WO1994022797A1

WO1994022797A1 - Azeotropic mixture composed of pentafluoroethane and hydrogen fluoride and process for producing pentafluoroethane

Info

Publication number: WO1994022797A1
Application number: PCT/JP1994/000559
Authority: WO
Inventors: Takehide Tsuda; Satoshi Komatsu
Original assignee: Daikin Industries, Ltd.
Priority date: 1993-04-06
Filing date: 1994-04-05
Publication date: 1994-10-13
Also published as: AU6293094A; JPH06293674A

Abstract

The invention provides a minimum-boiling-point azeotropic binary mixture substantially composed of hydrogen fluoride (HF) and pentafluoroethane (HFC-125). Also provided is a process for producing HFC-125 comprising the steps of distilling a mixture containing HFC-125 and HF, drawing an azeotropic mixture out of the column top, and recovering either HFC-125-free HF or HF-free HFC-125 from the column bottom, thereby recovering more effectively either HFC-125-free HF or HF-free HFC-125 from the mixture containing HFC-125 and HF.

Description

Specification An azeotropic mixture of pentafluoroene and hydrogen fluoride and a process for producing pentafluoroethane

【Technical field】

The present invention relates to an azeotropic mixture of pentafluoroethane (hereinafter, referred to as HFC125) and hydrogen fluoride (hereinafter, referred to as HF) and a mixture comprising HFC125 and 1 ^ F. The present invention relates to a method for producing HFC 125, which comprises a step of recovering HFC 125 in a state substantially free of the other component.

[Background Art]

HFC 125 has received attention as an alternative refrigerant to monochlorofluoromethane, and is useful as a refrigerant for refrigerators and the like.

HFC 125 is usually produced by reacting carbon chloride, such as tetrachloroethylene, with HF in the gas or liquid phase in the presence of a catalyst. During this production, unreacted HF remains in the reaction product.

Heretofore, as a method of separating HF from this product, a method of separating a HF by washing a mixture of a reaction product such as HFC 125 and an unreacted product such as HF with an aqueous phase has been used. However, this method is not an effective method because a large amount of alkali is required for the neutralization treatment of the washing solution, and the neutralized waste solution needs to be treated.

Therefore, instead of the conventional method as described above, HF C having a step of more effectively recovering HF without HFC 125 or HFC 125 without HF from a mixture comprising HF and HFC 125 125 methods are desired. DISCLOSURE OF THE INVENTION

The present inventors have repeatedly studied a method for separating HF from a mixture comprising at least HFC125 and HF, and have found that HFC125 and HF form a minimum azeotropic mixture. The problem was found to be solved by using this azeotropic mixture.

Thus, in a first aspect, the present invention provides an azeotrope consisting essentially of HFC 125 and HF. This azeotrope can be used as a stream in a distillation operation for separating HF from a mixture comprising at least HFC125 and HF. That is, a mixture comprising HFC125 and HF is distilled, the azeotrope is distilled off from the top of the distillation column, and a part of the distillate is returned to the distillation column as an ascending stream, whereby the mixture is removed from the mixture. HF or HFC 125 can be effectively separated and removed, and HFC 125 without HF or HF without HFC 125 can be recovered as a bottom product.

As mentioned above, binary systems of HFC125 and HF have (minimum) azeotropes. This azeotrope has been found for the first time by the present inventors.

It has been found that distillation of a mixture of 110125 and ^ 1 ?, for example, under atmospheric pressure, cannot concentrate HFC125 to a molar ratio of HFC125ZHF above about 955. based on. In other words, the liquid phase of this composition is identical to the composition of the gas phase in equilibrium.

The boiling point of this azeotropic mixture is 0. SkgZcni ² —abs is 1-67. The composition at that time is about 7 mol% of 11? And about 93 mol% of HFC125. Under about atmospheric pressure, it is about 55 ° C, and the composition at that time is HF About 5 mol%, about 95 mol% of HFC125. At a pressure of 7 kg ZcE ² -abs, the azeotropic temperature is about 0 ° C, and the azeotropic composition is about 4 mol% HF and about 96 mol% HFC125. At 30 kg / cm ² — abs, the azeotropic temperature is about 61 The azeotropic composition is about 3 mol of HF and about 97 mol% of HFC125. The azeotropic composition changes depending on the pressure.

— In abs, HF is about 7 to 3 mol%, HFC125 is about 93 to 97 mol%, and the azeotropic temperature is 1 67 to 61 ° C.

