GB2567919A

GB2567919A - Compositions and uses thereof

Info

Publication number: GB2567919A
Application number: GB1812952.8A
Authority: GB
Inventors: Mccarthy John; Smith John; Paul Sharratt Andrew
Original assignee: Mexichem Fluor SA de CV
Current assignee: Mexichem Fluor SA de CV
Priority date: 2017-08-09
Filing date: 2018-08-09
Publication date: 2019-05-01
Also published as: WO2019030527A1; GB201812952D0; GB201712775D0

Abstract

A composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF3CCl=CH2, 1233xf) and 1233xf oligomers in an amount less than about 0.5wt%. The reduced oligomer content prevents blocking of equipment and fluorination catalysts used in the formation of hydrofluoroolefins (HFOs). The composition may comprise a polymerisation inhibitor. The reduction in oligomer concentration may be produced by the purification of 3,3,3-trifluoro-2-chloro-prop-1-ene (1233xf), preferably by distillation. A fluorination process is also disclosed, the process comprising the steps of providing said composition and then contacting the composition with a fluorinating agent in the presence of a catalyst to produce a fluorination product stream. Preferably the fluorinating agent is hydrogen fluoride (HF). The fluorination product stream may comprise HF, HCl and a compound having the formula CF3CFXCH3 wherein X is F or Cl. The product stream may also comprise 2,3,3,3-tetrafluoropropene (CF3CF=CH2, 1234yf). Preferably the fluorination reaction is carried out in the vapour phase. The process may also comprise the step of converting the compound having the formula CF3CFXCH3 to 2,3,3,3-tetrafluoropropene (CF3CF=CH2, 1234yf). Also claimed is a process for preparing 2,3,3,3-tetrafluoropropene (CF3CF=CH2, 1234yf) comprising the step of fluorination of said composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF3CCl=CH2, 1233xf) and 1233xf oligomers in an amount less than about 0.5wt%.

Description

The present invention is concerned with compositions comprising 3,3,3-trifluoro-2-chloro-prop1-ene (CF3CCI=CH₂, HCFO-1233xf or 1233xf) and uses thereof. More particularly, the present invention is concerned with a composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF3CCI=CH2, 1233xf) and 1233xf oligomers in an amount of less than about 0.5 wt.%.

Hereinafter, unless otherwise stated, 3,3,3-trifluoro-2-chloro-prop-1-ene will be referred to as 1233xf. 1233xf is known to have utility as, for example, an intermediate in the manufacture of hydrofluoroolefins (HFOs). In particular, 1233xf is a key intermediate in the manufacture of 2,3,3,3-tetrafluoropropene, which is also known as HFO-1234yf, HFC-1234yf or simply 1234yf. Hereinafter, unless otherwise stated, 2,3,3,3-tetrafluoropropene will be referred to as 1234yf.

There are a number of processes being developed for the manufacture of 1234yf from 1233xf. Some of these processes involve preparing 1234yf by contacting 1233xf with a fluorinating agent, such as hydrogen fluoride (HF), in the presence of a catalyst. Other processes involve separation steps involving contacting 1233xf alone, or in combination with a fluorinating agent (e.g., HF), with reactive solids and surfaces. Further processes involve storage operations where 1233xf and a fluorinating agent (e.g., HF) are stored together prior to onward processing steps.

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.

The applicant has discovered that the use of 1233xf as an intermediate in the manufacture of HFOs suffers from a number of drawbacks, including fouling of equipment surfaces such as heat transfer surfaces and column packings. This fouling leads to the need to shut equipment down for regular cleaning. The applicant has also discovered that processes that use 1233xf as an intermediate in the manufacture of HFOs also suffer from fouling of catalysts and adsorbents, which leads to the requirement to replace these components on a regular basis and a reduction in overall yield of the processes.

There is a need for a more economical means for producing HFOs from 1233xf. In particular, the applicant has come to appreciate a need to reduce the level of fouling occurring when using 1233xf as an intermediate in the manufacture of HFOs.

