Amine-Grafted Silica Gels for CO2 Capture Including Direct Air Capture

Carbon capture from controlled degassing of deep meromictic lakes: Insights to techno-economic and environmental feasibility, from the "killer lakes" in Cameroon

Carbon dioxide (CO2) accumulation and emission are well-known features of deep lakes, making them a significant unavoidable carbon source to the atmosphere. In the case of meromictic lakes, degassing devices are installed to controllably release through a pipe the CO2 trapped in the bottom waters. Otherwise, the gas is emitted diffusely at the air-water surface or accidentally through a limnic eruption when the saturation limit is reached. This controlled degassing operation gives rise to an end-of-pipe carbon capture opportunity that has yet to be explored. In the perspective of promoting negative emission technologies, as this is required to reach the near-term global carbon neutrality objective, this study outlines an end-of-pipe solid sorbent-based carbon capture technique that targets the CO2 released through controlled degassing of deep meromictic lakes. A direct air capture (DAC) system astutely dimensioned and optimised by the vacuuming of air enriched with CO2 from the controlled degassing of the lake is therefore proposed and its technical, economic, and environmental feasibility discussed based on the cases of lakes Nyos and Monoun in Cameroon. It resulted that, even on a small scale, capturing CO2 from lake degassing at 8 vol% (80,000 ppm) can achieve a life cycle cost of 15 bar-compressed CO2 between $200 and $350 tCO2-1, two to three times less than that of conventional DAC depending on the energy source used, with potentially attractive marginal abatement costs of CO2, especially if natural gas, hydro or solar PV are considered.

Asymmetrical Modification of Cyclopentadienyl Cobalt in Eu-MOF for C2H2/CO2 Separation

The development of novel adsorption materials is of significance for the efficient and low-energy purification of acetylene (C2H2). Emerging metal-organic framework (MOF) adsorbents demonstrate great application prospects in the field of gas adsorption and separation. Herein, we synthesized a Eu-MOF asymmetrically modified with cyclopentadienyl cobalt exhibiting two different types of cages, denoted as UPC-119. Adsorption isotherms and dynamic breakthrough curves confirm its potential in C2H2/CO2 separation, which is further evidenced by theoretical simulations. The high adsorption capacity and low adsorption enthalpy render UPC-119 as a promising adsorbent for C2H2/CO2 separation with ease of regeneration.

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.

Synthesis of Mesoporous Silica Using the Sol-Gel Approach: Adjusting Architecture and Composition for Novel Applications

The sol-gel chemistry of silica has long been used for manipulating the size, shape, and microstructure of mesoporous silica particles. This manipulation is performed in mild conditions through controlling the hydrolysis and condensation of silicon alkoxide. Compared to amorphous silica particles, the preparation of mesoporous silica, such as MCM-41, using the sol-gel approach offers several unique advantages in the fields of catalysis, medicament, and environment, due to its ordered mesoporous structure, high specific surface area, large pore volume, and easily functionalized surface. In this review, our primary focus is on the latest research related to the manipulation of mesoporous silica architectures using the sol-gel approach. We summarize various structures, including hollow, yolk-shell, multi-shelled hollow, Janus, nanotubular, and 2D membrane structures. Additionally, we survey sol-gel strategies involving the introduction of various functional elements onto the surface of mesoporous silica to enhance its performance. Furthermore, we outline the prospects and challenges associated with mesoporous silica featuring different structures and functions in promising applications, such as high-performance catalysis, biomedicine, wastewater treatment, and CO2 capture.

Chemically Reversible CO2 Uptake by Dendrimer-Impregnated Metal-Organic Frameworks

Industrialization over the past two centuries has resulted in a continuous rise in global CO2 emissions. These emissions are changing ecosystems and livelihoods. Therefore, methods are needed to capture these emissions from point sources and possibly from our atmosphere. Though the amount of CO2 is rising, it is challenging to capture directly from air because its concentration in air is extremely low, 0.04%. In this study, amines installed inside metal-organic frameworks (MOFs) are investigated for the adsorption of CO2, including at low concentrations. The amines used are polyamidoamine dendrimers that contain many primary amines. Chemically reversible adsorption of CO2 via carbamate formation was observed, as was enhanced uptake of carbon dioxide, likely via dendrimer-amide-based physisorption. Limiting factors in this initial study are comparatively low dendrimer loadings and slow kinetics for carbon dioxide uptake and release, even at 80 °C.

