Process for the purification of chlorotrifluoroethylene

Abstract

The present invention relates to a process for purifying chlorotrifluoroethylene from a mixture comprising chlorotrifluoroethylene (CTFE) and a hydrofluoroolefin;said method comprising a step (a') of bringing said mixture into contact with a membrane M 3 to form a stream F 1' comprising chlorotrifluoroethylene and a stream F2 ' comprising said fluoroolefin, characterized in that said hydrofluoroolefin is selected from the group consisting of 1,1-difluoroethylene, E / Z-1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Z-1,2-difluoropropene, E / Z-1,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.;

Description

Title of the invention: Process for the purification of chlorotrifluoroethylene Technical field

[0001] The present invention relates to a process for purifying fluoroolefins. In particular, the present invention relates to a process for purifying chlorotrifluoroethylene. Technological background of the invention

[0002] A Li-ion battery comprises at least one negative electrode or anode coupled with a copper current collector, one positive electrode or cathode coupled with an aluminum current collector, a separator, and an electrolyte. The electrolyte consists of a lithium salt mixed with a solvent which is a mixture of organic carbonates, chosen to optimize the transport and dissociation of ions. A high dielectric constant promotes the dissociation of ions, and therefore, the number of ions available in a given volume, while a low viscosity is favorable to ionic diffusion which plays a vital role, among other parameters, in the charging and discharging rates of the electrochemical system. Rechargeable or secondary batteries are more advantageous than primary (non-rechargeable) batteries because the associated chemical reactions which take place at the positive and negative electrodes of the battery are reversible.The electrodes of secondary cells can be regenerated multiple times by applying an electrical charge. Many advanced electrode systems have been developed to store electrical charge. At the same time, much effort has been devoted to developing electrolytes capable of improving the capabilities of electrochemical cells.

[0003] Polyvinylidene fluoride (PVDF) and its derivatives are of interest as the main constituent material of the separator or binder present at the electrodes. The copolymer P(VDF-co-HFP) (copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP)) has been studied as a gelled membrane because it has a lower crystallinity than PVDF. Therefore, the interest of these P(VDF-co-HFP) copolymers is that they allow greater swellings to be achieved and thus promote conductivity. Copolymers based on vinylidene fluoride and chlorotrifluoroethylene (CTFE) are also used for these same applications. Generally, during the preparation of polyvinylidene fluoride, the residual mixture comprising the unreacted monomers is destroyed.

[0004] There is therefore a need to improve the processes for preparing polymers such as poly(vinylidene fluoride). In particular, there is a need to provide processes with limited impact on the environment. Summary of the invention

[0005] The present invention aims to solve the technical problems mentioned above. The present invention provides an improved, more economical and more environmentally friendly PVDF production process. The present invention makes it possible, in particular, to recover unreacted starting materials in order to separate them and recycle all or part of them. Surprisingly, it has been observed that starting materials, such as vinylidene fluoride and chlorotrifluoroethylene, can be separated by membrane separation.

[0006] According to a first aspect, the present invention provides a process for purifying chlorotrifluoroethylene from a mixture comprising chlorotrifluoroethylene (CTFE) and a hydrofluoroolefin;said method comprising a step (a') of bringing said mixture into contact with a membrane M3 to form a stream F1' comprising chlorotrifluoroethylene and a stream F2' comprising said fluoroolefin, characterized in that said hydrofluoroolefin is selected from the group consisting of 1,1-difluoroethylene, E / Z1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Z-1,2-difluoropropene, E / Zl,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene. ;

[0007] According to a preferred embodiment, said membrane M3 is made of a polyolefin, polyimide, polyether or cellulose-based material.

[0008] According to a preferred embodiment, said membrane M3 is made of a material selected from the group consisting of polyethylene, polypropylene, polymethylpentene, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)], polyimide and cellulose acetate.

[0009] According to a preferred embodiment, said membrane M3 is made of polymethylpentene, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)], cellulose acetate or polyimide.

[0010] According to a preferred embodiment, when said membrane M3 is made of polyolefin, the latter has a selectivity greater than 20; said selectivity being calculated by the ratio between the permeability of chlorotrifluoroethylene and the permeability of said hydrofluoroolefin through said membrane M3; preferably at a differential pressure between the inlet and the outlet of the membrane of 100 to 500 kPa.

[0011] According to a preferred embodiment, when said membrane M3 is made of polyimide or cellulose, the latter has a selectivity greater than 5; said selectivity being calculated by the ratio between the permeability of said hydrofluoroolefin and the permeability of chlorotrifluoroethylene through said membrane M3; preferably at a differential pressure between the inlet and the outlet of the membrane of 100 to 500 kPa.

