Light activated reverse boudouard process

Abstract

A light assisted photochemical process for converting carbonaceous materials and carbon dioxide to carbon monoxide under ambient operating conditions, and system therefor are disclosed.

Description

LIGHT ACTIVATED REVERSE BOUDOUARD PROCESSFIELD OF THE INVENTION

[0001] The present invention relates to a process for the synthesis of a carbon monoxide from solid-state carbon and carbon dioxide gas using a light-driven reverse- Boudouard reaction. The process of the invention allows the reverse-Boudouard reaction to proceed under more sustainable and practicable conditions than those currently used by way of using sunlight and / or light-emitting diodes, which may be powered 24 / 7 by silicon photovoltaics, and / or lithium-ion batteries to provide the required light. The process of the present invention is adapted to utilize carbon dioxide and various forms of carbonaceous materials, including but not limited to various forms of carbon black, biochar, and carbonaceous waste to synthesize carbon monoxide in a practical and environmentally friendly way.BACKGROUND

[0002] Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen (H2), carbon monoxide (CO), and potentially some carbon dioxide (CO2). It is used, for example, as an intermediate in the production of hydrocarbon fuels, such as diesel fuel and methanol, in creating synthetic natural gas and and in the production of industrial chemicals such as ammonia and methanol. Currently, the industrial production of syngas occurs via steam-methane reformation and / or coal or coke steam gasification. Syngascan also be obtained from pyrolysis initiated on residues, biomass, and waste. Both processes are highly energy consuming and carbon footprint-intensive.

[0003] Previous attempts at more eco-friendly carbon monoxide production have utilized thermal steam-gasification of fossil fuels, biomass, and / or waste materials, usually through auto-combustion of the carbonaceous feedstock. Notably, the large-scale application of this technology has been limited by high temperatures required, ash melting, and tar contamination. In additional generally, thermal steam gasification generates a large carbon footprint, requires injections of pure oxygen, and produces combustion-related contaminants like dioxins and furans.

[0004] The reverse-Boudouard reaction has been used to convert carbon and carbon dioxide to carbon monoxide under purely thermally-driven conditions at temperatures up to 900°C (according to the reaction expressed in equation 1 below). Such high temperatures present technical challenges associated with large-scale high-temperature energy-intensive operations, and these challenges limit the reaction’s utility.C + CO22 CO AH°298K = + 172 kJ / mol (1 )While it has been shown that the use of alkali, alkali-earth, and transition metal catalysts can decrease the required reverse-Boudouard reaction temperature to a limited extent, reactor degradation from catalyst melting and deposition remain a problem for extent practical application.

[0005] The global CO market is expected to reach USD 6.643 billion by the end of 2026, growing at a combined annual growth rate of 2.7% during 2021 -2026.SUMMARY OF THE INVENTION

[0006] The present invention encompasses methods and apparatuses for the preparation of syngas containing carbon monoxide by a modified reverse Boudouard process while avoiding the very high operating temperatures required for the production of carbon monoxide under purely thermally-driven conditions. It has surprisingly been found that a light-driven reverse-Boudouard process, using sunlight or LED-based lighting, with or without additional heating, can effectively convert carbonaceous materials to carbon monoxide without the elevated temperatures of the prior art. The process of the present invention can be carried out in either batch or flow-type reactors where the solid carbonaceous material is contacted with a gaseous medium containing carbon dioxide in an environment where the interface between the solid carbonaceous material and the carbon dioxide is irradiated by light. The reaction occurs on the surface of the solid carbonaceous material and consumes both carbon and carbon dioxide in approximately equivalent molar amounts, resulting in the production of two carbon monoxides for every atom of carbon and every molecule of carbon dioxide consumed.

[0007] While solar light can be used to reduce the heat requirements of the reaction, its intermittency has the potential to limit its effectiveness. The proposed solution of the present invention also permits the production of CO in light-driven reverse-Boudouard process, using light-emitting diodes (LEDs) instead of natural light; the LEDs may be powered using the energy and production storage capacity of silicon photovoltaics and lithium-ion batteries. This Photochemical Reverse Boudouard Reaction can facilitate 24- 7 CO production, under ambient operating conditions even in the absence of sunlight and continuous electrical power.

[0008] The solar light and the LED light may be filtered to optimize the wavelengths of the light to which the carbonaceous material is exposed. The LEDs used to generate the LED light may be selected to provide the desired light wavelengths.

