Direct Air Capture Systems Research Articles

System design of a novel open-air brayton cycle integrating direct air capture

The Direct Air Capture (DAC) technology is essential for achieving carbon neutrality, as it enables processes with net-negative CO2 emissions. However, its widespread commercialization faces significant challenges due to high energy requirements. Numerous attempts have been made to address this issue through thermal integration, yet the fundamental challenge of the high cost associated with extracting large volumes of low-concentration CO2 from ambient air remains unresolved. In this study, the integration of Open-Air Brayton Cycle (OABC) as a solution to enhance overall system utilization by simultaneously utilizing large volumes of ambient air is introduced. Various OABC coupled temperature swing adsorption based DAC system layouts are analyzed while considering different regeneration temperatures, and the results revealed the optimal configurations that significantly reduce energy cost per captured unit of CO2 with high purity and recovery. By combining an equilibrium short-cut model for temperature swing adsorption with process simulation methodologies, this research proposes the concept of “energy cost”—a metric that represents the amount of CO2 captured against the energy penalty incurred by integrating DAC with OABC systems. The findings demonstrate that combining DAC and OABC systems could yield high purity and recovery rates of CO2 through strategic thermal management and advanced adsorbent usage, offering a synergistic approach to carbon capture from an energy consumption perspective.

Investigation of microwave-based CO2 regeneration in a packed bed reactor for Direct Air Capture

This study investigates a microwave-assisted Direct Air Capture (DAC) application using Zeolite 13X to capture CO2 from the atmospheric air in Tuscaloosa, Alabama. For the regeneration process, a mono-mode solid state microwave generator with E orientation cavity was applied to desorb CO2 from the sorbent. The main purpose of this study is to explore microwave-based DAC system since there is no detailed parametric study which evaluates all desorption characteristics including temperature and microwave initial power effects on CO2 productivity, regeneration efficiency, desorption kinetics, energy consumption, temperature homogeneity, adsorption, and desorption capacities. In order to investigate all these desorption characteristics, sixteen non-cycling and ten cycling experiments were performed. In non-cycling experiments, regeneration temperature and microwave initial power changed from 45 ℃ to 100 ℃ and from 5 W to 60 W, respectively. The results illustrate that energy consumption to desorb a kg of CO2 can be as low as 60.37 MJ and 23.97 MJ for 100 % and 70 % regeneration, respectively. In cycling experiments, adsorption capacity of each experiment and the effects of 70 % desorption on the adsorption capacity of following experiments were analyzed at the lowest temperature and power conditions (45 ℃ and 5 W). It was found that 70 % desorption does not have significant effects on the adsorption capacity for the following cycles. This study also proves that complete CO2 regeneration can be achieved even at low temperature and initial power values in 3100 seconds.

Corrigendum to “The impact of climate on solvent-based direct air capture systems” [Applied Energy 325 (2022) 119895]

Corrigendum to “The impact of climate on solvent-based direct air capture systems” [Applied Energy 325 (2022) 119895]

Advancing the deployment and information management of direct air capture: A solution enabled by integrating consortium blockchain system

