WO2016156870A1

WO2016156870A1 - Process

Info

Publication number: WO2016156870A1
Application number: PCT/GB2016/050933
Authority: WO
Inventors: Claire REES; Maxine DORAN; Andrew Sharratt
Original assignee: Mexichem UK Ltd; Mexichem Fluor SA de CV
Current assignee: Mexichem UK Ltd; Mexichem Fluor SA de CV
Priority date: 2015-04-02
Filing date: 2016-04-01
Publication date: 2016-10-06
Anticipated expiration: 2017-10-02
Also published as: GB201505712D0

Abstract

A process for preparing a (hydro)haloalkene comprising dehydrohalogenating a hydrohaloalkane in the presence of a catalyst comprising a ceramic material.

Description

PROCESS

The present invention relates to a process for preparing (hydro)haloalkenes and particularly to a process for preparing C3-7 (hydro)haloalkenes by the catalytic dehydrohalogenation of C3-7 hydrohaloalkanes.

The listing or discussion of information or a prior-published document in this specification should not necessarily be taken as an acknowledgement that the information or document is part of the state of the art or is common general knowledge.

C3-7 (hydro )fluoroalkenes such a hydrofluoropropenes can be conveniently prepared from corresponding hydro(halo)fluoroalkanes by dehydrohalogenation. The transformation can be effected thermally, i.e. by pyrolysis, catalytically, by contacting a hydro(halo)fluoroalkane with a catalyst under suitable conditions, or chemically, typically by contacting a hydro(halo)fluoroalkane with strong bases such as alkali metal hydroxides. For commercial operation, catalytic dehydrohalogenation is believed to be preferred, and is discussed in more detail below.

The hydrofluoropropene 1 ,1 ,1 ,2,3-pentafluoropropene (HFO-1225ye), for example, can be prepared by contacting and dehydrofluorinating 1 ,1 ,1 ,2,3,3-hexafluoropropane in the gaseous state with trivalent chromium oxide or partially fluorinated trivalent chromium oxide, optionally in the presence of oxygen (see US 5,679,875).

EP-A-1900716 describes the use of a variety of catalysts, including fluorinated chromia, fluorinated alumina, metal fluorides, metal fluorides and carbon-supported transition metals, in the dehydrofluorination of 1 ,1 ,3,3,3-pentafluoropropane (HFC-245fa) to 1 ,3,3,3- tetrafluoropropene (HFO-1234ze).

WO 2008/040969 describes the use of a zinc/chromia catalyst for the preparation of various (hydro )fluoropropenes, including HFO-1225ye and 2,3,3,3-tetrafluoropropene (HFO-1234yf) by dehydrohalogenation of corresponding hydro(halo)fluoropropanes.

Notwithstanding the above processes, catalytic dehydrohalogenation has its problems, one of which is because the chemistry is thought to inherently foul the catalyst. Catalyst fouling typically is controlled by one or more of (a) using the mildest conditions possible, (b) increasing the concentration of hydrogen fluoride, and (c) limiting the exposure of the catalyst to high partial pressure of unsaturates. The use of measures (b) and (c) above is very limited in the preparation of C3-7 (hydro)fluoroalkenes by the catalytic dehydrohalogenation (particularly dehydrofluorination) of C3-7 hydro(halo)fluoroalkanes. Consequently, operating cycles and catalyst life are believed generally to be relatively short compared to (hydro)fluorination chemistry. Short operating cycles and catalyst life require more frequent catalyst regeneration, or simply more catalyst, each of which have cost implications. Some catalysts, particularly certain alumina-supported catalysts and/or zirconia-based catalysts, can be difficult to regenerate. This is believed to be because the coke in a used dehydrohalogenation catalyst can be difficult to combust.

Moreover, many known catalysts can be temperamental in that selectivity for the preferred reaction product may be diminished or lost following an unexpected event in the process, including a deactivation of the process, or through, say, the presence and/or build-up of impurities in the reaction vessel and/or on the catalyst.