[0009] This chemistry of the present invention allows for carbon waste, or any carbonaceous material, and greenhouse gas CO2 to be converted sustainably into a value-added commodity chemical, without the complications associated with extreme operating temperatures. The viability of this platform is a step towards decarbonization of many large scale industries.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic representation of one embodiment of the laboratory scale batch reactor used to carry out some of the testing described herein.

[0011] Figure 2 is a schematic representation of one embodiment of the laboratory continuous flow reactor used to carry out some of the testing described herein. The photoflow reactor consists of heatable stainless steel or glass body which facilitates the flow of gas through a fixed reactant bed.

[0012] Figure 3 shows graphically the rate of CO production using a photo-driven reverse-Boudouard reaction performed on several carbon sources with a Xe lamp at an irradiation intensity of 12.7 W cm-2.

[0013] Figure 4 shows graphically the rate of CO production obtained in power intensity studies using a CnB CABOT sample, confirming . photochemical behaviour for CO production rates at intensities lower than 21 W cm’2(R2= 0.998)

[0014] Figure 5 shows graphically the rate of CO production using in wavelength dependence studies with applied heating to 350 °C (to nullify the photothermal effect) on ultrapure CnB and CABOT CnB samples at light intensities of 15 W cm’2

[0015] Figure 6 shows graphically the rate of CO production underdark and light conditions in the temperature range of 500-560 °C using a photo-flow reactor;.

[0016] Figure 7 shows graphically the amount of CO production and the loss in mass of the sample of carbonaceous material used in the photothermal reverse-Boudouard reaction without the application of any external heat; Xe lamp light intensity was set to 34.1 W cm’2. Measurements were done in triplicate. Irradiation time and reactor pressure for a, b, d and f tests were 5 minutes and between 24-30 psig of CO2 without external heat applied

[0017] Figure 8 shows graphically the rate of CO production using a “rooftop” natural solar irradiation and red LED lighting on the reverse-Boudouard reaction at various light intensity levels.

[0018] Figure 9 shows graphically the effect on CO production by varying light intensity using several light filters.

[0019] Figures 10a to 10e show the rates of CO production using different colours of LED lighting at various light intensity levels.DETAILED DESCRIPTION OF THE INVENTION / EMBODIMENTS

[0020] According to one embodiment of the invention, the high temperatures required to convert carbonaceous materials and a gaseous medium containing carbon dioxide to carbon monoxide can be avoided by irradiating the carbonaceous materials with light at the time that the carbonaceous materials are exposed to and come into contact with the gaseous carbon dioxide. The gaseous carbon dioxide medium may optionally contain an inert gas such as argon.

[0021] According to another embodiment of the invention, the process of the present invention may be carried out at ambient or elevated temperatures; carrying out the process at elevated temperatures up to about 560°C, but below those temperatures required by a conventional reverse-Boudouard process, was demonstrated to increase the rate of production of CO2.

[0022] According to another embodiment of the invention, the process of the present invention may be carried out in a batch or flow process at pressures from about 24 to 30 psi, or at other pressures within the skill and knowledge of a person skilled in the art.

[0023] According to yet another embodiment of the invention, the process of the present invention may be carried out using light intensities above about 10 W cm’2, or alternatively ranging from about 12 to about 90 W cm’2, at which intensities the conversion of carbonaceous materials and carbon dioxide to carbon monoxide has been demonstrated to occur. Light intensities may be increased, in the case of solar power, by the use of magnifying lenses to concentrate incoming light on a smaller surface, or in the case of light emitting diodes, by increasing the power to the LEDs.

[0024] According to yet another embodiment of the invention, the wavelengths of the light used in the light-assisted reverse-Boudouard process of the present invention may be selected or adjusted to improve the efficiency of the conversion of carbonaceous materials and carbon dioxide to carbon monoxide. Alternatively, the wavellengths of the light generated by LEDs may be selected or adjusted by selecting LEDs generating light wavelengths towards the red end of the visible light spectrum.

