GB2543872A - Process - Google Patents

Abstract

A process for preparing 2,3,3,3-tetrafluoropropene (R-1234yf), the process comprising: (a) contacting 3,3,3-trifluoropropene (R-1243zf) with fluorine (F2) to produce 1,2,3,3,3-pentafluoropropane (R-245eb); and (b) dehydrofluorinating R-245eb to produce R-1234yf. Step (a) may be carried out in the presence of one or more free radical suppressants, in particular ethanol. Preferably step (b) is carried out in the gas phase and in the presence of a catalyst, in particular an oxide of a metal, preferably zinc/chromia catalysts. Preferably the process further comprises contacting 1,1,1,3-tetrachloropropane (R-250fb) with HF to produce R-1243zf, where preferably the R-250fb is prepared by telomerising ethylene and carbon tetrachloride (CCl4) in the liquid and/or vapour phase in the presence of a catalyst in an amount of from about 0.01 to about 50 mol %.

Description

Process

The invention relates to a process for preparing 2,3,3,3-tetrafluoropropene. In particular, the invention relates to a process for preparing 2,3,3,3-tetrafluoropropene comprising contacting 3,3,3-trifluoropropene (R-1243zf) with fluorine (F2) to produce 1,2,3,3,3-pentafluoropropane (R-245eb); and dehydrofluorinating R-245eb to produce R-1234yf.

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge. 2,3,3,3-tetrafluoropropene is also known as HFO-1234yf, HFC-1234yf or simply R-1234yf. Hereinafter, unless otherwise stated, 2,3,3,3-tetrafluoropropene will be referred to as R-1234yf. The known processes for preparing R-1234yf typically suffer from disadvantages such as low yields, and/or the handling of toxic and/or expensive reagents, and/or the use of extreme conditions, and/or the production of toxic by-products. Methods for the preparation of R-1234yf have been described in, for example, Journal Fluorine Chemistry (82), 1997, 171-174. In this paper, R-1234yf is prepared by the reaction of sulphur tetrafluoride with trifluoroacetylacetone. However, this method is only of academic interest because of the waste materials produced when using reagents such as sulphur tetrafluoride and the potential for contamination of the 1234yf product with highly odoriferous impurities. Another method for the preparation of R-1234yf is described in US-2931840. In this case, pyrolysis of C1 chlorofluorocarbons with or without tetrafluoroethylene was purported to yield R-1234yf. However, the yields described were very low and again it was necessary to handle hazardous chemicals under extreme conditions. It would also be expected that such a process would produce a variety of very toxic by-products.

It is desirable to provide a new method for the preparation of 1234yf that use only readily available feedstocks. Further to this, the use of fluorine (F2) as a reagent in processes for preparing R-1234yf is desirable as F2 readily adds across carbon-carbon double bonds. However, F2 is expensive to obtain and its high reactivity can lead to the formation of numerous side products. There is therefore a need to maximise the efficiency of processes using fluorine as a reagent.

The present invention addresses the above deficiencies and provides a process for preparing 2,3,3,3-tetrafluoropropene (R-1234yf), the process comprising: (a) contacting 3,3,3-trifluoropropene (R-1243zf) with fluorine (F2) to produce a mixture comprising1,2,3,3,3-pentafluoropropane (R-245eb); and (b) dehydrofluorinating R-245eb to produce R-1234yf.

Step (a): Fluorination of R-1243zf to R-245eb 1st Embodiment

In a first embodiment of the invention, step (a) is carried out in the presence of one or more free radical suppressants. Preferably the free radical suppressant is one of more of alcohols, phenols, amines, ethers and compounds containing a number of these functional groups such as morpholine, even more preferably the free radical suppressant is an alcohol, such as ethanol. 2nd Embodiment

In a second embodiment of the invention, the R-1243zf has a purity of greater than 99.8%.

Advantageously, the first or second embodiment of the invention may comprise step (a) being carried out with an excess of F2:R-1243zf, optionally with any unreacted F2 being recycled. 3rd Embodiment

In a third embodiment of the invention, step (a) is carried out with an excess of R-1243zf to F2. Preferably, the molar ratio of R-1243zf:F2 is from about 1.01:1 to about 2:1, such as from about 1.02:1 to about 1.8:1. However, in some alternative embodiments the ratio of R-1243zf:F2is from about 3:2 to about 10:1.

Without wishing to be bound by theory, it is believed that the excess R-1243zf absorbs excess heat, as well as ensuring all the fluorine used is rapidly consumed thereby preventing or reducing the formation of fluorinated side-products.

