EP4240713A1

EP4240713A1 - Process for the production of trifluoroethylene

Info

Publication number: EP4240713A1
Application number: EP21815555.4A
Authority: EP
Inventors: Alexandre CAMBRODON; Thierry Lannuzel; Cédric LAVY; Philippe Leduc; Kevin HISLER
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2020-11-03
Filing date: 2021-10-27
Publication date: 2023-09-13
Also published as: WO2022096803A1; FR3115786A1; FR3115786B1; CN116390901A; JP2023547657A; US20230391694A1

Abstract

The present invention relates to a process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: (i) a step of activating said catalyst, comprising bringing the catalyst into contact with a gas stream containing a reducing agent, an inert gas or a mixture thereof; and (ii) a step of reacting the chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step (i) and in the gas phase so as to produce a stream containing trifluoroethylene; said process being characterised in that, during said step (i), the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 greater than T1 at a a temperature gradient less than 0.5° C/min.

Description

Trifluoroethylene production process

Technical area

The present invention relates to a process for the production of hydrofluoroolefins. In particular, the present invention relates to a process for the production of trifluoroethylene (VF3) by hydrogenolysis of chlorotrifluoroethylene.

Technological background of the invention

Fluorinated olefins, such as VF3, are known and are used as monomers or comonomers for the manufacture of fluorocarbon polymers having remarkable characteristics, in particular excellent chemical behavior and good heat resistance. Trifluoroethylene is a gas under normal conditions of pressure and temperature. The main risks associated with the use of this product concern its flammability, its propensity for self-polymerization when it is 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.

Given the main risks above, the synthesis as well as the storage of VF3 pose particular problems and impose strict safety rules throughout these processes. A known way of preparing trifluoroethylene uses as starting materials chlorotrifluoroethylene (CTFE) and hydrogen in the presence of a catalyst and in the gas phase. 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.

Summary of the invention

According to a first aspect, the present invention relates to a process for producing trifluoroethylene in a reactor equipped with a catalytic bed comprising a catalyst, said process comprising: i) a step of activating said catalyst comprising bringing it into contact with a gas stream comprising a reducing agent, an inert gas or a mixture thereof; and ii) a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step i) and in the gas phase to produce a stream comprising the trifluoroethylene; characterized in that during said step i) the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 greater than T1 with a temperature gradient of less than 0.5°C/min. The temperature gradient implemented during the activation makes it possible to avoid premature degradation of the catalyst and thus to allow better yield or better productivity of the hydrogenolysis reaction. It was observed that the activation of the catalyst with a temperature gradient above 0.5° C./min resulted in a less efficient process, ie a lower productivity of trifluoroethylene.

According to a preferred embodiment, the temperature T1 is 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. °C, in particular between 20°C and 100°C, more particularly between 20°C and 75°C, preferably between 20°C and 50°C.

According to the first aspect, the present invention also relates to a process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: i) a step of activating said catalyst comprising bringing it into contact with a gas stream comprising a reducing agent, an inert gas or a mixture thereof; and ii) a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step i) and in the gas phase to produce a stream comprising the trifluoroethylene; characterized in that during said step i) the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 greater than T1 in stages.

The present process thus makes it possible to improve the efficiency of the reaction of hydrogenolysis of chlorotrifluoroethylene to trifluoroethylene thanks to the present stage of activation of the catalyst implementing heating in successive stages. In particular, the productivity of the hydrogenolysis reaction (step ii)) is markedly improved by the activation step i).

According to a preferred embodiment, 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 premature degradation of the catalyst and thus to allow a better yield or a better productivity of the hydrogenolysis reaction.

According to a preferred embodiment, step i) comprises at least one stage at a temperature Tla of between 90 and 120°C.

According to a preferred embodiment, each level lasts between 5 min and 24 h, preferably between 30 min and 1 Oh.

According to a preferred embodiment, the temperature T2 is between 150°C and 400°C.

According to a particular embodiment, the reducing agent is chosen from the group consisting of hydrogen, carbon monoxide, nitrogen monoxide, formaldehyde, Ci-Cg alkanes and Ci-Cio hydrohalocarbons, or a mixture thereof; preferably from hydrogen and C 1 -C 10 hydrohalocarbons, or a mixture thereof; in particular from hydrogen, chlorotrifluoroethylene, trifluoroethane, trifluoroethylene, chlorotrifluoroethane or difluoroethane or a mixture thereof.

According to the first aspect, the present invention also relates to a process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: i) a step of activating said catalyst; and ii) a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step i) and in the gas phase to produce a stream comprising the trifluoroethylene; characterized in that said step i) comprises bringing said catalyst into contact with a gas stream comprising chlorotrifluoroethylene, and optionally hydrogen.

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' greater than T1', preferably the temperature of the catalytic bed is increased by a temperature T1' at a temperature T2' greater than T1' with a temperature gradient of less than 0.5°C/min.

