[0001 ] This application claims priority to European patent application

EP 16179182.7, filed on July 13, 2016, the whole content of this

application being incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention relates to a method for the hydrodehalogenation of halofluoroethers to perfluorovinylethers.

Background Art

[0003] Perfluorovinylethers are useful monomers for the manufacture of various fluoropolymers, in particular thermoprocessable tetrafluoroethylene-based plastics and fluoroelastomers.

[0004] Methods for manufacturing perfluorovinylethers from halofluoroethers are known in the art. Generally known methods involve the dehalogenation of suitable halofluoroether precursors in liquid phase in the presence of transition metals. For instance, US 2007203368 (SOLVAY SOLEXIS SPA) 8/30/2007 discloses a liquid-phase process for the manufacture of perfluorovinylethers by dehalogenation of certain halofluoroethers in the presence of transition metals as zinc, copper, manganese or metal couples as Zn/Cu, Zn/Sn, Zn/Hg. However, liquid phase processes generally suffer from the disadvantage that significant amounts of metal halides solutions or muds are typically obtained as by-products (e.g. ZnC solutions/muds are produced when a chlorofluoroether is dechlorinated over zinc). Separation of said by-products from target perfluorovinylethers and their handling and disposal are time-consuming, costly and very burdensome from an industrial point of view, as these muds are highly corrosive and possibly have a detrimental environmental impact.

[0005] In order to overcome such problems, gas-phase processes have been developed. For example, WO 2009150091 (SOLVAY SOLEXIS SPA) 12/17/2009 discloses a process for the manufacture of a

perfluorovinylether by hydrodehalogenation of a halofluoroether, said process comprising contacting the halofluoroether with hydrogen in the presence of a catalyst comprising at least one transition metal of group VIII B at a temperature of at most 340°C. The process proceeds with high selectivity and without the formation of by-products which are difficult to handle.

[0006] WO 2012/104365 (SOLVAY SPECIALTY POLYMERS IT) 8/9/2012

discloses a process for the manufacture of a perfluorovinylether by hydrodehalogenation of a halofluoroether, said process comprising contacting the halofluoroether with hydrogen in the presence of a catalyst comprising palladium and at least one transition metal selected from the group consisting of the metals of group VI 11 B, other than palladium, and of group IB. The presence of at least a second transition metal selected from group VI 11 B and group IB allows retaining the activity of the catalyst (i.e. its ability to transform the halofluoroether in the desired halofluoroether) for a longer period of time, thus increasing the economic profitability of the process.

[0007] On the other hand, it is known to add tin to metal catalysts; for example, the aforementioned patent application US 2007203368 teaches to use Sn in combination with Zn in a liquid phase dehalogenation process.

[0008] EP 0499158 (AUSIMONT SPA) 19/08/1995 discloses the selective

hydrodechlorination or 1 , 1 ,2-trichlorotrifluoroethane (CFC-1 13) over a palladium catalyst comprising selected metal additives such as Ag, Bi, Cd, Cu, Hg, In, Pb, Sn and Tl to chlorotrifluoroethylene (3FCI) and

trifluoroethylene (3FH). One examples specifically discloses the

hydrodechlorination of CFC-1 13 over a palladium catalyst comprising Sn. This document is silent on the use of catalyst comprising palladium or any other metal of group VI 11 B and Sn in the hydrodechlorination of

halofluoroethers.

[0009] It is also known to add tin to platinum catalysts in the hydrogen-assisted dechlorination of chlorinated alkanes. [0010] For example, EP 0640574 A (THE DOW CHEMICAL COMPANY) 3/1/1995 teaches the hydrodechlorination of a chlorinated alkane feedstock to provide a less chlorinated reaction product using a metal of group VI 11 B as active hydrogenating metal and a surface segregating metal. The surface segregating metal, preferably belonging to group IB of the periodic table, decreases the hydrogenating activity of the metal of group VI 11 B and allows controlling the selectivity towards a desired less chlorinated product. Table 1 1 on page 23 reports the results of the dechlorination of 1 ,2-dichloropropane in the presence of a Sn/Pt catalyst: even though selectivity towards propene is high (96%), the reported conversion is 25%, which means that the reduction of the hydrogenating activity entails a reduction in yields.

