Improved co2 to co conversion process and system

Abstract

The invention relates to a method for producing CO from CO2, the method comprising the steps of: providing a plasma jet generator with a process gas comprising CO2 and optionally CO; exciting a plasma in the process gas by the plasma jet generator, thereby obtaining a plasma jet comprising CO and O species; introducing the plasma jet into a carbon reaction chamber; extracting a product gas from the reaction chamber, the product gas comprising the CO and CO2; and recycling at least a portion of the product gas and providing the product gas comprising CO and CO2 to a plasma jet generator. The invention also relates to a system for converting CO2 to CO, the system comprising: a carbon reaction chamber and a plasma jet generator wherein the gas outlet of the reaction chamber is in fluid communication with the process gas inlet of the plasma jet generator.

Description

Technical Field

[0001] The present invention relates to a method and system for producing carbon monoxide (CO) from carbon dioxide (CO2). The present invention also relates to the field of plasma-assisted and / or plasma-induced chemical reactions. Background Art

[0002] The transition to a climate-neutral society is both an urgent challenge and an opportunity to build a better future for all. All parts of society and the economic sector will play a role, from the power sector to industry, transport, construction, agriculture and forestry. For many years, Carbon Capture and Storage (CCS) has been seen as a viable option for CO2 mitigation. Most competing technologies and subsequently emerging companies in CCS aim to capture CO2 and store it in specially designed sites, usually underground. While this approach is currently effective, storing CO2 is not a sustainable solution and can lead to many long-term problems related to storage maintenance and transportation.

[0003] CCS is evolving into CCU (Carbon Capture and Utilization). The CCU approach is different because it aims to use CO2 gas as a feedstock. Using innovative methods to crack CO2 molecules into valuable products such as carbon monoxide (CO), molecular oxygen (O2) and C is key to redistributing them into reusable products. For example, CO is a very valuable commodity used in a variety of chemical processes from metal production to fuels and plastics. CO is directly used to produce new polyurethane materials such as Much like plastics, metals and biomass, there are also conversion pathways for reusing CO2 in the future.

[0004] In the CCU market, different types of technologies have emerged. Membrane reactor systems for direct thermal cracking have been tested to varying degrees of success, with conversion rates between 0.5% and 2%. Conversion using a co-reactant gas (methane, CH4) is also a recurring area of ​​research. However, this approach suffers from problematic soot deposition. Electrochemical conversion of CO2 is in advanced development, but relies on the solubility of CO2 in liquids (which is limited) and leads to the formation of many residues that are difficult to separate. In solar thermochemical conversion of CO2, concentrated solar energy is used to heat the CO2 to cracking temperatures. In order for this technology to become viable in industry, many fundamental issues are bound to be challenging.

[0005] The present invention relates to a plasma-based CO2 to CO conversion technology. The plasma-based conversion technology is described in the following article: "Plasma technology - a novel solution for CO2 conversion?", Ramses Snoeckx ORCID logo* and Annemie Bogaerts ORCID logo*, Chem. Soc. Rev., 2017, 46, 5805-5863, DOI: 10.1039 / C6CS00066E (review article).

[0006] In the article, it is stated that "the highest conversion efficiency of 42% was obtained for packed bed DBD, while the highest energy efficiency of 23% was obtained with pulsed power DBD". DBD in the article refers to dielectric barrier discharge (DBD), also known as "silent discharge". A DBD consists of two planar parallel or concentric metal electrodes and, as its name implies, contains at least one dielectric barrier (e.g. glass, quartz, ceramic material or polymer) between the electrodes. The purpose of the dielectric barrier is to limit the current and thus prevent the formation of sparks and / or arcs. A gas flow is applied across the (discharge) gap, which can typically vary from 0.1 mm to more than 1 mm to several centimeters. Typically, DBD is operated at approximately atmospheric pressure (0.1-10 atm, but typically about 1 atm), while an alternating voltage with an amplitude of 1-100 kV and a frequency of several Hz to MHz is applied between the two electrodes.

[0007] US4190636 describes a method for producing carbon monoxide in a plasma arc reactor, wherein carbon dioxide is fed to an arc to form a plasma and solid carbon is fed into the plasma. WO2015039195 discloses a method for capturing carbon dioxide and converting it into a gaseous fuel, wherein carbon dioxide alone or mixed with water vapor and / or methane is subjected to a pulse and / or acoustic treatment and passed through a thermal activation zone at a temperature of 800°C to 1000°C. WO2021142919 discloses a plasma-based carbon fixation system, the system comprising: a plasma reactor, a first separator, a condenser, and a second separator.

[0008] Plasma-based conversion of CO2 to CO has two main drawbacks: limited conversion rate and limited energy efficiency; both of which prevent it from entering the industrial stage. In addition, the lack of methods for heat and oxygen recovery limits this technology.

[0009] The present invention aims to provide an alternative and / or improvement to prior art plasma-based conversion technologies, which alternative and / or improvement can be expanded to industrial scale and / or improve conversion efficiency. Summary of the invention

[0010] The present invention relates to methods and systems for converting CO2 into its original building blocks to achieve a carbon-based circular economy. Heretofore, plasma technology, preferably atmospheric pressure plasma technology, is used to crack CO2 into carbon monoxide (CO) and oxygen (O or O2), which CO can be used downstream to produce syngas or other value-added products such as biofuels, formic acid, toluene diisocyanate and other products.

[0011] The technology of the present invention is a scalable plasma-based CO2 conversion technology. In particular, the present invention aims to:

[0012] - Increase the conversion of CO2 to CO;

[0013] - Increased CO production; and

[0014] -Increase energy efficiency.

[0015] Recycling unreacted reagents is a known technique in chemical processing. A problem associated with recycling unreacted CO2 to a plasma reactor is the need to separate it from CO and oxygen species, which greatly increases energy requirements and reduces its energy efficiency.

[0016] Recycling the plasma generator product stream as a whole results in the recombination of oxygen and CO species into CO2; this reduces the conversion rate and energy efficiency of each pass. The recombination of oxygen and CO eventually reaches an equilibrium where CO2 dissociates into oxygen and CO with each pass; preventing high concentrations of CO from being obtained without separation.

[0017] The present invention and its embodiments serve to provide a solution to one or more of the above disadvantages. To this end, the present invention relates to a method according to claim 1. Preferred embodiments of the method are shown in any of claims 2 to 9.

[0018] In particular, claim 1 allows the fixation of oxygen species to CO; preventing recombination to CO2. This advantageously allows the product stream of CO2 and CO to be recycled without significantly reducing the conversion rate of a single pass; thereby achieving much higher energy efficiency and allowing higher final concentrations of CO.

[0019] In a second aspect, the invention relates to a system according to claim 10 .

[0020] Preferred embodiments of the method are indicated in any one of claims 11 to 15 .