According to a preferred embodiment, the temperature of the catalytic bed is increased by increasing the contact time calculated as being the ratio between the volume, in liters, of catalyst and the total flow rate of said gas stream, in normal liters per second, at the entrance to the reactor.

According to a preferred embodiment, step ii) is carried out at a temperature T3 and the temperature T2' is lower than the temperature T3 for carrying out step ii). According to a second aspect, the present invention relates to a process for producing trifluoroethylene in a reactor equipped with a catalytic bed comprising a catalyst, said process comprising: a) a step of reacting chlorotrifluoroethylene with hydrogen carried out in the presence catalyst, in the gas phase and at a catalyst bed temperature T3 to produce a stream comprising the trifluoroethylene; b) a step for regenerating the catalyst used in step a); c) repeating steps a) and b) using the catalyst regenerated in step b). characterized in that step b) is carried out at a temperature of the catalytic bed T4 of 90°C to 300°C and in the presence of hydrogen, preferably at a temperature of the catalytic bed T4 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 temperature of the catalytic bed T4 from 90°C to 150°C.

According to a preferred embodiment, the temperature difference AT between the temperature of the catalytic bed in stage a) and the temperature of the catalytic bed in stage b), AT = T3 - T4, is comprised in absolute value between 0 and 50, preferably between 0 and 20.

According to a preferred embodiment, step a) is preceded by a catalyst activation step, preferably as described in step i) according to the first aspect of the present invention.

According to a preferred embodiment, the method also comprises a step d) of heat treatment of said catalyst at a temperature T5 greater than T4, preferably at a temperature T5 greater than 230° C., in particular at a temperature T5 greater than 250° C. vs. According to a preferred embodiment, said catalyst is a catalyst based on a metal from columns 8 to 10 of the periodic table of the elements, preferably deposited on a support, in particular an aluminum-based support.

According to a third aspect, the present invention relates to a method for producing trifluoroethylene in two reactors each comprising at least one catalytic bed comprising a catalyst, said method comprising: in a first reactor, a step of reacting chlorotrifluoroethylene with hydrogen operated in the presence of the catalyst and in the gas phase to produce a stream comprising the trifluoroethylene; in a second reactor, a heat treatment step of said catalyst.

According to a preferred embodiment, said reaction step and said heat treatment step are implemented alternately in each of said two reactors. According to a preferred embodiment, said heat treatment step is a catalyst activation step as described in step i) according to the first aspect of the present invention, or a catalyst regeneration step as described in l step b) according to the second aspect of the present invention or a heat treatment according to step d) according to the second aspect of the present invention.

Brief description of figures

[Fig. 1] schematically represents a device for implementing the method according to a particular embodiment of the invention in which the reaction step is implemented in a reactor.

[Fig. 2] schematically represents a device for carrying out the method according to a particular embodiment of the invention in which the step of activating or regenerating the catalyst is carried out in a reactor in the presence of nitrogen from a temperature T1 to T1a.

[Fig. 2a] schematically represents a device for carrying out the method according to a particular embodiment of the invention in which the step of activating or regenerating the catalyst is carried out in a reactor in the presence of hydrogen from a temperature Tla to T2.

[Fig. 2b] schematically represents a device for carrying out the method according to a particular embodiment of the invention in which the step of activating or regenerating the catalyst is carried out in a reactor in the presence of chlorotrifluoroethylene of a temperature Tla to T2.

[Fig. 3] schematically represents a device comprising two reactors for implementing the method, according to a particular embodiment of the invention, in which the regeneration and reaction steps are alternated; the regeneration step being carried out in the presence of hydrogen.

[Fig. 4] schematically represents a device comprising two reactors for implementing the method, according to a particular embodiment of the invention, in which the regeneration and reaction steps are alternated; the regeneration step being carried out in the presence of a hydrohalocarbon.

[Fig. 5] schematically represents a device comprising two reactors for implementing the method, according to another particular embodiment of the invention, in which the regeneration and reaction steps are alternated. Detailed description of the invention

According to a preferred embodiment, the methods according to the invention described in the present application are implemented continuously.

According to a preferred embodiment, in any of the processes described in the present application, the hydrogen is in anhydrous form.

According to a preferred embodiment, in any of the processes described in the present application, the chlorotrifluoroethylene is in anhydrous form.

The implementation of 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 water content 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 under consideration.

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. Preferably, the catalyst is supported. The support is preferably selected from the group consisting of activated carbon, alumina, calcium carbonate, and graphite. Preferably, the support is based on aluminium. In particular, the support is alumina. Thus, the catalyst is more particularly palladium supported on 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.

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.

Activation of the catalyst (step i))

Embodiment (1)

According to a first embodiment, the step of activating said catalyst comprises bringing it into contact with a gas stream comprising a reducing agent, an inert gas or a mixture thereof. 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 greater than Tl with a temperature gradient of less than 0.5°C/min. The temperature gradient implemented makes it possible to avoid premature degradation of the catalyst and thus to allow 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 at 0.05°C/min.

