JPH08301800A - Production of pentafluoroethane and composition suitable to be converted into pentafluoroethane - Google Patents

Abstract

PURPOSE: To prepare pentafluoroethane in high purity with good productivity without causing problems when separating a by-product because the formation of chloropentafluoroethane as the by-product can be reduced or eliminated according to a specific method comprising a process of three stages.

CONSTITUTION: This method comprises performing a step for producing a composition containing a compound of the formula: C₂HCl_xF_y [(x) is 1-3; (y) is 2-4] containing a compound of the formula: C₂Cl_x+1F_y mixed therein, a step for separating the compound of the formula: C₂HCl_xF_y from the compound of the formula: C₂Cl_x+1F_y and a step for bringing the compound of the formula: C₂ HCl_xF_y into contact with hydrogen fluoride in the presence of a fluorinating catalyst (preferably chromia or the chromia supporting zinc) preferably in the order. The method is preferably the one, etc., for chlorinating trichloroethylene or a compound of the formula: C₂H₂X₄ (X is F or Cl) and a composition in which the mixed compound of the formula: C₂Cl_x+1F_y is dichlorotetrafluoroethane and the compound of the formula C₂HCl_xF_y is chlorotetrafluoroethane is obtained.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing pentafluoroethane.

[0002]

BACKGROUND OF THE INVENTION Pentafluoroethane (HFA 125) is a non-ozone depleting agent in many applications where chlorofluorocarbons and hydrochlorofluorocarbons are used, especially in low temperature cooling.
proposed as a component of a refrigerant formulation; for example, pentafluoroethane is a suitable substitute for various chlorofluorocarbons and hydrochlorofluorocarbons difluoromethane HFA 32,1,1,1-trifluoroethane HFA. Proposed as a component of blends with other hydrofluoroalkanes such as 143a and / or 1,1,1,2-tetrafluoroethane HFA 134a, especially R502 in refrigerant blends and blends with chlorodifluoromethane HCFC 22. Has been done.

Recently, a number of processes have been proposed for the production of pentafluoroethane, such as the hydrogenation of chloropentafluoroethane CFC 115 and the hydrofluoriation of perchlorethylene.
nation).

Hydrogenation of chloropentafluoroethane is
It is typically carried out under conditions such that the conversion of chloropentafluoroethane is incomplete, thus producing pentafluoroethane contaminated with chloropentafluoroethane. Chloropentafluoroethane and pentafluoroethane have very close boiling points, namely -38 ° C and-, respectively.
It has a boiling point of 48 ° C and the lowest boiling point azeotrope (minimum
um boiling azeotrope), and is therefore difficult to separate by conventional methods such as distillation, so that the pentafluoroethane that forms forms a significant amount of CFC 115,
For example, there is a large amount of CFC 115, 5%,
It may have an unacceptably low purity.

In the hydrogen fluoride treatment of perchlorethylene, it is necessary to carry out many halogen exchange reactions in order to obtain pentafluoroethane, so that the productivity is markedly limited. Furthermore, the catalysts typically used in hydrofluorination of perchlorethylene are heavily coked (cok).
e), and thus is inactivated by the continuous halogen exchange reaction that occurs.

Furthermore, tetrachlorofluoroethane HCFC 1
21, trichlorodifluoroethane HCFC 122, dichlorotrifluoroethane HCFC 123 and chlorotetrafluoroethane HCFC 124, in addition to a continuous halogen exchange reaction to produce pentafluoroethane, under certain conditions and in the presence of a catalyst. Then, pentachlorofluoroethane CF
A continuous reaction takes place through C 111, tetrachlorodifluoroethane CFC 112, trichlorotrifluoroethane (CFC 113 and 113a) and dichlorotetrafluoroethane (CFC 114 and 114a) to produce chloropentafluoroethane, which results in penta Fluoroethane is contaminated with significant amounts of chloropentafluoroethane.

Much attention has recently been directed to the satisfactory separation of chloropentafluoroethane from pentafluoroethane. That is, for example, US patents
5,087,329, WO94 / 22793, WO93 / 23355, JP6-92879
Nos. WO94 / 20441, WO94 / 19301 and EP0612709 disclose various methods for purifying pentafluoroethane, all of which are intended to remove chloropentafluoroethane from pentafluoroethane. Is interested in.

In contrast, the present inventors are now able to substantially reduce or even eliminate the formation of chloropentafluoroethane, and thus the problems in separating chloropentafluoroethane from pentafluoroethane. We have developed a process for the production of pentafluoroethane that can be reduced or even eliminated altogether.

[0009]

Therefore, according to the present invention, the formula C ₂
A compound of formula C ₂ HCl _x F _{y in which} a compound of Cl _{x + 1} F _y is mixed (where x = 1,2 or 3, and y = 2,3 or 4, but x + y is 5) (i), separating the compound of formula C ₂ HCl _x F _{y from} the compound of formula C ₂ Cl _{x + 1} F _y (ii) and A process for producing pentafluoroethane, comprising the step (iii) of contacting a compound of formula C ₂ HCl _x F _y with hydrogen fluoride in the presence of a fluorination catalyst, thereby producing pentafluoroethane. Will be provided.

In many aspects of the invention, step (i),
(ii) and (iii) are carried out in the above order, which is not necessary to produce pentafluoroethane containing chloropentafluoroethane at a low level (see below), step (i) , (Ii) and (iii) may be performed in another order; for example, especially under the condition that the step (iii) has a low conversion of the compound of the formula C ₂ Cl _{x + 1} F _y to chloropentafluoroethane, For example, when it is carried out under the conditions of about 50% or less, preferably 25% or less, the step (ii)
It can be performed after (i) and (iii).

In step (i) of the method of the present invention, the composition comprises a haloethene such as perchloroethylene, trifluoroethylene, chlorodifluoroethylene or dichlorofluoroethylene or hydrohaloethane such as tetrafluoroethane or chlorotrifluoroethane. It can be produced by chlorination or hydrogen fluoride treatment.

Another preferred embodiment of the present invention ((A) and (B))
In (described later in detail), step (i) of the method of the present invention comprises (A) trichlorethylene or the formula C ₂ H ₂ X ₄ (wherein X is
Is fluorine or chlorine), such as tetrachloroethane, tetrafluoroethane or chlorotrifluoroethane, or (B) perhaloethylene or pentahaloethane in liquid or gas phase and in a fluorination catalyst In the presence of hydrogen fluoride.

