Direct Air Capture of CO2 Using Amine/Alumina Sorbents at Cold Temperature

Platform Materials for Moisture-Swing Carbon Capture

Energy and cost efficiency limit the viability of direct air carbon capture. Developing and testing materials that can improve these efficiencies and fit into the carbon capture, storage, and utilization ecosystem will be essential to advance negative emissions technologies. This study builds on the moisture-swing modality of carbon capture, directly comparing carbon-based and metal oxide nanomaterials based on their humidity-dependent adsorptive properties. The moisture-swing modality allows for the cyclical sequestration of CO2 under dry conditions and release under humid conditions. While previous work has explored individual material systems, generally focusing on the use of ion-exchange resins and comparing across different anion types, this work broadens the toolbox of platform materials available, focusing on materials with potential dual-function uses for carbon conversion and storage. Activated carbon, nanostructured graphite, and iron and aluminum oxide nanoparticles showed particular promise, among the studied materials, while manganese oxide, flake graphite, and carbon nanotube powders underperformed. The effects of surface area and pore distributions─the subject of prior theoretical work─were investigated experimentally, yielding insights into establishing design rules for platform materials for moisture-swing carbon capture and other sorbent materials.

A Dataset for Investigations of Amine-Impregnated Solid Adsorbent for Direct Air Capture

Amine-impregnated solid adsorbents are widely explored for point source capture and direct air capture (DAC) to address climate change. Existing literature serves as a valuable source for the investigation of amine-functionalized solid adsorbents. This study selected 52 articles from bibliographic platforms using GPT-assisted data source screening. A total of 1,336 data points were manually collected. Each data point is characterized by 28 features including the CO2 capture performance of various adsorbents from diluted to concentrated sources, resulting in 29,857 records. The methodology addresses inconsistencies in units and terminologies in the published articles and demonstrates database reliability, regularity and integrity through statistical analysis. The diverse types of amines and mesoporous solids in the database offer innovation potential for future research. In addition, two machine learning models were trained to promote dataset reuse by scientists from lab-based research and cheminformatics. This study provides opportunities to explore the use of machine learning on small databases and encourages data sharing and uniform reporting among DAC communities.

In Pursuit of Carbon Neutrality: Progresses and Innovations in Sorbents for Direct Air Capture of CO2

Direct air capture (DAC) is of immense current interest, as a means to facilitate CO2 capture at low concentrations (∼400 ppm) directly from the atmosphere, with the aim of addressing global warming caused by excessive anthropogenic CO2 production. Traditionally, DAC of CO2 has relied on amine scrubbing and metal carbonate /hydroxide solutions. However, recent years have seen notable progress in DAC sorbents, with key advancements aimed at improving efficiency, capacity, and regenerability while reducing energy consumption. This review delivers an exhaustive analysis of contemporary developments in DAC sorbents, addressing the innovations in material design and consequent performance enhancement. The limitations of the sorbents have also been discussed, with future perspectives for improving sustainable CO2 capture strategies. We anticipate that this overview will help lay the groundwork for further development and large-scale implementation of sustainable sorbents and cutting-edge technologies toward attaining carbon neutrality.

Behavior, mechanisms, and applications of low-concentration CO2 in energy media

This review explores the behavior of low-concentration CO2 (LCC) in various energy media, such as solid adsorbents, liquid absorbents, and catalytic surfaces. It delves into the mechanisms of diffusion, adsorption, and catalytic reactions, while analyzing the potential applications and challenges of these properties in technologies like air separation, compressed gas energy storage, and CO2 catalytic conversion. Given the current lack of comprehensive analyses, especially those encompassing multiscale studies of LCC behavior, this review aims to provide a theoretical foundation and data support for optimizing CO2 capture, storage, and conversion technologies, as well as guidance for the development and application of new materials. By summarizing recent advancements in LCC separation techniques (e.g., cryogenic air separation and direct air carbon capture) and catalytic conversion technologies (including thermal catalysis, electrochemical catalysis, photocatalysis, plasma catalysis, and biocatalysis), this review highlights their importance in achieving carbon neutrality. It also discusses the challenges and future directions of these technologies. The findings emphasize that advancing the efficient utilization of LCC not only enhances CO2 reduction and resource utilization efficiency, promoting the development of clean energy technologies, but also provides an economically and environmentally viable solution for addressing global climate change.

