Method

Abstract

Described herein is a method for reducing the amount of carbon dioxide in a gaseous composition comprising exposing the gaseous composition to a sorbent composition comprising calcined marble; wherein the gaseous composition comprises less than about 1 vol.% of carbon dioxide and the gaseous composition has a temperature of about 70°C or less. Also, a method for producing a gaseous composition comprising carbon monoxide comprising (i) exposing a first gaseous composition comprising carbon dioxide to a sorbent composition comprising calcined marble; wherein the first gaseous composition comprises less than about 1 vol.% of carbon dioxide and the first gaseous composition has a temperature of 70°C or less; and (ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a second gaseous composition comprising carbon monoxide.

Description

METHODINTRODUCTION

[0001] Provided herein is a means for capturing carbon dioxide (CO2), in particular direct air capture (DAC) of carbon dioxide. The carbon dioxide is captured using a sorbent composition from which the carbon dioxide can be subsequently desorbed and utilised for the preparation of value-added products, such as carbon monoxide (CO). Accordingly, described herein is a method for integrated carbon capture and utilisation (ICCU).BACKGROUND OF THE INVENTION

[0002] CO2 capture and utilisation (CCU) is an important technology to reduce CO2 levels. In particular, capturing CO2 directly from the air has drawn great attention as it can be deployed in a wide range of locations. However, direct air capture (DAC) has challenges including high energy requirements, particularly when it is connected to CO2 utilisation. Converting CO2 to CO represents a promising strategy for dealing with captured CO2, as CO can be used as feedstock for the production of useful organic compounds, including hydrocarbons, ethers and alcohols.

[0003] There is a need in the art for a means for efficient sorption of CO2, particularly from the air, which advantageously has one or more benefits selected from (i) high sorption capacity, (ii) high selectivity, (iii) capable of cyclic operation without losing carrying capacity, (iv) good mechanical resistance to attrition, and (v) good economically viability.SUMMARY OF THE INVENTION

[0004] Methods of capturing CO2 are provided. The presently claimed methods employ a low cost and abundant sorbent which is stable at high temperatures, is capable of consistently high levels of cyclic sorption of CO2 from the air at ambient temperatures and subsequent release of CO2 for storage or utilisation.

[0005] In another aspect, the CO2-loaded sorbent can be utilised as a CO2 source in a method for the conversion of released CO2 to CO via hydrogenation (e.g. reverse water gas shift). As such, the presently claimed subject matter provides for a method of integrated carbon capture and utilisation (ICCU).

[0006] In one aspect, the present invention provides a method for reducing the amount of carbon dioxide in a gaseous composition comprising exposing the gaseous composition to a sorbent composition comprising calcined marble; wherein the gaseous composition comprisesless than about 1 vol.% of carbon dioxide and the gaseous composition has a temperature of about 70°C or less.

[0007] In another aspect, the present invention provides a method for reducing the amount of carbon dioxide in air comprising exposing the air to a sorbent composition comprising calcined marble; suitably wherein the air temperature is about 70°C or less.

[0008] In another aspect, the present invention provides a method for producing a gaseous composition comprising carbon monoxide comprising:(i) exposing a first gaseous composition comprising carbon dioxide to a sorbent composition comprising calcined marble; wherein the first gaseous composition comprises less than about 1 vol.% of carbon dioxide and the first gaseous composition has a temperature of 70°C or less;(ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a second gaseous composition comprising carbon monoxide.

[0009] In another aspect, the present invention provides a method for producing a gaseous composition comprising carbon monoxide comprising:(i) exposing a sorbent composition comprising calcined marble to air; suitably wherein the air temperature is about 70°C or less;(ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a gaseous composition comprising carbon monoxide.

[0010] Preferred, suitable, and optional features of any one particular aspect of the present invention are also preferred, suitable, and optional features of any other aspect.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 provides details of the elemental analysis of the 6 calcined marble samples.

[0012] Figure 2 shows the XRD of (a) the samples as the natural marble stone and (b) stone samples after calcination at 950°C.

[0013] Figure 3 shows the XRD of each calcined marble sample after 5 hours exposed to air.

[0014] Figure 4 presents SEM images of stone sample 2 after calcination at (a) 950°C, (b) 850°C, (c) 750°C and (d) 650°C.

[0015] Figure 5 shows (a) XRD of stone sample 2 after calcination at various temperatures and (b) XRD of the calcined marble sample after 5 hours of DAC.

[0016] Figure 6 shows the performance of the stone samples with respect to (a) capacity of CO2 capture; (b) CO yield from the hydrogenation of captured CO2.

[0017] Figure 7 shows SEM images of sample 2 (a) as the fresh stone sample, (b) after calcination at 950°C, and after 10 cycles of absorption and calcination and at (c) 617 times and (d) 100,000 times magnification.

[0018] Figure 8 shows SEM images of commercial calcium oxide powder (CaO) as a fresh sample at (a) 9000 times and (b) 12800 times magnification, (c) after calcination and (d) after DAC and hydrogenation.

[0019] Figure 9 shows the effect of DAC duration on the CO2 hydrogenation performance for stone sample 1.

[0020] Figure 10 shows the effect of air moisture on DAC performance for stone sample 2.

[0021] Figure 11 shows the effect of air moisture on CO2 hydrogenation performance for stone sample 2.

[0022] Figure 12 shows the results of stability assessment of stone sample 2 over 10 cycles of DAC and CO2 hydrogenation with respect to (a) CO2 capture and (b) CO2 hydrogenation performance.

[0023] Figure 13 shows the effect of high temperature on DAC and subsequent CO2 hydrogenation using stone sample 1.DETAILED DESCRIPTION OF THE INVENTIONDefinitions

[0024] As used herein the term “gaseous composition” refers to a composition which is gaseous at standard ambient temperature and pressure (SATP), i.e. at a temperature of 298.15 K (25 °C) and at 100,000 Pa (1 bar, 14.5 psi, 0.9869 atm).

[0025] As used herein, “carbon dioxide capture” refers to the removal or sequestration of an amount of CO2 from a gaseous composition comprising CO2 so that some or all of the CO2 originally present in the gaseous composition has been removed. Suitably, removal or sequestration of CO2 is achieved using a sorbent, suitably a CC>2-specific sorbent.

[0026] As used herein, “direct air capture” (DAC) refers to the removal or sequestration of an amount of carbon dioxide from air, i.e. the gaseous composition of which the Earth’s atmosphere is comprised. Said removal or sequestration of CO2 is achieved by directly contacting the air with a sorbent.

[0027] As used herein, “ambient air” refers to atmospheric air as it occurs in the immediate surroundings.

[0028] As used herein, “sorbent” refers to a material that is capable of absorbing and / or adsorbing a liquid or gas on contact. Suitably, the sorbent is capable of adsorbing CO2, optionally selective adsorption of CO2.