[0021] The combination of oxygen fixation by carbon donor particles and recycling of at least a portion of the resulting CO / CO mixture without purification or separation has a beneficial effect on the overall CO conversion as well as energy efficiency. The product gas is recycled two or more times through the plasma jet generator and the carbon reaction chamber for oxygen fixation, which significantly increases the overall CO conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following numbers refer to:

[0023] (1) plasma jet outlet; (2) plasma jet generator; (3) carbon reaction chamber; (4) plasma jet afterglow; (5) carbon donor particles; (6) carbon reaction chamber; (7) fixed carbon particle bed; (8) inlet for a mixture of CO2, CO and O2; (9) CO-rich gas flow; (10) carbon reaction chamber; (11) crushed carbon particles; (12) inlet for a mixture of CO2, CO and O2; (13) CO-rich gas flow; (14) inlet for carbon donor particles; (15) process gas containing CO2 and CO; (16) reaction gas containing CO2; (17) recycled gas containing CO2 and CO product gas; (18) plasma jet; (19) plasma jet generator; (20) plasma jet afterglow; (21) conversion of CO2 into CO and 1 / 2O2; (22) carbon reaction chamber containing carbon donor particles; (23) conversion of CO, C and O into 2CO; (24) carbon donor particle inlet; (25) product gas containing CO2 and CO; (26) extracted product gas; (27) separation unit; (28) CO flow; (29) CO2 flow; (30) plasma generating device; (31) fluid communication between the plasma jet generator and the carbon reaction chamber.

[0024] The following description of the drawings of specific embodiments of the invention is merely exemplary in nature and is not intended to limit the invention, its application, or uses. Throughout the drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0025] Figure 1 The temperature dependence of the reversible Boudoir reaction is shown.

[0026] Figure 2 An embodiment of the system of the present invention is shown wherein the carbon reaction chamber is a fluidized carbon bed.

[0027] Figure 3 An embodiment of the system of the present invention is shown wherein the carbon reaction chamber is a fixed carbon bed.

[0028] Figure 4 A carbon reaction chamber using pulverized carbon donor particles is shown according to an embodiment of the present invention.

[0029] Figure 5A and Figure 5B The CO2 conversion rate and energy efficiency per pass are shown for a system without a carbon reaction chamber (Comparative Example 5) and a system with a carbon reaction chamber according to the present invention (Example 6).

[0030] Fig. 6A and Figure 6B A process flow and associated mass balance according to an embodiment of the invention is shown.

[0031] Figure 7 A schematic diagram showing an embodiment of the present invention is shown.

[0032] Figure 8 A schematic continuous feed mechanism for a fluidized carbon bed according to an embodiment of the present invention is shown.

[0033] Fig. 9 A system is shown in accordance with an embodiment of the present invention wherein multiple plasma reactors share a continuous fluidized carbon bed. DETAILED DESCRIPTION

[0034] The present invention relates to a method and system for producing CO from CO2.

[0035] Unless otherwise defined, all terms used in disclosing the present invention, including technical and scientific terms, have the meanings commonly understood by ordinary technicians in the field to which the present invention belongs. By further guidance, term definitions are included to better understand the teachings of the present invention.

[0036] As used herein, the following terms have the following meanings:

[0037] The expressions "carbon reaction chamber" and "reaction chamber" refer to the same carbon reaction chamber comprising carbon donor particles as described in the present disclosure.

[0038] As used herein, "a", "an", and "the" refer to both singular and plural referents unless the context clearly dictates otherwise. For example, "a compartment" means one or more than one compartment.

[0039] As used herein, "about" refers to a measurable value, such as a parameter, amount, duration, etc., and is intended to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less of the specified value, to the extent such variations are suitable for implementation in the disclosed invention. However, it should be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0040] As used herein, "comprise" is synonymous with "include" or "contains", and is an inclusive or open-ended term that specifies the existence of what follows the word (e.g., components) and does not exclude or inhibit the existence of additional, unlisted components, features, elements, members, steps known in the art or disclosed herein.

[0041] In addition, the terms "first", "second", "third", etc. in the specification and claims are used to distinguish similar elements, and are not necessarily used to describe a sequential or chronological order unless otherwise specified. It should be understood that the terms used in this way are interchangeable under appropriate circumstances, and the embodiments of the invention described herein are capable of operating in other sequences than those described or illustrated herein.

[0042] The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

[0043] Unless otherwise defined, the expressions "weight %", "weight percent", "% wt" or "wt %" herein and throughout the specification refer to the relative weight of each component based on the total weight of the formulation.

[0044] Although the term "one or more" or "at least one", such as one or more or at least one member of a group of members, is clear in itself, by way of further example, the term specifically covers reference to any one of the members or to any two or more of the members, such as any ≥3, ≥4, ≥5, ≥6 or ≥7 of the members, etc., and up to all of the members.

[0045] Unless otherwise defined, all terms used in disclosing the present invention, including technical and scientific terms, have the meanings commonly understood by those of ordinary skill in the art to which the present invention belongs. By way of further guidance, definitions of the terms used in the specification are included to better understand the teachings of the present invention. The terms or definitions used herein are intended only to aid in understanding the present invention.

[0046] References to "one embodiment" or "an embodiment" throughout the specification mean that the particular features, structures, or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily all refer to the same embodiment, but may refer to the same embodiment. In addition, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner, which will be apparent to those skilled in the art from this disclosure. In addition, although some embodiments described herein include some other features that are not included in other embodiments, the combination of features of different embodiments is intended to be within the scope of the present invention and to form different embodiments, as will be understood by those skilled in the art. For example, in the claims below, any claimed embodiment may be used in any combination.

[0047] In a first aspect, the present invention relates to a method for producing CO from CO2; the method comprises the following steps:

[0048] i. providing a process gas comprising CO2 and optionally CO and oxygen to a plasma jet generator;

[0049] ii. exciting a plasma in the process gas by the plasma jet generator, thereby obtaining

[0050] a plasma jet comprising CO and oxygen species;

[0051] iii. introducing the plasma jet into a carbon reaction chamber containing carbon donor particles, thereby allowing the

[0052] Oxygen species in the plasma jet preferentially combine with carbon to form CO;

[0053] iv. extracting a product gas from the reaction chamber, the product gas comprising the CO and CO2; and

[0054] v. Recirculating at least a portion of the product gas and providing the product gas comprising CO and CO2 to a plasma jet generator.

[0055] The combination of carbon donor particles (step iii.) and recycling of the product gas without separation of CO2 and CO is synergistic. By introducing carbon donor particles, the O species is fixed on CO instead of forming O2. When the product gas is fully recycled, this fixation of the O species significantly increases the conversion of CO2 because it prevents recombination (i.e., the reverse reaction of oxygen and CO to form CO2). This effectively allows the reflux or recycling of a mixture of CO and CO2, rather than separating CO2 from the product gas and recycling only the separated CO2. Recycling without fixing the O species (according to step iii.) results in a significant reduction in the conversion rate and energy efficiency of each pass, because the amount of recombination between CO and O species increases with their concentration in the process gas mixture. Another advantage is that much higher CO concentrations and CO / CO2 ratios can be obtained. This significantly reduces or even completely eliminates the requirements for separating CO2 and CO.

[0056] It has been shown that recycling at least a portion of the product gas and providing said product gas comprising CO and CO2 to a plasma jet generator has a beneficial effect on the CO2 conversion rate. Recirculation of the product gas through the plasma jet generator two or more times in combination with a carbon reaction chamber for oxygen removal significantly increases the overall CO2 conversion rate.

[0057] Recycling referred to in the present disclosure may refer to: recycling at least a portion of the product gas and providing the product gas containing CO and CO2 to the same plasma jet generator (as a reflux) or providing the product gas containing CO and CO2 to a different or second plasma jet generator (as a multi-stage recycling).

