Process for producing trifluoroethylene

Abstract

The present invention relates to a process for producing trifluoroethylene in a reactor provided with a fixed catalytic bed comprising a catalyst, the process comprising a step a) of reacting a composition (A) comprising chlorotrifluoroethylene with hydrogen in the presence of a catalyst and in the gaseous phase in order to produce a stream (B) comprising trifluoroethylene, characterised in that the composition (A) also comprises 1,2-dichlorohexafluorocyclobutane. The present invention also relates to a chlorotrifluoroethylene composition.

Description

[0001] Description

[0002] Title: Process for the production of trifluoroethylene

[0003] Technical field of the invention

[0004] The present invention relates to a process for producing hydrofluoroolefins. In particular, the present invention relates to a process for producing trifluoroethylene (HFO-1123 or VF3) by hydrogenolysis of chlorotrifluoroethylene. The present invention also relates to a composition comprising chlorotrifluoroethylene.

[0005] Technological background of the invention

[0006] Fluorinated olefins, such as VF3, are known and used as monomers or comonomers for the manufacture of fluorocarbon polymers with remarkable characteristics, in particular excellent chemical resistance and good thermal resistance. Trifluoroethylene is a gas under normal pressure and temperature conditions. The main risks associated with the use of this product concern its flammability, its propensity for self-polymerization when not stabilized, its explosiveness due to its chemical instability and its supposed sensitivity to peroxidation, by analogy with other halogenated olefins. Trifluoroethylene has the particularity of being extremely flammable, with a lower explosive limit (LEL) of approximately 10% and an upper explosive limit (UEL) of approximately 30%.The major danger, however, is associated with the propensity of VF3 to decompose violently and explosively under certain pressure conditions in the presence of an energy source, even in the absence of oxygen.

[0007] Given the above major risks, the synthesis and storage of VF3 pose particular challenges and require strict safety regulations throughout these processes. A known route for the preparation of trifluoroethylene uses chlorotrifluoroethylene (CTFE) and hydrogen as starting materials in the presence of a catalyst and in the gas phase.

[0008] WO 2013 / 128102 discloses a process for producing trifluoroethylene by hydrogenolysis of CTFE in the gas phase and in the presence of a catalyst based on a group VIII metal at atmospheric pressure and at low temperatures.

[0009] EP 2 993 213 discloses a process for producing trifluoroethylene. This can be obtained by hydrogenolysis of chlorotrifluoroethylene or by thermal decomposition of chlorodifluoromethane and chlorofluoromethane. The production process involves the implementation of a distillation step at a pressure of 10 barg and by which the trifluoroethylene is recovered by lateral withdrawal. The implementation of high-pressure distillation requires the establishment of specific operating conditions given the explosive nature of trifluoroethylene above 3 barg.

[0010] There is therefore a need to provide a simpler and safer process for producing trifluoroethylene while maintaining high yields and selectivities.

[0011] Summary of the invention

[0012] According to a first aspect, the present invention provides a process for producing trifluoroethylene in a reactor provided with a fixed catalytic bed comprising a catalyst, said process comprising a step a) of reacting a composition A comprising chlorotrifluoroethylene with hydrogen in the presence of a catalyst and in the gas phase to produce a stream B comprising trifluoroethylene, characterized in that said composition A also comprises 1,2-dichlorohexafluorocyclobutane in the form of two stereoisomers D1 and D2 ; the mass ratio D2 / D1 being greater than 1, said mass ratio D2 / D1 corresponding to the ratio between the mass content of the stereoisomer D2 in said composition A and the mass content of the stereoisomer DI in said composition A.

[0013] Surprisingly, it was observed that trifluoroethylene productivity was increased in the presence of 1,2-dichlorohexafluorocyclobutane in the form of two stereoisomers in the mass ratio as provided according to the present invention. The presence of this compound in moderate quantity in addition to chlorotrifluoroethylene makes it possible to improve the trifluoroethylene production process. The present invention demonstrates that it is not necessary to have high purity chlorotrifluoroethylene to achieve significant productivities. This makes it possible to simplify the production process and limit its overall cost.

[0014] According to a preferred embodiment, the total mass content of said stereoisomers D1 and D2 is less than 25% based on the total weight of said composition A, preferably less than 20% based on the total weight of said composition A, in particular less than 15% based on the total weight of said composition A.

[0015] According to a preferred embodiment, said composition A comprises at least 75% by weight of chlorotrifluoroethylene based on the total weight of said composition A, preferably at least 80% by weight of chlorotrifluoroethylene based on the total weight of said composition A, in particular at least 85% by weight of chlorotrifluoroethylene based on the total weight of said composition A.

[0016] According to a preferred embodiment, said composition A also comprises at least one of the additional compounds C2 selected from the group consisting of 1, 1,1,2-tetrafluoroethane, 1,1-difluoroethane, 2-chloro-1,1-difluoroethylene, E / Zl-chloro-1,2-difluoroethylene, 2-chloro-1,1,1-trifluoroethane, l-chloro-1,2,2-trifluoroethane, l-chloro-1,1,2-trifluoroethane.

