Direct air capture with integrated co 2 reduction

Abstract

The present invention relates to a method and a system for producing carbon monoxide. In particular, the present invention relates to a method and a system for producing carbon monoxide by electrolysing a molten metal carbonate obtained by absorbing carbon dioxide in a metal oxide.

Description

DIRECT AIR CAPTURE WITH INTEGRATED C02REDUCTION

[0001] This application claims priority from Australian Provisional Patent Application No. 2024903945 filed on 29 November 2024, the content of which is incorporated herein by reference in its entirety.Field of the Invention

[0002] The present invention relates to a method and a system for producing carbon monoxide. In particular, the present invention relates to a method and a system for producing carbon monoxide by electrolysing a molten metal carbonate obtained by absorbing carbon dioxide in a metal oxide. However, it will be appreciated that the invention is not limited to these particular fields of use.Background of the Invention

[0003] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0004] Global energy demand continues to increase year on year. While there are many sources of energy such as coal, natural gas, nuclear and oil, coal continues to be one of the major sources for electricity energy production. However, use of coal-fired power stations is highly polluting and releases harmful greenhouse gases. Development of low-carbon or carbon-neutral energy sources has been of particular interest in many industries due to environmental concerns and in pursuit of net-zero carbon emissions.

[0005] Two of the industries that require low-carbon or carbon neutral energy sources are the aviation and shipping sectors. Many countries, for example Australia which is an island continent, rely on air and sea transport to connect with the rest of the world. Yet the planes and ships that power these sectors have few viable technological options to decarbonise within the next 20 to 30 years. The aviation industry spends half a trillion dollars on aviation fuel annually, which when burnt accounts for 2.5% of global CO2 emissions. International governments such as the EU, UK and US have mandated for the increasing use of sustainable aviation fuels (SAFs), including a requirement that by 2030 6% of all EU sold aviation fuel must be SAF, rising to 63% in 2050. The International Maritime Organisation is pursuing similar incentive schemes to increase synthetic fuel use (renewable diesel and methanol) in the shipping sector.

[0006] In the aviation industry, current SAFs, which account for about 0.1% of the total market, are produced from tallows and used cooking oils. These and other biological feedstocks cannot scale to meet the volumes required of this rapidly expanding SAF market, with land-use constraints and process efficiency being limiting. Alternatively, synthetic and sustainable hydrocarbon fuels may be produced from a mixture of carbon monoxide and hydrogen, known as syngas, using processes such as the Fischer- Tropsch process, or methanol synthesis. If the carbon monoxide and hydrogen used to form the syngas comes from low carbon sources, using renewable energy, then the resulting hydrocarbon fuels can be produced using only low or zero carbon emissions. Hence synthetic fuels represent a viable pathway for the aviation and shipping sectors to decarbonise.

[0007] A possible precursor of carbon monoxide is carbon dioxide. Direct air capture (DAC) refers to a chemical or physical process that extracts carbon dioxide from ambient air. Under conventional thinking, the captured carbon dioxide is stored or used as feedstock to produce industrial products. DAC has seen a surge in interest because it has the potential to achieve carbon neutrality. Current DAC processes are expensive due to Sherwood's Rule, that states that the cost of an absorption process scales as the magnitude of the driving concentration decreases. For DAC the driving CO2 concentration in the atmosphere is only about 400ppm, which is very low, hence requiring a large surface area to drive meaningful mass transfer, potentially combined with fans to drive large volumes of air over the sorbent. Processes that utilise conventional process equipment therefore tend to be very expensive as massive scale is required (that is, large numbers of large vessels) to achieve the large sorbent surface area. Use of fans to further drive mass transfer further increases the cost. Finally, many proposed absorbants such as the amine-based ones degrade to toxic products in high oxygen environments or deteriorate through use in dirty environments or after multiple cycles, adding additional costs and environmental constraints. Alternatively, other carbon dioxide sources may be considered, for example, gases containing a high concentration of CO2 or flue gas.

[0008] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0009] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.Summary of the Invention

[0010] According to a first aspect of the present invention there is provided a method of producing carbon monoxide, the method comprising the steps of: a) providing an absorbant comprising a metal oxide; b) allowing the absorbant to absorb carbon dioxide to thereby convert at least a portion of the metal oxide to a metal carbonate; c) heating the absorbant to produce a heated absorbant comprising a molten metal carbonate; d) subjecting the heated absorbant to an electrolysis process to thereby produce carbon monoxide and oxygen.

[0011] In some embodiments, the absorbant is a solid absorbant. In some embodiments, the absorbant is a granular absorbant. In some embodiments, the absorbant is a solid and granular absorbant.

[0012] In some embodiments, the heated absorbant comprises any unconverted metal oxide from step b), the unconverted metal oxide forming a precipitate during the electrolysis process.

[0013] In some embodiments, about 1 %, 5 %, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or 100% of the metal carbonate in the absorbant (molar basis) is converted to the metal oxide by electrolysis. In preferred embodiments, about 5% to about 20% of the metal carbonate in the absorbant (molar basis) is converted to the metal oxide by electrolysis.

[0014] In some embodiments, about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or 100% of the metal oxide in the absorbant is converted to the metal carbonate in step (b).

[0015] In some embodiments, about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or 100% of the heated absorbant is the molten metal carbonate.