[0029] As used herein, “marble” refers to a natural, metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. The major components of marble are most commonly calcite (CaCCh) or dolomite (CaMg(CC>3)2. Trace elements (such as Si, O, Al, Fe etc.) may also be present.

[0030] As used herein, “calcined marble” refers to marble that has been subjected to calcination. Calcination refers to heating a material to a predetermined temperature, for a predetermined amount of time, in a controlled atmosphere. Suitably, this results, for example, in the oxidation of a target component, removal of a volatile component or organic matter, chemical dehydration, and / or the decomposition of carbonate. In the case of calcite or dolomite, typical major components of marble, calcination leads to decomposition of the carbonate minerals leading to release of CO2 and generation of metal oxides, such as CaO and MgO.

[0031] As used herein a “metal species” is any compound comprising a metal or a bulk metal. As such, a metal species includes the elemental metal, metal oxides and other compounds comprising a metal, i.e. metal salts, alloys, hydroxides, carbides and hydrides. When a specific example of a metal species is stated, said term includes all compounds comprising that metal, e.g. iron species includes elemental iron, iron oxides, iron salts, iron alloys, iron hydroxides, iron carbides and iron hydrides for instance.Method for carbon dioxide capture

[0032] In one aspect, provided herein is a method for reducing the amount of carbon dioxide in a gaseous composition comprising exposing the gaseous composition to a sorbent composition comprising calcined marble; wherein the gaseous composition comprises less than about 1 vol.% of carbon dioxide and the gaseous composition has a temperature of about 70°C or less.

[0033] In one embodiment, the gaseous composition comprises less than about 0.8 vol. % of carbon dioxide, suitably less than about 0.5 vol. % of carbon dioxide, suitably less than about 0.3 vol. % of carbon dioxide, suitably less than about 0.1 vol. % of carbon dioxide.

[0034] In one embodiment, the gaseous composition comprises about 0.01 vol. % to about 1 vol. % of carbon dioxide, suitably about 0.01 vol. % to about 0.5 vol. %, suitably about 0.01 vol. % to about 0.3 vol. %, suitably about 0.01 vol. % to about 0.1 vol. %, suitably about 0.01 vol. % to about 0.06 vol. % of carbon dioxide.

[0035] In one embodiment, the gaseous composition comprises about 0.03 vol. % to about 1 vol. % of carbon dioxide, suitably about 0.03 vol. % to about 0.5 vol. %, suitably about 0.03 vol. % to about 0.3 vol. %, suitably about 0.03 vol. % to about 0.1 vol. %, suitably about 0.03 vol. % to about 0.06 vol. % of carbon dioxide.

[0036] In another embodiment, the gaseous composition comprises about 0.04 vol. % to about 1 vol. % of carbon dioxide, suitably about 0.04 vol. % to about 0.5 vol. %, suitably about 0.04 vol. % to about 0.3 vol. %, suitably about 0.04 vol. % to about 0.1 vol. % of carbon dioxide.

[0037] In one embodiment, the gaseous composition comprises less than about 1000 parts per million by volume (ppmv) of carbon dioxide, suitably less than about 800 ppmv of carbon dioxide, suitably less than about 600 ppmv of carbon dioxide, suitably less than about 500ppmv of carbon dioxide, suitably less than about 450ppmv of carbon dioxide.

[0038] In another embodiment, the gaseous composition comprises about 100 ppmv to about 1000 ppmv of carbon dioxide, suitably about 100 ppmv to about 800 ppmv, suitably about 100 ppmv to about 700 ppmv, suitably about 100 ppmv to about 600 ppmv, suitably about 100 ppmv to about 500 ppmv, suitably about 100 ppmv to about 450 ppmv of carbon dioxide.

[0039] In another embodiment, the gaseous composition comprises about 200 ppmv to about 1000 ppmv of carbon dioxide, suitably about 200 ppmv to about 800 ppmv, suitably about 200 ppmv to about 700 ppmv, suitably about 200 ppmv to about 600 ppmv, suitably about 200 ppmv to about 500 ppmv, suitably about 200 ppmv to about 450 ppmv of carbon dioxide.

[0040] In another embodiment, the gaseous composition comprises about 300 ppmv to about 1000 ppmv of carbon dioxide, suitably about 300 ppmv to about 800 ppmv, suitably about 300 ppmv to about 700 ppmv, suitably about 300 ppmv to about 600 ppmv, suitably about 300 ppmv to about 500 ppmv, suitably about 300 ppmv to about 450 ppmv of carbon dioxide.

[0041] In another embodiment, the gaseous composition comprises about 400 ppmv to about 1000 ppmv of carbon dioxide, suitably about 400 ppmv to about 800 ppmv, suitably about 400 ppmv to about 700 ppmv, suitably about 400 ppmv to about 600 ppmv, suitably about 400 ppmv to about 500 ppmv, suitably about 400 ppmv to about 450 ppmv of carbon dioxide.

[0042] In one embodiment, the vol.% of carbon dioxide is measured using an infrared gas analyzer; suitably using a non-dispersive infrared (NDIR) analyzer using infrared radiation containing wavelengths in mid-infrared radiation of 2.5 to 25 pm. Suitably, the vol.% of carbon dioxide is measured at atmospheric pressure and ambient temperature, e.g. about 20°C.

[0043] In one embodiment, the gaseous composition is air, i.e. the gaseous composition of which the Earth’s atmosphere is comprised, suitably ambient air. Thus, in one aspect, the present invention provides a method for reducing the amount of carbon dioxide in air comprising exposing the air to a sorbent composition comprising calcined marble; suitably wherein the air temperature is about 70°C or less.

[0044] As of 2023, the CO2 content of the air is about 418 ppmv to about 425 ppmv. In recent decades the trend has been one of increasing atmospheric levels of CO2 (NOAA, measured at the Mauna Loa Observatory).

[0045] In one embodiment, the temperature of the gaseous composition / air is about 65°C or less, suitably about 60°C or less, suitably about 55°C or less, suitably about 50°C or less.

[0046] In another embodiment, the temperature of the gaseous composition / air is about -60°C to about 55°C, suitably about -40°C to about 55°C, suitably about -20°C to about 55°C, suitably about 0°C to about 55°C. In another embodiment, the temperature of the gaseous composition / air is about 0°C to about 50°C, suitably about 0°C to about 40°C.

[0047] The temperature of the gaseous composition / air may be measured by any suitable means, such as thermometer, thermocouple or resistance temperature sensor. Suitable measurement methods would be familiar to the skilled person.

[0048] When the gaseous composition is ambient air, the air temperature in one embodiment may be measured using a single-level, near-surface (typically 2 metres above surface)measurement with electrical resistance temperature sensors. In one embodiment, the air temperature is measured in accordance with ASTM D6176-97(2022).

[0049] In one embodiment, the temperature of the gaseous composition / air is ambient atmospheric temperature.

