JPH05178768A - Method for separating 1,1,1,2-tetrafluoroethane and hydrogen fluoride - Google Patents

Abstract

PURPOSE:To efficiently separate a mixture of 1,1,1,2-tetrafluoroethane (134a) with hydrogen fluoride simply through distillation by keeping the internal pressure in the system of the first column low and the internal pressure in the system of the second column high. CONSTITUTION:A reactional product discharged from a reactional system 1 where 134a is synthesized is fed to a crude distillation system 2 to separate a mixture 3 of the 134a with HF. The resultant mixture, together with a distillate 6 from the second column 5, is introduced as a raw material 7 for the first column 4 therein. The raw material 7 at an HF concentration D mol% higher than that (C mol%) in an azeotropic mixture of the first column 4 is distilled under conditions of A kg/cm<2> G internal pressure in the system, B deg.C minimum azeotropic temperature and C mol% HF concentration in the azeotropic mixture in the first column 4 to recover the high- purity HF from the column bottom. A mixture at C mol% HF concentration is simultaneously distilled from the column top. The obtained distillate mixture is then distilled at A' kg/cm<2>G internal pressure in the system higher than A kg/cm<2>G in the second column 5 to distill a mixture at an HF concentration of C' mol% higher than C mol% from the column top and the high-purity 134a is simultaneously recovered from the column bottom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises reacting a halogenated hydrocarbon with hydrogen fluoride (hereinafter referred to as HF) to produce 1,1,
1,2-tetrafluoroethane (hereinafter referred to as 134a)
It relates to a method for separating a mixture of 134a and HF obtained in the production of

[0002]

2. Description of the Related Art Conventionally, CFC 12 which has been widely used as a refrigerant for car air conditioners and refrigerators has a problem of depletion of the ozone layer. It has the same physical properties and does not deplete the ozone layer in the stratosphere. , Is expected to be used as a substitute for Freon 12, and is in the limelight.

Excess HF is used in the production of the above 134a, and efficient recovery and repeated use of HF is important from the viewpoint of economy and process operability.
Since a minimum azeotropic relationship exists between a and HF, and separation is difficult only by distillation, means such as extraction and acid washing are often used together.

[0004]

By the way, the method using the above-mentioned acid washing or extraction is complicated in operation, and if the acid washing is carried out,
Both operability and economical efficiency such as loss of expensive HF have been problems.

The inventors of the present invention have found that only the distillation of 134a
As a result of various studies to separate the mixture of HF and HF, 13
It was found that when the mixture of 4a and HF was distilled, the system pressure increased and the HF concentration in the lowest azeotrope increased.

The present invention has been made based on the above findings, and an object thereof is to provide a separation method for separating a mixture of 134a and HF by only distillation.

[0007]

In the method for separating 134a and HF according to the present invention, the system pressure: Akg / cm
² G, minimum azeotropic temperature: B ° C, HF concentration in azeotrope: C
Under the condition of mol%, a mixture having a HF concentration higher than C mol% was distilled as a raw material to obtain a high concentration of HF from the bottom of the column.
And a mixture of HF containing Cmol% was distilled from the top of the column, and the distillate mixture was distilled at a system pressure A'kg / cm ² G higher than A kg / cm ² G to obtain the HF concentration from the top of the column. Was used as a means for solving the problem, by distilling out a mixture of C′mol% higher than Cmol% and recovering highly pure 134a from the column bottom.

[0008]

Since a mixture containing HF at a concentration higher than the HF concentration in the lowest azeotrope of the first column is used as a raw material, azeotropic components are distilled from the top of the column and surplus HF is distilled from the bottom of the column. Be recovered.

Since the system pressure in the second column is higher than that in the first column, the HF concentration C'in the azeotrope of the second column is higher than C.
Therefore, highly pure 134a is recovered from the bottom of the column.

[0010]

EXAMPLE FIG. 1 shows an example of an apparatus for carrying out the separation method according to the present invention. In the figure, reference numeral 1 is a reaction system in which 134a is synthesized. The reaction product discharged from the reaction system 1 is sent to the crude distillation system 2, the mixture 3 of 134a and HF is separated, and introduced as the raw material 7 of the first column 4 together with the distillate 6 of the second column 5 described later. To be done.

In the first tower, the system pressure is Akg / cm.
It is distilled at ² G. In that case, 134a and HF distilled out
The HF concentration in the mixture of and is C mol% defined by the system internal pressure A.

In this case, the HF concentration D in the mixture of 134a as the raw material 7 and HF needs to be higher than the HF concentration C in the azeotrope of the first column, and D> C 134a is distilled into the distillate 8, and HF with high purity is obtained as the bottom product 9 of the first column. This collected product 9 is the reaction system 1
And used to synthesize 134a.

Next, the distillate 8 from the first column is sent to the second column. In the second column, azeotropic distillation is carried out while the system internal pressure is maintained at A'which is higher than A. The HF concentration in the distillate of this second column becomes C'higher than C because the system internal pressure is high. Therefore, the second column distillate 6 has a HF concentration of C'mol% and becomes a part of the raw material 7 of the first column, and the bottom product 10 becomes high purity 134a.