The present invention addresses the foregoing deficiencies by providing a composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF₃CCI=CH2, 1233xf) and 1233xf oligomers in an amount of less than about 0.5 wt.%. For the avoidance of doubt, it is the 1233xf oligomers that are present in the composition in an amount of less than about 0.5 wt.%.

Surprisingly, the applicant has found that 1233xf readily oligomerises and that it is these oligomers which have been found to lead to a large amount of fouling as detailed above. 1233xf containing significant amounts of 1233xf oligomers is undesirable for contacting with catalysts and HF in order to prepare HFOs unless steps are taken to control the levels of oligomeric products in it.

The 1233xf oligomers typically are compounds according to formula I:

cf₃

I H₂-c—c

Cl

Formula I wherein, n is 2 to 50. Preferably, n is from 2 to 20, such as from 2 to 15, for example from 2 or 3 to 10. It is to be understood that when, for instance, n = 2 to 20, this means that the oligomers may be a mixture of compounds according to formula I having varying degrees of polymerisation ranging from n = 2 to n = 20.

In one embodiment, the 1233xf oligomers have a molecular weight of from about 250 to about 2700 g/mol, such as from about 250 to about 2100 g/mol, for example from about 250 or 290 to about 1400 g/mol. It will be appreciated that these oligomers are formed through uncontrolled processes and so the oligomers formed can vary widely in structure. The term 1233xf oligomer then should be understood to include the meaning of oligomers formed from 1233xf repeating units with a variety of end group functionalisation and branching.

The 1233xf oligomers typically have a boiling point higher than non-polymerised 1233xf. For example, the oligomers of the composition may have a boiling point of from about 100°C to about 600°C, such as from about 110°C to about 500°C, for example from about 120°C to about 400°C.

Conveniently, the compositions of the invention contain 1233xf oligomers in an amount of less than about 0.45 wt.% or 0.4 wt.%, such as less than about 0.3 wt.%, 0.2 wt.%, 0.1 wt.% or 0.05 wt.%, for example less than about 0.01 wt.%.

As used herein, all wt.% amounts mentioned in compositions herein, including in the claims, are by weight based on the total weight of the composition, unless otherwise stated.

The compositions of the invention typically contain 1233xf oligomers in an amount of at least about 0.0001 wt.% or 0.0002 wt.%, such as at least about 0.0005 wt.%, 0.001 wt.%, 0.002 wt.% or 0.005 wt.%, for example at least about 0.01 wt.%.

For avoidance of doubt, the upper and lower limits on the amount of 1233xf oligomers in the compositions of the invention referred to in the preceding two paragraphs can be combined in anyway. Preferably, the compositions of the invention contain 1233xf oligomers in an amount of from about 0.0001 wt.% to about 0.5 wt.% or from about 0.0002 wt.% to about 0.45 wt.%, such as from about 0.0005 wt.% to about 0.4 wt.% or from about 0.001 wt.% to about 0.3 wt.%, for example from about 0.002 wt.% to about 0.2 wt.%.

If a 1233xf composition contains greater than desirable amounts of 1233xf oligomers, the applicant has found that the compositions of the invention can be obtained by removing some 1233xf oligomers from the compositions, for example by fractional distillation. The applicant believes that fractional distillation is currently preferred to other possible methods of removing 1233xf oligomers. For example, adsorbents might be contemplated to separate 1233xf from its oligomers. However, the applicant believes that adsorbents might catalyse the oligomerisation of 1233xf.

The distillation can be carried out by any suitable method bearing in mind the boiling point of 1233xf (12-13 °C) and the boiling point of the 1233xf oligomers as described herein. The Examples described hereinafter provide one such method of separating 1233xf from 1233xf oligomers.

In one embodiment, the content of the 1233xf oligomers in the compositions of the invention can be kept to the low amounts defined herein by the presence of a polymerisation inhibitor. This can be useful if, for example, the 1233xf is stored for a significant amount of time prior to use.

