WO1999040053A1

WO1999040053A1 - Production of heptafluoropropane

Info

Publication number: WO1999040053A1
Application number: PCT/GB1999/000175
Authority: WO
Inventors: Paul Nicholas Ewing
Original assignee: Imperial Chemical Industries Plc
Priority date: 1998-02-06
Filing date: 1999-01-19
Publication date: 1999-08-12
Also published as: JP2002502834A; AU2287199A; AR018067A1; GB9802487D0; EP1051377A1; ZA99531B

Abstract

Production of heptafluoropropane from chlorocarbon feedstocks, e.g. 2-hydro-2-chloropropane or a 2-chloro-propene, by reaction with HF in a 2-stage reaction process.

Description

Production of Heptafluoropropane

The present invention relates to a process for the production of 1,1,1,2,3,3,3-heptafluoropropane from chlorocarbon feedstocks, particularly from certain 2-hydro-2-chloropropanes or certain 2-chloropropenes as hereinafter defined, more particularly in a 2-reaction stage process.

Hydrofluorocarbons, referred to hereinafter for convenience as HFC's, are widely used as replacements for chlorofiuorocarbon compounds. Such uses include use in medical applications, for example as an aerosol propellant, use as a fire suppressant, use in refrigeration applications and in other applications. 1,1,1,2,3,3,3-heptafluoropropane, which will be referred to hereinafter for convenience as HFC 227ea, has zero ozone depletion potential and is particularly beneficial in medical propellant applications in the light of its combination of properties including low toxicity, non-flammability, solvent properties and boiling point. It is known in the art to produce HFC 227ea by the hydrofluorination of hexafluoropropene, hereinafter referred to for convenience as HFP, using hydrogen fluoride as the hydrofluorination agent, optionally in the presence of a catalyst, in the liquid phase or vapour phase.

The liquid phase reaction of HFP with hydrogen fluoride for the preparation of HFC 227ea is well known in the art. For example, as is more fully described in WO 97/11042, EP 0,634,383, WO 96/02483 and EP 0,634,384.

The vapour phase reaction of HFP with hydrogen fluoride for the preparation of HFC 227ea has been described in, for example, GB 902590 and US 4,158,023.

A major disadvantage in the production of HFC 227ea from HFP is the high cost ofHFP. The production of HFC 227ea from chlorocarbon feedstocks, eg octachloropropane, has been described.

The conversion of octachloropropane into HFC 227ea via hydrodechlorination of 2-chloro-heptafluoro-propane has been described in EP 0,539,989. This process is a 2-reaction stage process which, it will be appreciated, has the disadvantage of requiring two reaction technologies, namely fluorination and hydrodechlorination, to convert the chlorocarbon starting material into HFC 227ea.

The conversion of octachloropropane into HFC 227ea by a circuitous 3-reaction stage process has been described in WO 96/17815. This process has the further

1 disadvantage of requiring two reaction technologies, namely fluorination and hydrodechlorination, to convert the chlorocarbon staring material into HFC 227ea.

We have now found that certain hydrochloropropanes or certain chloropropenes as hereinafter defined can surprisingly be readily converted into HFC 227ea in a 2-reaction stage production process, both of which reaction stages involve fluorination with hydrogen fluoride, hereinafter referred to for convenience as HF.

2-Chloro-l,l,l,3,3,3-hexafluoropropane, hereinafter referred to for convenience as HCFC 226da, is an intermediate in the process according to the present invention and we have found surprisingly that conversion thereof into HFC 227ea is equilibrium limited. Accordingly, removal of at least a major part of the HCl generated in the first step of the process according to the present invention facilitates conversion of HCFC

226da into HFC 227ea

According to the present invention there is provided a process for the production of HFC 227ea which process comprises the steps of: A) reacting a 2-hydro-2-chloropropane of formula C₃HC1_(7.X)F_X where x = 0-5 or a

2-chloropropene of formula C₃Cl₍₆__y)F_y where y = 0-4 with HF to form a product mixture comprising HCFC 226da and HCl;

B) separating at least a major part of the HCl from the HCFC 226da produced in

Step (A); and C) reacting the HCFC 226da depleted in HCl from Step B with HF in the vapour phase to form HFC 227ea.