[0012] According to a second aspect, the present invention relates to a method for producing a fluoropolymer P2 comprising the steps of:

[0013] A') Preparation of a polymer P2 comprising monomeric units of chlorotrifluoroethylene and at least one hydrofluoroolefin;

[0014] B') Recovery of a stream F3' comprising chlorotrifluoroethylene and said hydrofluoroolefin not reacted during step A');

[0015] C') Implementation of the purification method according to the present invention from of said stream F3'; characterized in that said hydrofluoroolefin is selected from the group consisting of l-fluoroethylene, l, l-difluoroethylene, E / Zl,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Zl,2-difluoropropene, E / Zl,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.

[0016] According to a preferred embodiment, step A') comprises the steps of:

[0017] Al') Forming an aqueous emulsion comprising at least one initiator, at least one chain transfer agent, chlorotrifluoroethylene and said at least one hydrofluoroolefin;

[0018] A2') Initiate the polymerization of chlorotrifluoroethylene and said at least one hydrofluoroolefin to form said polymer P2.

[0019] According to a preferred embodiment, said process comprises a step D) of recycling to step A) the stream separated in step C) and comprising chlorotrifluoroethylene or the stream separated in step C) and comprising the hydrofluoroolefin or the recycling of both. Detailed Description of the Present Invention

[0020] Separation between vinylidene fluoride and hexafluoropropene

[0021] According to a first aspect, the present invention relates to a method for separating a mixture comprising vinylidene fluoride (VDF) and hexafluoropropene (HFP). Said method comprises a step (a) of contacting said mixture with a membrane M1 to form a stream F1 comprising vinylidene fluoride and a stream F2 comprising hexafluoropropene.

[0022] Preferably, said mixture comprises a molar content of vinylidene fluoride greater than 10%, preferably greater than 25%, in particular greater than 50% based on the total amount in moles of the mixture.

[0023] Preferably, said mixture comprises a molar content of hexafluoropropene greater than 1%, preferably greater than 5%, in particular greater than 10% based on the total amount in moles of the mixture.

[0024] Preferably, said mixture is in gaseous form.

[0025] The present process thus makes it possible to produce a flow Fl enriched in fluoride of vinylidene fluoride relative to the initial mixture before contacting with the membrane M1. Preferably, said stream F1 has a reduced molar content of hexafluoropropene relative to said mixture. According to a preferred embodiment, said stream F1 comprises at least 25% by weight of vinylidene fluoride, advantageously at least 35% by weight of vinylidene fluoride, preferably at least 45% by weight of vinylidene fluoride, more preferably at least 55% by weight of vinylidene fluoride, in particular at least 65% by weight of vinylidene fluoride, more particularly at least 75% by weight of vinylidene fluoride based on the total weight of said stream F1.

[0026] Preferably, said stream F1 comprises less than 20% by weight of hexafluoropropene based on the total weight of said stream F1. Advantageously, said stream F1 comprises less than 15% by weight of hexafluoropropene, preferably less than 10% by weight, in particular less than 5% by weight, more particularly less than 1% by weight of hexafluoropropene based on the total weight of said stream F1.

[0027] In the present process, the stream F2 is enriched in hexafluoropropene. According to a preferred embodiment, said stream F2 has an increased molar content of hexafluoropropene relative to said mixture. Preferably, said stream F2 comprises at least 25% by weight of hexafluoropropene, more preferably at least 50% by weight of hexafluoropropene, in particular at least 75% by weight of hexafluoropropene, more particularly at least 80% by weight of hexafluoropropene, preferably at least 95% by weight of hexafluoropropene based on the total weight of said stream F2.

[0028] In the present application, the term membrane refers to a membrane that is selectively permeable to one or more compounds such that it allows different compounds to migrate therethrough at different flow rates. The membrane restricts the movement of molecules passing through it so that some molecules move more slowly than others or are completely excluded (i.e., impermeable). For example, the membrane may be selectively permeable to vinylidene fluoride and impermeable (or weakly permeable) to hexafluoropropene.

[0029] The permeability of a membrane depends on its ability to limit or not the diffusion of these compounds through it. Membranes can selectively separate components over a wide range of solubility parameters and molecular sizes, from macromolecular materials to simple ionic or covalent compounds. The determining property for membrane performance is mainly selectivity. The membrane separation process is characterized by the fact that a feed stream is divided into two streams: retentate and permeate. The retentate is the part of the feed that does not pass (or only slightly) through the membrane, while the permeate is the part of the feed that passes through the membrane.

[0030] In the present application, the retentate may be one of the streams described depending on the membrane used and the compounds considered.

[0031] Unlike distillation processes, membrane separation does not require phase separation, which generally allows for significant energy savings compared to distillation processes. Capital costs can also be reduced because membrane separation processes generally have no moving parts, no complex control schemes, and little auxiliary equipment compared to other separation processes known in the art.

[0032] Membranes can be produced with extremely high selectivity for the components to be separated. In general, the selectivity values are well above the typical relative volatility values for distillation operations. Membrane separation processes may also be able to recover minor but valuable components from the main stream without substantial energy cost. Membrane separation processes are potentially better for the environment since the membrane approach requires the use of relatively simple and non-harmful materials.