[0017] According to a preferred embodiment, the mass content of said at least one of the additional compounds C2 is less than 0.5% based on the total weight of said composition A.

[0018] According to a preferred embodiment, the catalyst comprises palladium supported on alpha alumina.

[0019] According to a preferred embodiment, the chlorotrifluoroethylene and the hydrogen are in anhydrous form.

[0020] According to a preferred embodiment, said method comprises a step i') of activation of the catalyst, carried out prior to step a), by bringing the latter into contact with a gaseous flow comprising a reducing agent, an inert gas or a mixture thereof.

[0021] According to a preferred embodiment, during said step i'): the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 higher than T1 with a temperature gradient of less than 0.5°C / min; or the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 higher than T1 in stages.

[0022] According to a second aspect, the present invention provides a composition comprising at least 75% by weight of chlorotrifluoroethylene and less than 25% by weight of 1,2-dichlorohexafluorocyclobutane in the form of two stereoisomers D1 and D2

[0023] J | ; the mass ratio D2 / D1 being greater than 1, said mass ratio D2 / D1 corresponding to the ratio between the mass content of the stereoisomer D2 in said composition and the mass content of the stereoisomer DI in said composition based on the total weight of said composition.

[0024] Detailed description of the invention

[0025] The present invention relates to a process for producing trifluoroethylene comprising a step of hydrogenolysis reaction of chlorotrifluoroethylene (CTFE) with hydrogen in the gas phase and preferably in the presence of a catalyst.

[0026] According to a preferred embodiment, the method according to the invention described in the present application is implemented continuously.

[0027] According to a preferred embodiment, in the method described in the present application, the hydrogen is in anhydrous form.

[0028] According to a preferred embodiment, in the process described in the present application, the chlorotrifluoroethylene is in anhydrous form.

[0029] Carrying out the processes according to the invention in the presence of hydrogen and / or anhydrous chlorotrifluoroethylene makes it possible to effectively increase the lifetime of the catalyst and thus the overall productivity of the process. The term anhydrous refers to a mass content of water of less than 1000 ppm, advantageously 500 ppm, preferably less than 200 ppm, in particular less than 100 ppm based on the total weight of the compound in question.

[0030] Catalyst

[0031] Preferably, the catalyst is based on a metal from columns 8 to 10 of the periodic table of elements. In particular, the catalyst is based on a metal selected from the group consisting of Pd, Pt, Rh, and Ru; preferably palladium.

[0032] Preferably, the catalyst is supported. The support is preferably selected from the group consisting of activated carbon, an aluminum-based support, calcium carbonate, and graphite. Preferably, the support is aluminum-based. In particular, the support is alumina. The alumina may be alpha alumina. Preferably, the alumina comprises at least 90% alpha alumina. It has been observed that the conversion of the hydrogenolysis reaction is improved when the alumina is an alpha alumina. Thus, the catalyst is more particularly palladium supported on alumina, advantageously palladium supported on an alumina comprising at least 90% alpha alumina, preferably palladium supported on an alpha alumina.

[0033] Preferably, the palladium represents from 0.01% to 5% by weight based on the total weight of the catalyst, preferably from 0.1% to 2% by weight based on the total weight of the catalyst.

[0034] In particular, said catalyst comprises from 0.01% to 5% by weight of palladium supported on alumina, preferably the alumina comprises at least 90% alpha alumina, more preferably the alumina is an alpha alumina.

[0035] Activation of the

[0036] Said catalyst is preferably activated before its use in step a). Preferably, the activation of the catalyst is carried out at high temperature and in the presence of a reducing agent, an inert gas or a mixture thereof.

[0037] According to a particular embodiment, the reducing agent is chosen from the group consisting of hydrogen, carbon monoxide, nitrogen monoxide, formaldehyde, C1-C8 alkanes and C1-C10 hydrohalocarbons, or a mixture thereof; preferably hydrogen or a C1-C10 hydrohalocarbon, or a mixture thereof; in particular hydrogen, chlorotrifluoroethylene, trifluoroethylene, chlorotrifluoroethane, trifluoroethane or difluoroethane or a mixture thereof.

[0038] The inert gas can be nitrogen or argon; preferably nitrogen.

[0039] Preferably, the activation of the catalyst is carried out at a temperature between 100°C and 400°C, in particular at a temperature between 150°C and 350°C. In particular, the activation of the catalyst is carried out at a temperature between 100°C and 400°C, in particular at a temperature between 150°C and 350°C, in the presence of hydrogen as reducing agent.