The temperature T1 represents the initial temperature of the activation step. This temperature T1 may be ambient 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 1 Oh, preferably from 1 h to 1 Oh.

As mentioned above, the gas stream can include a reducing agent, an inert gas or a mixture of both. According to a particular embodiment, the reducing agent is selected from the group consisting of hydrogen, carbon monoxide, nitrogen monoxide, formaldehyde, Ci-Cg alkanes and Ci-Cio hydrohalocarbons, or a mixture thereof; preferably from hydrogen, a C1-C10 hydrohalocarbon, or a mixture thereof; in particular from hydrogen, chlorotrifluoroethylene, trifluoroethane, trifluoroethylene, chlorotrifluoroethane or difluoroethane or a mixture thereof.

The inert gas can be nitrogen or argon; preferably nitrogen.

Preferably, the gas stream used during step i) does not include oxygen. Preferably, step i) can be implemented with a quantity 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 implemented with a quantity 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.

Embodiment (2)

According to a second embodiment, the step of activating said catalyst comprises bringing it into contact with a gas stream comprising a reducing agent, an inert gas or a mixture thereof. Preferably, during step i), the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 in stages. The activation of the catalyst in stages makes it possible to make the catalyst more efficient. The implementation of bearings makes it possible to avoid degradation of the catalyst. It has also been observed that the properties of the catalyst were also all the more improved if the rise in temperature between the stages is gradual and relatively slow compared to the usual conditions for activating a catalyst.

Thus, preferably, in step i), between two plateaus, 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 premature degradation of the catalyst and thus to allow 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 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, so as more preferred 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.

Stage i) of activating the catalyst contains at least one level between the temperature T1 and the temperature T2. Stage i) of activating the catalyst can comprise several stages between the temperature T1 and the temperature T2. Preferably, step i) comprises at least one stage at a temperature Tla of between 90 and 120°C. The presence of a plateau between 90°C and 120°C is to be preferred in order to increase the life of the catalyst. Step i) can also comprise one or more stages between the temperature T1 and Tla and/or between the temperature Tla and T2.

Preferably, each plateau between the temperature T1 and the temperature T2 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. 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 1 Oh. In particular, the plateau at temperature Tla 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 plateau at the temperature Tla 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 1 Oh.

As mentioned above, the gas stream can include a reducing agent, an inert gas or a mixture of both. According to a particular embodiment, the reducing agent is selected from the group consisting of hydrogen, carbon monoxide, nitrogen monoxide, formaldehyde, Ci-Cg alkanes and Ci-Cio hydrohalocarbons, or a mixture thereof; preferably from hydrogen or a C1-C10 hydrohalocarbon, or a mixture thereof; in particular from hydrogen, chlorotrifluoroethylene, trifluoroethane, trifluoroethylene, chlorotrifluoroethane or difluoroethane or a mixture thereof.

The inert gas can be nitrogen or argon; preferably nitrogen.

Preferably, the gas stream used during step i) does not include oxygen. The gas flow used during step i) may be different over time. For example, the gas flow can comprise an inert gas between two bearings and for example comprise a reducing agent between two other bearings. In particular, the gas stream comprises an inert gas when step i) is implemented between the temperature T1 and Tla and the gas stream comprises a reducing agent, preferably hydrogen or Ci-Cio hydrohalocarbons as defined above, when step i) is implemented between the temperature Tla and T2. Thus, the gas flow used during step i) is modified during the plateau implemented at the temperature Tla.

Alternatively, the gas stream may comprise a reducing agent such as hydrogen or Ci-Cio 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 Ci-Cio hydrohalocarbons as defined above, optionally mixed with an inert gas such as nitrogen, during the rise in temperature between the temperature Tla of said bearing and the temperature T2 represents an additional advantage in terms of productivity.

As mentioned above, the temperature T2 is maintained for a certain time. During this stage at the temperature T2, the gas flow can be modified. Thus, the gas stream during the plateau at the temperature T2 can comprise hydrogen or a Ci-Cio hydrohalocarbon as defined above; in particular the gas flow during the plateau at the temperature T2 can comprise hydrogen, chlorotrifluoroethylene, trifluoroethane, trifluoroethylene, chlorotrifluoroethane or difluoroethane.

Preferably, step i) can be implemented with a quantity 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 implemented with a quantity 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.

Embodiment (3)

According to a third 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 noticed that chlorotrifluoroethylene (CTFE) makes it possible to activate the catalyst, in particular when hydrogen is also present. This allows an improvement in the process for the production of trifluoroethylene. Activation in the presence of CTFE makes it possible to activate the catalyst at a lower temperature and therefore provides a process that consumes less energy. 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' of less than 100°C. This temperature T2' can be reached from a temperature T1' by 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' greater than T1', preferably the temperature of the catalytic bed is increased from a temperature T1' to a temperature T2' greater than T1' with a temperature gradient of less than 0.5°C/min. The temperature gradient implemented makes it possible to avoid premature degradation of the catalyst and thus to allow 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.