Preferably HCFC 226da is the major product of Step (A) of the process according to the present invention.

As examples of the 2-hydro-2-chloropropane of formula C₃HC1_(7.X)F_X where x = 0-5 which may be used in Step A of the process according to the present invention may be mentioned inter alia l,l,l-trifluoro-2,3,3,3-tetrachloropropane, l,l,l,3-tetrafluoro-2,3,3-trichloropropane, or preferably 2-hydroheptachloropropane, which is hereinafter referred to for convenience as "HHCP"

As examples of the 2-chloropropene of formula C₃C1₍₆__X)F_X where x = 0-4 which may be used in Step A of the process according to the present invention may be mentioned inter alia 1-fluoropentachloropropene, 1,1-difluorotetrachloropropene or preferably 1,1,1-trifluoro-trichloropropene or more preferably hexachloropropene. Where the 2-hydro-2-chloropropane of formula C₃HCl_{(7 x)}F_λ where x = 0-5 used in Step A of the process according to the present invention is HHCP the process may be represented by the following equations.

CC1₃CHC1CC1₃ + 6HF — > CF₃CHC1CF₃ + 6HC1 CF₃CHC1CF₃ + HF — > CF₃CHFCF₃ + HCl

Step (A) of the process according to the present invention may be carried out in the liquid or vapour phase.

Where Step (A) is carried out in the liquid phase it is carried out in the presence of a suitable catalyst, at a temperature within the range 50-150°C, at pressures up to 30 bar, using a molar ratio of HF: organic feed at least as required by stoichiometry to fluorinate the organic starting material to HCFC 226da. As examples of suitable Lewis and or Bronsted catalysts therefor may be mentioned inter alia antimony pentahalides, tantalum pentahalides, niobium pentahalides, tin tetrahalides, titanium tetrahalides, boron trihalides, HF:amine complexes, eg nHF:NR₃ where n = 1-10 and R = alkyl, SO₃, FSO₃H and mixtures thereof.

Where Step (A) is carried out in the vapour phase it is carried out in the presence of a suitable catalyst, at a temperature within the range 150-450°C, using a molar ratio of HF:organic feed at least as required by stoichiometry to fluorinate the organic starting material to HCFC 226da, preferably an excess of HF is used. For example, where the starting material is HHCP a 6: 1 molar ratio of HF:HHCP is required, preferably the molar ratio of HF:HHCP is in the range 6:1-100:1, more preferably in the range 6:1- 50: 1. The reaction can be carried out at within a wide range of pressures, from subatmospheric to superatmospheric, preferably at a pressure within the range 1-50 bar. As examples of suitable fluorination catalysts which may be used in Step (A) of the process according to the present invention, where it is carried out in the vapour phase, may be mentioned inter alia (i) fluorination catalysts based on metal oxides, halides or oxyhalides or mixed metal oxides/halides/oxyhalides, for example chromia or alumina; (ii) other metallic oxides/halides/oxyhalides supported on chromia or alumina, for example oxides of zinc, iron, magnesium or nickel; and (iii) metal oxides/halides/oxyhalides, or mixed metal oxides/halides/oxyhalides supported on carbon.

Preferably, the fluorination catalyst is dried and subjected to a pretreatment, eg with hydrogen fluoride, prior to use.

3 Preferred fluorination catalysts, where Step (A) in the process of the present invention is carried out in the vapour phase, are disclosed in our EP 0,502,605 and WO 93/25508, the disclosures in which are incorporated herein by way of reference.

The fluorination catalyst may be compressed into pellets and used in the vapour phase in a fixed bed or, alternatively, catalysts of appropriate particle size may be used in a fluidised bed.

We do not exclude the possibility that the product stream from Step (A) may contain under-fluorinated propenes and propanes, eg isomers of dichloro-pentafluoropropane such as HCFC 225 da, which can either be recycled to Step (A) for conversion into HCFC 226da or, optionally, fed to Step (C).