[0025] The viability of the Photochemical Reverse Boudouard Process may be validated by comparative techno-economic analyses. Table 1 below summarizes the rates of CO production in prior art methods utilizing thermal and microwave radiation, compared to the inventive solar and LED methods. The results unambiguously demonstrate that sunlight and light-emitting diodes can efficiently enable the Reverse Boudouard Reaction under eco-friendly conditions providing a sustainable pathway for making a renewable, highly valued feedstock CO.Table 1Prior art thermal and microwave results shown in Table 1 are taken from Hunt, J. et al.Microwave-Specific Enhancement of the Carbon-Carbon Dioxide Boudouard Reaction. J. Phys. Chem. C 117, 26871-26880 (2013).

[0026] To investigate the effect of the irradiation of carbonaceous materials with light on the conversion of those materials to carbon monoxide and the concurrent conversion of carbon dioxide to carbon monoxide, experiments were carried out in laboratory scale reactors shown schematically in Figures 1 and 2.

[0027] Carbon Black (CnB) was purchased from CABOT (VULCAN XC72R GP-3921 ) and used as received. The material was found to have a surface area of 216 m2g-1. Carbon nanotubes, natural graphite, carbon black (13CnB) and carbon-13C dioxide (13CO2 99%) were purchased from Sigma-Aldrich and used as received. Ultrapure carbon black was purchased from AlfaAesar. Before use, carbon dioxide (99.9% purity and purchased from Praxair) was passed through a dry alumina column. Carbon black samples were suspended in distilled water and placed in an ultrasound bath for 30 minutes before dropwise addition under vacuum onto glass fibre filters with a Pasteur pipette. After drying for 2 hours in a vacuum oven at 60 °C, the samples were exposed to simulated and natural solar light with and without external heat. For the natural solar tests, CnB pellets were made with different diameters (4-13 mm) between 2-3 mm thickness and were prepared using a commercial pellet press at 2 metric tonnes for 5 minutes. Biochar was produced by slow pyrolysis of wood chips at 200°C under N2 atmosphere in a flow furnace for 6 hours. Then, the temperature was raised to 400°C at 20°C / min and maintained for 12 hours, during which the wood samples were monitored for pyrolysis completion.Depending on the size of the chips, the extra time and intermediate grinding were needed to ensure biochar formation.

[0028] Figure 1 depicts schematically one embodiment of the laboratory scale batch reactor used, which may have stainless steel reactor body A with quartz glass window disposed on its circumference, and valves B controlling the inflow and outflow of gas to and from the reactor body. The quartz glass window in reactor allows light from an Xe lamp, simulating solar light, to irradiate the surface of the carbonaceous material within the reactor and to promote the production of carbon monoxide. The reactor had a volume of 11 .8 mL and utilized a quartz window, temperature thermocouple and pressure gauge. The reactor was used with a Perfect Light™ solar simulator 300W Xe lamp. A Newport™ power meter with an 18 mm detector spot diameter was used. Manually varying the power (adjusting the current between 10 to 20 amp) in the Xe lamp yielded light intensities from 7.00 W to 27.05 W. By adjusting the diameter of the light spot (6 to 10 mm using focusing lenses), net light intensities from 12.7 W cm-2 to 34.4 W cm-2 used in this study could be achieved.

[0029] Reactions carried out in the batch reactor used an average sample mass of ~0.3 to 1.1 mg and deposited on borosilicate filters. Alternatively, pellets of 13 mm diameter were placed in a reactor equipped with a quartz window and pressurized with 24 to 30 psi of CO2.

[0030] A pellet of carbonaceous material is placed in the reactor and the reactor is sealed. The gas is evacuated by means of a vacuum pump and replaced with pure carbon dioxide or a mixture of inert gas and carbon dioxide. The reactor is again sealed by closing the valves, B. Light from a light source is shined on the carbonaceous material’s surfacethrough a quartz glass window affixed to a sealed port in the stainless steel reactor. During and after the reaction, one valve may be opened allowing gas from the reactor to be sampled and analyzed by conventional means, including gas chromatography-flame ionization detection (GC-FID).

[0031] As shown in Figure 2, the photoflow reactor allows a continuous flow of a gaseous medium containing carbon dioxide through the carbonaceous material. The photoflow reactor consists of heatable stainless steel body which facilitates the flow of gas through a fixed reactant bed. A quartz glass window allows the bed to be irradiated with light. The body of the continuous flow photoflow reactor is connected to a gas inlet and outlet lines and may be configured by conventional means to allow gas flow through the reactor while preventing particle movement. The reactor body may be partially surrounded by a heating element and insulation so that chosen material for reaction in the tube can be irradiated.

