PROCESS FOR PREPARING FLUOROHALOGENOETHERS

Cross-Reference to Related Application

This application claims priority to European application No. 17205588.1 filed on December 6, 2017, the whole content of this application being incorporated herein by reference for all purposes.

Technical Field

The present invention relates to a process for preparing fluorohalogenoethers in a microreactor. More specifically the invention relates to the preparation of fluorohalogenoethers which, by dehalogenation or dehydrohalogenation, allow to obtain perfluorovinylethers.

Background Art

It is known that perfluorovinylethers are useful monomers for preparing various polymers such as fluorinated elastomers and fluorinated thermoprocessable semicrystalline polymers.

Processes and methods for preparing fluorohalogenoethers in conventional scale reactors have already been disclosed in the art.

US4900872 (AUSIMONT S.p.A.) discloses a process for the preparation of fluorohalogenated ethers having the formula:

(R) _n C(F) _m -O-CAF-CA ¹ F ₂

wherein A and A ¹ , alike or different from each other, are chlorine or bromine, R is an alkyl or polyether radical containing from 1 to 20 carbon atoms, wholly halogenated with bromine, chlorine and/or fluorine, n is an integer from 1 to 2, m is an integer equal to 3-n, said process consisting in reacting in liquid phase a fluoroxycompound (R) _n - C(F) _m -OF with an olefin CAF=CA ¹ F, at temperature between -150 ° and 0 °C, wherein the fluoroxycompound is continuously fed into the reaction phase in the form of a mixsture having a concentration less than 50% by weight in an inert diluent, the olefin being fed in the liquid state, optionally in an inert solvent, all at the beginning into the reactor or continuously, in such a manner to have always an excess of the olefin in the reaction phase. A preferred temperature range is between -40°C and -100°C, and a chlorofluorocarbon or a perfluoroether or a perfluoropolyether is preferably used as inert solvent.

Journal of Fluorine Chemistry, 74 (1995) 199-201 discloses thermal gas-phase reaction of CF ₃ OF with tetrachloroethene at temperatures between 313.8 K (40.65 °C) and 343.8 K (70.65°C), to produce trifluoromethyl-1 ,1 ,2,2-tetrachloro-2-fluoroethyl ether CF ₃ OCCI2CCI2F as a major product.

Similarly, EP0404076 (AUSIMONT S.p.A.) discloses a process for preparing perhaloethers from perhaloolefins by reacting at least one fluorooxy compound Rx-OF, wherein Rx is a perhaloalkyl radical, with a perfluoroolefin in a liquid phase, optionally containing an organic solvent inert to the perfluoroolefin, while maintaining the temperature of the liquid phase in the range of -30° to -120° C. The process includes continuously feeding to the liquid phase a stream of an inert gas and a gaseous stream of the fluorooxy compound.

US7612242 (SOLVAY SOLEXIS S.p.A.) discloses a process for preparing perfluorovinylethers having the general formula: R _f O— CF=CF ₂ , wherein R _f is a C ₁ -C ₃ perfluorinated substituent; comprising a step of reacting a hypofluorite of formula R _f OF, wherein R _f is as above, with an olefin of formula CY”Y=CY’CI, wherein Y’ and Y” are selected from the group consisting of H, Cl, and Br with the proviso that Y, Y’ and Y” are not contemporaneously hydrogen.

US7795477 (SOLVAY SOLEXIS S.p.A.) discloses a process for preparing perfluorovinylethers having the general formula: R _f O— CF=CF ₂ , wherein R _f is a C ₁ -C ₃ alkyl perfluorinated substituent; comprising a step of reacting a hypofluorite of formula R _f OF with an olefin of formula FCYrCYnF, wherein Y _| and Yu, equal to or different from each other, are Cl, Br, H but not contemporaneously H.

Chemical processes carried out in microreactors are also known.

W099/22857 (BRITISH NUCLEAR FUELS PLC) discloses a method of carrying out a chemical reaction between two fluids using a microreactor.

WO2016/193248 discloses a process for the manufacture of 1 ,2,3,4-tetrachloro- hexafluoro-butane in a microreactor.

