Understanding the significance of in situ coal properties for CO2 sequestration: An experimental and numerical study

Over the years, there has been a rapid increase in atmospheric CO₂ concentrations, from 280 ppm in 1850 to 360 ppm in 1998. Therefore, mitigation methods such as carbon sequestration in subsurface reservoirs have been suggested. CO₂ sequestration is attractive, especially in relation to coal, with the additional potential benefit of CH₄ recovery. However, the potential of CO₂ sequestration is not well understood for various types of coals due to important in situ properties of coal. In this study, data from previous studies for coal permeability, density, moisture content, mineral content, vitrinite reflectance, compressive strength and temperature are compared with the CO₂ adsorption results to understand the significance of these in situ coal properties on CO₂ sequestration. To verify the findings, a custom‐designed advanced core flooding apparatus is used to simulate the effects of various in situ properties on CO₂ sequestration. This apparatus can test samples of 203 mm in diameter and up to 1000 mm in length. Hence, heterogeneity effects can be understood, as previous CO₂ sequestration‐related formulae have been based on coal samples of sizes ranging up to only about 100 mm. However, initially, a reconstituted coal core sample has been used to simplify the heterogeneity effects. Flow rates are estimated by analysing the lag of downstream pressures over time. With the use of a 203‐mm‐diameter and 816‐mm‐long reconstituted Victorian brown coal sample, flow rate reductions of 70% and 98% are observed for injection pressures of 2 and 4 MPa, respectively, due to CO₂ injection. This study highlights the appropriateness of a candidate coal reservoir for CO₂ storage in terms of in situ properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of Mg‐MOF‐74 for post‐combustion carbon dioxide capture through pressure swing adsorption

This paper presents a computational study of an energy‐efficient technique for post‐combustion CO₂ capture using novel material, namely, Mg‐MOF‐74, using pressure swing adsorption (PSA) processes. A detailed one‐dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multicomponent mass diffusion. The PSA model has been further extended by incorporating a heat regenerating process to enhance CO₂ sequestration. The heat dissipated during adsorption is stored in packed sand bed and released during desorption step for heating purpose. The model has been implemented on a MATLAB program using second‐order discretization. Validation of the model was performed using a complete experimental data set for CO₂ sequestration using zeolite 13X. Simulation of the PSA experiment on fixed bed has been carried out to evaluate the capacity of Mg‐MOF‐74 for CO₂ capture with varying feed gas temperature of 28 and 100 °C, varying pressurization and purge times and heat regeneration. It was discovered that the PSA process with heat regeneration system might be advantageous because it achieves equivalent amount of CO₂ sequestration in fewer PSA cycles compared with PSA without heat regeneration system. Based on the simulated conditions, CO₂ recovery with Mg‐MOF‐74 gives high percentage purity (above 98%) for the captured CO₂. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon dioxide sequestration effects on coal's hydro‐mechanical properties: a review

Carbon dioxide (CO₂) sequestration in deep un‐minable coal seam causes the seam's permeability and strength to be significantly reduced because of CO₂ adsorption‐induced matrix swelling. This paper reviews this swelling process in coal and its influence on coal's flow and strength properties. The amount of swelling depends on the properties of both the gas and the coal mass. The swelling caused by CO₂ adsorption is higher compared with that caused by CH₄ and N₂ and greatly depends on the state of the CO₂ phase. The super‐critical state of CO₂ adsorption causes greater swelling compared with the sub‐critical state. It has been observed that the swelling rate increases with increasing CO₂ pressure; however, high saturation pressures may cause the coal matrix to shrink. The swelling rate reduces with increasing temperature, and the effect of coal rank on swelling still remains unclear. The CO₂ adsorption‐induced swelling effect causes the coal mass permeability to be significantly reduced, and the reduction is significant for super‐critical CO₂.The effect of swelling on coal permeability reduces with increasing temperature. The coal matrix swelling and associated polymer structure re‐arrangement occur in the coal mass during and after the CO₂ injection, resulting in the weakening of the coal mass strength. The strength reduction is much higher for high rank coal compared with low rank coal. It is also observed that the influence of super‐critical CO₂ on strength is more powerful than that of sub‐critical CO₂. Although CO₂ sequestration in deep coal seams has been carried out in several main coal seams in the USA, Australia and some other countries, none of these projects has achieved the original target of storing large amounts of CO₂, possibly because initial analysis did take into account the effects of coal seam property changes because of the adsorption of CO₂ during and after injection. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of contaminants from flue gas on CO2 sequestration in saline formation