Amine-Functionalized Meso-Macroporous Polymers for Efficient CO2 Capture from Ambient Air

Over the past decade, direct air capture (DAC) of carbon dioxide (CO2) using solid nanoadsorbents has garnered attention as a negative emission technology with high energy efficiency. Although operational, the large-scale deployment of DAC technologies has been significantly delayed due to the low performance and high cost of solid DAC nanoadsorbents. Herein, we present a novel family of meso-macroporous melamine formaldehyde (MF) materials with a facile preparation methodology, low capital cost, and unique physicochemical characteristics for DAC. The fabricated MF materials exhibit an extra-large pore volume of 5.19 cm3/g with a 24.6 nm average pore diameter. We show that the synthesized MF materials can be used as substrates and impregnated with different amounts of tetraethylenepentamine (TEPA) to act as chemical nanoadsorbents for DAC. Owing to the ultrahigh pore volume of MF, a substantial amount of 71 wt % TEPA (i.e., MF-TEPA71%) can be loaded, resulting in 2.65 mmol/g of CO2 uptake under DAC conditions. In addition, the superior physicochemical properties of MF lead to a high CO2 loading of 2.07 mmol/g with low TEPA loading in MF-TEPA33%. The prepared MF-TEPA nanoadsorbents can be successfully employed in different shapes (i.e., droplets, pellets, and coatings) and maintain their superiority across different temperatures and CO2 concentrations. This study provides a promising approach for developing meso-macroporous substrates through a straightforward and scalable synthesis method, representing a new avenue for the next generation of DAC nanoadsorbents with superior performance for practical applications.

Amine-functionalized porous silica production via ex- and in-situ method using silicate precursors as a selective adsorbent for CO2 capture applications

A comparison of the amine-modified silica particle's characteristics via ex- and in-situ routes and their application as a CO2 gas adsorbent is reported. Modifying silica particles via ex-situ involves two separate steps: forming porous silica particles with sodium lauryl sulfate (SLS) as a template and impregnation using ultrasound assistance. In contrast to ex-situ modification, in-situ modification of silica particles is carried out in one step by mixing directly between the silica source and the modifying agent. Controlling the characteristics of modified silica particles via in-situ is carried out by adding an SLS template removed simultaneously with particle formation to increase the surface area and porosity. Increasing the SLS template concentration shows a linear relationship between increasing particle surface area and amine loading. However, two different modification routes exert a direct influence on aminopropyl distribution. Silanization via in-situ which involves a simultaneous condensation reaction produces a higher amine loading reaching 1.2845 mmol/g of silica than via ex-situ which is only 0.9610 mmol/g of silica. The amount of aminopropyl that can be grafted on the silica surface shows a linear relationship to the quantity of CO2 gas adsorption capacity. Amine-modified silica particles obtained the highest adsorption capability via the in-situ route with an SLS 3 CMC template of 2.32 mmol/g silica at an operating pressure of 6 bar.

Use of Ball Drop Casting and Surface Modification for the Development of Amine-Functionalized Silica Aerogel Globules for Dynamic and Efficient Direct Air Capture

Amine-functionalized silica aerogel globules (AFSAGs) were first synthesized via a simple ball drop casting method followed by amine grafting. The effect of grafting time on the structure and CO2 adsorption performance of the AFSAGs was investigated. The CO2 adsorption performance was comprehensively studied by breakthrough curves, adsorption capacity and rates, surface amine loading and density, amine efficiency, adsorption halftime, and cyclic stability. The results demonstrate that prolonging the grafting time does not lead to a significant increase in surface amine content owing to pore space blockage by superabundant amine groups. The CO2 adsorption performance shows obvious dependence on surface amine density, determined by both the surface amine content and specific surface area, and working temperature. AFSAGs with a grafting time of 24 h (AFSAG24) with a moderate surface amine density have optimal CO2 adsorption capacities, which are 1.78 and 2.14 mmol/g at 25 °C with dry and humid 400 ppm CO2, respectively. The amine efficiency of AFSAG24 with low CO2 concentrations, 0.38-0.63 with dry 400 ppm-1% CO2, is the highest among the reported amine-functionalized adsorbents. After estimation with different diffusion models, the CO2 adsorption process of AFSAG24 is governed by film diffusion and intraparticle diffusion. In the range of 1-4 mm, the ball size does not affect the CO2 adsorption capacity of AFSAG24 obviously. AFSAG24 offers significant advantages for practical direct air capture compared with its state-of-the-art counterparts, such as high dynamic adsorption capacity and amine efficiency, excellent stability, and outstanding adaptation to the environment.

