodiment, one implements an extraction agent that selectively absorbs the R142.

In yet another embodiment, the method of the invention uses the T1 12, the starting reactant in the production of R142, as extractant, which is optimal from the industrial point of view. Indeed, using the T1 12, it is not necessary to subsequently separate the T1 12 of TDCE because mixing T1 12-impurities can be reused as such in the R142 in the manufacturing process.

The method according to the invention has a selectivity and / or a satisfactory capacity for the recovery of the desired species.

BRIEF DESCRIPTION OF THE FIGURE

Figure 1 is a diagram showing an embodiment of the invention.

EMBODIMENTS DESCRIPTION OF THE INVENTION

The invention is now described in more detail and not limited to the following description.

The present invention provides a method for separating a mixture comprising R142 (CHF 2 -CH 2 CI) and TDCE (CHCl = CHCl) by extractive distillation.

The extractive distillation is carried out using an extracting agent, also called extractant or solvent, which has a strong affinity with one of the two compounds in the mixture.

The principle of extractive distillation is well known to the skilled artisan.

In an extractive distillation process, the separation of the components of a binary mixture is done using a so-called extraction column (Column I) comprising successively, from the boiler to the head, three sections, one of exhaustion, the second and third absorption recovery.

The binary mixture to be fractionated is injected at the top of the exhaustion portion (stream 1), while the third body acting as a selective solvent or extraction agent is introduced at the top of the absorption section (flow 2) to circulate in the liquid state to its point of introduction to the boiler.

The third section of said recovery serves to separate by distillation constituting the less absorbed (stream 3), traces of solvent entrained under the effect of its non-zero vapor pressure.

A solvent regeneration column (column II) can separate the solvent / absorbed component (stream 5) according to their difference in boiling point. The recovered solvent (stream 7) can be reused for the extraction in column I (flow 8).

The diameter and the number of stages of the extractive distillation column, the reflux ratio and optimum temperatures and pressures can be readily calculated by those skilled in the art from data specific to the individual components and their mixtures (relative volatilities , vapor pressure and physical constants).

According to one embodiment of the invention, the distillation is carried out under a pressure ranging from 0.005 bar to 10 bar, preferably 0.3 bar to 4 bar.

The distillation can be carried out at a temperature ranging from -50 ° C to 250 ° C, preferably from -20 ° C to 185 ° C, and more preferably from 5 ° C to 145 ° C.

According to one embodiment of the invention, the extractive distillation is carried out using a molar ratio extractant / product to be disposed of from 0.01 to 20, preferably from 0.1 to 10, and more preferably 0, 5 to 10.

The mixture to be separated comprises at least 2-chloro-1, 1-difluoroethane and TDCE. As indicated above, the mixture comprising R142 and TDCE can be obtained after a reaction of fluorination of 12 T1 (CHCI2-CH2Cl).

According to one embodiment, the molar ratio R142 / TDCE in the mixture before extractive distillation is 2 to 100, preferably from 2 to 50, more preferably from 3 to 30.

According to one embodiment, the molar ratio R142 / TDCE after extractive distillation going from 9 to 99 999, preferably from 20 to 9999, more preferably from 40 to 9999.

Depending on the choice of the extractant, said extractant can selectively absorb either the R142 or the TDCE.

According to a first embodiment, the extractant selectively absorbs TDCE.

In this first embodiment, then the extractant preferably has a separation factor F to 25 ° C, as defined below, greater than 1, 1, preferably greater than 1, 4, preferably preferably greater than 2.

The separation factor (F) is defined as follows:

P _ 7(R142) P(R142)

7 (TDCE) P(TDCE)

where Y (R142) is the activity coefficient of R142 compound in the solvent considered at infinite dilution.

Y (TDCE) represents the coefficient of activity of TDCE compound in the solvent considered at infinite dilution.

P (R142) represents the vapor pressure of R142 compound at the temperature considered.

P (TDCE) represents the vapor pressure of the compound TDCE at the temperature considered.

The P ratio (R142) / P (TDCE) corresponds to the relative volatility of R142 with respect to TDCE.

The activity coefficient values ​​of the compounds i (i is R142 or TDCE), Y ,, are calculated according to the equation:

^Yj = (^ - ^)IRT ,

where μ) corresponds to the chemical potential of compound i at infinite dilution in the solvent considered, and μ } ρ is the chemical potential of the pure compound i, and R is the gas constant, and T is temperature.