[0033] According to a preferred embodiment, said membrane M1 is made of a material selected from the group consisting of polyolefin, polyether and polymethyl methacrylate.

[0034] In the present application, the term polyolefin refers in particular to polyethylene, polypropylene, polymethylpropene, polybutene, polypentene, polymethylpentene, polymethylbutene, polyhexene, polymethylpentene and polyethylbutene.

[0035] In the present application, the term polyether refers in particular to a polyarylether comprising the monomeric unit -[-O-Ar-]- or -[-Ar'-O-Ar2-]- in which Ar, Ar1 and Ar2 are independently of each other an aromatic ring comprising from 6 to 12 carbon atoms optionally substituted by one or more Cl-CIO alkyl functional groups; preferably Ar is a phenyl group optionally substituted by one, two, three or four Cl-C3 alkyl functional groups. In particular, the polyether is poly[oxy-(2,6-dimethyl-1,4-phenylene)] or poly(phenylene oxide).

[0036] Preferably, said membrane M1 is made of a material selected from the group consisting of polyethylene, polypropylene, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)] and polymethylpentene. In particular, said membrane M1 is made of polymethylpentene or poly[oxy-(2,6-dimethyl-1,4-phenylene)] or poly(phenylene oxide).

[0037] It can be considered that there is a separation between vinylidene fluoride and hexafluoropropene when the selectivity is greater than 5. The higher the selectivity, the more efficient the separation. The method is particularly efficient when the selectivity is greater than 10, preferably greater than 25, in particular greater than 35.

[0038] When the permeability of said membrane M1 with respect to vinylidene fluoride is greater than the permeability of said membrane M1 with respect to hexafluoropropene, the selectivity is calculated by the ratio between the permeability of vinylidene fluoride and the permeability of hexafluoropropene through said membrane M1, i.e. selectivity = [permeability of vinylidene fluoride] / [permeability of hexafluoropropene].

[0039] Preferably, said membrane M1 has a selectivity greater than or equal to 5, preferably greater than or equal to 6, more preferably greater than or equal to 7, in particular greater than or equal to 8, more particularly greater than or equal to 9; said selectivity being calculated by the ratio between the permeability of vinylidene fluoride and the permeability of hexafluoropropene through it. In particular, the selectivity of said membrane M1 may be greater than or equal to 10, or greater than or equal to 12, or greater than or equal to 14, or greater than or equal to 16, or greater than or equal to 18, or greater than or equal to 20, or greater than or equal to 22, or greater than or equal to 24, or greater than or equal to 26, or greater than or equal to 28, or greater than or equal to 30, or greater than or equal to 32, or greater than or equal to 34, or greater than or equal to 36, or greater than or equal to 38; said selectivity being calculated by the ratio between the permeability of vinylidene fluoride and the permeability of hexafluoropropene through said membrane Ml.

[0040] Step (a) can be carried out over a wide range of temperature and pressure.

[0041] Preferably, step (a) of bringing said mixture into contact with said membrane M1 is carried out at a pressure of 0.1 bara to 30 bara, advantageously of 0.2 bara to 25 bara, preferably of 0.3 bara to 20 bara, more preferably of 0.4 bara to 15 bara, in particular of 0.5 bara to 10 bara, more particularly of 0.5 bara to 5 bara. The pressure corresponds to the pressure applied to the inlet of the membrane.

[0042] Preferably, step (a) of bringing said mixture into contact with said membrane M1 is carried out at a temperature of 0°C to 150°C, advantageously of 0°C to 125°C, preferably of 5°C to 100°C, more preferably of 10 to 75°C, in particular of 10 to 50°C.

[0043] When implementing the method, a pressure difference is observed between the inlet of the membrane and the outlet of the membrane. The differential pressure expressed here corresponds to the pressure difference existing between the inlet and the outlet of said membrane. Preferably, the differential pressure is from 1 to 3000 kPa, preferably from 50 to 2000 kPa, in particular from 100 to 1000 kPa, more particularly from 100 to 500 kPa. The pressure at the outlet is preferably lower than the pressure at the inlet of the membrane.

[0044] Said mixture used in the present process and brought into contact with said membrane M1 may also contain chlorotrifluoroethylene (CTFE). When this mixture is subjected to step (a) of the present process, said stream F1 also comprises chlorotrifluoroethylene (CTFE). Said stream F1 may be subjected to a second membrane separation step. Said process comprises a step of bringing said stream F1 into contact with a membrane M2 to form a stream F3 comprising said chlorotrifluoroethylene and a stream F4 comprising said vinylidene fluoride.