Preferably, the temperature of the catalytic bed is increased by increasing the contact time calculated as being the ratio between the volume, in liters, of catalyst and the total flow rate of said gas stream, 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' can 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 implementing step ii). 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.

Hydrogenolysis reaction (step ii) according to the first aspect of the invention or step a) according to the second aspect of the invention)

The present invention comprises, as mentioned above, a reaction step of hydrogenolysis of chlorotrifluoroethylene (CTFE) with hydrogen (step ii) or step a)). 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 said activated catalyst and in the gas phase.

The hydrogenolysis step consists of simultaneously introducing hydrogen, the CTFE and optionally an inert gas, such as nitrogen, in the gas phase and in the presence of said catalyst, preferably activated. The temperature of the catalytic bed T3 is controlled by circulation in the jacket of the reactor of a heat transfer fluid. The temperature of the heat transfer fluid is adapted according to the target temperature T3.

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.

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

Step ii) is preferably carried out at a pressure of 0.05 MPa to 0.2 MPa, in particular at atmospheric pressure.

The contact time calculated as being the ratio between the volume, in liters, of catalyst and the total flow rate of the gaseous 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.

The hydrogenolysis step of the present process results in the production of a stream A comprising the trifluoroethylene. Said stream A may also comprise unreacted hydrogen and unreacted CTFE. Stream A may also include trifluoroethane and/or chlorotrifluoroethane as by-products of the hydrogenolysis reaction.

Stream A may also include HCl and HF. Preferably, stream A is recovered at the reactor outlet in gaseous form. Preferably, at the outlet of the hydrogenolysis reactor, stream A is treated to eliminate HCl and HF. Stream A is passed through water in a wash column followed by a wash with a dilute base such as NaOH or KOH. The rest of the gas mixture, consisting of the unconverted reactants (H2 and CTFE), dilution nitrogen (if present), and reaction products (VF3, 143, 133 and other organic products) which form the gas mixture B, is sent to a dryer in order to eliminate traces of washing water. The drying can be carried out using products such as sodium or magnesium calcium sulphate, calcium chloride, potassium carbonate, silica gel (silicagel) or zeolites. In one embodiment, a molecular sieve (zeolite) such as siliporite is used for drying. Stream B thus dried is subjected to a step of separation of hydrogen and inerts from the rest of the other products present in mixture B, 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. Hydrogen and inert gases, insoluble in ethanol at this temperature, are eliminated at the top of the absorption column. The organics are then recovered in the form of a gas mixture C, by heating the ethanol to its boiling point (desorption), to then be distilled.

Pure trifluoroethylene (VF3) is then distilled from mixture C, to be separated from the other organic products (CTFE, F143, F133 and other organics, forming mixture D). Mixture D comprising the other organic compounds is recovered at the bottom of the column. The distillation of said mixture D in a second column makes it possible to recover and recycle the unconverted CTFE at the top of the column and to eliminate the by-products of the reaction at the bottom of this second column.

Catalyst regeneration (step b))

Preferably, the regeneration implemented in step b) is carried out at a temperature of the catalytic bed T4 of 90° C. to 300° C. in the presence of hydrogen, preferably at a temperature of the catalytic bed T4 of 90° C. at 250°C, more preferably from 90°C to 200°C, in particular from 90°C to 175°C, more particularly at a temperature of the catalytic bed T4 from 90°C to 150°C.

The implementation of step b) makes it possible to improve the yield of the reaction with respect to the initial yield before regeneration. In particular, the implementation of step b) 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.

According to a preferred embodiment, the temperature difference AT between the temperature of the catalytic bed in step a) and the temperature of the catalytic bed in step b), AT = T3 - T4, is comprised in absolute value between 0 and 50. Advantageously, the temperature difference AT is between 0 and 45, preferably between 0 and 40, in particular between 0 and 35, more particularly between 0 and 30, preferably between 0 and 25, advantageously between 0 and 20, preferably privileged between 0 and 15, in a particularly preferred manner between 0 and 10. The present method makes it possible to implement at low temperature, the hydrogenolysis reaction such as the regeneration of the catalyst. This represents a significant energy gain. As mentioned above, the regeneration at low temperature makes it possible to improve the initial yield of step a) and not only to recover the initial yield.

Preferably, step b) can be implemented for a period of 1 hour to 500 hours, preferably 1 hour to 400 hours, in particular 1 hour to 300 hours, more particularly 1 hour to 200 hours.

As mentioned above, step b) is carried out in the presence of hydrogen. Stage b) of regeneration of the catalyst is preferably implemented in the absence of oxidizing agent, more particularly in the absence of a flow containing oxygen. Oxygen as mentioned here refers to pure oxygen or air or a mixture containing oxygen and nitrogen. Indeed, the presence of an oxidant during step b) can cause a modification of the structure of the catalyst which would require the implementation of step a) at higher temperature. Thus, the present step b) can consist of a regeneration of the catalyst in the presence of a stream consisting of hydrogen, optionally mixed with an inert gas. The present step b) can consist of a regeneration of the catalyst in a single step in the presence of a flow of hydrogen.