[001 1] OHNISHI, R., et al. Selective hydrodechlorination of CFC-1 143 on Bi and Tl -modified palladium catalysts. Applied Catalysis A: general 113. 1994, p.29 - 41 , illustrate the results of the hydrodechlorination of CFC-1 13 on modified palladium catalysts and teach that best results are achieved when Bi and Tl are used as modifiers. When Pd supported on AI2O3 is modified with Sn, chlorothrifluoroethylene is obtained with a selectivity of 78%, but the conversion is of 12% only (see Table 2 on page 33).

[0012] US 5498806 (DAIKIN INDUSTRIES LTD) 3/12/1996, relates to a process for preparing 1 -chloro-1 ,2,2-trifluoroethylene (3FCL) or

1 ,2,2-trifluoroethylene (3FH) by reacting 1 ,1 ,2-trichloro-1 ,2,2- trifluoroethane and hydrogen in the presence of a catalyst which comprises at least one metal selected from the group consisting of palladium, rhodium and ruthenium and at least one metal selected from the group consisting of mercury, lead, cadmium, tin, indium, copper, bismuth, thallium and silver and a carrier selected from the group consisting of AI2O3, S1O2 and activated carbon. Example 4 shows that, when a Sn/Pd catalyst supported on AI2O3 is used, 3FCL is obtained with a selectivity of 79.3% with a conversion of 15.9%.

[0013] EARLY, K.O., et al. Hydrogen-assisted 1 ,2,3-trichloropropane

dechlorination on supported Pt-Sn catalysts. Applied catalysis B.

Environmental. 2000, vol.26, p.257-263. report on the hydrogen-assisted 1 ,2,3-trichloropropane dechlorination on supported Pt-Sn catalysts; the main reaction products are propane, propene and allyl chloride. It is taught that the addition of Sn decreases the Pt hydrogenating activity.

[0014] Hydrogen-assisted 1 ,2-dichloroethane dechlorination catalyzed by Pt- Sn/SiO2 is discussed in and RHODES, W.D., et al. Hydrogen-assisted 1 ,2-dichloroethane dechlorination catalyzed by Pt-Sn/SiO2: Effect of the Pt/Sn Atomic ratio. Journal of catalysis 2002, vol.21 1 , p.173-182. and in RHODES, W.D., et al. Hydrogen-assisted 1 ,2-dichloroethane

dechlorination catalyzed by Pt-Sn/SiO2 catalysts of different preparations. Journal of catalysis. 2005, vol.230, p.86-97.

[0015] No hint or suggestion is provided in the above three articles to the use of Pt/Sn catalysts in the hydrogen-assisted declorination of

chlorofluoroethers.

[0016] VINCENTE, A., et al. The relationship between the structural properties of bimetallic Pd-Sn/SiO2 catalysts and their performance for selective citral hydrogenation. Journal of catalysis. 201 1 , vol.283, p.133-142. relates to the liquid phase hydrogenation of citral in the presence of a Pd-Sn/SiO2 catalyst. No hint or suggestion is given on the gas phase hydrogen- assisted dechlorination of chlorofluoroethers.

[0017] The overall teaching of the above-discussed prior art is that the addition of Sn to metal catalysts improves selectivity by decreases the conversion capacity.

[0018] The Applicant has now found out that when a catalyst comprising a metal of group VI 11 B, in particular palladium, is added with tin instead of a metal selected from group VI 11 B and group IB, the catalyst activity is retained for a longer period of time with respect to catalysts comprising a metal of group VI 11 B, without reducing the catalyst conversion capacity.

Summary of invention

[0019] It is thus an object of the present invention a method for the

hydrodehalogenation of a halofluoroether (HaloFE) having general formula (l-A) or (l-B):

(l-A) RfO-CRf'X-CRf"Rf"'X' wherein Rf represents a C1-C6 perfluoro(oxy)alkyl group; Rf', Rf" and Rf'", equal or different from each other, independently represent fluorine atoms or C1-C5 perfluoro(oxy)alkyl groups; X and X', equal or different from each other, are independently selected from CI, Br or I;

(l-B)

wherein Rf* and Rf*', equal or different from each other, independently represent fluorine atoms or C1-C3 perfluoro(oxy)alkyl groups;

Yi and Y2, equal or different from each other, independently represent fluorine atoms or C1-C3 perfluoroalkyl groups; X and X' are as above defined;

said method comprising contacting said halofluoroether (HaloFE) with hydrogen in the presence of a catalyst comprising at least one transition metal of group VI 11 B and tin (Sn).