Thus, there is a need for an economic process for preparing (hydro)haloalkenes, such as hydrofluoropropenes and hydrochlorofluoropropenes, using highly stable and regenerable catalysts, which exhibit consistent selectivity, including after an outage in the process or when in the presence of impurities.

The invention addresses the foregoing and other deficiencies by the provision of a process for preparing a (hydro)haloalkene comprising dehydrohalogenating a hydrohaloalkane in the presence of a catalyst comprising a ceramic material.

Ceramic materials such as those described herein surprisingly provide catalysts of highly stable performance for use in dehydrohalogenation processes.

Preferably, the process comprises the preparation of a (hydro)(chloro)fluoroalkene comprising dehydrohalogenating a hydro(chloro)fluoroalkane in the presence of a catalyst comprising a ceramic material.

Advantageously, the process comprises the preparation of a C3-7 (hydro)haloalkene comprising dehydrohalogenating a C3-7 hydrohaloalkane in the presence of a catalyst comprising a ceramic material. In preferred embodiments, the process comprises the preparation of a C3-7 (hydro )fluoroalkene comprising dehydrohalogenating a C3-7 hydro(halo)fluoroalkane in the presence of a catalyst comprising a ceramic material. The ceramic catalysts of the present invention are nonmetallic solids comprising metal, nonmetal or metalloid atoms primarily held in ionic and covalent bonds. The metalloid and non metalloid species being selected from the elements Al, Si, B, C, N, Ti, Zr, Ce, Y, W. Particularly useful ceramic catalysts include but are not limited to metal and non-metal carbides, nitrides, silicides and borides, for example silicon carbide and nitride, boron carbide and nitride, titanium carbide and tungsten carbide. The ceramic materials may also include ceramic alloys. Ceramic alloys comprise combinations of materials that include ceramics and additional materials such as metal alloys or indeed other ceramics. For example, a ceramic alloy can be prepared by combining the metal alloy of boron, aluminium and magnesium (AIMgBi4) with titanium boride (T1B2).

Preferably, the catalyst comprises at least one ceramic material selected from the group silicon carbide, silicon nitride, metal and/or non-metal silicides and metal and/or non-metal borides. Most preferably, the catalyst comprises silicon carbide.

Preferably, the catalyst further comprises a metal, metal halide and/or a metal oxide. The metal, the metal halide or the metal oxide may be one or more of aluminium, calcium, magnesium, chromium, iron, nickel, copper, potassium, titanium, vanadium, manganese, cobalt, tin and cerium, preferably copper or nickel.

The metal may be deposited or embedded on the surface of the ceramic material, with the ceramic material acting as a support or as a co-catalyst. The catalysts of the invention typically have a surface area of between 0.001 m²/g and 50 m²/g, for example from 0.1 to about 10 or 20 m²/g. The ceramic catalysts of the present invention may be subject to various pre-treatments and conditioning steps before and during use. For example, they may be pre-treated with hydrogen fluoride, hydrogen chloride, chlorine, air, water or hydrogen. Such treatment typically has the effect of improving some aspect of the physical and catalytic properties of the catalyst for dehydrohalogenation reactions. The catalysts of the invention may be provided in any suitable form known in the art. For example, they may be provided in the form of pellets or granules of appropriate size for use in a fixed bed or a fluidised bed. They may be provided as monoliths of varying shape, size and aspect ratio or even as foams or sponges. Additionally or alternatively, the catalysts may form at least part of the internal surface of the or a reaction vessel.

In use, the catalyst may be regenerated or reactivated periodically by heating in air at a temperature of from about 300°C to about 1000°C. Air may be used as a mixture with an inert gas such as nitrogen or with hydrogen fluoride, which emerges hot from the catalyst treatment process and may be used directly in fluorination processes employing the reactivated catalyst. It has been found that the spent catalyst from the process of the invention typically is unexpectedly easy to regenerate because of their high thermal stability compared to known catalysts such as those based on chromia which suffer thermochemical damage and activity loss during regeneration steps, especially regeneration steps requiring prolonged treatment at high temperatures.