Step (a) may be carried out in the vapour and/or liquid phase and at a temperature of from about -100 to about 400 °C. Preferably, the process is carried out at a temperature of from about -80 to about 100 °C, such as from about -70 to about 50 °C, or even from about -65 to about 0 °C. Advantageously, the process may be carried out at a temperature of from about -80 to about -60 °C.

The fluorine and 1243zf (step a) can be contacted in the liquid or vapour phases. If performed in the vapour phase the process may be carried out at atmospheric, sub- or super-atmospheric pressure, preferably from about 0 to about 30 bara and more preferably from 0-10 bara.

Step (a) can be carried out in any suitable apparatus, such as a static mixer, a stirred tank reactor or a stirred vapour-liquid disengagement vessel. Preferably the apparatus used is one where the reactants can be quickly bought into contact in a controlled manner and the heat of reaction rapidly dissipated. Preferably, this or any other apparatus described herein is made from one or more materials that are resistant to corrosion, e.g. Hastelloy® or Inconel® or fluoropolymers such as PTFE and FEP.

Fluorine may be used in step (a) in conjunction with an inert, diluent gas such as nitrogen or argon. The diluent gas may be present in an amount of from about 5 to about 95 wt.%, preferably from about 50 to about 90 wt.%.

If carried out in the liquid phase, step (a) may be carried out in the presence of a solvent. Preferably, the solvent is selected from CFCs (such as R-11, R-12, and R-13), acetonitrile, R-227ea, R-365mfc, R-4310-mee and perfluorinated solvents.

Preferably, at least some of any HF produced by step (a) or step (b) is recovered and used to produce F2.

Step (a) of the present invention may be carried out either batch-wise or continuously.

If step (a) is carried out continuously it is preferable that the arrangement allows for good mixing of the components and rapid dispersion of heat of the reaction. In one preferred embodiment, the continuous reaction is carried out using micro-fluidic multi-channel reactors. In a second preferred embodiment the reaction is carried out in a liquid phase reactor whose liquid contents comprise a low-boiling component such as R1243zf, and where the heat of reaction is removed by vaporisation of a portion of the liquid, said vapour being fed to a distillation column where a portion is condensed and returned to the reactor. In a third preferred embodiment step (a) is carried out in a reactive distillation column system. In this embodiment gaseous fluorine and a stream of R1243zf in either liquid or vapour state are fed to suitable points in the column: the top product from said column comprises largely unreacted R1243zf with any light feed impurities or by-products of reaction, at least a portion of which is condensed as reflux, and the bottom product comprises substantially the R245eb and any heavy impurities or by-products of the reaction.

Step (b): Dehydrofluorination ofR-245eb to R-1234yf

Step (b) of the process of the invention may be carried out by any suitable reactions conditions effective to dehydrofluorinate R-245eb to produce R-1234yf.

Preferably, the dehydrofluorination is carried out in the vapour and/or liquid phase and may be carried out at a temperature of from about -70 to about 1000 °C (e.g. about 0 to about 500 °C). The process may be carried out at atmospheric sub- or super atmospheric pressure, preferably from about 0 to about 30 bara.

Even more preferably, step (b) is carried out in the vapour phase, preferably at a temperature of from about 250 to about 400 °C, preferably at a pressure of from 0 to 20 bara.

Step (b) may be induced thermally, may be base-mediated and/or may be catalysed by any suitable catalyst. Suitable catalysts include metal and carbon based catalysts such as those comprising activated carbon, alkali metals, main group (e.g. alumina-based or indium catalysts) and transition metals, such as chromia-based catalysts, nickel-based catalysts (e.g. nickel mesh) or supported zirconium catalyst (e.g. zirconium supported on alumina).

Preferably, step (b) is carried out in the presence of a catalyst, such as a metal oxide catalyst. Advantageously, the catalyst may comprise chromia. The chromia may be supported or unsupported. The chromia catalyst may also contain promoters such as zinc.

Zinc/chromia catalysts are preferred for step (b). By the term “zinc/chromia catalyst’ we mean any catalyst comprising chromium or a compound of chromium and zinc or a compound of zinc.

Typically, the chromium or compound of chromium present in the zinc/chromia catalysts of the invention is an oxide, oxyfluoride or fluoride of chromium such as chromium oxide.

The total amount of the zinc or a compound of zinc present in the zinc/chromia catalysts of the invention is typically from about 0.01 % to about 25%, preferably 0.1 % to about 25%, conveniently 0.01% to 6% zinc, and in some embodiments preferably 0.5% by weight to about 25 % by weight of the catalyst, preferably from about 1 to 10 % by weight of the catalyst, more preferably from about 2 to 8 % by weight of the catalyst, for example about 4 to 6 % by weight of the catalyst.

