Method for conversion of carbon dioxide with production of hydrogen and / or methane

Abstract

Method for upgrading carbon dioxide comprising: (a) a step of providing a gaseous effluent to be upgraded containing a volume ratio of carbon dioxide of at least 0.5; (b) a step of electrolysis of the gaseous effluent to be upgraded producing a first effluent containing carbon monoxide, during which at least one portion of the carbon dioxide contained in the gaseous effluent to be upgraded is converted to carbon monoxide by electrolysis; (c) at least one step of converting the carbon monoxide from the first effluent, which step is catalyzed by a plasma generated by a dielectric barrier discharge process coupled to a catalyst, said step (c) producing a value-added effluent, during which at least one portion of the carbon monoxide contained in the first effluent is converted to at least one product chosen from methane and / or dihydrogen.

Description

Process for converting carbon dioxide with production of hydrogen and / or methane

[0001] Field of invention

[0002] The invention relates to a method for treating a gaseous effluent, in particular a treatment for converting carbon dioxide with production of hydrogen and / or methane.

[0003] State of the art

[0004] Carbon dioxide (CO2) emissions have been identified as one of the main factors contributing to global warming. CO2 is a by-product of many processes such as combustion, anaerobic digestion, etc. This by-product also creates operational, economic, and environmental problems. High atmospheric concentrations of CO2 and other greenhouse gases are expected to facilitate heat storage in the atmosphere, leading to increased surface temperatures and rapid climate change. In addition, high atmospheric CO2 levels are also expected to further acidify the world's oceans due to the dissolution of CO2 and the formation of carbonic acid. The impact of climate change and ocean acidification is likely to be economically costly and environmentally hazardous if not addressed in time.Reducing the risks of climate change will require capturing and processing CO2 from various anthropogenic processes.

[0005] The challenge is therefore to implement carbon capture, storage, and recovery strategies, also known as Carbon Capture, Utilization, and Storage (CCUS). To date, the most widely used strategy involves capturing carbon dioxide and then trapping it in old oil and natural gas wells. However, the carbon dioxide is not then recovered.

[0006] Chemical conversion processes for carbon dioxide produce various molecules such as urea used as fertilizer, or methane, methanol, synthesis gas used as fuel, or even hydrocarbons. These include hydrogenation, biological methanation, or methanation in the presence of a catalyst, or the Fischer-Tropsch process. These processes are advantageous because they allow CO2 to be recycled and recovered. However, they require the addition of a second electron-donating reagent such as hydrogen. The second reagent to be used must therefore be generated upstream of this process, which requires additional installation, energy, and materials. In addition, these processes are carried out using conventional energy-intensive installations that often require high-pressure and high-temperature operating conditions.Such processes are particularly economical from a minimum installation size, they are therefore not suitable for the treatment of any emission source.

[0007] There is therefore a need for a process to convert carbon dioxide carbon and to valorize it, in particular without adding a second electron-donating reagent during the carbon dioxide conversion step and by using less energy-intensive and flexible processes in terms of the size of the installation and the location to be used.

[0008] Summary of the invention

[0009] A first object of the invention relates to a process for recovering carbon dioxide comprising: (a) a step of supplying a gaseous effluent to be recovered containing a carbon dioxide volume ratio of at least 0.5; (b) a step of electrolysis of the gaseous effluent to be recovered producing a first effluent containing carbon monoxide, during which at least part of the carbon dioxide contained in the gaseous effluent to be recovered is converted into carbon monoxide by electrolysis; (c) at least one step of converting the carbon monoxide of the first effluent catalyzed by a plasma generated by a dielectric barrier discharge process coupled to a catalyst, said step (c) producing an effluent, during which at least part of the carbon monoxide contained in the first effluent is converted into at least one product chosen from methane and / or dihydrogen.

[0010] This sequence of steps, including in particular the use of a carbon dioxide electrolysis step to convert it into carbon monoxide, makes it possible to recover carbon dioxide, in particular without adding any additional reagent and using only electrical energy to carry out step (b).

[0011] Additionally, the generated carbon monoxide is a compound often used in chemistry to generate other molecules, so it is a reaction intermediate that can be easily converted into another molecule of interest.

[0012] The effluent produced in step (c) thus comprises at least one product chosen from methane and dihydrogen and forms a value-added effluent.

[0013] The use of plasma generated by a dielectric barrier discharge process allows the use of a catalyst at temperatures and pressures lower than the temperatures and pressures at which reactions are carried out in the presence of catalysts that are not activated by plasma, which results in energy savings and reduces installation and operating costs of the process. Indeed, the plasma generated by a dielectric discharge process does not require a rise in temperature for catalyst activation, the start-up and shutdown of the installation are immediate and there is therefore no waiting time between the start-up of the installation and the moment when the catalyst can be used. In addition, the use of plasma also makes it possible to reduce the quantity of catalyst used and to obtain a high conversion quickly. Finally, the use of high temperatures to activate the catalyst leads to the formation of solid carbon which will deactivate it, so working at a lower temperature, for example at room temperature, allows you to overcome this drawback.

[0014] The sequence of steps of the present invention thus makes it possible to recover carbon dioxide using an installation using several nascent, clean, entirely electric and energy-efficient processes since the operating conditions are temperatures and pressures lower than the temperatures and pressures for implementing the reactions in the presence of catalysts which are not coupled to a plasma, and without heat input other than that provided by the ambient air (i.e. without external heat input) when the operating conditions are at ambient pressure and temperature. The electricity used will advantageously be chosen from decarbonized energies to thus have a completely carbon-neutral process.