[0016] In some embodiments, the electrolysis process converts the molten metal carbonate to metal oxide, the metal oxide forming a precipitate.

[0017] In some embodiments, the electrolysis process converts the molten metal carbonate to metal oxide, the metal oxide forming a separate phase within the molten metal carbonate when solidified.

[0018] In some embodiments, the method further comprises a step of recycling the precipitate as the absorbant in step a).

[0019] In some embodiments, the method comprises a step of collecting the precipitate in a settling suspension.

[0020] In some embodiments, the suspension comprises the precipitate and the molten metal carbonate.

[0021] In some embodiments, the suspension is a molten suspension.

[0022] In some embodiments, metal oxide is present in the suspension in an amount of about 20% to about 30%, about 30% to about 40%, about 40% to about 50%, about 50% to about 60%, about 60% to about 70%, about 70% to about 80%, about 80% to about 90%, about 90% to 99%, or about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 99% (molar basis). In some embodiments, metal oxide is present in the suspension in an amount of about 20% to about 99% (molar basis)

[0023] In some embodiments, the precipitate is present in an amount of about 30% v / v to about 90% v / v in the molten suspension, for example, about 30% v / v to 40% v / v, about 40% to 50% v / v, about 50% to 60% v / v, about 60% to 70% v / v, or about 70% to 80% v / v, or about 80% to 90% v / v, or about 30% v / v, 40% v / v, 50% v / v, 60% v / v, 70% v / v, 80% v / v, or 90% v / v.

[0024] In some embodiments, the method further comprises a step of solidifying the molten metal carbonate in the suspension, and recycling the solidified metal carbonate.

[0025] The skilled person would appreciate that the recycled metal carbonate may be mixed with the absorbant in step a) to be melted and electrolysed. Alternatively, the recycled metal carbonate may be directly melted and electrolysed.

[0026] In some embodiments, the method further comprises a step of solidifying the suspension to provide a solidified suspension.

[0027] In some embodiments, the method further comprises a step of subjecting the solidified suspension to a milling process.

[0028] In a specific embodiment, at least a portion of the suspension is solidified into granules and recycled as absorbant in step a).

[0029] In some embodiments, a portion of thermal energy required to heat the absorbant in the step c) is provided by the suspension via heat exchanging means.

[0030] In some embodiments, a portion of thermal energy required to heat the absorbant in the step c) is provided by the recycled precipitate via heat exchanging means.

[0031] In some embodiments, melting point of the metal oxide is higher than that of the metal carbonate.

[0032] In some embodiments, density of the metal oxide is higher than that of the molten metal carbonate. The skilled person would understand that the metal oxide would settle in the molten metal carbonate.

[0033] In some embodiments, the absorbant is in the form of granules. The skilled person would understand that the granular form may facilitate CO2 absorption by allowing CO2 containing gas to move or diffuse between the granules.

[0034] In some embodiments, the step a) comprises providing the absorbant as an absorbant bed with a depth of about 1 cm to about 6 m, preferably about 50 cm, for example about 1 cm to about 10 cm, about 10 cm to about 20 cm, about 20 cm to about 30 cm, about 30 cm to about 40 cm, about 40 cm to about 50 cm, about 50 cm to about 60 cm, about 60 cm to about 70 cm, about 70 cm to about 80 cm, about 80 cm to about 90 cm, about 90 cm to about 1 m, about 1 m to about 2 m, about 2 m to about 3 m, about 3 m to about 4 m, about 4 m to about 5 m, or about 5 m to about 6 m.

[0035] In some embodiments, the step a) comprises providing the absorbant as an absorbant bed with a depth of about 0.1 mm to about 5 cm, preferably about 5 cm, for example about 0.1 mm to about 0.5 cm, about 0.1 mm to about 50 mm, about 0.1 mm to about 10 mm, about 0.1 mm to about 5 mm, about 0.1 mm to about 2 mm, about 0.1 cm to about 0.5cm, about 0.5cm to about 1cm, about 1cm to about 2cm, about 2 cm to about 3 cm, about 3 cm to about 4 cm, about 4 cm to about 5 cm.

[0036] In certain embodiments, the absorbant bed has a height of about 5 mm.

[0037] In some embodiments, the absorbant bed occupies an area of about 10 m2to about 1 ,000,000 m2, for example, about 10 m2to about 100 m2, about 100 m2to about 500 m2, about 500 m2to about 1000 m2, about 1000 m2to about 2500 m2, about 2500 m2to about 5000 m2, about 5000 m2to about 7500 m2, about 7500 m2to about 10,000 m2, about 10,000 m2to about 20,000 m2, about 20,000 m2to about 30,000 m2, about 30,000 m2to about 40,000 m2, about 40,000 m2to about 50,000 m2, about 50,000 m2to about 60,000 m2, about 60,000 m2to about 70,000 m2, about 70,000 m2to about 80,000 m2, about 80,000 m2to about 90,000 m2, about 90,000 m2to about 100,000 m2, about100,000 m2to about 200,000 m2, about 200,000 m2to about 300,000 m2, about 300,000 m2to about 400,000 m2, about 400,000 m2to about 500,000 m2, about 500,000 m2to about 600,000 m2, about 600,000 m2to about 700,000 m2, about 700,000 m2to about 800,000 m2, about 800,000 m2to about 900,000 m2, about 900,000 m2to about 1 ,000,000 m2.