[0040] Preferably, during step i'), the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2. In particular, during said step i'), the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 higher than T1 with a temperature gradient of less than 0.5°C / min. The temperature gradient used makes it possible to avoid early degradation of the catalyst and thus to allow a better yield or better productivity of the hydrogenolysis reaction. In particular, the temperature is increased with a temperature gradient of less than 0.45°C / min or less than 0.40°C / min, or less than 0.35°C / min, or less than 0.30°C / min, or less than 0.25°C / min, or less than 0.20°C / min, or less than 0.15°C / min, or less than 0.10°C / min, or less than 0.05°C / min. The temperature Tl represents the initial temperature of the activation step. This temperature Tl may be room temperature.Alternatively, the temperature T1 may be between 0°C and 150°C, advantageously between 0°C and 120°C, preferably between 0°C and 100°C, more preferably between 10°C and 100°C, in particular between 20°C and 100°C, more particularly between 20°C and 75°C, preferably between 20°C and 50°C. The temperature T2 represents the temperature to be reached during the activation phase. The temperature T2 is advantageously between 150°C and 400°C, preferably between 155°C and 375°C, more preferably between 160°C and 350°C, in particular between 165°C and 325°C, more particularly between 170°C and 320°C, preferably between 175°C and 310°C, more preferably between 180°C and 300°C. According to a preferred embodiment, the temperature T2 is advantageously between 185°C and 290°C, preferably between 190°C and 280°C, more preferably between 195°C and 270°C, in particular between 200°C and 260°C.The temperature T2 can be maintained from 5 min to 200 h, preferably from 10 min to 100 h, in particular from 15 min to 75 h, more particularly from 30 min to 50 h, preferably from 1 h to 25 h. The temperature T2 can be maintained from 5 min to 24 h, preferably from 10 min to 20 h, in particular from 15 min to 15 h, more particularly from 30 min to 10 h, preferably from 1 h to 10 h.

[0041] Preferably, the gas stream used during step i') does not comprise oxygen. Preferably, step i') can be carried out with an amount of reducing agent greater than 0.01 mol per gram of catalyst, preferably greater than 0.05 per gram of catalyst. In particular, step i') can be carried out with an amount of reducing agent of between 0.01 and 10 mol per gram of catalyst, preferably between 0.05 and 5 mol per gram of catalyst.

[0042] According to another embodiment, during step i'), the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 in stages. Activating the catalyst in stages makes it possible to make the catalyst more efficient. The use of stages makes it possible to avoid degradation of the catalyst. It has also been observed that the properties of the catalyst are further improved if the temperature rise between the stages is gradual and relatively slow compared to the usual conditions for activating a catalyst. Thus, preferably, in step i'), between two stages, the temperature is increased with a temperature gradient of less than 0.5°C / min. The temperature gradient implemented between two stages makes it possible to avoid early degradation of the catalyst and thus to allow a better yield or better productivity of the hydrogenolysis reaction.In particular, the temperature is increased with a temperature gradient less than 0.45°C / min or less than 0.40°C / min, or less than 0.35°C / min, or less than 0.30°C / min, or less than 0.25°C / min, or less than 0.20°C / min, or less than 0.15°C / min, or less than 0.10°C / min, or less than 0.05°C / min. The temperature Tl represents the initial temperature of the activation step. This temperature Tl may be room temperature. Alternatively, the temperature T1 may be between 0°C and 150°C, advantageously between 0°C and 120°C, preferably between 0°C and 100°C, more preferably between 10°C and 100°C, in particular between 20°C and 100°C, more particularly between 20°C and 75°C, preferably between 20°C and 50°C. The temperature T2 represents the temperature to be reached during the activation phase.The temperature T2 is advantageously between 150°C and 400°C, preferably between 155°C and 375°C, more preferably between 160°C and 350°C, in particular between 165°C and 325°C, more particularly between 170°C and 320°C, preferably between 175°C and 310°C, more preferably between 180°C and 300°C. According to a preferred embodiment, the temperature T2 is advantageously between 185°C and 290°C, preferably between 190°C and 280°C, more preferably between 195°C and 270°C, in particular between 200°C and 260°C. The temperature T2 can be maintained from 5 min to 200 h, preferably from 10 min to 100 h, in particular from 15 min to 75 h, more particularly from 30 min to 50 h, preferably from 1 h to 25 h. The temperature T2 can be maintained from 5 min to 24 h, preferably from 10 min to 20 h, in particular from 15 min to 15 h, more particularly from 30 min to 10 h, preferably from 1 h to 10 h.Step i') of activating the catalyst contains at least one stage between the temperature T1 and the temperature T2. Step i') of activating the catalyst may comprise several stages between the temperature T1 and the temperature T2. Preferably, step i') comprises at least one stage at a temperature T1a of between 90 and 120°C. The presence of a stage between 90°C and 120°C is preferred to increase the lifetime of the catalyst. Step i') may also comprise one or more stages between the temperature T1 and T1a and / or between the temperature T1a and T2. Preferably, each stage between the temperature T1 and the temperature T2 may last between 5 min and 200 h, preferably between 10 min and 100 h, in particular between 15 min and 75 h, more particularly between 30 min and 50 h.In particular, each stage between the temperature T1 and the temperature T2 can last between 5 min and 24 h, preferably between 10 min and 20 h, in particular between 15 min and 15 h, more particularly between 30 min and 10 h. In particular, the stage at the temperature T1a can last between 5 min and 200 h, preferably between 10 min and 100 h, in particular between 15 min and 75 h, more particularly between 30 min and 50 h. Preferably, the stage at the temperature T1a can last between 5 min and 24 h, preferably between 10 min and 20 h, in particular between 15 min and 15 h, more particularly between 30 min and 10 h.