Direct air capture (DAC) is a critical and emerging Negative Emissions Technology (NET) that directly removes CO2 from the atmosphere, significantly contributing to climate change. However, the deployment and management of large-scale DAC faces challenges such as collections and analysis of energy consumption data, intricate device and system management, emission prediction and operation strategy, precise carbon footprint tracking, etc. This paper proposes the integration of blockchain technology with DAC systems to address these challenges, utilizing blockchain's inherent properties of immutability, security, and transparency. The implementation strategy includes the development of a DAC consortium blockchain system, leveraging a consensus mechanism,11Consensus mechanism: The programming and process used in blockchain systems to achieve distributed agreement about the ledger's state or the state of a data set. (Source: Investopedia) ECDSA encryption,22Elliptic Curve Digital Signature Algorithm (ECDSA): In cryptography, the Elliptic Curve Digital Signature Algorithm (ECDSA) offers a variant of the Digital Signature Algorithm (DSA) which uses elliptic-curve cryptography. As with elliptic-curve cryptography in general, the bit size of the private key believed to be needed for ECDSA is about twice the size of the security level, in bits. (Source: Wikipedia) IoT33Internet of things (IoT): describes devices with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other communication networks. (Source: Wikipedia) integration, and digital signatures. Preliminary modeling of the proposed system suggests potential improvements in operational efficiency and a reduction in data inaccuracies. The proposed system underscores the system's ability to streamline identity verification, improve data collection accuracy, and facilitate secure, confidential information sharing among DAC stakeholders. By enhancing the efficiency and reliability of DAC operations, this approach supports the scalable and effective deployment of NETs in the global effort to combat climate change. Future research will focus on empirical validation through pilot projects and simulations to further substantiate these claims.

Module optimization and array design of moisture swing direct air capture based on 2D-3D coupled analysis

Direct Air Capture (DAC) is crucial for offsetting carbon emissions. Moisture Swing Adsorption (MSA), a DAC method switches between adsorption and desorption through humidity adjustment without relying on heat, offering significant energy-saving potential but lacking engineering solutions. Therefore, using a validated 2D-3D coupled model, a moisture swing DAC array was proposed, and multi-dimensional evaluations were used to optimize the system. Unlike the preferred capture rate around 90 % for post-combustion gas, the ultra-low CO2 concentration in the air resulted in a different rate range for DAC. Simulation indicated that although the capture rate of DAC could reach 90 %, the trade-off was energy consumption exceeding 3000 kWh/t CO2 with low adsorbent utilization. Consequently, a detailed evaluation method based on adsorbent utilization, energy consumption and cost analysis optimized the preferred capture rate range to 50–60 %, and the total energy consumption was reduced to 873.55 kWh/t CO2, including 276.33 kWh/t CO2 for capture energy and 597.22 kWh/t CO2 for vacuum-concentration energy. The lowest cost was $209.17/t CO2 at the optimal capture rate of 53.91 %. Afterwards, the Ordos Plateau, as a typical preferred sub-environment with abundant wind resources and dry climate, was choose for DAC system deployment study. Wind field simulation determined the layout of a 10000-ton array occupying only 0.298 km2. Finally, based on savings in capture energy due to prevailing winds, regeneration energy savings from the utilization of low-grade waste heat, and the improved performance of the adsorbent itself, it was found that this DAC unit showed great potential to reduce the energy and capture costs to 564.91 kWh/t CO2 and $140.25/t CO2, and at wind speed exceeding 16.8 m/s, the unit switched to passive adsorption, further reducing energy consumption to 408.89 kWh/t CO2, with the minimum fix investment estimated at 21.71 million USD.

Modeling and control of heating and heat circulation in direct air capture system

Direct air capture (DAC) is a critical technology for mitigating climate change. However, the high heat consumption of temperature vacuum swing adsorption (TVSA)-based DAC processes hinders its widespread deployment. This study focuses on developing a control strategy to optimize the energy efficiency of the TVSA heating phase. A novel adsorbent temperature estimation method, validated through experimental data, was integrated into a cascaded PI controller with a fuzzy gain scheduler (FGS). Experimental results demonstrate that the proposed control strategy effectively regulates the heating process, achieving a potential energy saving of up to 14%. This work contributes to enhancing the feasibility and sustainability of DAC technologies.