[0050] Accordingly, in one embodiment, the present invention provides a method for reducing the amount of carbon dioxide in air comprising exposing the air to a sorbent composition comprising calcined marble. Suitably, the air is at ambient atmospheric temperature.

[0051] In one embodiment, the relative humidity of the air (RH%) is about 20 % or more. Suitably the relative humidity of the air is about 30 % or more, suitably about 40 % or more, suitably about 45 % or more.

[0052] In another embodiment, the relative humidity of the air (RH%) is about 20 % to about 99 %. Suitably the relative humidity of the air is about 30 % to about 99 %, suitably about 40 % to about 99 %, suitably about 45 % to about 99 %.

[0053] In another embodiment, the relative humidity of the air (RH%) is about 20 % to about 90 %. Suitably the relative humidity of the air is about 30 % to about 90 %, suitably about 40 % to about 90 %, suitably about 45 % to about 90 %.

[0054] In another embodiment, the relative humidity of the air (RH%) is about 20 % to about 70 %. Suitably the relative humidity of the air is about 30 % to about 70 %, suitably about 40 % to about 70 %, suitably about 45 % to about 70 %.

[0055] In another embodiment, the relative humidity of the air (RH%) is about 20 % to about 50 %. Suitably the relative humidity of the air is about 30 % to about 50 %, suitably about 40 % to about 50 %, suitably about 45 % to about 50 %.

[0056] The relative humidity of air may be measured by any suitable means, which would be familiar to the skilled person, such as a digital hygrometer or psychrometer.Sorbent Composition

[0057] The sorbent composition comprises calcined marble. In addition to calcined marble the sorbent composition may comprise binders or supports. In one embodiment, the sorbent composition comprises an inorganic binder.

[0058] In one embodiment, the sorbent composition consists essentially of calcined marble. In another embodiment, the sorbent composition consists of calcined marble.

[0059] In one embodiment, the sorbent composition is a solid composition. In one embodiment, the sorbent composition is in the form of a powder, pellet(s), granule(s) or a shaped article (e.g. a structured monolith or sculptured framework).

[0060] In one embodiment, the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C or more, suitably about 600°C or more, suitably about 650°C or more, suitably about 700°C or more, suitably about 750°C or more, suitably about 800°C or more, suitably about 850°C or more, suitably about 900°C or more.

[0061] In one embodiment, the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C to about 1000°C, suitably about 600°C to about 1000°C, suitably about 650°C to about 1000°C, suitably about 700°C to about 1000°C, suitably about 750°C to about 1000°C, suitably about 800°C to about 1000°C, suitably about 850°C to about 1000°C, suitably about 900°C to about 1000°C.

[0062] In one embodiment, the marble is heated in an oxygen free atmosphere. In another embodiment, the marble is heated in air, nitrogen or a hydrogen-containing atmosphere. In one embodiment, the marble is heated in a 5% H2, oxygen free atmosphere. In another, embodiment the marble is heated under a nitrogen atmosphere.

[0063] In one embodiment, the marble is heated at a rate of about 5°C / min to about 20°C / min, suitably about 5°C / min to about 15°C / min, suitably about 10°C / min.

[0064] In one embodiment, the calcined marble or marble is in the form of a powder or dust.

[0065] In one embodiment, the calcined marble or marble has a particle size of 500 pm or less, suitably a particle size of 400 pm or less, suitably a particle size of 300 pm or less, a particle size of 250 pm or less.

[0066] In another embodiment, the calcined marble or marble has a particle size of about 100 pm to 500 pm, suitably about 100 pm to about 400 pm, suitably about 100 pm to 300 pm, suitably about 100 to about 250 pm.

[0067] Suitably, the particle size analysis is performed by sieving. As used herein, the term “particle size’’ means the diameter of the particle if the particle is spherical or, if the particle is non-spherical, the minimum feret diameter.

[0068] In one embodiment, the specific surface area of the calcined marble is about 5 m2 / g or more, suitably about 10 m2 / g or more, suitably about 15 m2 / g or more.

[0069] In another embodiment, the specific surface area of the calcined marble is about 5 m2 / g to about 25 m2 / g, suitably about 10 m2 / g to about 25 m2 / g, suitably about 12 m2 / g to about 25 m2 / g, suitably about 13 m2 / g to about 25 m2 / g, suitably about 14 m2 / g to about 25 m2 / g.

[0070] In another embodiment, the specific surface area of the calcined marble is about 5 m2 / g to about 20 m2 / g, suitably about 10 m2 / g to about 20 m2 / g, suitably about 12 m2 / g to about 20 m2 / g, suitably about 13 m2 / g to about 20 m2 / g, suitably about 14 m2 / g to about 20 m2 / g.

[0071] In another embodiment, the specific surface area of the calcined marble is about 5 m2 / g to about 16 m2 / g, suitably about 10 m2 / g to about 16 m2 / g, suitably about 12 m2 / g to about 16 m2 / g, suitably about 13 m2 / g to about 16 m2 / g, suitably about 14 m2 / g to about 16 m2 / g.

[0072] In one embodiment, the specific surface area is measured by determining the adsorption amount of a sample, where the surfaces of the sample adsorb a molecule having a known adsorption occupied area at the temperature of liquid nitrogen (-196°C, 77 K). In one embodiment, the specific surface area is measured by the BET method (BET multipoint measurement) using isothermal N2absorption-desorption at 77K. For example, an automated specific surface area and pore distribution analyzer TriStar II 3020 (product of Micromeritics) can be used for the measurement.

[0073] In one embodiment, the calcined marble has a total pore volume of about 0.01 cm3 / g or more, suitably about 0.02 cm3 / g or more, suitably about 0.025 cm3 / g or more, suitably about 0.03 cm3 / g or more.

[0074] In another embodiment, the calcined marble has a total pore volume of about 0.01 cm3 / g to about 0.05 cm3 / g, suitably about 0.02 cm3 / g to about 0.05 cm3 / g, suitably about 0.025 cm3 / g to about 0.05 cm3 / g, suitably about 0.03 cm3 / g to about 0.05 cm3 / g.

[0075] In another embodiment, the calcined marble has a total pore volume of about 0.01 cm3 / g to about 0.04 cm3 / g, suitably about 0.02 cm3 / g to about 0.04 cm3 / g, suitably about 0.025 cm3 / g to about 0.04 cm3 / g, suitably about 0.03 cm3 / g to about 0.04 cm3 / g.

[0076] In another embodiment, the calcined marble has a total pore volume of about 0.01 cm3 / g to about 0.035 cm3 / g, suitably about 0.02 cm3 / g to about 0.035 cm3 / g, suitably about 0.025 cm3 / g to about 0.035 cm3 / g, suitably about 0.03 cm3 / g to about 0.035 cm3 / g.

[0077] In one embodiment, total pore volume can be measured by isothermal N2adsorptiondesorption at 77 K, and the pore size distributions plotted by the Barrett-Joyner-Halenda (BJH) method using the desorption branch. Suitably, an automated specific surface area and poredistribution analyzer TriStar II 3020 (product of Micromeritics) can be used for the measurement.