[0045] More particularly, this step of separation between chlorotrifluoroethylene and vinylidene fluoride recovered in step a) can be carried out under the conditions described below according to the process of separation between CTFE and a hydrofluoroolefin. Generally, this step is carried out at a pressure of 0.1 bara to 30 bara, advantageously of 0.2 bara to 25 bara, preferably of 0.3 bara to 20 bara, more preferably of 0.4 bara to 15 bara, in particular of 0.5 bara to 10 bara, more particularly of 0.5 bara to 5 bara. The pressure corresponds to the pressure applied to the inlet of the membrane. Preferably, step b) is carried out at a temperature of 0°C to 150°C, advantageously 0°C to 125°C, preferably 5°C to 100°C, more preferably 10 to 75°C, in particular 10 to 50°C. When carrying out this step, a pressure difference is observed between the inlet of the membrane and the outlet of the membrane.The differential pressure expressed here corresponds to the pressure difference existing between the inlet and the outlet. of said membrane. Preferably, the differential pressure is from 1 to 3000 kPa, preferably from 50 to 2000 kPa, in particular from 100 to 1000 kPa, more particularly from 100 to 500 kPa. The outlet pressure is preferably lower than the pressure at the inlet of the membrane.

[0046] Preferably, said membrane M2 is made of polyolefin; preferably polyethylene, polypropylene or polymethylpentene; in particular polymethylpentene. In this embodiment, said membrane M2 may be more permeable to said chlorotrifluoroethylene than to vinylidene fluoride. Thus, said membrane M2 has a selectivity greater than or equal to 5, advantageously greater than or equal to 10, preferably greater than or equal to 15, more preferably greater than or equal to 20, in particular greater than or equal to 30, more particularly greater than or equal to 35; said selectivity being calculated by the ratio between the permeability of said chlorotrifluoroethylene and the permeability of vinylidene fluoride through said membrane M2.

[0047] Alternatively, said membrane M2 is made of polyimide or a cellulose-based material. In this embodiment, said membrane M2 may be more permeable to said vinylidene fluoride than to chlorotrifluoroethylene. Thus, said membrane M2 has a selectivity greater than or equal to 5, advantageously greater than or equal to 10, preferably greater than or equal to 20, more preferably greater than or equal to 30, in particular greater than or equal to 40, more particularly greater than or equal to 50; said selectivity being calculated by the ratio between the permeability of said vinylidene fluoride and the permeability of chlorotrifluoroethylene through said membrane M2. As explained below, the selectivity may vary depending on the differential pressure between the inlet and the outlet of the membrane M2. More particularly, the selectivity values are obtained for a differential pressure of from 100 to 500 kPa.

[0048] According to a preferred embodiment, said membrane M1 and said membrane M2 can be chosen from a film, a laminated structure, hollow fibers and coated fibers.

[0049] Separation between chlorotrifluoroethylene and a hydrofluoroolefin

[0050] According to another aspect, the present invention also provides a process for purifying chlorotrifluoroethylene from a mixture comprising chlorotrifluoroethylene (CTFE) and a hydrofluoroolefin. Said process comprises a step (a') of contacting said mixture with a membrane M 3 to form a stream F1' comprising chlorotrifluoroethylene and a stream F2' comprising said fluoroolefin.

[0051] Advantageously, said hydrofluoroolefin is selected from the group consisting of 1-fluoroethylene, 1,1-difluoroethylene, E / Zl,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Zl,2-difluoropropene, E / Zl,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.

[0052] Preferably, said hydrofluoroolefin is selected from the group consisting of 1-fluoroethylene, 1,1-difluoroethylene, E / Zl,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.

[0053] In particular, said hydrofluoroolefin is selected from the group consisting of 1,1-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Zl,3,3,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene.

[0054] Surprisingly, it has been demonstrated by the present application that it is possible to separate chlorotrifluoroethylene from a hydrofluoroolefin by membrane separation.

[0055] Preferably, said mixture comprises a molar content of chlorotrifluoroethylene greater than 1%, preferably greater than 5%, in particular greater than 10% based on the total amount in moles of the mixture.

[0056] Preferably, said mixture is in gaseous form.

[0057] The present method thus makes it possible to produce a flow Fl ' enriched in chlorotrifluoroethylene relative to the initial mixture before contacting with the membrane. Preferably, said stream Fl' has a reduced molar content of hydrofluoroolefin relative to said mixture. According to a preferred embodiment, said stream Fl' comprises at least 25% by weight of chlorotrifluoroethylene, advantageously at least 30% by weight of chlorotrifluoroethylene, preferably at least 35% by weight of chlorotrifluoroethylene, more preferably at least 40% by weight of chlorotrifluoroethylene, in particular at least 45% by weight of chlorotrifluoroethylene, more particularly at least 50% by weight of chlorotrifluoroethylene based on the total weight of said stream Fl'.