Heat treatment (step d))

According to a preferred embodiment, the method also comprises a step d) of heat treatment of said catalyst at a temperature T5 greater than T4, preferably at a temperature T5 greater than 200° C., advantageously greater than 230° C., preferably greater than at 250°C, in particular above 300°C. Step d) can be implemented periodically depending on the productivity or the conversion obtained in step a). Preferably, step d) is consecutive to step a) after several repetitions of steps a), b) and c). Following the implementation of step d), steps a), b) and c) are repeated.

Step d) preferably consists of bringing said catalyst into contact with a gas stream comprising a reducing agent, an inert gas or a mixture of both. The reducing agent is as defined above in the first aspect of the present invention.

Stage d) can be implemented by increasing the temperature of the catalytic bed in stages as described for stage i) according to the present invention. Thus, step d) can be implemented from a temperature T6 to reach at least one plateau at a temperature T6a, greater than T6, then increase the temperature T6a to reach the temperature T5. Preferably, in step d), the temperature of the catalytic bed is increased with a temperature gradient of less than 0.5° C./min. 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 T5 is advantageously 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 temperature T5 can be between 300°C and 450°C, preferably between 300°C and 400°C.

The temperature T5 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.

Preferably, in step d), the temperature T6 is generally room temperature. Alternatively, the temperature T6 can be between room temperature and 50°C. Preferably, step d) comprises at least one stage at a temperature T6a of between 90 and 120°C.

Preferably, each plateau between the temperature T6 and the temperature T5 lasts 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.

Prior to step d), the present process may comprise a step of cooling the catalytic bed. Thus, the catalytic temperature can be reduced from temperature T3, temperature of the catalytic bed during step a) to temperature T6, initial temperature of the heat treatment in step d).

The inert gas can be nitrogen or argon; preferably nitrogen.

Preferably, the gas stream does not include oxygen. Preferably, the gas stream used in step d) is the same as that used in step i).

For example, the gas flow can comprise an inert gas between two bearings and for example comprise a reducing agent between two other bearings. In particular, the gas stream comprises an inert gas when step d) is implemented between the temperature T6 and T6a and the gas stream comprises a reducing agent, preferably hydrogen or Ci-Cio hydrohalocarbons as defined above, when step d) is implemented between the temperature T6a and T5. Thus, the gas flow used during step d) is modified during the plateau implemented at the temperature T6a. Alternatively, the gas stream may comprise a reducing agent such as hydrogen or Ci-Cio hydrohalocarbons as defined above throughout step d), optionally mixed with an inert gas such as nitrogen. It has been observed that the use of a reducing agent such as hydrogen or Ci-Cio hydrohalocarbons as defined above during the temperature rise between the temperature T6a of said bearing and the temperature T5 represents an advantage. consequent in terms of productivity.

Preferably, step d) can be implemented with a quantity of reducing agent greater than 0.01 per gram of catalyst, preferably greater than 0.05 per gram of catalyst. In particular, step d) can be implemented with a quantity 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.

First and second aspects of the invention

As mentioned above, according to a first aspect, the present invention relates to a process for the production of trifluoroethylene. Said process is implemented in a reactor equipped with a catalytic bed comprising a catalyst. The method comprises a step of activating the catalyst (step i) according to any one of the embodiments (1) to (3)) and a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst, preferably activated, and in the gas phase to produce a stream comprising the trifluoroethylene (step b)).

As mentioned above, according to a second aspect, the present invention relates to a process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: a) a step of reacting chlorotrifluoroethylene with hydrogen carried out in the presence of the catalyst, in the gas phase and at a temperature of the catalytic bed T3 to produce a stream comprising the trifluoroethylene; b) a step for regenerating the catalyst used in step a); c) repeating steps a) and b) using the catalyst regenerated in step b). Preferably, in this aspect of the invention, the regeneration implemented in step b) is carried out at a temperature of the catalytic bed T4 of 90° C. to 300° C. in the presence of hydrogen.

According to a preferred embodiment, step a) is preceded by a catalyst activation step, preferably as described in step i) above according to any one of the embodiments (1) to (3).

Thus, preferably, the present invention provides a process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: a step of activating said catalyst, preferably according to any one of the modes of carrying out (1) to (3) of step i); a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the activated catalyst and in the gas phase to produce a stream comprising the trifluoroethylene (step ii) or a)); a stage of regeneration of the catalyst, preferably at a temperature of the catalytic bed T4 of 90° C. to 300° C. in the presence of hydrogen (stage b)); repeating the reaction and regeneration steps from the regenerated catalyst (step c)); optionally, a stage of heat treatment of the catalyst (stage d)).