The process according to the invention is advantageously carried out as a continuous process, in which the product stream from step (iii) is conveniently treated by distillation to obtain the unconverted formula C ₂ HCl _x.
The compound of F _y is separated from pentafluoroethane and the unconverted compound of formula C ₂ HCl _x F _y is recycled to step (i) or step (iii), preferably step (i). Further, the product stream from step (iii) may contain a compound of formula C ₂ Cl _{x + 1} F _y , in which case the recycle stream is of the formula C present in the recycle stream. ₂ HCl _x F compound of _y and the formula C ₂ Cl based on the total weight of the compound of _{x + 1} F _y 15 wt% or less, more preferably 10 wt% or less, particularly 5 wt% or less of the formula C ₂ Cl _{x +} It preferably contains ₁ F _y of the compound.

The composition formed in step (i) of the method of the present invention is a single compound of formula C ₂ HCl _x F _y contaminated with a single compound of formula C ₂ Cl _{x + 1} F _y . For example, it may be chlorotetrafluoroethane contaminated with dichlorotetrafluoroethane, dichlorotrifluoroethane contaminated with trichlorotrifluoroethane or trichlorodifluoroethane contaminated with tetrachlorodifluoroethane.
Usually, the raw material composition, in particular, this raw material composition is an alternative preferred embodiment (A) or step (i) of the method of the present invention or
Made by one of (B), consisting of two or more compositions, contaminated with two or more compounds of the formula C ₂ Cl _{x + 1} F _y , or It may be a composition consisting entirely of compounds of the formula C ₂ HCl _x F _y , which may even be all contaminated. However, the composition usually consists of at least chlorotetrafluoroethane and dichlorotetrafluoroethane and a particularly preferred operation to be carried out in step (ii) of the process of the invention is the separation of dichlorotetrafluoroethane from chlorotetrafluoroethane. It is to be.

The composition which is the product of step (i) of the process of the present invention comprises a compound of formula C ₂ Cl _{x + 1} F _{y and} a compound of formula C ₂ HCl _x F _{y which is produced.}
Typically about 0.1 to about 2 based on the total weight of the compound of
0 wt%, more typically about 0.5 to about 15 wt% of the formula C ₂ Cl _{x + 1} F
_Contains the compound of _y . The process of step (i) is
The composition, which is the product formed in (i), has the formula C
Performed to contain about 0.5 to about 10% by weight of the compound of formula C ₂ Cl _{x + 1} F _y , based on the total weight of the compound of ₂ Cl _{x + 1} F _{y and} the compound of formula C ₂ HCl _x F _y. It is preferable. The composition that is the product of step (i) also contains unconverted starting material, by-product hydrogen chloride and minor amounts of other by-products, depending on the particular process used in step (i).

According to the method of the present invention, compounds of the formula C ₂ HCl _x F _y , in particular chlorotetrafluoroethane (HCFC 124 and
124a, boiling point; 11.0 ℃ ± 1.0 depending on the type of isomer
° C) and dichlorotrifluoroethane (HCFC 123, 123a
And 123b, boiling point; 27.5 ° C ± 1. depending on the type of isomer.
0 ° C.) to compounds of the formula C ₂ Cl _{x + 1} F _y , in particular dichlorotetrafluoroethane (CFC 114 and 114a, boiling point; 3.3 ° C. ± 0.3 ° C. depending on the type of its isomers) and trichlorotrifluoroethane. (CFC 113 and 113a, boiling point; 46.6 ° C ± 1.0 ° C depending on the type of its isomer) is effectively separated,
Substantial benefits are obtained. Separation step (ii) comprises at least 50% by weight, more preferably at least 75% by weight, especially at least 95% by weight, of the compound of formula C ₂ Cl _{x + 1} F _y present in the composition prepared in step (i). It is preferred to carry out such that the% is separated from the compound of formula C ₂ HCl _x F _y .

Thus, according to the method of the present invention, the chlorofluorocarbon which produces chloropentafluoroethane is removed before the reaction step which produces chloropentafluoroethane when the chlorofluorocarbon is not removed. Or substantially reduced. Separation step (ii)
Is recovered by separation and the steps of the method of the invention
10 wt% or less, preferably 5 wt% or less, more preferably 2 wt% of the compound of the formula C ₂ HCl _x F _y supplied to (iii)
The following may in particular be carried out so as to contain up to 1% by weight of a compound of the formula C ₂ Cl _{x + 1} F _y . The step (i) of the method of the present invention is a step
In the embodiment of the present invention comprising one of the preferred embodiments (A) or (B) for (i), particularly, the step (i) comprises the preferred embodiment (B) or 1,1,1,2- When consisting of chlorination of tetrafluoroethane, the separation of dichlorotetrafluoroethane from chlorotetrafluoroethane should essentially be achieved, which was recovered by this separation operation and step (iii) of the process of the invention. It is preferable that the chlorotetrafluoroethane to be supplied to 2) contains 2% by weight or less of dichlorotetrafluoroethane, more preferably 1.0% by weight or less, and particularly 0.5% by weight or less. The CFCs, particularly trichlorotrifluoroethane and dichlorotetrafluoroethane, are effectively removed from the process of the present invention prior to the formation of substantial amounts of chloropentafluoroethane, resulting in the process of the present invention. Pentafluoroethane, the amount of chloropentafluoroethane in the pentafluoroethane before carrying out a special purification step carried out to remove the chloropentafluoroethane from the pentafluoroethane is 5% by weight or less, preferably 3% by weight or less, more preferably 2% by weight or less, based on the total weight of and pentafluoroethane.
In particular, it can be as low as 1% by weight or less.

Step (i) is trichlorethylene or the formula C ₂ H ₂ X
_In a preferred embodiment (A) of the invention consisting of chlorination of a compound of the formula ₄ (wherein X is fluorine or chlorine), the starting material is tetrachloroethane, tetrafluoroethane or chlorotrifluoroethane, , The starting material is 1,
It is preferably 1,1,2-tetrafluoroethane.

Chlorination techniques are well known to those skilled in the art and any such chlorination technique may be used in step (i) of the process of the present invention. For example, the chlorination can be carried out in the liquid phase or in the gas phase, and the chlorination can be activated photochemically, catalytically or thermally.

When the starting material is 1,1,1,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane and chlorine are used to reduce the amount of dichlorotetrafluoroethane produced. Is preferably used in a molar ratio of about 10: 1 to about 1: 1, more preferably about 6: 1 to about 1: 1 and especially about 5: 1 to about 2: 1. preferable.