[0058] The present invention relates to a method for producing CO from CO2; the method comprises the following steps:

[0059] i. providing a process gas comprising CO2 and optionally CO and oxygen to a plasma jet generator;

[0060] ii. exciting a plasma in the process gas by the plasma jet generator, thereby obtaining a plasma jet containing CO and oxygen species;

[0061] iii. introducing the plasma jet into a carbon reaction chamber containing carbon donor particles, thereby allowing oxygen species in the plasma jet to preferentially combine with carbon to form CO;

[0062] iv. extracting a product gas from the carbon reaction chamber, the product gas comprising the CO and CO2; and

[0063] v. recycling at least a portion of the product gas and providing the product gas comprising CO and CO 2 to the plasma jet generator or a second plasma jet generator.

[0064] Therefore, in some embodiments, the present invention relates to a method for producing CO from CO2; the method comprises the following steps:

[0065] i. providing a process gas comprising CO2 and optionally CO and oxygen to a plasma jet generator;

[0066] ii. exciting a plasma in the process gas by the plasma jet generator, thereby obtaining a plasma jet containing CO and oxygen species;

[0067] iii. introducing the plasma jet into a carbon reaction chamber containing carbon donor particles, thereby allowing oxygen species in the plasma jet to preferentially combine with carbon to form CO;

[0068] iv. extracting a product gas from the carbon reaction chamber, the product gas comprising the CO and CO2; and

[0069] and

[0070] v. Recirculating at least a portion of the product gas and providing the product gas comprising CO and CO 2 to the plasma jet generator.

[0071] Therefore, in other embodiments, the present invention relates to a method for producing CO from CO2; the method comprising the following steps:

[0072] i. providing a process gas comprising CO2 and optionally CO and oxygen to a first plasma jet generator;

[0073] ii. exciting a plasma in the process gas by the plasma jet generator, thereby obtaining a plasma jet containing CO and oxygen species;

[0074] iii. introducing the plasma jet into a carbon reaction chamber containing carbon donor particles, thereby allowing oxygen species in the plasma jet to preferentially combine with carbon to form CO;

[0075] iv. extracting a product gas from the carbon reaction chamber, the product gas comprising the CO and CO2; and

[0076] v. Recirculating at least a portion of the product gas and providing the product gas comprising CO and CO 2 to a second plasma jet generator.

[0077] Subsequently, plasma is excited in the product gas by a second plasma jet generator, thereby obtaining a plasma jet containing CO and oxygen species; the plasma jet is introduced into a second carbon reaction chamber containing carbon donor particles, thereby causing the oxygen species in the plasma jet to preferentially combine with carbon to form CO, and a product gas is extracted from the carbon reaction chamber, wherein the product gas contains the CO and CO2.

[0078] These embodiments can also be combined, wherein a portion of the product gas is recycled to the same plasma jet reactor and a portion is directed to a second plasma jet reactor. Examples of these embodiments are described below. Fig. 6A , Figure 6B and Figure 7 Given.

[0079] In an embodiment of the present invention, plasma jet technology, preferably atmospheric pressure plasma jet technology, is combined with carbon donor particles for the industrial conversion of CO2 to CO. Thus, the plasma cleavage of CO2 molecules is carried out in an environment where CO radicals cannot immediately recombine with oxygen radicals, because these will be captured more quickly by the carbon donor particles in the plasma region and / or in the plasma afterglow region. The carbon donor particles preferably comprise pure carbon. This is achieved, for example, by activating CO2 with a plasma of appropriate energy in a carbon bed of small particles of (pure) carbon, thus:

[0080]

[0081] The idea is to add carbon to the process by using carbon donor particles, preferably pure carbon, in the reaction chamber. In this configuration, activated O can be brought into contact with the added carbon, thereby reacting efficiently with it to form CO. The carbon donor may preferably be natural coal, carbon black, activated coal, carbon fiber, coke, etc., or any combination thereof. The gas flow may preferably be continuous. At least a portion of the resulting product gas is recycled and supplied to the same or another plasma reactor together with additional fresh reaction gas containing CO2.

[0082] The method comprises the step of converting CO2 into CO using a reversible Boudouard reaction. The reversible Boudouard reaction is used to convert pure CO2 into pure CO based on the addition of carbon at a high temperature of at least 800°C.

[0083] Preferably, the plasma jet includes an afterglow region. The afterglow region refers to the region downstream of the electrode group in which excited species of the process gas are present. In the present case, these excited species can be: ionized species of O, CO, CO2; O, CO, CO2 radicals; excited neutral or charged O, CO, CO2 species; or any combination or mixture thereof. Preferably, the plasma jet afterglow includes CO radicals and / or oxygen (O) radicals.

[0084] Preferably, the reaction chamber comprises an afterglow zone of the plasma jet and / or preferably, the carbon donor particles in the reaction chamber are subjected to an afterglow zone of the plasma jet. Advantageously, heat and the presence of highly reactive species are utilized to improve the reaction equilibrium and reaction kinetics of the reverse Boudoir reaction. Advantageously, heat drives oxygen fixation in the carbon bed.

[0085] Preferably, the afterglow zone is optimized in length. This can preferably be achieved by using a CO2 volume flow rate of 10 to 1000 standard liters / minute / single plasma reactor. In addition, the afterglow zone can be optimized by adjusting the plasma reactor power, each individual plasma reactor in the range between 100W and 100,000W.

[0086] In a preferred embodiment, the plasma jet generator is selected from the following list: sliding arc (GA), glow discharge (GD), microwave discharge (MW), radio frequency discharge (RF), capacitively coupled discharge (CCD) or dielectric barrier discharge, preferably sliding arc (GA) or glow discharge (GD), most preferably sliding arc.

[0087] In another preferred embodiment, the plasma jet generator is selected from:

[0088] i. Gliding Arc Plasma Tube (GAP),

[0089] ii. Double Vortex Plasma Tube (DVP), or

[0090] iii. Atmospheric pressure glow discharge (APGD) plasma generator.

[0091] These plasma generators differ in their main performance characteristics, namely conversion efficiency and energy efficiency, as described below.

[0092] Reverse vortex flow (RVF) stabilized gliding arc plasma tube (GAP)

[0093] The GAP is somewhere in between, with conversion rates typically around 6%-7% and energy efficiencies around 30%.

[0094] GAP is a medium to high power (500W-800W) atmospheric pressure plasma source with established conversion performance of about 6%-7% (for pure CO2 cracking) and energy efficiency up to 32%, and for dry reforming of methane, conversion is 15% and energy efficiency is 65%.

[0095] Atmospheric Pressure Glow Discharge (APGD)

[0096] On the other hand, APGD can provide higher conversion (about 13%), but its energy efficiency is limited (25%). However, in all cases, the lower energy efficiency is not a limiting factor. In cases where heat recovery is desired, the lower energy efficiency means that more heat will be available to be recovered from the gas and fed back into the main process. Furthermore, if the price of electricity is low at a given moment (peak trimming of renewable resources), the lower energy efficiency becomes less of a problem (see below), while the high conversion is beneficial.