Solid amine adsorbent with surfactant modification for Direct Air Capture (DAC) under different temperature and humidity conditions

Direct air capture (DAC) technologies have been vigorously pursued to achieve the goal of net-zero CO2 emissions due to the dramatic increase in atmosphere CO2 concentrations and global temperatures. In practical DAC conditions, variations in temperature and humidity can lead to different CO2 adsorption outcomes. Current studies lack comprehensive information on the optimal temperature and humidity conditions for DAC. In this study, a comparison between PMSU-F (impregnating polyethyleneimine (PEI600) on MSU-F support) and PPMSU-F (co-impregnating polyethylene glycol (PEG200) with PEI600 on MSU-F support) under different temperature and relative humidity conditions were conducted. Under dry conditions, the addition of PEG200 effectively enhanced the adsorption capacity, adsorption rate, and amine efficiency and decreased the energy consumption for desorption depending on the comparison of the two absorbents. Under the popular atmospheric temperature ranges (−5 °C–45 °C), an increase in temperature favors CO2 adsorption. Under humid conditions, the presence of PEG200 had a negative effect due to its strong hydrophilicity. By comparing dry and humid conditions, the introduction of moisture generally enhanced overall CO2 adsorption performance, and the adsorption capacity interestingly further increased under low-temperature conditions. The highest CO2 adsorbing capacity of PMSU-F (3.82 mmol/g) and PPMSU-F (3.76 mmol/g) appeared at −5 °C and 75% relative humidity, indicating that low temperature and relatively high relative humidity were more favorable for DAC, which is possibly attributed to the thermodynamic control under low temperatures with moisture. The results indicate that the adsorbents chosen in this study are promising for DAC under low temperatures and relatively high humidity conditions. The performances of modified DAC adsorbents, e.g., adsorption capacity, stability, antioxidant property for industrial-grade DAC system should be evaluated in the next work.

Optimizing Air Contactor Design for Efficient Carbon Capture in Direct Air Capture Systems: A Multi-Disciplinary Approach

As carbon dioxide (CO2) emissions continue to rise, direct air capture (DAC) has emerged as an important technology for removing CO2 from ambient air to combat climate change. The air contactor design is a critical factor impacting DAC system performance and costs. This research describes a strategy for improving the design of a single air contactor unit to increase CO2 capture flux while minimizing costs using optimization techniques grounded in experimental data .The research focuses on a 100 m2 slab air contactor modeled utilizing cooling tower and scrubber principles. The system includes the chemical, mechanical, and structural engineering disciplines. The mass transfer coefficient, air velocity, packing depth, and capital cost per frontal area are four major design characteristics that were maximized.The model integrated requirements for low air velocity, pressure drop, and energy consumption, as well as adequate gas-liquid interaction via structured packing selection and depth.The design space was explored using a multi-objective optimization strategy based on gradient-based and heuristic methods. Initial sampling via a design of experiments methodology demonstrated response surface trends in the objective function across the design space. The response surfaces mapped the optimization objective as a function of the design variables. Using gradient information, sequential quadratic programming efficiently located an optimal design vector that met all constraints on the design variables and feasibility requirements. The constraints included bounds on mass transfer coefficient, air velocity, packing depth, and capital cost per frontal area. The optimized air contactor design achieved a CO2 capture flux of 10,440 kg/m2-yr at a cost of $ 0.068 per kg CO2 captured. The developed optimization framework maximizes contactor performance while decreasing operational costs. A multi-objective genetic algorithm approach was used to identify the trade-offs between the two competing objectives of maximized CO2 capture and minimized cost by expanding the formulation. The Pareto-optimal front of the optimization results offered numerous optimized solutions with specific DAC system setups. This methodology, as well as the optimum configurations identified, serve as the foundation for constructing larger-scale DAC systems, in future. Ongoing research aims to improve solution approaches by including advanced optimization software packages such as DAKOTA, which offers global optimization algorithms, as well as to boost model accuracy via integrating additional choice variables. Future optimization and modeling studies will include contactor interactions and the modeling of a full DAC facility to boost confidence that a globally optimal design has been established.Overall, this study illustrated an efficient optimization strategy for air contactor design and contributes to the improvement of sustainable carbon capture technology, which is crucial to controlling rising global CO2 levels. Contactor configuration optimization enables superior DAC system designs at lower costs, hence promoting the urgent deployment of negative emissions solutions.