[0032] Sampling of the output stream of the photoflow or continuous flow reactor for analysis was accomplished through a direct connection to the output gas flow. A GCMS spectrometer (Agilent 7890B-5977A MSD, using He as carrier gas) equipped with an automated injection gas sampling valve over three capillary columns (Molsieve, HP- PLOT / Q+PT and DB-FFAP) was used to analyze the amounts of12CO / 13CO produced.

[0033] Natural solar light could be used to irradiate the samples in each of the reactors with measured intensities between 15 - 90 W cm-2 for up to 10 minutes. In some experiments, a 300WXe arc lamp from PerfectLight™ company was used to simulate the sun during the preliminary and wavelength experiments (Fig. S9). Following this, LEDmeasurements were conducted by a flame ionization detector (FID) on an SRI8610 GC instrument

[0034] The selection of an appropriate carbonaceous material for production of CO by the reverse Boudouard process is generally based on its activity (i.e. the likely rate of CO production). This activity, which can be determined in TGA experiments, is in many cases dependent on the metal content of the carbonaceous material. However, as biochar may come from many sources and thus may have a wide range of metals, a commercial carbon black was chosen as the material of study.

[0035] Conventional analytical testing, including Ultraviolet-Visible (UV-Vis) spectroscopy, elemental analysis, powder X-ray diffraction (PXRD) (Fig. S3), Raman spectroscopy (Fig. 1 c), and X-ray photoelectron spectroscopy (XPS) characterizations were initially conducted on two kinds of carbon black, one ultrapure and the other containing a low level of metal impurities (denoted ultrapure CnB and CnB CABOT, both before and after light irradiation. This characterization provided a better understanding of the specific characteristics of the selected materials but is not a requirement for carrying out the novel process disclosed herein.

[0036] The TGA experiments performed on CnB samples (ultrapure, CABOT and Biochar CnB) in a CO2 atmosphere had demonstrated the influence of the metal impurities on the production of CO. The conversion follows the order Ultrapure Alfa Aesar < CABOT < Biochar confirming enhancements in CO production from metal impurities. Several reported studies on reverse Boudouard reactions using metals as catalysts have shown improved CO rate and decreased apparent activation energies with such use.Example 1 - Exploratory photo-driven reverse-Boudouard reactivity test

[0037] To assist in selecting appropriate carbonaceous materials for the studies reported herein, probe tests were performed at room temperature using a 300 WXe lamp (12.7 W cm’2irradiation intensity, where 0.1 W cm’2is equal to 1 sun) to select the optimal carbonaceous material (CM). These probe tests were initial screening tests conducted to screen the activity of the carbonaceous materials tested. Samples of each of the materials used were placed in the reactor of Figure 1 , irradiated with light, and the rate of CO production measured.As shown in the results presented graphically in Figure 3, Ultrapure CnB black (made from acetylene by Alfa Aesar) and carbon nanotubes (Sigma-Aldrich) were found to be stable under CO2 and light and presented low carbon monoxide production rates. Natural graphite samples were the most stable under light regardless of irradiation intensity or exposure time due to a lack of oxygenated functionalities and surface defects. CABOT CnB and biochar samples demonstrated the highest carbon monoxide production under light irradiation. Although biochar showed the highest rates of CO production, CABOT CnB was chosen for further study due its well-defined composition, size, structure, aggregation state, porosity, commercial availability and surface functionality.Example 2 - Effect of Light Intensity on CO Production

[0038] Various light intensities from the 300W Xe lamp, namely 15.3, 18.2, 20.9, 24.2, and 34.1 W / cm2, were used to determine the photoresponsivity of CO production on CABOT CnB and to evaluate its photochemical and photothermal behaviour. The experiments were carried out in the reactor of Figure 1 at ambient temperature withoutexternal heating. These results are shown in Figure 4, demonstrating the increased CO production rates as the intensity of the light increased. These results demonstrated that the highly endothermic reverse-Boudouard process could be photochemically driven and suggested dominant photothermal contribution under high-intensity light and dominant photochemical behaviour at lower intensities below 21 W cm’2. In addition, it showed that metal impurities, surface defects, C and 0 vacancies could dramatically increase the rate of CO production without interfering with the photochemical behaviour under low light intensities.Example 3 - Removing the photothermal effect of LED lighting

