CO2 Capture Research Articles

Reactive carbon capture using electrochemical reactors.

The electrolytic upgrading of CO2 presents a promising strategy to mitigate global CO2 emissions while generating valuable carbon-based products such as carbon monoxide, formate, and ethylene. However, the adoption of industrial-scale CO2 electrolyzers is hindered by the high energy and capital costs associated with the purification and pressurization of captured CO2 prior to electrolysis. One promising solution is "reactive carbon capture," which involves the electrolytic conversion of the eluent from CO2 capture units, or the "reactive carbon solution," directly into valuable products. This approach circumvents the energy-intensive processes required for electrolyzers fed with gaseous CO2. This Tutorial Review highlights recent advances for reactive carbon capture, showcasing its potential as a scalable solution for electrolyzers that upgrade CO2 into fuels and products.

Advancements and Challenges in Adsorption-Based Carbon Capture Technology: From Fundamentals to Deployment.

Carbon dioxide (CO2) adsorption on solid sorbents represents a promising technology for separating carbon from different sources and mitigating anthropogenic emissions. The complete integration of carbon capture technologies in various industrial sectors will be crucial for a sustainable, low-carbon future. Despite developing new sorbents, a comprehensive strategy is essential to realize the full potential and widespread adoption of CO2 capture technologies, including different engineering aspects. This study discusses the pathway for deploying adsorption-based carbon capture technology in fundamental material science aspects, thermo-physical properties behavior at the molecular level, and industrial pilot scale demonstrations. When integrated with process simulation and economic evaluations, these techniques are instrumental in enhancing the efficiency and cost-effectiveness of the capturing processes. While advancements in adsorption-based carbon capture technologies have been notable, their deployment still encounters significant hurdles, including technical, economic, and environmental challenges. Leveraging hybrid systems, renewable energy integration, and the strategic application of emerging machine learning techniques appear promising to address global warming effectively and will consequently be discussed in this investigation.

Tailoring Borate Mediator Species Enables Industrial COProduction with Improved Overall Energy Efficiency by Sustainable Molten Salt CO2 Electrolysis.

The electrochemical conversion of CO2 into CO represents a promising strategy for mitigating excessive global greenhouse gas emissions. Nevertheless, achieving industrial-scale electrochemical CO2-to-CO conversion with enhanced selectivity and reduced energy consumption presents significant challenges. In this study, a borate-enhanced molten salt process for CO2 capture and electrochemical transformation is employed, achieving over 98% selectivity for CO and over 55% energy efficiency without the necessity for complex and costly electrocatalysts. Cathodic CO2 electro-reduction (CO2ER) with the anodic oxygen evolution reaction (OER) at an overall current density of 500mAcm-2 using non-nanostructured transition-metal plate electrodes at 650°C is coupled. By regulating the electrolyte's oxo-basicity with earth-abundant borax (Na2B4O7), a borate-enhanced electrolyte is established that accelerates the overall electrochemical reaction efficiently. This system involved a series of well-designed target borate species (BO3 3-, BO2 -, and B4O7 2-) that acted as mediators shuttling between the cathode and anode, favoring CO as the primary cathodic product. Manipulating the atmosphere above the anode facilitated a spontaneous transformation of borates, further enhancing OER performance with long-term operational stability over a cumulative period of 50h, while also reducing overall energy consumption. This work presents a cost-effective strategy for the industrial-scale production of CO derived from CO2, contributing to a lower carbon footprint by establishing a sustainable borate-mediated closed loop.

Improving CO2 desorption performance in monoethanolamine solutions by adding titanium pyrophosphate catalyst