Water-Enhanced Direct Air Capture of Carbon Dioxide in Metal-Organic Frameworks

We have developed two series of amine-functionalized zirconium (Zr) metal-organic framework-808 (MOF-808), which were produced by postsynthetic modifications to have either amino acids coordinated to Zr ions (MOF-808-AAs) or polyamines covalently bound to the chloro-functionalized structure (MOF-808-PAs). These MOF variants were comprehensively characterized by liquid-state 1H nuclear magnetic resonance (NMR) measurements and potentiometric acid-base titration to determine the amounts of amines, energy-dispersive X-ray spectroscopy to assess the extent of covalent substitution by polyamines, powder X-ray diffraction analysis to verify the maintenance of the MOF crystallinity and structure after postsynthetic modifications, nitrogen sorption isotherm measurements to confirm retention of the porosity, and water sorption isotherm measurements to find the water uptake in the pores of each member of the series. Evaluation and testing of these compounds in direct air capture (DAC) of CO2 showed improved CO2 capture performance for the functionalized forms, especially under humid conditions: In dry conditions, the l-lysine- and tris(3-aminopropyl)amine-functionalized variants, termed as MOF-808-Lys and MOF-808-TAPA, exhibited the highest CO2 uptakes at 400 ppm, measuring 0.612 and 0.498 mmol g-1, and further capacity enhancement was achieved by introducing 50% relative humidity, resulting in remarkable uptakes of 1.205 and 0.872 mmol g-1 corresponding to 97 and 75% increase compared to the dry uptakes, respectively. The mechanism underlying the enhanced uptake efficiency was revealed by 13C solid-state NMR and temperature-programmed desorption measurements, indicating the formation of bicarbonate species, and therefore a stoichiometry of 1:1 CO2 to each amine site.

Comprehensive review and assessment of carbon capturing methods and technologies: An environmental research

A majority of the primary contributors of carbon dioxide (CO2) emissions into the environment have really been out of human-made activities. The levels of CO2 in the atmosphere have increased substantially since the time of the industrial revolution. This has been linked to the use of fossil fuels for energy production, as well as the widespread production of some industrial components like cement and the encroaching destruction of forests. An extreme approach is now necessary to develop the right policies and address the local and global environmental issues in the right way. In this regard, CO2 capturing, utilization, and storage are reliable options that industrial facilities can initiate to overcome this problem. Therefore, we have evaluated the two leading technologies that are used for carbon capture: direct (pre-combustion, post-combustion, and oxy-combustion) and indirect carbon (reforestation, enhanced weathering, bioenergy with carbon capture, and agricultural practices) capturing to provide their current status and progresses. Among the considered processes, the post-combustion techniques are widely utilized on a commercial scale, especially in industrial applications. Technology readiness level (TRL) results have showed that amine solvents, pressure-vacuum swing adsorption, and gas separation membranes have the highest TRL value of 9. In addition, the environmental impact assessment methods have been ranked to evaluate their sustainability levels. The highest global warming potential of 219.53 kgCO2 eq./MWh has been obtained for the post-combustion process. Overall, through this comprehensive review, we have identified some critical research gaps in the open literature in the field of CO2-capturing methods where there are strong needs for future research and technology development studies, for instance, developing stable and cost-effective liquid solvents and improving the adsorption capacity of commercialized sorbents. Furthermore, some research areas, like novel process design, environmental and economic impact assessment of capturing methods with different chemicals and modeling and simulation studies, will require further effort to demonstrate the developed technologies for pilot and commercial-scale applications.

Adsorption of CO2 by a novel zeolite doped amine modified ternary aerogels

Novel amine functionalized materials can capture greenhouse gas CO₂. In this study, SiO₂-Al₂O₃-ZrO₂ ternary composite aerogel was prepared by sol-gel method, supercritical drying, ultrasonic non-in-situ synthesis and other processes using aluminum chloride hexahydrate as aluminum source, ethyl orthosilicate as silicon source and tetrabbutyl zirconate as zirconium source. The composite material was used as the carrier material. By impregnation method, the modified agent bis - (3-trimethoxy-silpropyl) amine and the composite were fully mixed and modified, and the novel zeolite doped amine functionalized ternary composite aerogel was obtained by doping acidification activation zeolite. The results show that the prepared novel zeolite amine-modified ternary aerogels have rich microporous structure and ordered mesoporous structure. After loading different contents of amine-based materials (CAA-X) in the ternary aerogels, the comparison between CAAZ-X and zeolite amine-modified ternary aerogels is conducted. Zeolite doped CAAZ-30 material shows the best adsorption performance, with a maximum adsorption capacity of 5.30 mmol/g. In the presence of water vapor, CAAZ-30 material also showed the best adsorption performance, with a maximum adsorption capacity of 5.33 mmol/g. This can help us design suitable adsorbent materials for CO₂ capture in different practical applications.