The activity coefficient and the vapor pressure data are well known and accessible to the skilled person.

In a second embodiment, the extractant selectively absorbs R142. In this case, when the extraction agent has a separation factor, as defined above, less than 1, preferably less than 0.9, more preferably less than 0.7, and still more preferably less 0.5.

According to this second embodiment and with reference to Figure 1, stream 1 comprising mixing R142 / TDCE to be separated is introduced in Column I of distillation and stream 2 comprising the extractant is introduced in Column I via a different input. According to this embodiment, the flux 3 predominantly comprises TDCE and flow 4 predominantly comprises R142 and the extractant. In order to recover the purified R142, the flux 4 is sent to a distillation column II wherein a stream 5 comprising R142 and the extractant is separated to obtain a stream 6 comprising predominantly the R142 and a stream 7 mainly comprising the extractant. Stream 7 can then be reintroduced into the column I for the extractive distillation.

According to one embodiment, the method according to the invention is implemented using an extractant which is selected:

from compounds having a boiling point above 35 ° C, preferably greater than or equal to 50 ° C, more preferably greater than or equal to 60 ° C, and / or

- from the compounds having a dipole moment lower or equal to 5 Debye, preferably less than or equal to 4.5 Debye, more preferably less than or equal to 4 Debye, preferably less than or equal to 3 Debye, more preferably less than or equal to

2 Debye.

The dipole moment is a well known grandeur of the art. The electric dipole moment illustrates the heterogeneity of the molecules, and reflects the fact that the center of gravity of the positive charge of a molecule does not coincide with the centroid of negative charges of the molecule. The dipole moment is usually expressed in Debye unit (1 Debye = 3.33 10 "30 Cm), and there are tabulated databases for accessing dipole moments of many molecules. In the absence of known value available it can also be measured using standard protocols well known to those skilled in the art, including those based on the correlation between the dielectric constants of the media and dipole moments. for all practical purposes, the details of such protocols will given below.

According to one embodiment, the extractant can be chosen from linear hydrocarbons, branched or unbranched, cyclic or aromatic, saturated or unsaturated, optionally substituted.

Preferably, the hydrocarbon is substituted in which case the substituent or substituents is / are selected (s) from a nitrogen atom, an oxygen atom, a halogen atom, an alcohol function or an amine function and preferably the hydrocarbon is substituted by at least one halogen atom, preferably by at least one chlorine atom.

Preferably, the hydrocarbons have from 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms.

According to one embodiment, the extractant is chosen from linear hydrocarbons, branched or unbranched, cyclic or aromatic containing from 6 to 8 carbon atoms, such as hexane, cyclohexane, methylcyclohexane, n heptane, octane, 2-methylpentane or toluene.

According to one embodiment, the extractant is chosen from linear hydrocarbons, branched or unbranched, cyclic or aromatic substituted with at least one oxygen atom. According to this embodiment, the extractant may be an alcohol such as 1-butanol or 1 -décanol.

According to one embodiment, the extractant is chosen from linear hydrocarbons, branched or unbranched, cyclic or aromatic substituted with at least one nitrogen atom. According to this embodiment, the extracting agent can be an amine, such as N-ethyl-2-dimethylaminoethylamine.

According to another embodiment, the extractant is selected from halogenated hydrocarbons comprising from 2 to 4 carbon halogen. Among halogenated hydrocarbons which can be used include carbon tetrachloride, 1, 1, 2-trichloroethane, 1, 1, 1 trichloroethane, tetrachloroethene, 1, 1, 2,2-tetrachloroethane, 1, 1, 1, 2-tetrachloroethane, trichlorethylene, tribromomethane or triiodométhane.

According to an embodiment, the extracting agent is 1, 1, 2-trichloroethane (T 1 12). Preferably, the T1 R142 12 comes from the manufacturing process. The method according to the invention can use the T1 12 as the extractant is of major economic interest because TT12 selectively extracted TDCE. With reference to Figure 1, it is not necessary in this embodiment to separate the T1 12 comprising TDCE in a second distillation column II, the flux comprising 12 T1 and TDCE can be used as such in the synthesis of R142.