The chlorination step (i) and the hydrogen fluoride treatment step (iii) can be carried out in the same reactor, in which case the process is chlorofluorination,
The product from the reactor is treated, for example by distillation, to give the formula C ₂
A pentafluoroethane stream to recover one or more recycle streams of a compound of HCl _x F _y and unreacted starting material of the formula C ₂ H ₂ X ₄ and a formula C ₂ Cl _{x + 1} Separated from waste streams containing compounds of F _y .

Suitable temperature and pressure conditions for chlorofluorination of 1,1,1,2-tetrafluoroethane are well known to those skilled in the art, and are described in, for example, US Pat. No. 5,258,561. It is preferred to use 1,1,1,2-tetrafluoroethane in the proportions as stated above rather than those stated in the above-mentioned US patent specifications.

Alternatively, in the preferred embodiment (A) of the present invention, step (i) and step (iii) can be carried out in separate reactors, and the chlorination reactor of step (i) and the step The hydrogen fluoride treatment reactors (iii) are preferably arranged in series or in parallel.

In a reactor system arranged in series, tetrafluoroethane is chlorinated in the gas phase in the reactor of step (i) and the product stream is fed to a separator where hydrogen chloride, for example aqueous The unconverted tetrafluoroethane is separated off, for example by distillation, using a scrubber or by distillation and fed to a chlorination reactor, leaving a product stream consisting of chlorotetrafluoroethane and dichlorotetrafluoroethane. The chlorotetrafluoroethane / dichlorotetrafluoroethane mixture is fed to a distillation apparatus, where chlorotetrafluoroethane is separated from dichlorotetrafluoroethane and then chlorotetrafluoroethane is fluorinated in step (iii) containing a fluorination catalyst. Feed to the hydrotreating reactor.

In a reactor system arranged in parallel, the chlorination reactor and the hydrofluorination treatment reactor are arranged in parallel and the product streams from each reactor are combined and / or a common purification is carried out. It can be fed to an apparatus, for example, a series of distillation apparatus systems, in which pentafluoroethane, tetrafluoroethane, chlorotetrafluoroethane and dichlorotetrafluoroethane are separated, and chlorotetrafluoroethane is subjected to a hydrofluorination treatment reaction. Feed the reactor and recycle tetrafluoroethane to the chlorination reactor. In this parallel operation, the product stream from the hydrofluoride treatment reactor is
First, before combining with the product stream from the chlorination reactor,
It is preferred to work up by removing, for example, phase separation and distillation to remove most of the unreacted hydrogen fluoride and recycle.

A second preferred embodiment of the invention wherein step (i) comprises contacting perhaloethylene or pentahaloethane with hydrogen fluoride in the liquid or gas phase and in the presence of a fluorination catalyst. In B), the starting material is preferably perhaloethylene, and the method of step (i) is preferably carried out in the gas phase and at an elevated temperature.

The temperature for carrying out step (i) is about 150 ° C to about 400 ° C,
It may preferably be about 180 ° C to about 380 ° C, especially about 200 ° C to about 370 ° C. Atmospheric pressure or pressure above atmospheric pressure (superatmosphe
ric pressure) can be used, but pressures above atmospheric pressure, eg up to 30 barg, in particular from about 5 barg to about 20.
Preference is given to using pressures of bar g.

The relative proportions of hydrogen fluoride and perchlorethylene can be varied within a very wide range, but it is preferred to use a stoichiometric excess of hydrogen fluoride. The molar ratio of hydrogen fluoride to perchlorethylene is usually greater than about 3: 1 and is preferably greater than 5: 1. Using a molar ratio of hydrogen fluoride to perchlorethylene in the range of about 5: 1 to about 20: 1, preferably about 7: 1 to about 15: 1, especially about 7: 1 to about 12: 1. Is preferred.

The catalyst used in the preferred embodiment (B) of the process according to the invention is any known fluorination catalyst, in particular a fluorination catalyst having a high activity for the conversion of perchlorethylene to hydrochlorofluoroethane, Chromia, for example
It may be a catalyst based on chromium oxyfluoride, alumina or aluminum fluoride and which may also contain one or more metals such as nickel, cobalt, iron, zinc and the like. It is preferred to use chromia or zinc-supported chromia catalysts, because these catalysts have a particularly high perpass conversion of perchlorethylene to hydrochlorofluoroethane.

In this preferred embodiment (B) of the invention, wherein step (i) comprises hydrogen fluoride treatment, step (i) and step (ii)
Both i) are hydrogen fluoride treatment processes and the catalysts used in step (i) and step (iii) can be the same or different, so if desired two steps
(i) and step (iii) can be carried out in a single reactor on a single catalyst bed consisting of a fluorination catalyst, thereby producing pentafluoroethane. In this case, the product stream from a single reactor is fed to a refinery system, for example a series of distillation columns, to form a compound of formula C ₂ HCl _x F _y and unreacted starting material, for example perchlorethylene. Or more recycle stream with pentafluoroethane stream to recover C ₂ Cl
_It can be separated from the waste stream containing _{x + 1} F _y compounds. In this embodiment using a single reactor, the catalyst can be a catalyst as described for step (i) or step (iii), if desired.

However, in this preferred embodiment (B) of the process of the invention it is in some cases preferred to use a different catalyst for step (i) or step (iii) of the process of the invention. It was approved to get. For example, for the conversion of perchlorethylene in step (i) of the process of the invention it is preferred to use a catalyst having a high activity (single flow conversion), while in step (iii) from the hydrochlorofluoroethane For the production of pentafluoroethane it is preferred to use a catalyst with a high selectivity.

The catalysts used in steps (i) and (iii) of the process according to the invention can be present in different reaction zones of the same reactor or each catalyst can be present in a separate reactor.

When the catalyst for step (i) and the catalyst for step (iii) are present in separate reactors,
The two reactors can be arranged in parallel or in series.

In the embodiment in which the two reactors of step (i) and step (iii) are arranged in series, step (i) or step
The product stream from one reactor of (iii) may be passed to the other reactor and the product stream from this other reactor may be fed to the refiner system in which step (ii) is carried out. For example, the product stream from the reactor of step (i) is passed to the reactor of step (iii) and the product stream from the reactor of step (iii) is fed to the purifier system in which step (ii) is performed. You can Alternatively, step (i)
The product stream from the reactor of formula C ₂ HCl _x F ₂ is passed to the purifier system in which step (ii) is carried out and the unreacted starting material and the compound of formula C ₂ Cl _{x + 1} F _y are separated. One or more of the effluent streams from the purifier consisting of the compound of _y may be passed to the reactor of step (iii). The product stream from the step (iii) reactor can be passed to the step (i) reactor.