In Step (B) of the process according to the present invention, separation of the HCl liberated in Step (A) from the product stream therefrom is typically carried out by distillation.

Step (C) in the process according to the present invention is carried out in the vapour phase over a suitable fluorination catalyst in the temperature range 200-450°C, using a molar feed ratio of HF:HCFC 226da of between 1 :1 and 50:1, preferably between 1 :1 and 20:1 and a contact time of 0.2 -120 sees., preferably 0.5 - 30 sees. The reaction can be carried out within a wide range of pressures, from subatmospheric to superatmospheric, preferably from 1-50 bar. A suitable fluorination catalyst for use in Step (C) of the process according to the present invention may be chosen from the aforementioned fluorination catalysts for use in carrying out Step (A). Preferred fluorination catalysts for use in Step C are disclosed in our EP 0,502,605 and WO 93/25508.

It will be appreciated that for the production of pure HFC 227ea by the process according to the present invention HCl produced in Step (C) needs to be separated therefrom.

Separation of HCl from a reaction or product stream is an expensive process. In the process hereinafter described in relation to Figure 4 two distillation columns for the separation of HCl are employed, ie there are two distillation columns in which essentially pure HCl is removed as an overhead product.

In preferred embodiments of the present invention, the process thereof is carried out in systems containing only one distillation column for the separation of byproduct HCl. In a first preferred embodiment of the present invention, in which both Steps (A) and (B) are carried out in the vapour phase, the product stream from Step (C) is combined with the product stream from Step (A) and fed to a distillation column for the separation of HCl as is more fully described hereinafter in relation to Figure 1. In a second preferred embodiment of the present invention, in which both Steps

(A) and (B) are carried out in the vapour phase, the product stream from Step (C) is combined with starting material and fed to Step (A) and the product stream from Step (A) is fed to a distillation column/condenser for the separation of HCl as is more fully described hereinafter in relation to Figure 2. In a third preferred embodiment of the present invention, in which Step (A) is carried out in the liquid phase, the product stream from Step (C) is combined with a portion of the product stream from Step (A) and fed to a distillation column for the separation of HCl as is more fully described hereinafter in relation to Figure 3.

For simplicity the present invention will hereinafter be described by reference to the use of HHCP as starting material.

The present invention is further illustrated, by way of example only, by reference to the drawings appended hereto.

In the drawings: Figure 1 illustrates a so-called Parallel Reactor Configuration; Figure 2 illustrates a so-called Reverse Series Reactor Configuration;

Figure 3 illustrates a process comprising a liquid phase HCFC 226da production stage and a vapour phase HFC 227ea production stage; and Figure 4 illustrates a so-called Two HCl-Still Process Configuration.

In Figure 1, reactor (102), in which HCFC 226da is formed in the presence of a suitable vapour phase fluorination catalyst in Step (A), is fed with stream (113) containing HHCP and HF in a molar ratio of at least 7:1, and stream (112) containing underfluorinated precursors to HCFC 226da. Stream (104), the off-gas from reactor (102) containing HCFC 226da, is combined with stream (103), the off-gas from reactor (101), and fed to distillation column (106) via line (105). HCl is removed from column (106) in stream (107) in Step (B), while HF, HFC 227ea, HCFC 226da and underfluorinated HCFC 226da precursors are removed from the base of column (106) via stream (108) and fed to distillation column (109). The HFC 227ea HF azeotrope is removed from column (109) in stream (110) and subjected to further purification in order to obtain product HFC 227ea. A side-stream (111) containing HF and HCFC 226da is removed from column (109) and fed to reactor (101) in which HFC 227ea is formed in the presence of a suitable vapour phase fluorination catalyst in Step (C). Stream (112), containing underfluorinated precursors to HCFC 226da, is removed from the bottom of distillation column (109) and fed to reactor (102).