Catalytic CO2 desorption has emerged as a crucial strategy for enhancing the efficiency of CO2 capture and reducing energy requirements, thereby advancing chemical absorption methods. This study examines the catalytic effectiveness of titanium pyrophosphate (TiP2O7) in improving monoethanolamine (MEA)-based CO2 absorption and desorption processes, comparing its performance with other titanium-based catalysts, including titanium dioxide (TiO2), titanium tetrahydroxide (TiO(OH)2), and titanium carbide (TiC). In TiP2O7, Ti ions function as Lewis acid sites by accepting electron pairs (LASs), P2O74− anions act as proton carriers, facilitating rapid proton transfer as Lewis base sites (LBSs), and active hydroxyl groups on the surface, resulting from water molecule dissociation or the deprotonation reaction, function as Brönsted acid sites (BASs). These sites work synergistically to accelerate CO2 desorption. TiP2O7 outperforms the other catalysts tested, primarily due to its optimal Brönsted/Lewis (B/L) ratio. This characteristic is particularly advantageous for regenerating RNHCOO−, as the reaction predominantly follows a hydrogen transfer pathway facilitated by the BASs. Consequently, TiP2O7 enhances the CO2 desorption rate by 41.5% at a desorption temperature of 91 °C, while simultaneously reducing the relative heat duty by 13% compared to processes without catalysts.

Advanced systems for enhanced CO2 electroreduction.

Carbon dioxide (CO2) electroreduction has extraordinary significance in curbing CO2 emissions while simultaneously producing value-added chemicals with economic and environmental benefits. In recent years, breakthroughs in designing catalysts, optimizing intrinsic activity, developing reactors, and elucidating reaction mechanisms have continuously driven the advancement of CO2 electroreduction. However, the industrialization of CO2 electroreduction remains a challenging task, with high energy consumption, high costs, limited reaction products, and restricted application scenarios being the issues that urgently need to be addressed. To accelerate the progress of CO2 electroreduction towards practical application, this review shifts the research focus from catalysts to aspects such as reactions and systems, aiming to improve reaction efficiency, reduce technical costs, expand the range of products, and enhance selectivity, offering readers a new perspective. In particular, innovative and specific design strategies such as CO2 reduction coupled with alternative oxidation, co-reduction reaction of CO2 and C/N/O/S-containing species, cascade systems, and integrated CO2 capture and reduction systems are discussed in detail. Additionally, personal views on the opportunities and future challenges of the aforementioned innovative strategies are provided, offering new insights for the future research and development of CO2 electroreduction.

Polarization-Induced Internal Electric Field-Dominated S-Scheme KNbO3-CuO Heterojunction for Photoreduction of CO2 with High CH4 Selectivity.

The polarization-induced internal electric field (IEF) in ferroelectric materials could promote photogenerated charge transfer across the heterojunction interface, but the effect of polarization-induced IEF on the mechanism of photogenerated charge transfer is ambiguous. In this study, a KNbO3-CuO heterojunction was synthesized by depositing copper oxide (CuO) onto KNbO3. Incorporating CuO broadens the light absorption of KNbO3, thereby enhancing the dissociation of the photogenerated charges. The results show that the polarization-induced IEF in KNbO3 determines that the charge transport mechanism in the KNbO3-CuO heterojunction follows the S-scheme. Owing to the S-scheme heterojunctions and efficient CO2 capture and activation by CuO, the CH4 production rate of KNbO3-CuO increased by nearly 26 times compared to KNbO3. Additionally, the CH4 selectivity of KNbO3-CuO could reach up to 97.80%. This research offers valuable insights into enhancing the photogenerated charge separation and constructing heterojunctions.

Mathematical Modelling for Fixed-Bed Column and Batch Adsorption Studies of Antibiotic and CO2 Capture Using Soybean Stover Biochar

Mathematical Modelling for Fixed-Bed Column and Batch Adsorption Studies of Antibiotic and CO2 Capture Using Soybean Stover Biochar

Synergized Effects of Amino Acids and NaCl to Enhance Silicate Mineral Dissolution in Aqueous Environments for Efficient Atmospheric CO2 Removal.

Enhanced weathering of silicate minerals is a promising approach for reducing atmospheric CO2 levels by increasing the aquatic pH and facilitating CO2 dissolution. However, the slow and unsustainable dissolution of silicate minerals in natural environments remains a challenge. This study proposed a new CO2 capture system that uses the combined effect of amino acids and NaCl to promote mineral dissolution, and its characteristics were investigated experimentally. The results showed that amino acids are promising for enhancing the near-congruent dissolution of silicate minerals, specifically at weakly alkaline pHs (i.e., 8), implying the long-term effectiveness of the system. Comprehensive findings revealed a 13-fold increase in the level of Ca extraction from wollastonite (CaSiO3) in the presence of 0.1 mol/L glutamic acid (Glu) over 72 h at 35 °C and a 22-fold increase in the level of CO2 capture efficiency. However, Fe-bearing minerals, such as olivine ((Mg,Fe)2SiO4), are unsuitable for application, because the enhanced Fe extraction results in the generation of Fe hydroxide, which lowers pH and consequently reduces CO2 capture efficiency. Moreover, NaCl facilitates the release of the Ca-Glu complex from mineral surfaces into the solution, synergizing amino acids to promote mineral dissolution. A semiclosed application system is proposed, with future studies needed to assess ecological impacts and ensure long-term sustainability.