Suitable polymerisation inhibitors are selected from the group consisting of 4-tbutylpyrocatechol, p-methoxyphenol, t-amylphenol, 2,6-di-t-butyl-p-cresol, 2,6-di-tbutylphenol, phenothiazine, 1,1-dipheyl-2-picrylhydrazyl free radical, limonene, quinones (e.g. 1,4-benzoquinone), hydroquinones (e.g. t-butylhydroauinone), epoxides, terpenes, amines and mixtures thereof.

If the compositions of the invention contain a polymerisation inhibitor, typically the polymerisation inhibitor is present in an amount of from about 0.005 to about 2 wt.%, such as from about 0.01 to about 1 wt.%, for example from about 0.01 to about 0.5 wt.%.

Alternatively, it may not be necessary to use a polymerisation inhibitor, for example if the composition of the invention is used relatively quickly following lowering of the concentration of 1233xf oligomers in the composition to acceptable levels (e.g. by fractional distillation). Thus, in one embodiment, the composition is essentially free of polymerisation inhibitors. An advantage of this is that polymerisation inhibitors than themselves cause fouling/poisoning of fluorination catalysts or deydrofluorination catalysts. By the term “essentially free”, we include the meaning that the composition contains less than about 0.01 wt.% polymerisation inhibitors, such as less than about 0.005 wt.%, for example less than about 0.002 wt.% or 0.001 wt.%, preferably less than about 0.0001 wt.%.

The applicant has discovered that the use of the compositions of the invention in processes for the manufacture of HFOs can significantly improve the efficiency and economy of such processes. In particular, fouling of equipment surfaces such as heat transfer surfaces and column packings typically is reduced when using the compositions of the invention (compared to 1233xf compositions that contain greater quantities of 1233xf oligomers). This reduces the need to shut equipment down for regular cleaning.

It is believed that the use of the compositions of the invention in processes for the manufacture of HFOs can also significantly reduce fouling of equipment surfaces, catalysts and/or adsorbents (compared to 1233xf compositions that contain greater quantities of 1233xf oligomers). Replacement of these components is therefore less frequent when using the compositions of the invention, leading to a more economic process and, typically, an increase in the overall yield of the processes.

Thus, in a further aspect the present invention is concerned with a fluorination process comprising the steps of:

(a) providing a composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF3CCI=CH2, 1233xf) and 1233xf oligomers in an amount of less than about 0.5 wt.%; and (b) contacting the composition with a fluorinating agent in the presence of a catalyst to produce a fluorination product stream.

For the avoidance of doubt, the composition in step (a) of the above process of the invention is a composition of the invention as described herein.

Providing step (a) may include the removal of 1233xf oligomers from a composition containing 1233xf so as bring the concentration of 1233xf oligomers in the composition to the levels defined herein. Such removal may be achieved by, for example, fractional distillation.

Any suitable fluorinating agent may be used in step (b), including any suitable source of nucleophilic fluoride, optionally in a polar aprotic solvent. Examples of suitable fluorinating agents include HF, NaF, KF and amine:HF complexes such as Olah’s reagent. HF is a preferred fluorinating agent.

Advantageously, the fluorination product stream comprises HF, HCI and a compound having the formula CF3CFXCH3, wherein X is F or Cl.

Conveniently, in step (b) at least a portion of 1233xf in the provided composition is converted to 1,1,1,2,2-pentafluoropropane (CF3CF2CH3, 245cb), 2-chloro-1,1,1,2-tetrafluoropropane (CF3CFCICH3,244bb) or mixtures thereof in the fluorination product stream.

Preferably, at least 80 wt.% of the 1233xf is fluorinated in step (b), such as greater than 85 wt.%, 90 wt.% or 95 wt.%, more preferably at least 99 wt.% of the 1233xf is fluorinated in step (b). Therefore, the fluorination product stream may also comprise unreacted 1233xf.

Advantageously, the fluorination product stream comprises or further comprises 2,3,3,3tetrafluoropropene (CF3CF=CH2,1234yf).

Typically, step (b) is carried out at a temperature of from about 0 to about 450 °C and a pressure of from 0 to about 30 bara, preferably at a temperature of from about 200 to about 400 °C and a pressure of from about 1 to about 20 bara, more preferably at a temperature of from about 300 to about 380 °C and a pressure of from about 2 to about 20 bara.