However, step (iii) of the method of the present invention
It is preferred to substantially remove the hydrogen chloride before carrying out. Hydrogen chloride is produced as a substantial by-product from step (i) of the process of the present invention and therefore the product stream from the reactor of step (i) is fed to the purifier system in which step (ii) is carried out. The product stream from the step (iii) reactor is then preferably passed to the step (i) reactor.

According to another preferred embodiment of the present invention, (i)
Formula C ₂ H containing perchlorethylene in contact with hydrogen fluoride in the presence of a fluorination catalyst, contaminated with a compound of formula C ₂ Cl _{x + 1} F _y
Compound of Cl _x F _y (where x = 1,2 or 3 and y =
2, 3 or 4 with the proviso that x + y is 5) and (ii) a compound of formula C ₂ HCl _x F _y is added to formula C ₂ Cl
separating from the compound of _{x + 1} F _y and then contacting (iii) the compound of formula C ₂ HCl _x F _y with hydrogen fluoride in the presence of a fluorination catalyst, thereby producing pentafluoroethane, and There is provided a process for producing pentafluoroethane, characterized in that the product stream from step (iii) is recycled to the reactor of step (i).

In an embodiment in which the reactors of step (i) and step (iii) are arranged in parallel, the product streams from the two reactors are fed to the common purifier system in which step (ii) is carried out, Pentafluoroethane was recovered from this purification unit, unconverted perhaloethylene was recycled to the reactor of step (i) and unconverted compound of formula C ₂ HCl _x F _y was added to the reactor of step (iii). It is preferred to recycle.

In step (ii), the purifier system is fed from either the reactor in the embodiment using a single reactor or from the two reactors in the embodiment using two reactors. The product stream is typically a compound of formula C ₂ HCl _x F _y , especially dichlorotrifluoroethane and chlorotetrafluoroethane, a compound of formula C ₂ Cl _{x + 1} F _y , especially trichlorotrifluoroethane and dichlorotetrafluoroethane. Ethane, pentafluoroethane, chloropentafluoroethane, unreacted hydrogen fluoride and perchlorethylene, by-product hydrogen chloride and small amounts of other by-products such as 1,1,1-trifluoro-2-chloroethane and 1, Consists of 1,1,2-tetrafluoroethane.

This product stream is fed, for example, to a purifier system consisting of a first distillation column from which hydrogen fluoride, dichlorotrifluoroethane [HCFC 123 / 123a] and other heavy products are bottomed off. It is taken as a fraction and the rest of the product stream is taken as a top fraction. The bottom fraction from this first distillation column may be recycled to one or both of the single reactor or the two reactors described above.

The top fraction from the first distillation column is optionally subjected to aqueous scrubbing and then dried to remove the acidic components, hydrogen chloride and hydrogen fluoride, and then fed to the second distillation column, where Pentafluoroethane from the distillation column
[HFA 125] was taken out as a top fraction together with chloropentafluoroethane [CFC 115], mainly chlorotetrafluoroethane [HCFC 124 / 124a], chlorotrifluoroethane [HCFC 133 / 133a], tetrafluoroethane [HFA
134 / 134A] and dichlorotetrafluoroethane [CFC 114 /
The remainder of the product stream consisting of 114a] is withdrawn as the bottom fraction. The pentafluoroethane containing chloropentafluoroethane, taken off as the top fraction, can be further processed to carry out purification of this pentafluoroethane.

The bottom fraction from the second distillation column is separated into a third
It is fed to a distillation column, and tetrafluoroethane [HFA 134 / 134A] is taken out from this third distillation column as a top fraction,
The rest of the product stream is withdrawn as a bottom fraction and then fed to a fourth distillation column from which chlorotetrafluoroethane [HCFC 124 / 124a] is withdrawn as a top fraction, while dichlorotetrafluoroethane [CFC
114 / 114a] and chlorotrifluoroethane [HCFC 133/133
a] is taken as the bottom fraction. Chlorotetrafluoroethane [HCFC 124 / 124a] is pentafluoroethane [HF
It can be recycled to the reactor for carrying out the fluorination to A 125]. The bottom fraction from the fourth distillation column can usually be treated, for example by thermal oxidation.

The purifier system used in the preferred embodiment (B) of the present invention comprises unreacted perchlorethylene and unconverted formula C ₂ HC.
a first distillation column for separating the l _x F _y compound as a bottom stream from the other components (as a top stream) and recycling to the reactor of step (i), and pentafluoroethane in the top stream. At least one additional (other) for separating and recovering from other components and separating and recycling chloropentafluoroethane from dichlorotetrafluoroethane
It consists of a distillation column.

The top stream from the first distillation column is preferably treated to remove at least hydrogen chloride. In particular,
The top stream from the first distillation column may be scrubbed with water to remove hydrogen fluoride and hydrogen chloride before feeding to at least one additional distillation column. However, in this case, the hydrogen fluoride in the top stream is also removed, resulting in a reduction in the efficiency of hydrogen fluoride in the process of the invention. Alternatively, the top stream itself from the first distillation column may be distilled to separate the top stream consisting of hydrogen chloride, pentafluoroethane and chloropentafluoroethane from the bottom stream consisting of other components. This bottom stream is then fed to at least one further distillation column,
Alternatively, the top stream may be fed to a distillation column to separate pentafluoroethane from the top stream.

If aqueous scrubbing is used to remove hydrogen chloride and hydrogen fluoride, it is preferred that the at least one additional distillation column comprises two distillation columns; in the first additional distillation column. Pentafluoroethane is separated from chlorotetrafluoroethane and dichlorotetrafluoroethane, and dichlorotetrafluoroethane is separated from chlorotetrafluoroethane in a second additional distillation column. When distillation is used to remove hydrogen chloride from the top stream from the first distillation column, at least one additional distillation column is used to separate chlorotetrafluoroethane from dichlorotetrafluoroethane. Need only a distillation column. 114/11 if this optional method (ie distillation to remove hydrogen chloride) was used
The distillation for separating 4a from 124 / 124a is carried out in the presence of hydrogen fluoride, the top stream from the distillation column carrying out this separation consisting of chlorotetrafluoroethane, dichlorotetrafluoroethane and hydrogen fluoride and It is a novel composition which is particularly suitable for the treatment of fluoroethane with hydrogen fluoride, i.e. with hydrogen fluoride as in step (iii) of the process of the present invention.