However, the two last mentioned patent applications are silent about reactions involving a hypofluorite. Indeed, it is known that the processes involving reactions of hypofluorites are peculiar and object of major concerns due to the high reactivity of this class of compounds, as well as to their instability, requiring strict safety precautions. Hypofluorites are intrinsically unstable and may self-decompose upon simple contact with organic impurities and metal surfaces thus generating hot spots in the reaction vessels. For this reason, according to the prior art, harsh conditions and high temperatures need to be avoided in the reactions involving hypofluorites, whereas high dilution of the hypofluorite with inert fluids is normally used to reduce the risk of decomposition.

Journal of Fluorine Chemistry, 74 (1995) 199-201 discloses that hypofluorite thermal decomposition is also observed in the reaction with perfluoro-olefins. Decomposition occurs at temperatures as low as -100°C and forms a competitive pathway to the alkoxy-radical addition to perfluoro-olefins.

Summary of the Invention

The Applicant has noted that, despite fluorohalogenoethers can be prepared by the processes known in the art, the productivity of the processes disclosed in the previous cited prior art documents was from about 25 kg/h-m ³ to about 250 kg/h-m ³ .

Thus, the need was felt to have available an industrial process for preparing fluorohalogenoethers that allows a higher productivity to be obtained without jeopardizing the safety of the process.

Surprisingly, the Applicant has found that by a process for preparing fluorohalogenoethers that is carried out in a microreactor, productivity can be dramatically increased up to 10000-30000 kg/h-m ³ .

In addition, in the process for preparing fluorohalogenoethers in a microreactor, according to the present invention, it is possible to employ harsher conditions, such as a reduced dilution of the reagents and relatively high temperatures, thus improving the economic value without affecting the safety of the process and minimizing the amounts of undesired side-products.

A subject of the present invention is therefore a process for preparing fluorohalogenoethers of formula (IA), (IB) or (IC):

(IA) R _f OCY”Y-CY’CIF

(IB) R _f OCY’CI-CY”CIF

(IC) R _f OCFY’-CF ₂ Y” wherein R _f is a C ₁ -C ₃ peril uorinated substituent, Y, Y’ and Y” equal to or different from each other, are H, Cl, Br with the proviso that Y, Y’ and Y” are not contemporaneously hydrogen, said process comprising the step of reaction between a hypofluorite of formula R _f OF, wherein R _f is as defined above, and an olefin selected in the group of formula:

(la) CY”Y=CY’CI

(lb) FCY’=CFY”,

wherein said reaction step is carried out in a microreactor.

Detailed Description of the Invention

General definitions, symbols and abbreviations

The term “perfluorinated” denotes a fully or partially fluorinated straight or branched alkyl group.

Unless otherwise indicated, the term “halogen” includes fluorine, chlorine, bromine and iodine.

As used within the present description and in the following claims:

- the term“productivity” indicates the rate of speed at which a product can be obtained in a chemical reaction and, more in particular, it is used to indicate the amount, expressed for example in Kg or tons, of fluorohalogenoethers produced per hour and per cubic meter of the reactor or of the microreactor. Thus, the term “productivity” is different from the term“yield” that indicates the amount of product obtained in a chemical reaction;

- the expression“residence time” is intended to indicate the ratio between the reaction volume and the volumetric flow of the gas phase fed into the microreactor. When the process is performed in gas phase, the reactions take place in the gas phase and the reaction volume corresponds to the volume of the gas into the microreactor. When the process is performed in liquid/gas phase or in liquid phase, the reactions take place at the interface between the gas and the liquid phase and in the liquid phase, respectively, and in both cases the reaction volume corresponds to the volume of the liquid phase into the microreactor;

- the term “microreactor” (also known as “microstructured reactors” or

“microchannel reactors”) is intended to mean a device in which chemical reactions take place in a confinement with typical cross sectional dimensions below 1 mm. Said confinements are typically microchannels (also referred to as fine“flow ducts”), which are channels with a cross sectional dimension below 1 mm.

Microreactors can be used for reactions in liquid phase only (in this case they are also referred to as“micromixers”), in gas phase only, and in liquid/gas phase.