Molecular Simulation of Adsorption of CO2 from a Combustion Exhaust Mixture of Zeolites with Different Topological Structures

In this work, a molecular simulation method was used to study the adsorption of seven combustion products (CO2, H2O, SO2, N2, O2, NO and NO2) on three zeolites with different topological structures (4A, MIF and MOR). Adsorption isotherms of pure components and mixtures at a wide range of temperatures (253–333 K) were calculated using the Monte Carlo method, obtaining equilibrium parameters including the adsorption capacity, adsorption heat and energy distribution. The calculation results indicated that 4A zeolite with more micropores has a stronger adsorption performance for CO2. The presence of water significantly reduced the CO2 capture efficiency of the three zeolites, and the CO2 adsorption amount decreased by more than 80%. Adsorption kinetics was studied using the molecular dynamic (MD) method, MFI and MOR, with channel-type pore structures exhibiting stronger gas diffusion performance, though their separation efficiency was not high. A 4A zeolite has the potential for kinetic separation of CO2.

Biobased ionic liquid solutions for an efficient post-combustion CO2 capture system

This study explores the use of ionic liquids (ILs) as a novel and efficient alternative to conventional monoethanolamine (MEA) for CO2 capture. While MEA scrubbing is well-known for carbon sequestration, it faces limitations such as high energy consumption, toxicity, and rapid degradation. In contrast, ILs offer advantages such as non-volatility, stability, and reduced corrosiveness. We focus on a biodegradable IL comprising choline ([Cho]) and proline ([Pro]) amino acids to create an eco-friendly solution. Dimethyl sulfoxide (DMSO) is introduced as a diluent to mitigate viscosity issues during CO2 uptake. Our research measures the thermo-physical properties, including density and viscosity of [Cho][Pro] in DMSO at different concentrations. The addition of DMSO resulted in a viscosity reduction of >97 % at a temperature of 303 K for the three virgin solutions compared to the pure IL. In addition, the CO2 capture performance was evaluated using a system of absorption and desorption reactors. The results show that the 25 % wt [Cho][Pro] solution excels, achieving over 90 % CO2 absorption, 0.66 molCO2/molIL in the first cycle, and demonstrating high reusability and regeneration efficiency over multiple cycles. Comparisons indicate that the IL solution outperforms traditional aqueous MEA solutions. Longer term testing confirms the solution's stability and minimal degradation, achieving a regeneration efficiency of >55 % over 30 cycles, suggesting the potential of [Cho][Pro] for sustainable long-term CO2 capture applications.

Enhancing CO2 capture in cement-based materials with alkanolamines: A comprehensive study on efficiency, phase-specific impact, and carbonation mechanisms

The escalating issue of global warming, driven by the surge in CO2 emissions, necessitates innovative strategies for reducing CO2 emissions. A novel approach is explored in this study, where amines featuring a basic N atom with a lone pair are incorporated into cement paste to facilitate CO2 capture from the environment. Unlike conventional applications, the focus is on the collaborative effect of various amines on CO2 capture within diverse calcium-rich phases, encompassing portlandite and Calcium-Silicate-Hydrate (C-S-H). This investigation seeks to discern the most efficient amine and optimal concentration for CO2 capture, particularly within distinct phases of cement paste. Notably, 2-(methylamino) ethanol (MAE) demonstrates superior performance in promoting CO₂ mineralisation and has been selected to further evaluate its ability in cement paste under natural carbonation conditions. Importantly, this research presents an exhaustive analysis of C-S-H carbonation with varying Ca/Si ratios, revealing carbonation mechanisms and consequential microstructural alterations in the presence of amine. Additionally, the presence of amine significantly influences crystal growth and the polymerisation of C-S-H. Furthermore, natural carbonation experiments underscore the efficacy of MAE, showcasing a 2.5-fold increase in calcite formation in the cement paste compared to scenarios without MAE.