According to a second aspect of the invention, (i) at least 50% to about 95% by weight of chlorotetrafluoroethane, (ii) about 0.5% to about 20% by weight of hydrogen fluoride and ( iii)
A composition suitable for conversion to pentafluoroethane is provided which comprises up to 2% by weight of dichlorotetrafluoroethane (the above% by weight being based on the total weight of these three components present in the composition). It

The above composition may have other ingredients such as other formula C ₂
A small amount of the compound of HCl _x F _y and other compounds of the formula C ₂ Cl _{x + 1} F _y ,
Generally, it may further comprise up to 10% by weight of the composition, typically up to 5% by weight of the composition. Thus, the above weight percentages for the components of the composition are also typically weight percentages based on the total weight of the composition. Preferably, the amount of dichlorotetrafluoroethane in the composition will be 1% by weight or less, in particular 0.5% by weight or less. The composition comprises from about 1% to about 1% by weight.
It also preferably contains 0% by weight hydrogen fluoride and will usually contain at least 75% by weight chlorotetrafluoroethane.

Step (iii) of the process of the present invention can be carried out in the liquid or vapor phase, especially when step (i) is a vapor phase hydrofluorination treatment of perhaloethylene or pentahaloethane,
It is preferably carried out in the gas phase. Gas phase reactions of dichlorotrifluoroethane and chlorotetrafluoroethane with hydrogen fluoride are well known to those skilled in the art, and suitable temperature and pressure conditions,
The relative proportions of suitable fluorination catalysts and reactants are well documented in the literature.

Suitable fluorination catalysts include those based on chromia and chromium oxyfluoride or alumina and aluminum fluoride. An amount of another metal that promotes activity,
For example zinc, nickel and iron may also be present. EP502605
Or the catalysts described in WO 93/16798, in particular EP502605.
Preference is given to using the catalysts described in U.S. Pat. No. 5,096,009 in which an activity-promoting amount of zinc is supported on chromia or chromium oxyfluoride.

The temperature of step (iii) of the method of the present invention is about 200 ° C.
To about 500 ° C, preferably about 250 ° C to about 350 ° C.
This step is conveniently carried out near atmospheric pressure, but if desired, subatmospheric or superatmospheric pressures, for example up to about 20 bar, can also be used. In fact, superatmospheric pressures of up to about 2 to about 15 bar are used to accelerate the throughput of the gas and to reduce the required reactor size [2 reactions In the preferred embodiment (B) of the present invention, where two reactors are used, it is preferable to operate the two reactors at substantially the same pressure, and the slight pressure difference between the reactors causes It naturally occurs as a result of flow].

The molar ratio of hydrogen fluoride to chlorotetrafluoroethane can be from about 1 to about 10; it is preferred to use an excess number of moles of hydrogen fluoride.

The present invention will be described below with reference to the drawings. In the system shown in FIG. 1, a gaseous chlorine feed stream 101 and a gaseous 1,1,1,2-tetrafluoroethane feed stream 102 are fed to a chlorination reactor 103. The product gas stream 124 from the chlorination reactor is fed to the aqueous scrubber unit 104.
Where hydrogen chloride and unreacted chlorine are separated from the organic stream 125 as an aqueous stream 105. Organic stream 125 is dried, compressed in compressor 106 and then fed to distillation column 107, where 1,1,
1,2-Tetrafluoroethane (HFA 134a) is separated from chlorotetrafluoroethane (HCFC 124) and dichlorotetrafluoroethane (CFC 114a). The HFA 134a stream 108 is recycled to the chlorination reactor 103. HCFC 124 / CFC 114a stream distillation column
Feed to 109, where HCFC 124 stream 110 is separated from CFC 114a stream 111. The HCFC 124 product stream 110 from the distillation column is fed with gaseous hydrogen fluoride 112 to a hydrofluoride treatment reactor 113 containing a chromia catalyst. The product gas stream 126 from this reactor is fed to a distillation column 114 where a fluid 115 of unreacted hydrogen fluoride and HCFC 124 is separated from other components of the product stream and recycled to reactor 113. Let The remainder 127 of the product stream from the distillation column is fed to the aqueous scrubber unit 116,
Here, hydrogen chloride and the rest of the hydrogen fluoride are separated from the organic stream 128 as an aqueous stream 117. Organic stream 128 is fed to compressor 118 and then to distillation column 119, where pentafluoroethane product stream 120 is separated from organic stream 129 of other organic components. The organic stream 129 is fed to the second distillation column 121, where the HCFC 124 stream 122 is separated from the heavy byproduct stream 123. HCFC
Stream 122 is recycled to reactor 113.

In the embodiment shown in FIG. 2, a gaseous chlorine feed stream 201 and a gaseous 1,1,1,2-tetrafluoroethane feed stream 202 are fed to a chlorination reactor 203 consisting of an Inconel tube. To do.

HCFC 124 from hydrogen fluoride stream 204 and distillation column 215
A recycle stream 216 (described below) is fed to a hydrofluoric acid treatment reactor 205 containing a chromia catalyst, and a product gas stream 220 is fed to a distillation column 206 where a fluid consisting of unreacted hydrogen fluoride. 207 and HCFC 124 are separated from fluid 221 which comprises the rest of the product stream and fluid 207 is recycled to reactor 205. Fluid 221 from distillation column 206 is combined with product stream 219 from chlorination reactor 203 and fed to aqueous scrubber unit 208, where the balance of hydrogen chloride, chlorine and hydrogen fluoride is organic stream 222 as aqueous stream 209. Separate from. The organic stream 222 from the scrubber unit 208 is dried, compressed in a compressor 210 and then a distillation column.
Feed 211 to pentafluoroethane stream 212 to HFA 134a,
Separated from an organic stream 223 consisting of HCFC 124 and CFC 114a. Organic stream 223 is fed to distillation column 213, where HFA 134a stream.
214 is separated from an organic stream 224 consisting of HCFC 124 and CFC 114a. HFA 134a stream 214 is recycled to reactor 203. Organic style
224 is fed to distillation column 215 where HCFC 124 stream 216 is fed to CFC 1
Separated from stream 14a 217 and recycled HCFC 124 stream 216 to reactor 205.