[0020] The Applicant has found out that by using such catalyst it is possible to successfully isolate compounds comprising a O-CRf'=CRf"Rf"' or a -O-CRf*=CR _f *'-O- moiety, wherein R _f ', R _f ", R _f '", R _f * and R _f *' are as defined above (said compound being herein after referred to as

"perfluorovinylether(s)"), with high selectivity, without decreasing the catalyst conversion activity. In particular, hydrogenation side-reactions are remarkably reduced and contaminating hydrogenation by-products difficult to handle and separate are not formed, thereby making the recovery of the desired perfluorovinylether easier and more convenient on an industrial scale.

[0021] The method of the present invention enables to selectively obtain

perfluorovinylethers of formulae (A ^* ) and (B ^* ), respectively:

RfO-CRf'=CR _f "Rf

wherein Rf, Rf', Rf", Rf'", Yi, Y2, Rf ^* and Rf ^* ' have same meanings as above defined

without the need to frequently regenerate the catalyst at high temperature with H2 due to its high stability.

[0022] The method is carried out at temperatures generally not exceeding 340°C, thus poisoning from HF, sintering or coking phenomena otherwise known as significantly reducing the life of group VI 11 B transition metal catalysts can be essentially avoided.

[0023] The term "hydrodehalogenation", as used therein, is intended to denote the selective elimination of two halogen atoms, X, X' in formulae (l-A) an (l-B), selected from CI, Br or I from two adjacent fluorine-substituted carbon atoms of said halofluoroether (HaloFE), in the presence of hydrogen, to yield the corresponding perfluorovinylether.

[0024] The expression "perfluoro(oxy)alkyl group" is intended to indicate either a perfluoroalkyl group or a perfluorooxyalkyl group, that is a perfluoroalkyl group comprising one or more than one catenary oxygen atom.

[0025] According to a first embodiment of the invention, the halofluoroether

(HaloFE) of the invention is a chlorofluoroether (HaloFE-1 ) having general formula (l-A) as described above, wherein X and X', equal or different from each other, are independently selected from CI, Br or I, with the proviso that at least one of X and X' in said formula (l-A) is a chlorine atom.

[0026] The halofluoroether (HaloFE) of this first embodiment is preferably a

chlorofluororoether (HaloFE-2) having general formula (l-A) as described above, wherein X and X' are equal to each other and are chlorine atoms, that is to say that chlorofluoroether (HaloFE-2) complies with formula (ll-A) here below:

(ll-A) RfO-CRf'CI-CRf"Rf"'CI

wherein:

Rf represents a C1-C6 perfluoro(oxy)alkyl group, preferably a Ci-C ₄ perfluoroalkyl group, more preferably a C1-C3 perfluoroalkyl group;

Rf', Rf" and Rf'", equal or different from each other, independently represent fluorine atoms or C1-C5 perfluoro(oxy)alkyl groups, preferably fluorine atoms or C1-C3 perfluoroalkyl groups, more preferably fluorine atoms or C1-C2 perfluoroalkyl groups, even more preferably fluorine atoms.

[0027] The chlorofluoroether (HaloFE-2) is typically a gaseous compound under process conditions.

[0028] Representative chlorofluoroethers (HaloFE-2) described by formula (ll-A) useful in the method of the present invention include, but are not limited to, the following compounds: CF3OCFCICF2CI, CF3CF2OCFCICF2CI,

CF3CF2CF2OCFCICF2CI, CF3OCF2OCFCICF2CI,

CF3CF2OCF2OCFCICF2CI, CF3OCF2CF2OCF2OCFCICF2CI.

[0029] According to a second embodiment of the invention, the halofluoroether (HaloFE) of the invention is a chlorofluorodioxolane (HaloFE-3) having general formula (l-B) as described above, wherein X and X', equal or different from each other, are independently selected from CI, Br or I, with the proviso that at least one of X and X' in said formula (l-B) is a chlorine atom.