Figures 1, 2, 2a and 2b illustrate particular embodiments of the present invention according to the first aspect or the second aspect of the present invention.

Fig. 1 schematically represents a device for carrying out a method according to the present invention during a hydrogenolysis reaction step. Reactor 3 comprises a catalytic bed 4 and is supplied with chlorotrifluoroethylene 2 and hydrogen 1 via valves 2b and 1b and lines 1a and 2a. In an embodiment in which the reaction between hydrogen and CTFE is carried out (step ii) of the first aspect of the invention or step a) of the second aspect of the invention), the valves 1b and 2b are configured to allow reactor 3 to be fed with CTFE 2 and hydrogen 1. The gases from the hydrogenolysis reaction (stream A) are evacuated from reactor 3 via line 3'. Valve 5 supplies via line 6 a device 7 for processing current A to remove acids such as HF or HCl. The treatment device 7 can be a column for washing with water or with soda or a combination of the two (first a wash with water then a wash with an alkaline solution such as soda) which makes it possible to limit the formation of salts. The residues of this aqueous or basic treatment are eliminated at 8. The stream B comprising the rest of the gaseous mixture feeds via line 9 a first purification device 10 aimed at separating the hydrogen and the inert gases from the organic compounds present in the stream. B. Prior to separation, stream B can be dried over a molecular sieve. The purification device 10 implements an absorption/desorption step in the presence of ethanol at atmospheric pressure and at a temperature below room temperature. Hydrogen and inert gases (if present) are recycled via line 12 to valve 1b and reactor 3. The organics are then recovered in the form of a gas mixture C, by heating ethanol to its d point. boiling (desorption). Stream C feeds a second purification device 13 via line 11. Device 13 is preferably a distillation column. The trifluoroethylene is recovered at the top of the distillation column 14. The other organic compounds including the CTFE are recovered at the bottom of the distillation column and form the mixture D. This feeds a third purification device 13a via line 15, preferably a distillation column, to recover the CTFE which is recycled to valve 2b and reactor 3 via line 15a. The other organic compounds separated from the CTFE are sent, for example, to an incinerator or impurity recovery device 14a.

Fig. 2 shows a device for implementing the present process during a catalyst activation or regeneration phase. The reactor 3 comprising a catalytic bed 4. In this particular embodiment, the catalytic bed is supplied with an inert gas (such as nitrogen) via the valve ld. The gases resulting from the regeneration or the activation are evacuated from the reactor 3 via the line 3'. The valve 5 transfers the regeneration or activation gases to an incinerator or a device for recovering them 16. The regeneration or activation gases can optionally be recycled after purification (washing with water and with a solution alkaline such as soda) and can be dried over a molecular sieve. For example, in the case of an activation step, the temperature of the catalytic bed 4 can increase from a temperature T1 to T1a. During the hold at the plateau Tla, the valve ld is closed and the valve lb is open to supply the reactor with hydrogen 1. The temperature of the catalytic bed 4 is then increased by a temperature Tla to T2. This is shown in Fig. 2a. Alternatively, during maintenance at the plateau Tla, the valve ld is closed and the valve 2b is open to supply the reactor with chlorotrifluoroethylene. The temperature of the catalytic bed 4 is then increased from a temperature Tla to T2. This is shown in Fig. 2b.

Third aspect of the invention

According to a preferred embodiment, said reaction step and said heat treatment step are implemented alternately in each of said two reactors.

According to a preferred embodiment, said heat treatment step is a catalyst activation step as described in step i) according to the first aspect of the present invention, or a catalyst regeneration step as described in l step b) according to the second aspect of the present invention or a heat treatment as described in step d) according to the second aspect of the present invention.

The reaction step of chlorotrifluoroethylene with hydrogen in this third aspect of the invention is equivalent to the reaction step described in step ii) of the first aspect of the invention or in step a) according to the second aspect of the invention.