[0058] Preferably, said stream F1' comprises less than 20% by weight of hydrofluoroolefin based on the total weight of said stream F1'. Advantageously, said stream F1' comprises less than 15% by weight of hydrofluoroolefin, preferably less than 10% by weight, in particular less than 5% by weight, more particularly less than 1% by weight of hydrofluoroolefin based on the total weight of said stream Fl

[0059] In the present process, the stream F2' is enriched in hydrofluoroolefin. According to a preferred embodiment, said stream F2' has an increased molar content of hydrofluoroolefin relative to said mixture. Preferably, said stream F2' comprises at least 25% by weight of hydrofluoroolefin, more preferably at least 50% by weight of hydrofluoroolefin, in particular at least 75% by weight of hydrofluoroolefin, more particularly at least 80% by weight of hydrofluoroolefin, preferably at least 95% by weight of hydrofluoroolefin based on the total weight of said stream F2

[0060] According to a preferred embodiment, said membrane M 3 is made of a material selected from the group consisting of polyolefin, polyether, polyimide and a cellulose-based material. The term polyolefin and polyether is defined above in relation to the first aspect of the present invention. Preferably, the cellulose-based material is preferably cellulose acetate.

[0061] Thus, according to a particular embodiment, said membrane M 3 is made of a material selected from the group consisting of polyethylene, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)], polypropylene, polymethylpentene, polyimide and a cellulose-based material. In particular, said membrane M 3 is made of polymethylpentene, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)], cellulose acetate or polyimide.

[0062] Preferably, step (a') is carried out at a pressure of 0.1 bara to 30 bara, advantageously of 0.2 bara to 25 bara, preferably of 0.3 bara to 20 bara, more preferably of 0.4 bara to 15 bara, in particular of 0.5 bara to 10 bara, more particularly of 0.5 bara to 5 bara. The pressure corresponds to the pressure applied to the inlet of the membrane. When carrying out step (a'), a pressure difference is observed between the inlet of the membrane and the outlet of the membrane. The differential pressure expressed here corresponds to the pressure difference existing between the inlet and the outlet of said membrane. Preferably, the differential pressure is 1 to 3000 kPa, preferably 50 to 2000 kPa, in particular 100 to 1000 kPa, more particularly 100 to 500 kPa. The outlet pressure is preferably lower than the pressure at the inlet of the membrane.It has been observed that differential pressure can influence the value of the permeability of chlorotrifluoroethylene. Thus, for example, to obtain a selectivity greater than 5, when this is calculated by the ratio between the permeability of chlorotrifluoroethylene and the permeability of the hydrofluoroolefin, the differential pressure is about 2.5 bar. To obtain a selectivity greater than 10, when this is calculated by the ratio between the . permeability of chlorotrifluoroethylene and permeability of hydrofluoroolefin, the differential pressure is about 3.5 bar.

[0063] Preferably, step (a') is carried out at a temperature of 0°C to 150°C, advantageously of 0°C to 125°C, preferably of 5°C to 100°C, more preferably of 10 to 75°C, in particular of 10 to 50°C.

[0064] According to a first embodiment, said membrane M 3 is more permeable to hydrofluoroolefin than to chlorotrifluoroethylene. This embodiment, with the selectivities mentioned below, is preferably obtained when said membrane M3 is made of a material consisting of polyimide or cellulose-based, in particular polyimide or cellulose acetate. Preferably, said membrane M 3 has a selectivity greater than or equal to 5, advantageously greater than or equal to 10, preferably greater than or equal to 20, more preferably greater than or equal to 30, in particular greater than or equal to 50, when this is calculated by the ratio between the permeability of the hydrofluoroolefin and the permeability of chlorotrifluoroethylene through said membrane M 3, preferably at a differential pressure between the inlet and the outlet of the membrane of between 100 and 500 kPa.

[0065] According to a second embodiment, said membrane M 3 is more permeable to chlorotrifluoroethylene than to hydrofluoroolefin. This embodiment, with the selectivities mentioned below, is preferably obtained when said membrane M3 is made of polyolefin or polyether, in particular polyethylene, polypropylene, polymethylpentene, poly(phenylene oxide) or poly[oxy-(2,6-dimethyl-1,4-phenylene)], preferably polymethylpentene, poly(phenylene oxide) or poly[oxy-(2,6-dimethyl-1,4-phenylene)].Preferably, said membrane M 3 has a selectivity greater than or equal to 5, advantageously greater than or equal to 10, preferably greater than or equal to 15, more preferably greater than or equal to 20, in particular greater than or equal to 30, when this is calculated by the ratio between the permeability of chlorotrifluoroethylene and the permeability of hydrofluoroolefin through said membrane M 3, preferably at a differential pressure between the inlet and the outlet of the membrane of 100 to 500 kPa.

[0066] According to a preferred embodiment, said membrane M 3 can be chosen from a film, a laminated structure, hollow fibers and coated fibers. Process for producing a fluoropolymer

[0067] According to another aspect of the present invention, a method for producing a fluoropolymer. According to a first embodiment, the present invention provides a method for producing a fluoropolymer PI comprising monomeric units of vinylidene fluoride and at least one monomer copolymerizable therewith. Preferably, said fluoropolymer PI comprises monomeric units of vinylidene fluoride and at least one copolymerizable monomer selected from hexafluoropropene, chlorotrifluoroethylene or a mixture of the two.