Assessment of Long-Term Degradation of Adsorbents for Direct Air Capture by Ozonolysis

Porous adsorbents are a promising class of materials for the direct air capture of CO2 (DAC). Practical implementation of adsorption-based DAC requires adsorbents that can be used for thousands of adsorption-desorption cycles without significant degradation. We examined the potential degradation of adsorbents by a mechanism that appears to have not been considered previously, namely, ozonolysis by trace levels of ozone from ambient air. We focused on amine-appended metal-organic frameworks, specifically amine-functionalized Mg2(dobpdc), as a representative DAC adsorbent. Estimates based on the number of amine sites in these adsorbents and the ozone concentration in air suggest that degradation by ozone may be relevant over thousands of adsorption-desorption cycles if reactions with adsorbed ozone are fast. We used density functional theory calculations to estimate reaction rates for amine groups and carbon-carbon double bonds in amine-functionalized Mg2(dobpdc).

Development of Amino-Functionalized Silica by Co-condensation and Alkylation for Direct Air Capture

CO2 chemisorption using amine-based sorbents is one of the most effective techniques for carbon capture and storage. Solid CO2 sorbents with amines immobilized on their surface have been attracting attention due to the easy collection of sorbents and reusability. In this study, we developed a solid CO2 adsorbent by co-condensation of a silanizing reagent having a chloroalkyl group and tetraethyl ethoxysilane, followed by alkylation of the chloroalkyl group with diamine. The fabricated amine-immobilized silica with a high density of amino groups on its surface achieved the chemical adsorption of 400 ppm of CO2 with 4.3 wtCO2 % loading, CO2 release upon heating at 80 °C, and reusability for adsorption and desorption cycles with high amine utilization efficiency (0.20 molCO2 /mol-N). This surface modification method is applicable to various amines bearing more than two amino functional groups, enabling the development of solid CO2 sorbents for the selective capture of low-concentration CO2 directly from the air.

Recent advances in CO2 capture and mineralization using layered double hydroxide-based materials: A review

The continuous release of substantial amounts of carbon dioxide (CO2) to the atmosphere has resulted in numerous severe adverse effects. Several materials have been synthesized and utilized for CO2 capture. One class of such materials is layered double hydroxides (LDHs), which have emerged as promising materials for CO2 capture due to their tunable properties, high surface area, and excellent CO2 adsorption capabilities. Although there are some review articles on CO2 capture and conversion using various materials, there is still a notable lack of thorough reviews focusing on the utilization of LDH-based materials for CO2 capture. Additionally, the field of CO2 capture and mineralization using LDH-based materials is rapidly evolving, necessitating up-to-date comprehensive reviews to analyze, evaluate, and condense the dispersed information found in recently published research articles. Accordingly, this review article provides a comprehensive overview of recent advancements in CO2 capture using LDH-based materials. After briefly introducing the topic, different synthesis protocols of LDH-based materials are briefly reviewed. Then, CO2 capture using LDHs, calcined LDHs, impregnated LDHs, composites containing LDHs, amine functionalized LDHs, and during steam methane reforming, are thoroughly analyzed and discussed. Additionally, the effects of synthesis method and post treatment of LDH-based materials on CO2 capture, effect of modification and functionalization on LDHs, and the effects of various process conditions including temperature, pressure, water vapor, and gas composition on the performance of CO2 capture by LDH-based materials are reviewed. Limitations, challenges, obstacles, and remaining knowledge gaps are highlighted, and future research works to address them are proposed.