Carbonate Electrolysis for Energy Efficient Direct Air Capture of CO2

Yearly global energy related CO2 emissions continue to increase, reaching a record breaking 37 billion metric tons in 2022. As a major greenhouse gas, CO2 levels need to be reduced by 10s of gigatons to prevent the worst of climate change, something that is no longer feasible with net-zero emissions alone. Removing atmospheric CO2 is therefore of critical importance for the future of our planet. While major improvements have been made in CO2 capture from large point sources, a significant portion of CO2 emitted each year from the United States comes from distributed sources such as cars and smaller factories. Due to the dilute concentrations of CO2 in ambient air, Direct Air Capture (DAC) needs to be highly selective to preferentially absorb CO2 to collect useable amounts. These challenges have made current DAC systems quite costly, both energetically and economically, and require vastly different strategies than carbon capture from concentrated sources.At Giner, we are developing a novel process for the capture and regeneration of CO2 from air into a purified, concentrated CO2 stream that can be redirected as a feedstock for a wide range of applications, including chemical manufacturing and syngas formation. This process involves the capture of CO2 in a concentrated KOH solution using a high-surface area air contactor to form potassium carbonate. The potassium carbonate is then efficiently electrolyzed in a hydrogen-assisted process to regenerate the CO2 at a low operating potential, increasing the electrical efficiency of the process while producing concentrated and purified CO2. In addition, water, hydrogen, and KOH are also regenerated as byproducts that can be recycled back into the CO2 capture and electrolysis processes, reducing both overall energy and chemical consumption.Giner has developed a unique 3-compartment carbonate electrolysis flow cell. Using our electrolyzer, we have seen operating voltage as low as 1.2 V at 100 mA/cm2 in a 5 cm2 cell for potassium carbonate conversion to CO2 with H2 assisted electrolysis. Significant improvements in operating voltage have come from optimization of gas-diffusion layers (GDLs), cell geometry, and membrane selection. Furthermore, we have achieved >97% pure CO2 formation in the internal flow-through compartment. Currently, scale-up is in progress to apply these developments to approach comparable conditions in a 50 cm2 multi-cell stack. Further developments will enable pairing with an in-house, carbonate based, air contactor allowing for capture and regeneration of over 1 ton CO2 per year. Acknowledgement: The project is financially supported by the Department of Energy's ARPA-E Office under the Grant DE-AR0001495

A digital-twin for rapid simulation of modular Direct Air Capture systems

There has been tremendous recent interest in Direct Air Capture (DAC) systems. A key part of any DAC system are the multiple air intake units. In particular, the arrangement of such units for optimal capture and sequestration is critical. Accordingly, this work develops an easy to use model for a modular unit system, where an approximate flow field is computed for each unit and the aggregate flow field is developed by summing the fields from each unit. This allows for a modular framework that can be used for rapid simulation and design of an overall DAC system. The rapid rate at which these simulations can be completed enables the ability to explore inverse problems seeking to determine which parameter combinations can deliver the maximum sequestration of tracer plume particles for the minimum amount of energy input. In order to cast the objective mathematically, we set up an inverse as a Machine Learning Algorithm (MLA); specifically a Genetic MLA (G-MLA) variant, which is well-suited for nonconvex optimization. Numerical examples are provided to illustrate the framework.

Strategic Siting of Direct Air Capture Facilities in the United States

Direct air capture (DAC) systems that capture carbon dioxide (CO2) directly from the atmosphere are garnering considerable attention for their potential role as negative emission technologies in achieving net-zero CO2 emission goals. Common DAC technologies are based either on liquid–solvent (L-DAC) or solid–sorbent (S-DAC) to capture CO2. A comprehensive multi-factor comparative economic analysis of the deployment of L-DAC and S-DAC facilities across various United States (U.S.) cities is presented in this paper. The analysis considers the influence of various factors on the favorability of DAC deployment, including local climatic conditions such as temperature, humidity, and CO2 concentrations; the availability of energy sources to power the DAC system; and costs for the transport and storage of the captured CO2 along with the consideration of the regional market and policy drivers. The deployment analysis in over 70 continental U.S. cities shows that L-DAC and S-DAC complement each other spatially, as their performance and operational costs vary in different climates. L-DAC is more suited to the hot, humid Southeast, while S-DAC is preferrable in the colder, drier Rocky Mountain region. Strategic deployment based on regional conditions and economics is essential for promoting the commercial adoptability of DAC, which is a critical technology to meet the CO2 reduction targets.