[0043] The gas stream used during step i') may be different over time. For example, the gas stream may comprise an inert gas between two stages and for example comprise a reducing agent between two other stages. In particular, the gas stream comprises an inert gas when step i') is carried out between temperature T1 and T1a and the gas stream comprises a reducing agent, preferably hydrogen or C1-C10 hydrohalocarbons as defined above, when step i') is carried out between temperature T1a and T2. Thus, the gas stream used during step i') is modified during the stage carried out at temperature T1a. Alternatively, the gas stream may comprise a reducing agent such as hydrogen or C1-C10 hydrohalocarbons as defined above throughout step i'), optionally mixed with an inert gas such as nitrogen.It has been observed that the use of a reducing agent such as hydrogen or C 1 -C 10 hydrohalocarbons as defined above, optionally in admixture with an inert gas such as nitrogen, during the temperature rise between the temperature T1a of said stage and the temperature T2 represents an additional advantage in terms of productivity. As mentioned above, the temperature T2 is maintained for a certain period. During this stage at the temperature T2, the gas flow can be modified. Thus, the gas flow during the stage at the temperature T2 may comprise hydrogen or a C 1 -C 10 hydrohalocarbon as defined above; in particular the gas flow during the stage at the temperature T2 may comprise hydrogen, chlorotrifluoroethylene, trifluoroethane, trifluoroethylene, chlorotrifluoroethane or difluoroethane.Preferably, step i') can be carried out with an amount of reducing agent greater than 0.01 per gram of catalyst, preferably greater than 0.05 per gram of catalyst. In particular, step i') can be carried out with an amount of reducing agent of between 0.01 and 10 mol per gram of catalyst, preferably between 0.05 and 5 mol per gram of catalyst.

[0044] According to another embodiment, the catalyst activation step i') comprises bringing said catalyst into contact with a gas stream which comprises chlorotrifluoroethylene, and optionally hydrogen. It has been noted that chlorotrifluoroethylene (CTFE) makes it possible to activate the catalyst, in particular when hydrogen is also present. This allows an improvement in the trifluoroethylene production process. Activation in the presence of CTFE makes it possible to activate the catalyst at a lower temperature and therefore provides a less energy-consuming process. The process is further simplified since the reducing agent during activation is also one of the reactants for the subsequent reaction. Preferably, in this embodiment, step i') is carried out at a temperature T2' below 100°C. This temperature T2' can be reached from a temperature T1' using a low temperature gradient.Thus, during said step i'), the temperature of the catalytic bed is increased from a temperature T1' to a temperature T2' higher than T1', preferably the temperature of the catalytic bed is increased from a temperature T1' to a temperature T2' higher than T1' with a temperature gradient of less than 0.5°C / min. The temperature gradient used makes it possible to avoid early degradation of the catalyst and thus to allow a better yield or better productivity of the hydrogenolysis reaction. In particular, the temperature is increased with a temperature gradient of less than 0.45°C / min or less than 0.40°C / min, or less than 0.35°C / min, or less than 0.30°C / min, or less than 0.25°C / min, or less than 0.20°C / min, or less than 0.15°C / min, or less than 0.10°C / min, or less than 0.05°C / min.

[0045] Preferably, the temperature of the catalytic bed is increased by increasing the contact time calculated as the ratio between the volume, in liters, of catalyst and the total flow rate of said gas flow, in normal liters per second, at the inlet of the reactor. The contact time is between 1 and 60 seconds, preferably between 5 and 45 seconds, in particular between 10 and 30 seconds, more particularly between 15 and 25 seconds. The temperature T1' may be between 0°C and 50°C, advantageously between 10°C and 50°C, preferably between 20°C and 50°C. Preferably, the temperature T2' is lower than the temperature T3 for carrying out step a). The temperature T3 is preferably between 100°C and 180°C, more preferably between 100°C and 160°C, in particular between 120°C and 160°C.

[0046] Catalyst regeneration

[0047] Said catalyst used in the present process can be regenerated. This regeneration step can be carried out in a temperature range of the catalytic bed between 90°C and 450°C. Preferably, the regeneration step is carried out in the presence of hydrogen. The implementation of the regeneration step makes it possible to improve the yield of the reaction compared to the initial yield before regeneration.