[0015] Advantageously, the at least one step (c) can be implemented in at least one conversion unit typically comprising one or more reactors equipped with an electrical barrier discharge system and comprising at least one catalyst. Such a discharge system can in particular comprise at least two electrodes separated by at least one dielectric material and connected to a voltage generator configured to apply a discontinuous voltage to the electrodes sufficiently high to generate a plasma.

[0016] Advantageously, the at least one conversion step (c) may be chosen from a step (cl) of converting carbon monoxide into methane by methanation producing a first gaseous effluent containing methane, a step (c2) of converting carbon monoxide into dihydrogen in the presence of water, producing a second gaseous effluent containing dihydrogen.

[0017] In an advantageous embodiment, the at least one step (c) may consist of a step chosen from the first step (c1) and the second step (c2). In an advantageous embodiment, step (c) does not comprise a step of converting carbon monoxide into hydrocarbons by a Fischer-Tropsch reaction.

[0018] The conversion steps chosen in step (c) are known steps that make it possible to obtain reusable products in many areas such as energy.

[0019] In one embodiment, the method may comprise at least one step (c) chosen from a step (c1) of converting carbon monoxide by methanation and a step (c2) of converting carbon monoxide in the presence of water. At least one effluent, produced by the at least one step (c1, c2) and comprising carbon dioxide not converted during step (b) and / or formed during step (c2), may be (i) sent to a step (d) of separating and concentrating carbon dioxide producing a third gaseous effluent containing a carbon dioxide volume ratio of at least 0.5 recycled upstream of the electrolysis step (b) and a fourth purified gaseous effluent containing a product chosen from dihydrogen and methane, or (ii) sent, at least in part or in whole, upstream of step (a) of supplying carbon dioxide by recirculation.

[0020] Indeed, during step (b), the carbon dioxide is generally not entirely converted: some of it therefore remains in the first effluent entering step (c) and in the effluent leaving step (c), in particular in the first effluent leaving step (c1) and / or in the second gaseous effluent leaving step (c2). In addition, the carbon monoxide conversion reaction in the presence of water produces carbon dioxide in addition to dihydrogen. Thus, to make the process carbon neutral, it is advantageous to recycle the streams containing the unconverted carbon dioxide upstream of the electrolysis step (b).

[0021] The value-added effluent leaving step (c) containing the unconverted carbon dioxide also includes the product formed during step (c) as well as a portion of the unconverted carbon monoxide and / or formed during this step (c). Similarly, the second gaseous effluent leaving step (c2) may also contain the unconverted and formed carbon dioxide, the unconverted carbon monoxide and the dihydrogen produced. The carbon dioxide present is therefore diluted. However, at the inlet of electrolysis step (b), the effluent must have a carbon dioxide volume ratio of at least 0.5. The addition of step (d) makes it possible to concentrate the stream to have a carbon dioxide volume ratio of at least 0.5. Alternatively, only a portion of the effluent may be returned directly upstream of step (a) in a quantity making it possible to obtain at the outlet of step (a) a gaseous effluent to be recovered having an adequate carbon dioxide content.

[0022] In one embodiment, the method may comprise at least one step (c2) of converting carbon monoxide into dihydrogen in the presence of water, producing a second effluent comprising the dihydrogen produced and carbon dioxide which has not been converted during step (b) and / or which has been formed during step (c2). The method may then comprise at least one step (c1) of converting carbon monoxide into methane by methanation in the presence of dihydrogen. The fourth purified gaseous effluent leaving the separation and concentration step (d) containing the dihydrogen produced by the at least one step (c2) may then be sent to the at least one conversion step (c1).

[0023] This embodiment thus makes it possible to reduce, or even eliminate, an external supply of dihydrogen for the implementation of at least one step (cl).

[0024] In another embodiment, step (c) of the method may comprise at least one step (c2) of converting carbon monoxide into dihydrogen in the presence of water, producing a second effluent comprising the dihydrogen produced and the carbon dioxide which was not converted during step (b) and / or which was formed during step (c2) and at least one step (c1) of converting carbon monoxide into methane by methanation in the presence of dihydrogen. The second value-added effluent may then be sent to the at least one step (c1) of conversion by methanation. This embodiment also makes it possible to reduce, or even eliminate, an external dihydrogen supply for the implementation of the at least one step (cl), but without implementing a step (d) of separation and concentration of carbon dioxide.

[0025] Advantageously, step (a) of supplying the gaseous effluent to be recovered may comprise a step (e) of separating and concentrating the carbon dioxide from a source effluent containing a carbon dioxide volume ratio of less than 0.5 producing the gaseous effluent to be recovered and a source effluent depleted in carbon dioxide.

[0026] The effluent to be recovered provided by step (a) must in fact contain a minimum quantity of carbon dioxide in order to be able to be converted during the electrolysis step (b). In the case where the source effluent contains a carbon dioxide volume ratio of less than 0.5, step (e) of separation and concentration of carbon dioxide makes it possible to reach at least the minimum limit set by the electrolysis process.

[0027] Advantageously, step (d) or (e) of separation and concentration of carbon dioxide can be chosen from an electrically assisted adsorption step, a membrane separation step and / or an amine washing step.

[0028] Another subject of the invention relates to a carbon dioxide recovery plant, in particular for implementing the method according to the invention. The carbon dioxide recovery plant according to the invention comprises: - a supply line for a gaseous effluent to be recovered containing a carbon dioxide volume ratio of at least 0.5; - a unit for electrolysis of the gaseous effluent to be recovered, comprising a supply pipe connected to the supply pipe and a pipe for discharging a first effluent containing carbon monoxide; - at least one unit for converting carbon monoxide from the first effluent equipped with an electrical barrier discharge system for generating a plasma coupled to a catalyst, said at least one unit comprising a supply line connected to the discharge line of the electrolysis unit and a discharge line for a value-added effluent containing at least one product chosen from methane, dihydrogen or hydrocarbons.