Deep saline aquifers are reported to have the largest estimated capacity for CO₂ sequestration. Most geochemical studies on CO₂ storage in saline formations are focused on the interactions of pure CO₂ and do not consider the potential impacts of contaminants such as SO₂ found in typical post‐composition flue gas streams. This paper reports on results of a combined CO₂–co‐contaminant–brine–rock experimental and a simple modeling study of the potential impact of flue gas contaminants on saline formations. Chemical reactions of the sandstone from Mount Simon formation exposed to CO₂ mixed with other gas species under sequestration conditions were studied (i.e. solid material — representative Mount Simon sandstone; liquid — synthetic Illinois Basin brine; T and P — 50 °C, 110 bar; gas composition — 1% SO₂, 4% O₂, 95% CO₂). The experimental study indicates that the co‐injection of 1% SO₂ would lead to substantially reduced brine pH due to the formation of sulfuric acid and the formation of bassanite (major) and anhydrites. Preliminary equilibrium computational modeling yielded similar results. Copyright © 2013 John Wiley & Sons, Ltd.     

Combination of double and single cyclic pressure alternation technique to increase CO2 sequestration with heat mining in enhanced geothermal reservoirs by thermo-hydro-mechanical coupling method

The rise in global temperature due to an unceasingly increase in non-condensable gases (NCG) prompts more development of safe and economical CCUS (Carbon Capture Utilization and Storage) technologies. Carbon dioxide (CO₂) sequestration with heat mining in deep enhanced geothermal systems (EGSs) is one of the promising methods to reduce CO₂ emitted to the atmosphere. In this study, a cyclic alternation of pressures at the injection and production wells is applied in an EGS for heat mining together with CO₂ deposit. Simultaneous alternation of the injection and production pressures can significantly increase the amount of CO₂ sequestrated compared to applying a fixed pumping or withdrawing pressures at the injector and producer respectively. At the injection well, alternation in pumping pressures at high frequency (small interval of days) increased CO₂ sequestration rate. Reducing the pumping frequency resulted in the lowering of the total amount of CO₂ sequestrated, lesser than using a fixed pumping pressure. The alternation in pumping frequency has a direct relationship to the CO₂ sequestration rate. The frequency of the injection and production pressures refers to the interval in days of the interchange in pressure between high to a low value and vice-versa. Furthermore, simultaneous alternation of pressures at the injection and production wells respectively (double cyclic method) improved geothermal heat extraction efficiency, thus higher performance for both geothermal and CO₂ sequestration projects.     

Nanoscale surface observation of feldspar dissolved under supercritical CO2–water–mineral system

As part of our assessment program on underground CO₂ storage, we studied the dissolution of feldspar in aqueous solutions of supercritical CO₂ at 25, 50, 65, and 80 °C with a constant CO₂ pressure of 10 MPa. Atomic force microscopy (AFM) was then used to observe nanoscale dissolution features on the feldspar surface. The average dissolution rates of anorthite during the initial 1 week of dissolution were estimated from surface retreat based on vertical cross-section profiles.     

Effects of additives on the hydrogen generation of Al–H2O reaction at low temperature

Water displacement method is used to study the influence of temperatures (60–80°C), additives (Na₂CO₃, NaCl, Na₂CO₃/NaCl) and concentrations on the reaction characteristics and kinetics of Al–H₂O. Results show that the reaction rate and the hydrogen yield are enhanced with the increase of the temperature or by adding Na₂CO₃. The reaction rate is decreased by adding NaCl, but which has less effect on the hydrogen yield. For the mixture additive, Na₂CO₃ plays a key role in improving the hydrogen yield and the reaction rate. The influence degree of different factors is analyzed by orthogonal method. The most obvious factor is additive, but additive concentration has a minimum influence. The solid products are collected and analyzed by X‐ray diffraction and transmission electron microscopy. Al, Al(OH)₃ and AlO(OH) are detected. The spherical particles are obviously found at the initial reaction stage. However, they change to flocs at the end of reaction. Kinetic analysis shows that the reaction mechanism of Al–H₂O is changed by adding Na₂CO₃ or mixture, but it is not affected by adding NaCl. Moreover, the apparent activation energy of Al–H₂O is 74.49 kJ mol^?1, while it is only 43.03 kJ mol^?1 for Al–H₂O with 5 wt% Na₂CO₃ addition. Copyright © 2017 John Wiley & Sons, Ltd.     