[0068] Thus, the present method for producing a fluoropolymer PI comprises the steps of: A. Preparation of a PI polymer comprising monomeric units of vinylidene fluoride and at least one monomer copolymerizable therewith selected from hexafluoropropene, chlorotrifluoroethylene or a mixture of the two; B. Recovery of a stream F5 comprising vinylidene fluoride and said at least one copolymerizable monomer not having reacted during step A); C. Implementation of the process for separation between vinylidene fluoride and hexafluoropropene according to the present invention or of the process for purification of chlorotrifluoroethylene according to the present invention.

[0069] According to a preferred embodiment, said method for producing a fluoropolymer PI comprises the steps of: A. Preparation of a PI polymer comprising monomeric units of vinylidene fluoride, hexafluoropropene and optionally chlorotrifluoroethylene; B. Recovery of a stream F5 comprising vinylidene fluoride, hexafluoropropene and optionally chlorotrifluoroethylene not having reacted during step A); C. Implementation of the separation process between vinylidene fluoride and hexafluoropropene according to the present invention.

[0070] According to a particular embodiment, said method for producing a fluorinated polymer PI comprises the steps of: A. Preparation of a PI polymer comprising monomeric units of vinylidene fluoride and hexafluoropropene; B. Recovery of a stream F5 comprising vinylidene fluoride and hexafluoropropene not having reacted during step A); C. Implementation of the separation process between vinylidene fluoride and hexafluoropropene according to the present invention.

[0071] Step A) of production of the fluorinated polymer PI can be carried out by different methods known from the prior art, for example by emulsion or by suspension.

[0072] Preferably, step A) comprises the steps of:

[0073] Al) Formation of an aqueous emulsion comprising at least one initiator, at least one chain transfer agent, a surfactant, vinylidene fluoride and said at least one monomer copolymerizable therewith selected from hexafluoropropene, chlorotrifluoroethylene or a mixture of both;

[0074] A2) Initiating the polymerization of vinylidene fluoride and said at least one monomer copolymerizable therewith to form said PI polymer.

[0075] Advantageously, step A2) is carried out at a temperature of 35 to 130°C, preferably of 70 to 125°C.

[0076] Advantageously, step A2) is carried out at a pressure of 280 to 20000 kPa, preferably of 2750 to 6900 kPa.

[0077] Preferably, the initiator is a persulfate salt such as sodium, potassium or ammonium persulfate or an organic peroxide such as, for example, di-tert-butyl peroxide, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, tert-amyl peroxypivalate, tert-butyl peroxypivalate, succinic acid peroxide, 2,2'-azobis(2-methyl-propionamidine)dihydrochloride. The initiator may be present in a content of between 0.002 and 5% by weight based on the total weight of monomer. Document WO 2019 / 199753 describes in detail the conditions for implementing steps A1) and A2) described above. Examples of surfactant and chain transfer agent are also described in WO 2019 / 199753. Preferably, the surfactant is non-fluorinated such as, for example, poly(acrylic acid), polyethylene glycol or polypropylene glycol.

[0078] Alternatively, step A) may be carried out by a step of polymerization of vinylidene fluoride and said at least one monomer copolymerizable therewith selected from hexafluoropropene, chlorotrifluoroethylene or a mixture of the two, in aqueous medium and in the presence of a radical initiator at a pressure greater than 45 bars, preferably greater than 50 bars, in particular greater than 100 bars. In this embodiment, step A) is carried out at a temperature of at least 35°C, preferably at least 40°C, in particular at least 45°C.

[0079] Preferably, said process for producing the fluoropolymer PI also comprises a step D) of recycling the stream separated in step C) and comprising vinylidene fluoride or the stream separated in step C) and comprising hexafluoropropene, chlorotrifluoroethylene or a mixture of both; or recycling both.

[0080] More specifically, said process for producing the fluoropolymer PI also comprises a step D) of recycling to step A) the stream separated in step C) and comprising vinylidene fluoride or the stream separated in step C) and comprising hexafluoropropene and optionally chlorotrifluoroethylene; or recycling both.

[0081] According to a second embodiment, the present invention provides a method for producing a fluoropolymer P2 comprising the steps of:

[0082] A') Preparation of a polymer P2 comprising monomeric units of chlorotrifluoroethylene and at least one hydrofluoroolefin;

[0083] B') Recovery of a stream F3' comprising chlorotrifluoroethylene and said unreacted hydrofluoroolefin;

[0084] C') Implementation of the purification method according to the present invention from of said stream F3'; characterized in that said hydrofluoroolefin is selected from the group consisting of 1,1-difluoroethylene, E / Zl,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Zl,2-difluoropropene, E / Zl,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.

