Process and system for the production of gas and solid carbon by plasma pyrolysis of a hydrocarbon or a mixture of hydrocarbons

Abstract

A process for producing hydrogen and carbon by plasmalysis of a hydrocarbon or a mixture of hydrocarbons, involving a step of injecting this hydrocarbon or mixture of hydrocarbons in gaseous form into an active zone (30) of a reaction chamber (15) of a plasmalysis reactor (10) controlled to produce a plasma. This process includes a repetition of steps applied to the gas stream during its path between the inlet and outlet of the active zone (30), generating a plasma pulse for a pulsed duration until a target heating temperature is reached, maintaining an optimal activation regime of the heated plasma in the active zone (30) for a predetermined residence time, and cooling the resident plasma for a predetermined cooling time. See Figure 1

Description

Title of the invention: Process and system for the production of gas and solid carbon by plasma pyrolysis of a hydrocarbon or a mixture of hydrocarbons. FIELD OF THE INVENTION

[0001] The invention relates to the field of devices for the production of gas, and more particularly hydrogen, and solid carbon by hydrocarbon reforming. PRIOR TECHNOLOGY

[0002] Hydrocarbon reforming is commonly used to produce hydrogen on a large scale, often employed as a feedstock in the petrochemical industry and other industrial applications. For example, hydrogen is essential in the manufacture of products such as ammonia, methanol, and other chemical compounds, as well as in applications such as hydrogen as a clean fuel.

[0003] In a plasma pyrolysis process, also called plasmalysis, there is also production of solid carbon.

[0004] Although solid carbon extracted by reforming hydrocarbons is not in principle a desired product in this process because it is generally considered an undesirable by-product, it remains nonetheless that carbon black is a versatile material with high added value which finds various applications in different industries depending on the quality obtained (tires, polymers, inks and paints, batteries, catalysts, electronic applications, ...).

[0005] Carbon production is one of the aims of the invention.

[0006] However, the solid carbon that forms during reforming also causes operational problems by clogging catalysts and reactors, thus reducing the efficiency of the process. Therefore, reforming operations are generally designed to minimize the formation of solid carbon and prevent its accumulation.

[0007] In the state of the art, the methods of cleaning carbon or decoking are mainly of two types: mechanical cleaning of coke, chemical cleaning of coke.

[0008] The mechanical cleaning method for coke can consist of removing the coking material using a scraper or cleaning the coke by shock wave. For example, cleaning systems using hydraulic means such as high-pressure water jets or hydraulic sandblasting are widely used and make it possible to fracture the coke layer.

[0009] Oxidizing chemical cleaning by a superheated air-steam mixture, possibly with an addition of hydrogen, is also known.

[0010] But all these processes have the constraint of stopping the reactor due to decoking of the installation.

[0011] The overall reaction is CH4 => 2 H2 + C(s) if the input hydrocarbon is methane. The problem is to control carbon growth to prevent the formation of carbon bridges in undesirable locations, particularly between the two electrodes, which would cause a reactor short circuit and the cessation of plasmalysis. This control must be performed continuously while the installation is operating normally.

[0012] The pyrolysis reaction of methane CH4 → C(s) + 2 H2 allows the production of hydrogen without CO2 emissions since the carbon is produced in solid form (without oxidation). The formation of solid carbon is the desired outcome of the process; however, this carbon can form at the wrong time or in the wrong place, for example by depositing on the electrodes, which ultimately short-circuits the system and interrupts the operation: this is the carbon bridge.

[0013] Carbon deposition on the walls or electrodes is one of the major difficulties reported in the literature: "solid carbon or soot deposits on flow channel walls," for example in Fincke et al. [2]. This document suggests diluting the input methane by injecting hydrogen to reduce carbon formation, which is detrimental to energy efficiency.

[0014] Carbon bridges are frequently encountered in the academic literature. (Sun et al. 2016) [7] also reports problems with carbon bridges blocking the operation of a thermal plasma generated by a DC arc. In another DC arc system, (Li et al. 2017) [4] shows the phenomenon of growth on the electrode.

[0015] (Gao et al. 2018) [3] mentions coking problems characteristic of intermediate temperature (warm) plasmas, typically gliding arc, spark, microwave or RF. They use pulsed plasmas to limit this problem, but still encounter carbon deposition problems on the electrodes for certain geometries (gap of 8 to 10 mm).

[0016] (Maqueo, Coulombe, and Bergthorson 2019) demonstrates carbon growth on the anode of their NRP plasma system in a point / plane configuration.

[0017] (Delikonstantis et al. 2020) [1] mentions mechanical solutions and alternatively suggests using alternating air plasmas to enable decoking. This solution, which oxidizes carbon and thus eliminates the entire benefit of the pyrolysis process for decarbonizing hydrogen, is not acceptable here.

[0018] In microwave plasmas, carbon deposition in the chamber is also a problem that prevents continued operation. (Zherlitsyn, Shiyan, and Demchenko 2016) [8]. Carbon deposition on the walls makes them opaque to waves.

[0019] Finally, the problems of carbon bridges and carbon deposition have also been encountered by industry. Document WO2010037237Al [5] expressly mentions carbon bridges (Fig. 14, Fig. 15). Documents US9812295B1 and US10332726B2 mention carbon deposition on the chamber walls, typically quartz, which makes them opaque, reduces the power deposited in the plasma, and limits operating times.

[0020] This is therefore a known problem often overcome by interrupting the process or by diluting at the expense of process performance.

[0021] In thermal torch processes, the problem is circumvented by using a plasma gas primarily composed of a component other than hydrocarbons, preferably hydrogen, which is then mixed with hydrocarbons. This prevents carbon growth on the electrodes. However, the hydrocarbons are consequently diluted in an additional gas to be heated, which increases energy consumption and lowers energy efficiency. When the diluent gas is hydrogen, this also shifts the chemical equilibrium towards rehydrogenation of the products, which necessitates increasing the operating temperature compared to operation without hydrogen diluent, thus further increasing energy consumption. For example, in document WO 2015 / 116943

[0008] , it is mentioned that the plasma torch can be used with a plasma gas composed of at least 60% H2 by volume.

[0022] US20210245133 discloses a plasma-based hydrocarbon gas processing system for producing acetylene and hydrogen. This system primarily comprises: - a distribution subsystem consisting of a distribution conduit and a gas injector allowing the combination of the hydrocarbon-containing gas flow with a hydrogen-containing gas flow and an optional auxiliary gas flow, and which directs and disperses, by means of a nozzle arrangement, the different flows in directions and at speeds such that a vortex mixture of the three separate flows is produced in the plasma reaction chamber. - a tube-shaped plasma reaction chamber where gases are excited by microwave energy, - A microwave subsystem directing microwave energy into the plasma reaction chamber, - a cooling subsystem to protect the reactor tube against thermal stress, - a subsystem for separating gas mixtures using an adsorption process.

[0023] The maintenance measure recommended in this document is a periodic shutdown of the reactor to remove the accumulation of carbon soot either by manual cleaning or by using a cleaning gas.