[0078] In one embodiment, the calcined marble comprises CaO. Suitably, the calcined marble comprises about 25 wt.% of CaO or more, suitably about 30 wt.% of CaO or more, suitably about 35 wt.% of CaO or more, suitably about 40 wt.% of CaO or more, suitably about 45 wt.% of CaO or more, suitably about 50 wt.% of CaO or more, suitably about 60 wt.% of CaO or more.

[0079] In another embodiment, the calcined marble comprises about 40 wt.% to about 99% wt.% of CaO, suitably about 50 wt.% to about 99% wt.% of CaO, suitably about 60 wt.% to about 99% wt.% of CaO.

[0080] In one embodiment, the calcined marble comprises MgO. Suitably, the calcined marble comprises about 0.01 wt.% to about 50 wt. % of MgO, suitably about 0.01 wt.% to about 40 wt. % of MgO, suitably about 0.01 wt.% to about 30 wt. % of MgO, suitably about 0.01 wt.% to about 20 wt. % of MgO, suitably about 0.01 wt.% to about 10 wt. % of MgO, suitably about 0.01 wt.% to about 5 wt. % of MgO, suitably about 0.01 wt.% to about 3 wt. % of MgO, suitably about 0.01 wt.% to about 3 wt. % of MgO.

[0081] In another embodiment, the calcined marble comprises about 0.5 wt.% to about 40 wt. % of MgO, suitably about 1 wt.% to about 40 wt. % of MgO, suitably about 10 wt.% to about 40 wt. % of MgO, suitably about 20 wt.% to about 40 wt. % of MgO, suitably about 30 wt.% to about 40 wt. % of MgO.

[0082] In one embodiment, the calcined marble comprises one or more species selected from the group consisting of a cobalt species, a chromium species, an iron species and a potassium species.

[0083] In one embodiment, the calcined marble does not comprise a silicon species and / or an aluminium species. In another embodiment, the calcined marble comprises less than about 1 wt. % of a silicon and / or an aluminium species; suitably less than about 0.5 wt. % of a silicon and / or an aluminium species; suitably less than about 0.2 wt. % of a silicon and / or an aluminium species; suitably less than about 0.1 wt. % of a silicon and / or an aluminium species.

[0084] The sorbent composition may be exposed to the gaseous composition / air by any suitable means. For example, the gaseous composition / air may be allowed to passively pass over or through the sorbent composition. Alternatively, the gaseous composition / air may be actively pushed or drawn over or through the sorbent composition. In one embodiment of thepresently claimed method, the gaseous composition / air is actively drawn over or through the sorbent composition.

[0085] In one embodiment, the sorbent composition is exposed to gaseous composition / air for about 6 hours or more, suitably about 12 hours or more, suitably about 24 hours or more, suitably about 3 days or more.

[0086] In another embodiment, the sorbent composition is exposed to the gaseous composition / air for about 12 hours to about 14 days; suitably for about 12 hours to about 7 days; suitably for about 12 hours to about 3 days; suitably about 12 hours to about 36 hours.

[0087] In another embodiment, the sorbent composition is exposed to the gaseous composition / air for about 1 day to about 14 days; suitably for about 1 day to about 7 days; suitably for about 1 day to about 3 days; suitably about 1 day.Utilisation

[0088] In one embodiment, the method further comprises utilisation of the carbon dioxide captured by the sorbent composition. Utilisation of the carbon dioxide includes using the captured carbon dioxide without chemically altering the carbon dioxide as well as transforming the carbon dioxide into other products, such as carbon monoxide, a hydrocarbon or methanol. In one embodiment, the carbon dioxide is transformed into carbon monoxide.

[0089] In one embodiment, there is provided a method for reducing the amount of carbon dioxide in a gaseous composition comprising (i) exposing the gaseous composition to a sorbent composition comprising calcined marble; wherein the gaseous composition comprises less than 1 vol.% of carbon dioxide and the gaseous composition has a temperature of 70°C or less; (ii) desorbing carbon dioxide from the sorbent composition; and (iii) reacting the desorbed carbon dioxide to provide another product, such as carbon monoxide, methanol or a hydrocarbon.

[0090] In another embodiment, there is provided a method for reducing the amount of carbon dioxide in air comprising (i) exposing a sorbent composition comprising calcined marble to air; suitably at a temperature of 70°C or less; (ii) desorbing carbon dioxide from the sorbent composition; and (iii) reacting the desorbed carbon dioxide to provide another product, such as carbon monoxide, methanol or a hydrocarbon.

[0091] The carbon dioxide may be desorbed by any suitable method. Typically, desorption is effected by subjecting the sorbent composition to one or more stimuli, e.g. a change intemperature and / or pressure. In one embodiment, desorption is mediated by heating the sorbent composition, suitably to a temperature of about 550°C or more, suitably about 600°C or more, suitably about 650°C or more, suitably about 700°C or more, suitably about 750°C or more, suitably about 800°C or more, suitably about 850°C or more, suitably about 900°C or more.

[0092] In one embodiment, desorption is mediated by heating the sorbent composition to a temperature of about 550°C to about 1000°C, suitably about 600°C to about 1000°C, suitably about 650°C to about 1000°C, suitably about 700°C to about 1000°C, suitably about 750°C to about 1000°C, suitably about 800°C to about 1000°C, suitably about 850°C to about 1000°C, suitably about 900°C to about 1000°C.

[0093] In one embodiment, desorption is mediated by heating the sorbent composition in an oxygen free atmosphere. In another embodiment, the sorbent composition is heated in air, nitrogen or an hydrogen-containing atmosphere. In one embodiment, the sorbent composition is heated in a 5% H2, oxygen free atmosphere. In another, embodiment the sorbent composition is heated under a nitrogen atmosphere.

[0094] In one embodiment, the sorbent composition is heated at a rate of about 5°C / min to about 20°C / min, suitably about 5°C / min to about 15°C / min, suitably about 10°C / min.

[0095] In one embodiment, the desorbed carbon dioxide is reacted with hydrogen to produce a gaseous composition comprising carbon monoxide. In one embodiment, the reaction with hydrogen is performed at a temperature of about 550°C to about 1000°C, suitably about 600°C to about 1000°C, suitably about 650°C to about 1000°C, suitably about 700°C to about 1000°C, suitably about 750°C to about 1000°C, suitably about 800°C to about 1000°C, suitably about 850°C to about 1000°C, suitably about 900°C to about 1000°C.

[0096] In another embodiment, the reaction with hydrogen is performed at a temperature of about 600°C to about 900°C, suitably about 600°C to about 800°C, suitably about 600°C to about 700°C, suitably about 650°C to about 700°C.