Prospective environmental burdens and benefits of fast-swing direct air carbon capture and storage

Direct air capture (DAC) in combination with storage of CO2 can lower atmospheric CO2 concentrations. This study investigates the environmental impact of a new fast-swing solid sorbent DAC system, including CO2 transport and storage, over its life cycle, using prospective life cycle assessment. This DAC technology is currently on technology readiness level 5 and is expected to operate on an industrial scale by 2030. The technology was upscaled to the industrial scale and future changes in the background over the lifetime of the system were included, such as electricity grid mix decarbonization. Environmental trade-offs for the new DAC system were assessed by comparing environmental benefits from CO2 sequestration with environmental burdens from production, operation and decommissioning. We considered three electricity generation configurations: grid-connected, wind-connected, and a hybrid configuration. We found net environmental benefits for all configurations and background scenarios for ecosystem damage and climate change. Net human health benefits were observed when the electricity grid decarbonizes quickly and without the use of a battery. The environmental benefits increase with decreasing electricity footprint and are comparable with other DAC technologies. This illustrates that the new DAC system can help to meet the climate goals.

On Comparing Packed Beds and Monoliths for CO2 Capture from Air Through Experiments, Theory, and Modeling.

This study compares the performance of amine-functionalized γ-alumina sorbents in the form of 3 mm γ-alumina pellets and of a γ-alumina wash-coated monolith for CO2 capture for direct air capture (DAC). Breakthrough experiments were conducted on the two contactors to analyze the adsorption kinetics and performance for different gas feeds. A constant pattern analysis revealed dominant mass transfer resistances in the gas film and in the pores, with axial dispersion also observed, particularly at higher concentrations. A 1D, physical model was used to fit the experiments and thus to estimate mass transfer and axial dispersion coefficients, which appear to be consistent with the hypotheses derived from constant pattern analysis. A dual kinetic model to describe mass transfer was found to better describe the tail behavior in the monolith, whereas a pseudo-first-order model was sufficient to describe breakthroughs on packed beds. A substantial two-order magnitude decrease in mass transfer coefficients was noted when reducing the feed concentration from 5.6% to 400 ppm CO2, thus underscoring the significant mass transfer limitations observed in DAC. Comparison between the contactors revealed notably higher mass transfer coefficients in the monolith compared to the packed beds, which are attributed to shorter diffusion lengths and lower equilibrium capacity. While the faster mass transfer coefficients observed in the monolith experiments led to reduced specific energy consumption and increased adsorption productivity compared to the packed bed at 400 ppm, no significant improvement was observed for the same process at the higher concentration of 5.6% CO2 in the feed. This finding highlights the need to tailor the contactor design to the specific gas separation requirements. This research contributes to the understanding and quantification of mass transfer kinetics at DAC concentrations in both packed bed and monolith contactors. It demonstrates the crucial role of the contactor in DAC systems and the importance of optimizing the adsorption step to enhance productivity and DAC performance.

