CO2 Capture at High Temperature Using Fly Ash-Derived Sodium Silicates

Harnessing Ash for Sustainable CO2 Absorption: Current Strategies and Future Prospects

This review explores the potential of using different types of ash, namely fly ash, biomass ash, and coal ash etc., as mediums for CO2 capture and sequestration. The diverse origins of these ash types - municipal waste, organic biomass, and coal combustion - impart unique physicochemical properties that influence their suitability and efficiency in CO2 absorption. This review first discusses the environmental and economic implications of using ash wastes, emphasizing the reduction in landfill usage and the transformation of waste into value-added products. Then the chemical/physical treatments of ash wastes and their inherent capabilities in binding or reacting with CO2 are introduced, along with current methodologies utilize these ashes for CO2 sequestration, including mineral carbonation and direct air capture techniques. The application of using ash wastes for CO2 capture are highlighted, followed by the discussion regarding challenges associated with ash-based CO2 absorption approach. Finally, the article projects into the future, proposing innovative approaches and technological advancements needed to enhance the efficacy of ash in combating the increasing CO2 levels. By providing a comprehensive analysis of current strategies and envisioning future prospects, this review aims to contribute to the field of sustainable CO2 absorption and environmental management.

Lithium–Sodium Fly Ash-Derived Catalyst for the In Situ Partial Deoxygenation of Isochrysis sp. Microalgae Bio-Oil

The catalytic potential of Na and LiNa fly ash (FA) obtained through a simple solid-state synthesis was investigated for the pyrolysis of Isochrysis sp. microalgae using a fixed bed reactor at 500 °C. While both LiNa-FA and Na-FA catalysts reduced the bio-oil yield and increased char and gas production, LiNa-FA was found to enhance the quality of the resulting bio-oil by decreasing its oxygen content (−25 wt.%), increasing paraffins and olefins and decreasing its acidity. The deoxygenation activity of LiNa-FA was attributed to the presence of weak and mild base sites, which enabled dehydration, decarboxylation, ketonisation, and cracking to form olefins. The bio-oil generated with LiNa-FA contained higher amounts of alkanes, alkenes, and carbonated esters, indicating its capacity to chemisorb and partially desorb CO2 under the studied conditions. These findings suggest that LiNa-FA catalysts could be a cost-effective alternative to acidic zeolites for in situ deoxygenation of microalgae to biofuels.

H2O-prompted CO2 capture on metal silicates in situ generated from SBA-15

A series of metal silicates, NaMSi₁₀Ox (M = Cu, Mn and Ni), were prepared by in situ doping of metals into mesoporous SBA-15 under a hydrothermal process, displaying a continuous framework of SiO₄ structure with a narrow pore size distribution. These metal silicate materials were tested for CO₂ adsorption behavior in the absence and presence of water. The results exhibited that the effect of H₂O on the CO₂ capture capability of metal silicates depends on the types of metal inserted into SBA-15. Compared to the dry condition, H₂O addition enhances CO₂ uptake dramatically for NaCuSi₁₀Ox by 25%, and slightly for NaNiSi₁₀Ox (∼10%), whereas little effect is shown on NaMnSi₁₀Ox. The metal silicate materials are stable after adsorption of CO₂ under wet conditions, which is benefited from their synthesis method, hydrothermal conditions. The improvement of CO₂ uptake on metal silicates by H₂O is attributed to the competitive and synergistic adsorption mechanism on the basis of IR investigations, where initially adsorbed H₂O acts as a promoter for further CO₂ capture through a hydration reaction, i.e., formation of bicarbonate and carbonates on the surface of the samples. These observations provide new possibilities for the design and synthesis of porous metal silicate materials for CO₂ capture under practical conditions where moisture is present.

Porous metal silicates prepared by an in situ doping strategy of metals into SBA-15 under hydrothermal conditions display efficient CO₂ capture performances in the absence and presence of moisture.

Solid-Waste-Derived Carbon Dioxide-Capturing Materials

Solid sorbents are considered to be promising materials for carbon dioxide capture. In recent years, many studies have focused on the use of solid waste as carbon dioxide sorbents. The use of waste resources as carbon dioxide sorbents not only leads to the development of relatively low-cost materials, but also eliminates waste simultaneously. Different types of waste materials from biomass, industrial waste, household waste, and so forth were used as carbon dioxide sorbents with sufficient carbon dioxide capture capacities. Herein, progress on the development of carbon dioxide sorbents produced from waste materials is reviewed and covers key factors, such as the type of waste, preparation method, further modification method, carbon dioxide sorption performance, and kinetics studies. In addition, a new research direction for further study is proposed. It is hoped that this critical review will not merely sum up the major research directions in this field, but also provide significant suggestions for future work.

Alkali carbonates promote CO2 capture by sodium orthosilicate

The C₂O₅²⁻ combined with alkali cations are the intermediates during the CO₂ uptake with Na₄SiO₄ and alkali carbonates.

Structural and CO2capture analyses of the Li1+xFeO2(0 ≤ x ≤ 0.3) system: effect of different physicochemical conditions

α-Li_1+xFeO₂compounds have been synthesized by nitrate decomposition at low temperature. Their CO₂capture were evaluated in CO₂and CO₂+ steam atmospheres. The amount captured in CO₂+ steam atmosphere was 24 wt%, also magnetite was formed.