Facile Synthesis of Self-Supported Solid Amine Sorbents for Direct Air Capture

Conventional usage of tetraethylenepentamine (TEPA) via being supported on porous solid materials for carbon capture is susceptible to oxidative degradation during regeneration cycles. This study reports a novel method to synthesize a TEPA based solid polymer for efficient CO2 removal via direct air capture (DAC). The polymer was obtained through epoxy-amine crosslinking reaction, leading to the transformation of liquid TEPA to a self-supported solid polymer. The synthesis was conducted under ambient conditions via a one-pot process with no waste products, which is aligned with green synthesis. The performance of the solid amine was evaluated in DAC under realistic conditions and compared with TEPA supported on SiO2 and zeolite 13X prepared through the conventional method. The solid TEPA amine exhibited a high CO2 uptake of 6.2 wt.% comparable to the conventional counterparts. More importantly, the solid TEPA amine demonstrated high resistance to oxidation during the accelerated ageing process at 80 °C in air for 24 h, whereas the two supported TEPA samples experienced severe degradation, with zeolite 13X supported TEPA incurring a reduction of 86.5 % in CO2 capturing capacity after the ageing. This work sheds light on the novel usage of TEPA as an efficient solid amine for practical DAC operation.

Implications of Defect Density and Polymer Interactions for CO2 Capture on Amine-Functionalized MIL-101(Cr)

Rising anthropogenic carbon emissions have dire environmental consequences, necessitating remediative approaches, which includes use of solid sorbents. Here, aminopolymers (poly(ethylene imine) (PEI) and poly(propylene imine) (PPI)) are supported within solid mesoporous MIL-101(Cr) to examine effects of support defect density on aminopolymer-MOF interactions for CO2 uptake and stability during uptake-regeneration cycles. Using simulated flue gas (10 % CO2 in He), MIL-101(Cr)-ρhigh (higher defect density) shows 33 % higher uptake capacity per gram adsorbent than MIL-101(Cr)-ρlow (lower defect density) at 308 K, consistent with increased availability of undercoordinated Cr adsorption sites at missing linker defects. Increasing aminopolymer weight loadings (10-50 wt.%) within MIL-101(Cr)-ρlow and MIL-101(Cr)-ρhigh increases amine efficiencies and CO2 uptake capacities relative to bare MOFs, though both incur CO2 diffusion limitations through confined, viscous polymer phases at higher (40-50 wt.%) loadings. Benchmarked against SBA-15, lower polymer packing densities (PPI>PEI), weaker and less abundant van der Waals interactions between aminopolymers and pore walls, and open framework topology increase amine efficiencies. Interactions between amines and Cr defect sites incur amine efficiency losses but grant higher thermal and oxidative stability during uptake-regeneration cycling. Finally, >25 % higher CO2 uptake capacities are achieved for aminopolymer/MIL-101(Cr)-ρhigh under humid conditions, demonstrating promise for realistic applications.

Machine learning demonstrates the impact of proton transfer and solvent dynamics on CO2 capture in liquid ammonia

Direct air capture of CO2 using supported amines provides a promising means to achieve the net-zero greenhouse gas emissions goal; however, many mechanistic details regarding the CO2 adsorption process in condensed phase amines remain poorly understood. This work combines machine learning potentials, enhanced sampling and grand-canonical Monte Carlo simulations to directly compute experimentally relevant quantities to elucidate the mechanism of CO2 chemisorption in liquid ammonia as a model system. Our simulations suggest that CO2 capture in the liquid occurs in a sequential fashion, with the formation of a metastable zwitterion intermediate. Furthermore, we identified the importance of solvent-mediated proton transfer and solvent dynamics, not only in the reaction pathway but also in the efficiency of CO2 chemisorption. Beyond liquid ammonia, the methodology presented here can be readily extended to simulate amines with more complex chemical structures under experimental conditions, paving the way to elucidate the structure-performance of amines for CO2 capture.