CO2 chemical conversion to useful products: An engineering insight to the latest advances toward sustainability

In the fossil‐fuel‐based economies, current remedies for the CO₂ reduction from large‐scale energy consumers (e.g. power stations and cement works) mainly rely on carbon capture and storage, having three proposed generic solutions: post‐combustion capture, pre‐combustion capture, and oxy fuel combustion. All the aforementioned approaches are based on various physical and chemical phenomena including absorption, adsorption, and cryogenic capture of CO₂. The purified carbon dioxide is sent for the physical storage options afterwards, using the earth as a gigantic reservoir with unknown long‐term environmental impacts as well as possible hazards associated with that. Consequently, the ultimate solution for the CO₂ sequestration is the chemical transformation of this stable molecule to useful products such as fuels (through, for example, Fischer–Tropsch chemistry) or polymers (through successive copolymerization and chain growth). This sustainably reduces carbon emissions, taking full advantage of CO₂‐derived chemical commodities, so‐called carbon capture and conversion. Nevertheless, the surface chemistry of CO₂ reduction is a challenge due to the presence of large energy barriers, requiring noticeable catalysis. This work aims to review the most recent advances in this concept selectively (CO₂ conversion to fuels and CO₂ copolymerization) with chemical engineering approach in terms of both materials and process design. Some of the most promising studies are expanded in detail, concluding with the necessity of subsidizing more research on CO₂ conversion technologies considering the growing global concerns on carbon management. Copyright © 2013 John Wiley & Sons, Ltd.     

CO2 mineral sequestration mechanisms and capacity of saline aquifers of the Upper Silesian Coal Basin (Central Europe) - Modeling and experimental verification

Significant part of CO₂ emissions from industrial sources in Central Europe originates from the territory of the Upper Silesian Coal Basin (USCB). This paper presents a study of the suitability of saline aquifers within the USCB, as potential greenhouse gas repositories.Evaluation of mineral-trapping mechanisms and assessment of storage capacity of the aquifers is based on hydrochemical modeling and experimental tests of rock-water-gas interactions.Two stages of modeling enabled prediction of the immediate changes in the aquifer and insulating rocks impacted by the beginning of CO₂ injection, and the assessment of long-term effects of sequestration. In the analyzed sandstone aquifers the minerals able to trap CO₂ are dawsonite and dolomite, while siderite or calcite are able to degrade. The phases capable of mineral CO₂ trapping in the cap rocks are: dawsonite, dolomite, and siderite. Mineral-trapping capacity, for the sandstone aquifers is relatively low: 1.2 to 1.9 kgCO₂/m³, with the exception of the Upper Silesian Sandstone Series - over 6.6 kgCO₂/m³. The solubility trapping capacity does not exceed 4.07 kgCO₂/m³.     

Carbon capture and storage using alkaline industrial wastes

Carbon capture and storage (CCS) is gaining momentum as a means for combating climate change. It is viewed as an important bridging technology, allowing emission targets to be met during fossil fuel dependence while sufficient renewable energy generation is installed. Mineral carbon sequestration is the only known form of permanent carbon storage and has the potential to capture and store CO₂ in a single step. It is based on the geologic process of natural rock weathering where CO₂ dissolved in rain water reacts with alkaline rocks to form carbonate minerals. While the reactions are thermodynamically favourable, in nature the process occurs over thousands of years. The challenge of mineral carbon sequestration is to accelerate carbonation and exploit the heat of reaction with minimal energy and material losses. Minerals commonly selected for carbonation include calcium and magnesium silicates. These minerals require energy-intensive pre-treatments, such as fine grinding, heat treatment, and chemical activation with strong acids, to provide adequate conversions and reaction kinetics. Industrial waste residues present alternative sources of mineral alkalinity that are more reactive than primary minerals and are readily and cheaply available close to CO₂ sources. In addition, the carbonation of waste residues often improves their environmental stability. This paper provides an overview of the types of industrials wastes that can be used for mineral carbon sequestration and the process routes available.     