[0024] US patent 10332726 discloses a microwave plasma-based device for chemically treating a hydrocarbon-containing gas, comprising a waveguide receiving two gas streams, a feed stream and a treatment stream. Plasma is generated in the feed gas, and its average energy is controlled by adjusting the pulse frequency to convert the treatment gas into separate components.

[0025] This microwave plasma-based device aims to enhance the efficiency of the coupling between microwave radiation and the gas flow within the reaction chamber in order to improve energy absorption by the circulating gas for better decomposition of gas molecules into constituent species. It is demonstrated that controlling the energy transmitted to the plasma by adjusting the pulse frequency, duty cycle, and pulse shape can be used to select specific reaction pathways for the creation of separate components from a treatment gas.

[0026] US patent 9812295B1 discloses a chemical treatment process employing pulsed microwave radiation through a waveguide, the microwave radiation propagating in one direction along the waveguide. The pressure inside the waveguide is at least 0.1 atmospheres. A feed gas is provided at a first location along a length of the waveguide, the majority of the feed gas flowing in the direction of microwave radiation propagation. A plasma is generated in the feed gas, and a process gas is added to the waveguide at a second location downstream of the first location. The majority of the process gas flows in the direction of microwave propagation at a velocity greater than 5 sim (standard liters per minute).An average plasma energy is controlled to convert the process gas into separate components, by controlling at least one pulse frequency of the pulsed microwave radiation and / or one duty cycle of the pulsed microwave radiation. To avoid carbon accumulation, which is considered a waste product in this document, a windowless device between the waveguide and the reaction chamber is proposed, thus increasing the volume where carbon can be deposited, a larger volume compared to similar devices in the prior art.

[0027] One object of the invention is to provide a technical solution that can prevent the formation of carbon bridges in a gas production process by plasma pyrolysis, and that can be carried out continuously while the installation is in normal operation (i.e., without stopping the reactor). The objective is therefore to avoid the formation of carbon bridges in undesirable places, particularly between the two electrodes, as such carbon bridges can cause a short circuit in the reactor and the cessation of pyrolysis. REFERENCES

[0028] 1. Delikonstantis, Evangelos, Marco Scapinello, Orelie Van Geenhoven, and Georgios D. Stefanidis. 2020. “Nanosecond Pulse Discharge-Driven Non-Oxidative Methane Coupling in a Plate-to-Plate Electrode Configuration Plasma Reactor.” Chemical Engineering Journal 380 (August): 122477. http s: / / doi. org / 10.1016 / j. cej.2019.122477. 2. Fincke, James R., RP Anderson, T. Hyde, R. Wright, R. Bewley, DC Haggard, and WD Swank. 2000. “SER Thermal Conversion of Methane to Acetylene Final Report.” Idaho National Engineering and Environmental Laboratory, no. January: 69. 3. Gao, Yuan, Shuai Zhang, Hao Sun, Ruixue Wang, Xin Tu, and Tao Shao. 2018. “Highly Efficient Conversion of Methane Using Microsecond and Nanosecond Pulsed Spark Discharges.” Applied Energy 226 (September): 534-45. https: / / doi.Org / 10.1016 / j.apenergy.2018.06.006. 4. Li, Tianyang, Christophe Rehmet, Yan Cheng, Yong Jin, and Yi Cheng. 2017. “Experimental Comparison of Methane Pyrolysis in Thermal Plasma.” Plasma Chemistry and Plasma Processing 37 (4): 1033-49. https: / / doi.org / 10.1007 / sll090-017-9806-x. 5. Liu, Zhuomin, Thomas Whidden, Tobie Boutot, and Yun Yang. 2008. Apparatus and Method for Effecting Plasma-Based Reactions. W02010037237A1_I, issued 2008. 6. Maqueo, P. D.G. G, S. Coulombe, and J. M. Bergthorson. 2019. “Energy Efficiency of a Nanosecond Repetitively Pulsed Discharge for Methane Reforming.” Journal of Physics D: Applied Physics 52 (27): 274002. https: / / doi.org / 10.1088 / 1361-6463 / abl99b. 7. Sun, DL, F. Wang, RY Hong, and CR Xie. 2016. “Preparation of Carbon Black via Arc Discharge Plasma Enhanced by Thermal Pyrolysis.” Diamond and Related Materials 61 (January): 21-31. https: / / doi.org / 10.1016 / j.diamond.2015.11.004. 8. Zherlitsyn, Alex G., Vladimir P. Shiyan, and Paul V. Demchenko. 2016. “Microwave Plasma Torch for Processing Hydrocarbon Gases.” Resource-Efficient Technologies 2 (1): 11-14. https: / / doi.Org / 10.1016 / j.reffi t.2016.04.001. Description of the invention

[0029] This objective is achieved with a process for producing hydrogen and carbon by plasmalysis of a hydrocarbon or a mixture of hydrocarbons, implementing a step of injecting this hydrocarbon or mixture of hydrocarbons in gaseous form into the active zone of a reaction chamber within a reactor controlled to produce a plasma, characterized in that it comprises a repetition of the following steps: - production of a plasma pulse (El) for a pulse duration until a target heating temperature is reached, - maintaining an optimal activation regime (E2) of the heated plasma in the active zone of the reaction chamber, for a predetermined residence time, - cooling (E3) of the resident plasma in the active zone of the reaction chamber for a predetermined cooling time.

[0030] The residence time, or duration of residence, is the time during which the volume of gas to be treated is exposed to the plasma. This time affects the rate of chemical reactions: a longer residence time can allow for more complete reactions, while a shorter residence time can prevent the decomposition or dissociation of certain products and inhibit certain recombinations.

[0031] The active zone of the reaction chamber of the reactor is the volume of gas treated by the plasma in the space between the electrodes of the reactor.

[0032] The optimal activation regime is defined as the moment when the plasma reaches stable conditions to maximize interactions with the treated gas.

[0033] It should be noted that the production process according to the invention is designed to treat both pure and diluted hydrocarbons. The gas stream entering a reactor is composed mainly of hydrocarbons, i.e., the gas stream is composed of more than 50% hydrocarbons, but a dilution gas can be introduced at 10%, 20%, 30%, or even 40%. This dilution gas can be H2, or non-combustible gases such as nitrogen, argon, or helium.

[0034] The hydrocarbon gas flow can be injected into an active zone of a reaction chamber of a plasmalysis reactor comprising electrodes whose power supply is controlled to generate a pulsed plasma in the active zone of the reaction chamber, and the step of cooling the plasma for a cooling time, can be triggered by interrupting the power supply to the electrodes for a predetermined interruption time.

[0035] The hydrocarbon gas flow passing through the active zone of the reaction chamber of the plasmalysis reactor can undergo a progressive increase in temperature on its path between the inlet and outlet of the active zone.

