JP3171685B2 - Purification method of 1,1,1,2 tetrafluoroethane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of reacting trichloroethylene (hereinafter referred to as CCl ₂ ＣCHCl or trichlene) with HF to form 1,1,1,2 tetrafluoroethane (hereinafter referred to as CF ₃ CH ₂ F or F134a). HF obtained by subjecting the reaction product to a distillation treatment.
The present invention relates to a method for purifying F134a, which removes HF from the concentrated F134a containing HF in a state that can be used later.

[0002]

2. Description of the Related Art Generally, tricrene and HF are used as raw materials for F
In the case of producing 134a, the first step of reacting tricrene represented by the formula (1) with HF to produce 1,1,1 trifluoro-2-chloroethane (hereinafter referred to as CF ₃ CH ₂ Cl or F133a) is performed. The reaction is performed by a second-stage reaction in which F133a and HF shown in the formula (1) and (2) are reacted with CHCl = CCl ₂ + 3HF → CF ₃ CH ₂ Cl + 2HCl. CF ₃ CH ₂ Cl + HF → CF ₃ CH ₂ F + HCl (2)

[0003] All of the above reactions are carried out in the presence of an alumina or chromina catalyst, but the reaction conditions are different.
In the second-stage reaction, the pressure was 4 kg / cm ² G (hereinafter, the pressure is represented by G), the temperature was 250 ° C., the molar ratio of HF / trichlene was 6, and in the second-stage reaction, the pressure was 4 kg / cm ² , the temperature was 350 ° C. The HF / F133a is performed at a molar ratio of 4.
The reaction products are separated by distillation. There are various distillation systems. In any of the distillation systems, HCl is separately used as by-product HCl, and HF and F133a are recycled as a reaction raw material. The desired product, F134a, is concentrated in this distillation to produce a small amount of F13a.
3a and HF are separated.

[0004] Thus, the product F134a is a small amount of F1
33a and HF are contained in the above-mentioned F133a and H
F, F134a and HF both have the lowest azeotropic point, and at a pressure of 4 kg / cm ² in the second stage reaction,
The former has an azeotropic point of 41 ° C., and the component ratio at this azeotropic point is
F133a (62 mol%): HF (38 mol%),
The latter has an azeotropic point of 14 ° C., and the component ratio at this azeotropic point is F134a (87 mol%): HF (13 mol%).
%).

For these reasons, distillation alone results in F13
Since F133a or HF cannot be removed from 4a, HF was conventionally removed by alkali washing. When HF is removed, F133a and other fluorocarbons do not have an azeotropic relationship with F134a, and can be separated by distillation.

[0006]

Conventionally, as described above, F
HF was removed from the concentrated fraction of 134a by alkali washing. However, this requires not only the need for alkali, but also the disadvantage that expensive HF is wasted and wastewater treatment is required. Accordingly, an object of the present invention is to provide a method for purifying F134a that can economically recover HF from F134a containing a small amount of concentrated F133a and HF.

[0007]

According to the present invention, a small amount of F13
3a and F134a containing HF and hydrofluoric acid having an HF concentration equal to or higher than the concentration at the azeotropic point of water-HF as an extractant, and then contacted at a low temperature.
By removing 134a, there is provided a method for purifying F134a in which HF can be effectively used and economically separated. At this time, it is preferable that the concentration of hydrofluoric acid used as the extracting agent is 38 to 70% by weight, and the operating temperature at the time of extraction and separation into two layers is −35 to 35 ° C.

Next, the method of the present invention will be described based on embodiments. FIG. 1 shows one embodiment of a method for purifying F134a according to the present invention, and reference numeral 1 in the figure denotes a reaction system comprising a reactor and a distillation column. Although there are various flows in the reaction system 1, any reaction system
Concentrated F134a flowing out from this is a small amount of HF, F13
3a and the like, and have substantially the same composition. This concentrated F134a; 11 is led to the extraction column 2.

The extraction column 2 has a maximum azeotropic point of 112.4 ° C.
And the component ratio at this time is HF (35.8 mol
%): The hydrofluoric acid (bottom liquid of the HF recovery tower 6, described later) having an HF concentration higher than the HF concentration at the azeotropic point of the HF / water system to be H ₂ O (64.2 mol%) is the extractant 15
And kept at low temperature to perform the extraction.

After the completion of the extraction, the liquid flowing out from the bottom of the extraction tower 2; 12 is sent to the first decanter 3, where it is separated into two layers, and the lower layer effluent 13 is washed with alkali in the washing tower 4 and remains. Traces of HF and HCl are removed.
The liquid flowing out from the bottom of the washing tower 4 is guided to the second decanter 5, where it is separated into two layers, the lower F134a is taken out, and the upper aqueous layer is sent to a wastewater treatment system.

Further, the hydrofluoric acid 14 with an increased HF concentration in the upper layer of the first decanter 3 is sent to the HF recovery tower 6,
F is separated by distillation. The separated HF is recycled to the reaction system 1 and used for the reaction. The bottom liquid of the HF recovery tower 6 has a concentration of H or more that is equal to or higher than the azeotropic component concentration of HF and water.
It is hydrofluoric acid containing F, and is used as an extractant in the extraction tower 2;

Although a small amount of F133a and other fluorocarbons contained in the above-mentioned concentrated F134a; 11 are contained in the lower layer liquid of the second decanter 5, the components having no HF have an azeotropic relationship. Since they do not exist, they can be separated and purified by subsequent distillation.