[0029] The at least one conversion unit may typically comprise one or more reactors equipped with an electrical barrier discharge system and comprising at least one catalyst. Such a discharge system may in particular comprise at least two electrodes separated by at least one dielectric material and connected to a voltage generator configured to apply a discontinuous voltage to the electrodes sufficiently high to generate a plasma.

[0030] Advantageously, the at least one conversion unit can be chosen from a first unit for converting carbon monoxide into methane by methanation comprising a pipe for discharging a first gaseous effluent containing methane and a second unit for converting carbon monoxide into dihydrogen in the presence of water, comprising a pipe for discharging a second gaseous effluent containing dihydrogen.

[0031] In an advantageous embodiment, the at least one conversion unit may consist of a conversion unit chosen from a first conversion unit and a second conversion unit as previously defined. In an advantageous embodiment, the at least one conversion unit does not comprise a unit for converting carbon monoxide into hydrocarbons by a Fischer-Tropsch reaction.

[0032] The treatment installation may in particular comprise at least one conversion unit chosen from a first methanation conversion unit and a second unit for converting carbon monoxide into dihydrogen. The discharge pipe for the first gaseous effluent and the second gaseous effluent may then be (i) connected to a supply pipe of a first carbon dioxide separation and concentration unit comprising a discharge pipe for a third gaseous effluent containing a carbon dioxide volume ratio of at least 0.5 connected to the supply pipe of the electrolysis unit and a discharge pipe for a fourth gaseous effluent containing a product chosen from dihydrogen and methane, or the discharge pipe for the first gaseous effluent and the second gaseous effluent may be (ii) connected to the supply pipe (1) by a recycle pipe.

[0033] The treatment installation may comprise at least one second unit for converting carbon monoxide into dihydrogen in the presence of water, producing a second gaseous effluent comprising the dihydrogen produced and the carbon dioxide which has not been converted in the electrolysis unit and / or which has been formed in the second conversion unit and at least one unit for converting carbon monoxide into methane by methanation in the presence of dihydrogen. The discharge pipe for the fourth effluent from the first separation and concentration unit may then be connected to the supply pipe of the at least one unit for converting carbon monoxide into methane by methanation.

[0034] The treatment installation may comprise at least one second unit for converting carbon dioxide in the presence of water and at least one first unit for converting by methanation. The discharge pipe for the second gaseous effluent comprising the dihydrogen produced by the at least one second conversion unit may then be connected to a supply pipe of the at least one first conversion unit.

[0035] Advantageously, upstream of the supply line, the installation may comprise a second unit for separating and concentrating carbon dioxide from a source effluent containing a carbon dioxide volume ratio of less than 0.5 comprising a supply line for the source effluent and the supply of the gaseous effluent to be recovered.

[0036] Advantageously, the first and second carbon dioxide separation and concentration units may be selected from an electrically assisted adsorption zone, a membrane separation zone and / or an amine washing zone. Each zone is typically positioned inside a suitable enclosure, such as a reactor, a column or the like.

[0037] Description of figures

[0038] Other features and advantages of the invention will emerge from reading the description given below of several particular embodiments of the invention, given for informational purposes but not as a limitation, with reference to the appended drawings in which:

[0039] Figure 1 is a schematic representation of the recovery installation according to one embodiment of the invention.

[0040] Figure 2 is a schematic representation of the recovery installation according to one embodiment of the invention.

[0041] Figure 3 is a schematic representation of the recovery installation according to one embodiment of the invention.

[0042] Detailed description of the invention

[0043] Process

[0044] The method according to the invention is a method for recovering carbon dioxide from an effluent to be recovered.

[0045] The recovery process comprises a step (a) of providing a gaseous effluent to be recovered containing a carbon dioxide volume ratio of at least 0.5, a step (b) of electrolysis of the gaseous effluent to be recovered producing a first effluent containing carbon monoxide and a step (c) of conversion of the carbon monoxide of the first effluent producing a value-added effluent. The conversion step (c) being a step catalyzed by a catalyst activated by a plasma generated by a dielectric barrier discharge process.

[0046] Step (b) is thus a step of electrolysis of carbon dioxide converting it into carbon monoxide while step (c) is a step of conversion of carbon monoxide during which at least part of the carbon monoxide is converted into at least one product chosen from methane, dihydrogen and hydrocarbons.

[0047] The alternative configurations of the different stages of the process presented below can be combined depending on the treatment objective decided.

[0048] Step (a) of supplying a gaseous effluent to be recovered

[0049] Supply step (a) is a step of supplying a gaseous effluent to be recovered containing a carbon dioxide volume ratio of at least 0.5.

[0050] The effluent to be recovered can come from different sources, in particular from all processes producing a gaseous effluent containing carbon dioxide such as digesters producing biogas or coal-fired power stations which produce high carbon dioxide flows.

[0051] However, most of the effluents from these processes do not have a sufficient dioxide concentration to be supplied directly to step (b). Indeed, for example, the biogas produced in a digester contains approximately 40% carbon dioxide, the flue gas produced by coal-fired power plants or combustion processes comprises approximately 15 to 21% carbon dioxide, or the syngas produced by pyrolysis comprises approximately 20 to 40% carbon dioxide. However, for the continuation and proper operation of the process, a minimum volume ratio of carbon dioxide of 0.5 is required at the inlet of step (b). These source effluents may therefore contain a volume ratio of carbon dioxide less than 0.5.

[0052] Thus, in one embodiment, the supply step (a) comprises a step (e) of separating and concentrating the carbon dioxide from a source effluent containing a carbon dioxide volume ratio of less than 0.5, producing the gaseous effluent to be recovered and a source effluent depleted in carbon dioxide.