[0048] According to a preferred embodiment, the regeneration step can be carried out at a catalytic bed temperature of 90°C to 300°C, preferably at a catalytic bed temperature of 90°C to 250°C, more preferably from 90°C to 200°C, in particular from 90°C to 175°C, more particularly at a catalytic bed temperature of 90°C to 150°C. In particular, the implementation of the regeneration step at a low temperature, for example from 90°C to 200°C or from 90°C to 175°C or from 90°C to 150°C, allows the desorption of compounds harmful to the activity of the catalyst and / or to limit phase transitions modifying the structure of the catalyst.

[0049] According to another preferred embodiment, the regeneration step can be carried out at a temperature of the catalytic bed above 200°C, advantageously above 230°C, preferably above 250°C, in particular above 300°C. The regeneration step can be carried out periodically depending on the productivity or conversion obtained in step a). The regeneration step can be carried out advantageously at a temperature of the catalytic bed between 200°C and 300°C, preferably between 205°C and 295°C, more preferably between 210°C and 290°C, in particular between 215°C and 290°C, more particularly between 220°C and 285°C, preferably between 225°C and 280°C, more preferably between 230°C and 280°C. Alternatively, the regeneration step may be carried out at a temperature between 300°C and 450°C, preferably between 300°C and 400°C.The regenerated catalyst can be reused in step a) of the present process.

[0050] Hydrogenolysis reaction

[0051] The present invention comprises, as mentioned above, a hydrogenolysis reaction step between a composition A and hydrogen to produce a stream B comprising trifluoroethylene. Said composition A comprises chlorotrifluoroethylene. The hydrogenolysis step is carried out in the presence of a catalyst and in the gas phase. Preferably, the hydrogenolysis step is carried out in the presence of a previously activated catalyst and in the gas phase. The hydrogenolysis step consists of simultaneously introducing hydrogen, CTFE and optionally an inert gas, such as nitrogen, into the gas phase and in the presence of said catalyst, preferably activated.

[0052] Preferably, said step a) is carried out at a fixed catalytic bed temperature of between 50°C and 250°C. Said step a) may be carried out at a fixed catalytic bed temperature of between 50°C and 240°C, advantageously between 50°C and 230°C, preferably between 50°C and 220°C, more preferably between 50°C and 210°C, in particular between 50°C and 200°C. Said step a) can also be carried out at a fixed catalytic bed temperature of between 60°C and 250°C, advantageously between 70°C and 250°C, preferably between 80°C and 250°C, more preferably between 90°C and 250°C, in particular between 100°C and 250°C, more particularly between 120°C and 250°C.Said step a) may also be carried out at a fixed catalytic bed temperature of between 60°C and 240°C, advantageously between 70°C and 230°C, preferably between 80°C and 220°C, more preferably between 90°C and 210°C, in particular between 100°C and 200°C, more particularly between 100°C and 180°C, preferably between 100°C and 160°C, particularly preferably between 120°C and 160°C.

[0053] The H2 / CTFE molar ratio is between 0.5 / 1 to 2 / 1 and preferably between 1 / 1 and 1.2 / 1. If an inert gas such as nitrogen is present in step a), the nitrogen / Fh molar ratio is between 0 / 1 to 2 / 1 and preferably between 0 / 1 and 1 / 1.

[0054] Step a) is preferably carried out at a pressure of 0.05 MPa to 1.1 MPa, more preferably of 0.05 MPa to 0.5 MPa, in particular at atmospheric pressure.

[0055] The contact time calculated as the ratio between the volume, in liters, of catalyst and the total flow rate of the gas mixture, in normal liters per second, at the inlet of the reactor, is between 1 and 60 seconds, preferably between 5 and 45 seconds, in particular between 10 and 30 seconds, more particularly between 15 and 25 seconds.

[0056] According to the present invention, said composition A also comprises 1,2-dichlorohexafluorocyclobutane. The term "1,2-dichlorohexafluorocyclobutane" refers to two isomers, D1 and D2. These are of formula: Di

[0057] Preferably, the mass ratio D2 / D1 is greater than 1. Said mass ratio D2 / D1 corresponds to the ratio between the mass content of the stereoisomer D2 in said composition A and the mass content of the stereoisomer DI in said composition A.

[0058] Advantageously, the mass ratio D2 / D1 is greater than 1.1, preferably greater than 1.2, more preferably greater than 1.3, in particular greater than 1.4, more particularly greater than 1.5, preferably greater than 1.6, advantageously greater than 1.7, preferably greater than 1.8. According to a preferred embodiment, the mass ratio D2 / D1 is less than 10, advantageously less than 9, preferably less than 8, more preferably less than 7, in particular less than 6, more particularly less than 5, preferably less than 4. The particular mass ratio between the two stereoisomers makes it possible to obtain better productivity.