Aerosol emissions and mitigation of aqueous AMP/PZ solvent for postcombustion CO2 capture

Aerosol emissions from the CO2-capture process have a significant impact on both solvent depletion and environmental contamination. This work comprehensively investigated the emissions of AMP (2-amino-2-methyl-1propanol)/PZ (piperazine) from a bench-scale platform and a CO2-capture pilot plant. The concentration of nuclei in flue gas is a key factor affecting aerosol emissions, and a high nuclei concentration leads to more serious aerosol emission problems. The amine emissions after the absorber in the three different scenarios (no added nuclei, nuclei added, and pilot plant) were 273, 1051, and 1347 mg/Nm3, respectively. Increasing the lean-solvent temperature promoted aerosol emissions, and increasing the liquid/gas ratio and CO2 loading in the lean solvent suppressed aerosol emissions. In the pilot plant, the effects of four mitigation measures were evaluated, and it was found that dry bed and acid washing had better mitigation effects than did conventional water washing; amine emissions could be reduced to as low as 21 mg/Nm3 PZ and 25 mg/Nm3 AMP. This study provides a reference for the design and optimization of carbon-dioxide-capture systems, which can help to reduce the impact on the environment.

Membrane-cryogenic hybrid CO2 capture—A review

The membrane-cryogenic hybrid process is a promising CO2 capture process, which combines the advantages of membrane and cryogenic, such as high efficiency (up to 98 % CO2 captured) and low energy consumption (specific energy consumption around 1.7 MJ/kg CO2 avoided). Through pretreatment by membranes, CO2 concentration can be increased, which makes it possible to separate CO2 via phase change in the cryogenic unit. This work reviews the current status of the development of membrane-cryogenic hybrid processes. The synergy between membrane and cryogenic separation is summarized to identify the bottleneck of such processes and provide insights for process improvement. It was found that cold temperatures would be beneficial to reduce CO2 activation energy and then improve CO2 selectivity of membranes. To further improve the CO2 separation performance, the potential intensification methods of the membrane-cryogenic hybrid process including cold-membrane synthesis, process optimization via heat integration are discussed and envisioned.

Ether chain-modified Alkanolguanidine for CO2 capture and subsequent conversion

Capturing CO2 and converting it into valuable chemicals has attracted considerable attention in recent years. Herein, a kind of ether chain-modified alkanolguanidines (ECMAs) was designed and synthesized as a dual functional reagent for carbon dioxide capture and conversion. Due to the presence of basic sites and CO2-philic ether chains, these ECMAs demonstrated almost equimolar CO2 capture at room temperature and atmospheric pressure through the synergy of physical and chemical absorption. Even for diluted CO2 (15 % CO2), 0.7 mol CO2 per mole capture reagent can still be achieved, showing their potential application in post-combustion capture. The synthesized ECMAs can also serve as catalyst in the cycloaddition reaction of CO2 with various epoxides, affording 75–99 % yield of corresponding cyclic carbonates under 3 MPa CO2 with tetrabutylammonium iodide (TBAI) as co-catalyst. Moreover, these ECMAs can be applied to the integrated CO2 capture and conversion, in which the ECMAs can react with CO2, forming the alkyl carbonate zwitterion as active CO2 species in the capture step. And in the subsequent cycloaddition reaction with propylene oxide, 52 % yield of propylene carbonate was obtained.