[0053] The effluent separation and concentration step (e) may be selected from an electrically assisted adsorption step (e1), a membrane separation step (e2) and an amine washing step (e3). Each step (e1), (e2), (e3) may be carried out in a reactor comprising a suitable zone such as an electrically assisted adsorption zone, a membrane separation zone and an amine washing zone respectively.

[0054] The electrically assisted adsorption (ESA) step (el) is a process for capturing and concentrating a compound that includes an electrical system that adsorbs and expels CO2. In this step, the source gas enters one side of a stack and is sent through the electrodes that make up the stack, where the CO2 is absorbed. The remaining gas simply passes through the stack and exits the other side. Once the stack is saturated with CO2, the incoming gas is stopped, and pure CO2 exits the stack on the other side. Installing stacks in parallel with alternating cycles allows for a continuous flow of incoming mixed gas and outgoing pure CO2. The electrically assisted adsorption step (el) is notably detailed in document US2021387139, which presents an electrically assisted adsorption process for the separation of several compounds in a gaseous effluent.Such a process can thus be implemented in a reactor comprising electrodes and forming an adsorption cell called an “electroswing adsorption cell”.

[0055] The membrane separation step (e2) consists of separating several compounds from a gas by sending a gaseous effluent through a module comprising one or more membranes. Depending on the difference in permeability of the membrane with respect to the compounds of the gaseous effluent, certain compounds will pass through the membrane more quickly while others will pass through it slowly. Thus, in the case of the invention, on one side or the other of the module, there will be different concentrations of carbon dioxide, one effluent will be concentrated in CO2 while the other effluent will be depleted in CO2. A person skilled in the art is able to select an appropriate membrane in order to obtain an effluent having a target CO2 content.

[0056] The amine washing step (e3) is a process for separating a gas mixture using an aqueous amine solution. The gaseous effluent comprising carbon dioxide will, here, pass through the amine solution and the CO2 will then be adsorbed by the amines present. Then, the CO2 is desorbed from the amines to recover an effluent concentrated in carbon dioxide. The amines often used are, for example, diethanolamine (DEA), ethanolamine (MEA) or N-methyldiethanolamine. These amines can be in solution or immobilized on a solid support. The desorption of amines in solution can be carried out by stripping, the desorption of amines on a solid support can be carried out by lowering the partial pressure of CO2, for example by placing the adsorbent material under vacuum, or by contacting the adsorbent material with a purge gas, preferably water vapor, or a combination of both.This washing can be carried out in a reactor in which the amine and the effluent circulate countercurrently or in which the effluent passes through the amine immobilized on a solid support.

[0057] Preferably, step (e) of separation and concentration of carbon dioxide may be step (el) of electrically assisted adsorption. However, a person skilled in the art may choose step (a), and in particular the addition or not of a step (e) from steps (el), (e2) and (e3) previously described, in a usual manner depending on the size of the plant, the source effluent or the objective in terms of volume ratio of carbon dioxide in the effluent to be recovered.

[0058] Step (b) of electrolysis of the gaseous effluent to be recovered

[0059] The gaseous effluent to be recovered from supply step (a) is then electrolyzed to produce a first gaseous effluent containing carbon monoxide. During step (b), at least part of the carbon dioxide contained in the gaseous effluent to be recovered is converted into carbon monoxide by electrolysis.

[0060] Carbon dioxide electrolysis is a process for the electrochemical reduction of carbon dioxide. This process consists of circulating the gaseous effluent near the cathode of an electrolysis device comprising an anode and a cathode and then applying a potential between the two electrodes, thereby reducing the carbon dioxide to carbon monoxide. The anode of this device can be chosen from any electrode traditionally used in the prior art and well known to those skilled in the art. The cathode, for its part, is an electrode comprising an electrically conductive support such as copper, zinc, nickel, iron, etc., at least part of the surface of which is covered with a metal deposit. The metal deposit can be an alloy, for example an alloy of zinc and silver as described in document EP3670701. Other examples of electrodes can be found in document EP3918111.Conventionally, the electrodes are immersed in an electrolytic solution, usually an aqueous solution. This solution may contain bicarbonates, such as CsHCCh, NaHCCh, or KHCO3. Electrolysis devices. usable as described in documents EP3670701 and EP3918111.

[0061] Carbon dioxide conversion by electrolysis is generally controlled by the CO2 partial pressure in the gaseous effluent to be recovered. The higher the partial pressure, the more efficient the electrolysis will be. Therefore, the effluent to be recovered must contain a volume ratio of at least 0.5 in carbon dioxide. Furthermore, the conversion of CO2 to CO by electrochemical reduction is typically controlled according to the potential applied between the electrodes. This conversion can be carried out at room temperature.

[0062] Step (b) can be implemented in an electrolysis unit comprising one or more electrolysis devices of the type previously described.

[0063] In general, at the outlet of step (b), not all the carbon dioxide present in the effluent to be recovered has been converted. Thus, the first effluent generally contains unconverted carbon dioxide.

[0064] Step (c) of carbon monoxide conversion

[0065] The first effluent from electrolysis step (b) is then sent to a carbon monoxide conversion step (c) to produce a value-added effluent. During conversion step (c), at least a portion of the carbon monoxide contained in the first effluent is converted into at least one product chosen from methane and / or dihydrogen.

[0066] Step (c) of carbon monoxide conversion is carried out in the presence of a catalyst coupled to a plasma generated by a dielectric barrier discharge process.