[0030] The halofluoroether (HaloFE) of this second embodiment is preferably a chlorofluorodioxolane (HaloFE-4) having general formula (l-B) as described above, wherein X and X' are equal to each other and are chlorine atoms, that is to say that chlorofluorodioxolane (HaloFE-4) complies with formula ( I l-B) here below:

(MB)

wherein Rf* and Rf*', equal or different from each other, independently represent fluorine atoms or C1-C3 perfluoro(oxy)alkyl groups, preferably fluorine atoms or C1-C3 perfluorooxyalkyl groups, more preferably fluorine atoms or -OCF3 groups; Yi and Y2, equal or different from each other, independently represent fluorine atoms or C1-C3 perfluoroalkyl groups, preferably fluorine atoms.

[0031] The chlorofluorodioxolane (HaloFE-4) is typically a gaseous compound under process conditions. [0032] Representative chlorofluorodioxolanes (HaloFE-4) described by

formula (ll-B) useful in the present invention include, but are not limited to, the following compound

[0033] The method of the present invention is carried out in the presence of a catalyst comprising at least one transition metal M selected from those of group VI 11 B, and Sn.

[0034] For the avoidance of doubt, the term "transition metal of group VI II B" is hereby intended to denote the following metals: Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt. Preferably, the catalyst comprises only one metal of group VI 11 B, preferably one of Rh, Ir, Pd and Pt; more preferably, the metal is Pd.

[0035] The molar ratio between metal M, preferably Pd, and tin (M:Sn ratio)

preferably ranges from 1 :0.5 to 1 :4. More preferably, the ratio ranges from 1 : 1 to 1 :2.5.

[0036] The catalyst used in the method of the invention typically is a supported catalyst, that is to say that it comprises the composition of metals as above described and an inert carrier.

[0037] The inert carrier is generally selected from activated carbon, silica and alumina; preferably, the carrier is activated carbon. Suitable inert carriers generally have a BET surface area of from 800 to 1600 m ² /g, preferably from 1000 to 1600 m ² /g, even more preferably from 1 100 to 1500 m ² /g.

[0038] The BET surface area is measured by N2 adsorption as per the Brunauer,

Emmett and Teller method of calculation, according to ISO 9277.

[0039] When supported, the catalyst generally comprises metal M, preferably Pd, in an amount of from 0.1 wt% to 2 wt%, preferably from 0.3 wt % to

1.8 wt %, more preferably from 0.5 wt % to 1.5 wt %.

[0040] The amount of Sn in the supported catalyst is determined, on the basis of the weight of metal M, in order to obtain a M:Sn molar ratio falling within the above identified range of from 1 :0.5 to 1 :4.

[0041] When supported, the catalyst may be advantageously prepared by the incipient wetness impregnation method. In such a method, an aqueous solution of a suitable metal precursor is added to the inert carrier and dried. The metal is then typically reduced by treatment with h . Among suitable precursors mention can be made of the transition metal halides, preferably chlorides, like PdCh, and tin halides, preferably tin chloride (SnCI ₂ ).

[0042] In the preparation of the catalyst to be used in the inventive method

impregnation of the inert carrier with the at least one metal M and Sn may be carried out either sequentially or simultaneously. In a sequential method, the inert carrier is first impregnated with a solution of the at least one metal M, optionally dried and then impregnated with a solution of Sn. In a simultaneous method, the inert carrier is impregnated with a solution comprising both the at least one metal M and tin, followed by drying and reduction, if needed.

[0043] Catalysts used in the method of the invention are generally activated

before use by pre-reduction under hydrogen at temperatures comprised between 250°C and 450°C, more preferably between 250°C and 400°C, even more preferably between 300°C and 400°C.

[0044] Typically, regeneration of the catalyst is also carried out under hydrogen at temperatures comprised between 300°C and 500°C, more preferably between 350°C and 500°C, even more preferably between 400°C and 500°C. The term "regeneration" refers to the process of restoring the catalytic activity of the catalyst which has been deactivated by use in the hydrodehalogenation process.