[0059] According to a preferred embodiment, the total mass content of said stereoisomers DI and D2 is less than 50%, advantageously less than 45%, preferably less than 40%, more preferably less than 35%, in particular less than 30% based on the total weight of said composition A. Advantageously, the total mass content of said stereoisomers DI and D2 is less than 25% based on the total weight of said composition A. Preferably, the total mass content of said stereoisomers DI and D2 is less than 24%, advantageously less than 23%, preferably less than 22%, more preferably less than 21%, in particular less than 20% based on the total weight of said composition A. Advantageously, the total mass content of said stereoisomers DI and D2 is greater than 1% based on the total weight of said composition A.Preferably, the total mass content of said stereoisomers D1 and D2 is greater than 1.5%, more preferably greater than 2%, in particular greater than 3%, more particularly greater than 4%, preferably greater than 5% based on the total weight of said composition A.

[0060] According to a preferred embodiment, the total mass content of said stereoisomers DI and D2 is between 1 and 25%, advantageously between 2 and 24%, preferably between 3 and 23%, more preferably between 4 and 22%, in particular between 5 and 21% based on the total weight of said composition A. Surprisingly, it has been observed that a high proportion of compounds DI and D2 in the composition makes it possible to improve the productivity of the trifluoroethylene preparation reaction.

[0061] According to a preferred embodiment, said composition A comprises at least 75% by weight of chlorotrifluoroethylene based on the total weight of said composition A, advantageously at least 77% by weight, preferably at least 79% by weight, more preferably at least 81% by weight, in particular at least 83% by weight, more particularly at least 85% by weight of chlorotrifluoroethylene based on the total weight of said composition A.

[0062] Said composition A may optionally comprise at least one of the additional compounds C2 selected from the group consisting of 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, 2-chloro-1,1-difluoroethylene, E / Zl-chloro-1,2-difluoroethylene, 2-chloro-1,1,1-trifluoroethane, l-chloro-1,2,2-trifluoroethane, l-chloro-1,1,2-trifluoroethane. The mass content of said at least one of the additional compounds C2 may be less than 0.5% based on the total weight of said composition A, advantageously less than 0.4%, preferably less than 0.3%, more preferably less than 0.2%, in particular less than 0.1% based on the total weight of said composition A. If composition A comprises one or more compounds C2 as defined below, the total mass content of compounds C2 is greater than 1 ppm, advantageously greater than 10 ppm.

[0063] Preferably, if composition A contains it, the mass content of 1,1,1,2-tetrafluoroethane is between 1 ppm and 400 ppm, in particular between 1 ppm and 300 ppm based on the total weight of composition A.

[0064] Preferably, if composition A contains it, the mass content of 1,1-difluoroethane is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm based on the total weight of composition A.

[0065] Preferably, if composition A contains it, the mass content of 2-chloro-1,1-difluoroethylene is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm based on the total weight of composition A.

[0066] Preferably, if composition A contains it, the mass content of El-chloro-1,2-difluoroethylene is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm based on the total weight of composition A.

[0067] Preferably, if composition A contains it, the mass content of Zl-chloro-1,2-difluoroethylene is between 1 ppm and 400 ppm, in particular between 1 ppm and 300 ppm based on the total weight of composition A.

[0068] Preferably, if composition A contains it, the mass content of 2-chloro-1,1,1-trifluoroethane is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm based on the total weight of composition A.

[0069] Preferably, if composition A contains it, the mass content of l-chloro-1,2,2-trifluoroethane is between 1 ppm and 200 ppm, in particular between 1 ppm and 150 ppm based on the total weight of composition A.

[0070] Preferably, if composition A contains it, the mass content of l-chloro-1,1,2-trifluoroethane is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm based on the total weight of composition A.

[0071] Reaction flow treatment

[0072] Stream B from step a) may be treated to recover a purified trifluoroethylene (HFO-1123) stream. Said stream B may comprise, in addition to trifluoroethylene, HF, HCl, unreacted hydrogen, unreacted chlorotrifluoroethylene, optionally 1,2-dichlorohexafluorocyclobutane in the form DI and D2 and / or one or more of the additional compounds C2.

[0073] Said stream B can be treated according to the following steps: i) Removal of HF and / or HCl from said product stream obtained in step a) to form a gas mixture; ii) Drying of the gas mixture from step i); iii) Treatment of the dried gas mixture in step ii) to remove hydrogen and optionally inert gases; iv) Distillation of the mixture from step iii).