[0097] In one embodiment, the desorption and reaction with hydrogen may be combined in a single heating process. Suitably desorption and the reaction with hydrogen are performed at a temperature of about 600°C to about 900°C, suitably about 600°C to about 800°C, suitably about 600°C to about 700°C, suitably about 650°C to about 700°C. In one embodiment, the heating rate is about 5°C / min to about 20°C / min, suitably about 5°C / min to about 15°C / min, suitably about 10°C / min.

[0098] In another aspect, the present invention provides a method for producing a gaseous composition comprising carbon monoxide comprising:(i) exposing a first gaseous composition comprising carbon dioxide to a sorbent composition comprising calcined marble; wherein the first gaseous composition comprises less than about 1 vol.% of carbon dioxide and the first gaseous composition has a temperature of 70°C or less;(ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a second gaseous composition comprising carbon monoxide.

[0099] In one embodiment, the first gaseous composition may be a gaseous composition according any one of the embodiments of the above-described aspects of the invention.

[0100] In another aspect, the present invention provides a method for producing a gaseous composition comprising carbon monoxide comprising:(i) exposing a sorbent composition comprising calcined marble to air; suitably wherein the air has a temperature of 70°C or less;(ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a gaseous composition comprising carbon monoxide.

[0101] In one embodiment, the sorbent composition may be a sorbent composition according to any one of the embodiments of the above-described aspects of the invention.

[0102] In one embodiment, the calcined marble may be calcined marble according to any one of the embodiments of the above-described aspects of the invention.

[0103] In one embodiment, the sorbent composition is heated with hydrogen in step (ii) at a temperature of about 600°C to about 900°C, suitably about 600°C to about 800°C, suitably about 600°C to about 700°C, suitably about 650°C to about 700°C.

[0104] In one embodiment, the gaseous composition produced comprises at least about 1 vol. % of carbon monoxide. In one embodiment, the vol.% of carbon monoxide is measured using an infrared gas analyzer; suitably using a non-dispersive infrared (NDIR) analyzer using infrared radiation containing wavelengths in mid-infrared radiation of 2.5 to 25pm. Suitably, the vol. % of carbon monoxide is measured at atmospheric pressure and ambient temperature, e.g. about 20°C.

[0105] In one embodiment, the hydrogen in step (ii) is provided as purified H2 gas (>99.9%) or a mixture of H2 in an inert gas, e.g. nitrogen.

[0106] In one embodiment, the sorbent composition obtained in (ii) is employed as the sorbent composition in (i) in a further cycle of method steps (i) and (ii). In one embodiment, 5 or more consecutive cycles of method steps (i) and (ii) are performed, suitably 10 or more, suitably 20 or more, suitably 50 or more.