Steps (b) may be carried out in the liquid phase or the gas phase. Preferably, step (b) is carried out in the vapour phase.

Steps (b) may be carried out batch-wise, semi-continuously or continuously, preferably semicontinuously or continuously.

The on-stream time for the process of the invention, for example step (b), may vary over a wide range. However, as noted above, by using the composition of the invention, cleaning of equipment surfaces and/or replacement of components such as catalysts and/or adsorbents typically is less frequent with the process of the invention compared to corresponding processes in which there are higher amounts of 1233xf oligomers present. Thus, the onstream time for the process of the invention (when operated semi-continuously or continuously) typically will range from about 1 to about 1000 hours, such as from about 2 to about 3000 hours, for example from about 5 to about 5000 hours.

The catalyst used in step (b) may be any suitable catalyst that is effective to fluorinate 1233xf. Preferred catalysts are those comprising activated carbon, a zero-valent metal, a metal oxide, a metal oxyhalide, a metal halide, or mixtures of the foregoing. A further group of preferred catalysts are transition metals, alkaline earth metals or aluminium.

For the avoidance of doubt, by catalysts comprising activated carbon, a zero-valent metal, a metal oxide, a metal oxyhalide, a metal halide, transition metals, alkaline earth metals or aluminium we include catalysts that are essentially only activated carbon, a zero-valent metal, a metal oxide, a metal oxyhalide, a metal halide, transition metals, alkaline earth metals or aluminium and catalysts that are activated carbon, a zero-valent metal, a metal oxide, a metal oxyhalide, a metal halide, transition metals, alkaline earth metals or aluminium modified, for example, by the addition of one or more metals (e.g. transition metals) and/or compounds thereof.

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 and pelleted activated carbon. Activated carbon which has been modified (e.g. impregnated) by the addition of Cr, Mn, Au, Fe, Sn, Ta, Ti, Sb, Al, Co, Ni, Mo, Ru, Rh, Pd and/or Pt and/or a compound (e.g. a halide) of one or more of these metals may be used.

Catalysts based on chromia currently are particularly preferred. Typically, the chromium or compound of chromium present in the chromia-based catalysts of the invention is an oxide, oxyfluoride and/or fluoride of chromium such as chromium (III) oxide.

A preferred chromia-based catalyst is a zinc/chromia catalyst. By the term “zinc/chromia catalyst” we mean any catalyst comprising chromium or a compound of chromium and zinc or a compound of zinc. Such catalysts are known in the art, see for example EP-A-0502605, EP-A-0773061, EP-A-0957074 and WO 98/10862.

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 fluorination/dehydrohalogenation 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 percentage of crystalline material in the catalysts of the invention can be determined by any suitable method known in the art. Suitable methods include X-ray diffraction (XRD) techniques. When XRD is used the amount of crystalline material such as the amount of crystalline chromium oxide can be determined with reference to a known amount of graphite present in the catalyst (e.g., the graphite used in producing catalyst pellets) or more preferably by comparison of the intensity of the XRD patterns of the sample materials with reference materials prepared from suitable internationally recognised standards, for example NIST (National Institute of Standards and Technology) reference materials.

The zinc/chromia catalysts of the invention typically have a surface area of at least 50 m²/g and preferably from 70 to 250 m²/g and most preferably from 100 to 200 m²/g before it is subjected to pre-treatment with a fluoride containing species such as hydrogen fluoride or a fluorinated hydrocarbon. During this pre-treatment, which is described in more detail hereinafter, at least some of the oxygen atoms in the catalyst are replaced by fluorine atoms.

Conveniently, the process comprises a step of (c) converting the compound of the formula CF3CFXCH3 in the fluorination product stream to 2,3,3,3-tetrafluoropropene (CF₃CF=CH₂,1234yf).

Step (c) may be carried out in the liquid phase or the gas phase. Preferably, step (c) is carried out in the vapour phase.

Step (c) may be carried out batch-wise, semi-continuously or continuously, preferably semicontinuously or continuously.