In Figure 2, feedstock HHCP and HF is fed to the process via stream (202) and mixed with the off-gas from reactor (201) and the recycle stream (212) to form the feedstream (203) to reactor (204) in which HCFC 226da is formed in Step (A) in the presence of a suitable vapour phase fluorination catalyst. Stream (205), containing the off-gas from (204), is fed to distillation column (206) in which HCl is removed as an overhead product via stream (207) in Step (B). Stream (208), containing HF, HFC 227ea, HCFC 226da, and underfluorinated precursors of HCFC 226da, is removed as bottoms stream from distillation column (206) and fed to distillation column (209). Stream (210), containing the HFC 227ea/HF azeotrope, is removed as an overheads stream from distillation column (209) for further work-up to obtain product HFC 227ea. A side-stream (211) containing HF and HCFC 226da is removed from column (209) and fed to reactor (201) in which HCFC 226da is reacted with HF in Step (C) in the presence of a suitable vapour phase fluorination catalyst to form HFC 227ea. Stream (212), containing underfluorinated precursors to HCFC 226da, is removed from the bottom of distillation column (209) and fed to reactor (204).

It is preferred in the so-called reverse series configuration illustrated in Figure 2 that the operating temperature of reactor (204) in which Step (A) is carried out is less than that of reactor (201) in which Step (C) is carried out to reduce the extent of back reaction of HFC 277ea formed in (201) to HCFC 226da in reactor (204). In Figure 3, a feedstream (301) comprising HHCP and HF is fed to liquid-phase reactor (302), in which Step (A) is carried out, charged with a suitable liquid-phase fluorination catalyst. The off-gas from the reactor, stream (303), is fed to separation column (304) from which a heavies stream (305) containing HF and underfluorinated precursors to HCFC 226da and a lights stream (306) containing HCl, HF and HCFC 226da, are removed. Stream (305) is returned to reactor (302). Stream (306) is combined with stream (314), containing HF, HFC 227ea and unconverted HCFC 226da from the HFC 227ea production stage, and fed to distillation column (307) in which Step (B) is carried out, from which an overheads stream (308) containing HCl, and a bottoms

6 stream (309) containing HF,HFC 227ea and HCFC 226da are removed. Stream (309) is fed to distillation column (310) from which stream (311), containing the HFC 227ea HF azeotrope is removed as an overheads stream for further work-up in order to obtain product HFC 227ea. The bottoms product (312) from column (310), containing HF and HCFC 226da, is fed to reactor (313) in which Step (C) is carried out in which HCFC 226da is reacted with HF in the presence of a suitable vapour phase fluorination catalyst to form HFC 227ea. Stream (314), containing the off-gas from reactor (313) is combined with stream (306) as described above.

In Figure 4, stream (401) containing HHCP and HF is combined with stream (406) containing underfluorinated HCFC 226da precursors and fed as a vapour to reactor (402) charged with a suitable vapour-phase fluorination catalyst in which Step (A) is carried out. The off-gas (403) from reactor (402) is fed to a distillation column (404) in which Step (B) is carried out in which HCl is removed as lights stream (405). A bottoms stream (406) of underfluorinated HCFC 226da precursors is recycled to reactor (402) and a side-stream (407) of HF and HCFC 226da is combined with a HF and HCFC 226da recycle stream (415) and fed to reactor (408) in which Step (C) is carried out. Reactor (408) is charged with a suitable vapour-phase fluorination catalyst. The off-gas (409) from reactor (408), containing HF, HCFC 226da, HFC 227ea and HCl, is fed to distillation column (410) in which HCl is removed as overheads stream (41 1). HF, HFC 227ea and HCFC 226da is removed as bottoms stream (412) and fed to distillation column (413). In distillation column (413), an overhead stream (414), containing HFC 227ea/HF azeotrope, is separated from the bottoms stream (415) containing HF and HCFC 226da, which is recycled to reactor (408).

The present invention is illustrated but not limited by the following Examples. Example 1

This Example illustrates the effect of the presence of HCl on the conversion of HFC 226da into HFC 227ea in Step C of the process according to the present invention. The results are shown in Table 1. Table 1

Run No Molar Feed Ratio HFC 226da conversion at HF : HFC 226da : HCl equilibrium (mole %)

1 10 : 1 : 0 34

2 10 : 1 : 1 14

3 5 : 1 : 0 26

4 5 : 1 : 1 8

From Table 1 the advantages of carrying out the conversion of HFC 226da into

HFC 227ea in the absence of HCl can be readily seen.