[0036] The hydrocarbon gas stream injected into the active zone of the reaction chamber of the plasmalysis reactor can be a methane gas stream, said active zone being the site of a series of reactions (R1-R4) of respective dissociations of the injected methane, ethane, ethylene, and acetylene, and the cooling step is triggered before the initiation of the (R4) decomposition step of acetylene, for a predetermined cooling time.

[0037] The repetition N of steps (E1, E2, E3) applied to the gas flow during its path between the inlet and outlet of the active zone can stop when the initiation of step (R4) coincides with the ejection of the gas flow from the active zone. Preferably, the repetition N of steps (E1, E2, E3) is periodic.

[0038] In a particular embodiment of the invention, the production process may further comprise: - a step to preheat the gas injected into the plasmalysis reactor (10) until it reaches a plasma temperature within a target heating temperature range, so that the first three dissociation reactions (RI, R2, R3) are initiated and triggered, - a plasma interruption step by controlling the electrodes (13,14) for a predetermined interruption time such that the first three dissociation reactions are sufficiently advanced and the acetylene dissociation step (R4) is not completely initiated, - a plasma cooling step until a plasma temperature is reached within a target cooling temperature range, followed by a return to the preheating step.

[0039] Cooling occurs during the interruption period during which the plasma no longer receives energy to maintain its temperature.

[0040] Cooling is achieved during this same period by heat diffusion, advection of fresh gas, or by radiative exchange of the plasma with the walls of the reactor.

[0041] The cooling time is equivalent to the plasma interruption time.

[0042] The target heating temperature range is preferably within the range [1500 - 3000 K], it can advantageously be within the range [1800 K-2000 K].

[0043] The target cooling temperature range is preferably within the range [1000 K - 1500 K]. When the catalytic effect of the plasma, i.e. the cumulative effect of the energetic excitation of methane molecules, the formation of reactive species, the localized temperature effect, and the non-equilibrium Thermodynamics, triggers the first dissociation reaction of methane; the process may further include the following steps: - a step to control the supply of energy to the electrodes (13,14) so ​​that the energy input from the plasma leads to a plasma temperature such that the second and third dissociation reactions are faster than the dissociation reaction of acetylene, - a plasma interruption step by controlling the supply of the electrodes (13,14) for a predetermined interruption time, before initiation of the acetylene dissociation step (R4), - a plasma cooling stage until a temperature is reached plasma within a target cooling temperature range, followed by a return to the preheating stage, followed by a return to the control stage.

[0044] The predetermined interruption time can be between 1Ops and 100 ps.

[0045] The inlet gas stream may further include a methane dilution gas.

[0046] The dilution gas can be chosen from dihydrogen H2, Argon or helium He.

[0047] According to another aspect of the invention, a production system is proposed of hydrogen and carbon by plasmalysis of a hydrocarbon or a mixture of hydrocarbons, comprising a reactor having a reaction chamber including an active zone and provided for receiving an incoming gas stream of this hydrocarbon or mixture of hydrocarbons, a pair of electrodes supplied by a pulse generator controlled by control means, piping means provided for channeling the flow of the incoming gas stream towards the active zone and for ejecting the products of the plasmalysis from the active zone, implementing the production process according to the invention.

[0048] According to the invention, the control means are programmed to generate a pulsed plasma in the active area of ​​the reaction chamber and in that the channeling means are arranged to avoid stationarity of the gaseous products from plasmalysis on the surface of the electrodes.

[0049] The electrodes can be arranged to produce a homogeneous electric field over the active area (30).

[0050] The channeling means may advantageously include a nozzle arranged to provide a secondary flow of a gaseous stream distinct from that of incoming hydrocarbon subjected to plasmalysis, in the vicinity of the electrodes.

[0051] The nozzle can be made of an electrically conductive material and has a floating electrical potential with respect to either of the electrodes so as to constitute a relay for plasma discharges between said electrodes.

[0052] In a first configuration of an electrode-nozzle system implemented In the invention, the nozzle is designed to surround a first electrode so as to channel the incoming gas flow between said first electrode and the inner wall of said nozzle, said nozzle comprising at its end opposite said first electrode an opening provided to allow said channeled gas flow to pass through.

[0053] In this first configuration, the nozzle can also have an hourglass shape comprising a first flared nozzle part surrounding a first electrode and a second flared nozzle part surrounding the second electrode within the reaction chamber, said first and second nozzle parts being connected by a conduit arranged to constitute a first active zone for the gas flow.

[0054] In a second configuration of the electrode-nozzle system, the nozzle comprises a frustoconical cylinder interposed between a first electrode of substantially conical shape and a second hollow electrode of substantially frustoconical shape, said frustoconical cylinder forming the nozzle comprising: - a first opening opposite said first electrode and separated from the first electrode by a first electrically insulating element having a central opening with a diameter greater than that of the interface end of said first electrode, so as to provide an annular gap to allow a channeled gas flow to pass along the external surface of said first electrode, - a second opening separated from an open end of said second electrode by a second electrically insulating element having a central opening of diameter substantially equal to that of the interface end of said second electrode, so as to channel the gas flow exiting the nozzle inside said second electrode.

[0055] In this second configuration, the nozzle can advantageously have a convergent shape from the first insulating element to the second insulating element.

[0056] The control means of the production system according to the invention can be programmed to produce a pulsed plasma at a frequency between 1 kHz and 1 MHz.

[0057] It can also be provided that the control means are programmed to produce a pulsed plasma with a pulse duration of less than 100 ns for a gas pressure between 100 mbar and 1 bar, less than 1 ps for a gas pressure between 10 mbar and 100 mbar, and less than 10 ps for a gas pressure less than 10 mbar.

[0058] The plasma control means may also be provided for: - produce a plasma pulse (1) for a pulse duration until a target heating temperature is reached, - to maintain this heated plasma fully active in the active zone (30) of the reactive chamber (15) of the reactor (10), for a predetermined residence time, - cool (3) the resident plasma for a predetermined cooling time.

[0059] When the production system according to the invention is implemented for the production of solid carbon and dihydrogen from methane, the active zone of the reaction chamber of the reactor being the site of a series of reactions (R1-R4) of respective dissociation of injected methane, ethane, ethylene, and acetylene, the control means are programmed to interrupt the plasma before the (R4) acetylene dissociation step, for a predetermined interruption time.

[0060] The production system according to the invention may then include means for preheating the gas injected into the plasmalysis reactor until it reaches a plasma temperature within a target heating temperature range, so that the first three dissociation reactions are initiated and triggered.

[0061] The control means can be programmed to control the supply of the electrodes so that the energy input from the plasma leads to a plasma temperature such that the second and third dissociation reactions are faster than the dissociation reaction of acetylene.

[0062] The control means may be provided to provide in operation a modulation of the plasma pulse frequency and / or a modulation of the voltage applied to the electrodes.

[0063] The predetermined interruption time can be between 1Ops and 100 ps.

[0064] The electrodes are preferably arranged to produce an electric field homogeneous over the active area.