3D printing of poly(ethyleneimine)-functionalized Mg-Al mixed metal oxide monoliths for direct air capture of CO2

Direct air capture (DAC) of CO2 plays an indispensable role in achieving carbon-neutral goals as one of the key negative emission technologies. Since large air flows are required to capture the ultradilute CO2 from the air, lab-synthesized adsorbents in powder form may cause unacceptable gas pressure drops and poor heat and mass transfer efficiencies. A structured adsorbent is essential for the implementation of gas-solid contactors for cost- and energy-efficient DAC systems. In this study, efficient adsorbent poly(ethyleneimine) (PEI)-functionalized Mg-Al-CO3 layered double hydroxide (LDH)-derived mixed metal oxides (MMOs) are three-dimensional (3D) printed into monoliths for the first time with more than 90% adsorbent loadings. The printing process has been optimized by initially printing the LDH powder into monoliths followed by calcination into MMO monoliths. This structure exhibits a 32.7% higher specific surface area and a 46.1% higher pore volume, as compared to the direct printing of the MMO powder into a monolith. After impregnation of PEI, the monolith demonstrates a large adsorption capacity (1.82 mmol/g) and fast kinetics (0.7 mmol/g/h) using a CO2 feed gas at 400 ppm at 25 °C, one of the highest values among the shaped DAC adsorbents. Smearing of the amino-polymers during the post-printing process affects the diffusion of CO2, resulting in slower adsorption kinetics of pre-impregnation monoliths compared to post-impregnation monoliths. The optimal PEI/MeOH ratio for the post-impregnation solution prevents pores clogging that would affect both adsorption capacity and kinetics.

The performance of solvent-based direct air capture across geospatial and temporal climate regimes

IntroductionLiquid-solvent direct air capture (DAC) is a prominent approach for carbon dioxide removal but knowing where to site these systems is challenging because it requires considering a multitude of interrelated geospatial factors. Two of the most pressing factors are: (1) how should DAC be powered to provide the greatest net removal of CO2 and (2) how does weather impact its performance?.MethodsTo investigate these questions, this study develops a process-level model of a liquid-solvent DAC system and couples it to a 20-year dataset of temperature and humidity conditions at a ~9km resolution across the contiguous US.Results and discussionWe find that the amount of CO2 sequestered could be 30% to 50% greater than the amount of CO2 removed from the atmosphere if natural gas is burned on site to power DAC, but that the optimal way to power DAC is independent of capture rate (i.e., weather), depending solely on the upstream GHG intensity of electricity and natural gas. Regardless of how it is powered, air temperature and humidity conditions can change the performance of DAC by up to ~3x and can also vary substantially across weather years. Across the continuous US, we find that southern states (e.g., Gulf Coast) are preferrable locations for a variety of reasons, including higher and less variable air temperature and relative humidity. Lastly, we also find the performance of liquid-solvent DAC calculated with monthly means is within 2% of the estimated performance calculated with hourly data for more than a third of the country, including in the states with weather most favorable for liquid-solvent DAC.

Scaling considerations and optimal control for an offshore wind powered direct air capture system

The optimal design and operation of an offshore wind powered direct air capture (DAC) system is complex owing to the intermittent energy supply and the modularity of the units. A solid amine DAC process involves multiple individual units which undergo periodic loading to capture carbon dioxide (CO2) from ambient air, followed by regeneration to produce pure CO2 for utilisation or sequestration. The modular nature of a solid DAC process is exploited in this study to investigate the optimal design and coordinated operation of multiple DAC units mounted on a single 15 MW offshore wind turbine platform, with battery energy storage for additional short term power buffering. Important design parameters considered include the number of independently controllable units, the cyclic capacity of each unit (proportional to the amount of adsorbent) and the battery capacity and maximum power ratings. The design study results highlighted the diminishing returns to the CO2 capture rate with scaling, with a full design optimisation based upon cost estimations left for future work as the technology matures. It was found the optimal configuration was 14 DAC units, each with a cyclic capacity of 2000 kg CO2 , giving a total annual capture rate of 45 600 ton yr−1 and a wind utilisation factor of 96.6%. Furthermore, it was found that a rules-based control strategy based on high and low loading limits was competitive with a machine learning based controller and outperformed a model predictive control scheme.

Towards Energy-Efficient Direct Air Capture with Photochemically-Driven CO2 Release and Solvent Regeneration.