In the above separation method, the first tower 4 and the second tower 5
It is important to select the system pressures A and A'of A. If A and A'are too close to each other, the distillate 8 of the first tower 4 and the second
The HF concentrations C and C'in the distillate 6 of the column are close to each other, and the bottoms recovered liquid 9 (HF) of the first column and the bottoms recovered liquid of the second column (134)
The collection efficiency of a) deteriorates. HF in the raw material of the first tower
The concentration D is preferably much higher than the HF concentration in the distillate 8 of the first column.

Next, the present invention will be specifically described with reference to examples. The HF concentration in the azeotrope, the azeotropic temperature, and the boiling point of 134a in the case of distilling a mixture of 134a and HF under various system pressures with an Osmer type gas-liquid equilibrium measuring device made of stainless steel are shown in Table 1. become.

[0016]

[Table 1]

From the above table, for example, A is 0 kg / cm
^{When 2} G and A ′ are 4 kg / cm ² G, HF in the azeotrope of the first column is 8 mol% and HF in the azeotrope of the second column is 17%.
Since this is used as a part of the raw material for the first tower, HF is efficiently recovered from the bottom of the first tower and 134a is efficiently recovered from the bottom of the second tower.

(Embodiment 1) 20 theoretical plates having a diameter of 40 mmφ
In a single-stage stainless packed column, the system internal pressure was 3 kg /
134a in cm ² G: 80mol% and the HF: 20mol
% Mixture at the position of about 10 plates from the top of the tower 205 g / hr
At a rate of 203 g / hr from the top of the tower at a reflux ratio of 20
Distilled in. The column top temperature was 8 ° C, the column bottom temperature was 65 ° C, and the column bottoms recovered was 100% HF.

(Example 2) 20 theoretical plates with a diameter of 40 mmφ
While maintaining the internal pressure of the system in a single-stage stainless packed column at 0 kg / cm ² G, 134a: 80 mol%, HF: 20 mol
% Of the mixture was fed at a position of 10 stages from the top of the column at a rate of 250 g / hr, and distilled at a reflux ratio of 20 from the top of the column at 198 g / hr. The HF concentration in this distillate was 8 mol%, the distillate temperature was -27 ° C, the tower bottom temperature was 20 ° C, and the tower bottom recovered product was 19 g.
100 mol% HF was obtained at a rate of / hr.

(Example 3) 20 theoretical plates with a diameter of 40 mm
A stainless steel packed column in a single stage was kept at a system internal pressure of 3 kg / cm ² G, and HF distilled in Example 2 was 8 mol% of 134.
198 g of the mixture of a and HF was placed at the 10th stage from the top of the tower.
/ Hr, 100 g / hr from the top of the tower at a reflux ratio of 20
Distilled at the speed of. Distillation temperature is 8 ° C, HF concentration is 1
It was 4.9 mol% and almost 100 mol% of 134a was recovered from the column bottom at a rate of 98 g / hr. The tower bottom temperature was 9 ° C.

[0021]

As described above, according to the present invention,
As a method for separating the 34a and HF mixture, 134a and HF can be effectively separated by keeping the system internal pressure of the first column low and the system internal pressure of the second column high. Particularly, by keeping the internal pressure of the first tower at 0 kg / cm ² G or less and the internal pressure of the second tower at about 3 kg / cm ² G or more, substantially pure 134a and HF can be efficiently obtained.
The HF contained in the product is completely removed by alkali cleaning to form a product, and the HF is recycled to the reaction system and can be used as a raw material without waste.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus used in a method of separating a mixture of 134a and HF according to the present invention by only distillation.

[Explanation of symbols]

1 Reaction system for synthesizing 134a 2 Crude distillation system 3 Mixture of 134a and HF separated by crude distillation system 4 1st tower 5 2nd tower 6 Distillate of 2nd tower 7 Raw material of 1st tower 8 1st tower Distillate 9 Tower bottoms recovered from the first tower 10 Tower bottoms recovered from the second tower A System pressure of the first tower A'System pressure of the second tower B Azeotropic temperature of the first tower B ' Azeotropic temperature of one tower C HF concentration in azeotrope of first tower (HF concentration of 8) C'HF concentration in azeotrope of second tower (HF concentration of 6) D In raw material of first tower HF concentration (7 HF concentration)

Claims (2)

[Claims] 1. A method for separating a mixture of 1,1,1,2-tetrafluoroethane and hydrogen fluoride using azeotropic distillation, wherein system pressure: Akg / cm ² G, minimum azeotropic distillation At a temperature of B ° C. and a hydrogen fluoride concentration of Cmol% in the azeotrope, a mixture having a hydrogen fluoride concentration higher than Cmol% is distilled as a raw material to obtain a high concentration of hydrogen fluoride from the bottom of the column. concentration of hydrogen fluoride from the top as well as recovered tighten distill a mixture of C mol%, the distillate mixture a kg / cm ² higher than the G system pressure: distilled A'kg / cm ² G, from the top A mixture of C'mol% having a hydrogen fluoride concentration higher than C mol% was distilled off, and at the
A method for separating 1,1,1,2-tetrafluoroethane and hydrogen fluoride, which comprises recovering 1,1,2-tetrafluoroethane. 2. A is about 0 kg / cm ² G and A'is about 3 k.
g / cm ² G, wherein the hydrogen fluoride concentration in the raw material mixture is about 10 mol% or more.
A method for separating 2-tetrafluoroethane and hydrogen fluoride.