Typically, the process of the invention comprises contacting the hydrohaloalkane (e.g. a C3-7 hydrohaloalkane such as a C3-7 hydro(chloro)fluoroalkane) with the catalyst with or without added hydrogen fluoride (HF) in the vapour or liquid phase (preferably the vapour phase) and may be carried out at a temperature of from 0 to 700 °C, e.g. 50 to 500 °C, for example from about 300 to about 500°C. In certain preferred embodiments, the process may be carried out with no co-feed of HF. The process may be carried out at atmospheric, sub- or super atmospheric pressure, preferably up to about 30 bara, for example from about 1 to about 25 bara.

Preferably, the hydrohaloalkane (e.g. hydro(halo)fluoroalkane) is contacted without HF (e.g. without a HF feed) in the vapour phase at a temperature of from about 400 to about 500°C, e.g. from about 420 to about 470°C. Preferably, the process is conducted at a pressure of from 1 to 20 bara. Of course, the skilled person will appreciate that the preferred conditions (e.g. temperature, pressure for conducting the process of the invention may vary (even outside the above ranges) depending on the nature of the hydrohaloalkane and (hydro)haloalkene, and the catalyst being employed.

The process of the invention can be carried out in any suitable apparatus, such as a static mixer, a stirred tank reactor or a stirred vapour-liquid disengagement vessel. The process may be carried out batch-wise, or continuously. Either the batch-wise process or the continuous process may be carried out in a "one-pot" fashion, or using two or more discrete reaction zones and/or reaction vessels. Of course, even in a "continuous" process, the skilled person will appreciate that the process will need to paused periodically, e.g. for maintenance and/or catalyst regeneration. The dehydrohalogenation can be carried out in the absence of an HF feed but it may be desirable in certain embodiments to use some HF in order to prevent and/or retard excessive decomposition of the organic feed and/or coking of the catalyst. Typically, the HF:organics ratio in the process of the invention if an HF feed is utilised will range from about 0.01 :1 to about 1 :1 , preferably from about 0.1 :1 to about 1 :1 , more preferably from about 0.5: 1 to about 1 :1.

Unless otherwise stated, as used herein, a (hydro)haloalkene is an alkene in which at least one of the hydrogen atoms has been replaced by a halogen selected from one or more of fluorine, chlorine, bromine and iodine (preferably fluorine and/or chlorine).

Preferably, the (hydro)haloalkene is a (hydro)(chloro)fluoroalkene. By the term (hydro)(chloro)fluoroalkene, we include hydrochlorofluoroalkenes, hydrofluoroalkenes and perfluoroalkenes. Unless otherwise stated, as used herein, a (hydro)fluoroalkene is an alkene in which at least one of the hydrogen atoms has been replaced by fluorine, i.e. a hydrofluoroalkene or a perfluoroalkene.

Unless otherwise stated, as used herein, a hydro(halo)fluoroalkane is an alkane in which at least one but not all hydrogen atom has been replaced by a fluorine atom and optionally at least one hydrogen atom has been replaced by a halogen selected from chlorine, bromine and iodine. Thus, hydro(halo)fluoroalkanes contain at least one hydrogen, at least one fluorine and optionally at least one halogen selected from chlorine, bromine and iodine. In other words, the definition of a hydro(halo)fluoroalkane includes, for example, a hydrofluoroalkane, i.e., an alkane in which at least one but not all of the hydrogen atoms have been replaced by fluorine, and a hydrochlorofluoroalkane.