[0085] Preferably, said hydrofluoroolefin is selected from the group consisting of 1-fluoroethylene, 1,1-difluoroethylene, E / Zl,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.

[0086] In particular, said hydrofluoroolefin is selected from the group consisting of 1,1-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Zl,3,3,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene.

[0087] Step A') of production of the fluorinated polymer P 2 can be carried out by different methods known from the prior art, for example by emulsion or by suspension.

[0088] Preferably, step A') comprises the steps of:

[0089] Al') Forming an aqueous emulsion comprising at least one initiator, at least one chain transfer agent, chlorotrifluoroethylene and said at least one hydrofluoroolefin;

[0090] A2') Initiate the polymerization of chlorotrifluoroethylene and said at least one hydrofluoroolefin to form said polymer P2.

[0091] The conditions for implementing steps A'), Al') and A2') are described above in relation to steps A), Al) and A2). Examples

[0092] The permeability of a gaseous compound through a polymer is measured using an Evonik MET Crossflow Filtration Cell (with an inner diameter of 52 mm and active surface area of 14 cm2) for polymers in film form or a commercial module for polymers in fiber form. The polyimide film is a Dupont Kapton HN film, the polymethylpentene film has the reference MX004, the silicone has the reference USP class VI. The films are supplied by Goodfellow.

[0093] In the examples below, the membranes tested are in the form of a film with an active surface area of 14 cm2 and whose thickness is shown in Table 1 below.

[0094] [Tables 1] Material Thickness Polyimide 25 pm PMMA 50 pm Cellulose acetate 35 pm PMP 50 pm Polypropylene 25 pm PPO 50 pm

[0095] PMP = polymethylpentene; PMMA: polymethyl methacrylate; PPO = poly(phenylene oxide)

[0096] The permeability is calculated according to the following formula: P = QxexS* x AP 1

[0097] With P: Permeability in cm 2 .s 1 .Pa 7

[0098] Q: permeate flow rate in cm 3 / s

[0099] e: thickness of the membrane in cm

[0100] S: membrane surface in cm2

[0101] AP: Pressure difference across the membrane in Pa (i.e. pressure differential mentioned in this application)

[0102] Permeability is generally expressed in Barrer (10 lo.cm3(STP).cm.cm2.s '.cm Hg ') according to the conversion: PBarr = P x 1010 / (7.500615 x 10-4)

[0103] Thus, it is possible to calculate the permeability of a compound through a material from the material data (surface area, thickness), the pressure difference across the membrane and the measurement of the permeate flow rate through the membrane. The permeability is thus measured by maintaining a compound under pressure upstream of the membrane in the absence of an outlet on the retentate side, and to measure the flow rate of this same compound at atmospheric pressure on the permeate side. The tests are carried out at a temperature of 25°C except for silicone, the tests of which were carried out at 35°C. The tests are repeated several times, possibly at different pressures, to obtain a more precise permeability value. Unless otherwise stated, permeability remains constant regardless of DeltaP (i.e. the pressure difference across the membrane).

[0104] Example 1: Separation of vinylidene fluoride / hexafluoropropene

[0105] The experimental protocol detailed above was implemented independently for each compound of the mixture considered: vinylidene fluoride (VF2) and hexafluoropropene (HFP). The membrane used is made of polypropylene, low density polyethylene, polymethylpentene, polymethyl methacrylate. The results are shown in Table 2 below. The permeability value is expressed in Barrer. The selectivity mentioned in the table corresponds to the ratio between the permeability measured for the two species considered.

[0106] [Tables2] Permeability (Barr) Selectivity VF2 HFP VF2 / HFP PP 2 0.4 5 PMP 9.2 0.2 37 PMMA 0.8 0.1 5 PE LD 6.3 1.0 7 PPO 5300 193 27

[0107] PP = polypropylene; PMP = polymethylpentene; PMMA = polymethyl methacrylate; PE LD = low density polyethylene; PPO = poly(phenylene oxide)

[0108] As shown in the above data, polyolefin or PMMA membranes are more permeable to vinylidene fluoride than to hexafluoropropene. Polyolefin (polypropylene, polyethylene or polymethylpentene) or PMMA membranes therefore make it possible to effectively separate vinylidene fluoride and hexafluoropropene.