[0097] APGD is a low to medium power (100W-200W) atmospheric pressure plasma reactor. At laboratory scale (shown below), CO2 conversion rates of about 13% and energy efficiency of 25% are achieved.

[0098] Double Vortex Plasma Tube (DVP)

[0099] DVP can provide moderate conversion rates (9%-10%) with high energy efficiency. This means that it uses most of the electrical energy for CO2 separation, potentially saving electricity costs.

[0100] The DVP atmospheric pressure plasma reactor is a GA discharge type that uses both vortex and reverse vortex stabilization. It is a novel concept of configuring a dual-outlet symmetrical configuration. At a power of 450W, it is able to achieve a CO2 conversion rate of about 9.5% and an efficiency of up to 41%.

[0101] Since GAP, DVP and APGD can run on the same type of power supply, the system of the present invention may preferably include a combination of these three variants. Fundamentally, these three reactor technologies are very similar, so the ultimate goal is the reactor that provides its best performance metric.

[0102] Preferably, the plasma jet is obtained at about atmospheric pressure. Atmospheric pressure refers to a pressure close to 1 atm, preferably between 500 and 5000 hPa, more preferably at least 900 hPa, still more preferably at least 950 hPa, and / or more preferably at most 1100 hPa, still more preferably at most 1070 hPa, most preferably between 970 hPa and 1050 hPa, for example about 1013 hPa.

[0103] In a preferred embodiment of the present invention, the process gas comprises CO2 and CO in a weight ratio of at most 9 / 1, more preferably at most 8 / 2, more preferably at most 7 / 3, more preferably at most 6 / 4, more preferably at most 5 / 5. In another preferred embodiment of the present invention, the process gas comprises CO2 and CO in a weight ratio of at least 1 / 9, more preferably at least 2 / 8, more preferably at least 3 / 7, more preferably at least 4 / 6, more preferably at least 5 / 5. In another embodiment, the process gas comprises CO2 and CO in a ratio of 1 / 9-9 / 1, more preferably in a ratio of 2 / 8-8 / 2, more preferably in a ratio of 3 / 7-7 / 3, more preferably in a ratio of 4 / 6-6 / 4, and most preferably in a ratio of about 5 / 5. Mixtures with lower and higher CO2 to CO ratios have low thermal efficiency of the entire process; that is, after separation of the individual product streams.

[0104] High CO concentrations in the process gas are often a direct result of recycling or recirculation of product gas without first separating CO from said product gas, combined with oxygen removal by carbon donor particles, which inhibits recombination of O2 and CO to CO2.

[0105] In a preferred embodiment, the product gas contains O2 in an amount of at most 10 wt.%, more preferably at most 8 wt.% O2, more preferably at most 6 wt.% O2, more preferably at most 5 wt.% O2, more preferably at most 4 wt.% O2, more preferably at most 3 wt.% O2, more preferably at most 2 wt.% O2, more preferably at most 1 wt.% O2, more preferably at most 0.5 wt.% O2. The lack of oxygen is due to the fixation of O2 to the carbon donor particles, thereby preferentially forming CO and optionally forming CO2. In another preferred embodiment, the process gas contains O2 in an amount of at most 10 wt.%, more preferably at most 8 wt.% O2, more preferably at most 6 wt.% O2, more preferably at most 5 wt.% O2, more preferably at most 4 wt.% O2, more preferably at most 3 wt.% O2, more preferably at most 2 wt.% O2, more preferably at most 1 wt.% O2, more preferably at most 0.5 wt.% O2. Recirculation at high oxygen content results in the recombination of O2 and CO into CO2. Fixation of oxygen to CO by carbon donor particles allows oxygen to be avoided in the process gas without gas phase separation.

[0106] In a preferred embodiment of the present invention, the process gas comprises a product gas and a reaction gas in a weight ratio of at most 9 / 1, more preferably at most 8 / 2, more preferably at most 7 / 3, more preferably at most 6 / 4, more preferably at most 5 / 5. In another preferred embodiment of the present invention, the process gas comprises a product gas and a reaction gas in a weight ratio of at least 1 / 9, more preferably at least 2 / 8, more preferably at least 3 / 7, more preferably at least 4 / 6, more preferably at least 5 / 5. In another embodiment, the process gas comprises a product gas and a reaction gas in a ratio of 1 / 9-9 / 1, more preferably a ratio of 2 / 8-8 / 2, more preferably a ratio of 3 / 7-7 / 3, more preferably a ratio of 4 / 6-6 / 4, and most preferably a ratio of about 5 / 5.

[0107] In a preferred embodiment of the present invention, the reaction gas comprises CO2 which accounts for at least 80% by weight of the reaction gas. Preferably, the reaction gas comprises 90% by weight of CO2, more preferably 95% by weight of CO2. As used herein, the reaction gas refers to the fresh reactant added to the recycled portion of the product gas. Preferably, in this case, the reaction gas is close to the pure reactant, in which case the reactant is CO2. However, since the purification of CO2 is a very energy- and equipment-intensive process, from an energy point of view, it is preferred to use a waste gas stream containing a large amount of CO2 with minimal purification. Advantageously, the present method handles impurities well, in particular the reaction gas may contain oxygen, hydrogen, CO, hydrocarbons, nitrogen, nitrogen oxides, sulfur, sulfur oxides and hydrocarbons containing sulfur. In contrast, impurities usually need to be removed in the catalytic process.

[0108] In a preferred embodiment of the invention, the recycled portion of the product gas containing CO and CO2 is provided to the same plasma jet generator in the first step (i.). In this way, the recycling is carried out as a reflux process in the same reactor. This arrangement increases the residence time of the gas in the plasma jet and the reaction chamber. In addition, the use of one reactor reduces heat and radiation losses.

[0109] In another preferred embodiment of the present invention, the recycled portion of the product gas containing CO and CO2 is provided to the second plasma jet generator. In this way, the recycling is carried out as a multi-stage recycling, wherein the method comprises two or more reactors, wherein each reactor comprises a carbon reaction chamber and a plasma jet generator. This arrangement makes the method easier to scale up.

[0110] In a preferred embodiment of the present invention, a portion of the product gas is extracted as an extracted product gas, the extracted product gas comprising CO2 and CO in a weight ratio of 9 / 1, 8 / 2, 7 / 3, 6 / 4, 5 / 5, 4 / 6, 3 / 7, 2 / 8, 1 / 9 or any ratio therebetween. Preferably, the extracted product gas comprises CO2 and CO in a weight ratio of 6 / 4, 5 / 5, 4 / 6, 3 / 7, 2 / 8, 1 / 9 or any ratio therebetween. More preferably, the extracted product gas comprises CO2 and CO in a weight ratio of 4 / 6, 3 / 7, 2 / 8, 1 / 9 or any ratio therebetween. A low CO2 to CO ratio makes separation easier in separation. The high CO concentration in the extracted product gas is a direct result of the recycling or reflux of the product gas without first separating CO from the product gas.

[0111] In a preferred embodiment, the process gas may include additional gaseous species. In a preferred embodiment, the process gas may include inert or substantially inert gases, such as N2 and argon. In another preferred embodiment, the inlet gas may include flue gas, preferably flue gas of a combustion or metallurgical process. Flue gas typically contains nitrogen, argon, a small amount of oxygen and organic compounds. Oxygen and organic compounds are not required, but are typically decomposed into CO2 and / or CO after a single pass through the plasma generator and the carbon reaction chamber. The inventors surprisingly found that nitrogen and argon had little effect on the conversion of CO2 to CO.