The [Fig. 3] schematically represents a device comprising two reactors for implementing a method according to the third aspect of the invention. The device comprises two reactors 3a and 3b each comprising a catalytic bed 4a and 4b containing a catalyst. In the embodiment represented, the reactor 3a is in production mode, that is to say the reactor implements the hydrogenolysis reaction of the CTFE with hydrogen. The reactor 3b is in heat treatment mode, that is to say the reactor implements a catalyst activation step as described in step i) according to the first aspect of the present invention, or a catalyst regeneration step as described in step b) according to the second aspect of the present invention or a heat treatment as described in step d) according to the second aspect of the present invention. The reactor 3a comprises a catalytic bed 4a and is supplied with chlorotrifluoroethylene 2 and hydrogen 1 via valves 2b and 1a. Valves 1a and 2b are configured to allow reactor 3a to be fed with CTFE 2 and hydrogen 1. The gases resulting from the hydrogenolysis reaction (stream A) are evacuated from reactor 3a via line 3a'. Valve 5a feeds via line 6 a processing device 7 with current A to remove acids such as HF or HCL. Processing device 7 can be a water or sodium hydroxide washing column. The residues of this aqueous or basic treatment are eliminated at 8. The stream B comprising the rest of the gaseous mixture feeds via line 9 a first purification device 10 aimed at separating the hydrogen and the inert gases from the organic compounds present in the stream. B. Prior to the separation, stream B can be dried over a molecular sieve. The purification device 10 implements an absorption/desorption step in the presence of ethanol at atmospheric pressure and at a temperature below room temperature. The hydrogen and inert gases are recycled via line 12 to valve 1a and reactor 3a. The organics are then recovered in the form of a gas mixture C, by heating the ethanol to its boiling point (desorption). Stream C feeds a second purification device 13 via line 11. Device 13 is preferably a distillation column. The trifluoroethylene is recovered at the top of the distillation column 14. The other organic compounds including the CTFE are recovered at the bottom of the distillation column and form the mixture D. This feeds a third purification device 13a via line 15, preferably a distillation column, to recover the CTFE which is recycled to valve 2b and reactor 3a via line 15a. The other organic compounds separated from the CTFE are sent, for example, to the incinerator. Reactor 3b is supplied with hydrogen 1 via valve lb and/or with an inert gas le (for example nitrogen via valve ld. The supply of hydrogen 1 or inert gas le is easily regulated by the valves 1b and 1d to allow the implementation of the activation or regeneration steps The gaseous flow resulting from the heat treatment of the catalyst implemented in the reactor 3b is recovered via the line 3b' and sent via the valve 5b to an incinerator or recovery device 16.

If the heat treatment carried out is an activation according to step i) or according to a treatment according to step d), the reducing agent may for example be a hydrohalocarbon as defined in the present application. In this case, the reactor 3b is fed with reducing agent via the valve lf. This is shown in [Fig. 4], In this case, the valve lb is configured not to supply the reactor 3b with hydrogen ([Fig. 4]). Alternatively, if the hydrohalocarbon is CTFE, it can supply reactor 3b via valve 2b. The [Fig. 5] represents an embodiment in which the reactor 3b is in production mode, that is to say implements the hydrogenolysis reaction of the CTFE with hydrogen in the gas phase and in the presence of a catalyst as described in this application. Reactor 3b is therefore supplied with CTFE 2 via valve 2b and with hydrogen via valve 1b. In this case, reactor 3a is in catalyst heat treatment mode. The reactor 3a is in this particular embodiment supplied with hydrogen via the valve la and with an inert gas via the valve ld. The supply in each of the gases is regulated over time if necessary as explained in the present application. Thus, at the outlet of reactor 3b, the reaction gases (ie stream A) are sent to device 7 via line 3b' and line 6. Valve 5b is configured for this purpose. Current A is processed as described above. At the outlet of the reactor 3a, the gases are sent to the incinerator or a recovery device 16 via the valve 5a configured for this purpose.

Examples

Example 1

25 cm ³ of catalyst (0.2% palladium supported on alumina alpha). The catalyst thus charged was then activated in the following manner: the reaction tube was placed in a tube furnace and was fed with a flow of hydrogen (from 0.05 to 0.1 moles per gram of catalyst). The catalytic bed was then 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 ambient temperature then was insulated to then be installed on a hydrogenolysis test bench. The reactor was fed with 1 mol/h of CTFE and 1 mol/h of hydrogen. It is also possible to supply the reactors with an inert gas (here nitrogen). The catalyst bed temperature was between 100°C and 130°C. The contact time, calculated as being 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. After reaction and purification of the gases obtained at the reactor outlet, the trifluoroethylene productivity was 18 g/h.

Example 2 (comparative) Example 1 was reproduced with a temperature gradient of 0.7° C./min. After reaction and purification of the gases obtained at the reactor outlet, the trifluoroethylene productivity was less than 7.5 g/h.

Example 3: Regeneration according to the invention

The device of example 1 is used in this example. The catalyst was activated as in Example 1. The reactor was fed with 1 mole/h of CTFE and 1 mole/h of hydrogen. It is also possible to supply the reactors with an inert gas (here nitrogen). The catalyst bed temperature was between 100°C and 130°C. The contact time, calculated as being 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. The productivity was of the order of 18.5 g/h. After 100 h, the catalyst was regenerated under a flow of hydrogen (stopping the flow of CTFE) at a temperature of between 90° C. and 150° C. for 48 h. The reactor was then fed with 1 mole/h of CTFE and 1 mole/h of hydrogen. After reaction and purification of the gases obtained at the reactor outlet, the trifluoroethylene productivity was 25 g/h.

Claims

23 Claims

1. Process for producing trifluoroethylene in a reactor equipped with a catalytic bed comprising a catalyst, said process comprising: i) a step of activating said catalyst comprising bringing it into contact with a gas stream comprising a reducing agent, an inert gas or mixture thereof; and ii) a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step i) and in the gas phase to produce a stream comprising the trifluoroethylene; characterized in that during said step i) the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 greater than T1 with a temperature gradient of less than 0.5°C/min.