[0065] For channeling gas flows in a production system according to the invention, two types of piping are available, each with different functions: - One of them is responsible for bringing the gas into the active zone, - The other's function is to extract the treated gas from the active zone.

[0066] The channels used may be: - A channel defined by a solid profile, - A channel channeled by a gas flow.

[0067] In a particular configuration of the production system according to the invention, the channel channeled by a solid profile is the incoming piping channel and includes a single-flow nozzle bringing the gas into the active zone.

[0068] In another particular configuration of the production system according to the invention, the channel formed by a solid profile is the incoming channel and comprises a dual-flow type nozzle bringing the gas into the active zone and arranged to provide a secondary gas flow close to the electrodes.

[0069] With the plasma pulse technique implemented in the present invention, it is now possible to overcome the thermal runaway mechanism observed in prior art processes: a plasma with a high power density becomes resistive due to the high electron density and therefore heats up by Joule heating. This heating reduces the gas density and facilitates ionization, which further increases the electron density. The temperature rises sharply over very short periods. At atmospheric pressure, the temperature increase can occur in a few nanoseconds. Cooling on these timescales is not possible, and it is therefore necessary to interrupt the energy supply, thus drawing on the plasma to control the temperature increase. This means ceasing the energy supply during the interval between pulses so that the plasma no longer receives energy to maintain its high temperature.

[0070] The principle of the invention is thus to shift the growth phase of solid carbon, both temporally and spatially, downstream of the active plasma zone. This is achieved by drawing on sufficiently short durations so that, in a pulse, the threshold temperatures for carbon nucleation and growth are not exceeded.

[0071] The production process according to the invention also makes it possible to avoid the effects of pulse-to-pulse heat accumulation: - with an electrode geometry designed to produce a homogeneous electric field over a large volume, distributing the plasma filaments in space and thus avoiding local temperature concentration effects. - With a mechanical flow control element preventing any stationary zone, i.e. a zone of product stagnation and a gradual increase in temperature.

[0072] The process for producing solid carbon and dihydrogen according to the invention provides the following advantages: - No short circuits or premature interruptions of plasmalysis, - Guaranteed continuous operation over long periods, - Increased energy efficiency because there is no dilution with other gases. - Usable generation of carbon product in solid form, - simplicity of use, no active or mechanical component to prevent the growth of carbon bridges.

[0073] Volume production of carbon in the gas is acceptable, but production on the surface of the electrodes is not. The production process according to the invention makes it possible to produce carbon in volume while avoiding the production of this Carbon production occurs on the surface of the electrodes. Carbon production makes sense in the invention: it is one of the objectives sought by the device.

[0074] It is therefore necessary to adjust several parameters: - find the temperature range that allows carbon production to begin while also promoting H2 production, - distribute the hot zones to avoid thermal accumulation that would create carbon and prevent a runaway mechanism, - eliminate stationary areas of the flow, - expose the gas sufficiently so that the first three reactions are triggered but reduce the residence time relative to the carbon growth time. DESCRIPTION OF THE FIGURES

[0075] [Fig. 1] The [Fig. 1] is a synoptic diagram of a first example of the realization of a system for the production of solid carbon and dihydrogen according to the invention;

[0076] [Fig.2] Fig.2 is a block diagram of a second example of an embodiment of a solid carbon and dihydrogen production system according to the invention;

[0077] [Fig.3] Fig.3 is a diagram representing the variation of constants of reaction as a function of temperature for the main reactions implemented in the production process according to the invention;

[0078] [Fig.4] Fig.4 represents in a synthetic way the reaction processes put in work in the production process according to the invention;

[0079] [Fig.5] Fig.5 represents a first configuration of an electrode system nozzle implemented in a combustion reactor according to the invention, in a cross-sectional view (5A) and in a partial perspective view (5B);

[0080] [Fig.6] Fig.6 illustrates, on the views of Fig.5, the path of the gas flow and the examples of arcs produced between the electrodes and the nozzle;

[0081] [Fig.7] Figure [Fig.7] represents a second configuration of an electrode system nozzle implemented in a combustion reactor according to the invention, in a partial perspective view (7A) and in a cross-sectional view (7B);

[0082] [Fig.8] Fig.8 illustrates on the views of Fig.7 the path of the gas flow and examples of arcs produced between the electrodes and the nozzle;

[0083] [Fig.9] The [Fig.9] represent several possibilities (9A-9D) for generating the impulses, depending on the local parameters of the reactor;

[0084] [Fig. 10] The [Fig. 10] is a diagram representing a relationship between production time and temperature, to cause a shift in the growth phase of carbon, temporally and spatially, downstream of the plasma zone;

[0085] [Fig. 11] [Fig. 11] illustrates an example of control pulses with a pulse repetition frequency between 10 and 100 kHz. DETAILED DESCRIPTION

[0086] A system 1 for the production of dihydrogen gas and solid carbon by plasma pyrolysis according to the invention comprises, with reference to [Fig. 1], a hydrocarbon source, for example methane 2, a plasma reactor 10 receiving via an inlet 3 this gas and producing at the outlet solid carbon stored in a chamber 5 connected via a collection conduit 4 downstream of the reactor 10 and dihydrogen gas in a storage unit 7 connected via an outlet conduit 6 downstream of the reactor 10.

[0087] The hydrocarbon treated by the production system according to the invention can be supplied pure or in the form of hydrocarbon mixtures or even in a diluted form with a minor dilution gas i.e. in a proportion of less than 50%.

[0088] The reactor 10 includes a first stage 11 for heating the incoming hydrocarbon gas, leading to an active zone 30 of a reaction chamber 15 of the reactor 10 comprising a pair of electrodes 13, 14, one of the electrodes 13 being surrounded by a pipe nozzle 12. In the following, the terms reaction chamber and reactor may be used interchangeably.

[0089] The electrodes 13,14 of the plasma reactor 10 have a geometry arranged to prevent any stationary zone, by distributing the discharges spatially so as to have a homogeneous electric field.

[0090] In a second embodiment illustrated by [Fig.2], for which components identical to those of [Fig.1] have identical references, the production system 1' comprises two reactors 10 coupled in parallel supplied with methane gas from a common feed unit 2 and whose respective outlets of H2 and solid carbon lead to a hot column 23 leading to a heat exchanger 24 intended to recover some of the heat to preheat the methane from a methane storage unit 25 and leads to the feed unit 2. The mixture of dihydrogen and solid carbon passing through the exchanger 24 is led to a separation unit 26 having on the one hand a gas outlet 4 connected to the inlet of a dihydrogen storage unit 7 and on the other hand an outlet connected to a solid carbon recovery unit 5.

[0091] The two reactors 10 each comprise a first heating stage 11 and a reaction chamber 15 comprising a pair of electrodes 13,14.

[0092] The gas and solid carbon production system 1' according to the invention comprises a control device for the two reactors 10, including a unit 20 designed to control, on the one hand, a heating control device 21 and, on the other hand, a high-voltage power supply device 22 for each pair of electrodes. These two The respective heating control and high-voltage power supply devices 21, 22 are respectively supplied with electrical energy 23.