Suppressing cyclic deactivation of magnesium-calcium dual-functional materials via dispersed metal-carbonate interfaces for integrated CO2 capture and conversion

The integrated CO2 capture and utilization employs chemical looping approach for suppressing the equilibrium limitations of traditional gas-solid catalytic reactions, enabling efficient conversion of dilute CO2 into high-value fuels with minimal energy consumption. However, the diminishing cyclic activity of dual-functional materials poses significant challenges to their industrial application. Herein, we tailored a series of magnesium-calcium materials, the influence of coordinated metals on the cyclic performance were quantitatively investigated. Notably, Fe2Ni2Ce2Mg5Ca20CO3 achieves a cumulative CO yield of 121.0 mmol/g over 15 cycles at 650°C, with a maximum CO yield of 8.3 mmol/g per cycle and 99.0% CO selectivity, and its CO2 capture capacity remains stable at 10.6 mmol/g over 37 adsorption/desorption cycles. Experimental results indicate that lattice phase separation is a fundamental mechanism underlying the decline in cyclic activity. The strategic incorporation of transition metal intermediates promotes the formation of dispersed metal-carbonate interfaces, providing surface hydrogenation sites and accelerating the lattice decomposition and reconstruction of CO3* within a dispersed lattice. This modification mitigates the adsorption/catalytic lattice phase separation, boosts metal migration and deoxygenation activity for cyclic nanoparticle construction. The findings offer valuable strategies for designing highly efficient and stable DFMs in CO2 capture and utilization.

Vacuum assisted desorption of sodium zirconate sorbent for enhancing cyclic stability in pre-combustion CO2 capture

Sodium zirconate (Na2ZrO3) is a promising material for pre-combustion CO2 capture due to its fast sorption kinetics and excellent cyclic stability at high temperatures under ideal condition (desorption in 100% N2). Still, there is a lack of study on the performance of Na2ZrO3 cyclic capture under harsh condition (desorption in high concentration CO2). In this study, Na2ZrO3 was prepared by wet-mixing and heated-drying, and the difference in the cyclic CO2 capture performance of the sample was compared between desorption under harsh condition and vacuum condition. The crystal structure of Na2ZrO3 was identified during the sorption-desorption cycles. The crystal structure was also modeled and simulated to analyze the reason for the superior capture performance from the monoclinic Na2ZrO3. It was found that the special interlocked and multilayered stacked structure of the monoclinic Na2ZrO3 allowed for high reactivity with CO2. It was found that high temperature solely had little help in the desorption of Na2ZrO3 under harsh condition, but vacuum condition promoted desorption of Na2ZrO3 in high fraction CO2, and vacuum desorption at 1000 °C-1050 °C resulted in Na2ZrO3 with both good capture performance and cycling stability. Vacuum desorption led to more complete reversion of Na2ZrO3 to the monoclinic state, benefiting for CO2 capture. This study attempted to simulate the harsh capture environments of real industrial applications and to explore the possibility of Na2ZrO3 as a carbon capture material for pre-combustion capture.

Hydrothermal-calcination synthesis of lithium orthosilicate microspheres for high-temperature CO2 capture

In recent years, the Li4SiO4 adsorbent has become a promising candidate for high-temperature CO2 capture. The fabrication of micro-structured Li4SiO4 could enhance the capture performance effectively. However, there exists a conflict between the purity and the morphology of prepared micro-structured Li4SiO4. This study proposed a novel hydrothermal-calcination method, which could produce Li4SiO4 microspheres with great morphology and relatively high purity. The physicochemical properties, CO2 capture performance and forming mechanisms of Li4SiO4 microspheres are evaluated and investigated systematically. It is found that the hydrothermal process could fabricate micro-spherical LiOH@Li2SiO3 precursor, which was further converted to Li4SiO4 microspheres during the subsequent calcination process. The LiOH@Li2SiO3 precursor could not only maintain the microstructure but also reduce the Li4SiO4 generation temperature, thus improving the morphology as well as the purity of obtained Li4SiO4 microspheres. As a result, the adsorbents could reach a CO2 capture capacity of 0.167–0.222 g/g within 30 min's adsorption under 15 vol.% CO2, and their cyclic stability are diverse depending on the used calcination temperatures. The hydrothermal-calcination contributes to the future preparation of high-performance Li4SiO4-based CO2 adsorbents.