In other embodiments, the catalyst conveniently comprises 0.01% to 1%, more preferably 0.05% to 0.5% zinc.

The preferred amount depends upon a number of factors such as the nature of the chromium or a compound of chromium and/or zinc or a compound of zinc and/or the way in which the catalyst is made. These factors are described in more detail hereinafter.

It is to be understood that the amount of zinc or a compound of zinc quoted herein refers to the amount of elemental zinc, whether present as elemental zinc or as a compound of zinc.

The zinc/chromia catalysts used in the invention may include an additional metal or compound thereof. Typically, the additional metal is a divalent or trivalent metal, preferably selected from nickel, magnesium, aluminium and mixtures thereof. Typically, the additional metal is present in an amount of from 0.01 % by weight to about 25 % by weight of the catalyst, preferably from about 0.01 to 10 % by weight of the catalyst. Other embodiments may comprise at least about 0.5 % by weight or at least about 1 % weight of additional metal.

The zinc/chromia catalysts used in the present invention may be amorphous. By this we mean that the catalyst does not demonstrate substantial crystalline characteristics when analysed by, for example, X-ray diffraction.

Alternatively, the catalysts may be partially crystalline. By this we mean that from 0.1 to 50 % by weight of the catalyst is in the form of one or more crystalline compounds of chromium and/or one or more crystalline compounds of zinc. If a partially crystalline catalyst is used, it preferably contains from 0.2 to 25 % by weight, more preferably from 0.3 to 10 % by weight, still more preferably from 0.4 to 5 % by weight of the catalyst in the form of one or more crystalline compounds of chromium and/or one or more crystalline compounds of zinc.

During use in a reaction the degree of crystallinity may change. Thus it is possible that a catalyst of the invention that has a degree of crystallinity as defined above before use in a fluorination/dehydrohalogenation reaction and will have a degree of crystallinity outside these ranges during or after use in a fluorination/dehydrohalogenation reaction.

The dehydrofluorination of step (b) may also be base-mediated.

This base-mediated dehydrohalogenation process of step (b) comprises contacting the R245eb with base such as a metal hydroxide or amide (preferably a basic metal hydroxide or amide, e.g. an alkali or alkaline earth metal hydroxide or amide).

Unless otherwise stated, as used herein, by the term “alkali metal hydroxide”, we refer to a compound or mixture of compounds selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide and caesium hydroxide. Similarly, by the term “alkali metal amide”, we refer to a compound or mixture of compounds selected from lithium amide, sodium amide, potassium amide, rubidium amide and caesium amide.

Unless otherwise stated, as used herein, by the term “alkaline earth metal hydroxide”, we refer to a compound or mixture of compounds selected from beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide. Similarly, by the term “alkaline earth metal amide”, we refer to a compound or mixture of compounds selected from beryllium amide, magnesium amide, calcium amide, strontium amide and barium amide.

Typically, the base-mediated dehydrohalogenation process of step (b) is conducted at a temperature of from -50 to 300 °C. Preferably, the process is conducted at a temperature of from 20 to 250 °C, for example from 50 to 200 °C. The base-mediated dehydrohalogenation may be conducted at a pressure of from 0 to 30 bara.

The reaction time for the base-mediated dehydrohalogenation process of step (b) may vary over a wide range. However, the reaction time will typically be in the region of from 0.01 to 100 hours, such as from 0.1 to 50 hours, e.g. from 1 to 20 hours.

Of course, the skilled person will appreciate that the preferred conditions (e.g. temperature, pressure and reaction time) for conducting the base-mediated dehydrohalogenation may vary depending on a number of factors such as the base being employed, and/or the presence of a catalyst etc.

The base-mediated dehydrohalogenation process of step (b) may be carried out in the presence or absence of a solvent. If no solvent is used, the 245eb may be passed into or over molten base or hot base, for example in a tubular reactor. If a solvent is used, in some embodiments a preferred solvent is water, although many other solvents may be used. In some embodiments solvents such as alcohols (e.g. propan-1-ol), diols (e.g. ethylene glycol) and polyols such as polyethylene glycol (e.g. PEG200 or PEG300) may be preferred. These solvents can be used alone or in combination. In further embodiments, solvents from the class known as polar aprotic solvents may be preferred. Examples of such polar aprotic solvents include diglyme, sulfolane, dimethylformamide (DMF), dioxane, acetonitrile, hexamethylphosphoramide (HMPA), dimethyl sulphoxide (DMSO) and N-methyl pyrrolidone (NMP). The boiling point of the solvent is preferably such that it does not generate excessive pressure under reaction conditions. A preferred base is an alkali metal hydroxide selected from the group consisting of lithium hydroxide, sodium hydroxide and potassium hydroxide, more preferably, sodium hydroxide and potassium hydroxide and most preferably potassium hydroxide.