[0039] To minimize any photothermal effects under high-light intensity conditions and to confirm the presence of photochemical contributions to the reverse-Boudouard process, the temperature to which a known intensity of light would heat the carbonaceous material in the reactor was determined by using a fixed photon flux at the sample. The results at light intensities below 21 W cm’2had presented a linear correlation with CO formation rate, suggesting photochemical behaviour. Therefore, a light intensity of 15 W cm’2was selected for further tests to determine the role of light in CO2 reduction over CnB samples. An unfiltered Xe-arc lamp set at the stated light intensity was used to heat the sample surface. An IR camera was used to measure the temperature generated on the sample surface under CO2 in a photoreactor with a CaF2 window. The measured temperature was 350°C due to the expectedly high optical absorption by a black carbon material. All systems were then heated to this temperature for subsequent experiments, with the expectation that any thermal contribution from the Xe lamp would become negligible. Ultrapure and CABOT CnB pellets (13 mm diameter and 2-3 mm thickness)were placed in a batch reactor in separate experiments, and, after several vacuum / C02 purges, tested for photoactivity under CO2 using the aforementioned conditions. The Xe lamp intensity was set to ensure all samples had an incident photon flux of 15 W cm’2on the surface regardless of wavelength. The results are presented graphically in Figure 5. Using unfiltered light from (“Pure Xe”) the Xe lamp, CO production rates of 1.5 and 5.3 mmol cm’2h’1for the ultra-pure and CABOT CnB were observed, respectively. The “Dark” columns shown by comparison the rate of production of CO at the moderately elevated temperature of 350°C with no irradiation from the Xe light source.

[0040] To expand this comparison, bandpass filters were used to evaluate the wavelength dependency of the reaction and the tests were repeated with highpass filters of AM 1.5G, 420, 495, and 595 nm added to the Xe lamp, the intensity of which was adjusted to ensure all samples had an incident photon flux of 15 W cm’2on the surface regardless of wavelength in use.

[0041] As shown graphically in Figure 5, observed CO production rates were 0.16 (dark), 1 .63, 2.93, 2.29, and 2.14 mmol cm’2h’1for ultrapure CnB, and 1.16 (dark), 5.53, 7.43, 8.43, and 9.24 mmol cm’2h’1for CABOT CnB respectively. A linear increase in CO production rate was observed with each filter, confirming that photochemical behaviour varies with spectral wavelength range with CABOT CnB, whereas the ultrapure CnB sample presented a decreasing trend at increasing nm. The unique photochemical behaviour of CABOT CnB under irradiation for wavelengths higher than 595 nm for the highly endothermic reverse-Boudouard process was documented by irradiation with a Xe lamp at increasing intensities through the 595 nm highpass filter. It presented the highest activity towards CO, and the observed linear trend of the CO formation rate with the lightintensity supports the photochemical contribution to the solar-driven reverse-Boudouard reaction.Example 4 - Effect of Light Irradiation at Elevated Temperatures

[0042] Additional experiments evaluating the photochemical activation of the reverse Boudouard process in the dark vs light conditions were performed in a photo-flow reactor discussed above and schematically depicted in Figure 2. In each experiment, the total gas flow was set to 6 seem (1 seem CO2: 5 seem Ar) with an irradiated sample surface area of 0.126 cm2; each sample weighed about 2-3 mg. LED simulated white light intensity used 4.8 W cm’2. New samples were used for every test condition. As shown in Figure 6, the light-assisted reactions increased the CO production rate compared to the dark process. This confirmed light’s contribution to the process and suggested that the light-driven reaction likely proceeds through a different mechanism than the thermal reaction.Example 5 - Kinetic experiments

[0043] Kinetic experiments were conducted assuming a non-equilibrium batch reactor system, namely a batch system which chemical equilibrium is not achieved in the system. In other words, not all of the reagents are consumed and where the total conversion of CO2 did not exceed 5%. In these experiments, the samples were subjected to irradiation at 34.1 W / cm2 for reaction times of 1 ,2, 3, 4, 5 minutes with CO2 pressure of about 24-30 psig without external heat, and the total CO2 conversion was not greater than 2% following up to 5 minutes of irradiation under a simulated solar light intensity of 34.1 W cm’2The results are plotted graphically in Figure 7.Example 6 - Natural solar reverse-Boudouard reaction