[0109] Example 2: Chlorotrifluoroethylene / hydrofluoroolefin separation

[0110] The experimental protocol detailed above was implemented independently for each compound of the mixture considered: chlorotrifluoroethylene (CTFE), vinylidene fluoride (VF2), 2,3,3,3-tetrafluoropropene (HFO-1234yf) and hexafluoropropene (HFP). The membrane used is made of polymethylpentene, cellulose acetate or polyimide. The results are shown in Table 3 below. The permeability value is expressed in Barrer. The selectivity mentioned in the table corresponds to the ratio between the permeability measured for the two species considered. [YES] [Tables3] Permeability (Barr) Selectivity VF2 HFP 123 4yf CTFE CTFE / V F2 CTFE / HFP CTFE / 1234 yf PMP 9.2 0.2 2.6 380 41 1900 146 PPO - 193 na 4591 - 24 na VF2 / CT FE HFP / CTFE 1234yf / CT FE Cel. 0.6 0.1 na 0.01 60 10 na PI 0.7 0.2 na 0.01 70 20 na

[0112] PMP = polymethylpentene; PI = Polyimide; Cel. = cellulose acetate; na = not applicable; The permeability of CTFE is an average of two measurements: 387 bar and 373 bar obtained respectively with a pressure difference between the inlet and outlet of the membrane of 4.8 bar and 4.7 bar.

[0113] The above results show that polyolefin or polyether membranes are permeable to chlorotrifluoroethylene rather than to hydrofluoroolefins. The above results also show that polyimide and cellulose acetate membranes are more permeable to hydrofluoroolefins than to chlorotrifluoroethylene. Thus, polyolefin, polyimide or cellulose-based membranes can separate CTFE from hydrofluoroolefins.

Claims

Claims

1. A process for purifying chlorotrifluoroethylene from a mixture comprising chlorotrifluoroethylene (CTFE) and a hydrofluoroolefin;said method comprising a step (a') of bringing said mixture into contact with a membrane M 3 to form a stream F 1' comprising chlorotrifluoroethylene and a stream F2 ' comprising said fluoroolefin, characterized in that said hydrofluoroolefin is selected from the group consisting of 1,1-difluoroethylene, E / Zl,2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Zl,2-difluoropropene, E / Zl,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Zl,l,l,4,4,4-hexafluorobut-2-;

2. C11C. Method according to the preceding claim characterized in that said membrane M 3 is made of a polyolefin, polyether, polyimide or cellulose-based material.

3. A method according to any one of the preceding claims characterized in that said membrane M 3 is made of a material selected from the group consisting of polyethylene, polypropylene, polymethylpentene, polyimide, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)] and cellulose acetate.

4. Method according to any one of the preceding claims, characterized in that said membrane M 3 is made of polymethylpentene, poly(phenylene oxide), poly[oxy-(2,6-dimethyl-1,4-phenylene)], cellulose acetate or polyimide.

5. Method according to any one of the preceding claims 1 to 3 characterized in that, when said membrane M 3 is made of polyolefin, the latter has a selectivity greater than 20; said selectivity being calculated by the ratio between the permeability of chlorotrifluoroethylene and the permeability of said hydrofluoroolefin through said membrane M 3; preferably at a differential pressure between the inlet and the outlet of the membrane of 100 to 500 kPa.

6. Method according to any one of the preceding claims 1 to 3 characterized in that, when said membrane M 3 is made of polyimide or cellulose-based, the latter has a selectivity greater than 5; said selectivity being calculated by the ratio between the permeability of said hydrofluoroolefin and the permeability of chlorotrifluoroethylene through said membrane M 3; preferably at a differential pressure between the inlet and the outlet of the membrane of 100 to 500 kPa.

7. Process for producing a fluoropolymer P2 comprising the steps of: A') Preparation of a polymer P2 comprising monomeric units of chlorotrifluoroethylene and at least one hydrofluoroolefin; B') Recovery of a stream F3' comprising chlorotrifluoroethylene and said hydrofluoroolefin not having reacted during step A'); C') Implementation of the purification process according to any one of claims 1 to 6 from said stream F3';characterized in that said hydrofluoroolefin is selected from the group consisting of l-fluoroethylene, l, l-difluoroethylene, E / Zl, 2-difluoroethylene, tetrafluoroethylene, hexafluoropropene, 2,3,3,3-tetrafluoropropene, E / Z-1,3,3,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene, E / Z-1,2,3,3-tetrafluoropropene, 1,1,2,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,1,2-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3,3-pentafluoropropene, 1,1,2,3,3-pentafluoropropene, 1,1-difluoropropene, E / Zl,2-difluoropropene, E / Zl,3-difluoropropene, 2,3-difluoropropene, 3,3-difluoropropene, 1-fluoropropene, 2-fluoropropene, 3-fluoropropene, E / Z-1,1,1,4,4,4-hexafluorobut-2-ene.;

8. Process for producing a fluoropolymer P2 according to the preceding claim, characterized in that step A') comprises the steps of: A1') Forming an aqueous emulsion comprising at least one initiator, at least one chain transfer agent, chlorotrifluoroethylene and said at least one hydrofluoroolefin; A2') Initiating the polymerization of chlorotrifluoroethylene and said at least one hydrofluoroolefin to form said polymer P2.

9. Production process according to claim 7 or 8 characterized in that said process comprises a step D) of recycling to step A) the stream separated in step C) and comprising chlorotrifluoroethylene or the stream separated in step C) and comprising hydrofluoroolefin or the recycling of both.