The intensive energy demands associated with solvent regeneration and CO2 release in current direct air capture (DAC) technologies makes their deployment at the massive scales (GtCO2/year) required to positively impact the climate economically unfeasible. This challenge underscores the critical need to develop new DAC processes with significantly reduced energy costs. Recently, we developed a new approach to photochemically drive efficient release of CO2 through an intermolecular proton transfer reaction by exploiting the unique properties of an indazole metastable-state photoacid (mPAH), opening a new avenue towards energy efficient on-demand CO2 release and solvent regeneration using abundant solar energy instead of heat. In this Concept Article, we will describe the principle of our photochemically-driven CO2 release approach for solvent-based DAC systems, discuss the essential prerequisites and conditions to realize this cyclable CO2 release chemistry under ambient conditions. We outline the key findings of our approach, discuss the latest developments from other research laboratories, detail approaches used to monitor DAC systems in situ, and highlight experimental procedures for validating its feasibility. We conclude with a summary and outlook into the immediate challenges that must be addressed in order to fully exploit this novel photochemically-driven approach to DAC solvent regeneration.

Water management and heat integration in direct air capture systems

Water management and heat integration in direct air capture systems

Evaluation of potassium glycinate as a green solvent for direct air capture and modelling its performance in hollow fiber membrane contactors

Current direct air capture (DAC) technology is largely cost-prohibitive for large scale implementation due to the excessive energy required to operate a combined absorption–desorption cycle. As the desorption process consumes much of the supplied energy, there is a demand to find more sustainable sorbent materials that maintain high absorptive capacities yet can be regenerated at lower working temperatures. This work evaluates potassium glycinate (GlyK) as one such alternative absorbent. Through conducting vapor–liquid equilibria and wetted wall column kinetic studies, GlyK is found to have comparable working capacities and liquid mass transfer coefficients to those reported for the industrial standard, monoethanolamine (MEA), yet outperforms it with regards to its distinctly low regeneration temperature. To further understand how GlyK would perform in an industrial scale DAC system, an Aspen Custom Modeler® (ACM) model is developed that integrates the experimentally obtained equilibria and kinetic data with the performance characteristics of a gas-solvent hollow fiber membrane contactor (HFMC). Full-scale simulations show that via implementing a 20°–90 °C absorption–desorption cycle, GlyK can capture up to 83 % of the CO2 in atmospheric air and be 55 % regenerated within a single membrane contactor pass. As these low working temperatures vastly outperform the conventional ∼ 40°–140 °C temperature swing currently implemented in industrial CO2 processing, GlyK is concluded to be a viable and sustainable option for use within energy-efficient DAC technology whereby renewable heat sources can be used.

Photo-thermal CO2 desorption from amine-modified silica / carbon aerogel for direct air capture

Direct air capture (DAC) is a promising approach for combating global warming, but its energy-intensive CO2 desorption process presents a significant challenge. Especially, the DAC process requires much amount of thermal energy by heating the adsorbent for CO2 desorption. In order to eliminate the heating for CO2 desorption, we have developed an amine-modified silica / carbon (AmSiC) aerogel that can desorb CO2 by light irradiation, utilizing carbon black as a photo-thermal material. The AmSiC aerogel with high porosity was obtained via a supercritical CO2 drying method at 20 MPa and 40 ˚C for 3 h, enabling CO2 adsorption due to its amine content. After the aerogel adsorbed CO2 from the air, LED light with the intensity of 2.0 kW m−2 was irradiated to the aerogel with CO2, raising the temperature to approximately 70 ˚C and leading to CO2 desorption. Compared to xerogel dried through heating evaporation, the AmSiC aerogel exhibited approximately 60 times higher CO2 desorption due to its porous structure serving as thermal insulation during photo-thermal heating. By adjusting the carbon black concentration, the photo-thermal desorption efficiency reached nearly 80 %. Solar illumination can be employed in the DAC process with the AmSiC aerogel, which would significantly reduce the energy requirements for DAC system operation.