[0044] To confirm the reactivity observed with LED lighting under solar light, photodriven reverse-Boudouard experiments were conducted using natural sunlight to test reactivity, rather than the Xe lamp used in the previous trials to simulate solar power. Several 13 mm diameter and 1 -2 mm thick CnB pellets were prepared by compressing the CnB material under two metric tonnes of pressure for 5 minutes using a commercial pellet press. The pellets were irradiated with natural sunlight focused to a 2-4 mm diameter spot using 7.5 cm and 12.7 cm diameter lenses in a CO2 atmosphere to intensities of 43, 63, and 90 W / crrr2Typical unfocused natural solar light intensities ranged between 0.070-0.088 W cm’2. Notably, Xe-arc lamps and natural sunlight have comparable spectra and photon fluxes and were expected to produce comparable large- scale production rates.

[0045] It had been found that irradiation with solar light at approximately 20 W cm’2without external heating yielded higher CO production rates than the reported thermal process at 850°C. Raising the incident light intensity to 43 W cm’2yielded rates above those reported at 75 W of microwave radiation at 813°C. As expected, CO production rates increased with natural-light intensity, showing a linear trend characteristic of photochemical reaction pathways or near photothermal-photochemical equilibrium due to the high conversion rate. The results are shown in Figure 8.

[0046] Overall, simulated solar Xe-arc lamp CO production rates agreed with those of natural solar experiments. A light-driven reverse-Boudouard process was proven to be accessible using sunlight. Thus, the results of the experiments of the present invention demonstrated the feasibility of a solar-powered reverse Boudouard reaction.

[0047] Like with the Xe lamp simulated solar irradiation experiments, the use of solar irradiation through a 595 nm bandpass filter showed higher CO rates than the same intensity irradiation using the full spectrum, implying that the photo reverse-Boudouard process performance can be optimized by using mostly IR photon flux. The rate of formation and yield of CO agreed with the expected experiments conducted under natural light at intensities of 65 to 90 W cm’2(Fig. 8). To demonstrate that high-intensity LED systems can be employed to drive the reverse Boudouard process to overcome the intermittency of natural sunlight, experiments were conducted using high-intensity red LEDs (625 nm at 95 W cm’2). The results are also shown in Figure 8.Example 7 - Effect of filtering solar light without intensity adjustment

[0048] The wavelength dependence of the light-driven reverse-Boudouard reaction was also evaluated using 75 W cm’2unfiltered solar light, and with UV, Visible and IR bandpass filters (Figure 9). The total irradiation power decreased from 75 to 62, 42, and 34 W cm’2when the filters were used, yielding corresponding CO production rates of 3706, 1814, 161 , and 176 mmol CO cm’2h’1, respectively.Example 8 - LED wavelength dependence

[0049] To further determine the dependency of CO conversion on LED wavelength, tests were conducted using specific colour generating LEDs. UV-vis spectroscopy measurements and the black nature of the carbonaceous material suggested that the selected carbon sample would absorb strongly across a broad wavelength spectrum. The wavelength dependence of the photo-driven reverse-Boudouard reaction was studied using UV (365 nm), blue (470 nm), white (440-600 nm), green (525 nm), and red (625 nm) LEDs.

[0050] CO production under blue LED light was found to follow Arrhenius behaviour, implying that blue wavelengths provide photothermal contributions to the solar-powered reverse-Boudouard reaction. The green LED-driven reverse-Boudouard required intensities greater than 1.8 W cm’2for CO formation. The red LED showed a linear relationship between power intensity and CO formation rates.As shown in Figures 10a - 10e, red LEDs yielded the highest CO production rate, confirming the bandpass filter experiments of Example 3 using simulated solar light. Consequently, red LED light was used as the primary light source for subsequent experiments to compare to natural solar light irradiation experiments.Example 9 - Isotopic13C photo-driven reverse Boudouard reaction

[0051] To confirm that the CO generated in the reaction chamber comes from the carbonaceous materials and the carbon dioxide in the reaction chamber, isotopically labelled13CO2 was reacted with a Cabot12CnB sample. Equal amounts of12CO and13CO were observed in the reaction chamber as determined by GC-MS establishing that carbon monoxide formed in equal amounts from each precursor and confirming the role of carbon dioxide in the reaction with natural solar irradiation.