In the embodiment shown in FIG. 3, feed hydrogen fluoride stream 301, feed perchlorethylene stream 302, recycled hydrogen fluoride and organic stream 307 (described below) and HCFC 124 recycle stream 316.
A gaseous feed stream 318 consisting of is fed to a hydrofluoride treatment reactor 303 containing a chromia catalyst. Product gas stream 304
Is fed to a distillation column 305 where unreacted hydrogen fluoride, perchlorethylene and incomplete (or partial) fluorination (underfluo).
A fluid 307 containing an organic intermediate such as HCFC 121, 122 and 123 is added to the product HFA 125, HCFC 124, CFC 114/11.
Separated from fluid 306 consisting of 4a and hydrogen chloride and HF.
Fluid 306 is fed to aqueous scrubber unit 309, where hydrogen chloride and residual HF are separated from organic stream 310 as aqueous stream 308. Organic stream 310 is dried, compressed in compressor 311 and fed to distillation column 312 to provide HFA 125 stream 313 to HCFC 124 and CFC 114.
Separated from fluid 314 containing / 114a. Fluid 314 is fed to distillation column 325 where HCFC 124 stream 316 is separated from CFC 114 / 114a rich fluid 317.

In the embodiment shown in FIG. 4, the feed hydrogen fluoride 401, the feed perchlorethylene stream 402 and the recirculated hydrogen fluoride.
/ Perchlorethylene / Incompletely fluorinated intermediate to HFA 125 4
A gaseous fluid 403 consisting of 07 and is supplied to a hydrofluoric acid treatment reactor 404 containing a chromia catalyst. The product gas stream 405 is mixed with a fluid 413 containing product gas from a parallel hydrofluorination reactor 412 and fed to a distillation column 406 where HF and perchlorethylene (and some incomplete fluorine). Fluid 407 containing purified HCFC 121, 122, etc.) is withdrawn from the bottom of the distillation column and recycled to reactor 404. Fluid 408 containing HF and (mainly) HCFC123 is withdrawn as a side stream from the side of distillation column 406 and fluid containing recirculated HCFC124 4
22 and optionally the feedstock HF is mixed with a fluid 410; a mixed stream 411 is fed as a gas to a hydrofluoride treatment reactor 412 containing a chromia catalyst. The product gas from this reactor, the fluid 413, is the distillation column 4 as described above.
Supply to 06. Products HFA 125, HCFC 124, CFC 114 and 11
A light fluid 409 containing 4a, hydrogen chloride and some HF is withdrawn from the top of the distillation column 406 and fed to an aqueous scrubber unit 414 where HF and hydrogen chloride are treated as an aqueous stream 415 in an organic stream 416.
Separate from. Organic stream 416 is dried, compressed in compressor 417 and fed to distillation column 418 where HFA 125 stream 419
Separate from fluid 420 containing FC 124 and CFC 114 / 114a. Fluid 420 is fed to distillation column 421 where HCFC 124 stream 42
2 is separated from CFC 114 / 114a rich fluid 423.

In the embodiment shown in FIG. 5, the feed hydrogen fluoride stream 501, the feed perchlorethylene stream 502 and the incompletely fluorinated intermediate recycle stream 506 to the hydrogen fluoride / perchlorethylene / HFA 125 and the fluorine. A gaseous fluid 522 consisting of the product gas from the hydrofluoride treatment reactor 510 is fed to the hydrofluoride treatment reactor 503 containing the chromia catalyst. Product gas 5
04 is fed to distillation column 505, where fluid 506 containing HF and perchlorethylene (and some incompletely fluorinated HCFC 121, 122, etc.) is withdrawn from the bottom of the distillation column and recycled to reactor 503. Fluid containing HF and (mainly) HCFC 123 50
7 is withdrawn as a side stream and mixed with fluid 520 containing recycled HCFC 124 and optionally fluid 508 providing feed HF; mixed stream 509 is a hydrofluoride treatment containing chromia catalyst as gas. Feed reactor 510. From the top of the distillation column 505 Light organic substances-Products HFA 125, HCFC 124, CFC 1
Withdraw fluid 511 containing hydrogen chloride and HF, such as 14, 114a. Hydrogen chloride and HF in this fluid are treated with an aqueous scrubber.
Separated as an aqueous acidic stream 513 at 512, while the organic stream 514 is dried, compressed in a compressor 515 and fed to a distillation column 516, where an HFA 125 stream 517 contains HCFC 124 / CFC 114 / 114a. Fluid body 518 to be separated. Fluid 518 is fed to distillation column 519 where HCFC 124 recycle stream 520 is fed to CFC 114 / 114a.
From the bottom fluid 521, which is rich in water.

In the embodiment shown in FIG. 6, raw material HF601
And raw materials perchlorethylene 602 and HF / perchlorethylene
A gas stream 603 consisting of an incompletely fluorinated intermediate recycle stream 609 to / HFA 125 is fed to a hydrofluoride treatment reactor 604 containing a chromia catalyst. Product gas 605 is mixed with a combined fluid of recycle stream 610 containing HF and (mainly) HCFC 123 and HCFC 124 recycle stream 620 to form gas stream 605. This gas stream 605 is fed to another hydrofluoride treatment reactor 606 which also contains a chromia catalyst. The product gas 607 is fed to a distillation column 608 where HF and perchlorethylene (and some incompletely fluorinated HCFC 121, 122).
Withdrawing fluid 609 from the bottom of the column and recirculating to reactor 604; fluid 61 consisting of HF and HCFC 123.
0 as sidestream, combined with recycle stream 620 and then returned to reactor 606; and products HFA 125, HCFC 124, CFC
Light fluid containing 114, 114a, hydrogen chloride and some HF
Feed 611 to the aqueous scrubber unit 612. In unit 612, hydrogen chloride and HF are separated from organic stream 614 as aqueous stream 613. Organic stream 614 is dried, compressed in compressor 615 and then fed to distillation column 616, where HFA 125 stream 617 is passed to HCFC 12
Separated from fluid body 618 containing 4 / and CFC 114 / 114a. Fluid 618 is fed to distillation column 619 where HCFC 124 recycle stream 620 is separated from CFC 114 / 114a rich bottom fluid 621.