[0107] The invention will now be further described by the following numbered clauses which are not claims:1. A method for reducing the amount of carbon dioxide in a gaseous composition comprising exposing the gaseous composition to a sorbent composition comprising calcined marble; wherein the gaseous composition comprises less than about 1 vol % of carbon dioxide and the gaseous composition has a temperature of about 70°C or less.2. A method according to clause 1 , wherein the gaseous composition comprises less than about 0.1 vol. % of carbon dioxide.3. A method according to clause 1, wherein the gaseous composition comprises about 0.01 vol. % to about 1 vol. % of carbon dioxide.4. A method according to clause 1 , wherein the gaseous composition comprises about 0.03 vol. % to about 0.06 vol. % of carbon dioxide.5. A method according to clause 1 , wherein the gaseous composition comprises less than about 450ppmv of carbon dioxide.6. A method according to any one of the preceding clauses, wherein the gaseous composition is air, suitably ambient air.7. A method according to clause 6, wherein the relative humidity of the air is about 40 % or more.8. A method according to any one of the preceding clauses, wherein the temperature of the gaseous composition / air is about 55°C or less.9. A method according to any one of the preceding clauses, wherein the temperature of the gaseous composition / air is about -40°C to about 55°C.10. A method according to any one of the preceding clauses, wherein the temperature of the gaseous composition is ambient atmospheric temperature.11. A method according to any one of the preceding clauses, wherein the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C or more.12. A method according to any one of the preceding clauses, wherein the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C to about 1000°C.13. A method according to clause 12, wherein the marble is heated in air, nitrogen or an hydrogen-containing atmosphere.14. A method according to clause 12 or clause 13, wherein the marble is heated at a rate of about 5°C / min to about 20°C / min, suitably about 5°C / min to about 15°C / min, suitably about 10°C / min.15. A method according to any one of the preceding clauses, wherein the specific surface area of the calcined marble is about 5 m2 / g or more.16. A method according to any one of the preceding clauses, wherein the specific surface area of the calcined marble is about 10 m2 / g or more.17. A method according to any one of the preceding clauses, wherein the specific surface area of the calcined marble is about 5 m2 / g to about 25 m2 / g.18. A method according to any one of clauses 15 to 17, wherein the specific surface area is measured by the BET method (BET multipoint measurement) using isothermal N2absorption-desorption at 77K.19. A method according to any one of the preceding clauses, wherein the calcined marble has a total pore volume of about 0.01 cm3 / g or more.20. A method according to any one of the preceding clauses, wherein the calcined marble has a total pore volume of about 0.025 cm3 / g or more.21. A method according to any one of the preceding clauses, wherein the calcined marble has a total pore volume of about 0.03 cm3 / g to about 0.05 cm3 / g.22. A method according to any one of clauses 19 to 21 , wherein the total pore volume measured by isothermal N2adsorption-desorption at 77 K, and the pore size distributions plotted by the Barrett-Joyner-Halenda (BJH) method using the desorption branch.23. A method according to any one of the preceding clauses, wherein the calcined marble comprises CaO.24. A method according to any one of the preceding clauses, wherein the calcined marble comprises about 50 wt.% of CaO or more.25. A method according to any one of the preceding clauses, wherein the calcined marble comprises about 50 wt.% to about 99% wt.% of CaO.26. A method according to any one of the preceding clauses, wherein the calcined marble comprises MgO.27. A method according to any one of the preceding clauses, wherein the calcined marble comprises about 0.01 wt.% to about 50 wt. % of MgO.28. A method according to any one of the preceding clauses, wherein the calcined marble comprises one or more species selected from the group consisting of a cobalt species, chromium species, iron species and potassium species.29. A method according to any one of the preceding clauses, wherein the calcined marble comprises less than 1 wt. % of a silicon and / or an aluminium species.30. A method according to any one of the preceding clauses, wherein gaseous composition is actively drawn over or through the sorbent composition.31. A method according to any one of the preceding clauses, wherein the sorbent composition is exposed to the gaseous composition for about 12 hours or more.32. A method according to any one of the preceding clauses, wherein the sorbent composition is exposed to the gaseous composition for about 1 day to about 7 days.33. A method according to any one of the preceding clauses, wherein the method further comprises desorbing carbon dioxide from the sorbent composition.34. A method according to clause 33, wherein the desorption is mediated by heating the sorbent composition, suitably to a temperature of about 550°C or more.35. A method according to clause 33 or 34, wherein the method further comprises reacting the desorbed carbon dioxide to provide another product, such as carbon monoxide, methanol or a hydrocarbon.36. A method according to clause 35, wherein the desorbed carbon dioxide is reacted with hydrogen to produce a gaseous composition comprising carbon monoxide.37. A method according to clause 36, wherein the reaction with hydrogen is performed at a temperature of about 600°C to about 900°C.38. A method according to any one of clauses 33 to 37, wherein the desorption and reaction with hydrogen may be combined in a single heating process.39. A method according to clauses 38, wherein the desorption and the reaction with hydrogen are performed at a temperature of about 600°C to about 700°C.40. A method for producing a gaseous composition comprising carbon monoxide comprising:(i) exposing a first gaseous composition comprising carbon dioxide to a sorbent composition comprising calcined marble; wherein the first gaseous composition comprises less than about 1 vol.% of carbon dioxide and the first gaseous composition has a temperature of 70°C or less;(ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a second gaseous composition comprising carbon monoxide.41. A method according to clause 40, wherein the first gaseous composition comprises less than about 0.1 vol. % of carbon dioxide.42. A method according to clause 40, wherein the first gaseous composition comprises about 0.01 vol. % to about 1 vol. % of carbon dioxide.43. A method according to clause 40, wherein the first gaseous composition comprises about 0.03 vol. % to about 0.06 vol. % of carbon dioxide.44. A method according to clause 40, wherein the first gaseous composition comprises less than about 450ppmv of carbon dioxide.45. A method according to any one of clauses 40 to 44, wherein the first gaseous composition is air, suitably ambient air.46. A method according to clause 45, wherein the relative humidity of the air is about 40 % or more.47. A method according to any one of clauses 40 to 46, wherein the temperature of the gaseous composition / air is about 55°C or less.48. A method according to any one of clauses 40 to 47, wherein the temperature of the gaseous composition / air is about -40°C to about 55°C.49. A method according to any one of clauses 40 to 48, wherein the temperature of the gaseous composition is ambient atmospheric temperature.50. A method according to any one of clauses 40 to 59, wherein the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C or more.51. A method according to any one of clauses 40 to 50, wherein the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C to about 1000°C.52. A method according to clause 51 , wherein the marble is heated in air, nitrogen or an hydrogen-containing atmosphere.53. A method according to clause 51 or clause 52, wherein the marble is heated at a rate of about 5°C / min to about 20°C / min, suitably about 5°C / min to about 15°C / min, suitably about 10°C / min.54. A method according to any one of clauses 40 to 53, wherein the specific surface area of the calcined marble is about 5 m2 / g or more.55. A method according to any one of clauses 40 to 54, wherein the specific surface area of the calcined marble is about 10 m2 / g or more.56. A method according to any one of clauses 40 to 55, wherein the specific surface area of the calcined marble is about 5 m2 / g to about 25 m2 / g.57. A method according to any one of clauses 54 to 56, wherein the specific surface area is measured by the BET method (BET multipoint measurement) using isothermal N2absorption-desorption at 77K.58. A method according to any one of clauses 40 to 57, wherein the calcined marble has a total pore volume of about 0.01 cm3 / g or more.59. A method according to any one of clauses 40 to 58, wherein the calcined marble has a total pore volume of about 0.025 cm3 / g or more.60. A method according to any one of clauses 40 to 59, wherein the calcined marble has a total pore volume of about 0.03 cm3 / g to about 0.05 cm3 / g.61 . A method according to any one of clauses 58 to 60, wherein the total pore volume measured by isothermal N2adsorption-desorption at 77 K, and the pore size distributions plotted by the Barrett-Joyner-Halenda (BJH) method using the desorption branch.62. A method according to any one of clauses 40 to 61 , wherein the calcined marble comprises CaO.63. A method according to any one of clauses 40 to 62, wherein the calcined marble comprises about 50 wt.% of CaO or more.64. A method according to any one of clauses 40 to 63, wherein the calcined marble comprises about 50 wt.% to about 99% wt.% of CaO.A method according to any one of clauses 40 to 64, wherein the calcined marble comprises MgO.A method according to any one of clauses 40 to 65, wherein the calcined marble comprises about 0.01 wt.% to about 50 wt. % of MgO.A method according to any one of clauses 40 to 66, wherein the calcined marble comprises one or more species selected from the group consisting of a cobalt species, chromium species, iron species and potassium species.68. A method according to any one of clauses 40 to 67, wherein the calcined marble comprises less than 1 wt. % of a silicon and / or an aluminium species.69. A method according to any one of clauses 40 to 68, wherein first gaseous composition is actively drawn over or through the sorbent composition.70. A method according to any one of clauses 40 to 69, wherein the sorbent composition is exposed to the first gaseous composition for about 12 hours or more.71. A method according to any one of clauses 40 to 70, wherein the sorbent composition is exposed to the first gaseous composition for about 1 day to about 7 days.72. A method according to any one of clauses 40 to 71 , wherein the sorbent composition is heated with hydrogen in step (ii) at a temperature of about 600°C to about 900°C, suitably about 650°C to about 700°C.73. A method according to any one of clauses 40 to 72, wherein the sorbent composition obtained in (ii) is employed as the sorbent composition in (i) in a further cycle of method steps (i) and (ii).74. A method according to clauses 73, wherein 5 or more consecutive cycles of method steps (i) and (ii) are performed, suitably 10 or more, suitably 20 or more, suitably 50 or more.75. A method according to any one of the preceding clauses wherein the sorbent composition is a solid composition.76. A method according to clause 75, wherein the sorbent composition is in the form of a powder, pellet(s), granule(s) or a shaped article (e.g. a structured monolith or sculptured framework).EXAMPLESPreparation and Characterisation of the Sorbents

[0108] Sorbents were prepared using waste marble, which had been ground to a given size (Table 1A). Six different types of marble are sourced as shown in Table 1A. The partial marble blocks were manually crushed and sieved to ensure uniform particle size before being collected for the experiments. For the direct air capture and regeneration process, BOC Ltd. supplied ultra-high purity (>99.998%) H2, N2, and air gas cylinders.Table 1A - Summary of raw marble samples

[0109] The 6 marble samples (Table 1A) were calcined by a muffle furnace at 950 °C for 2 hours to prepare the sorbents at a heating rate of 10°C min-1. The samples were cooled to room temperature. The calcined samples were stored in sealed sample bottles and filled with pure nitrogen gas as a protective measure. Each sample was clearly labelled to ensure proper identification of different samples.

[0110] Elemental analysis of the calcined marble sample was performed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Figure 1 provides details of the elemental analysis of the 6 calcined marble samples.