Step (c) of the process of the invention may be carried out under any suitable reactions conditions effective to dehydrohalogenate the compound of formula CF3CFXCH3 to produce 1234yf. The dehydrohalogenation may be carried out in the vapour and/or liquid phase and typically is carried out at a temperature of from about -70 to about 1000 °C (e.g. 0 to 400 °C). Step (c) may be carried out at atmospheric sub- or super atmospheric pressure, preferably from about 0 to about 30 bara. Ideally, step (c) is carried out at a temperature of from about 0 to about 400 °C and a pressure of from 0.01 to about 25 bara, preferably from about 200 to about 360 °C and from about 1 to about 10 bara.

Suitable catalysts for step (c) include metal and carbon based catalysts such as those comprising activated carbon, main group (e.g. alumina-based catalysts) and transition metals, such as chromia-based catalysts (e.g. zinc/chromia) or nickel-based catalysts (e.g. nickel mesh). One preferred method of effecting the dehydrohalogenation of the compound of formula CF3CFXCH3 to produce 1234yf is by contacting CF3CFXCH3 with a metal catalyst, such as a chromia-based (e.g. zinc/chromia) catalyst.

Advantageously, step (b) is carried out in a first reactor and step (c) is carried out in a second reactor. It is believed that there are advantages associated with the use of separate reactors for these two steps, including modifying the conditions in each reactor to facilitate the reactions in steps (b) and (c) respectively.

For example, step (b) can be carried out in the gas phase and step (c) in the liquid phase. A higher temperature can be used in step (b) compared to step (c). A higher pressure can be used in step (b) compared to step (c).

When the catalyst used in step (b) is the same as in step (c) (e.g. when using a chromia-based catalyst such as a zinc/chromia catalyst), steps (b) and (c) may be carried out in a “one-pot” manner, i.e. simultaneously. Alternatively, when both steps (b) and (c) are carried out in the presence of different catalysts, the fluorination and dehydrohalogenation reactions may be carried out in two discrete steps, for example using two or more discrete reaction zones or reactors.

Any suitable apparatus may be used as a reactor for steps (b) and (c), such as a static mixer, a stirred tank reactor or a stirred vapour-liquid disengagement vessel. Preferably, the apparatus is made from one or more materials that are resistant to corrosion, e.g. Hastelloy® or Inconel®.

Conveniently, the fluorination product stream is subjected to a purification step to remove at least some of the HCI before step (c). Preferably, distillation is used to remove at least some of the HCI.

The preferred conditions for fluorination step (b) are set out above. Dehydrohalogenation step (c) may be carried out in the vapour or liquid phase, preferably the vapour phase. When conducted in the vapour phase, in the presence of a metal catalyst, such as a chromia-based (e.g. zinc/chromia) catalyst, step (c) preferably is conducted at a temperature of from about 200 to about 360 °C, such as from about 240 to about 340 °C.

It is currently considered to be advantageous to use a higher pressure in step (b) (to promote fluorination) than in step (c) (to promote dehydrohalogenation). Thus, step (c) preferably is carried out from about 0.01 to about 25 bara or about 0.1 to about 20 bara, such as from about 1 to about 10 bara (e.g. 1 to 5 bara).

Fluorination step (b) of the invention preferably is carried out by contacting 1233xf with HF. Step (c) of the invention may be carried out in the presence of HF. For example residual HF from step (b) may be present, and/or HF from a separate feed. Alternatively, step (c) may be carried out in the absence of HF, for example following separation of the compound of formula CF3CFXCH3 from HF prior to step (c), and with no additional co-feed of HF. In certain embodiments it may be desirable to use some HF in order to prevent and/or retard excessive decomposition of the organic feed and/or coking of the catalyst in step (c).

Advantageously, the fluorination product stream is subjected to a purification step to remove at least some of the HF before step (c). Techniques that may be used to remove at least some of the HF include distillation, phase separation and scrubbing.