Greenificated Molecularly Imprinted Materials for Advanced Applications

Molecular imprinting technology (MIT) produces artificial binding sites with precise complementarity to substrates and thereby is capable of exquisite molecular recognition. Over five decades of evolution, it is predicted that the resulting host imprinted materials will overtake natural receptors for research and application purposes, but in practice, this has not yet been realized due to the unsustainability of their life cycles (i.e., precursors, creation, use, recycling, and end-of-life). To address this issue, greenificated molecularly imprinted polymers (GMIPs) are a new class of plastic antibodies that have approached sustainability by following one or more of the greenification principles, while also demonstrating more far-reaching applications compared to their natural counterparts. In this review, the most recent developments in the delicate design and advanced application of GMIPs in six fast-growing and emerging fields are surveyed, namely biomedicine/therapy, catalysis, energy harvesting/storage, nanoparticle detection, gas sensing/adsorption, and environmental remediation. In addition, their distinct features are highlighted, and the optimal means to utilize these features for attaining incredibly far-reaching applications are discussed. Importantly, the obscure technical challenges of the greenificated MIT are revealed, and conceivable solutions are offered. Lastly, several perspectives on future research directions are proposed.

Synthesis and CO2 Capture of Porous Hydrogel Particles Consisting of Hyperbranched Poly(amidoamine)s

We successfully synthesized new macroporous hydrogel particles consisting of hyperbranched poly(amidoamine)s (HPAMAM) using the Oil-in-Water-in-Oil (O/W/O) suspension polymerization method at both the 50 mL flask scale and the 5 L reactor scale. The pore sizes and particle sizes were easily tuned by controlling the agitation speeds during the polymerization reaction. Since O/W/O suspension polymerization gives porous architecture to the microparticles, synthesized hydrogel particles having abundant amine groups inside polymers exhibited a high CO2 absorption capacity (104 mg/g) and a fast absorption rate in a packed-column test.

Recent advances in direct air capture by adsorption

Significant progress has been made in direct air capture (DAC) in recent years. Evidence suggests that the large-scale deployment of DAC by adsorption would be technically feasible for gigatons of CO₂ capture annually. However, great efforts in adsorption-based DAC technologies are still required. This review provides an exhaustive description of materials development, adsorbent shaping, in situ characterization, adsorption mechanism simulation, process design, system integration, and techno-economic analysis of adsorption-based DAC over the past five years; and in terms of adsorbent development, affordable DAC adsorbents such as amine-containing porous materials with large CO₂ adsorption capacities, fast kinetics, high selectivity, and long-term stability under ultra-low CO₂ concentration and humid conditions. It is also critically important to develop efficient DAC adsorptive processes. Research and development in structured adsorbents that operate at low-temperature with excellent CO₂ adsorption capacities and kinetics, novel gas-solid contactors with low heat and mass transfer resistances, and energy-efficient regeneration methods using heat, vacuum, and steam purge is needed to commercialize adsorption-based DAC. The synergy between DAC and carbon capture technologies for point sources can help in mitigating climate change effects in the long-term. Further investigations into DAC applications in the aviation, agriculture, energy, and chemical industries are required as well. This work benefits researchers concerned about global energy and environmental issues, and delivers perspective views for further deployment of negative-emission technologies.

Amine-Functionalized Mesoporous Silica Adsorbent for CO2 Capture in Confined-Fluidized Bed: Study of the Breakthrough Adsorption Curves as a Function of Several Operating Variables

Carbon capture, utilization, and storage (CCUS) is one of the key promising technologies that can reduce GHG emissions from those industries that generate CO2 as part of their production processes. Compared to other effective CO2 capture methods, the adsorption technique offers the possibility of reducing the costs of the process by setting solid sorbent with a high capacity of adsorption and easy regeneration and, also, controlling the performance of gas-solid contactor. In this work, an amine-functionalized mesoporous sorbent was used to capture CO2 emissions in a confined-fluidized bed. The adoption of a confined environment allows the establishment of a homogeneous expansion regime for the sorbent and allows to improve the exchange of matter and heat between gas and solid phase. The results illustrate how the different concentration of the solution adopted during the functionalization affects the adsorption capacity. That, measured as mg of CO2 per g of sorbent, was determined by breakthrough curves from continuous adsorption tests using different concentrations of CO2 in air. Mesoporous silica functionalized with a concentration of 20% of APTES proves to be the best viable option in terms of cost and ease of preparation, low temperature of regeneration, and effective use for CO2 capture.