Another preferred base is an alkaline earth metal hydroxide selected from the group consisting of magnesium hydroxide and calcium hydroxide, more preferably calcium hydroxide.

The base is typically present in an amount of from 1 to 50 weight % based on the total weight of the components which make up step (b). Preferably, the base is present in an amount of from 5 to 30 weight %.

The molar ratio of base to R-245eb is typically from 1:20 to 50:1, preferably from 1:5 to 20:1, for example from 1:2 to 10:1.

As mentioned above, the base-mediated dehydrohalogenation may preferably employ water as the solvent. Thus, the dehydrohalogenation reaction may preferably use an aqueous solution of at least one base, such as an alkali (or alkaline earth) metal hydroxide, without the need for a co-solvent or diluent. However, a co-solvent or diluent can be used for example to modify the system viscosity, to act as a preferred phase for reaction byproducts, or to increase thermal mass. Useful co-solvents or diluents include those that are not reactive with or negatively impact the equilibrium or kinetics of the process and include alcohols such as methanol and ethanol; diols such as ethylene glycol; ethers such as diethyl ether, dibutyl ether; esters such as methyl acetate, ethyl acetate and the like; linear, branched and cyclic alkanes such as cyclohexane, methylcyclohexane; fluorinated diluents such as hexafluoroisopropanol, perfluorotetrahydrofuran and perfluorodecalin.

The base-mediated dehydrohalogenation of step (b) is preferably conducted in the presence of a catalyst. The catalyst is preferably a phase transfer catalyst which facilitates the transfer of ionic compounds into an organic phase from, for example, a water phase. If water is used as a solvent, an aqueous or inorganic phase is present as a consequence of the alkali metal hydroxide and an organic phase is present as a result of the fluorocarbon. The phase transfer catalyst facilitates the reaction of these dissimilar components. While various phase transfer catalysts may function in different ways, their mechanism of action is not determinative of their utility in the present invention provided that they facilitate the dehydrohalogenation reaction. The phase transfer catalyst can be ionic or neutral and is typically selected from the group consisting of crown ethers, onium salts, cryptands and polyalkylene glycols and derivatives thereof (e.g. fluorinated derivatives thereof).

An effective amount of the phase transfer catalyst should be used in order to effect the desired reaction, influence selectivity to the desired products or enhance the yield; such an amount can be determined by limited experimentation once the reactants, process conditions and phase transfer catalyst are selected. Typically, the amount of catalyst used relative to the amount of R-245eb present is from 0.001 to 20 mol %, such as from 0.01 to 10 mol %, e.g. from 0.05 to 5 mol %.

In an embodiment, at least some of the HF produced by step (b) is converted to F2 and recycled into step (a).

Fluorination of R-250fb to R-1243zf R-1243zf of the invention may be prepared from the fluorination of 1,1,1,3-tetrachloropropane (R-250fb) with HF.

The fluorination of R-250fb to R-1243zf may be carried out batch-wise or (semi-)continuously. The reaction can be carried out in the liquid or vapour phases. Typically, the process is carried out in the vapour phase.

The process may be carried out at atmospheric, sub- or super atmospheric pressure, typically at from 0 to about 30 bara, preferably from about 1 to about 20 bara, such as 15 bara

Typically, the process of the invention is carried out a temperature of from about 100 °C to about 500 °C (e.g. from about 150 °C to about 500 °C or about 100 to about 450 °C). Preferably, the process is conducted at a temperature of from about 150 °C to about 450 °C, such as from about 150 °C to about 400 °C, e.g. from about 175 °C to about 300 °C. Lower temperatures may also be used in the conversion of 250fb to 1243zf, such as from about 150 °C to about 350 °C, e.g. from about 150 °C to about 300 °C or from about 150 °C to about 250 °C.

The process typically employs a molar ratio of HF:organics of from about 1:1 to about 100:1, such as from about 3:1 to about 50:1, e.g. from about 4:1 to about 30:1 or about 5:1 or 6:1 to about 20:1 or 30:1.

The reaction time for the process generally is from about 1 second to about 100 hours, preferably from about 10 seconds to about 50 hours, such as from about 1 minute to about 10 or 20 hours. In a continuous process, typical contact times of the catalyst with the reagents are from about 1 to about 1000 seconds, such from about 1 to about 500 seconds or about 1 to about 300 seconds or about 1 to about 50, 100 or 200 seconds.