[0112] In another embodiment, the extracted product gas comprising CO2 and CO is provided to a separation unit in which CO is purified from the extracted product gas. The separation unit separates a higher concentration of CO from a smaller gas stream compared to conventional techniques in which the separation unit is provided in a recycle loop.

[0113] In a preferred embodiment of the present invention, at least 20% of the product gas is recycled, more preferably at least 25% of the product gas is recycled, more preferably at least 30% of the product gas is recycled, more preferably at least 35% of the product gas is recycled, more preferably at least 40% of the product gas is recycled, more preferably at least 45% of the product gas is recycled, more preferably at least 55% of the product gas is recycled, more preferably at least 65% of the product gas is recycled, more preferably at least 70% of the product gas is recycled, more preferably at least 80% of the product gas is recycled, more preferably at least 85% of the product gas is recycled, more preferably at least 90% of the product gas is recycled.

[0114] In a preferred embodiment of the present invention, the recycling step (v.) is repeated at least 2 times, preferably at least 4 times, more preferably at least 6 times, and most preferably at least 8 times. The overall CO2 conversion rate increases with the increase in the amount of the recycling step.

[0115] In a preferred embodiment of the invention, the carbon donor particles are carbon particles in the form of a fine powder. These can preferably be supplied through an additional inlet together with a carrier gas (e.g. air), or together with the main process gas supply. These methods are most likely different, because one method will help the conversion in the post-plasma region (additional inlet), while the other method will affect the plasma chemistry in the discharge itself. For example, carbon particles in the plasma can promote faster CO formation, but on the other hand, consume molecular oxygen (O), which generally helps the CO2 cracking process (neutral impact).

[0116] Preferably, the carbon donor particles further comprise a CO2 to CO conversion catalyst.

[0117] In a particularly preferred embodiment of the present invention, the carbon donor particles are in a fluidized state. In another embodiment, the carbon donor particles are located in a fixed bed. In another embodiment, the downward flow of carbon donor particles is preferably generated under the influence of gravity, and the downward flow of carbon donor particles is exposed to O radicals, which are preferably countercurrent to the downward flow.

[0118] In fixed bed mode, the carbon particles preferably have a size with an average radius of 0.1 mm to 50 mm. Most preferably, the average radius is between 0.5 mm and 5 mm. In fluidized bed mode, the carbon particles preferably have a size with an average radius of 5 microns to 5000 microns. Most preferably, the average radius is between 50 microns and 500 microns.

[0119] In a further preferred embodiment, the porous carbon has a high specific surface area. The inventors have found that solid carbon particles with a high specific surface area reduce oxygen content after each pass, increase conversion rate and increase energy efficiency. In a preferred embodiment, the porous carbon has at least 300 m 2 / g, more preferably at least 400m 2 / g, more preferably at least 500m 2 / g, more preferably at least 600m 2 / g, more preferably at least 700m 2 / g, more preferably at least 800m 2 / g, more preferably at least 900m 2 / g, more preferably at least 1000m 2 / g, more preferably at least 1100m 2 / g, more preferably at least 1200m 2 The surface area is measured according to ISO 9277.

[0120] In a preferred embodiment of the present invention, the carbon donor particles are in the form of a fine powder. The powder is preferably supplied through an additional inlet for the carbon donor particles to aid in the conversion in the plasma afterglow region, and thus the supply may preferably be achieved using a carrier gas (e.g., air or CO2), or the powder may be supplied together with the main CO2 supply to affect the plasma chemistry in the discharge. For example, the carbon donor particles in the plasma may promote faster CO formation, while the carbon donor particles provided in a separate inlet may allow for more efficient cracking of CO2 into CO and O.

[0121] In a second aspect, the present invention relates to a system for converting CO2 into CO.

[0122] In a preferred embodiment of the present invention, the system comprises:

[0123] - a carbon reaction chamber comprising a gas inlet and a gas outlet;

[0124] - a plasma jet generator, the plasma jet generator comprising:

[0125] □ a process gas inlet adapted to supply a process gas comprising CO2 to the plasma jet generator;

[0126] □ a plasma jet outlet in fluid communication with a gas inlet of the carbon reaction chamber; and

[0127] □ a set of electrodes suitable for exciting a plasma in the process gas,

[0128] The gas outlet of the carbon reaction chamber is fluidically connected to the process gas inlet of the plasma jet generator.

[0129] In a particularly preferred embodiment of the present invention, the gas outlet of the reaction chamber is in fluid communication with the process gas inlet of the plasma jet generator.

[0130] The fluid communication between the gas outlet and the process gas inlet allows for the recirculation of the product gas. It has been shown that recirculating at least a portion of the product gas and providing the product gas comprising CO and CO2 to the plasma jet generator has a beneficial effect on the CO2 conversion rate. The product gas is recirculated two or more times through the plasma jet generator and the carbon reaction chamber to remove O2, which significantly improves the overall CO2 conversion rate.

[0131] The recycling referred to in the present disclosure may refer to: recycling at least a portion of the product gas and providing the product gas containing CO and CO2 to the same plasma jet generator (as a return flow) or providing the product gas containing CO and CO2 to a second plasma jet generator (as a multi-stage recycling).

[0132] In some embodiments, the system includes:

[0133] - a carbon reaction chamber comprising a gas inlet and a gas outlet;

[0134] - a plasma jet generator, the plasma jet generator comprising:

[0135] □ a process gas inlet adapted to supply a process gas comprising CO2 to the plasma jet generator;

[0136] □ a plasma jet outlet in fluid communication with a gas inlet of the carbon reaction chamber; and

[0137] □ a set of electrodes suitable for exciting a plasma in the process gas,

[0138] Wherein, the gas outlet of the carbon reaction chamber is in fluid communication with the process gas inlet of the plasma jet generator.

[0139] In other embodiments, the system includes:

[0140] - a first carbon reaction chamber, the first carbon reaction chamber comprising a gas inlet and a gas outlet;

[0141] - a first plasma jet generator, the first plasma jet generator comprising:

[0142] □ A process gas inlet adapted to supply a process gas containing CO2 to the plasma jet generator

[0143] □ a plasma jet outlet in fluid communication with the gas inlet of the first carbon reaction chamber; and

[0144] □ a set of electrodes suitable for exciting a plasma in the process gas,

[0145] The gas outlet of the first carbon reaction chamber is fluidically connected to the process gas inlet of the second plasma jet generator.

[0146] Thus, the second plasma jet generator comprises a process gas inlet, a plasma jet outlet in fluid communication with a gas inlet of a second carbon reaction chamber, which also comprises a gas inlet and a gas outlet, and a set of electrodes adapted to ignite a plasma in the process gas or product gas.

[0147] These embodiments may also be combined such that the gas outlet of the first carbon reaction chamber is in fluid communication with the process gas inlet of the first plasma jet generator and in fluid communication with the process gas inlet of the second plasma jet generator.

[0148] Based on the addition of carbon at a high temperature of at least 800° C., the reverse Boudouard reaction is used to convert pure CO 2 into pure CO. Therefore, preferably, the reaction chamber comprises a temperature control system, which is preferably configured to maintain the temperature in the reaction chamber at at least 800° C.