In a second aspect, the present invention provides a method for extracting HFC125 and HF as an azeotrope from the top by directly distilling a mixture comprising at least HFC125 and HF, thereby obtaining a HFC125 containing substantially no HF. Or a method for producing HFC 1.25, comprising recovering, from the bottom, a mixture containing at least HFC 125, or HF containing substantially no HFC 125 or a mixture containing at least HF.

In a particularly preferred embodiment of the present invention, the process of the present invention provides for the direct distillation of a mixture of HFC 125 and HF to withdraw HFC 125 and HF as an azeotrope from the top of the column and to obtain substantially HF-free HF C 125 or HF substantially free of HF C 125 is recovered from the bottom.

[Brief description of the drawings]

FIG. 1 shows a flow sheet of an example of a process for producing pentafluorochloro mouth ethane to which the method of the present invention is applied.

In the drawing, reference numeral 1 indicates the reactor, reference number 2 indicates the decomposer, reference number 3 indicates the distillation apparatus, reference number 4 indicates the reflux stream, reference number 5 indicates the distillate stream, and reference number 6 indicates the can. The outgoing stream, the reference number indicates the starting material stream, the reference number '8 indicates the azeotrope product stream, and the reference number 9 indicates the hydrogen chloride stream.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the present invention, it has been found that HF C 125 and HF form an azeotrope, so the mixing of HFC 125 and HF fed to the distillation unit If the composition of HF in the product is smaller than the azeotropic composition, an azeotropic mixture of HFC 125 and HF is distilled off, and a part of the azeotropic mixture is returned to the top of the column as reflux, and HF C containing substantially no HF from the bottom of the column 125 can be obtained efficiently.

Conversely, if the HF composition in the mixture to be supplied is higher than the azeotropic composition, the azeotropic mixture of HFC 125 and HF is distilled off in the same manner, and if a part of the azeotropic mixture is used as reflux, HFC 125 is substantially removed from the bottom of the column. It is possible to efficiently obtain HF that is not included in HF.

Even if the mixture contains other components in addition to HFC125 and HF, the method of the present invention can be carried out, in which case, depending on the relationship between the boiling point and the azeotropic temperature of the other components, other The distillation apparatus may be operated such that the components are concentrated on the concentration side of the distillation apparatus or concentrated on the recovery side. That is, if the azeotropic temperature is lower than the boiling point of the other components, the other components are concentrated on the recovery side, and conversely, the azeotropic temperature is reduced so that they are contained in the bottom product and recovered. If it is higher than this component, the other components can be condensed on the port side, and thus the distillation apparatus can be operated so as to be contained and recovered in the distillate.

Any distillation apparatus can be used as long as it has the functions necessary for general distillation operations. For example, particularly preferable results can be obtained when a rectifying device such as a tray column or a packed column is used. In addition, either batch distillation or continuous distillation can be performed. The operating conditions for the distillation are not particularly limited. Generally, from the energy point of view, the optimal top and bottom temperatures and the optimal operating pressure are selected. Suitably, the operating pressure is selected from the range of 0.5 kg ZciD ² -abs to 30 kg Zcni ² at) s. In this range, the overhead temperature is in the range of about 167 to 61 ° C. The bottom temperature is the boiling point of HF or HF C 125 at the operating pressure, if pressure losses are not taken into account. In the method of the present invention, HF is recovered from a reaction mixture containing HFC 125 obtained by fluorinating tetrachloroethylene with a large excess of HF in the gas phase in the presence of a catalyst and a large amount of unreacted HF, and the HF is recovered again. It is most effective when used for reactions.

Preferred embodiments for utilizing the method of the present invention for such a reaction are described below.

FIG. 1 is a flow chart showing an example of the HF C 125 production process in which HF C 125 is recovered from a mixture comprising HFC 125 and HF by applying the HF C 125 production method having the recovery step of the present invention. It is shown. In the reactor 1, tetrachlorethylene and HF supplied as the stream 7 react with each other, and the product is usually withdrawn from the reactor 1 in a gas phase. The resulting reaction mixture mainly contains HFC 125, monochlorotetrafluoroethane (hereinafter referred to as HCFC 124), dichloromouth trifluoroethane (hereinafter referred to as HCF C 123), HF, and purple chloride. It has been. After removing hydrogen chloride as a stream 9 from the mixture in the condensing device 2, the mixture containing HFC125, 11〇 (: 124 ぉ) 1 じ (: 123 and 11?) Is led to the distillation apparatus 3 .

In the mixture from which hydrogen chloride has been removed, HF is present in a large excess over the azeotropic composition (for example, HF 80-90 mol%, HF C 125 10-20 mol%). Accordingly, in the distillation apparatus 3, HF and HFC125 are distilled off from the top of the column with an azeotropic composition (stream 5), and a part thereof is used as a stream (stream 4) and returned to the top of the distillation apparatus 3.