The microchannels are typically linked to one or more entrances and/or exits via manifold or header channels. The microchannels may be linked, e.g., in series or in parallel or in other configurations.

The microchannel cross section may be rectangular, square, trapezoidal, circular, semi-circular, ellipsoidal, triangular, U-shaped or the like. In addition, the microchannels can contain wall extensions or inserts that modify the cross-sectional shape, such as fins, grooves, etc. The shape and/or size of the microchannel cross section may vary over its length. For example, the height or width may taper from a relatively large dimension to a relatively small dimension, or vice versa, over a portion or all of the length of the microchannel itself.

Preferably, the microchannels have at least one cross-sectional dimension of from 1 pm to 1000 pm, preferably from 5 pm to 800 pm and more preferably from 10 pm to 500 pm. In a preferred embodiment, said at least one cross-sectional dimension is the largest cross-sectional dimension or the diameter of the microchannels.

Preferably, said microchannels have a length of from 1 cm to about 10 meters, more preferably from 5 cm to about 5 meters, and even more preferably about 10 cm to about 3 meters.

The selection of microchannel dimensions and overall length can be made by the skilled person depending on the residence time desired for the reactants into the microreactor, the contact time between the multiphase components, and other parameters.

Typically, a microreactor has an extremely high surface to volume ratio and hence exhibits enhanced heat and mass transfer rates when compared to conventional reactors. Preferably, the surface to volume ratio of the microreactor is from 4,000 to 40,000 m ² /m ³ .

Preferably, the microreactor besides inlet(s) and outlet(s) contains other microchannel process control aspects, such as valves, mixing means, separation means, flow re-redirection conduit lines, heat flux control means, such as heat exchange conduits, pump(s), chambers or microchannels, for the controlled removal or introduction of heat to or from the solution or fluid flowing through the microchannels. The microreactor may also contain process control elements, such as pressure, temperature and flow sensor elements.

The temperature of the microreactor can be controlled for example by using a heat transfer fluid. Depending on the reaction to be performed, the microreactor is preferably kept at a temperature of from -150°C to +300°C, more preferably of from - 100°C to 100°C.

Preferably, the process according to the present invention is carried out in a continuous mode, i.e. by continuously feeding the reactants into the microreactor.

The microreactor can be exercised in co-current or in counter-current. Preferably, the microreactor is exercised in co-current, i.e. the reactants were flowed from the top inlet to the bottom outlet.

Preferably, the process according to the present invention is carried out in gas phase, in liquid phase or in gas-liquid phase.

More preferably, said gas phase comprises at least one gas selected from nitrogen, helium, argon, C0 ₂ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ .

More preferably, said liquid phase comprises at least one solvent that is inert in the reaction conditions, such as (per)fluorinated solvent selected from the group consisting of:

- (per)(halo)fluoroethers, comprising one or more than one ethereal oxygens and (per)fluorocarbon groups possibly including halogen atom(s) other than fluorine; preferably perfluoroethers, and most preferably perfluoroalkyl ethers;

- (per)fluoropolyethers (otherwise referred to as PFPEs), i.e. compounds consisting of a sequence of a plurality of recurring units comprising (per)fluorinated alkylene groups connected through ethereal bonds;

- (per)fluorinated amines, in particular perfluorinated amines; and

- (per)(halo)fluorocarbons, possibly comprising one or more halogen different from fluorine, preferably perfluorocarbons; and - mixtures of the above.

Preferably, the reaction step is carried out by introducing a stream of an olefin of formula (la) or (lb) as above defined and a stream of hypofluorite of formula R _f OF diluted in an inert gas such as nitrogen.

The olefins of formula (la) or (lb) are preferably selected in the group consisting of tetrachloroethylene, trichloroethylene, 1 ,2-dichloroethylene, 1 ,1-dichloroethylene, 1 ,2-dichloro-1 ,2-difluoroethylene and 1 ,2-dichloro-1 -fluoroethylene.

Perfluoroalkyl hypofluorite of formula R _f OF are known from US. Pat. No.4, 827, 024. Trifluoromethyl hypofluorite is known in the art.