[0149] Oxygen (O and O2) is fixed in carbon to form CO at a temperature of 700°C or higher. Therefore, preferably, the reaction chamber comprises a temperature control system, which is preferably configured to maintain the temperature in the reaction chamber at at least 700°C, more preferably, the temperature in the reaction chamber is at least 750°C, more preferably, the temperature in the reaction chamber is at least 800°C, more preferably, the temperature in the reaction chamber is at least 850°C, more preferably, the temperature in the reaction chamber is at least 900°C, more preferably, the temperature in the reaction chamber is at least 950°C, more preferably, the temperature in the reaction chamber is at least 1000°C.

[0150] In a preferred embodiment of the system, the plasma jet outlet is located in the reaction chamber, thereby ensuring that the plasma jet afterglow is within the reaction chamber and the carbon donor (preferably carbon donor particles, more preferably pure carbon particles) is subjected to the plasma jet afterglow containing excited CO2 species.

[0151] In a preferred embodiment, the plasma jet generator is selected from the following list: sliding arc (GA), glow discharge (GD), microwave discharge (MW), radio frequency discharge (RF), capacitively coupled discharge (CCD) or dielectric barrier discharge, preferably sliding arc (GA) or glow discharge (GD), most preferably sliding arc.

[0152] In another preferred embodiment, the plasma jet generator comprises:

[0153] i. Gliding Arc Plasma Tube (GAP), or

[0154] ii. Double Vortex Plasma Tube (DVP), or

[0155] iii. Atmospheric pressure glow discharge (APGD) plasma generator.

[0156] In a preferred embodiment, the plasma jet generator comprises a plurality of similarly sized (preferably equal-sized) plasma reactors suitable for parallel operation. Due to the nonlinear characteristics of atmospheric pressure plasma, it is generally difficult and problematic to scale up plasma reactors. Advantageously, the plasma generating device may include a stack of similarly sized plasma reactors operating in parallel. The plasma reactor stack may advantageously be connected to a single carbon reaction chamber. In a preferred embodiment, the plasma generating device comprises the following stack, preferably consisting of the following stack, which has at least 2, more preferably at least 3, more preferably at least 4, more preferably at least 5, more preferably at least 6, more preferably at least 8, more preferably at least 10, more preferably at least 12, more preferably at least 14, and most preferably at least 16 plasma reactor modules of similar size (preferably equal size) operating in series. In a preferred embodiment, the plasma generating device comprises the following stack, preferably consisting of the following stack, which has at most 50, more preferably at most 40, more preferably at most 30, more preferably at most 25, and most preferably at most 20 plasma reactor modules operating in series. In a preferred embodiment, a plurality of plasma reactor modules are connected to a single carbon reaction chamber, and a stack of plasma reactor modules (ie, all plasma reactor modules) are connected to a single carbon reaction chamber.

[0157] The carbon reaction chamber includes a device suitable for holding or providing a carbon donor. Preferably, the carbon donor is a solid particle containing carbon. More preferably, the carbon reaction chamber includes: (a) a device for maintaining a fixed carbon (preferably porous carbon) bed; and / or (b) a device for fluidizing carbon particles (preferably porous carbon particles). Solid carbon is preferred because it makes process control easier than the addition of gaseous species and because it allows the use of carbon donors with fewer non-carbon elements. For example, gaseous hydrocarbons can be used as carbon donors, but hydrogen is introduced into the circulation system. This has several undesirable effects, such as the formation of water, a reduction in conversion rate and energy efficiency, and an increase in scaling. Porous carbon is preferred because it greatly increases the gas-solid interface where the reaction occurs.

[0158] In a particularly preferred embodiment of the invention, the carbon reaction chamber is a fluidized bed reactor configured to fluidize the carbon donor particles. In a further preferred embodiment, the system comprises a continuous carbon feed device, preferably a gravity driven barrel, a rotating screw, a conveyor belt or a combination thereof; adapted to provide the carbon donor particles to the fluidized bed. This advantageously allows for fully continuous operation.

[0159] In another particularly preferred embodiment, the carbon reaction chamber is a fixed carbon bed. Preferably, the position of the fixed carbon bed can be adjusted.

[0160] In another embodiment, the carbon reaction chamber is a powder downflow reaction chamber configured to generate a downflow of carbon donor particles, preferably under the influence of gravity, while exposing the downflow of carbon donor particles to O radicals.

[0161] In an embodiment of the invention, the system comprises a catalyst. Catalysts of particular interest are CO2 to CO conversion catalysts and catalysts for the reverse Boudoir reaction.

[0162] In a preferred embodiment of the present invention, the reaction chamber comprises a particle inlet for introducing carbon donor particles into the reaction chamber, preferably for continuously introducing carbon donor particles into the reaction chamber.

[0163] In a preferred embodiment of the invention, said fluid communication between the gas outlet of the reaction chamber and the process gas inlet of the plasma jet generator does not comprise a gas separation unit. This allows the recirculation of product gas without purification or separation between recirculation passes.

[0164] In a preferred embodiment of the invention, the gas outlet of the reaction chamber is in fluid communication with the process gas inlet of the plasma jet generator. This allows a recirculation of product gas in a system, wherein the product gas can be redirected to the process gas inlet of the plasma generator. This arrangement increases the residence time of the gas in the plasma jet and the reaction chamber. Furthermore, the use of one reactor reduces heat and radiation losses.

[0165] In another preferred embodiment of the invention, the gas outlet of the reaction chamber is in fluid communication with the process gas inlet of a second plasma jet generator, which is preferably in a second reactor comprising a carbon reaction chamber. In this way, the recycling can be performed as a multi-stage recycling, wherein the system comprises two or more reactors, wherein each reactor comprises a carbon reaction chamber and a plasma jet generator. This arrangement makes the method easier to scale up.

[0166] In another preferred embodiment of the present invention, the gas outlet of the reaction chamber is fluidly connected to the process gas inlet of the first plasma jet generator and the process gas inlet of the second plasma jet generator, and the second plasma jet generator is preferably in a second reactor containing a carbon reaction chamber. In this way, recycling can be carried out as a multi-stage recycling with reflux, wherein the system includes two or more reactors and a reflux cycle, wherein each reactor includes a carbon reaction chamber and a plasma jet generator. This arrangement makes it easier to expand the method. The reflux cycle can be located between any reactors, for example, the gas outlet of the reaction chamber of the second reactor can be fluidly connected to the process gas inlet of the plasma jet generator of the third reactor and the process gas inlet of its own plasma jet generator.

[0167] The present invention is further described by the following non-limiting examples, which further illustrate the invention and are not intended, nor should they be construed, to limit the scope of the invention.

[0168] EXAMPLES AND DRAWINGS

[0169] Reverse Boudoir reaction

[0170] The Boudouard reaction, named after Octave Leopold Boudouard, is a redox reaction of a chemically balanced mixture of carbon monoxide and carbon dioxide at a given temperature. Of particular interest in this application is its reverse, the disproportionation of carbon monoxide to carbon dioxide and graphite or its reverse:

[0171]

[0172] The reverse Boudoir reaction is endothermic with a ΔH of 172 kJ / mol. Higher temperatures shift the equilibrium completely to the product side (carbon monoxide) according to the LeChatelier principle. As pressure increases, the equilibrium shifts to the other side because the number of gas molecules decreases. Figure 1 And Table 1 below shows the percent composition of the equilibrium mixture at various temperatures (each at a standard pressure of 100,000 Pa).