[0093] This second configuration is particularly suitable for the realization of industrial equipment, with an installation of a plurality of containers arranged one on top of the other with a set of cells working in parallel and managed in a fully automatic way.

[0094] An industrial installation may for example provide for the installation of the cells in a production system according to the invention, in which the cells inject their gas into the hot column 23 where the R4 reaction of acetylene decomposition can continue, followed by the heat exchanger 24 to cool the temperature of the outlet gases and preheat the gas mainly composed of hydrocarbons to be reformed 25, and where the hydrogen and carbon products are separated by a gas-solid separation unit 26. Electrode geometry

[0095] The geometry of the electrodes plays an important role in preventing the formation of carbon bridges. A cone-shaped or pointed geometry for both electrodes promotes carbon bridging and should therefore be avoided. An asymmetrical geometry, and more specifically a concave geometry for one of the two electrodes, allows for a spatial distribution of the discharges.

[0096] The placement of a solid profile between the two electrodes, channeling the incoming gas flow and passing it through a bottleneck, improves the desired technical effect by avoiding any point of contact between the two electrodes.

[0097] Several geometries, which will be described later, allow the inclusion of a secondary flow to prevent the formation of stationary zones.

[0098] It is observed that the carbon bridges (junctions) form outside the main flow. It is also observed that secondary injection allows the growth point to be moved outside the nozzle edges, which are bathed by the secondary flow.

[0099] The main flow is channeled by a secondary flow, avoiding any recirculation zone. The main flow is channeled by a mechanical part, avoiding any recirculation zone.

[0100] It should be noted that the incoming gas to be treated may experience turbulence and possess stationary zones. This has no impact because, since the gas has not been treated, it is not at risk of producing carbon. On the other hand, at the outlet of the active zone, the treated gas is ready to produce carbon and no stationary zone exists.

[0101] A flow tube or directed gas flow can be obtained either by means of a double flow nozzle or by means of an external flow.

[0102] The geometries of the electrodes can be different. They have in common that they have rotational symmetry but one can be a solid cone, while the other can be an open (or hollow) cone.

[0103] The plasma pyrolysis gas production process according to the invention implements a temporal and spatial shift in the growth phase of solid carbon downstream of the plasma zone. In the chain reactions triggered by pyrolysis, there are, with reference to [Fig. 3], four main recombinations:

[0104] RL 2CH4 H2+ C2H6 (ethane)

[0105] R2. H2 + C2H4 (ethylene)

[0106] R3. C2H4 H2+ C2H2(acetylene)

[0107] R4. CH2C + H2

[0108] The objective is to slow down or delay carbon growth in reaction R4, i.e., during the decomposition of acetylene in the active region. The amount of energy supplied to the plasma must be modulated over time to channel and select the reaction pathways, favoring reactions RI, R2, and R3 and delaying, or even preventing, the initiation of R4.

[0109] The production process according to the invention is inherently an iterative process, as shown in [Fig. 4]. Each gas molecule is subjected to a pulse from 1 to N times as it passes through the active zone of the reactor. This number N corresponds to the number of pulses of pulse duration t and can be between 1 and 1000, depending on the pulse frequency f, the length L of the distance between the two electrodes, and the velocity V of the gas flow through the active zone. During the time it takes for the gas molecule to travel from the inlet to the outlet of the active zone, multiple chemical dissociations and recombinations occur, and the temperature of the product of these various chemical reactions (hydrocarbon radicals, ionized particles, and other chemical combinations) increases non-linearly as they progress toward the outlet of the active zone.

[0110] It is the combination of the five main parameters, namely the distance L between the two electrodes, the velocity V of the flux, the number N of pulses, the pulse duration t (or the duty cycle) and the frequency of the pulses, that will make it possible to obtain the desired technical effect.

[0111] On the synthesis illustrated by [Fig.4], this means that the gas molecule which enters the active zone will undergo an iterative process of N pulses during its journey between the entry and exit of the active zone.

[0112] When the CH4 hydrocarbon molecule enters the active zone 30 at a temperature To, it undergoes a first impulse for a pulse duration t. This impulse contributes to dissociating and recombining the CH4 molecule into first by-products (hydrocarbon radicals) and increases the temperature of the molecules resulting from this first dissociation / recombination (RI to R3 reactions) to a temperature which will rise throughout the duration of the pulse then fall back down (inter-pulse cooling) and stabilize at a temperature Ti greater than To.

[0113] When the products resulting from the first dissociation / recombination undergo the second pulse, a new dissociation / recombination (RI to R3 reactions) will occur, and the temperature of the products from these new reactions will rise throughout the pulse duration, then fall (inter-pulse cooling) and stabilize at a temperature T2 higher than Th

[0114] Throughout this iterative process, the gas molecules move from the inlet to the outlet of the active zone.

[0115] When the products that have undergone N pulses have reached a temperature TN and arrive at the exit threshold of the active zone, there is no longer any interpulse cooling because it is at this precise moment that the products from the Nth plasma discharge are expelled from the active zone. This temperature TN is the temperature that initiates the R4 reaction of acetylene dissociation.

[0116] The temperature of the products exiting the active zone continues to rise, and reaction R4 continues outside the plasma zone. This is a self-sustaining exothermic reaction. Acetylene (C2H2) decomposes thermally to produce carbon black (C) and hydrogen (H2).

[0117] The production process according to the invention is therefore a process of N iterations applied to the CH4 hydrocarbon gas during its passage between the inlet and outlet of the active zone of the reaction chamber, consisting of a three-step sequence: a step to produce a plasma pulse, a step to maintain the heated plasma in an optimal activation regime for the duration of the pulse during which certain gas dissociations / recombinations occur, a step to cool the plasma for a plasma interruption time, followed by ejection of the gas from the active zone at the Nth iteration when the R4 reaction of acetylene decomposition is initiated. The cooling time is equivalent to the plasma interruption time.

[0118] Design of gas nozzles to avoid the formation of carbon bridges

[0119] The gas nozzles are designed to interact with the electrodes in such a way as to avoid Gas recirculation, and therefore the presence of carbon bridge precursors in a location conducive to carbon bridge formation, is a key feature. Furthermore, a geometric constraint has been added to the nozzle to prevent unwanted discharges and contamination of the solid carbon by the nozzle metal.

[0120] It is observed that carbon bridges grow from a stationary zone, sheltered from the flow. A second gas injection, coaxial with the torch, is designed to eliminate the stationary zones. In the case of heterogeneous staged injection, the gas is different from the gas to be reformed. In the present case, homogeneous staged injection is chosen, that is to say, a gas identical to the gas to be reformed is used, therefore pure CH4.

[0121] In a first configuration of an electrode-nozzle system 5 illustrated by Figures 5 and 6, two first and second electrodes 51, 52, of hollow frustoconical shape, are arranged opposite each other. The first electrode 51 is surrounded by a nozzle 50 which has an end opening 53 machined to have a substantially concave shape, this end opening 53 being interposed between the first and second electrodes 51, 52.