Another way of decreasing the concentration of HF in step (c) relative to step (b) (thereby facilitating thefluorination/dehydrohalogenation reactions in these steps) is by adding a diluent gas (e.g. nitrogen) to step (c).

Also provided by the invention is a process for preparing 2,3,3,3-tetrafluoropropene (CF3CF=CH2,1234yf) comprising the step of fluorination of a composition of the invention as described herein. Such a process can include any of the steps outlined above.

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

Examples

Oligomer Identification

A sample of 1233xf (ex-Apollo Scientific) was subjected to a fractional distillation process. The distillation was performed in a glass apparatus comprising a 2-litre reboiler, packed column, condenser, reflux divider and receiver operated at atmospheric pressure. Oligomer free batches of 1233xf were prepared as follows:

• Crude 1233xf was charged to the reboiler, brought to reflux and condensed against a cooling fluid at -3°C • The system was operated under total reflux for a period to equilibrate and remove any light components not condensed at -3°C • After 4 hours under total reflux fractions were collected • The fractions were analysed by GC-MS to determine their purity • All fractions that were of GC-MS purity better than 99 % were combined for use

This process produced a light fraction comprising 1233xf and a heavy fraction comprising 1233xf oligomers. The level of oligomeric impurities in the crude 1233xf was found to be in the region of 0.5 wt.% to 1.0 wt.%. The heavy oligomeric fraction was analysed by XRF, ¹NMR spectroscopy and TGA-DSC, which confirmed that the heavy fraction was composition of 1233xf oligomers with a boiling range of 130°C to 390°C.

Catalytic Fluorination of 1233xf

Liquid 1233xf (at a rate equivalent to 5 ml/min vapour at room temperature and pressure), either the crude or purified samples described above, and HF (at a rate equivalent to 125 ml/min vapour at room temperature and pressure) were fed to a heated evaporator where they were co-vapourised before the combined vapour stream was fed to a reactor containing fluorinated chromia catalyst (6 g) at 350°C and 5 bara pressure. The products exiting the reactor were periodically sampled and analysed by GC.

Great difficulty was encountered when feeding the 1233xf containing high levels of 1233xf oligomers and it was found that the feed evaporator became blocked and had to be cleaned every 24 hours.

When the 1233xf feedstock with highly reduced levels of 1233xf oligomers was used, no difficulties were encountered during the feeding process and it was found that the feed evaporator could be operated for 1000’s of hours without blocking.

Furthermore, catalyst performance was very stable when 1233xf with highly reduced levels of 1233xf oligomers was used and a very low reduction in rate of conversion loss was observed as detailed in Table 1.

Table 1

Catalyst	Rate of 1233xf conversion loss (catalyst mid-way through operating life) (%/hr)
Cr₂O3	0.296
2.7% ZnO/Cr₂O₃	0.231
6.5% ZnO/Cr₂O₃	0.139

The invention is defined by the following claims.

Claims

1. A composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF3CCI=CH2, 1233xf) and 1233xf oligomers in an amount of less than about 0.5 wt.%.

2. The composition according to claim 1, wherein the 1233xf oligomers have a molecular weight of from about 250 to about 2700 g/mol, such as from about 250 to about 2100 g/mol, preferably from about 250 or about 290 to about 1400 g/mol.

3. The composition according to claim 1 or claim 2, wherein the composition comprises 1233xf oligomers in an amount of less than about 0.45 wt.% or 0.4 wt.%, such as less than about 0.3 wt.%, 0.2 wt.%, 0.1 wt.% or 0.05 wt.%, preferably less than about 0.01 wt.%.

4. The composition according to any of claims 1 to 3, wherein the composition comprises 1233xf oligomers in an amount of from about 0.0001 wt.% to about 0.5 wt.%, for instance from about 0.0002 wt.% to about 0.45 wt.%, such as from about 0.0005 wt.% to about 0.4 wt.%, for example from about 0.001 wt.% to about 0.3 wt.%, or from about 0.002 wt.% to about 0.2 wt.%.

5. The composition according to any preceding claim, wherein the composition further comprises a polymerisation inhibitor.