[0067] The plasma state is defined as an electrically neutral ionized gas containing free electrons, ions, and energetically excited neutral species (atoms and molecules) characterized by collective behavior. In a non-thermal plasma, most of the coupled energy is primarily released to the free electrons, which are several orders of magnitude higher than the temperature of the heavy plasma components (ions and neutrals). The apparent temperature of the gas then remains similar to room temperature if exothermic or endothermic phenomena are absent. Non-thermal plasma refers to a plasma state that is not in thermal equilibrium: equilibrium is not reached because the electron number density is not high enough relative to other heavy particles to achieve sufficient energy transfer between electrons and heavy particles.Ionization and chemical processes in these plasmas are established by the temperature (or energy level) of the electrons and are not sensitive to thermal processes and gas temperature. The most common method of plasma generation is to apply an electric field between two metal electrodes surrounding a neutral gas. If the applied field exceeds a certain energy density threshold (called the breakdown field strength), a gas discharge is formed, thus initiating the formation of a plasma. This process is therefore a dielectric barrier discharge (DBD) process, also called Dielectric Barrier Discharge (DBD) plasma catalysis. in English, originally called silent discharge, where two electrodes are separated by at least one insulating dielectric barrier to generate the plasma.

[0068] The plasma-coupled catalyst generated by a dielectric barrier discharge process is typically a solid heterogeneous catalyst. The general principle of plasma catalysis is a heterogeneous catalysis activated by the presence of plasma. The molecules adsorb onto the surface of the catalyst and are then transformed by chemical reactions. The presence of plasma plays a synergistic role with the catalyst, promoting the adsorption of molecules onto the catalyst. It thus provides sufficient activation energy for the catalytic properties of the catalyst to be effective at atmospheric pressure and at temperatures lower than the reaction temperatures in the presence of catalysts that are not activated by plasma (thermal catalysis), for example at room temperature. This process can be a non-thermal plasma process when carried out at room temperature, without external heat input.

[0069] This conversion step can thus be implemented by means of one or more conversion units each comprising one or more reactors each equipped with an electrical barrier discharge system and comprising at least one catalyst. Such an electrical barrier discharge system can in particular comprise at least two electrodes connected to a voltage generator configured to apply a discontinuous voltage to the electrodes, this voltage being high enough to generate a plasma. The applied voltage is typically a discontinuous high voltage (sinusoidal or pulsed), which can have a value of 1 to 50 kV depending on the dimensions of the reactor and the operating conditions. The frequency of this voltage can vary between a few kiloHz and several megahertz.

[0070] The electrodes are separated by at least one insulating (dielectric) material. The electrodes may be located inside the reactor, in which case the insulating material is typically arranged around at least one of the electrodes. Alternatively, one of the electrodes may be located inside the reactor, for example in the center, and the other outside, for example along the reactor wall. The dielectric material may then be arranged around at least one electrode or be formed from the reactor wall or an insulating material covering this wall. Generally speaking, the distance separating the two electrodes may be defined by Paschen's law. The gas mixture circulates in the space between the two electrodes, inside which the at least one catalyst is arranged, and is electrically excited to generate the discharges creating the plasma.

[0071] The geometry of the reactor can be cylindrical with coaxial positioning of the two electrodes, or be parallelepiped with two parallel planar electrodes.

[0072] The conversion unit(s) implementing step (c) are separate from the electrolysis unit implementing step (b). The conditions for implementing the electrochemical reduction reaction of CO2 to CO are in fact incompatible with the generation of a plasma by a dielectric barrier discharge process. Indeed, the electrochemical reduction reaction of CO2 requires the application of a continuous overvoltage in a cell, for example of the fuel cell type, comprising two electrodes and a liquid or solid electrolyte which may have catalytic properties. The value of the applied overvoltage depends essentially on the standard potential of the redox couple (typically, this overvoltage does not exceed 2 V) and makes it possible to create a unidirectional direct current. On the contrary, the generation of a plasma requires the application of a discontinuous high voltage and the presence of a dielectric barrier does not allow the creation of a unidirectional direct current between the electrodes.

[0073] Furthermore, when step (c) involves several steps, the conversion units that implement them are also distinct from each other.

[0074] The conversion step (c) may comprise one or more of the following steps: a step (c1) of converting carbon monoxide into methane by methanation and a step (c2) of converting carbon monoxide into dihydrogen. The conversion step (c) (namely steps (c1) and / or (c2)) is typically carried out at atmospheric pressure and at a temperature of 20°C to 200°C, preferably at a temperature of 20°C to 50°C. The residence time is less than 10 minutes, preferably less than 1 minute. For this step, the dielectric barrier discharge process is typically installed inside the reactor (or reactors) in which the conversion step (c) takes place. The catalyst is then installed at the electrodes generating the plasma, for example in a fixed bed, and the effluent circulates between these electrodes through the catalyst.

[0075] The step (cl) of carbon monoxide conversion by methanation produces a first value-added effluent containing methane. Methanation is a reaction for the synthesis of methane from carbon monoxide and in the presence of dihydrogen, according to the reaction: CO + 3H2 = CH4 + H2O. Methanation is a well-known process which will not be detailed in more detail. The solid catalysts that can be used may be, for example, alloys of a metal and an oxide such as an alloy of nickel and zirconium oxide.

[0076] This conversion can be carried out in a reactor equipped with a dielectric barrier discharge system as previously described, inside which at least one catalyst is introduced, typically in a fixed bed. The reaction conditions are typically those previously mentioned for step (c).

[0077] The carbon monoxide conversion step (c2) produces a second value-added effluent containing dihydrogen. Carbon monoxide conversion, also known as the Water-Gas Shift Reaction (WGSR), is a process that converts carbon monoxide and water vapor into a mixture of carbon dioxide and dihydrogen according to the reaction: CO + H2O = CO2 + H2. Typically, as much water as the first effluent from step (b) is introduced at the inlet of this step. This conversion process is carried out in a single step using a solid catalyst. The solid catalysts that can be used may be, for example, alloys of a metal and an oxide such as an alloy of nickel and iron oxide or an alloy of gold and zirconium oxide.