Advantageously, the reaction is carried out in the presence of a catalyst, such as metal and carbon based catalysts such as those comprising activated carbon, alkali metals, main group (e.g. alumina-based or indium catalysts) and transition metals, such as chromia-based catalysts, nickel-based catalysts (e.g. nickel mesh), supported zirconium catalyst (e.g. zirconium supported on alumina), or pentavalent antimony compounds such as chloride, fluoride and mixed chlorofluorides(e.g. SbCIs SbFs, SbCLF, SbChF2, SbCbFs, SbCLFs, SbCIF4), trivalent antimony compounds such as antimony trichloride and trifluoride and chlorofluorides or mixtures of tri- and pentavalent antimony compounds, tantalumn pentachloride and perntafluoride and niobium pentafluoride and pentafluoride catalysts.

Preferably, R-1243zf is prepare using a zinc/chromia catalyst as described herein.

In an embodiment, the reaction products from the vapour phase reaction would pass downstream into a separation train to recover and recycle any unreacted HF, R-250fb and any partially-fluorinated intermediates (such as R-251fb, R-252fb and R-253fb). Separations are preferably carried out by distillation and/or phase separation. Advantageously, the separation train includes HCI removal apparatus, allowing for the production of anhydrous or aqueous HCI. Preferably, the HCI removal occurs prior to the removal or recovery of HF, which precedes the separation of R-1243zf from the remaining organic components.

In an alternative embodiment, R-250fb is fluorinated in the liquid phase to R-253fb using a liquid phase catalyst (such as SbCIs, SnCL or TiCU). Dehydrochlorination then occurs in situ to produce R-1243zf. The reactor off-gases contain R-1243zf, under reacted organics (such as R-250, R-251, R-252 and R-253), HF and HCI. Preferably, a separation train returns any under reacted organics to the reactor and allows HCI to be produced as above. Any azeotropes formed between under reacted organic compounds and HF can be separated or recovered by any method known in the art, e.g. adsorption into sulphuric acid, azeotropic distillation, or scrubbing with water or a basic solution fo example sodium or potassium hydroxide; then drying with sulphuric acid, molecular sieve, silica gel, calcium chloride or other drying method.

Advantageously, the R-1243zf produced is purified prior to step (a) being carried out.

Preferably, the purification comprises contacting a composition comprising the R-1243zf and one or more undesired (hydro)halocarbon compounds, such as those noted above, with an aluminium-containing absorbent, activated carbon, or a mixture thereof.

Either the aluminium-containing absorbent or activated carbon may be porous or non-porous, but preferably porous. A preferred aluminium-containing adsorbent for use in processes according to the invention is an alumina or alumina-containing substrate. Advantageously, the substrate is porous. Further information on the various crystalline forms of alumina can be found in Acta. Cryst., 1991, B47, 617, the contents of which are hereby incorporated by reference.

Preferred aluminium-containing adsorbents (e.g. alumina) for use according to the invention will have functionality that facilitates their combination with the compounds the adsorbent is removing. Examples of such functionality include acidity or basicity, which can be Lewis-type or Bronsted-type in nature, which will facilitate its combination with the compounds the adsorbent is removing. The acidity or basicity can be modified in a manner well known to those skilled in the art by using modifiers such as sodium sulphate. Examples of aluminium-containing adsorbents with acidic or basic functionality include Eta-alumina, which is acidic, and Alumina AL0104, which is basic.

Aluminosilicate molecular sieves (zeolites) are a further preferred group of aluminium-containing adsorbent that may be used in the subject invention. Typically, the zeolites have pores having openings which are sufficiently large to allow the desired and undesired compounds to enter into the interior of the zeolite whereby the undesired compounds are retained. Accordingly, zeolites having pores which have openings which have a size across their largest dimension in the range of 3 A to 12 A are preferred.

Preferred zeolites have a pore opening sufficiently large to allow the undesired compounds to enter into the interior of the zeolite whereby the undesired compounds are retained, whilst excluding the desired compound (R-1243zf) from entering the interior of the zeolite. Such zeolites typically have openings which have a size across their largest dimension in the range of 3 A to 12 A, preferably from 3 A to 10 A or 4 A to 12 A. Particularly preferred are those molecular sieves having pores which have openings having a size across their largest dimension in the range of 4 A to 10 A, such as 4 A to 8 A (e.g. 4 A to 5 A) and may include zeolite Y, ultra-stable Y (dealuminated-Y), zeolite beta, zeolite X, zeolite A and zeolite ZSM-5, AW-500.