[0038] The skilled person would appreciate that the area of the absorbant may be related to the desired production rate of CO or size of the facility.

[0039] In some embodiments, the step b) comprises allowing the absorbant to absorb carbon dioxide for a period of about 1 day to about 2 months, or about 0.5 to about 3 days, for example, about 0.1 , 0.5, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 days, or about 1 , 1.1 , 1.2, 1.3, 1.4, 1.5, 1 .6, 1.7, 1.8, 1.9 or 2 months.

[0040] In some embodiments, the step b) comprises allowing the absorbant to absorb carbon dioxide for a period of about 4 hours to about 60 days, about 4 hours to about 40 hours, about 20 hours to about 40 hours, about 4 hours to about 10 hours, about 10 hours to about 15 hours, about 15 hours to about 20 hours, about 20 hours to about 25 hours, about 25 hours to about 30 hours, about 30 hours to about 35 hours, about 35 hours to about 40 hours, about 40 hours to about 45 hours, about 45 hours to 2 days, about 2 days to about 5 days, about 5 days to about 10 days, about 10 days to about 15 days, about 15 days to about 20 days, about 20 days to about 30 days, about 30 days to about 40 days, about 40 days to about 50 days, about 50 days to about 60 days.

[0041] In certain embodiments, step b) comprises allowing the absorbant to absorb carbon dioxide for a period of about 48 hours.

[0042] In some embodiments, the step b) comprises absorbing the carbon dioxide from air. The skilled person will appreciate that this may be considered as direct air capture.

[0043] In certain embodiments, the step b) comprises passively absorbing the carbon dioxide from air. The skilled person would understand that this means carbon dioxide does not need to be injected or actively introduced to the absorbant.

[0044] In some embodiments, absorbing carbon dioxide comprises providing advection of air over the absorbant bed via wind.

[0045] The skilled person would appreciate that absorbing carbon dioxide in step (b) may not necessarily be passive. In some embodiments, absorbing carbon dioxide comprises providing advection of air over the absorbant bed via fans.

[0046] In some embodiments, the step b) comprises absorbing the carbon dioxide from a CO2 source, for example a gas containing a high concentration of CO2. In certain embodiments, the step b) comprises absorbing the carbon dioxide from flue gas.

[0047] In some embodiments, the metal oxide is lithium oxide.

[0048] In some embodiments, the metal carbonate is lithium carbonate.

[0049] In some embodiments, the step d) comprises electrolysing the molten metal carbonate with two or more than two electrodes.

[0050] In some embodiments, one or more of the electrodes is a louvered electrode.

[0051] In some embodiments, one or more of the electrodes is covered by a gas collection hood.

[0052] In some embodiments, one or more of the electrodes are separated from each other by a semi-permeable membrane or wall to keep product gases separate.

[0053] In some embodiments, the electrodes comprise one or more than one anodes and one or more than one cathodes.

[0054] In some embodiments, the anode comprises titanium, graphite, or titanium and graphite composite.

[0055] In some embodiments, the cathode comprises titanium, nickel, or titanium and nickel composite.

[0056] In some embodiments, an anode-cathode distance is about 0.5cm to about 40 cm, for example, about 0.5 cm to about 1 cm, about 1 cm to about 5 cm, about 5 cm to about 10 cm, about 10 cm to about 15 cm, about 15 cm to about 20 cm, about 20 cm to about 25 cm, about 25 cm to about 30 cm, about 30 cm to about 35 cm, about 35 cm to about 40 cm, or about 0.5, 0.6, 0.7, 0.8. 0.9. 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40 cm.

[0057] In some embodiments, the step d) comprises electrolysing at a voltage of about 0.5 V to about 3 V, for example, about 0.5 V to about 1 V, about 1 V to about 1 .5 V, about 1 .5 V to about 2 V, about 2 V to about 2.5 V, about 2.5 V to about 3 V, or about 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.5, 2, 2.5, or 3 V.

[0058] In some embodiments, the step d) comprises electrolysing at a current density of greater than or equal to about 10 mA / cm2, 20 mA / cm2, 30 mA / cm2, 40 mA / cm2, 50 mA / cm2, 60 mA / cm2, 70 mA / cm2, 80 mA / cm2, 90 mA / cm2, 100 mA / cm2, 150 mA / cm2, 200 mA / cm2, 250 mA / cm2, 300 mA / cm2, 350 mA / cm2, 400 mA / cm2, 450 mA / cm2, 500 mA / cm2, 600 mA / cm2, 700 mA / cm2, 800 mA / cm2, 900 mA / cm2, 1000 mA / cm2.

[0059] In some embodiments, the method further comprises a step of reacting the produced carbon monoxide with water to produce hydrogen and carbon dioxide.

[0060] In some embodiments, any obtained carbon dioxide from any complimentary or downstream process is recycled to the electrolytic cell to be converted directly to carbon monoxide.

[0061] In some embodiments, any obtained carbon dioxide from any complimentary or downstream process is recycled to the absorbant.

[0062] In some embodiments, the electrolysis process is powered by one or more solar photovoltaic cells, wind turbines or other producers of renewable power.

[0063] In some embodiments, the electrolysis process is conducted at a temperature greater than or equal to the melting point or decomposition point of the metal carbonate.

[0064] In some embodiments, the electrolysis process is conducted at a temperature of less than the melting point of the metal oxide.