[0052] The light-assisted reverse-Boudouard process of the present invention avoids the challenges posed by the conventional high-temperature reverse-Boudouard process and has been demonstrated to function at ambient temperatures. Compared to thermochemical and microwave reverse-Boudouard processes requiring temperatures greater than 900 °C, the solar-powered or light-powered process operates with lower activation energy and without external heating. The photo-driven reverse-Boudouardreaction described herein details methods for converting different carbon sources and CO2 into CO.

[0053] The solar or light-assisted reverse-Boudouard process is technically and economically feasible particularly with advancements in battery efficiency, solar concentrators, and LEDs, and the consequent reduction in the associated costs. Such a process would enable the production of CO from waste carbon and carbon dioxide and generate value-added feedstocks for a wide range of chemicals and chemical precursors.

Claims

CLAIMS1 . A process for the production of carbon monoxide comprising reacting one or more carbonaceous materials with a gaseous carbon dioxide feed stream, wherein the carbonaceous material is exposed to light concurrently with the contact of the carbonaceous material by the gaseous carbon dioxide source.

2. The process of claim 1 wherein the process is carried out at a temperature between ambient temperature and about 560-degrees C.

3. The process of claim 1 wherein the process is carried out at a temperature between ambient temperature and about 280-degrees C.

4. The process of any of claims 1 - 3 wherein the gaseous carbon dioxide source comprises carbon dioxide and an inert gas.

5. The process of claim 4 wherein the inert gas is argon.

6. The process of Claim 1 wherein the light is solar light.

7. The process of claim 1 wherein the light is from light emitting diodes.

8. The process of claim 1 , 6 or 7 where the intensity of the light as measured at the surface of the carbonaceous material is between 0.1 and 95 W cm-2.

9. The process of claim 1 , 6 or 7 where the intensity of the light as measured at the surface of the carbonaceous material is between 1 .0 and 95 W cm-2.

10. The process of claim 1 , 6 or 7 where the intensity of the light as measured at the surface of the carbonaceous material is between 1 .5 and 95 W cm-2.11 . The process of claim 1 , 6 or 7 where the intensity of the light as measured at the surface of the carbonaceous material is between about 10 and 95 W cm-2.

12. The process of claim 1 , 6 or 7 where the intensity of the light as measured at the surface of the carbonaceous material is between 15 and 95 W cm’2.

13. The process of any of claims 1 - 10 wherein the light source is amplified by optical or electronic means to achieve the desired intensities.

14. The process of any of claims 1 - 11 wherein the wavelength of the light to which the carbonaceous material is exposed is greater than about 420 nm.

15. The process of any of claims 1 - 11 wherein the wavelength of the light to which the carbonaceous material is exposed is greater than about 495 nm.

16. The process of any of claims 1 - 11 wherein the wavelength of the light to which the carbonaceous material is exposed is greater than 595 nm.

17. A process for the production of carbon monoxide comprising reacting one or more carbonaceous materials with a gaseous carbon dioxide feed stream, wherein: the carbonaceous material is irradiated with solar light at an intensity as measured at the surface of the carbonaceous material of at least 0.1 W cm’2.

18. A process for the production of carbon monoxide comprising reacting one or more carbonaceous materials with a gaseous carbon dioxide feed stream, wherein: the carbonaceous material is irradiated with solar light at an intensity as measured at the surface of the carbonaceous material of at least 1 W cm’2.

19. A process for the production of carbon monoxide comprising reacting one or more carbonaceous materials with a gaseous carbon dioxide feed stream, wherein: the carbonaceous material is irradiated with solar light at an intensity as measured at the surface of the carbonaceous material of at least 15 W cm’2.

0. A process for the production of carbon monoxide comprising reacting one or more carbonaceous materials with a gaseous carbon dioxide feed stream, wherein: a. the carbonaceous material is irradiated with light from one or more light emitting diodes; and b. the intensity of the light as measured at the surface of the carbonaceous material is at least 15 W cm’21 .A process for the production of carbon monoxide comprising reacting one or more carbonaceous materials with a gaseous carbon dioxide feed stream, wherein: a. the carbonaceous material is irradiated with light from one or more light emitting diodes; and b. the intensity of the light as measured at the surface of the carbonaceous material is at least 15 W cm’2; and c. the wavelength of the light from the light emitting diodes is above about400 nm.

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