Example 2

This Example illustrates the production of HCFC 226da from a 2-chloropropene of formula C₃Cl_(6.y)F_y where y = 3 in Step A of the process according to the present invention.

Fluorination of 1,1,1 -trifluoro-trichloropropene was carried out in the vapour phase at 280-300°C using a molar feed ratio of HF:CF₃CC1=C1₂ = 6.8:1, at a contact time of 1.8 seconds over an amorphous chromia catalyst pretreated with HF . The following results were obtained:

CF3CC1=C12 conversion = 47.3%

HCFC 226da selectivity = 45%

Selectivity to underfluorinated HCFC 226da precursors = 51 %

HFC 227ea selectivity = 0%

From the above results it can be seen that under the reaction conditions employed

HCFC 226da is formed in good yield and selectivity in Step (A) of the process according to the present invention

Example 3

This Example is a Comparative Test which illustrates the reaction of a

2-chloropropene of formula C₃Cl_(6.y)F_y where y = 3 with HF without an intermediate step for the separation of HCl.

CF3CC1=C12 conversion = 47.3%

HCFC 226da selectivity = 45%

Selectivity to underfluorinated HCFC 226da precursors = 51%

HFC 227ea selectivity = 0%

From the above results it can be seen that under the reaction conditions employed omparative Test no HFC 227ea was detected.

Claims

1. A process for the production of HFC 227ea which process comprises the steps of:

A) reacting a 2-hydro-2-chloropropane of formula C₃HCl_(7.x)F_╬╗ where x = 0-5 or a 2-chloropropene of formula C₃Cl_(6.y)F_y where y = 0-4 with HF in the presence of a suitable catalyst to form a reaction mixture comprising HCFC 226da and HCl;

B) separating at least a major part of the HCl from the product mixture produced in Step (A); and

C) reacting the product mixture depleted in HCl from Step (B) with HF in the vapour phase to form HFC 227ea.

2. A process as claimed in Claim 1 wherein HFC 226da is the major fluoro-organic product of Step (A).

3. A process as claimed in Claim 1 wherein the 2-hydro-2-chloropropane of formula C₃HC1_(7.X)F_X where x = 0-5 is 2-hydroheptachloropropane.

4. A process as claimed in Claim 1 wherein the 2-chloropropene of formula C₃Cl_(6.y)F_y where y = 0-4 is 1,1,1 -trifluoro-trichloropropene or preferably hexachloropropene.

5. A process as claimed in Claim 1 wherein, where Step (A) is carried out in the liquid phase, the fluorination catalyst is selected from antimony pentahalides, tantalum pentahalides, niobium pentahalides and mixtures thereof.

6. A process as claimed in Claim 1 wherein where Step (A) is carried out in the vapour phase a stoichiometric excess of HF is used.

7. A process as claimed in Claim 1 wherein the fluorination catalyst used in Step (C) or in Step (A), where Step (A) is carried out in the vapour phase, is selected from (i) fluorination catalysts based on metal oxides, halides or oxyhalides or mixed metal oxides/halides/oxyhalides; (ii) other metallic oxides/halides/oxyhalides supported on chromia or alumina; and (iii) metal oxides/halides/oxyhalides, or mixed metal oxides/halides/oxyhalides supported on carbon.

8. A process as claimed in Claim 1 wherein the fluorination catalyst is dried and subjected to a pretreatment prior to use.

9. A process as claimed in Claim 1 wherein both Steps (A) and (B) are carried out in the vapour phase and wherein the product streams from both steps are combined and fed to a distillation column for the separation of HCl.

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10. A process as claimed in Claim 1 wherein both Steps (A) and (B) are carried out in the vapour phase and wherein the product stream from Step (C) is combined with starting material and fed to Step (A) and wherein the product stream from Step (A) is fed to a distillation column for the separation of HCl.

11. A process as claimed in Claim 1 wherein Step (A) is carried out in the liquid phase and wherein the product stream from Step (C) is combined with a portion of the product stream from Step (A) and fed to a distillation column for the separation of HCl.

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