[0065] In some embodiments, solubility of the metal oxide (molar basis) is less than about 50%, less than about 45%, less than about 40%, less than about 35%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, less than about 1%, or less than about 0.1% in the molten metal carbonate. The skilled person would appreciate that the solubility limit of the metal oxide facilitates precipitation of metal oxide during the electrolysis process and thereby increases process efficiency. In certain embodiments, the solubility is about 24% (molar basis). In certain embodiments, the solubility of the metal oxide (molar basis) is determined in U2CO3 at about 900 °C.

[0066] In some embodiments, the method further comprises a step of producing one or more downstream products using the carbon monoxide obtained in step (d). The skilled person would appreciate that any known process that involves carbon monoxide may be used to produce the downstream product. For example, carbon monoxide may be reacted with water to form carbon dioxide and hydrogen, which may be further used in themanufacture of ammonia, hydrocarbons, methanol, synthetic aviation fuels, ethylene and plastic precursors and plastic.

[0067] In some embodiments, any carbon dioxide obtained during the production of the downstream products is recycled to the electrolysis process and / or to the absorbant.

[0068] According to a second aspect of the present invention there is provided carbon monoxide obtained from the method according to the first aspect of the invention.

[0069] According to a third aspect of the present invention there is provided a system for producing carbon monoxide, the system comprising: an absorbant field comprising an absorbant, the absorbant comprising a metal oxide and configured to absorb carbon dioxide to at least convert a portion of the metal oxide to a metal carbonate; and an electrolyser configured to receive the absorbant and melt the metal carbonate to produce a molten metal carbonate, and electrolyse the molten metal carbonate to produce carbon monoxide and oxygen.

[0070] The skilled person would understand that the embodiments of the first aspect of the invention may apply to the third aspect, where appropriate.

[0071] In some embodiments, the system further comprises heating means configured to heat the absorbant to provide a heated absorbant to the electrolyser.

[0072] In some embodiments, the heating means is configured to melt the metal carbonate and provide molten metal carbonate to the electrolyser.

[0073] The skilled person would appreciate that the absorbant may be directly dumped into the electrolyser and the electrolyte (which is the molten metal carbonate) may melt the absorbant. Alternatively, the absorbant may be melted before being introduced into the electrolyser. Further, the absorbant may be pre-heated (but not necessarily melted) before being introduced into the electrolyser. Current within the electrolyser may be used to heat the absorbant directly.

[0074] In some embodiments, any unconverted metal oxide from the absorbant field forms a precipitate in the electrolyser.

[0075] In some embodiments, the electrolyser converts the molten metal carbonate to metal oxide, the metal oxide forming a precipitate.

[0076] In some embodiments, the system further comprises recycling means configured to recycle the precipitate as the absorbant in the absorbant field.

[0077] In some embodiments, the recycling means is configured to collect the precipitate in a settling suspension. In some embodiments, the suspension comprises the precipitate and the molten metal carbonate. In some embodiments, the suspension is collected at the bottom of the electrolyser.

[0078] In some embodiments, the system comprises means to solidify the molten metal carbonate in the suspension, and the recycling means is configured to recycle the solidified metal carbonate as the absorbant in the absorbant field.

[0079] In some embodiments, the recycling means comprises spray dryer, spray nozzle, venturi solidifier, spinning disc atomiser, mill, crusher, particle grader or any combinations thereof configured to receive the suspension.

[0080] In some embodiments, the system further comprises heat exchanging means in energy communication with the heating means configured to provide a portion of the thermal energy required to heat the absorbant from the suspension.

[0081] In some embodiments, the system further comprises heat exchanging means in energy communication with the heating means configured to provide a portion of the thermal energy required to heat the absorbant from the recycled precipitate.

[0082] In another aspect of the present invention there is provided a method of producing carbon monoxide using the system according to the third aspect of the invention.

[0083] Other aspects of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention.Advantages of the invention

[0084] Advantageously, the inventors of the present invention have developed a method and a system that utilises critical minerals (for example, a metal oxide) while concurrently producing an industrially valuable CO feedstock that can be used to produce sustainable and synthetic fuels to meet carbon-emissions targets.

[0085] Advantageously, the present invention addresses the absorption requirement for large absorbant transfer area by utilising an absorbant that is relatively cheap (relative to its ability to absorb CO2), able to be handled using bulk material handling methods(such as dozers, excavators, trucks, conveyors, railcars etc) and due to its low environmental toxicity will not cause long term damage or unmanageable risks to the local or global environment. Further, the high surface area and scalability afforded by the solid granular absorbent allows CO2 to be captured using a passive mass transfer technique, limiting the direct air capture operational costs to those from bulk haulage (typically >$10 / tonne of material), with wind providing the advection of air over the absorbtion field. Distributing the absorbant over a large land area allows this level of air contact.

[0086] Advantageously, the present invention is relatively cheap, scalable and environmentally friendly. The electrolyser and the electrolysis process involve louvered electrodes and / or gas collection hoods and / or permeable walls that direct and separate the produced gases from the remainder of the electrolyte. By utilising the higher density of the oxide, and solubility limit of the oxide, the invention allows extraction of a high oxide particulate (precipitate) suspension continuously from the base region of the electrolyser. This suspension may then be solidified and then be fed to a mill which produces a fine solid granular mixture from this mix, while capturing the heat of solidification to be fed back to the electrolyser feedstock.