For the avoidance of doubt, as used herein, any reference to a C3-7 (hydro)haloalkene, (hydro )fluoroalkene, (hydro)(chloro)fluoroalkene, hydrofluoroalkane, hydro(chloro)fluoroalkane or hydro(halo)fluoroalkane refers to a (hydro)haloalkene, (hydro )fluoroalkene, (hydro)(chloro)fluoroalkene, hydrofluoroalkane, hydro(chloro)fluoroalkane or hydro(halo)fluoroalkane having from 3 to 7 carbon atoms. The (hydro)haloalkenes produced by the process of the invention contain a double bond and may thus exist as E (entgegen) and Z (zusammen) geometric isomers about each individual double bond. All such isomers and mixtures thereof are included within the scope of the invention.

Unless otherwise stated, as used herein, by the term "dehydrohalogenation" (or dehydrohalogenating), we refer to the removal of hydrogen halide (e.g. HF, HCI, HBr or HI), for example from a hydrohaloalkane (e.g. hydro(halo)fluoroalkane). Thus the term "dehydrohalogenation" includes "dehydrofluorination", "dehydrochlorination", "dehydrobromination" and "dehydroiodination".

The process of the invention is suitable for preparing any hydrohaloalkene, such as a C3-7 (hydro)fluoroalkene or C3-7 (hydro)(chloro)fluoroalkene, by dehydrohalogenating (e.g. dehydrofluorinating or dehydrochlorinating) a hydrohaloalkane, such as a C3-7 hydro(halo)fluoroalkane. Optionally, the or a C3-7 hydro(halo)fluoroalkane or C3-7 hydro(chloro)fluoroalkane may first be fluorinated to a C3-7 hydrofluoroalkane which may then be dehydrofluorinated to a C3-7 (hydro )fluoroalkene. A preferred group of (hydro)haloalkenes prepared by the process of the invention is (hydro)(chloro)fluoroalkenes, of which C3-7 (hydro)(chloro)fluoroalkenes are more preferred. The process of the invention is particularly suited to the preparation of C3-7 hydrochlorofluoroalkenes and C3-7 hydrofluoroalkenes. The invention is particularly suited to the preparation of (hydro)(chloro)fluoropropenes and (hydro)(chloro)fluorobutenes, especially (hydro)(chloro)fluoropropenes.

By way of example and for simplicity, unless otherwise stated, the remainder of the specification will describe the process of the invention with reference to the preparation of (hydro)(chloro)fluoropropenes. The skilled person will understand that such discussion is applicable to the preparation of other (hydro)haloalkenes such as C4-7 hydrochlorofluoroalkenes and C4-7 hydrofluoroalkenes. .

(Hydro )fluoropropenes prepared by the process of the invention may contain 0, 1 , 2, 3, 4 or 5 hydrogen atoms and 1 , 2, 3, 4, 5 or 6 fluorine atoms. Preferred (hydro )fluoropropenes are those having from 3 to 5 fluorine atoms (and thus from 1 to 3 hydrogen atoms), particularly 4 or 5 fluorine atoms (and thus 1 or 2 hydrogen atoms). In other words, preferred (hydro)fluoropropenes are trifluoropropenes, tetrafluoropropenes and pentafluoropropenes, particularly tetrafluoropropenes and pentafluoropropenes, and especially tetrafluoropropenes.

A preferred trifluropropene prepared by the process of the invention is 3,3,3- trifluoropropene (HFO-1243zf). HFO-1243zf can be conveniently prepared by dehydrohalogenation of compounds of the type CF3CH2CH2X, where X is a halogen (F, CI, Br, I). Particularly preferred are compounds of this type where X is F or CI, namely CF3CH2CH2F (HFC-254fb) or CF₃CH₂CH₂CI (HCFC-253fb).

A preferred pentafluoropropene prepared by the process of the present invention is 1 ,2,3,3,3-pentafluoropropene (HFO-1225ye) prepared by dehydrofluorination of 1 ,1 ,1 ,2,3,3-hexafluoropropane (HFC-236ea).

Preferred tetrafluoropropenes prepared by the process of the present invention include Z and/or E-1 ,3,3,3-tetrafluoropropene (HFO-1234ze, both E and Z isomers) and 2,3,3,3- tetrafluoropropene (HFO-1234yf).