Carbon Dioxide Capture by Emerging Innovative Polymers: Status and Perspectives

A significant amount of research has been conducted in carbon dioxide (CO2) capture, particularly over the past decade, and continues to evolve. This review presents the most recent advancements in synthetic methodologies and CO2 capture capabilities of diverse polymer-based substances, which includes the amine-based polymers, porous organic polymers, and polymeric membranes, covering publications in the last 5 years (2019-2024). It aims to assist researchers with new insights and approaches to develop innovative polymer-based materials with improved capturing CO2 capacity, efficiency, sustainability, and cost-effective, thereby addressing the current obstacles in carbon capture and storage to sooner meeting the net-zero CO2 emission target.

Assessment of Potential and Techno-Economic Performance of Solid Sorbent Direct Air Capture with CO2 Storage in Europe

Direct air capture with CO2 storage (DACCS) is among the carbon dioxide removal (CDR) options, with the largest gap between current deployment and needed upscaling. Here, we present a geospatial analysis of the techno-economic performance of large-scale DACCS deployment in Europe using two performance indicators: CDR costs and potential. Different low-temperature heat DACCS configurations are considered, i.e., coupled to the national power grid, using waste heat and powered by curtailed electricity. Our findings reveal that the CDR potential and costs of DACCS systems are mainly driven by (i) the availability of energy sources, (ii) the location-specific climate conditions, (iii) the price and GHG intensity of electricity, and (iv) the CO2 transport distance to the nearest CO2 storage location. The results further highlight the following key findings: (i) the limited availability of waste heat, with only Sweden potentially compensating nearly 10% of national emissions through CDR, and (ii) the need for considering transport and storage of CO2 in a comprehensive techno-economic assessment of DACCS. Finally, our geospatial analysis reveals substantial differences between regions due to location-specific conditions, i.e., useful information elements and consistent insights that will contribute to assessment and feasibility studies toward effective DACCS implementation.

Assessing Impacts of Atmospheric Conditions on Efficiency and Siting of Large-Scale Direct Air Capture Facilities

The cost and efficiency of direct air capture (DAC) of carbon dioxide (CO2) will be decisive in determining whether this technology can play a large role in decarbonization. To probe the role of meteorological conditions on DAC we examine, at 1 × 1° resolution for the continental United States (U.S.), the impacts of temperature, humidity, atmospheric pressure, and CO2 concentration for a representative amine-based adsorption process. Spatial and temporal variations in atmospheric pressure and CO2 concentration lead to strong variations in the CO2 available in ambient air across the U.S. The specific DAC process that we examine is described by a process model that accounts for both temperature and humidity. A process that assumes the same operating choices at all locations in the continental U.S. shows strong variations in performance, with the most influential variables being the H2O gas phase volume fraction and temperature, both of which are negatively correlated with DAC productivity for the specific process that we consider. The process also shows a moderate positive correlation of ambient CO2 with productivity and recovery. We show that optimizing the DAC process at seven representative locations to reflect temporal and spatial variations in ambient conditions significantly improves the process performance and, more importantly, would lead to different choices in the sites for the best performance than models based on a single set of process conditions. Our work provides a framework for assessing spatial variations in DAC performance that could be applied to any DAC process and indicates that these variations will have important implications in optimizing and siting DAC facilities.

Minimal Kinetic Model of Direct Air Capture of CO2 by Supported Amine Sorbents in Dry and Humid Conditions

Dilute concentration (∼400 ppm) and humidity are two important factors in the direct air capture (DAC) of CO2 by supported sorbents. In this work, a minimal DAC CO2 adsorption-kinetics model was formulated for supported amine sorbents under dry and humid conditions. Our model fits well with a recent DAC experiment with supported amine sorbent in both dry and humid conditions. Temperature and flow rate effects on breakthrough curves were quantitatively captured, and increasing temperature led to faster CO2 adsorption kinetics. Moisture was shown to broaden the breakthrough curve with slower CO2 adsorption kinetics but significantly improve the uptake capacity. The present minimal model provides a versatile platform for kinetic modeling of the DAC of CO2 on supported amine and other chemisorption systems.