[0078] This conversion can be carried out in a reactor equipped with a dielectric barrier discharge system as previously described, inside which at least one catalyst is introduced, typically in a fixed bed. The reaction conditions are typically those previously mentioned for step (c)

[0079] In one embodiment, to increase the efficiency of the installation, concerning the conversion of carbon dioxide, recycling of the effluent leaving step (c) containing the unconverted carbon dioxide, and optionally the carbon dioxide formed during step (c) in particular during step (c2), can be carried out. This recycling concerns steps (c1) of conversion by methanation and (c2) of conversion of carbon monoxide by the reaction of gas with water, and is carried out on the effluents comprising carbon dioxide formed during step (c) and / or not converted by step (b), namely the effluents chosen from the first effluent of step (c1) and the second effluent of step (c2). The effluent is then sent upstream of step (a) of supplying carbon dioxide by recirculation.

[0080] In one embodiment, the dihydrogen produced by step (c2) of converting carbon monoxide by the water gas reaction can be used to feed at least one methanation conversion step (cl). Thus, the second effluent leaving step (c2) is sent to the at least one methanation conversion step (cl).

[0081] Optional step (d) of separation and concentration of carbon dioxide

[0082] In a particular embodiment, at least one of the steps (c1) of conversion by methanation, (c2) of conversion of carbon monoxide by the reaction of gas with water can be followed by a step (d) of separation and concentration of carbon dioxide. The step (d) of separation and concentration is carried out on one or more of the effluents produced by the steps (c1, c2), which is chosen from the first effluent leaving step (c1) and the second effluent leaving step (c2). This step (d) then produces a third gaseous effluent containing a volume ratio of carbon dioxide of at least 0.5 recycled upstream of the electrolysis step (b).

[0083] The aim of step (d) is therefore to separate the carbon dioxide from the other products formed and to concentrate it to obtain a volume ratio of at least 0.5 in CO2 and thus to be able to recycle it upstream of step (b) of electrolysis.

[0084] When step (d) is placed downstream of steps (c1) of conversion by methanation and (c2) of conversion of carbon monoxide by the gas to water reaction, the effluent produced by these steps is separated into the third gaseous effluent containing a carbon dioxide volume ratio of at least 0.5 and a fourth gaseous effluent containing the value-added product, dihydrogen or methane depending on the reaction.

[0085] In one embodiment, the fourth effluent containing dihydrogen resulting from the succession of steps (c2) of conversion of carbon monoxide by the reaction of gas with water and (d) of separation and concentration can be sent to at least a methanation conversion step (cl) to use the dihydrogen produced as a reactant for the methanation reactions.

[0086] The different embodiments previously described can be combined according to the desired recovery objective, in particular to limit external inputs of dihydrogen and / or CO2.

[0087] Installation Description

[0088] With reference to Figure 1, the carbon dioxide recovery installation 100 comprises a pipe 1 for supplying an effluent to be recovered suitable for implementing step (a) of the process, a unit 120 for electrolysis of the effluent to be recovered suitable for implementing step (b) of the process and a unit 130 for converting carbon monoxide suitable for implementing step (c) of the process.

[0089] The carbon dioxide electrolysis unit 120 comprises a supply line 2 for the effluent to be recovered connected to the supply line 1 and a discharge line 3 for a first gaseous effluent comprising carbon monoxide. This electrolysis unit may be of the type described with reference to the description of the process.

[0090] The carbon monoxide conversion unit 130 comprises a supply line 4 for the first gaseous effluent connected to the discharge line 3 of the first unit 120 and a discharge line 5 for a value-added effluent containing at least one compound chosen from methane and / or dihydrogen. This conversion unit 130 also comprises a catalyst and an electrical barrier discharge system for generating a plasma in the area where the catalyst is located. This unit may be of the type described with reference to the description of the process.

[0091] Figure 2 shows an embodiment of the installation, including in particular an alternative implementation of step (a) of supplying the effluent to be recovered and, optionally, an implementation of a separation and a concentration downstream of step (c). The installation 200 includes the pipe 1 for supplying an effluent to be recovered suitable for implementing step (a) of the process, a unit 220 for electrolysis of the effluent to be recovered suitable for implementing step (b) of the process and a unit 230 for converting carbon monoxide suitable for implementing step (c) of the process. These units 220 and 230 are identical to the units 120 and 130 described with reference to Figure 1, the numbering of the pipes remains the same for these units.

[0092] With reference to Figure 2, the installation 200 comprises:

[0093] - downstream of the conversion unit 230, a first separation and concentration unit 240 capable of carrying out step (d) of the process, and

[0094] - upstream of the supply line 1, a second separation and concentration unit 210 capable of carrying out step (e) of the process.

[0095] Note that the installation may only include one of these separation and concentration units.

[0096] The second separation and concentration unit 210 comprises a pipeline supply line 6 of a source effluent. The supply line 1 of the effluent to be recovered corresponds to the discharge line of the second unit 210. The second unit 210 of this installation is typically chosen from an electrically assisted adsorption zone, a membrane separation zone and / or an amine washing zone. Each zone is typically positioned inside a suitable enclosure, such as a reactor, a column or other.

[0097] The first separation and concentration unit 240 comprises a supply line 8 connected to the discharge line 5 of the unit 230, a discharge line 9 for a third gaseous effluent containing a carbon dioxide volume ratio of at least 0.5.

[0098] The first unit 240 of this installation is typically selected from an electrically assisted adsorption zone, a membrane separation zone and / or an amine washing zone.