[0173] Table 1

[0174] Temperature(℃) %CO2 %CO 450 98 2 600 77 23 700 42 58 800 6 94 900 3 97 1000 1 99

[0175] Example 1: Composition of process gas

[0176] Preferably, the process gas comprises CO2 and CO and optionally a small amount of O2, and more preferably, the process gas consists of CO2 and CO and optionally a small amount of O2. However, most CO2 point sources available in the industry do not provide clean CO2. Therefore, in another preferred embodiment, in addition to CO2 and CO gases, the process gas may also include other gases. In a particularly preferred embodiment, the process gas is a mixed gas stream comprising CO2 and any one or any combination of the following gases: nitrogen (N2), hydrogen (H2), water (H2O) and methane (CH4).

[0177] In Table 2, an exemplary mixture of preferred process gases, preferably from a blast furnace, is disclosed:

[0178] Table 2

[0179] type vol% Nitrogen 46.59 Carbon dioxide (CO2) 24.50 Carbon monoxide (CO) 23.85 Hydrogen (H2) 3.84 Oxygen (O2) 1.20 Methane (CH4) 0.016

[0180] Other gases in the process gas may include benzene, toluene, ethylene and / or acetylene, preferably in very small concentrations (10 vol.ppm or less). Note that the main non-CO2 gas is preferably N2, for example 46.59 vol%. However, concentrations of up to 50% N2 do not appear to negatively affect effective conversion or energy efficiency. The oxygen content is preferably quite small (less than 5 vol%, for example about 1.2%). We note that the method and system of the present invention minimizes the oxygen content after the carbon bed, thereby reducing the oxygen content in the recycled process gas.

[0181] Example 2: Plasma Jet Exit

[0182] Figure 2 A preferred embodiment of the system is shown. A process gas 1 comprising CO2 is supplied to a pressure chamber 2 which is fluidically connected to four (three shown) gliding arc plasma generators 3. The plasma jet is introduced into a fluidized bed 4 which serves as a carbon reaction chamber in which the carbon particles are recirculated 5. At the top of the fluidized bed, a product gas 9 comprising CO is extracted. A portion of the extracted product gas 9 is recirculated and included in the process gas 1.

[0183] Example 3: Carbon Reaction Chamber

[0184] Example 3 is a preferred embodiment of the system according to the present invention using a fixed carbon bed. Figure 3 , a carbon reaction chamber 6 with a fixed bed of carbon particles 7 is shown. A process gas 1 including CO2 is supplied to a pressure chamber 2, which is fluidically connected to four (three are shown) sliding arc plasma generators 3. The plasma jet is directed into the carbon reaction chamber 6, in which the fixed porous carbon bed 7 is located. The longitudinal position of the fixed porous carbon bed 7 can be adjusted to optimize the fixation of oxygen and the production of CO. A product gas 9 is extracted from the carbon reaction chamber 6. A portion of the extracted product gas 9 is recycled and included in the process gas 1.

[0185] The goal is to promote the internal reverse Boudoir reaction. The fixed carbon bed can preferably be optimized using fluid dynamics and plasma model simulations or laboratory testing, and the focus can be on increasing the residence time within the carbon bed and achieving the optimal reaction temperature (preferably at least 1200 K). In addition, the carbon particle size, shape, porosity, surface area, and carbon bed length and residence time can be optimized.

[0186] Example 4

[0187] exist Figure 4In the figure, a carbon reaction chamber 10 with crushed carbon particles 11 is shown. A mixture of CO2, CO and O2 enters 12 the carbon reaction chamber 10. In the carbon reaction chamber 10, the carbon (C) in the crushed carbon particles 11 reacts with O to form CO. Thus, a CO-rich gas stream 13 leaves the carbon reaction chamber 10. Advantageously, the crushed carbon particles 11 are supplied to the carbon reaction chamber through two inlets 14 in a manner that forms a vortex. This improves mixing and increases the contact time between reactive species (especially in the afterglow of the plasma generator) and the carbon particles.

[0188] Comparative Example 5 and Example 6

[0189] An experiment was conducted to test the effect of a carbon bed on multiple passes through a plasma generator, with no separation between each pass. The output of the system was fully recycled and used as process gas. The CO2 conversion for each pass was determined as well as the energy efficiency of each pass. Three replicates were performed, each with four passes.

[0190] In comparative example 5, CO2 is passed through a system according to example 3 in which the fixed carbon bed is removed. No carbon donor is present.

[0191] In Example 6, CO2 was passed through the same system as shown in Example 3, but with a fixed carbon bed in place.

[0192] Figure 5A The conversion rate per pass for Comparative Example 5 and Example 6 is shown. Figure 5A It is shown that the CO2 conversion per pass dropped from 8.09% to 6.46% from the first pass to the fourth pass in Example 6. In the absence of a carbon donor, the conversion per pass dropped to 4.04% by the fourth pass.

[0193] Figure 5B The energy efficiency (expressed by specific energy input (SEI)) for each pass of Comparative Example 5 and Example 6 is shown. The energy efficiency shows the same trend as the conversion rate. Example 6 shows that the energy efficiency of each pass from the first pass to the fourth pass drops from 24% to 19%. Comparative Example 5 shows a greater drop in energy efficiency, from 24% to 12%, respectively.

[0194] We note that the effect of the carbon bed on each pass is very small. However, for each additional pass without separated product, the conversion and energy efficiency are improved when the carbon bed is present. The difference in cumulative conversion and energy efficiency is significant and increases with each additional pass.

[0195] Example 7: Process design and mass balance

[0196] Example 6 relates to an embodiment of the invention in which a portion of the plasma reactor output is recycled without separation. The extracted product is sent to a separation unit. This allows the separation unit to operate at higher CO to CO2 concentrations and smaller mass flow rates than a similar device without a carbon reaction chamber.

[0197] For a better example, refer to Fig. 6A and Figure 6B The process gas 15 comprising CO2 and CO enters the plasma jet generator 19, where a plasma 18 is generated by a plasma generating device 30, which is preferably an electrode with a high potential difference. The CO2 in the process gas 15 is converted into CO and 1 / 2O2 according to the following chemical reaction:

[0198]

[0199] The plasma jet generator 19 and the carbon reaction chamber 22 containing the carbon donor particles are fluidly connected 31. The plasma jet afterglow 20 reaches the carbon reaction chamber 22. In the carbon reaction chamber 22, oxygen is captured by the carbon donor particles and converted into CO according to a chemical reaction:

[0200]

[0201] Carbon donor particles are supplied to the carbon reaction chamber 22 via the carbon particle inlet 24. The product gas 25 comprising CO2 and CO2 leaves the carbon reaction chamber 22 via the gas outlet 32. A portion of the product gas 25 is recycled as recycled product gas 17. The recycled product gas 17 is enriched with the reaction gas 16 comprising CO2 to enter the plasma jet generator 19 as process gas 15. A second portion of the product gas 25 is extracted as an extracted product gas 26 comprising CO2 and CO and is provided to the separation unit 27. In the separation unit 27, the extracted product gas 26 is separated into a CO gas stream 28 and a CO2 gas stream 29.