By opening in this context we are referring to the mouth of the pore by which the undesired compound enters the body of the pore, where it may be retained. The openings to the pores may be elliptically shaped, essentially circular or even irregularly shaped, but will generally be elliptically shaped or essentially circular. When the pore openings are essentially circular, they should have a diameter in the range of about 3A across their smaller dimension. They can still be effective at adsorbing compounds provided that the size of the openings across their largest dimension is in the range of from about 3A to about 12A. Where the adsorbent has pores having elliptically shaped openings, which are below 3A across their smaller dimension, they can still be effective at adsorbing compounds provided that the size of the openings across their largest dimension is in the range of from about 3A to about 12A.

By “activated carbon”, we include any carbon with a relatively high surface area such as from about 50 to about 3000 m2 or from about 100 to about 2000 m2 (e.g. from about 200 to about 1500 m2 or about 300 to about 1000 m2). The activated carbon may be derived from any carbonaceous material, such as coal (e.g. charcoal), nutshells (e.g. coconut) and wood. Any form of activated carbon may be used, such as powdered, granulated, extruded and pelleted activated carbon.

Activated carbon is preferred which has been modified (e.g. impregnated) by additives which modify the functionality of the activated carbon and facilitate its combination with the compounds it is desired to removed. Examples of suitable additives include metals or metal compounds, and bases.

Typical metals include transition, alkali or alkaline earth metals, or salts thereof. Examples of suitable metals include Na, K, Cr, Mn, Au, Fe, Cu, Zn, Sn, Ta, Ti, Sb, Al, Co, Ni, Mo, Ru, Rh, Pd and/or Pt and/or a compound (e.g. a halide, hydroxide, carbonate) of one or more of these metals. Alkali metal (e.g. Na or K) salts are currently a preferred group of additive for the activated carbon, such as halide, hydroxide or carbonate salts of alkali metals salts. Hydroxide or carbonate salts of alkali metals salts are bases. Any other suitable bases can be used, including amides (e.g. sodium amide).

The impregnated activated carbon can be prepared by any means known in the art, for example soaking the carbon in a solution of the desired salt or salts and evaporating the solvent.

Examples of suitable commercially available activated carbons include those available from Chemviron Carbon, such as Carbon 207C, Carbon ST 1X, Carbon 209M and Carbon 207EA. Carbon ST1X is currently preferred. However, any activated carbon may be used, provided they are treated and used as described herein.

Advantageously, a combination of an aluminium-containing absorbent and activated carbon is used, particularly when each are separately effective at removing particular undesired compounds from a composition also containing R-1243zf. Examples of preferred combinations of aluminium-containing absorbent and activated carbon include zeolite and activated carbon and aluminium-containing absorbent and impregnated activated carbon.

The purification requires the composition (e.g. product stream) to be in the liquid or vapour phase. Liquid phase contacting is preferred.

Processing with a stationary bed of the adsorbent will typically be applied to continuous processes. The composition (e.g. product stream) is passed over or through the stationary bed comprising the aluminium-containing absorbent, activated carbon, or a mixture thereof.

The aluminium-containing absorbent, activated carbon, or a mixture thereof is normally pre-treated prior to use by heating in a dry gas stream, such as dry air or dry nitrogen. This process has the effect of activating the aluminium-containing absorbent, activated carbon, or a mixture thereof. Typical temperatures for the pre-treatment are in the range of from about 100 to about 400 °C (e.g. about 100 to about 300 °C).

The purification can be operated in a batch or continuous manner, although a continuous manner is preferred. In either case, during operation of the process, the absorption capability of the aluminium-containing absorbent, activated carbon, or a mixture thereof is gradually reduced as the pores become occupied with the one or more undesired (hydro)halocarbon compounds. Eventually, the ability of the aluminium-containing absorbent, activated carbon, or a mixture thereof to absorb the undesired compound(s) will be substantially impaired, at which stage it should be regenerated. Regeneration is typically effected by heating the used aluminium-containing absorbent, activated carbon, or a mixture thereof in a dry gas stream, such as dry air or dry nitrogen, at a temperature in the range of from about 100 to about 400 °C, such as from about 100 to about 300 °C (e.g. about 100 to about 200 °C), and a pressure in the range of from about 1 to about 30 bar (e.g. about 5 to about 15 bar).

The purification typically is conducted at a temperature in the range of from about -50 °C to about 200 °C, preferably from about 0°C to about 100°C, such as from about 10 to about 50 °C. This temperature range applies to the temperature of the interior of the purification vessel.

Typical operating pressures for the process are from about 1 to about 30 bar, such as from about 1 to about 20 bar, preferably from about 5 to about 15 bar.

In the (batch) purification, the aluminium-containing absorbent, activated carbon, or a mixture thereof typically is used in an amount of from about 0.1 to about 100 % by weight, such as from about 1 or 5 to about 50 % by weight, preferably from about 10 to about 50 % by weight, based on the weight of the composition comprising R-1243zf and one or more undesired compounds.