EXAMPLES

Various solvents were evaluated. The characteristics of these solvents are shown in Table 1.

Table 1: Solvent Features

Selectivity, capacity and the separation factor for the various solvents were determined and are shown in Table 2 below.

The selectivity corresponds to the ratio of the infinite dilution activity coefficients of R142 (γ142) and TDCE (yTDCE) in the solvent for the same partial pressure and at the same temperature.

The capacity represents the inverse of infinite dilution activity coefficient of component i in the j considered solvent.

The separation factor F represents the corrected selectivity relative volatility, as already defined above.

p _ 7(R142) P(R142)

7(TDCE) P(TDCE)

Table 2: Parameters of the separation

Table 2 shows that the 1, 1, 2-trichloroethane (T 1 12) has a separation factor of greater than 2. When the mixture R142 / TDCE comes from a fluorination reaction Q1 12, a distillation separation method extractive using the T1 12 as the extractant is very optimal from an industrial point of view.

Table 2 also shows that tetrachloroethene has excellent separation factor.

Protocol for determining the dipole moments:

Unlike the dielectric constant which is a global property of the medium, the dipole moment is a property of the molecule. But these two characteristics are related. The experimental determination of the dielectric constant, also called relative permittivity enables a relatively simple experimental determination of the dipole moment. The dipole moment of a substance can be determined from the constants of the pure product in the liquid state, or solutions (nonpolar solvents) comprising the product to be characterized. It can also be calculated by additive bonding moments.

Different experimental techniques, more or less complex can be used. Among different approaches are used in general dependence of the dielectric constant of a solution with the dipole moment of the molecules. The dielectric constant is measured relatively easily by measuring the electrical capacitance of a tank containing the solution to be examined (in fact, the capacity is proportional to the dielectric constant and the constant of proportionality depends only on the geometry of the cell used for the measurement).

The test thus consists in measuring first the vacuum capacity of the measuring cell, Co, and then measuring the ability of the full cell C, leading to the determination of the relative permittivity s r = C / Co .

Devices like the IRLAB may agree to such measures, but any other meter can accurately measure the electrical capacity is suitable.

To determine the dipole moment, it is also necessary to determine the refractive index of the product. For this, a refractometer is used.

Determination of the dipole moment from the constants of the pure product in the liquid state

Several theories have been developed to try to connect the dipole moment and dielectric constant of a pure product in the liquid state. Among the latter, we used the Onsager theory leads to the following equation:

In this formula, the different constants have the following meanings:

μ 0 : permanent dipole moment of the molecule.

ε 0 : permittivity of vacuum, equal to 8,85.10 "12 J " 1 .C2.m "1

k: Boltzmann's constant, equal to 1, 38. 10 "23 JK " 1 . mole "1

T is the absolute temperature in Kelvin.

N: Avogadro's number, equal to 6.0238. 10 23 mole "1

M: Molecular weight of the substance in kilograms

p: Density of the substance at the temperature T

ε: dielectric constant of the substance at the temperature T

"Optical dielectric constant"

"Optical dielectric constant" ε kappa can be confused with the square of the refractive index of the substance to the D line of sodium.

This theory assumes that polar molecules are spherical. It reflects the strong molecular interactions from permanent dipoles and introduces, to reflect this, the "reaction field of a dipole." However this theory becomes invalid lorsqu'interviennent interactions oriented to short-range as is the case for substances of intermolecular hydrogen bonds.

2 Determination of the dipole moment from solutions

In the case of the diluted solution of a polar compound in a nonpolar solvent, can be neglected molecular interactions. This will apply to the solutions of the equation Debye.

The polarization of a solution may be considered in first approximation as a linear function of its concentration.

These data were analyzed by GUGGENHEIM SMITH and to calculate the dipole moment of the solute as a function of variations in the dielectric constant and refractive index of the solution with the concentration.

We have the following formula:

In this μο formula εο, K, T, N and M have the same meaning as in formula Onsager (see above).

Pi = density of the solvent

μι: dielectric constant of the solvent

has S : slope of the line εΐ2 - ει = f (x)

a n : Gradient of right or 2 2 - no 2 = f (x)

ni: refractive index of the solvent

si2: dielectric constant of solutions

ni2: solutions Refractive index

x: solute weight of Report weight solution

CLAIMS

1. A method of separating a mixture comprising 2-chloro-1, 1-difluoroethane and trans-dichloroethylene by extractive distillation.