[0111] The crystalline phase or minerals in the raw marble samples, fresh calcined samples, and spent calcined samples were analysed by X-ray diffraction (XRD, Bruker D8 Advance eco XRD) with Cu Ka X-ray source; 1.5814A, 2°Theta from 5 to 80° and at 40 Kv and 25 mA. Figure 2 shows the XRD of (a) the samples as the natural marble stone and (b) stone samples after calcination at 950°C.

[0112] The microstructural morphology of the samples was analysed by scanning electron microscopy (SEM, DEI Quanta 250 FEG, UK) analysis, coupled with Energy Dispersive X-ray (EDX).

[0113] The sample pore size distribution and specific surface area was characterised by isothermal N2adsorption-desorption at 77 K by the Barrett-Joyner-Halenda (BJH) method using the desorption branch. The Brunauer-Emmett-Teller (BET) method was used to calculate the specific surface area.

[0114] Surface elements, quantitative spectroscopic measurements and chemical bonding were detected using by X-ray photoelectron spectroscopy (XPS).

[0115] Thermal behaviour was analysed using thermo-gravimetric analysis (TGA) to explore the thermal decomposition in different atmosphere conditions. Samples were heated to 850 °C at 10 °C min1with N2purging. The temperature-programmed reduction (H2-TPR) and temperature-programmed oxidation (TPO) of samples was performed using 2950 thermogravimetric analyser. Typically, the temperature rose to 40 °C and held for 3 mins for the sample pre-heat with N2purging, then the temperature was programmed to increase stepwise by 10 °C mins to 850 °C and kept for 5 mins, and N2was replaced by 5% H2as the temperature began to rise. For TPO, the temperature was set to 40 °C as pre-treatment temperature with N2fed in. Subsequently, airflow was introduced with a ramping rate of 10 °C min-1to 850 °C and kept for 5 mins.DAC-ICCU Evaluation

[0116] The 6 sorbent samples were investigated for direct air capture (DAC) and integrated carbon dioxide (CO2) capture and utilisation (ICCU).

[0117] In general, the DAC-Hydrogenation performance of the samples was performed as follows. Reactions were conducted in fixed bed furnaces and quartz tubes. To investigate direct air capture, 0.5 g of sorbent sample was subjected to a flow of 50 ml min-1air at room temperature. Samples were placed into quartz boats and loaded in the middle of a glass tube (OD: 25 mm, ID: 21 mm, L: 780 mm). The inlet air flow stream is controlled by mass flow meters (OMEGA; FMA-A2306), and air steam was connected with a glass tube by an adaptor, and the samples were placed on a fume hood workbench for 5 hours.

[0118] After the sorption period, the samples were removed and transferred to a quartz reaction tube (OD: 12 mm, ID: 10.5 mm, L: 650 mm) to perform the hydrogenation process. Quartz wool was used to secure the samples in the centre of the quartz tube, and a thermocouple was also inserted into the tube to calibrate the reaction temperature. The temperature set point of the fixed bed reactor is 600°C at 20°C min-1. N2purge with 100 ml min-1was conducted to remove any air from the tube, and then purified hydrogen gas (99.998%, BOC) was introduced at a flow rate of 100 ml min-1. The H2concentration wasmonitored by a CX-H02 H2analyser (Shanghai Cixi Instrument Co. Ltd) before the quartz tube was located in the furnace when the temperature stabilised. The fraction of the output gas (CO, CO2 and CH ) was analysed by an ENERAC™ 700AV Exhaust gas analyser (ENERAC, USA).

[0119] All experiments were conducted at atmospheric pressure. The CO2 capture capacity, CO2 conversion and selectivity, and CO yield were calculated using the following formulae:

[0120] Cco2 represents the CO2 capture capacity (%.s-1) during the 5-hour sorption and XCo2 denotes the CO2 conversion (%) during the hydrogenation stage, to is when CO2 starts to be released; ti is when CO2 sorption stops; t2is when CO starts to be released; and t3is when CO generation is completed.

[0121] Yeo is the yield of CO, Cco represents the amount of CO generated (% s-1), Vco is the flow rate of the CO stream (ml s-1), M represents molarity (ml mmol-1), and W denotes the weight of the sorbent sample (g).

[0122] Figure 3 shows the XRD of each calcined sample after 5 hours exposed to air. Based on Figures 1 to 3, it will be appreciated that CaO is present in most samples after calcination at 950°C. Calcined samples WP1 , WP2 and WP4 have a significant amount of Mg element.

[0123] Figure 4 presents SEM images of stone sample 2 after calcination as above but temperatures of (a) 950°C, (b) 850°C, (c) 750°C and (d) 650°C. It is apparent that the samples have a similar appearance with no cracking, indicating the mechanical stability of the material. Figure 5 shows (a) XRD of stone sample 2 after calcination at said various temperatures and (b) XRD of the calcined marble samples after 5 hours of DAC shows the formation of carbonates.

[0124] Table 1 B summarises the surface area and pore volume characteristics of the calcined marble samples and the results of DAC:Table 1B - Properties of calcined marble samples

[0125] After DAC, the samples were heated to a temperature of around 600°C in the presence of hydrogen for the regeneration of the calcined marble sample and the conversion of captured CO2 to carbon monoxide (CO) as described above. Table 2 summarises the results of the CO2 hydrogenation.Table 2 - CO2 hydrogenation

[0126] Figure 6 shows the performance of the calcined samples with respect to (a) capacity of CO2 capture; (b) CO yield from the hydrogenation of captured CO2. Samples 1, 2 and 6 show a higher production of CO.

[0127] Figure 7 shows SEM images of sample 2 (a) as the fresh stone sample, (b) after calcination at 950°C, and after 10 cycles of absorption and calcination and at 617 times (c) and 100,000 (d) times magnification. As is clear from Figure 7, there is little change in the surface of the marble sample after calcination, DAC and CO2 hydrogenation. In contrast, Figure 8 shows SEM images of commercial calcium oxide powder (CaO) as a fresh sample at 9050 (a) and 128000 times (b) magnification, after calcination (c) and after DAC and hydrogenation (d). Sintering is obvious after the calcination of CaO. The hydrogenation of captured CO2 restored some surfaces. However, a reduction in CO2 hydrogenation performance is expected and supported by the literature using CaO samples [Athanasios A. Scaltsoyiannes, Angeliki A. Lemonidou, Chemical Engineering Science, Volume 243, 2021 , 116797], The mechanical strength of CaO is also known to be poor.

[0128] The influence of DAC duration on the CO2 hydrogenation performance was assessed for calcined stone sample 1. Accordingly, 0.5 g of sorbent sample was exposed to air as described above for varying time periods. The results are presented in Table 3 and Figure 9.Table 3

[0129] As can be seen from the above, one day of sorption is sufficient using the sorbent in terms of optimising the subsequent production of CO. Longer sorption showed no improvement of CO production.