6. The composition according to claim 5, wherein the polymerisation inhibitor is selected from the group consisting of 4-t-butylpyrocatechol, p-methoxyphenol, t-amylphenol, 2,6-di-tbutyl-p-cresol, 2,6-di-t-butylphenol, phenothiazine, 1,1 -dipheyl-2-picrylhydrazyl free radical, limonene, quinones (e.g. 1,4-benzoquinone), hydroquinones (e.g. t-butylhydroquinone), epoxides, terpenes, amines and mixtures thereof.

7. The composition of claim 5 or 6 wherein the polymerisation inhibitor is present in the composition in an amount of from about 0.005 to about 2 wt.%, such as from about 0.01 to about 1 wt.%, for example from about 0.01 to about 0.5 wt.%.

8. The composition of any of claims 1 to 4, wherein the composition is essentially free of a polymerisation inhibitor selected from the group consisting of 4-t-butylpyrocatechol, pmethoxyphenol, t-amylphenol, 2,6-di-t-butyl-p-cresol, 2,6-di-t-butylphenol, phenothiazine, 1,1dipheyl-2-picrylhydrazyl free radical, limonene, quinones (e.g. 1,4-benzoquinone), hydroquinones (e.g. t-butylhydroquinone), epoxides, terpenes, amines and mixtures thereof.

9. A fluorination process comprising the steps of:

(a) providing a composition according to any preceding claim; and (b) contacting the composition with a fluorinating agent in the presence of a catalyst to produce a fluorination product stream.

10. The process according to claim 9, wherein the fluorinating agent is hydrogen fluoride (HF).

11. The process according to claim 9 or 10, wherein the fluorination product stream comprises HF, HCI and a compound having the formula CF3CFXCH3, wherein X is F or Cl.

12. The process according to any of claims 9 to 11, wherein the fluorination product stream comprises 2,3,3,3-tetrafluoropropene (CF3CF=CH2,1234yf).

13. The process according to any one of claims 9 to 12, wherein step (b) is carried out in the vapour phase.

14. The process according to any one of claims 9 to 13, wherein the process comprises a step of (c) converting the compound of the formula CFsCFXCHsto 2,3,3,3-tetrafluoropropene (CF3CF=CH2,1234yf).

15. The process according to claim 14, wherein step (c) is carried out in the vapour phase.

16. The process according to claim 14 or claim 15, wherein step (b) is carried out in a first reactor and step (c) is carried out in a second reactor.

17. The process according to any of claims 14 to 16, wherein the fluorination product stream is subjected to a purification step to remove at least some of the HCI prior to step (c).

18. The process according to claim 17, wherein the purification step comprises distillation.

19. The process according to any of claims 9 to 18, wherein step (b) is carried out at a temperature of from about 0 to about 450 °C and a pressure of from 0 to about 30 bara, preferably at a temperature of from about 200 to about 400 °C and a pressure of from about 1 to about 20 bara, more preferably at a temperature of from about 300 to about 380 °C and a pressure of from about 2 to about 20 bara.

20. The process according to any of claims 9 to 19, wherein the catalyst in step (b) is a bulk form or supported catalyst comprising activated carbon, a zero-valent metal, a metal oxide, a metal oxyhalide, a metal halide, or mixtures of the foregoing.

21. The process according to claim 20, wherein the metal is a transition metal, an alkaline earth metal or aluminium.

22. The process according to claim 20 or 21, wherein the catalyst is based on chromia, such as a zinc/chromia catalyst.

23. The process according to any of claims 13 to 22, wherein step (c) is carried out at a temperature of from about 0 to about 400 °C and a pressure of from 0.01 to about 25 bara, preferably from about 200 to about 360 °C and from about 1 to about 10 bara.

24. A process according to any of claims 9 to 23 wherein the providing step (a) comprises a purification step in which the concentration of 1233xf oligomers is reduced.

25. A process according to claim 24 wherein the purification step comprises distillation.

26. A process for preparing 2,3,3,3-tetrafluoropropene (CF3CF=CH2,1234yf) comprising the step of fluorination of a composition according to any of claims 1 to 6.