HFO-1234ze is preferably prepared by dehydrofluorination of 1 ,1 ,1 ,3,3- pentafluoropropane (245fa) or dehydrochlorination of 1 ,1 ,1 ,3-tetrafluoro-3-chloropropane (244fa).

HFO-1234yf can be prepared by dehydrofluorination of 1 ,1 ,1 ,2,2-pentafluoropropane (HFC-245cb) or 1 ,1 , 1 ,2,3-pentafluoropropane (HFC-245eb).

The preparation of HFO-1234yf by the present invention is especially preferred by dehydrochlorination of 1 ,1 ,1 ,2-tetrafluoro-2-chloropropane (HCFC-244bb).

In a preferred aspect of the invention, there is provided the use of silicon carbide as a catalyst in a dehydrohalogenation process for the preparation of HFO-1234yf from HCFC- 244bb.

Preferred hydrochlorofluoropropenes that can be prepared by the process of the invention include trifluorochloropropenes such as 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd) and 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf). HCFO-1233zd can be prepared in the accordance with the process of the invention by, for example, dehydrochlorinating 1 ,2-dichloro-3,3,3-trifluoropropane (HCFC-243db) and/or

1.1 - dichloro-3,3,3-trifluoropropane (HCFC-243fa) or by dehydrofluorinating HCFC-244fa. For the avoidance of doubt, we include both the c/^'s and trans isomers of HCFO-1233zd within the scope of the invention.

HCFO-1233xf can be prepared in the accordance with the process of the invention by, for example, dehydrochlorinating 1 ,2-dichloro-3,3,3-trif!uoropropane (HCFC-243db) and/or

2.2- dichloro-3,3,3-trifluoropropane (HCFC-243cb). Preferably, HCFO-1233xf is prepared by dehydrochlorinating HCFC-243db.

Preferred hydrofluorobutenes prepared by the process of the invention include Z,E or Z&E- 1 ,1 ,1 ,4,4,4-hexafluorobutene (HFO-1336mzz) and all possible fluorobutene isomers prepared by the dehydrohalogenation of 3-chloro-1 ,1 ,1 ,3-tetrafluorobutane, for example Z/E-3-chloro-1 ,1 ,1-trif!uorobut-2-ene, 3-chloro-1 , 1 ,1-trifluorobut-3-ene, Z/E-1 , 1 ,1 ,3- tetrafluorobut-2-ene and 1 ,1 ,1 ,3-tetrafluorobut-3-ene.

Figure 1 shows a plot of the results of Example 1 ; Figure 2 shows a plot of the results of Example 2.

The invention is illustrated by the following non-limiting Examples.

Example 1

A ½" diameter empty silicon carbide reactor tube was sealed with graphite ferrules and an Inconel thermocouple inside a Monel Thermowell was placed inside the tube. The tube was pre-dried at 450°C under 60ml/min N2 overnight prior to feeding organics to the reactor.

The tube was heated to an internal temperature of 350°C and a supply of 244bb (5ml/min) with N2 dilution (30ml/min) was provided for around 5 minutes before diverting the N2 stream to the bottom of the reactor. Reactions were carried out at a temperature ranges of 400 to 525°C with a 244bb flow at 5ml/min. An empty glass lined reactor (with & without a thermo-well) with no catalyst was tested first to form a baseline for other catalyst screening. The reaction was monitored by manually withdrawing samples from the reactor outlets and examining them via gas chromatography, the peak areas of the chromatographs being used to calculate the quantity of HCFC-244bb, HFO-1234yf and HCFO-1233xf in the product stream. The results are provided in Table 1 and shown in Figure 1. Figure 1 shows a plot of raw conversion data against time, while the conversion figures in Table 1 are adjusted to account for the effects of thermal conversion. As can be seen from Figure 1 and Table 1 , below the silicon carbide reactor showed extremely high stability with an excellent selectivity towards 1234yf that was maintained across a range of temperatures.