[0130] The influence of moisture on DAC was investigated using calcined stone sample 2. Humidity control was achieved by adjusting the temperature of air entry into a wash bottle containing deionised water and adding a portion of cotton or other media into the quartz tube to regulate the humidity in the introduced air. A diagnostic psychrometer (RS-3322) was used to measure the target humidity.

[0131] The effect of humidity on CO2 sorption are summarised in Table 4 and Figure 10. It is observed that the presence of moisture is beneficial to CO2 capture capacity of the sorbent.Table 4

[0132] The influence of moisture on CO production using calcined stone sample 2 and CaO powder is shown in Table 5 and Figure 11. It is evident that CO production can be enhanced from the utilisation of the captured CO2 at humidity of 45-50 RH%. The production of CH4is negligible.Table 5

[0133] Stone sample 2 was assessed for stability throughout 10 successive cycles of DAC and CO2 hydrogenation. Each cycle started with carbonation and was completed by hydrogenation as described above. First, the 0.5 g sample was placed in the quartz tube and was fed with 50 ml min-1air for 5 hours. After 100 ml min-1N2 purging of the sample was used to calibrate the exhaust gas analyser, and then 100% H2 100 ml min-1was introduced. The quartz tube was installed in the middle of the furnace when the reaction stabilised, and emission data collection was started. After hydrogenation finished, the sample was cooled down to room temperature with a purge of N2 and the cycle repeated.

[0134] The results are presented in Figure 12 in terms of (a) CO2 capture and (b) CO2 hydrogenation. The process shows good stability after 10 cycles of sorption, regeneration and CO2 utilisation, in terms of the yield of CO, CO2 and the conversion of the captured CO2.

[0135] Four experiments were conducted to test whether the samples can undergo high-temperature sorption. In detail, the calcined marble sample 1 (0.5g) was placed into the middle of a quartz tube secured by quartz wool. A 100 ml min-1N2purge was conducted before the 50 ml min-1air was fed in whilst installed in the middle of a furnace at 600° C for 30 mins. The carbon capture process emissions were detected by Kane 457 gas analyser. After 30mins of the carbonation process, the N2purging removes air in the tube and switches to pure H2with 100 ml min-1to start the hydrogenation process at the same temperature. This results in no production of CO (Figure 13, black line).

[0136] In another case, sample 1 (0.5g) was exposed to air as above for 30 mins in a high-temperature carbonation process at 600°C. However, N2was introduced for purging after removing the quartz tube from the reactor before starting the hydrogenation process. Similarly, negligible CO production was observed (Figure 13, red line).

[0137] Finally, calcined sample 1 (0.5g) and calcined sample 6 (0.5g) exposed to air as above for 20 mins in a high-temperature carbonation process at 600°C followed by 10 mins of air sorption outside the furnace with purging N2after sorption to cool down. This results in some production of CO, due to the capture of CO2when moving the sample tube outside the furnace to room temperature (Figure 13, blue and green line).

[0138] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference in their entirety and to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein (to the maximum extent permitted by law).

[0139] All headings and sub-headings are used herein for convenience only and should not be construed as limiting the invention in any way.

[0140] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise paragraphed. No language in the specification should be construed as indicating any non-paragraphed element as essential to the practice of the invention.

[0141] The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability, and / or enforceability of such patent documents.

[0142] This invention includes all modifications and equivalents of the subject matter recited in the paragraphs appended hereto as permitted by applicable law.

Claims

CLAIMS1. A method for reducing the amount of carbon dioxide in a gaseous composition comprising exposing the gaseous composition to a sorbent composition comprising calcined marble; wherein the gaseous composition comprises less than about 1 vol.% of carbon dioxide and the gaseous composition has a temperature of about 70°C or less.

2. A method according to claim 1 , wherein the gaseous composition comprises less than about 0.1 vol. % of carbon dioxide.

3. A method according to claim 1 or 2, wherein the gaseous composition is air, suitably ambient air.

4. A method according to claim 3, wherein the relative humidity of the air is about 40 % or more.

5. A method according to any one of the preceding claims, wherein the temperature of the gaseous composition / air is about 55°C or less.

6. A method according to any one of the preceding claims, wherein the temperature of the gaseous composition is ambient atmospheric temperature.

7. A method according to any one of the preceding claims, wherein the calcined marble is obtained or obtainable by heating marble to a temperature of about 550°C or more.

8. A method according to any one of the preceding claims, wherein the specific surface area of the calcined marble is about 5 m2 / g or more.

9. A method according to any one of the preceding claims, wherein the calcined marble has a total pore volume of about 0.025 cm3 / g or more.

10. A method according to any one of the preceding claims, wherein the calcined marble comprises about 50 wt.% of CaO or more.

11. A method according to any one of the preceding claims, wherein the calcined marble comprises about 0.01 wt.% to about 50 wt. % of MgO.

12. A method according to any one of the preceding claims, wherein gaseous composition is actively drawn over or through the sorbent composition.

13. A method according to any one of the preceding claims, wherein the sorbent composition is exposed to the gaseous composition for about 12 hours or more.

14. A method according to any one of the preceding claims, wherein the method further comprises desorbing carbon dioxide from the sorbent composition.

15. A method according to claim 14, wherein the method further comprises reacting the desorbed carbon dioxide to provide another product, such as carbon monoxide, methanol or a hydrocarbon.

16. A method according to claim 15, wherein the desorbed carbon dioxide is reacted with hydrogen to produce a gaseous composition comprising carbon monoxide.

17. A method according to claim 16, wherein the reaction with hydrogen is performed at a temperature of about 600°C to about 900°C.

18. A method for producing a gaseous composition comprising carbon monoxide comprising:(i) exposing a first gaseous composition comprising carbon dioxide to a sorbent composition comprising calcined marble; wherein the first gaseous composition comprises less than about 1 vol.% of carbon dioxide and the first gaseous composition has a temperature of 70°C or less;(ii) heating the sorbent composition obtained in (i) in the presence of hydrogen at a temperature of about 500°C or more to yield a second gaseous composition comprising carbon monoxide.

19. A method according to claim 18, wherein the first gaseous composition comprises less than about 500 ppmv of carbon dioxide.

20. A method according to claim 18, wherein the first gaseous composition is air.21 . A method according to any one of claims 18 to 20, wherein the specific surface area of the calcined marble is about 5 m2 / g or more.

22. A method according to any one of claims 18 to 21, wherein the calcined marble has a total pore volume of about 0.025 cm3 / g or more.

23. A method according to any one of claims 18 to 22, wherein the sorbent composition is heated with hydrogen in step (ii) at a temperature of about 600°C to about 900°C, suitably about 650°C to about 700°C.

24. A method according to any one of claims 18 to 23, wherein the sorbent composition obtained in (ii) is employed as the sorbent composition in (i) in a further cycle of method steps (i) and (ii).

25. A method according to claims 24, wherein 5 or more consecutive cycles of method steps (i) and (ii) are performed, suitably 10 or more, suitably 20 or more, suitably 50 or more.