[0074] Stream B from step a) is recovered at the reactor outlet in gaseous form. Preferably, at the outlet of the hydrogenolysis reactor, the product stream is first treated to remove HCl and HF. The product stream is passed through water in a washing column and then washed with a dilute base such as NaOH or KOH. The remainder of the gas mixture, consisting of the unconverted reactants (H2 and CTFE), diluting nitrogen (if present), trifluoroethylene and the additional compounds mentioned above, is directed to a dryer in order to remove traces of washing water. Drying can be carried out using products such as sodium or magnesium calcium sulfate, calcium chloride, potassium carbonate, silica gel (silica gel) or zeolites. In one embodiment, a molecular sieve (zeolite) such as siliporite is used for drying.The gas mixture thus dried is subjected to a step of separating the hydrogen and the inerts from the rest of the other products present in the gas mixture by absorption / desorption in the presence of an alcohol comprising 1 to 4 carbon atoms and preferably ethanol, at atmospheric pressure and at a temperature below room temperature, preferably below 10°C and even more preferably at a temperature of -25°C, for absorption. In one embodiment, the absorption of the organics is carried out in a countercurrent column with ethanol cooled to -25°C. The flow rate of ethanol is adjusted according to the flow rate of organics to be absorbed. The hydrogen and the inert gases, insoluble in ethanol at this temperature, are eliminated at the top of the absorption column. The organics are then recovered by heating the ethanol to its boiling point (desorption), to be subsequently distilled.Alternatively, step iii) may be carried out by a membrane separation process.

[0075] According to step iv), the organics thus obtained are distilled to form and recover a DI stream comprising trifluoroethylene and a D2 stream comprising chlorotrifluoroethylene and optionally 1,2-dichlorohexafluorocyclobutane in the DI and D2 form and / or one or more of the additional compounds C2. The D2 stream can be recycled to step a).

[0076] According to a preferred embodiment, distillation step iv) is carried out at a pressure of less than 3 bara, preferably at a pressure of between 0.5 and 3 bara, in particular at a pressure of between 0.9 and 2 bara. Carrying out distillation at a pressure of less than 3 bara makes it possible to secure the process given the explosive nature of trifluoroethylene above 3 bara. Preferably, distillation step iv) is carried out in a distillation column comprising structured packing. It has been observed that structured packing makes it possible to obtain a more efficient distillation step. Said structured packing may be made of a metallic material. Said DI stream is preferably recovered at the top of the distillation column. Before being recovered, the DI stream may optionally be partially condensed at the top of the distillation column.When partial condensation is implemented, the DI stream is brought to a temperature of -50°C to -70°C. The temperature is adjusted according to the applied pressure. Partial condensation makes it possible to improve the efficiency of the distillation by limiting the content of additional compounds in the DI stream. Said DI stream may comprise at least 95% of trifluoroethylene, advantageously at least 96%, preferably at least 97%, more preferably at least 98%, in particular at least 99%, more particularly at least 99.5% by weight based on the total weight of said DI stream.

[0077] According to a second aspect, the present invention provides a composition comprising chlorotrifluoroethylene. Said composition comprises at least 75% by weight of chlorotrifluoroethylene and less than 25% by weight of 1,2-dichlorohexafluorocyclobutane in the form D1 and D2 based on the total weight of said composition. In said composition, the mass ratio D2 / D1 being greater than 1, said mass ratio D2 / D1 corresponding to the ratio between the mass content of the stereoisomer D2 in said composition and the mass content of the stereoisomer D1 in said composition. Advantageously, the mass ratio D2 / D1 is greater than 1.1, preferably greater than 1.2, more preferably greater than 1.3, in particular greater than 1.4, more particularly greater than 1.5, preferably greater than 1.6, advantageously more preferably greater than 1.7, preferably more preferably greater than 1.8.According to a preferred embodiment, the mass ratio D2 / D1 is less than 10, advantageously less than 9, preferably less than 8, more preferably less than 7, in particular less than 6, more particularly less than 5, preferably less than 4.

[0078] Preferably, if the composition contains it, the mass content of 1,1,1,2-tetrafluoroethane is between 1 ppm and 400 ppm, in particular between 1 ppm and 300 ppm, more particularly 1 ppm and 200 ppm based on the total weight of the composition.

[0079] Preferably, if the composition contains it, the mass content of 1,1-difluoroethane is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm based on the total weight of the composition.

[0080] Preferably, if the composition contains it, the mass content of 2-chloro-1,1-difluoroethylene is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm, more particularly between 1 ppm and 20 ppm based on the total weight of the composition.

[0081] Preferably, if the composition contains it, the mass content of El-chloro-1,2-difluoroethylene is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm, more particularly between 1 ppm and 20 ppm based on the total weight of the composition.

[0082] Preferably, if the composition contains it, the mass content of Zl-chloro-1,2-difluoroethylene is between 1 ppm and 400 ppm, in particular between 1 ppm and 300 ppm, more particularly 1 ppm and 200 ppm based on the total weight of the composition.

[0083] Preferably, if the composition contains it, the mass content of 2-chloro-l,l,l-trifluoroethane is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm, more particularly between 1 ppm and 20 ppm based on the total weight of the composition.

[0084] Preferably, if the composition contains it, the mass content of l-chloro-1,2,2-trifluoroethane is between 1 ppm and 200 ppm, in particular between 1 ppm and 150 ppm, more particularly between 1 ppm and 100 ppm based on the total weight of the composition.

[0085] Preferably, if the composition contains it, the mass content of l-chloro-1,1,2-trifluoroethane is between 1 ppm and 50 ppm, in particular between 1 ppm and 25 ppm, more particularly between 1 ppm and 20 ppm based on the total weight of the composition.