Spiers Memorial Lecture: CO2 utilization: why, why now, and how?

This introduction to the Faraday Discussion on carbon dioxide utilization (CDU) provides a framework to lay out the need for CDU, the opportunities, boundary conditions, potential pitfalls, and critical needs to advance the required technologies in the time needed. CDU as a mainstream climate-relevant solution is gaining rapid traction as measured by the increase in the number of related publications, the investment activity, and the political action taken in various countries.

Zinc(ii) and cadmium(ii) amorphous metal-organic frameworks (aMOFs): study of activation process and high-pressure adsorption of greenhouse gases

Two novel amorphous metal-organic frameworks (aMOFs) with chemical composition {[Zn2(MTA)]·4H2O·3DMF} n (UPJS-13) and {[Cd2(MTA)]·5H2O·4DMF} n (UPJS-14) built from Zn(ii) and Cd(ii) ions and extended tetrahedral tetraazo-tetracarboxylic acid (H4MTA) as a linker were prepared and characterised. Nitrogen adsorption measurements were performed on as-synthesized (AS), ethanol exchanged (EX) and freeze-dried (FD) materials at different activation temperatures of 60, 80, 100, 120, 150 and 200 °C to obtain the best textural properties. The largest surface areas of 830 m2 g-1 for UPJS-13 (FD) and 1057 m2 g-1 for UPJS-14 (FD) were calculated from the nitrogen adsorption isotherms for freeze-dried materials activated at mild activation temperature (80 °C). Subsequently, the prepared compounds were tested as adsorbents of greenhouse gases, carbon dioxide and methane, measured at high pressures. The maximal adsorption capacities were 30.01 wt% CO2 and 4.84 wt% CH4 for UPJS-13 (FD) and 24.56 wt% CO2 and 6.38 wt% CH4 for UPJS-14 (FD) at 20 bar and 30 °C.

Direct CO2 Capture from Air via Crystallization with a Trichelating Iminoguanidine Ligand

Effectively reducing the concentration of CO2 in ambient air is essential to mitigate global warming. Existing carbon capture and storage technology can only slow down the carbon emissions of large point sources but cannot treat the already accumulated CO2 in the environment. Herein, we demonstrated a simple direct CO2 capture method from air via reactive crystallization with a new trichelating iminoguanidine ligand (BTIG). It could strongly bind CO2 to form insoluble carbonate crystals that could be easily isolated. In the crystal, CO2 was transformed to CO3 2- and trapped in a dense hydrogen bonding network in terms of carbonate-water clusters. This capture process was reversible, and the BTIG ligand could be regenerated by heating the BTIG-CO2 crystal at a mild temperature, which was much lower than the decomposition temperature of CaCO3 (∼900 °C). Thermodynamic and kinetics analyses indicate that the crystallization process was exothermic with an enthalpy of -292 kJ/mol, and the decomposition energy consumption was 169 kJ per mol CO2. In addition, BTIG could also be employed for CO2 capture from flue gas with a capacity of 1.46 mol/mol, which was superior to that of most of the reported sorbents.

Preparation, Characterization, and Application of Novel Ferric Oxide-Amine Material for Removal of Nitrate and Phosphate in Water

Ferric oxide-amine material was synthesized and applied as a novel adsorbent for nitrate and phosphate removal from aqueous solution. The properties of ferric oxide-amine were examined using TGA, FTIR, BET, SEM, EDX, SEM-mapping, and XRD analysis. The results showed that the adsorption using ferric oxide-amine material reached equilibrium after 30 and 60 min for nitrate and phosphate, respectively. The highest nitrate and phosphate adsorption capacities were 131.4 mg nitrate/g at pH 5-6 and 42.1 mg phosphate/g at pH 6. The effects of adsorbent dosage, initial concentrations of nitrate and phosphate, and adsorption temperature were also investigated. Among the three adsorbents of ferric oxide-amine, ferric oxide, and Akualite A420 ion exchange resin, ferric oxide-amine material had the highest adsorption capacity for nitrate and phosphate removal. These results suggest a great potential use of ferric oxide-amine material for water treatment in practical applications.