Preliminary investigation of a transcritical CO2 heat pump driven by a solar‐powered CO2 Rankine cycle

In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO₂ Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO₂ as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO₂ heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO₂ heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO₂ flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.     

The fate of CO2 hydrate released in the ocean

Disposal of anthropogenic CO₂ in the ocean has been considered as a method to counteract global warming. A desirable method of the ocean disposal is to convert the less dense liquefied CO₂ into denser CO₂ hydrate via a submerged hydrate crystallizer at a depth <500 m. The fate of CO₂ hydrate in the ocean has been investigated. It is shown in this study that hydrate particles released in the ocean are physicochemically unstable; however, hydrate decomposition occurs only as a surface phenomenon. Because CO₂ hydrate is denser than seawater, hydrate particles will sink in the ocean. During the descending process, the hydrate particles dissolve gradually in seawater owing to decomposition occurring continuously at surfaces of hydrate particles. This dissolution fate of CO₂ hydrate in the ocean is significantly different from the previous prediction that the disposed CO₂ hydrate would exist as a long‐lasting entity in the ocean. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermodynamic analysis of sorption‐enhanced water–gas shift reaction using syngases

Sorption‐enhanced water–gas shift (SEWGS) reaction performance using syngas as the feedstock is investigated in this study based on thermodynamic equilibrium analysis. It was found that the capability of CO₂ sorbent in CO₂ removal was independent of the dry syngas composition. Regardless of the dry gas composition, CO₂ sorbent loses its adsorption capability as the reaction temperature increases higher than a temperature limit. This CO₂ adsorption temperature limit was found to depend on the steam to carbon (SC) ratio and reaction pressure. With the decrease in SC and increase in pressure the CO₂ adsorption temperature limit can be raised to a higher value. However, the initial CO₂ content in the syngas composition affects the carbon and CH₄ formations in SEWGS. For syngas with low CO₂ concentration, carbon formation can be completely eliminated and CH₄ formation can be reduced by CO₂ removal. For syngas with high CO₂ concentration, no carbon and CH₄ suppression can be found. It was also found that the temperature at which no carbon and CH₄ formations was increased to a higher value as the initial CO₂ concentration was increased. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental parameters affecting the photocatalytic reduction performance of CO2 to methanol: A review

Photocatalytic conversion of CO₂ into value‐added hydrocarbon fuels and/or useful chemical products, using solar energy, has been the focus of active research, owing to its tremendous potential to provide a green fuel (eg, methanol) and simultaneously mitigate global warming by reducing CO₂ levels in the atmosphere. CO₂ photocatalytic reduction yields various hydrocarbon products. In this paper, we focus on methanol as it is an easily transportable energy‐dense fuel with multifarious applications in the automobile, industrial, and petrochemical sector. The photocatalytic conversion rate of CO₂ to methanol depends on 3 factors: the photocatalyst used, photoreactor design, and experimental parameters (or variables). The last factor—experimental parameters—forms the basis of this review paper. These parameters include the reaction temperature, CO₂ pressure, solvent used, intensity, wavelength, and duration of the incident light, concentration of organic impurities adsorbed on catalytic surface, addition of hole scavengers, type of reductant used, catalyst loading method, catalyst concentration, and the dissolved oxygen concentration. There have been numerous published works aiming to improve the methanol formation rate by optimizing these experimental parameters. In this paper, we consolidate and review these parameters, and investigate how optimizing them can enhance the photocatalytic conversion rate of CO₂ into methanol, thus ushering in the era of a green methanol‐based economy.     