[0202] Figure 6B Shows Fig. 6A The steady state mass balance of the reactor unit is determined by estimating that a mixture of CO2 and CO of 50 / 50 by weight can be obtained. The notation "u" is used as an arbitrary unit of mass flow rate. It is assumed that the fixation of oxygen in the carbon reaction chamber 22 is perfect, that is to say that no oxygen is present in the product. It is also assumed that the separation 27 is perfect. In this example, 10% of the product gas 25 is extracted product gas 26 to be separated. The recycle ratio R is the ratio of the mass flow rate of the recycle to the mass flow rate of the combined input (both carbon and CO2).

[0203] Example 8: Reaction Scheme

[0204] Example 8 relates to a preferred embodiment of the present invention, wherein the plasma reactor output is recycled to the second plasma reactor without separation. Figure 7 The reaction gas 16' containing CO2 and optionally CO enters the plasma jet generator 19', in which the plasma 18' is generated by the plasma generating device 30', which is preferably an electrode with a high potential difference. The CO2 in the reaction gas 16' is converted into CO and 1 / 2O2 according to the following chemical reaction:

[0205]

[0206] The plasma jet generator 19' is fluidly connected 31' to a carbon reaction chamber 22' containing carbon donor particles. The plasma jet afterglow 20' reaches the carbon reaction chamber 22'. In the carbon reaction chamber 22', oxygen is captured by the carbon donor particles and converted into CO according to a chemical reaction:

[0207]

[0208] Carbon donor particles are supplied to the carbon reaction chamber 22' through the carbon particle inlet 24'. The product gas 25' containing CO2 and CO leaves the carbon reaction chamber 22' and enters the second plasma reactor b as described above. In this embodiment of the present invention, the gas flow is sent through four plasma reactors (a, b, c, d). When the product gas 25" containing CO2 and CO leaves the carbon reaction chamber 22" of the last plasma reactor connected in series, in the plasma reactor d of this embodiment, the product gas 25" containing CO2 and CO is extracted and provided to the separation unit 27'. In the separation unit 27', the extracted product gas 25" is separated into a CO gas flow 28' and a CO2 gas flow 29'. Providing a reflux into the system or process is an option, wherein a portion of the product gas leaving the plasma reactor can be recycled to the inlet of the previous plasma reactor as recycled product gas 17'.

[0209] Example 9: Carbon Feed System

[0210] Figure 8 A schematic diagram of a fluidized carbon bed 4 ′ is shown which is continuously fed with carbon particles via a gravity based delivery system 31 connected to a carbon cartridge 30 .

[0211] Example 10: Parallel plasma reactors sharing a common fluidized carbon bed

[0212] Fig. 9 A schematic diagram of a system according to a preferred embodiment of the present invention is shown. Fig. 9A system is shown featuring a plurality of (four are shown) plasma reactor nodes 43 that share a common fluidized carbon bed. A continuous carbon feed device 44 supplies carbon particles to the fluidized carbon bed, which is delivered to an ash removal system 46 via a continuous conveying system having a rotating baffle 45. Product gas 47 flows upward to a gas collection system 48, which is preferably provided with a filter to prevent the passage of solids. A portion of the collected product gas is extracted 49. The remainder of the collected product gas, in addition to the fresh reactant 42 (i.e., the gas stream containing CO2), is recycled to the plasma reactor node 43 via a recirculation channel 41.

Claims

1. A method for converting CO2 into CO, the method comprising the following steps: i. providing a process gas (15, 16') comprising CO2 and optionally CO to a plasma jet generator (19, 19'); ii. exciting a plasma (18, 18') in the process gas (15, 16') by means of the plasma jet generator (19, 19'), thereby obtaining a plasma jet (20, 20') containing CO and O species; iii. introducing the plasma jet (20, 20') into a carbon reaction chamber (22, 22') containing carbon donor particles, thereby allowing O species in the plasma jet (20, 20') to preferentially combine with carbon to form CO; iv. extracting a product gas from the carbon reaction chamber (22, 22'), the product gas (25, 25') comprising the CO and CO2, Wherein, the method further comprises the following steps: v. Recirculating at least a portion of the product gas and providing the product gas comprising CO and CO2 to the plasma jet generator (19) or a second plasma jet generator.

2. The method according to claim 1, wherein: The process gas comprises a product gas and a reaction gas in a weight ratio of at most 8 / 2, and preferably, the reaction gas comprises at least 80 wt % of CO 2 relative to the total weight of the reaction gas.

3. The method according to claim 1 or 2, wherein: The recycled portion of the product gas comprising CO and CO 2 is provided to the same plasma jet generator as in the first step (i.).

4. The method according to claim 1 or 2, wherein: The recycled portion of the product gas comprising CO and CO 2 is provided to a second plasma jet generator.

5. The method according to any one of the preceding claims 1 to 4, wherein: A portion of the product gas is extracted as extracted product gas, which contains at most 50% CO2.

6. The method according to claim 5, wherein: The extracted product gas comprising 40% CO2 and CO is provided to a separation unit where CO is purified from the extracted product gas.

7. The method according to any one of the preceding claims 1 to 6, wherein: At least 50% of the product gas is recycled.

8. The method according to any one of the preceding claims 1 to 7, wherein: The carbon donor particles are in a fluidized state.

9. The method according to any one of the preceding claims 1 to 8, wherein: The recycling step (v.) was repeated at least 2 times.

10. A system for converting CO2 into CO, the system comprising: - a carbon reaction chamber (22, 22') comprising a gas inlet and a gas outlet; - a plasma jet generator (19, 19'), comprising: □ a process gas inlet adapted to supply a process gas containing CO2 to the plasma jet generator (19, 19'); □ a plasma jet outlet in fluid communication (31, 31') with a gas inlet of the carbon reaction chamber (22, 22'); and □ A set of electrodes (30, 30') suitable for exciting a plasma (18, 18')， wherein the gas outlet of the carbon reaction chamber (22) is fluidically connected to a process gas inlet of the plasma jet generator (19), or wherein the gas outlet of the carbon reaction chamber (22') is fluidically connected to a process gas inlet of a second plasma jet generator.

11. The system according to claim 10, wherein: The fluid communication between the gas outlet of the carbon reaction chamber (22, 22') and the process gas inlet of the plasma jet generator (19, 19') does not include a gas separation unit.

12. The system according to claim 10 or 11, wherein: The gas outlet of the carbon reaction chamber (22) is in fluid communication with the process gas inlet of the plasma jet generator (19).

13. The system according to any one of claims 10 to 11, wherein: The gas outlet of the carbon reaction chamber (22') is in fluid communication with a process gas inlet of a second plasma jet generator.

14. The system according to any one of claims 10 to 13, comprising a continuous carbon feed device (24, 24'), preferably, the continuous carbon feed device (24, 24') is a gravity driven barrel (30), a rotating screw, a conveyor belt or a combination thereof.

15. A system according to any one of claims 10 to 14, wherein: The plasma jet generator (19, 19') comprises a plurality of similarly sized plasma reactors adapted to operate in parallel, preferably the similar sizes being equal sizes.

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