By this distillation operation, a mixture of HF, HCFC 124 and HCFC 123 substantially free of HFC 125 can be extracted from the bottom of the distillation apparatus 3 as a bottom product (stream 6). The obtained bottoms (stream 6) may be subjected to a process for removing impurities (for example, additional distillation, extraction, etc.) or directly to newly supplied reaction raw materials (tetrachloroethylene and fluoride). Hydrogen is mixed with stream 7) and sent to reactor 1 for reuse.

The remainder of the distillate azeotrope used as reflux is obtained as stream 8 of an azeotropic composition of HF and HF C 125, which can be further processed (eg, additional distillation, HF absorption, etc.) Finally, HF C 125 is obtained.

In this way, HF can be efficiently recovered from a mixture comprising HF C 125 and HF.

Such an operation can be performed in a batch manner, but it is more efficient to perform it by a continuous operation as shown in FIG.

【Example】

Hereinafter, the present invention will be described in detail with reference to examples.

Example 1

A distillation column (still volume: 600 ml, diameter: 20 mm, height: lm, packed column) manufactured by SUS was charged with 240 g (2 mol) of HFC125 and lg (0.05 mol) of HF, and distillation was started under pressure and total reflux. Tower pressure

— Abs, Distillate was sampled when the top temperature reached 0 ° C. When this sample was analyzed, the molar ratio of HFC 125ZHF was 96Z4.

From this analysis result, it becomes clear that HF (HFC 1 atmospheric pressure boiling point 19.5 of atmospheric pressure boiling one 48.5 <11 25 ^e C) having a boiling point higher than HFC125 is concentrated at the top portion, and HFC 125 It was confirmed that HF formed the lowest co-mixture.

Similar experiments were conducted with different operating pressures. I got it. The results are shown in Table 1 below

Top pressure Top temperature HFC125ZHF azeotropic composition

(kg / cm ² -abs) (° C) (mol%)

3 -25 95.5 / 4.5 7 0 96/4

15 30 96. 5/3. 5 30 61 97/3 Example 2

In the same manner as in Example 1, 360 g (3 mol) of HFC125 and lg (0.05 mol) of HF were charged, and the distillation column was operated at total reflux, and the overhead pressure was 7 kg / cm ² — abs, and the overhead temperature was 0. It was stable at ^e C. After stabilization, the effluent from the top was gradually extracted, and the temperature of the top gradually increased. When the temperature of the top reached the still temperature, heating was stopped. The amount of liquid withdrawn from the top was about 150 g, and about 200 g of HFC containing about 3 Oppm of HF was obtained from the still.

Example 3

The distillation column overhead pressure TkgZcni ² at HFC 125 in the same apparatus as in Example 1 300 g (2.5 mol) and HF and 200g (1 Oinol) were charged, all Yaryu - abs, top temperature stabilized at o ^e c Was. After the stabilization, the effluent from the top was gradually extracted, and the temperature of the top gradually increased. When the temperature of the top became the same as the still temperature, heating was stopped. About 305 g of liquid was withdrawn from the top of the column, and about 190 g of HF containing about 5 kg of HF C125 was obtained from the still.

Claims

The scope of the claims

1. An azeotrope consisting essentially of pentafluoroethane and hydrogen fluoride.

2. 0.5 kg / cm ² -abs ~ 30 kgZcm ² — At the pressure of abs, the molar ratio of penfluorofluoroethanenohydrogen fluoride having a boiling point of about 16.7 ~ 61 ° C is about 93 ~ 7. 2. The azeotrope of claim 1 wherein the azeotrope is from -973.

3. Distilling a mixture comprising at least pentafluoroethane and hydrogen fluoride to distill an azeotrope of pentafluoroethane and hydrogen fluoride, containing pentafluoroethane A method for producing penfluorofluoroethane having a hydrogen fluoride recovery step, comprising extracting a bottom product containing hydrogen fluoride.

4. production method of penta full O b ethane operating pressure of claim 3, wherein a range of 0.5kg / cni ^² -abs~30kg / cni ² one abs when distilling the mixture.

5. Distill an azeotrope of pentafluoroethane and hydrogen fluoride by distilling a mixture comprising at least pentafluoroethane and hydrogen fluoride, containing no hydrogen fluoride, A method for producing pentafluoroethane, comprising a step of recovering pentafluoroethane, which comprises extracting a bottom product containing pentafluorofluoroethane.

6. mixtures operation pressure when the distillation of the 0.5kgZcni ^² - abs ~ 30kgZcni ² - method of manufacturing a penta full O b ethane according to claim 5, wherein the range of abs.