Post-combustion CO2 capture retrofit from diesel-powered Arctic mines – Techno-economic and environmental assessment

This study evaluates the economic feasibility and environmental impacts of retrofitting a diesel-based powerhouse in the Canadian Arctic with a post-combustion carbon capture process at an active gold mining site isolated from cheaper or cleaner electrical grids. A techno-economic analysis was conducted to determine the total annualized cost (TAC) of implementing a monoethanolamine (MEA) chemical absorption process to mitigate carbon dioxide emissions. The calculated cost per tonne of CO2 captured of $420 reflects the challenges of operating northern sites reliant on diesel fuel. Electricity generation costs, estimated at 0.44 $/kWh, are found to explain most of the variance in cost per tonne compared to other studies. A profitability model, comparing the additional annual expenditure to the current carbon tax exposure (CTE), suggests that carbon pricing alone is insufficient to incentivize investment in energy-intensive carbon capture technologies such as amine-based absorption processes. The sensitivity analysis, which evaluates profitability relative to variations in key variables, highlights the significant impact of the solvent regeneration heat demand. This major cost driver also contributes substantially to the carbon footprint of 0.55 tonnes emitted per tonne captured, as determined by a complementary life cycle assessment.

Eco-efficiency assessment of carbon capture and hydrogen transition as decarbonisation strategies in alumina production

Studies seeking to thoroughly couple the environmental and economic performances of a process or product are becoming more prominent as the needs for decarbonisation grow. This study explores the use of Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) in the alumina extraction industry. Models for various thermal energy supply methods and CO2 mitigation strategies were developed to obtain an inventory for analysis and the environmental impacts and life-cycle costs of the supply chain were evaluated. Finally, economic and ecological results were integrated using eco-efficiency indices and a sensitivity analysis of the most significant variables detected was conducted. The research indicated that the integration of a calcium-looping plant to capture post-combusted CO2 could reduce 55.5% of the CO2 equivalent emissions, while also obtaining a better economic performance due to the CO2 avoided taxes. However, other environmental indicators had slightly more significant impacts because of the additional use of natural gas. The potential use of green hydrogen instead of natural gas could enable a 70.0% reduction in CO2 equivalent emissions, as well as a reduction in all other environmental indicators studied, except for water consumption. However, transitioning to green hydrogen production could incur higher costs. This study introduced an eco-efficiency ratio index, indicating that CO2 capture and storage proved to be the most eco-efficient scenario, regardless of economic fluctuations in CO2 emission taxes. The substitution of natural gas with green hydrogen also emerged as a viable eco-efficient solution, provided electricity prices remain below 0.045€/kWh.

Deactivated Ca-based sorbent derived from calcium looping CO2 capture as a partial substitute for cement to obtain low-carbon cementitious building materials

Calcium looping CO2 capture is a highly promising technology for carbon capture, utilization, and storage. Nevertheless, the disposal of deactivated calcium-based sorbents following cyclic carbonation and calcination processes presents an unresolved challenge. Concurrently, the development of low-carbon cement products is also a critical priority. Given the calcium-rich composition and carbon-negative nature of the calcium-based sorbent, it is proposed that the deactivated sorbent could be utilized as a partial substitute for cement in the production of building materials. This paper explored the potential of using two types of deactivated calcium sorbent (DPC/DGC) to partial substitute cement for low-carbon cementitious materials production. The effects of partial substitution of cement materials on volume stability, compressive/flexural strength, hydration kinetics, and carbon emission of the composite cementitious materials were investigated. The results indicate that a 5% and 10% replacement of cement with DPC/DGC has modest impact on volumetric stability and compressive strength. The composite cement with 5% DPC replacement achieves a 28-day compressive strength of 48.1MPa, representing a 0.4% increase compared to the 47.9MPa observed in the reference sample. Specimens with 15% DPC/DGC substitution exhibit inferior volume stability and mechanical performance than the control sample. The total hydration heat releases decrease with the increasing substitution ratio due to the dilution effect by the introduction of DPC/DGC. Additionally, substituting cement with Ca-based sorbents significantly reduced the carbon footprint of construction materials. The net carbon footprints for the building materials that containing 1 ton of binder (substitued with 10wt% DPC and DGC) were 152.5kg and 43.5kg, corresponding to reductions of 79.6% and 94.2% compared to reference cement mortar. These carbon footprints are projected to further decrease to -108.5kg and -375.5kg when DPC and DGC were obtained after 100 CO2 capture cycles. A novel technological route combining the high-temperature calcium looping CO2 capture and CO2 mineralization curing was proposed, and the associated challenges of this method were also discussed.