The fluorohalogenoethers obtained by the process according to the present invention may be converted into the corresponding fluorovinylethers by reactions known in the art, such as dehalogenation or dehydrohalogenation reactions as described for example in previous patents US7612242 and US7795477.

Preferably, for the reaction step of the process according to the invention the residence time ranges from 0.01 to 0.6 seconds, more preferably from 0,05 to 0,5 seconds.

Preferably, the reaction step of the process according to the invention is performed by keeping the microreactor at a temperature of from - 100°C to -20°C, more preferably from -95°C to -55°C.

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.

The invention is described in greater detail in the following experimental section by means of non-limiting examples.

EXPERIMENTAL SECTION

Example 1

A stream of 0,04 mol/h of trichloroethylene and 1 ,125 Nl/h of CF ₃ OF diluted with 1 ,8 Nl/h of nitrogen was fed in a continuous flow microreactor system having a volume of 0,0004 I that was kept at -50°C. The liquid output stream contained 8,5 g/h of fluorohalogenether CF ₃ 0- CHCICFCI ₂ .

The selectivity towards adduct was 96% while trichloroethylene conversion was

95%.

Example 2

A stream of 0,056 mol/h of CHCI=CHCI and 0,9 Nl/h of CF ₃ CF ₂ CF ₂ OF diluted with 3 Nl/h of nitrogen was fed in a continuous flow microreactor system having a volume of 0,0004 I that was kept at -90°C.

The liquid output stream contained 3,63 g/h of fluorohalogenether CF ₃ CF ₂ CF ₂ 0- CHCI-CHCIF.

The yield calculated on the fed Hypofluorite was 30%.

Example 3

A stream of 0,033 mol/h of trichloroethylene and 0,75 Nl/h of CF ₃ CF ₂ OF diluted with 10 Nl/h of Nitrogen was fed in a continuous flow microreactor system having a volume of 0,0004 I that was kept at -70°C.

The liquid output stream contained 5,73 g/h of fluorohalogenether CF ₃ CF ₂ 0- CHCICFCI ₂ .

The yield calculated on the fed Hypofluorite was 60%.

Example 4

A stream of 0,046 mol/h of CFCI=CFCI and 2 Nl/h of CF ₃ OF diluted with 3,2 Nl/h of Nitrogen was fed in a continuous flow reactor system having a volume of 0,0004 I kept at -70°C.

The liquid output stream contained 10,73 g/h of fluorohalogenether CF ₃ 0- CFCICFzCI.

The yield calculated on the fed olefin was 97%.

Example 5

A stream of 0,1 14 mol/h of CFCI=CFCI and 1 ,15 Nl/h of CF ₃ CF ₂ CF ₂ OF diluted with 4,25 Nl/h of Nitrogen was fed in a continuous flow reactor system having a volume of 0,0004 I that was kept at -90°C.

The liquid output stream contains 7,73 g/h of fluorohalogenether

CF ₃ CF ₂ CF ₂ OCFCICF ₂ CI. The yield calculated on the fed Hypofluorite was 45%.

Example 6

A stream of 0,038 mol/h of CFCI=CFCI diluted at 20%w in CF ₃ 0-CFCICF ₂ CI and

1 Nl/h of CF ₃ CF ₂ OF diluted with 3,7 Nl/h of Nitrogen is fed in a continuous flow reactor system having a volume of 0,0004 I that was kept at -90°C.

The liquid output stream contains 10,12 g/h of fluorohalogenether CF ₃ CF2OCFCICF2CI.

The yield calculated on the fed Hypofluorite was 80%.

Comparative example 1 C

The procedure described in example 1 of US7612242 was followed.

Comparative example 2C

The procedure described in example 6 of US7612242 was followed.

Comparative example 3C

The procedure described in example 7 of US7612242 was followed.

Comparative example 4C

The procedure described in example 4 of US7795477 was followed.

Comparative example 5C

The procedure described in example 7 of US7795477 was followed.

Comparative example 6C

The procedure described in example 8 of US7795477 was followed.

The operational conditions applied in the examples and comparative examples as well as productivity obtained are summarized in Table 1.

Table 1

(b) ratio of reaction volume and gas phase volumetric flow