[0087] Advantageously, and differently from conventional DAC processes, the product of this invention is itself a product that can be used to replace traditional hydrocarbon fuels. Hence the cost of the present invention can be off-set by selling a product. Most conventional DAC systems only attempt to produce CO2, which then needs to be stored or utilised using methods that are not proven for long term use and / or not scalable (e.g, geosequestration).

[0088] Advantageously, and differently from most conventional DAC processes, this process only utilises one chemical system (a metal oxide mixed with a metal carbonate), which oscillates between lean and rich forms of the carbonate as it cycles around the single chemical loop. That the DAC to CO process only involves one chemical system and one chemical loop is simpler than alternative technologies, which is advantageous from a cost and complexity standpoint.

[0089] Advantageously, and differently from most conventional DAC processes, the materials within the one chemical system (a metal oxide mixed with a metal carbonate), are commodity chemicals which are already produced at the required scale for large scale DAC and synthetic fuel production. Advantageously, the present invention may lead to a new range of opportunities for Australia, and globally. By reducing the cost of CO2 absorption from the atmosphere, the point source of CO2 production (eg, airlines,shipping, industrial processes) can be isolated from the sink of CO2 absorption (the DAC process). Effectively this means that many existing technologies can remain in their present form, but with economical DAC offsetting or fuel sourced from this invention. Concurrently, as this invention is compatible with intermittent power, it can be run from large solar power farms, without a need to store the amounts of energy required to continue electrolysis throughout the night. Alternatively, the invention can run from grid connected power, renewable or otherwise, when power prices are low. Carbon-free chemicals and fuels can become an export, supporting a carbon-free 'mining' industry.

[0090] Advantageously, the present invention utilises recycling of materials and energy. These may include• Unconverted metal oxide in the absorbant will not be melted due to its higher melting point compared with the metal carbonate, and the unconverted metal oxide will precipitate in the electrolyser during the electrolysis process due to its limited solubility in the molten metal carbonate. Further, metal oxide is also the product of the electrolysis of the molten metal carbonate, which may also precipitate. The precipitate may be recycled to be mixed with the abosrbant;• The precipitate may settle in the electrolyser during the electrolysis process in a suspension comprising metal oxide and (unreacted) molten metal carbonate. The suspension may be recycled to recover metal carbonate to mixed with the absorbant, or directly fed into the electrolyser to be melted and electrolysed;• Heat from the suspension / precipitate may be recycled to heat and / or melt the absorbant;• Heat from the recycled metal oxide / metal carbonate may be recycled to heat and / or melt the absorbant.Definitions

[0091] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

[0092] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in aninclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0093] As used herein, the phrase “consisting of’ excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of’ (or variations thereof) appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase “consisting essentially of” limits the scope of a claim to the specified elements or method steps, plus those that do not materially affect the basis and novel characteristic(s) of the claimed subject matter.

[0094] With respect to the terms “comprising”, “consisting of”, and “consisting essentially of”, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not otherwise explicitly recited, any instance of “comprising” may be replaced by “consisting of” or, alternatively, by “consisting essentially of”.

[0095] Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, “%” will mean “weight %”, “ratio” will mean “weight ratio” and “parts” will mean “weight parts”.

[0096] The term ‘substantially’ as used herein shall mean comprising more than 50% by weight, where relevant, unless otherwise indicated.

[0097] The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1 , 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0098] Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0099] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply thatother embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

[0100] It must also be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0101] As used herein, with reference to numbers in a range of numerals, the terms “about,” “approximately” and “substantially” are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to +1 % of the referenced number, most preferably -0.1 % to +0.1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth.

[0102] Although exemplary embodiments of the disclosed technology are explained in detail herein, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the disclosed technology be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The disclosed technology is capable of other embodiments and of being practiced or carried out in various ways.Brief Description of the Drawings

[0103] Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0104] Figures 1 (a) - 1 (c) show the CO2 absorption performance of U2O inside / outside a climate oven: (a) - CO2 absorption amount over time; (b) - mole ratio of U2CO3 converted from U2O overtime; (c) - rate of conversion overtime. PD (x): petri dish loaded with about x g of Li2O powder.

[0105] Figures 2(a) and 2(b) show the CO2 absorption performance of U2O loaded in a petri dish loaded with about 2 g of sample inside a climate oven with and without stirring: (a) - CO2 absorption amount over time; (b) - absorption rate over time.

[0106] Figures 3 shows XRD patterns for absorbed U2O, pure U2O, and pure U2CO3.

[0107] Figure 4 is a schematic showing the preparation and testing of mixed Li2O / Li2COs (absorption test two) samples. The same method was used for the mixed tests conducted at 25 °C and 48% RH and 30 °C and 48% RH DAC conditions.

[0108] Figure 5 shows CO2 absorption performance of the samples containing mixtures of Li2O / Li2COs (absorption test two) with three different particle sizes at 30 °C and 48% RH. X is the molar conversion of the initial U2O contained within the samples.

[0109] Figure 6 shows XRD patterns of mixed Li2O / Li2COs (absorption test two) samples after DAC showing that product of CO2 absorption is primarily conversion of U2O to U2CO3. These results were produced using 25 °C and 48% RH DAC conditions.