In the embodiment shown in FIG. 7, a gaseous feed stream comprising feed hydrogen fluoride stream 701, perchlorethylene stream 702, recirculating HF / organic stream 707 and hydrogen fluoride / tetrafluorochloroethane recycle stream 712. 714 is fed to a hydrofluoride treatment reactor 703 containing a chromia catalyst. Product gas stream 704 is fed to distillation column 705 where unreacted hydrogen fluoride, perchlorethylene and incompletely fluorinated organic intermediates such as
The fluid 707 containing HCFC 121, 122, 123 and 1111 is separated from the fluid 706 containing the products HFA 125, HCFC 124, CFC 114 / 114a, hydrogen chloride and hydrogen fluoride. Fluid 706 is fed to distillation column 708 where hydrogen chloride, product HFA 125 and fluid 709 containing a small amount of HF are withdrawn as overhead effluent for final product treatment [eg, aqueous scrubbing, drying, compression and distillation]. On the other hand, tetrafluorochloroethane,
HF, CFC 114a, CFC 114 and HCFC 133 flow out at the bottom of the tower 71
Take out as 0. Supplying the bottom effluent stream 710 to a distillation column 711,
Here, a fluid 712 containing HF and tetrafluorochloroethane is withdrawn as an overhead stream and then recycled to the reactor 703, while a CFC 114 / 114a rich fluid 713 is withdrawn from the bottom of the column.

[0059]

Example 1 Treatment of chlorotetrafluoroethane with hydrogen fluoride 2 g of a chromia catalyst having a particle diameter of 1 mm was packed in a tubular reactor made of Inconel having an inner diameter of 1/4 inch and then placed on the catalyst.
Prefluorination was carried out by passing hydrogen fluoride at a flow rate of 20 ml / min for 24 hours at 0 ° C. Chlorotetrafluoroethane at a flow rate of 8 ml / min was then added to the starting hydrogen fluoride and the mixture was passed over the catalyst. Samples of reactor offgas were taken at various temperatures and analyzed by gas chromatography. Table 1 shows the results.

Table 1 Temperature (° C) 125 Yield (%) 300 14.2 310 16.1 320 36.1

No chloropentarafluoroethane was found in the product gas, so this example is CFC 114 / 114a
Illustrates that the production of chloropentafluoroethane is eliminated when is not present in the HCFC 124 starting material.

Example 2 A chromia catalyst (1 g) was charged into an Inconel reactor (1/4 inch in diameter). HF (60 ml / min) was passed over the catalyst at 340 ° C for 16 hours. The chlorine flow and the HCFC 133a flow were introduced at the flow rates shown below. The offgas composition from the reactor was monitored by gas chromatography. The results are shown in Table 2.

[0063]

Example 3 Purification of HCFC 124 from a mixture containing 124, 114 and 114a This example illustrates the separation of CFC 114 / 114a from HCFC 124 by distillation as compared to separating CFC 115 from HFA 125. To illustrate the ease. In this example, all compositions are given in mol%. 250 theoretical flask, 5 theoretical stage vacuum jacket
90 mol% of 124, 4.5 mol% of 114/114 in a still consisting of a d packed column), a condenser and a take-off controller.
150 g of a mixture of a and 5.5 mol% 133a was introduced. The packed column was stabilized at about -12 C under total reflux at atmospheric pressure. After equilibration, a vapor sample was taken overhead; gas chromatographic analysis showed that the sample had the following composition: 124-99.4 133a-0.15 114 / 114a-0.08

Distillation was continued at a reflux ratio of 5: 1 until about half of the original feed mixture had been distilled. A vapor sample was taken from the top of the distillation column; gas chromatographic analysis results showed that this sample had the following composition: HCFC 124-99.88 CFC 114 / 114a-not detected HCFC 133a-not detected

Comparative Example 1 Using the same equipment as used in Example 3 and HF
Example 3 was repeated using a mixture of A 125-98.2% and CFC 115-1.8%. After equilibrating to about -50 C under total reflux,
A vapor sample was taken; this vapor sample had the following composition: HFA 125-98.0 CFC 115-2.0 After continuing to distill at a reflux ratio of 5: 1 until about half of the feed mixture had been distilled, , The distillate had the following composition: HFA 125-98.3 CFC 115-1.7

[Brief description of drawings]

1 is an embodiment of the invention using two reactors, wherein step (i) is chlorination of 1,1,1,2-tetrafluoroethane, the two reactors being in series It is a schematic flow diagram when it is arranged.

FIG. 2 is an embodiment of the present invention using two reactors, wherein step (i) is chlorination of 1,1,1,2-tetrafluoroethane and the two reactors are in parallel. It is a schematic flow diagram when it is arranged.

FIG. 3: Step (i) is a hydrogen fluoride treatment of perchlorethylene, steps (i) and (iii) are performed in a single reactor and aqueous scrubbing is used to remove hydrogen chloride. 2 is a schematic flow diagram showing an embodiment of the present invention.

FIG. 4 shows an embodiment of the invention using two reactors, wherein step (i) is hydrofluorination of perchlorethylene and the two reactors are arranged in parallel. It is a schematic flow diagram shown.

FIG. 5 is an embodiment of the present invention using two reactors, wherein step (i) is hydrofluorination of perchlorethylene and the two reactors are arranged in series. It is a schematic flow diagram.

FIG. 6 is an embodiment of the present invention using two reactors, wherein step (i) is hydrofluorination of perchlorethylene and the two reactors are arranged in series. It is a schematic flow diagram.

FIG. 7 is a schematic flow diagram showing an embodiment of the present invention when step (i) is hydrofluorination of perchlorethylene and steps (i) and (iii) are performed in a single reactor. is there.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C07C 17/20 C07C 17/20 // C07B 61/00 300 C07B 61/00 300 (72) Inventor Chyars Jyon Shields United Kingdom. Checker. Runcorn. The Heath (No house number) (72) Inventor Jiyon David Scott United Kingdom. Checker. Runcorn. The Heath (No house number)

Claims (32)