In a continuous purification, the typical feed rate of the composition (e.g. product stream) comprising the R-1243zf and one or more undesired compounds to the aluminium-containing absorbent, activated carbon, or a mixture thereof is such that in the liquid phase the contact time of the adsorbate with the adsorbent is from about 0.1 to 24 hours, preferably from about 1 to 8 hours. In a preferred mode of operation the adsorbate is continuously recycled through the adsorbent bed until the level of the undesired components has reduced sufficiently. Where vapour phase contacting is utilised, the contact time of the adsorbate with the adsorbent is from about 0.001 to 4 hours, preferably from about to 0.01 to 0.5 hours. In a preferred mode of operation the adsorbate is continuously recycled through the adsorbent bed until the level of the undesired components has reduced sufficiently.

Preferably, the invention removes at least 50%, 60%, 70% or 80% of the undesired compound(s) present in the composition comprising the R-1243zf. More preferably, the composition removes at least 90%, 95% or even 99% of the undesired compound(s) present in the composition comprising the R-1243zf.

Following purification, the level of undesired compound(s) in the composition comprising the R-1243zf typically will be from not detectable (by currently available techniques, such as capillary gas chromatography) to about 10ppm, such as from about 0.01 ppm to about 5ppm, preferably from not detectable to about 1ppm.

Preferably, the R-1243zf is greater than 99.8% pure after the purification process. Preparation of R-250fb from carbon tetrachloride and ethylene R-250fb may be prepared by the telomerising of ethylene and carbon tetrachloride (CCU).

The above process typically comprises contacting ethylene with CCU in the liquid and/or vapour phase in presence of a catalyst under conditions suitable to produce 250fb.

Any suitable catalyst may be used in step (i), such as a catalyst which comprises iron, copper and/or peroxide. Preferably, the catalyst comprises iron (e.g. iron powder)

Catalysts which comprise peroxide include benzoyl peroxide and di-f-butyl peroxide. Catalysts which comprise iron include iron powder and ferric/ferrous halides (e.g. chlorides). Catalysts which comprise copper include salts of copper such as copper halides (e.g. CuCh), copper sulphate and/or copper cyanide.

Optionally, the catalysts which comprise copper and iron are used with a co-catalyst or ligand. Suitable co-catalysts include triethylorthoformate (HC(OEt)3), nitrogen/phosphorus-containing ligands, and/or ammonium/phosphonium salts. Preferred nitrogen-containing ligands include amines (e.g. primary and secondary amines), nitriles and amides. Preferred phosphorus containing ligands include phosphates, phosphites (e.g. triethylphosphite) and phosphines. Preferred ammonium and phosphonium salts include ammonium and phosphonium halides (e.g. chlorides).

The catalyst for the preparation of R-250fb typically is used in an amount from about 0.01 to about 50 mol % (e.g. about 0.1 to about 10 %), based on the molar sum of CCU and ethylene present. An excess of the carbon tetrachloride over ethylene generally is used. For example, the molar ratio of CCkCaHU typically is from about 1:1 to about 50:1, such as from about 1.1:1 to about 20:1, for example from about 1.2:1 to about 10:1 or about 1.5:1 to about 5:1.

The reaction temperature for the preparation of R-250fb typically is within the range of from about 20 to about 300 °C, preferably from about 30 to about 250 °C, such as from about 40 to about 200 °C, e.g. from about 50 to about 150 °C.

The reaction pressure for the preparation of R-250fb typically is within the range of from 0 to about 40 bara, preferably from about 1 to about 30 bara.

The reaction time for the preparation of R-250fb generally is from about 1 second to about 100 hours, preferably from about 10 seconds to about 50 hours, such as from about 1 minute to about 10 hours.

The preparation of R-250fb can be carried out in any suitable apparatus, such as a static mixer, a tubular reactor, a stirred tank reactor or a stirred vapour-liquid disengagement vessel. The preparation of R-250fb may be carried out batch-wise or continuously. Preferably, the 1,1,1,3-tetrachloropropane formed in the process is purified and/or isolated before the subsequent step. The purification may be achieved by separation of the 250fb from any other products or reagents by one or more distillation, condensation or phase separation steps and/or by scrubbing with water or aqueous base.

In an embodiment, the conversion of carbon tetrachloride and ethylene to R-1234yf is carried out as an integrated process involving all four reaction stages described above, optionally with any of the features or combination of features described herein.

The invention will now be illustrated by the following non-limiting Examples.