[0122] The specific concave shape of the nozzle interposed between the two electrodes has the remarkable technical effect of allowing a recirculation of the incoming flow, namely that no channel is privileged.

[0123] In operation, with reference to Figure 6A, a gas flow 6 is injected between the outer wall of the first electrode 51 and the inner wall of the nozzle 50, passes through the end opening 53 and then flows along the outer wall of the second electrode 52. The use of a lateral gas flow prevents the creation of any stationary zone from the central flow.

[0124] The nozzle has a floating electrical potential and acts as a relay by redistributing the flux. This nozzle, which redistributes the received gas flux, can be defined as a neutrode in the sense of plasma physics. Its concave portion, interposed between the two electrodes, constitutes an arc foot as the attachment zone for electric arcs.

[0125] The nozzle 50 thus acts as a neutrode and electric arcs 61 are established successively between the first electrode 51 and the neutrode nozzle 50, while other electric arcs 62.1,62.2,62.3 are established successively between the neutrode nozzle 50 and the second electrode 52.

[0126] This gives us the desired technical effect of non-stationarity of the gas within the active zone.

[0127] Other nozzle configurations with primary and secondary flow control can be considered. The inter-electrode space includes an active zone receiving the gas to be treated, which is channeled by a solid profile. Downstream of this active zone is a carbon production zone surrounded by a gas flow channeling the treated gas exiting the active zone.

[0128] The material used for the production of a nozzle must be electrically conductive, by way of non-limiting example, copper or graphite.

[0129] In a particular embodiment, the electrodes may have a conical shape.

[0130] Alternatively, a solid, hourglass-shaped profile can be considered for the nozzle, composed of two inverted cones connected by a thin cylinder, which is positioned inside the reaction chamber midway between the two electrodes. The constricted central section, or bottleneck, encloses the active zone in its middle. This profile allows for better flow control by creating a Venturi effect that influences the forces within the flow in such a way as to prevent the formation of stationary zones in the active zone.

[0131] In a second configuration of an electrode-nozzle system 7 illustrated in Figures 7 and 8, the two electrodes 71, 72 are asymmetrical: a first electrode 71 has a conical shape designed to allow gas to flow along its external surface, while a second electrode 72, coaxial with the first electrode 71, has a hollow frustoconical shape. The electrode-nozzle system 7 further comprises, between the first and second electrodes 71, 72: - a first electrically insulating element 73, of annular shape surrounding the outlet end of the first electrode 71 while leaving an annular gap 75 intended to allow the passage of a gas flow, - a truncated conical nozzle 70 extending from the first insulating element 73, this nozzle acting as a neutrode and designed to receive, via its large diameter opening, the gas flow exiting the annular gap 75, - a second electrically insulating element 74, of annular shape, the internal opening of which has a first surface on which the small diameter opening of the nozzle 70 is fixed and a second surface on which the small diameter opening of the second electrode 72 is fixed.

[0132] In this electrode-nozzle system 7 in operation, with reference to [Fig.8], a gas flow 6 is injected along the external surface of the first electrode 71. This gas flow passes through the gap 75 of the first insulating element 73, crosses the interior of the neutrode nozzle 70, passes through the opening of the second insulating element 74 and then enters the second hollow electrode 72 via its small diameter opening. Electric arcs 61 are created successively between the first electrode 71 and the neutrode nozzle 70 and other arcs are created successively between the neutrode nozzle 70 and the second electrode 72.A first active zone 81 covers the region between the first and second electrodes 71,72 while three other active zones 82, sites of the reactions indicated in [Fig.3], are generally located inside the second electrode 72, in the vicinity of its small diameter opening fixed to the second insulating annular element 74. Carbon growth control method

[0133] We will now describe an example of the implementation of a process for controlling carbon growth.

[0134] Use of a nanosecond pulsed plasma (pulse duration < 10 ns)

[0135] When using a pulsed plasma, short plasma times (or residence times, i.e., the time during which the volume of gas to be treated is exposed to the plasma) are used to increase the pulse power in order to maintain a constant average power over time, and short off-plasma times are used to limit the recombination of H atoms. Furthermore, a faster power-up time induces a faster propagation velocity of the plasma plume, allowing the formation of a higher electric field and increased radical formation efficiency. Consequently, pulsed systems crack methane into hydrogen and other hydrocarbon radicals more efficiently than continuous-wave systems. The type of plasma generated is described as non-thermal at atmospheric pressure.

[0136] Pulsed plasma offers many advantages: - The residence time of the gas in the plasma is less than the characteristic time of production of solid carbon (reaction R4). - Thanks to electron impact dissociations, the rate of dissociation of methane molecules (reaction 1) is faster than that of the carbon production reaction (reaction 4), including at low temperature ([Fig.3]). The impulsive nature of the plasma acts as a low-pass filter at the thermal level, causing an uneven distribution of energy transfer: a large amount of energy is received by the electrons in a very short time, and their temperature therefore increases exponentially. The residual energy is absorbed by the gas, but over a longer period, and the average temperature of the gas increases only linearly.

[0137] In other words, the strong electric field used allows for selectivity that limits heating: there is a strong transfer of energy from electrons to the electronic excitation and vibration modes of the molecules rather than to the translational modes responsible for heating the gas

[0138] These characteristics allow a time lag between the production of solid carbon and the dissociation of gas molecules. Distribution of landfills

[0139] The discharges must be spatially distributed over a wide area to avoid a sharp local temperature increase and the accumulation of precursors responsible for the production of solid carbon. A changing redistribution with each pulse prevents localized carbon distribution in a single location and immediate fouling that could cause a short circuit.

[0140] Several 9A-9D plasma pulse control waveforms can be envisaged, as illustrated in [Fig.9].

[0141] Pulsed plasma offers an advantage in this regard: - With each pulse, the initiation creates a shock wave which induces its own flow dynamics, and redistributes the reaction products in space. - The reaction products are also rapidly cooled by mixing with the ambient gas. 1. Control of average energy in the plasma

[0142] The average plasma energy must be controlled to improve energy absorption by the gas and to select the reaction pathways that best convert the gas into separate components. Indeed, radical production is directly related to the pulse power density and its associated plasma energy, which control the gas temperature and thermal dissociation.

[0143] To control the average energy in the plasma, it is necessary to control the duration and frequency of the radiation pulse of the wave, its duty cycle, i.e., the ratio between the period during which the pulsed radiation is activated and the period during which the pulsed radiation is deactivated, its shape, and the average output of the energy level over time. It is necessary to ensure that the following formula is respected:

[0144] “XL “Chemical Carbon Lamps

[0145] Where f = frequency, t = pulse duration, V = flow velocity, L = distance between the 2 electrodes

[0146] r is the characteristic time of the carbon (R4) formation reaction.

[0147] Depending on the local parameters of the reactor, there exists, with reference to [Fig.7], several possibilities for generating pulses.