In the purification method of the present invention, the HF concentration of hydrofluoric acid (bottom liquid of the HF recovery tower 6) used as the extractant 15 is determined by the distillation separation ability of the HF recovery tower 6 and the HF concentration. Hydrofluoric acid in the upper layer of the first decanter 3;
Although depending on the concentration, as long as HF is recovered by distillation separation, the lower limit of the concentration is equal to or higher than the HF concentration (38% by weight) at the highest azeotropic point of water and HF. Since the liquid density of hydrofluoric acid increases as the HF concentration increases, the extraction agent: 15 H
When the F concentration exceeds 70% by weight, the density difference between hydrofluoric acid and F134a disappears, and it becomes difficult to separate the two layers in the first decanter 3. Therefore, the HF concentration of hydrofluoric acid used as the extractant 15 in the extraction tower 2 is preferably controlled in the range of 38 to 70% by weight. More preferably 45-5
It is controlled at 5% by weight.

The operating temperatures in the extraction column 2 and the first decanter 3 are preferably controlled at -35 to 35 ° C. More preferably, the temperature is controlled at 5 to 25 ° C. The lower limit of the operating temperature is restricted by the freezing point of hydrofluoric acid or the forming temperature of hydrate of F134a at the operating pressure and the HF concentration during the operation. And the like. On the other hand, hydrofluoric acid and F134a have different liquid density change characteristics with respect to temperature. As the liquid temperature rises, both liquid densities gradually approach and eventually reverse. For this reason, if the temperature exceeds the above upper limit, the two-layer separation in the first decanter 3 becomes impossible.

As described above, there is a correlation between the HF concentration of the extractant 15 that can be selected in the purification method of the present invention and the extraction separation temperature. FIG. 2 is a conceptual diagram regarding the range of the operation conditions.
Shown in In FIG. 2, line A is a boundary defined by the freezing point of hydrofluoric acid at the HF concentration or the formation temperature of F134a hydrate. Line B is the first decanter 3 so that the density of F134a and hydrofluoric acid are not reversed.
This is a boundary defined based on the temperature change of the density of hydrofluoric acid. Line C is a boundary defined by the HF azeotropic concentration in hydrofluoric acid. As the operating conditions, a combination of conditions capable of controlling the interface can be appropriately selected within a range surrounded by lines A, B, and C in FIG.

Although there is no particular limitation on the operating pressure, it is 10 kg /
cm ² G or less is preferred. Furthermore, considering the limited temperature conditions and HF concentration conditions, and considering the operability and economy of the process, it is preferably 6 to 7 kg / cm ² . If the pressure is higher than this, special equipment for high pressure is required. If the pressure is lower, consideration must be given to suppress the volatilization of F134a, and the selection range of operation conditions is narrowed.

[0017]

EXAMPLE An experiment for extracting F134a from the reaction system 1 was conducted using the apparatus and process shown in FIG. Table 1 shows the weight percentage of the components in each part near the extraction column 2 and the flow rate of each part when the flow rate of the concentrated F134a;

[0018]

[Table 1]

As apparent from Table 1, the extractant containing HF at a higher concentration than the HF concentration at the azeotropic point;
Most of the HF in 11 is recovered and reused without waste.

[0020]

As described above, the F1 according to the present invention is used.
The purification method of 34a is a method of extracting HF in F134a, which cannot be separated by distillation, with hydrofluoric acid having an HF concentration equal to or higher than the concentration at the azeotropic point of water and HF as an extracting agent and separating the wastewater into two layers. There is an advantage that it can be used without circulation Further, by setting the concentration of hydrofluoric acid used as the extractant to 38 to 70% by weight and setting the operation temperature at the time of extraction and separation to -35 to 35 ° C, HF can be separated and recovered more smoothly.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of the method of the present invention.

FIG. 2 is a conceptual diagram showing a range of operating conditions when implementing the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reaction system, 2 ... Extraction tower, 3 ... 1st decanter, 4 ... Washing tower, 5 ... 2nd decanter, 6 ... HF recovery tower, 11 ... Concentrated F134a, 12 ... Extraction tower bottom effluent, 13 ... 1st Effluent in the lower layer of the decanter, 14: hydrofluoric acid in the upper layer of the first decanter, 15: extractant, A: boundary line defined by the freezing point of the aqueous hydrofluoric acid solution or the formation temperature of F134a hydrate, B: density of F134a and inversion phenomenon A boundary defined based on the temperature change of the hydrofluoric acid aqueous solution density in order to prevent the occurrence of the following: C: a boundary defined by the azeotropic concentration of the hydrofluoric acid aqueous solution.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yuge Definition 5-1 Ogimachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Denko Co., Ltd. Kawasaki Plant (72) Inventor Haruyuki Kawai 5-1 Ogimachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Showa Denko Inside the Kawasaki Plant (72) Inventor Yasuki Morito 5-1 Ogimachi, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Showa Denko Corporation Kawasaki Plant (56) References JP-A-2-196734 (JP, A) JP-A-2 JP-A-167803 (JP, A) JP-A-5-132434 (JP, A) JP-A-6-135867 (JP, A) JP-A-5-255144 (JP, A) (58) Fields investigated (Int. Cl) . ^7, DB name) C07C 17/38 C07C 19/08

Claims (2)

(57) [Claims] 1. A method for purifying 1,1,1,1,2-tetrafluoroethane containing HF, which is produced by reacting trichloroethylene with HF and is concentrated through a distillation step. HF was extracted at a low temperature using 1,1,2-tetrafluoroethane as a hydrofluoric acid having an HF concentration equal to or higher than the concentration at the azeotropic point of water and HF. A method for purifying 1,1,1,2 tetrafluoroethane, comprising recovering 1,1, tetrafluoroethane. 2. The method according to claim 1, wherein the concentration of hydrofluoric acid used as the extractant is 38 to 70% by weight, and the operating temperature at the time of extraction and separation into two layers is −35 to 35 ° C. To purify 1,1,1,2 tetrafluoroethane.