Table 1

Example 2 Example 1 was repeated with 1.8 g of silicon nitride in pellet form (0.5 to 1 mm) in a stainless steel glass-lined reactor tube. The pellet were obtained by crushing and sieving silicon nitride powder (a-Si3N 85% minimum) to obtain pellets of the correct size.

The results are provided in Table 2 and shown in Figure 2. Figure 2 shows a plot of raw conversion data against time, while the conversion figures in Table 2 are adjusted to account for the effects of thermal conversion. It can be seen that formation of 1234yf was selectively and consistently favoured over 1233xf formation. Moreover, the catalyst shows exceptional stability in providing a consistent conversion and high selectivity to HFO- 1234yf over a substantial operating period with little sign of deterioration. Temp /°C HFC-244bb HFC-244bb

Thermal + HFO-1234yf 1233xf

Time/h Catalytic

(external) Catalytic Selectivity % Selectivity %

Conversion %

400 3.5 1.7 0 30.2 62.9

425 31.5 5.1 1.7 82.0 17.9

450 25.5 6.8 3.9 89.9 10.1

475 73.5 24.0 6.0 95.3 4.3

500 3.5 23.0 0.0 93.1 6.0

525 2 37.0 0.0 91.4 7.0

Table 2

Example 3 Samples of residue found in the reaction tube used in Example 1 were subjected to X-ray fluorescence spectroscopy (XRF) to determine its elemental composition. The results are shown in Table 3, below.

Table 3

Without wishing to be bound by any particular theory, it is thought that metallic material and/or compounds, such as may be deposited from fittings and the thermocouple, may collect on the ceramic material and provide some catalytic activity. Copper chloride or nickel chloride represent an examples of such materials.

Example 4

Unused silicon nitride powder and a samples of the silicon nitride used in Example 2 were subjected to X-ray fluorescence spectroscopy (XRF) to determine their elemental composition. The results are shown in Table 4, below.

Table 4

As above, without wishing to be bound by any particular theory, it is thought that metallic material and/or compounds, such as may be deposited from fittings and the thermocouple, may collect on the ceramic material and provide some catalytic activity.

Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention.

The invention is defined by the following claims.

Claims

1. A process for preparing a (hydro)haloalkene comprising dehydrohalogenating a hydrohaloalkane in the presence of a catalyst comprising a ceramic material.

2. A process according to claim 1 , wherein the catalyst comprises at least one ceramic material which comprises nonmetallic solids comprising metal, nonmetal or metalloid atoms primarily held in ionic and covalent bonds, the metalloid and non-metalloid species being selected from the elements Al, Si, B, C, N, Ti, Zr, Ce, Y, W; and/or wherein the ceramic comprises ceramic alloys such as metal alloys of boron, aluminium and magnesium e.g. (AIMgB ) with titanium boride (T1B2).

3. A process according to claim 1 or claim 2, wherein the catalyst comprises one or more materials selected from the group metal and non-metal carbides, nitrides, silicides and borides, for example silicon carbide and/or nitride, boron carbide and/or nitride, titanium carbide and tungsten carbide.

4. A process according to any of the preceding claims, wherein the catalyst further comprises a metal, metal halide and/or a metal oxide.

5. A process according to claim 4, wherein the metal, metal halide or metal oxide is one or more of aluminium, calcium, magnesium, chromium, iron, nickel, copper, potassium, titanium, vanadium, manganese, cobalt, tin and cerium.

6. A process according to any preceding claims wherein the process is for preparing a (hydro )(chloro)fluoroalkene.

7. A process according to any preceding claim wherein the process is for preparing a C3-7 (hydro )fluoroalkene.

8. A process according to claim 7, wherein the C3-7 (hydro )fluoroalkene comprises a (hydro )fluoropropene.

9. A process according to claim 8 wherein the (hydro)fluoropropene comprises one or more tetrafluoropropenes, such as HFO-1234yf, HFO-1234ze(E) and/or HFO- 1234ze(Z).