[0148] The pulsed wave radiation capable of controlling plasma generation has a power level that also depends on the voltage level. Depending on the available voltage, the duty cycle differs: From 5kV to 10kV ON / OFF < 20% From 10kV to 15kV ON / OFF < 50% From 15kV to 50kV ON / OFF < 90%

[0149] To induce a shift in the carbon growth phase, temporally and spatially, downstream of the plasma zone, the following procedure can be used, with reference to [Fig.10]:

[0150] [Procedure 1: Local warm-up] - The gas is heated to 2000 K < T < 3500 K, - the reactions (RI) to (R3) are initiated and triggered, - The plasma is interrupted before (R4) for a time between 10 ps and 100 ps, - The gas is cooled to 1000 K < T < 1500 K to return to zone I - Then we start again.

[0151] Or [Procedure 2] - The gas is not preheated - The reaction (RI) is carried out thanks to the catalytic effect of the plasma - The energy input from the plasma is controlled so that the temperature, following the application of the plasma, places the gas in a zone where reactions (R2) and (R3) are faster than reaction (R4); i.e., a temperature T > -1200 K - The plasma is interrupted before (R4) for a time between 10 ps and 100 ps - Then we start again

[0152] The pulse width is between 1ns and 100ns. The pulse frequency must be between 10 MHz and 1 GHz, preferably around 100 MHz (10 ns width).

[0153] The pulse repetition frequency is between 10 and 100 kHz (every 10 to 100 ps), with reference to [Fig. 10].

[0154] Using short pulse durations prevents exceeding the threshold temperatures for carbon nucleation and growth. Since the repetition frequency is high, it is also necessary to control the heat accumulation pulse by pulse, which requires controlling the interpulse cooling.

[0155] Several examples are given and the recommended radiation source is configured to activate and deactivate pulsed radiation at a frequency between 500 Hz and 1000 kHz and with a duty cycle of less than 90%.

[0156] In most prior art plasmalysis devices, high pressure is used because it allows for greater efficiency. In contrast, low-pressure reactions allow for greater selectivity. Here, in the production process according to the invention, the reaction takes place at atmospheric pressure.

[0157] The ideal pressure can be considered to be between 100 mbars and 2 bars absolute. Extension of operating times

[0158] The combined hydrogen and carbon production process according to the invention makes it possible to considerably extend operating times, as illustrated by the three embodiment examples described below.

[0159] Thus, in a first embodiment corresponding to a frequency of 25 kHz, a voltage of 10 kV, a flow rate of 3 nl / min with a composition of 100% CH4, and a conventional nozzle, the process is interrupted by the growth of carbon on the electrodes or the nozzle after an average time of 30 s.

[0160] In a second embodiment, a secondary flow of CH4 is added outside the nozzle to eject carbon from the active zone. The average time before the process is interrupted by carbon growth on the electrodes or the nozzle remains 30 s. However, the carbon growth zones on the electrodes are affected by the presence of the external flow and move towards the inside of the nozzle, demonstrating that the control means is effective but not sufficient.

[0161] In a third embodiment, the nozzle is shaped with a concave outlet face to eliminate stationary zones in the flow, and is surrounded by an external flow. In this third embodiment, the average time before a process interruption due to carbon growth on the electrodes or the nozzle is 15 min.

[0162] In a fourth embodiment corresponding to a frequency of 20 kHz, a voltage of 12 kV, a flow rate of 1 nl / min and a composition of 100% CH4, an improved nozzle having a concave outlet face as shown in [Fig. 5], the average time before interruption of the process by carbon growth on the electrodes or the nozzle is 180 min. Thus, the flow control means and the use of pulses made it possible to go from an uninterrupted operating time of less than 30 s on a conventional nozzle to an uninterrupted operating time of 180 min on a prototype of an improved nozzle shown in [Fig. 5].[5], which allows for the implementation of an industrial operation with alternating production cycles of approximately one hour of interrupted operation, combined with means of detecting the presence of carbon, and mechanical or chemical regeneration methods lasting from a few seconds to a few tens of seconds. The use of several cells in parallel, as shown in [Fig. 2], also ensures continuous production at the installation level. Flow control without secondary flow Flow control with secondary flow Flow control with a concave nozzle Flow control with an improved nozzle (Figure 5) Frequency 25 kHz 25 kHz 25 kHz 20 kHz Voltage 10 kV 10 kV 10 kV 12 kV Flow rate 3 nl / min 3 nl / min 3 nl / min 1 nl / min Gas composition 100% ch4 100% ch4 100% ch4 100% ch4 Continuous operating time 30 s 30 s 15 min 180 min

[0163] Of course, the present invention is not limited to the embodiments just described and many other variants can be envisaged without departing from the scope of the invention.

[0164] The embodiments can be used with hydrocarbon mixtures, including, for example, methane, ethane, and ethylene, which will be decomposed into acetylene. The embodiments can be used with a hydrocarbon mixture containing acetylene in a minor quantity, <10% by volume.

Claims

Demands

1. A process for producing hydrogen and carbon by plasmalysis of a hydrocarbon or a mixture of hydrocarbons, implementing a step of injecting this hydrocarbon or mixture of hydrocarbons in gaseous form into the active zone of a reaction chamber within a controlled reactor to produce a plasma, characterized in that it comprises a repetition of the following steps: - production of a plasma pulse (E1) for a pulse duration until a target heating temperature is reached, - maintenance of an optimal activation regime (E2) of the heated plasma in the active zone of the reaction chamber, for a predetermined residence time, - cooling (E3) of the resident plasma in the active zone of the reaction chamber for a predetermined cooling time.

2. A production method according to the preceding claim, wherein the hydrocarbon gas stream is injected into an active zone (30) of a reaction chamber (15) of a plasmalysis reactor (10) comprising electrodes (13,14) whose supply (22) is controlled to generate a pulsed plasma in the active zone (30) of the reaction chamber (15), wherein the step of cooling the plasma for a cooling time is triggered by the interruption of the supply (22) of the electrodes (13,14) for a predetermined interruption time.

3. A production method according to any one of the preceding claims, wherein the hydrocarbon gas flow passing through the active zone (30) of the reaction chamber (15) of the plasmalysis reactor (10) undergoes a progressive increase in temperature along its path between the inlet and outlet of the active zone.

4. A production method according to any one of the preceding claims, wherein the hydrocarbon gas stream injected into the active zone (30) of the reaction chamber (15) of the plasmalysis reactor (10) is a methane gas stream, said active zone being the site of a series of reactions (R1-R4) of respective dissociations of the injected methane, ethane, ethylene, and acetylene, characterized in that the cooling step is triggered before the initiation of the (R4) acetylene decomposition step, for a predetermined cooling time.

5. A production method according to any one of the preceding claims, characterized in that the repetition N of steps (E1, E2, E3) applied to the gas flow during its path between the inlet and outlet of the active zone (30) stops when the initiation of step (R4) coincides with the ejection of the gas flow outside the active zone.