CO2 sequestration in depleted methane hydrate deposits with excess water

The recent increase in atmospheric CO₂ concentration makes it necessary to investigate new ways to reduce CO₂ emissions. Simultaneously, natural gas hydrate mining technology is developing rapidly. The use of depleted methane hydrate (MH) deposits as potential sites for CO₂ storage is relatively safe and economical. This method can alleviate the shortage of hydrate displacement gas with CO₂. The purpose of this study was to investigate CO₂ hydrate formation characteristics during the seepage process—in reservoirs with excess water—and their effect on CO₂ storage. The experimental process can be divided into 5 parts: MH formation, water injection, MH dissociation, CO₂ hydrate formation, and CO₂ hydrate dissociation. Magnetic resonance imaging was employed to monitor the distribution of liquid water, and the effects of different parameters on the formation and dissociation of CO₂ hydrates were analyzed. It was found that a state of initial water saturation can effectively control hydrate saturation in artificial MH reservoirs for hydrate reservoirs with excess gas. In the process of CO₂ flow, initial water saturation was not the main controlling factor for CO₂ hydrate formation. Increasing the flow pressure and reducing the flow rate were beneficial for CO₂ hydrate formation. This study is of great significance for advancing the science of CO₂ geological storage in the form of deep‐sea hydrates.     

A study of safe CO2 storage capacity in saline aquifers: a numerical study

An effective way of reducing greenhouse gas content in the atmosphere is carbon dioxide (CO₂) geo‐sequestration in saline aquifers. The main objective of this study is to develop a 3‐D numerical model to identify the optimum CO₂ storage capacity in saline aquifers by studying the factors affecting it and the possibility of the injected CO₂ back‐migrating into the atmosphere. A 1000m×1000m×184 m saline aquifer, lying 800 m below the ground surface, was therefore considered to develop a model using the COMET 3 reservoir simulator. The effects of injecting CO₂ properties (injection pressure) and the aquifer's properties (depth, temperatures and salinity) on the CO₂ storage capacity were examined first. According to the results of the model, CO₂ storage capacity increases with increasing injection pressure and salinity and decreasing depth and temperature, and 100% variations in injection pressure, depth, temperature and salinity levels cause the CO₂ storage capacity to be changed by 54%, 36%, 18% and 1.8%, respectively. The next stage of the study involved the determination of cap rock failure due to CO₂ injection pressure and the identification of the factors influencing it. A detailed parametric study was conducted, with changes to the depth, temperature and salinity with respect to injection pressure, to detect the effects of these factors on the optimum CO₂ injection pressure. According to the results, optimum CO₂ injection pressure clearly depends on the aquifer depth and the effects of salinity and temperature are negligible. An increment of 0.8 to 1.4 km in aquifer depth causes the optimum injection pressure to be increased from 19.55 to 42 MPa, which is about 10⁵ and 10⁷ higher than the effects of temperature (20 to 110 °C increment) and salinity level (100,000 to 160,000 ppm increment), respectively. The model can be used effectively in field studies to safely enhance CO₂ storage capacity in saline aquifers. Copyright © 2012 John Wiley & Sons, Ltd.     

Cycle improvements to ejector‐expansion transcritical CO2 two‐stage refrigeration cycle

In this paper, a new configuration of ejector‐expansion transcritical CO₂ (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. It was found that, compared with the conventional transcritical CO₂ cycle and ejector‐expansion transcritical CO₂ cycle, the simulation results show that the coefficient of performance and second law efficiency of the new cycle were increased by about 55.5 and 26%, respectively, under the operating conditions that evaporator temperature is 10°C, gas cooler outlet temperature is 40°C and gas cooler pressure is optimum pressure. It is also concluded that the entrainment ratio for the new ejector‐expansion TRCC cycle is on average 35% higher than that of the conventional ejector‐expansion TRCC cycle. The analysis results are of significance to provide theoretical basis for design optimization of the transcritical CO₂ refrigeration cycle with an ejector‐expansion device, internal heat exchanger and intercooler. Copyright © 2007 John Wiley & Sons, Ltd.     