[0099] With reference to Figure 2, the discharge pipe 9 of the unit 240 is connected to the supply pipe 2 of the electrolysis unit 220 by a recirculation pipe 10.

[0100] Figure 3 shows several embodiments of the installation.

[0101] The installation 300 shown firstly comprises a second unit 310 for separation and concentration of carbon dioxide supplied with source effluent by a supply pipe 6. The unit 310 comprises a pipe 1 for evacuating and supplying the effluent to be recovered containing a volume ratio of at least 0.5 in carbon dioxide and another pipe 11 for evacuating an effluent depleted in carbon dioxide.

[0102] The supply line 1 for the effluent to be recovered is connected to the supply line 2 of the carbon dioxide electrolysis unit 320. The electrolysis unit 320 also comprises a discharge line 3 for the first effluent.

[0103] Then, the discharge line 3 is connected to the supply line 4 of the carbon monoxide conversion unit. In this figure, several variants of the invention are presented.

[0104] In a first variant, the conversion unit is a unit 330-1 for converting carbon monoxide into methane by methanation. The unit 330-1 then comprises a feed line 4-1 for the first gaseous effluent and a discharge line 5-1 for a first value-added effluent containing methane, and generally unconverted carbon dioxide and carbon monoxide. The discharge line 5-1 is connected to a recirculation line 12-1 capable of carrying out choice (ii) of the process by sending a portion of the first value-added effluent upstream of the second unit 310 for separating and concentrating carbon dioxide. Alternatively, depending on the volume ratio of carbon dioxide it contains, this first effluent could be sent directly upstream of the electrolysis unit 320. The discharge line 5-1 is also connected to a supply line 8-1 of a first unit 340 for separating and concentrating carbon dioxide. optional carbon. The first separation and concentration unit 340 also comprises a discharge line 13-1 for a fourth gaseous effluent enriched in methane and depleted in unconverted carbon dioxide and a discharge line 9-1 for a third gaseous effluent enriched in carbon dioxide. When the third gaseous effluent contains a carbon dioxide volume ratio of at least 0.5, provision may be made to connect the discharge line 9-1 to a line 10-1 for recirculating the third gaseous effluent upstream of the electrolysis unit 320. When the third gaseous effluent contains a carbon dioxide volume ratio of less than 0.5, it may be returned upstream of the second separation and concentration unit 310.

[0105] In a second variant, the conversion unit is a unit 330-2 for converting carbon monoxide into dihydrogen. The unit 330-2 then comprises a supply line 4-2 for the first gaseous effluent and a discharge line 5-2 for a second value-added effluent containing dihydrogen as well as carbon dioxide, and generally unconverted carbon monoxide. The discharge line 5-2 is connected to a recirculation line 12-2 capable of carrying out choice (ii) of the process by sending a portion of the second value-added effluent upstream of the second unit 310 for separating and concentrating carbon dioxide. Alternatively, depending on the volume ratio of carbon dioxide it contains, this first effluent could be sent directly upstream of the electrolysis unit 320.The discharge line 5-2 is also connected to a supply line 8-2 of the first unit 340 for separating and concentrating carbon dioxide (optional unit). The first unit 340 for separating and concentrating also comprises a discharge line 13-2 for a fourth gaseous effluent enriched in dihydrogen and depleted in carbon dioxide and a discharge line 9-2 for a third gaseous effluent containing a carbon dioxide volume ratio of at least 0.5. The discharge line 9-2 is here connected to a recirculation line 10-2 for the third gaseous effluent upstream of the electrolysis unit 320 while the discharge line 13-2 is connected, in the example shown, to a supply line 15 for supplying dihydrogen to the methanation conversion unit 330-1.In the case where the volume ratio is less than 0.5 then the discharge pipe 9-2 can be connected to the pipe 6 upstream of the second unit 310 for separating and concentrating carbon dioxide.

[0106] The different variants presented with reference to Figures 1 to 3 can be combined depending on the decided recovery objective. In particular, the different variants described with reference to Figure 3 can be combined with each other, namely the conversion unit may comprise one or more of the conversion units 330-1 and 330-2.

[0107] In particular, preferably, the installation includes conversion units 330-1 and 330-2 each followed by its dedicated unit 340 with recirculation of the dioxide of carbon upstream of electrolysis unit 320 and recirculation of dihydrogen to unit 330-1.

[0108] Preferably, the installation comprises the conversion unit 330-2 coupled to a unit 340 and to a unit 330-1 with recirculation of the carbon dioxide from the unit 340 upstream of the electrolysis unit 320.