[0110] Figure 7 shows a schematic process flow diagram of the integrated Passive Direct Air Capture (PDAC) and Molten Salt Electrolysis (MSE) loop that produces CO from CO2 containing gas (here indicated as air).

[0111] Figure 8 shows a schematic process flow diagram showing how the invention (the PDAC plus MSE loop) could be integrated with hydrogen production via water electrolysis to produce syngas that is fed to fuel manufacturing processes.

[0112] Figure 9 shows a schematic process flow diagram showing how the invention (the PDAC plus MSE loop) could be integrated with the water gas shift reaction to produce syngas that is fed to fuel manufacturing processes. In this case any generated CO2 from the Fuel Manufacturing process can be fed back to the electrolyser.Detailed Description of the Invention

[0113] The skilled addressee will understand that the invention comprises the embodiments and features disclosed herein as well as all combinations and / or permutations of the disclosed embodiments and features.Carbon dioxide absorption testIn this test, the ability of a metal oxide, lithium oxide is tested for its ability to absorb carbon dioxide.Materials

[0114] Lithium oxide (U2O, 97%, powder, -60 mesh), sulfuric acid solution (H2SO4, 0.5 M), and triethylene glycol (CeHuC , 99%), lithium carbonate (U2CO3, >99.0%) were purchased from Sigma-Aldrich.Absorption test one - pure U2O

[0115] The experiments were conducted under controlled environmental conditions to simulate ambient scenarios. Specific climate oven parameters were set with the temperature fixed at 22 °C and relative humidity maintained at 48%.

[0116] U2O samples with varying amounts of (2.0837 g, 1.0206 g, 0.5376 g, 0.2737 g, and 0.131 g) were evenly spread on identical petri dishes. Subsequently, these petri dishes were placed inside the climate oven to facilitate the CO2absorption process. Additionally, Li2O sample (0.2691 g) was evenly spread on a petri dish, and left under ambient conditions for comparison. Similarly, daily monitoring was conducted over 17 days, where the samples were weighed, and photos were taken to visually document the changes.Acid titration test

[0117] After an appropriate absorption duration in the climate oven, the solid product was carefully extracted, ground, and collected for analysis. Approximately 0.08 g of the absorbed sample was transferred into a three-necked bottle for titration. This setup allowed for controlled addition of acid and collection of gas. Subsequently, a syringe was used to add approximately 5 mL of 0.5 M H2SO4 drop by drop to the solid product. The controlled addition ensured a complete reaction between the acid and the U2CO3 present in the sample. (U2CO3 + H2SO4 -> U2SO4 + H2O + CO2). The released CO2gas during the reaction was collected over triethylene glycol (TEG) saturated with CO2. Notably, the pure U2CO3 was used as a reference to determine the amount of CO2. From the measured CO2volume, the mass of U2CO3 in the final product was calculated, and the CO2absorption performance of the samples was then determined by comparing the amount of CO2absorbed to the initial amount of the sample.Materials characterizations

[0118] XRD: The powder XRD patterns of the original and absorbed samples were measured by a Bruker D8 Advance instrument using Cu Ka radiation (A = 1.5406 A) with a scanning rate of 0.2° s-1.

[0119] CO2 absorption test under dry conditions: The CO2 adsorption isotherms of the Li2O sample at 25 °C was measured using a BELSORP-max gas adsorption analyser. Before the measurement, the U2O sample was degassed at 150 °C for at least 12h to remove the pre-adsorbed gas and moisture from air.Absorption test two - mixed U2O / U2CO3 samples

[0120] A series of Li2O-Li2COs mixtures with varying U2O weight fractions of 40%, 60%, 80%, 100% (pure), and powdered samples were systematically prepared for CO2 sorption experiments. 5 g of sorbent sample was prepared for each case. Precise amounts of solid lithium oxide and lithium carbonate were measured, thoroughly mixed, and transferred into ceramic crucibles lined with nickel foil. The nickel lining was used to prevent sample adhesion to the crucibles at elevated temperatures, an issue previously observed. Each crucible was then placed at the centre of a tube furnace equipped with a programmable temperature control system. Prior to heating, the furnace chamber was purged with nitrogen (N2) to displace ambient air. Importantly, only one crucible was processed per run to ensure uniform temperature distribution, based upon prior observations of thermal gradients when multiple crucibles were used simultaneously. Subsequently, the loaded sample was subjected to a predefined thermal treatment, consisting of a controlled heating ramp, an isothermal holding period, and a final cooling phase. After the furnace had cooled to a safe temperature, the sample was removed, mechanically crushed, and immediately sieved using a standard pharmacopoeia mesh sizes to obtain sorbents with the desired particle size distributions. Three distinct size fractions with average diameters of 1425 pm, 600 pm and 250 pm, were collected with specified quantities and subsequently used for CO2 sorption measurements.

[0121] The CO2 uptake performance of the solid sorbents was evaluated using a climatic testing chamber (DHT-100-40-P-SD, DOAHO Shanghai Co., Ltd), which allows precise control and monitoring operating conditions during the sorption process. These mixed sorbent tests were conducted at 30 °C and 48% relative humidity (RH). The samples were weighed daily, with additional measurements taken during the initial days to ensure capturing the rapid kinetic phase accurately.Results

[0122] The results of the tests are shown in Figures 1 to 6 and the Table below. Specifically, Figures 1-3 relate to the pure U2O tests (absorption test one) while Figures 4-6 relate to the mixed Li2O / Li2COs tests (absorption test two).CO2 absorption performances determined by acid titrationDirect air capture with CO2 reduction

[0123] Figure 7 shows a schematic process flow diagram for an embodiment of the present invention.