[0045] Very good results were obtained using catalysts comprising Pd and Sn supported on carbon, wherein the molar ratio between Pd and Sn ranges from 1 :0.5 to 1 :4. As it will be clearer from the examples reported in the experimental section, these catalyst maintain unaltered catalytic

performances (in terms of conversion and selectivity) up to 80 hours on stream. Furthermore, they have the same conversion activity as catalysts comprising only Pd supported on carbon, but their selectivity is remarkably higher; when tested in the hydrodehalogenation of the same

halofluoroether, the former have a selectivity ranging from about 85% to about 95%, while the latter have a selectivity of about 40 - 45% at the steady state.

[0046] The expression "steady state" is hereby defined as the time at which the ratio between the desired perfluorovinylether and any reaction by-products remains constant.

[0047] The expression "time on stream" is hereby defined as the duration of

continuous operations between successive reactor shut down for catalyst regeneration.

[0048] The method of the present invention is preferably carried out at a

temperature of at most 340°C.

[0049] The Applicant has found that for obtaining perfluorovinylethers in high

yields it is generally advantageous to carry out the method at temperatures not exceeding 340°C, in order to avoid decomposition of the

halofluoroether (HaloFE).

[0050] Lower limits of temperatures suitable for achieving efficient conversion of halofluoroethers to perfluorovinylethers are not particularly limited.

Temperatures of advantageously at least 170°C, preferably at least 200°C, more preferably at least 210°C, and even more preferably at least 230°C are generally used. Best results have been obtained at temperatures comprised between 230°C and 320°C.

[0051] The method of the present invention is advantageously carried out in gas- phase, that is to say in conditions wherein hydrogen and both the halofluoroether (HaloFE) and corresponding perfluorovinylether are in gaseous state. It is nevertheless understood that the catalyst is generally used as a solid, so that the reaction takes place between reactants in the gas phase and catalyst in the solid state.

[0052] Hydrogen can be fed either as neat reactant or diluted with an inert gas, e.g. nitrogen, helium or argon. Conveniently, the inert gas is nitrogen.

[0053] The method of the invention is carried out in any suitable reactor, including fixed and fluidized bed reactors. The method is generally carried out in continuous using a plug flow reactor comprising a fixed bed of catalyst. [0054] The reaction pressure is not critical to the method. The method of the present invention is typically carried out under atmospheric pressure, even though pressures between 1 and 3 bar can be employed.

[0055] Contact time between the halofluoroether (HaloFE) and the catalyst is not particularly limited and will be chosen by the skilled in the art in relation, notably, with reaction temperature and other process parameters. Contact time, which, for continuous processes, is defined as the ratio of the catalyst bed volume to the gas flow rate in standard conditions at 0°C and 1 bar, may vary between a few seconds and several hours. Nevertheless, it is understood that this contact time is generally comprised between 2 and 200 seconds, preferably between 5 and 50 seconds.

[0056] For continuously operated processes, time on stream may vary between 5 and 500 hours, preferably between 20 and 200 hours. A time on stream of at least 50 hours without a significant decrease of conversion may generally be advantageous. Even more advantageous might be a time on stream of at least 50 hours without a significant decrease of both conversion and selectivity. It is also understood that spent catalyst can be advantageously regenerated as above mentioned and recycled in a further time on stream in the method of the invention.

[0057] Good conversions are generally obtained in the presence of a

hydrogen/halofluoroether (HaloFE) molar ratio comprised between 0.5 and 4, preferably between 0.5 and 3, more preferably between 0.5 and 2.

[0058] It has been found that conversion typically increases by increasing the hydrogen/halofluoroether (HaloFE) molar ratio up to 4. A

hydrogen/halofluoroether (HaloFE) molar ratio greater than 4 could be used but it does not provide any additional increase in conversion and is usually uneconomical.

[0059] A halogenidric acid is obtained as a by-product from the method of the invention. When the halofluoroether (HaloFE) is selected from a

chlorofluoroether (HaloFE-1 ), a chlorofluoroether (HaloFE-2), a

chlorofluorodioxolane (HaloFE-3) or a chlorofluorodioxolane (HaloFE-4), hydrogen chloride is typically obtained; halogenidric acids can be easily recovered by neutralization in an aqueous alkaline solution or by absorption in water.

[0060] The invention is described in more detail in the following Experimental

Section by means of examples whose purpose is merely illustrative and not limitative of the scope of the invention.