[Claims] 1. A formula C contaminated with a compound of formula C ₂ Cl _{x + 1} F _y
Compound of ₂ HCl _x F _y (where x = 1,2 or 3 and y
= 2, 3 or 4 with the proviso that x + y is 5) step (i), a compound of formula C ₂ HCl _x F _y is added to formula C ₂ Cl _{x + 1} Separating from the compound of F _y (ii) and the formula C ₂ H
A process for producing pentafluoroethane, comprising the step (iii) of contacting a compound of Cl _x F _y with hydrogen fluoride in the presence of a fluorination catalyst, thereby producing pentafluoroethane. 2. The method according to claim 1, wherein steps (i), (ii) and (iii) are performed in this order. 3. The product stream from step (iii) is treated to separate unconverted compound of formula C ₂ HCl _x F _y from pentafluoroethane and then to convert unconverted compound of formula C ₂ HCl _x F _y. The method according to claim 1, further comprising a step of recycling to step (i) or step (iii).
The method described in. 4. The recycle stream is of the formula C ₂ present in the recycle stream.
HCl _x compound of F _y and based on the total weight of the compound of formula C ₂ Cl _{x + 1} F _y, which contains a compound of formula C ₂ Cl _{x + 1} F _y of 15 wt% or less, according to claim 3 The method described in. 5. A compound of formula C ₂ HCl _x F _y is chlorotetrafluoroethane and a compound of formula C ₂ Cl _{x + 1} F _y is dichlorotetrafluoroethane. The method described. 6. The production ratio of chloropentafluoroethane is 2% by weight or less based on the amount of the compound of the formula C ₂ HCl _x F _y supplied to the step (iii). The method described in. 7. In step (ii), at least 50% by weight of the compound of formula C ₂ Cl _{x + 1} F _y present in the composition prepared in step (i) is represented by the formula C ₂ HCl _x F _y. The method according to any one of claims 1 to 5, wherein the method is separated from the compound according to. 8. At least 75% by weight of the compound of formula C ₂ Cl _{x + 1} F _y present in the composition prepared in step (i) is represented by the formula C ₂ HCl.
separated from the compound of _x F _y, The method of claim 7. 9. The method according to claim 1, wherein step (ii) comprises distilling the composition. 10. The composition prepared in step (i) comprises a compound of formula C ₂ HCl _x F _{y and} a compound of formula C ₂ Cl _{x + 1} F _y present in the composition.
About 0.1% to about 20% by weight, based on the total weight of the compound of
1 to 9 containing a compound of the formula C ₂ Cl _{x + 1} F _y
The method described in any one of. 11. A composition containing a compound of formula C ₂ HCl _x F _y fed to step (iii) has a formula present in said composition.
Contains a C ₂ HCl _x F _y compound with a compound of formula C ₂ Cl _{x + 1} F _y wherein C ₂ Cl _{x + 1} F _y based on the total weight of 10 wt% or less of the compound of Claim 10. The method according to 10. 12. A composition containing a compound of formula C ₂ HCl _x F _y fed to step (iii) has a formula present in said composition.
Contains a C ₂ HCl _x F _y compound with a compound of formula C ₂ Cl _{x + 1} F _y wherein C ₂ Cl _{x + 1} F _y total weight of 2 wt% or less based on the compound of Claim 11. The method according to 11. 13. The method according to claim 1, wherein step (iii) is carried out at an elevated temperature and in the gas phase. 14. The temperature is about 200 ° C. to about 500 ° C.,
The method according to claim 13. 15. The method according to claim 13, wherein in step (iii), the fluorination catalyst is chromia, chromium oxyfluoride, alumina or aluminum oxyfluoride. 16. In the step (iii), the fluorination catalyst is 1
Chromia with one or more metals, chromium oxyfluoride,
16. The method of claim 15, comprising alumina or aluminum oxyfluoride. 17. In step (iii), the fluorination catalyst is an activity promoting amount of zinc and chromia, chromium oxyfluoride,
17. The method according to claim 16, comprising alumina or aluminum oxyfluoride. 18. Step (i) comprises trichlorethylene or formula C
A process according to claim 1, which comprises chlorinating a compound of ₂ H ₂ X _{4 where} X is fluorine or chlorine. 19. Step (i) and step (iii) are carried out in separate reactors arranged in parallel, and the product stream from the reactors is fed to a common purifier, which pentafluoroethane. And the unconverted compound to be chlorinated from this purifier is recycled to the reactor of step (i) and the unconverted compound of formula C ₂ HCl _x F _y is fed to the reactor of step (iii). 19. The method of claim 18, wherein the method is recirculation. 20. The method according to claim 18, wherein step (i) and step (iii) are carried out in separate reactors arranged in series and the product stream from the reactor is fed to a separate purification unit. . 21. The method of claim 1, wherein step (i) comprises contacting perhaloethylene or pentahaloethane with hydrogen fluoride in the liquid or vapor phase in the presence of a fluorination catalyst. 22. The method of claim 21, wherein step (i) is performed at elevated temperature and in the vapor phase. 23. The method according to claim 22, wherein step (i) and step (iii) are carried out in a single reactor. 24. The method according to claim 21, wherein step (i) and step (iii) are carried out in separate reactors. 25. The product stream from one of the reactor of step (i) or the reactor of step (iii) is fed to the other reactor, and the product stream from the other reactor is carried out by step (ii). 24. The method of claim 23, wherein the method is provided to a purifying device that is called. 26. The reactor of step (i) and the reactor of step (iii) are arranged in parallel, and the product stream from these reactors is processed as a process.
(ii) is fed to a common purifier and the pentafluoroethane is recovered from this purifier, unconverted perhaloethylene is recycled to the reactor of step (i) and unconverted formula C ₂ HCl recirculating the compound of _x F _y to a reactor of step (iii), method according to claim 22. 27. The purifier comprises unreacted perhaloethylene and unconverted formula C ₂ HCl _x F _y (wherein X is 1, 2, or 3).
A first distillation column for separating the compound of Example 1 from other components and recycling to the reactor of step (i), separating and recovering pentafluoroethane from the other components, and also removing chlorotetrafluoroethane. 27. The process according to claim 25 or 26, comprising at least one additional distillation column for separating from the dichlorotetrafluoroethane and recycling. 28. The top stream from the first distillation column is scrubbed with water to remove hydrogen fluoride and hydrogen chloride and then fed to at least one additional distillation column.
The method described in. 29. The at least one additional distillation column comprises two distillation columns, wherein pentafluoroethane is separated from chlorotetrafluoroethane and dichlorotetrafluoroethane in the first additional distillation column, Dichlorotetrafluoroethane is separated from chlorotetrafluoroethane in an additional distillation column according to claim 26 or 2.
7. The method according to 7. 30. The method according to any of claims 21-29, wherein the perhaloethylene is perchlorethylene. 31. The method according to claim 21, wherein in step (iii), the fluorination catalyst comprises chromia, chromium oxyfluoride, alumina or aluminum oxyfluoride. 32. (i) at least 50% by weight to about 95% by weight
Chlorotetrafluoroethane, (ii) about 0.5% by weight to about 2
Consisting of 0% by weight hydrogen fluoride and (iii) up to 2% by weight dichlorotetrafluoroethane (the above% by weight is based on the total weight of these three components present in the composition),
A composition suitable for conversion to pentafluoroethane.