[0086] Said composition as described in this section can be used in a process for producing trifluoroethylene as described in the present invention.

[0087] In a tubular reactor consisting of a stainless steel tube with a length of 1200 mm and a diameter of 25 mm, and equipped with a double jacket, 275 ml of catalyst (0.2% palladium supported on alpha alumina) were introduced. The catalyst thus loaded was then activated as follows: the reaction tube was placed in a tubular furnace and was supplied with a flow of hydrogen (from 0.05 to 0.1 moles per gram of catalyst). The catalytic bed was heated to a temperature of 200°C to 250°C with a temperature gradient of 0.2°C / min. After this activation period, the tube was cooled to room temperature and then isolated for installation on a hydrogenolysis test bench.

[0088] Four test benches were used in parallel, each comprising a reactor prepared as described above. The four benches were supplied with 1 mol / h of starting composition and 1 mol / h of hydrogen in anhydrous form. The temperature of the reactor jacket was 25°C. The contact time, calculated as the ratio between the volume in liters of catalyst and the sum of the flow rates of the reactants in normal liters per second, was of the order of 22 seconds. Tests were carried out using different starting compositions. Comparative Example 1 was carried out using chlorotrifluoroethylene. Example 2 according to the invention was carried out using a composition comprising 85% by weight of chlorotrifluoroethylene used in the comparative example to which 15% of 1,2-dichlorohexafluorocyclobutane was added with a D2 / D1 ratio of 2.1.

[0089] The results are shown in Table 1 below:

[0090] [Table 1]

[0091] The productivity mentioned corresponds to the sum of the productivities obtained for all four hydrogenolysis benches. As can be seen, the trifluoroethylene productivity is significantly improved starting from the composition according to the invention compared to a chlorotrifluoroethylene composition without 1,2-dichlorohexafluorocyclobutane.

Claims

Claims 1. Process for the production of trifluoroethylene in a reactor equipped with a fixed catalytic bed comprising a catalyst, said process comprising a step a) of reacting a composition A comprising chlorotrifluoroethylene with hydrogen in the presence of a catalyst and in the gas phase to produce a stream B comprising trifluoroethylene, characterized in that said composition A also comprises 1,2-dichlorohexafluorocyclobutane in the form of two stereoisomers DI and D2 Di; the mass ratio D2 / D1 being greater than 1, said mass ratio D2 / D1 corresponding to the ratio between the mass content of the stereoisomer D2 in said composition A and the mass content of the stereoisomer DI in said composition A.

2. Method according to the preceding claim, characterized in that the total mass content of said stereoisomers DI and D2 is less than 25% based on the total weight of said composition A, preferably less than 20% based on the total weight of said composition A, in particular less than 15% based on the total weight of said composition A.

3. Process according to any one of the preceding claims, characterized in that said composition A comprises at least 75% by weight of chlorotrifluoroethylene based on the total weight of said composition A, preferably at least 80% by weight of chlorotrifluoroethylene based on the total weight of said composition A, in particular at least 85% by weight of chlorotrifluoroethylene based on the total weight of said composition A.

4. Method according to any one of the preceding claims, characterized in that said composition A also comprises at least one of the additional compounds C2 selected from the group consisting of 1,1,1,2-tetrafluoroethane, 1,1- difluoroethane, 2-chloro-l,l-difluoroethylene, E / Zl-chloro-l,2-difluoroethylene, 2- chloro-l,l,l-trifluoroethane, l-chloro-l,2,2-trifluoroethane, l-chloro-1,1,2- trifluoroethane.

5. Method according to the preceding claim, characterized in that the mass content of said at least one of the additional compounds C2 is less than 0.5% based on the total weight of said composition A.

6. Process according to any one of the preceding claims, characterized in that the catalyst comprises palladium supported on alpha alumina.

7. Process according to any one of the preceding claims, characterized in that the chlorotrifluoroethylene and the hydrogen are in anhydrous form.

8. Method according to any one of the preceding claims, characterized in that said method comprises a step i') of activation of the catalyst, carried out prior to step a), by bringing it into contact with a gaseous flow comprising a reducing agent, an inert gas or a mixture thereof.

9. Method according to the preceding claim, characterized in that during said step i'): the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 higher than T1 with a temperature gradient of less than 0.5°C / min; or the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 higher than T1 in stages.

10. Composition comprising at least 75% by weight of chlorotrifluoroethylene and less than 25% by weight of 1,2-dichlorohexafluorocyclobutane in the form of two stereoisomers DI and D2 ; the mass ratio D2 / D1 being greater than 1, said mass ratio D2 / D1 corresponding to the ratio between the mass content of the stereoisomer D2 in said composition and the mass content of the stereoisomer DI in said composition based on the total weight of said composition.

11. Composition according to the preceding claim, characterized in that the total mass content of said stereoisomers DI and D2 is between 1 and 25%.

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