6. A production method according to any one of the preceding claims, characterized in that it further comprises: - a step for preheating the gas injected into the plasmalysis reactor (10) until a plasma temperature is reached within a target heating temperature range, so that the first three dissociation reactions (RI, R2, R3) are initiated and triggered, - a step of interrupting the plasma by controlling the electrodes (13,14) for a predetermined interruption time such that the first three dissociation reactions are sufficiently advanced and the acetylene dissociation step (R4) is not completely initiated, - a step of cooling the plasma until a plasma temperature is reached within a target cooling temperature range, followed by a return to the preheating step.

7. A production method according to the preceding claim, characterized in that the target heating temperature range is within the range [1500 K - 3000 K].

8. A production method according to the preceding claim, characterized in that the target heating temperature range is within the range [1800 K - 2000 K].

9. A production method according to any one of the three preceding claims, characterized in that the target cooling temperature range is within the range [1000 K - 1500 K].

10. TS.J. A production method according to any one of claims 4 to 9, wherein the catalytic effect of the plasma causes the first dissociation reaction of methane, characterized in that it further comprises the following steps:

11.

12.

13.

14. - a step to control the supply of energy to the electrodes (13,14) so ​​that the energy input from the plasma leads to a plasma temperature such that the second and third dissociation reactions are faster than the dissociation reaction of acetylene, - a step of interrupting the plasma by controlling the supply of energy to the electrodes (13,14) for a predetermined interruption time, before initiation of the acetylene dissociation step (R4), - a plasma cooling step until a plasma temperature is reached within a target cooling temperature range, followed by a return to the preheating step, followed by a return to the control step. Production method according to any one of claims 4 to 10, characterized in that the predetermined interruption time is between 10 ps and 100 ps. Production process according to any one of claims 4 to 11, characterized in that the inlet gas stream further comprises a methane dilution gas. Production process according to the preceding claim, characterized in that the dilution gas is chosen from dihydrogen H2, Argon or helium He. A system (1, 1') for the production of hydrogen and carbon by plasmalysis of a hydrocarbon or a mixture of hydrocarbons, comprising a reactor (10) having a reaction chamber (15) comprising an active zone (30) provided for receiving an incoming gas stream of this hydrocarbon or mixture of hydrocarbons, a pair of electrodes (13, 14; 51, 52; 71, 72) powered by a pulse generator (22) controlled by control means (20), and channeling means (12, 50, 70) provided for channeling the flow of the incoming gas stream towards the active zone (30) and for ejecting the plasmalysis products from the active zone (30), implementing the production process according to any one of the preceding claims, characterized in that the control means (20) are programmed to generate a pulsed plasma in the active zone (30) of the reaction chamber (15) and in that the channeling means (12, 50, 70) are arranged to avoid stationarity gaseous products from plasmalysis on the surface of the electrodes (13,14; 51,52; 71,72).

15. Production system (1,1') according to the preceding claim, characterized in that the channeling means (50,70) comprise a nozzle arranged to provide a secondary flow of a gaseous stream distinct from that of incoming hydrocarbon subjected to plasmalysis, in the vicinity of the electrodes (51,52;71,72).

16. Production system according to the preceding claim, characterized in that the nozzle (50,70) is made of an electrically conductive material and has a floating electrical potential with respect to either of the electrodes (51,52;71,72) so as to constitute a relay for plasma discharges between said electrodes.

17. Production system according to claim 15 or 16, characterized in that the nozzle (50) is provided to surround a first electrode (51) so as to channel the incoming gas flow between said first electrode (51) and the inner wall of said nozzle (50), said nozzle (50) comprising at its end opposite said first electrode an opening (53) provided to allow said channeled gas flow to pass through.

18. Production system according to claim 15, characterized in that the nozzle has an hourglass shape comprising a first flared nozzle part surrounding a first electrode and a second flared nozzle part surrounding the second electrode, said first and second nozzle parts being connected by a conduit arranged to constitute a first active zone for the gas flow.

19. Production system according to claim 15, characterized in that the nozzle (70) comprises a frustoconical cylinder interposed between a first electrode (71) of substantially conical shape and a second hollow electrode (72) of substantially frustoconical shape, said frustoconical cylinder forming nozzle (70) comprising: - a first opening opposite said first electrode (71) and separated from the first electrode (71) by a first electrically insulating element (73) having a central opening of diameter greater than that of the interface end of said first electrode (71), so as to provide an annular gap to allow a channeled gas flow to pass along the external surface of said first electrode (71), - a second opening separated from an open end of said second electrode (72) by a second electrically insulating element (74) having a central opening of diameter substantially equal to that of the interface end of said second electrode (72), so as to channel the gas flow exiting the nozzle inside said second electrode (72).

20. Production system according to the preceding claim, characterized in that the nozzle (70) has a convergent shape from the first insulating element (73) to the second insulating element (74).

21. Production system (1) according to any one of claims 14 to 20, characterized in that the control means (20) are programmed to produce a pulsed plasma at a frequency between 1 kHz and 1 MHz.

22. Production system (1) according to the preceding claim, characterized in that the control means (20) are programmed to produce a pulsed plasma with a pulse duration of less than 100 ns for a gas pressure between 100 mbar and 1 bar, less than 1 ps for a gas pressure between 10 mbar and 100 mbar, and less than 10 ps for a gas pressure less than 10 mbar.

23. Production system (1) according to any one of the preceding claims 14 to 22, characterized in that the electrodes (13,14) are arranged to produce a homogeneous electric field over the active area (30).

24. Production system (1) according to any one of claims 14 to 23, characterized in that the plasma control means are provided to: - produce a plasma pulse for a pulse duration until a target heating temperature is reached, - maintain this heated plasma fully active in the active zone (30) of the reaction chamber (15) of the reactor (10), for a predetermined residence time, - cool the resident plasma for a predetermined cooling time.

25. A production system (1) according to any one of claims 14 to 24, implemented for the production of solid carbon and dihydrogen from methane, wherein the active zone (30) of the reaction chamber (15) of the reactor (10) is the site of a series of reactions (R1-R4) of respective dissociation of injected methane, ethane, ethylene, and acetylene, characterized in that the control means are programmed to interrupt the plasma before the (R4) acetylene dissociation step, for a predetermined interruption time.

26. Production system (1) according to the preceding claim, characterized in that it further comprises means (11) for preheating the gas injected into the plasmalysis reactor until it reaches a plasma temperature within a target heating temperature range, so that the first three dissociation reactions are initiated and triggered,

27. ​​Production system (1) according to any one of claims 25 or 26, characterized in that the control means (20) are programmed to control the supply of the electrodes (13,14) so ​​that the energy input from the plasma leads to a plasma temperature such that the second and third dissociation reactions are faster than the dissociation reaction of acetylene.

28. Production system (1) according to any one of claims 14 to 27, characterized in that the control means (20) are provided to provide in operation a modulation of the plasma pulse frequency and / or a modulation of the voltage applied to the electrodes (13,14).

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