Claims

Claims Method for recovering carbon dioxide comprising: (a) a step of supplying a gaseous effluent to be recovered containing a carbon dioxide volume ratio of at least 0.5; (b) a step of electrolysis of the gaseous effluent to be recovered producing a first effluent containing carbon monoxide, during which at least part of the carbon dioxide contained in the gaseous effluent to be recovered is converted into carbon monoxide by electrolysis; (c) at least one step of converting the carbon monoxide of the first effluent catalyzed by a plasma generated by a dielectric barrier discharge process coupled to a catalyst, said step (c) producing an effluent, during which at least a portion of the carbon monoxide contained in the first effluent is converted into at least one product chosen from methane and / or dihydrogen, the at least one conversion step (c) being chosen from a step (c1) of converting carbon monoxide into methane by methanation producing a first gaseous effluent containing methane and a step (c2) of converting carbon monoxide into dihydrogen in the presence of water, producing a second gaseous effluent containing dihydrogen.Recovery process according to claim 1, characterized in that the process comprises at least one step (c) chosen from a step (cl) of conversion of carbon monoxide by methanation and a step (c2) of conversion of carbon monoxide in the presence of water and in that at least one effluent produced by the at least one step (cl, c2) and comprising carbon dioxide not converted during step (b) and / or formed during step (c2), is (i) sent to a step (d) of separation and concentration of carbon dioxide producing a third gaseous effluent containing a volume ratio of carbon dioxide of at least 0.5 recycled upstream of the electrolysis step (b), and a fourth purified gaseous effluent containing a product chosen from dihydrogen and methane or (ii) sent, at least in part or in whole, upstream of step (a) of supplying carbon dioxide by recirculation.A recovery process according to claim 2, characterized in that step (c) of the process comprises at least one step (c2) of converting carbon monoxide into dihydrogen in the presence of water, producing a second effluent comprising the dihydrogen produced and carbon dioxide which has not been converted during step (b) and / or which has been formed during step (c2) and at least one step (c1) of converting carbon monoxide into methane by methanation in the presence of dihydrogen, and in that the fourth purified gaseous effluent leaving the separation and concentration step (d) containing the dihydrogen produced by the at least one step (c2) is sent to the at least one conversion step (c1). A recovery process according to any one of claims 1 to 3, characterized in that step (c) comprises at least one step (c2) of converting carbon monoxide. into dihydrogen in the presence of water, producing a second value-added effluent comprising the dihydrogen produced and the carbon dioxide which was not converted during step (b) and / or which was formed during step (c2), and at least one step (c1) of converting carbon monoxide into methane by methanation in the presence of dihydrogen, and in that the second value-added effluent is sent to the at least one step (c1) of conversion by methanation. Recovery method according to any one of claims 1 to 4, characterized in that step (a) of supplying the gaseous effluent to be recovered comprises a step (e) of separating and concentrating the carbon dioxide from a source effluent containing a carbon dioxide volume ratio of less than 0.5 producing the gaseous effluent to be recovered and a source effluent depleted in carbon dioxide.Recovery method according to any one of claims 2, 3 or 5, characterized in that step (d) or (e) of separation and concentration of carbon dioxide is chosen from an electrically assisted adsorption step, a membrane separation step and / or an amine washing step. Installation (100, 200, 300) for recovery of carbon dioxide, said installation comprising:. - a pipe (1) for supplying a gaseous effluent to be recovered containing a carbon dioxide volume ratio of at least 0.5; - a unit (120, 220, 320) for electrolysis of the gaseous effluent to be recovered, comprising a supply pipe (2) connected to the supply pipe (1) and a pipe (3) for discharging a first effluent containing carbon monoxide; - at least one unit (130, 230) for converting carbon monoxide from the first effluent equipped with an electrical barrier discharge system for generating a plasma coupled to a catalyst, said at least one unit (130, 230) comprising a supply line (4) connected to the discharge line (3) of the electrolysis unit and a line (5) for discharging an effluent containing at least one product chosen from methane and dihydrogen. the at least one conversion unit being chosen from a first unit (330-1) for converting carbon monoxide into methane by methanation comprising a line (5-1) for discharging a first gaseous effluent containing methane and a second unit (330-2) for converting carbon monoxide into dihydrogen in the presence of water, comprising a line (5-2) for discharging a second gaseous effluent containing dihydrogen.Recovery installation (300) according to claim 7, characterized in that the installation (300) comprises at least one conversion unit chosen from a first unit (330-1) for conversion by methanation and a second unit (330-2). conversion of carbon monoxide into dihydrogen, and in that the discharge pipe of the first gaseous effluent and the second gaseous effluent (5-1, 5-2) is (i) connected to a pipe (8-1, 8-2) for supplying a first unit (240, 340) for separating and concentrating carbon dioxide comprising a pipe (9-1, 9-2) for discharging a third gaseous effluent containing a carbon dioxide volume ratio of at least 0.5 connected to the supply pipe (2) of the electrolysis unit and a pipe (13-1, 13-2) for discharging a fourth gaseous effluent containing a product chosen from dihydrogen and methane, or the discharge pipe of the first gaseous effluent and the second gaseous effluent (5-1, 5-2) is (ii) connected to the supply pipe (1) by a recycle pipe (12-1, 12-2).Recovery plant (300) according to claim 8, characterized in that the plant (300) comprises at least one second unit (330-2) for converting carbon monoxide into dihydrogen in the presence of water, producing a second gaseous effluent comprising the dihydrogen produced and the carbon dioxide which has not been converted in the electrolysis unit and / or which has been formed in the second conversion unit and at least one unit for converting carbon monoxide into methane by methanation in the presence of dihydrogen, and in that the pipe (13-2) for discharging the fourth effluent from the first separation and concentration unit (340) is connected to the pipe (4-1, 14) for supplying the at least one unit for converting carbon monoxide into methane by methanation.Recovery installation (300) according to one of claims 7 to 9, characterized in that the installation (300) comprises at least one second unit (330-2) for converting carbon dioxide in the presence of water and at least one first unit (330-1) for conversion by methanation, and in that the pipe (13-2) for discharging the second gaseous effluent comprising the dihydrogen produced by the at least one second conversion unit (330-2) is connected to a pipe (4-1, 14) for supplying the at least one first conversion unit.Recovery installation (200, 300) according to any one of claims 7 to 10, characterized in that upstream of the supply pipe, the installation (200, 300) comprises a second unit (210, 310) for separating and concentrating carbon dioxide from a source effluent containing a carbon dioxide volume ratio of less than 0.5 comprising a pipe (6) for supplying the source effluent and the pipe (1) for supplying the gaseous effluent to be recovered. Recovery installation (200, 300) according to any one of claims 8, 9 or 11, characterized in that the first unit (240, 340) and the second unit (210, 310) for separating and concentrating carbon dioxide are chosen from an electrically assisted adsorption zone, a membrane separation zone and / or an amine washing zone.

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