10. A process according to any of claims 7 to 9, wherein the hydrohaloalkane comprises a C3-7 hydro(chloro)fluoroalkane.

1 1. A process according to claim 10, wherein the C3-7 hydro(chloro)fluoroalkane comprises a hydro(chloro)fluoropropane.

12. A process according to claim 1 1 where the hydro(chloro)fluoropropane comprises a tetrafluorochloropropane, e.g. HCFC-244bb or HCFC-244fa.

13. A process according to claim 11 , wherein the hydro(chloro)fluoropropane comprises a pentafluoropropane such as HFC-245fa.

14. A process according to any of the preceding claims comprising dehydrohalogenating the hydrohaloalkane in the absence of added hydrogen fluoride (HF).

15. A process according to any of the preceding claims carried out at a temperature of from about 0 to about 700 °C and a pressure of up to about 30 bara.

16. A process according to claim 15 carried out at a temperature of from about 300 to about 500°C, for example from about 400 to about 500°C, e.g. from about 420 to about 470°C.

17. A process according to any of claims 1 to 6 or 14 to 16 for preparing a (hydro )fluoropropene comprising dehydrohalogenating a hydro(halo)fluoropropane.

18. A process according to claim 15 wherein the (hydro )fluoropropene produced is selected from trifluoropropenes, tetrafluoropropenes and pentafluoropropenes.

19. A process according to claim 16 or 17 for preparing 1 ,3,3,3-tetrafluoropropene (HFO-1234ze) comprising dehydrofluorinating 1 ,1 ,1 ,3,3-pentafluoropropane (HFC-245fa).

20. A process according to claim 16 or 17 for preparing 1 ,3,3,3-tetrafluoropropene (HFO-1234ze) comprising dehydrochlorinating 3-chloro-1 ,1 ,1 ,3-tetrafluoropropane (HFC- 244fa).

21. A process according to claim 16 or 17 for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf) comprising dehydrofluorinating 1 ,1 ,1 ,2,2-pentafluoropropane (HFC-245cb) and/or 1 ,1 ,1 ,2,3-pentaafluoropropane (HFC-245eb).

22. A process according to claim 16 or 17 for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf) comprising dehydrochlorinating 2-chloro-1 ,1 ,1 ,2-tetrafluoropropene (HCFC-244bb).

23. A process according to claim 16 or 17 for preparing 1 ,2,3,3,3-pentafluoropropene (HFO-1225ye) comprising dehydrofluorinating 1 ,1 ,1 ,2,3,3-hexafluoropropane (HFC- 236ea).

24. A process according to claim 16 or 17 for preparing 3,3,3-trifuoropropene comprising dehydrohalogenating one or more compounds having the formula CF3CH2CH2X, where X is CI, F, Br or I.

25. A process according to any of claims 1 to 6 or 14 to 16 for preparing a C3-7 hydrochlorofluoroalkene comprising dehydrohalogenating a C3_-7 hydro(chloro)fluoroalkane.

26. A process according to claim 25 for preparing 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd) comprising dehydrochlorinating 1 ,2-dichloro-3,3,3-trifluoropropane (HCFC-243db) and/or 1 ,1-dichloro-3,3,3-trifluoropropane (HCFC-243fa) or by dehydrofluorinating HCFC-244fa.

27. A process according to claim 25 for preparing 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) dehydrochlorinating 1 ,2-dichloro-3,3,3-trifluoropropane (HCFC-243db) and/or 2,2-dichloro-3,3,3-trifluoropropane (HCFC-243cb).

28. Use of a ceramic material (e.g. silicon carbide) as a catalyst in a dehydrohalogenation reaction.

29. Use of a ceramic catalyst according to claim 28 in the preparation of 2,3,3,3- tetrafluoropropene (HFO-1234yf) from 2-chloro-1 ,1 ,1 ,2-tetrafluoropropene (HCFC- 244bb).

30. Any novel process substantially as herein described, optionally with reference to the Examples.