[0061 ] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

EXPERIMENTAL SECTION

Catalyst preparation

[0062] 100 g activate extruded carbon, having pellet size of about 1 .5 mm and specific surface area SSA (BET method) of about 1500 m ² /g [NORIX RX1 .5 EXTRA (Norit Nederland B.V.)] was dried under vacuum at 200°C and divided into five 20 g portions. Each portion was impregnated by incipient wet impregnation method with water hydrochloric acid solutions having different PdCh and SnCh content. Five different catalysts (A, B, C, D and E) with a palladium loading of about 1 %wt with respect to carbon and having different Pd:Sn molar ratios were obtained, as reported in detail in Table 1 below.

Table 1

Catalyst Carbon (grams) Pd (wt%) Sn (wt%) Sn:Pd

(molar ratio)

A 20 g - -

¹

B 20 g 0.56 0.5

¹

C 20 g 1 .12 1

¹

D 20 g 2.23 2

¹

E 20 g 3.35 3

¹ Each catalyst was subsequently dried at 120°C in a nitrogen flow for 6 hours and then reduced in H ₂ at 330°C for 1 hour.

Example 1 (reference example) - Hydrodechlorination of CF3OCFCICF2CI on catalyst A (no Sn)

[0063] A continuous gas-phase catalytic process was carried out at atmospheric pressure in a plug-flow reactor. The overall reaction is illustrated by the following equation:

CF3OCFCICF2CI + H ₂ + CF ₃ OCF=CF ₂ + 2 HCI

[0064] 2.7 g catalyst A was loaded in a Hastelloy C down-flow tubular reactor

(length = 53 cm, internal diameter = 10 mm) equipped with an internal AISI 316 net to support the catalyst bed. The catalyst was reduced in a pure H2 flow at 350°C for at least one hour.

[0065] The reactor temperature was cooled to 250°C at 10 min rate in a

hydrogen/nitrogen stream and CF3OCFCICF2CI was fed on the catalyst bed at a flow rate of 4.1 g/h and residence time of 10 seconds. The gaseous mixture coming off the reactor was sampled at different times-on- stream (15 hours and 65 hours) and at the steady state and analyzed by gas chromatography (GC) to calculate conversion and selectivity (internal standard method).

[0066] The results are reported in Table 2 below.

Table 2

Sampling time Conversion % Selectivity % Selectivity % Selectivity %

CF3OCFCICF2CI CF ₃ OCF=CF ₂ CF ₃ OCCI=CF ₂ CF3OCFHCF2CI

1 (15 hrs) 65 21 25 47

2 (65 hrs) 65 44 15 34

Steady state 62 48 12 34 Example 2 - Hydrodechlorination of CF3OCFCICF2CI on catalyst B

[0067] The same procedure as in reference Example 1 was followed with the sole difference that the gaseous mixture coming off the reactor was sampled at 15 hours and 30 hours times-on-stream and at the steady state.

[0068] The results are reported in Table 3 below.

Table 3

[0069] Example 3 - Hydrodechlorination of CF3OCFCICF2CI on catalyst C

[0070] The same procedure as in reference Example 1 was followed. The

gaseous mixture coming off the reactor was sampled at 15 hours and 65 hours times-on-stream and at the steady state.

[0071 ] The results are reported in Table 4 below.

Table 4

[0072] Example 4 - Hydrodechlorination of CF3OCFCICF2CI on catalyst D

[0073] The same procedure as in reference Example 1 was followed. The

gaseous mixture coming off the reactor was sampled at 15 hours and 65 hours times-on-stream and at the steady state.

[0074] The results are reported in Table 5 below. Table 5

Example 5 - Hydrodechlorination of CF3OCFCICF2CI on catalyst E

[0075] The same procedure as in reference Example 1 was followed. The

gaseous mixture coming off the reactor was sampled at 15 hours and 65 hours times-on-stream and at the steady state.

[0076] The results are reported in Table 6 below.

Table 6

[0077] The data reported in this Experimental section show that by using a catalyst comprising at least one transition metal of group VI 11 B and tin, high conversion of the starting halofluoroether is achieved with high selectivity over a long time-on-stream. In other words, in the gas-phase hydrodehalogenation of a halofluoroether, the catalyst has a high conversion capacity and maintains a high selectivity for a time-on-stream of at least 50 hours.