[0124] First, a solid absorbant such as Li2COs / Li2O is used to passively absorb CO2 (g) from the atmosphere on a massive scale. Massive scale is achieved by creating a high oxide content (for example, high in U2O for the lithium carbonate option) fine granular material that is spread out over multiple stacked trays or directly over low value land to a depth of around 5mm (with probable range from 1mm-50mm) using bulk solids handling equipment. The material is left for a period of up to several weeks (for example, 2 days) to absorb CO2 (g), converting a significant proportion of the oxide within the granules to carbonate (for example, U2O -> U2CO3).

[0125] Second, the now high carbonate material ('rich stream') is heated to above its melting temperature (for example, melting temperature of about 705 °C for U2CO3) and using electrolysis at the appropriate temperature (for example, about 900 °C for the lithium option) to produce CO (g) (carbon monoxide) and O2 (g) (oxygen) gases in a continuous process. The oxygen could be vented to the atmosphere. The carbon monoxide is the product of this process and can be fed directly to downstream processes as detailed in Figures 8 and 9 to produce zero- or low-carbon products. During the electrolysis the liquid carbonate converts to the metal oxide, which has a higher melting point than the carbonate (for example, 1570 °C for l_i2O), and a higher density than the carbonate, so precipitates as a suspension that settles to the bottom of the electrolyser. This high oxide solid / liquid suspension is continuously removed from the base of the electrolyser into a solidifier and mill that produces and subsequently cools the granular material. This granular material is now the feedstock for the passive absorption processdetailed in step 1 and is referred to as the 'lean stream'. Heat integration is used between the granular material continuously entering and leaving the electrolyser.

[0126] The electrolyser may be fed by solar photovoltaic cells or wind turbines located nearby to the electrolysers and absorbant fields or from excess renewable energy available from the grid. Such intermittent renewable power can be utilised for the electrolysers by cycling between high-current production phases, and low-current heatmaintenance phases, utilising Joule heating within the electrolytes as the heating mechanism in the latter. Additional heating of the electrolyser may be realised by combusting a portion of the produced fuel when required.

[0127] Potential downstream products from the CO produced include synthetic 'carbon-free' hydrocarbon fuels or other hydrocarbon based products, either using a water-gas shift reaction or water electrolysis to produce hydrogen, plus the well- established Fisher-Tropsch reaction or other well-established methods to produce other chemicals.

[0128] Figures 8 and 9 illustrate other examples of how the invention may be integrated with other processes.

[0129] Although the invention will be described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

[0130] Other embodiments of the present invention as described herein are defined in the following paragraphs:1. A method of producing carbon monoxide, the method comprising the steps of: a) providing an absorbant comprising a metal oxide; b) allowing the absorbant to absorb carbon dioxide to thereby convert at least a portion of the metal oxide to a metal carbonate; c) heating the absorbant to produce a heated absorbant comprising a molten metal carbonate; d) subjecting the heated absorbant to an electrolysis process to thereby produce carbon monoxide and oxygen.2. The method according to any one or more of the preceding paragraphs, wherein the heated absorbant comprises any unconverted metal oxide from step b), the unconverted metal oxide forming a precipitate during the electrolysis process.The method according to any one or more of the preceding paragraphs, wherein the electrolysis process converts the molten metal carbonate to metal oxide, the metal oxide forming a precipitate. The method according to any one or more of the preceding paragraphs, further comprising a step of recycling the precipitate as the absorbant in step a). The method according to any one or more of the preceding paragraphs, comprising a step of collecting the precipitate in a settling suspension. The method according to any one or more of the preceding paragraphs, wherein meting point of the metal oxide is higher than that of the metal carbonate. The method according to any one or more of the preceding paragraphs, wherein density of the metal oxide is higher than that of the molten metal carbonate. The method according to any one or more of the preceding paragraphs, wherein the absorbant is in the form of granules. The method according to any one or more of the preceding paragraphs, wherein the step a) comprises providing the absorbant as an absorbant bed with a depth of about 1mm to about 50mm, preferably about 5mm. The method according to any one or more of the preceding paragraphs, wherein the step b) comprises absorbing the carbon dioxide from air. The method according to any one or more of the preceding paragraphs, wherein the metal oxide is lithium oxide. The method according to any one or more of the preceding paragraphs, wherein the metal carbonate is lithium carbonate The method according to any one or more of the preceding paragraphs, wherein the step d) comprises electrolysing the molten metal carbonate with two or more than two electrodes. The method according to any one or more of the preceding paragraphs, further comprising a step of reacting the carbon monoxide with water to produce hydrogen and carbon dioxide. The method according to any one or more of the preceding paragraphs, wherein the obtained carbon dioxide is recycled to the electrolysis process and / or to the absorbant. Carbon monoxide obtained from the method according to any one or more of the preceding paragraphs. A system for producing carbon monoxide, the system comprising:an absorbant field comprising an absorbant, the absorbant comprising a metal oxide and configured to absorb carbon dioxide to at least convert a portion of the metal oxide to a metal carbonate; and an electrolyser configured to receive the absorbant and melt the metal carbonate to produce a molten metal carbonate, and electrolyse the molten metal carbonate to produce carbon monoxide and oxygen. The system according to any one or more of the preceding paragraphs, further comprising heating means configured to melt the metal carbonate and provide molten metal carbonate to the electrolyser. The system according to any one or more of the preceding paragraphs, wherein any unconverted metal oxide from the absorbant field forms a precipitate in the electrolyser. The system according to any one or more of the preceding paragraphs, wherein the electrolyser converts the molten metal carbonate to metal oxide, the metal oxide forming a precipitate. The system according to any one or more of the preceding paragraphs, further comprising recycling means configured to recycle the precipitate as the absorbant in the absorbant field. The system according to any one or more of the preceding paragraphs, wherein the recycling means is configured to collect the precipitate in a settling suspension. The system according to any one or more of the preceding paragraphs, wherein the recycling means comprises spray dryer, spray nozzle, venturi solidifier, spinning disc atomiser, mill, particle grader or any combinations thereof configured to receive the suspension. The system according to any one or more of the preceding paragraphs, wherein the meting point of the metal oxide is higher than that of the metal carbonate. The system according to any one or more of the preceding paragraphs, wherein the density of the metal oxide is higher than that of the molten metal carbonate. The system according to any one or more of the preceding paragraphs, wherein the absorbant is in the form of granules. The system according to any one or more of the preceding paragraphs, wherein the absorbant field comprises an absorbant bed having a depth of about 1mm to about 50mm, preferably about 5mm.The system according to any one or more of the preceding paragraphs, wherein the metal oxide is lithium oxide. The system according to any one or more of the preceding paragraphs, wherein the metal carbonate is lithium carbonate. The system according to any one or more of the preceding paragraphs, wherein the electrolyser comprises two or more electrodes. The system according to any one or more of the preceding paragraphs, wherein the electrodes comprise one or more than one anodes and one or more than one cathodes.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-1. A method of producing carbon monoxide, the method comprising the steps of: a) providing an absorbant comprising a metal oxide; b) allowing the absorbant to absorb carbon dioxide to thereby convert at least a portion of the metal oxide to a metal carbonate; c) heating the absorbant to produce a heated absorbant comprising a molten metal carbonate; d) subjecting the heated absorbant to an electrolysis process to thereby produce carbon monoxide and oxygen.