Study on a novel process for CO2 compression and liquefaction integrated with the refrigeration process

In order to transport and store the captured CO₂ from coal‐fired power plants, it is necessary to compress and liquefy CO₂ first. However, the power consumption of conventional process is enormous. In this paper, a novel process for CO₂ compression and liquefaction based on the analysis of the power consumption of traditional method is proposed. The new process integrates the refrigeration process driven by the lower level heat from the coal‐fired power plant. This paper analyzes and compares the energy consumptions of conventional process and new process for CO₂ compression and liquefaction. The research result indicates that, when CO₂ needs to be compressed and liquefied and an abundant low quality heat is available, the new process has obvious superiority in lowering the energy consumption. The new process for CO₂ compression and liquation integrated with the exhaust heat powered refrigeration can greatly reduce the work consumption of CO₂ compression and liquefaction. The refrigeration temperature has great effects both on the coefficient of performance of refrigeration process and work consumption of compressors. The refrigeration temperature can be selected by optimization. Using refrigerator with double stages of evaporation can further reduce the amount of the extracted steam and lower the total energy consumption for CO₂ compression and liquation. Recovering the cool energy of CO₂ is beneficial to the reduction of the total work consumption. The achievements obtained from this paper will provide a useful reference for CO₂ compression and liquefaction with the lower energy consumption. Copyright © 2012 John Wiley & Sons, Ltd.     

Modeling of CO2 storage as hydrate in vacated natural gas hydrate formation

Holding CO₂ at massive scale in enclathrated solid matter called hydrate can be perceived as one of the most reliable method for CO₂ storage in subsurface geological environment. In this study, a dynamically coupled mass, momentum, and heat transfer mathematical model is developed, which elaborates uneven behavior of CO₂ flowing into porous medium in space and time domain and converting itself into hydrates. The combined numerical model solution methodology by explicit finite difference iteration method is provided and through coupling the mass, momentum, and heat conservation relations, an integrated model can be presented to investigate the CO₂ hydrate growth within P-T equilibrium conditions. The article results illustrate that pressure distribution in hydrate formation becomes stable at initial phase of hydrate nucleation process, but formation temperature is unable to maintain its stability and varies during CO₂ injection and hydrate nucleation process. The hydrate growth rate increases by increasing injection pressure from 15 MPa to 16 and 17 MPa in 500-m-long formation, and it also expands overall hydrate-covered length from 200 m to 280 m and 320 m, respectively, in 1 month of hydrate growth period. Injection pressure conditions and hydrate growth rate affect other parameters like CO₂ velocity, CO₂ permeability, CO₂ density, and CO₂ and H₂O saturation. In order to enhance hydrate growth rate and expand hydrate-covered length, injection temperature is reduced from 282 K to 280 K, but it did not give satisfactory outcomes. In addition, hydrate growth termination and restoration effect is also witnessed due to temperature variations.     

CO2 valorisation based on Fe3O4/FeO thermochemical redox reactions using concentrated solar energy

The solar‐driven dissociation of CO₂ by thermochemical looping via Fe₃O₄/FeO redox reactions is considered. The process recycles and upgrades CO₂ to ultimately produce chemical synthetic fuels from high‐temperature solar heat and abundant feedstock as only inputs. The two‐step process encompasses the endothermic reduction of Fe₃O₄ to FeO and O₂ using concentrated solar energy as the high‐temperature source for reaction enthalpy and the nonsolar exothermic oxidation of FeO with CO₂ to generate CO. The resulting Fe₃O₄ is then recycled to the first step and carbon monoxide can be further processed to syngas and serve as the building block to synthesise various synfuels by catalytic processes. This study examines the thermodynamics and kinetics of the pertinent reactions. The high‐temperature thermal reduction of Fe₃O₄ is realised above the oxide melting point by using concentrated solar thermal power. The reactivity of the synthesised FeO‐rich material with CO₂ at moderate temperature is then investigated by thermogravimetry. FeO conversion higher than 90% can be achieved with reaction rates depending on temperature, particle size and CO₂ concentration. The solar‐produced nonstoichiometric FeO is more reactive with CO₂ than commercial pure FeO. Activation energies of 57 and 68 kJ/mol are derived from a kinetic analysis of the CO₂‐splitting reaction in the range of 600 °C to 800 °C with solar and commercial FeO, respectively. Copyright © 2012 John Wiley & Sons, Ltd.