2. Method according to the preceding claim, characterized in that the temperature T1 is 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.

3. Process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: i) a step of activating said catalyst comprising bringing it into contact with a gas stream comprising a reducing agent, an inert gas or mixture thereof; and ii) a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step i) and in the gas phase to produce a stream comprising the trifluoroethylene; characterized in that during said step i) the temperature of the catalytic bed is increased from a temperature T1 to a temperature T2 greater than T1 in stages.

4. Method according to the preceding claim, characterized in that in step i), between two levels, the temperature is increased with a temperature gradient of less than 0.5° C./min.

5. Method according to any one of the preceding claims 3 or 4, characterized in that step i) comprises at least one stage at a temperature Tla of between 90 and 120°C.

6. Method according to any one of the preceding claims 3 to 5 characterized in that each level lasts between 5 min and 24 h, preferably between 30 min and lOh.

7. Process according to any one of the preceding claims, characterized in that the temperature T2 is between 150°C and 400°C.

8. Process according to any one of the preceding claims, characterized in that the reducing agent is selected from the group consisting of hydrogen, carbon monoxide, nitrogen monoxide, formaldehyde, Ci-C8 alkanes and C1-C10 hydrohalocarbons, or a mixture thereof; preferably from hydrogen and C 1 -C 10 hydrohalocarbons, or a mixture thereof; in particular from hydrogen, chlorotrifluoroethylene, trifluoroethane, trifluoroethylene, chlorotrifluoroethane or difluoroethane or a mixture thereof.

9. Process for producing trifluoroethylene in a reactor equipped with a catalytic bed comprising a catalyst, said process comprising: i) a step of activating said catalyst; and ii) a step of reacting chlorotrifluoroethylene with hydrogen in the presence of the catalyst activated according to step i) and in the gas phase to produce a stream comprising the trifluoroethylene; characterized in that said step i) comprises bringing said catalyst into contact with a gas stream comprising chlorotrifluoroethylene, and optionally hydrogen.

10. Process 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′ greater than T1′, preferably the temperature of the catalytic bed is increased from a temperature T1' to a temperature T2' greater than T1' with a temperature gradient of less than 0.5° C./min.

11. Method according to any one of claims 9 or 10 characterized in that the temperature of the catalytic bed is increased by increasing the calculated contact time as being the ratio between the volume, in liters, of catalyst and the total flow rate of said gas stream, in normal liters per second, at the inlet of the reactor.

12. Process according to any one of claims 9 to 11, characterized in that step ii) is carried out at a temperature T3 and the temperature T2′ is lower than the temperature T3 for carrying out step ii).

13. Process for producing trifluoroethylene in a reactor provided with a catalytic bed comprising a catalyst, said process comprising: a) a step of reacting chlorotrifluoroethylene with hydrogen implemented in the presence of the catalyst, in the gas phase and at a catalyst bed temperature T3 to produce a stream comprising the trifluoroethylene; b) a step for regenerating the catalyst used in step a); c) repeating steps a) and b) using the catalyst regenerated in step b). characterized in that step b) is carried out at a temperature of the catalytic bed T4 of 90°C to 300°C and in the presence of hydrogen, preferably at a temperature of the catalytic bed T4 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 temperature of the catalytic bed T4 from 90°C to 150°C.

14. Process according to the preceding claim, characterized in that the temperature difference AT between the temperature of the catalytic bed in stage a) and the temperature of the catalytic bed in stage b), AT = T3 - T4, is comprised, in absolute value, between 0 and 50, preferably between 0 and 20.

15. Process according to any one of claims 13 or 14, characterized in that step a) is preceded by a catalyst activation step, preferably as described in step i) according to any of claims 1 to 12.

16. Process according to any one of claims 13 to 15, characterized in that it also comprises a step d) of heat treatment of said catalyst at a temperature T5 greater than T4, preferably at a temperature T5 greater than 230° C., in particular at a temperature T5 above 250°C. 26

17. Process according to any one of the preceding claims, characterized in that the said catalyst is a catalyst based on a metal from columns 8 to 10 of the periodic table of the elements, preferably deposited on a support, in particular a support based of aluminium.

18. Process for producing trifluoroethylene in two reactors each comprising at least one catalytic bed comprising a catalyst, said process comprising: in a first reactor, a step of reacting chlorotrifluoroethylene with hydrogen implemented in the presence of the catalyst and in gas phase to produce a stream comprising the trifluoroethylene; in a second reactor, a heat treatment step of said catalyst.

19. Method according to the preceding claim, characterized in that said reaction step and said heat treatment step are carried out alternately in each of said two reactors.

20. Process according to any one of claims 18 or 19, characterized in that said heat treatment step is a catalyst activation step as described in step i) according to any one of claims 1 to 12 and 17, or a catalyst regeneration step as described in step b) according to any one of claims 13 to 15 and 17 or step d) according to claim 16 or 17.