2. The method according to claim 1 , wherein the heated absorbant comprises any unconverted metal oxide from step b), the unconverted metal oxide forming a precipitate during the electrolysis process.

3. The method according to claim 1 or claim 2, wherein the electrolysis process converts the molten metal carbonate to metal oxide, the metal oxide forming a precipitate.

4. The method according to claim 2 or claim 3, further comprising a step of recycling the precipitate as the absorbant in step a).

5. The method according to any one of claims 1 to 4, wherein the absorbant is in the form of granules.

6. The method according to any one of claims 1 to 5, wherein the step a) comprises providing the absorbant as an absorbant bed with a depth of about 1mm to about 50mm, preferably about 5mm.

7. The method according to any one of claims 1 to 6, wherein the step b) comprises absorbing the carbon dioxide from air, preferably passively absorbing the carbon dioxide from air.

8. The method according to any one of claims 1 to 7, wherein the metal oxide is lithium oxide, and the metal carbonate is lithium carbonate.

9. The method according to any one of claims 1 to 8, further comprising a step of producing one or more downstream products using the carbon monoxide obtained in step (d), optionally the downstream product comprises carbon dioxide.

10. The method according to claim 9, wherein the downstream products comprise hydrocarbon, ammonia, hydrogen, methanol, synthetic aviation fuel, ethylene, carbon dioxide, plastic precursors and / or plastic.11 . The method according to claim 9 or claim 10, wherein any carbon dioxide obtained during the production of the downstream products is recycled to the electrolysis process and / or to the absorbant.

12. A system for producing carbon monoxide, the system comprising: an absorbant field comprising an absorbant, the absorbant comprising a metal oxide and configured to absorb carbon dioxide to at least convert a portion of the metal oxide to a metal carbonate; and an electrolyser configured to receive the absorbant and melt the metal carbonate to produce a molten metal carbonate, and electrolyse the molten metal carbonate to produce carbon monoxide and oxygen.

13. The system according to claim 12, further comprising heating means configured to melt the metal carbonate and provide molten metal carbonate to the electrolyser.

14. The system according to any one of claims 12 or claim 13, wherein any unconverted metal oxide from the absorbant field forms a precipitate in the electrolyser.

15. The system according to any one of claims 12 to 14, wherein the electrolyser converts the molten metal carbonate to metal oxide, the metal oxide forming a precipitate.

16. The system according to claim 14 or claim 15, further comprising recycling means configured to recycle the precipitate as the absorbant in the absorbant field.

17. The system according to claim 16, wherein the recycling means is configured to collect the precipitate in a settling suspension.

18. The system according to claim 17, wherein the recycling means comprises spray dryer, spray nozzle, venturi solidifier, spinning disc atomiser, mill, particle grader or any combinations thereof configured to receive the suspension.

19. The system according to any one of claims 12 to 18, wherein the absorbant field comprises an absorbant bed having a depth of about 1mm to about 50mm, preferably about 5mm.

20. The system according to any one of claims 12 to 19, wherein the metal oxide is lithium oxide, and the metal carbonate is lithium carbonate.

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