2. Separation process according to claim 1, wherein the molar ratio 2-chloro-1, 1-difluoroethane / trans dichloroethylene before extractive distillation is 2 to 100, preferably from 2 to 50, and more preferably from 3 30.

3. A separation process according to one of claims 1 or 2, wherein the molar ratio 2-chloro-1, 1-difluoroethane / trans dichloroethylene after extractive distillation going from 9 to 99 999, preferably from 20 to 9999 , and more preferably from 40 to 9999.

4. Separation process according to any one of claims 1 to 3, wherein the extractive distillation is carried out under a pressure of from 0.05 bar to 10 bar, preferably 0.3 bar to 4 bar.

5. A separation process according to one of claims 1 to 4, wherein the extractive distillation is carried out at a temperature ranging from -50 ° C to 250 ° C, preferably from -20 ° C to 185 ° C, preferably preferably from 5 ° C to 145 ° C.

6. A method of separating according to one of claims 1 to 5, wherein the extractive distillation is carried out using a molar ratio extractant / product to be disposed of from 0.01 to 20, preferably 0.1 to 10, preferably 0.5 to 10.

7. Separation process according to any one of claims 1 to

6, wherein the mixture comprising the 2-chloro-1, 1-difluoroethane and trans-dichloroethylene is derived from a reaction of fluorination of 1, 1, 2-trichloroethane.

8. A separation process according to one of claims 1 to 7, wherein use is made of an extraction agent selected from compounds having a boiling point above 35 ° C, preferably greater than 50 ° C, more preferably greater than 60 ° C.

9. A separation process according to one of claims 1 to 8, wherein one puts out an extracting agent having a dipole moment lower or equal to 5 Debye, preferably less than or equal to 4.5 Debye, of

5 preferably less than or equal to 4 Debye, preferably less than or equal to 3 Debye, more preferably less than or equal to 2 Debye.

10. A separation process according to one of claims 8 or 9, wherein the separation factor of 2-chloro-1, 1-difluoroethane and transit) dichloroethylene in the extractant is greater than 1, 1, preferably greater than 1, 4, more preferably greater than 2.

January 1. Separation process according to one of Claims 8 or 9, wherein the separation factor of 2-chloro-1, 1-difluoroethane and trans-dichloroethylene in 15 the extracting agent is less than 1, preferably less than 0.9, more preferably less than 0.7, and even more preferably less than 0.5.

12. A separation process according to one of claims 8-1 1, 20 wherein the extractant is a hydrocarbon chosen from linear hydrocarbons, branched or unbranched, cyclic or aromatic, saturated or unsaturated, optionally substituted.

13. A separation process according to claim 12, wherein the optionally substituted hydrocarbon 25 have from 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms.

14. A separation process according to one of claims 12 or 13, 30 wherein the hydrocarbons are substituted by at least one substituent selected from an oxygen atom, a nitrogen atom, a halogen atom, an alcohol group , an amino group.

15. A separation process according to one of claims 8 to 13, 35 wherein the extractant is selected from linear hydrocarbons, branched, cyclic or aromatic containing from 6 to 8 carbon atoms.

16. A separation process according to claim 15, wherein the extractant is selected from hexane, cyclohexane, methylcyclohexane, n-heptane, octane, 2-methylpentane or toluene.

17. A separation process according to one of Claims 8 to 14, wherein the extractant is selected from halogenated hydrocarbons comprising from 2 to 4 carbon halogen, preferably 2 to 4 carbon chlorine.

18. A separation process according to claim 17, wherein halogenated hydrocarbons are selected from tetrachloromethane, 1, 1, 2-trichloroethane, 1, 1, 1 trichloroethane, tetrachloroethene, 1, 1, 2,2 -tétrachloroéthane, 1, 1, 1, 2-tetrachloroethane, trichlorethylene, tribromomethane or triiodométhane, preferably 1, 1, 2-trichloroethane and tetrachlorethylene.

19. A separation process according to claim 7, wherein the extracting agent is 1, 1, 2-trichloroethane from said fluorination reaction.