Example 1 - The Direct fluorination of 1243zf -> 245eb A feed stream of diluted F2 gas (10% in N2) and 1243zf (equimolar to F2) were mixed in a cooled section of pipe before being passed to a tubular reactor section of 300 cm coiled 3/8” stainless steel tube within the body of a 10 L autoclave filled with a stirred glycol solution at -18°C. The tube length provided a residence time of 55 seconds. Upon exiting the reactor the product gases were passed through a bubbler of KOH solution to remove HF and F2 before being analysed by GC (3.9 area% 245eb, 32% selectivity, 60% conversion).

Example 2 - The Vapour Phase Conversion of 245eb ->1234yf without co-fed HF 2ml_/2.1g of catalyst (6.5% ZnO/Cr2C>3 TR2626) 0.5-1.0 mm was loaded into the centre of an 1/4” OD x 32 cm Inconel reactor tube, supported by Inconel mesh.

At atmospheric pressure, the reactor was heated to 250°C under 60 mL/min of nitrogen flow to dry the catalyst overnight. After this time the nitrogen flow was reduced to 30 mL/min and the catalyst was fluorinated overnight via the following programme: • Set HF flow to 30ml/min via sparging with 5ml/min N2 • Turn N2 (30ml/min) purge to reactor exit • Heat from 250°C to 400°C @ 100°C/hr • Heat from 400°C to 450°C @ 40°C/hr • Hold at 450°C for 10 hr • Cool to 350°C and hold overnight • Turn off HF to reactor and purge with N2 (30ml/min) for 1 hour

The temperature of the reactor was set to 250°C and 1,2,3,3,3-pentafluoropropane (245eb, Apollo Scientific, 98.9%) was sparged with 3ml_/min N2 co-feed to give a 245eb flow rate of 3ml_/min over the catalyst. Reaction progress was monitored by GC, by taking samples from the reactor off-gas, scrubbed through Dl water. Peak area percent’s were used to calculate the mol % the compounds in the reactor off-gas based on calibrations. Data was also collected at reactor temperatures of 300 and 250°C, the results of which are shown in the table below:

Example 3 - The Vapour Phase Conversion of 245eb -^1234yf with co-fed HF

Example 2 was repeated except that 20 ml/min of HF was co-fed with the 245eb

Example 4 - The Vapour Phase Conversion of 245eb -M234yf without co-fed HF

Example 2 was repeated except that 30 ml/min of HF was co-fed with the 245eb

Claims (18)

Claims

1. A process for preparing 2,3,3,3-tetrafluoropropene (R-1234yf), the process comprising: (a) contacting 3,3,3-trifluoropropene (R-1243zf) with fluorine (F2) to produce 1,2,3,3,3-pentafluoropropane (R-245eb); and (b) dehydrofluorinating R-245eb to produce R-1234yf.

2. A process according to claim 1, wherein step (a) is carried out in the presence of one or more free radical suppressants.

3. A process according to claim 2, wherein the free radical suppressant is ethanol.

4. A process according to claim 1, wherein the R-1243zf has a purity of greater than 99.8%.

5. A process according to any of the preceding claims, wherein step (a) is carried out with an excess of F2:R-1243zf, optionally with any unreacted F2 being recycled.

6. A process according to any of claims 1 to 4, wherein step (a) is carried out with an excess of R-1243zf to F2, optionally with any unreacted F2 being recycled.

7. A process according to claim 6, wherein the molar ratio of R-1243zf:F2 is from about 1.01:1 to about 2:1.

8. A process according to any of the preceding claims, wherein step (b) is carried out in the gas phase.

9. A process according to any of the preceding claims, wherein step (b) is carried out in the presence of a catalyst.

10. A process according to claim 9, wherein the catalyst comprises an oxide of a metal.

11. A process according to any of the preceding claims, which further comprises contacting 1,1,1,3-tetrachloropropane (R-250fb) with HF to produce R-1243zf.

12. A process according to claim 11, wherein the reaction is carried out in the gas phase.

13. A process according to claim 11 or 12, wherein the reaction is carried out in the presence of a catalyst.

14. A process according to any of claims 11 to 13, wherein at least part of the HCI produced as a by-product is separated and optionally purified.

15. A process according to any of claims 11 to 14, which further comprises telomerising ethylene and carbon tetrachloride (CCU) to produce R-250fb.

16. A process according to claim 15 comprising contacting ethylene with CCU in the liquid and/or vapour phase in the presence of a catalyst in an amount of from about 0.01 to about 50 mol %.

17. A process according to claim 15 or 16, wherein the catalyst comprises iron, copper and/or peroxide, preferably iron.

18. A process according to any of the preceding claims, wherein at least some of the HF produced by step (b) is converted to and recycled into step (a).