Journal of CO2 Utilization最新文献

Waste eggshells have been investigated as biomineralised CO₂ sorbents for the calcium looping cycle due to their high Ca content, low cost, availability, and high CO₂ uptake. This work investigates a novel heat-pre-treatment using eggshells as raw material. The eggshells were simultaneously calcined and thermally pre-treated via microwave heating using different powers and times whilst maintaining the same input energy in a single mode cavity reactor. The calcined eggshells were characterised using standard characterisation techniques such as TGA and isotherms of N₂ adsorption at 77 K. The dielectric properties were measured using the cavity perturbation technique at 2.45 GHz. Numerical electromagnetic simulations were performed using COMSOL Multiphysics and results were used to optimise the experimental setup. The treated materials were subjected to carbonation/calcination cycles in order to assess their suitability as a calcium-looping sorbent. The sorbent that exhibited a more stable CO₂ uptake was the one treated at the highest power (800 W) 4.5 mmol CO₂/g sorbent after 20 cycles under mild calcination conditions. Adsorbents prepared at 400, 600 and 800 W displayed similar CO₂ uptake after 20 cycles when the calcination conditions were under more realistic conditions.

Due to the depletion of river sand, the construction industry is eager to develop upcycling techniques for transforming secondary by-products derived from construction and demolition (C&D) waste into quality fine aggregates. This paper presents a study of replacing river sand with enhanced recycled fine aggregate through a wet carbonation process developed by the authors previously. The fine recycled concrete aggregate (FRCA) ranging from 0.15 to 5 mm was prepared by demolishing a concrete with a known mixture design. After wet carbonation, the particle size, water absorption, and density of the FRCA were tested and compared with the original samples. The chemical characteristics of the original and carbonated FRCA (C-FRCA) were analyzed by a series of experiments. The results showed that (1) an increase of carbonation products and a significant reduction of hydration products; (2) microscopic observation of the C-FRCA showed a surface layer densified by calcite after wet carbonation; and (3) no significant strength loss were observed when replacing up to 50% river sand by C-FRCA in mortar specimens. The potential environmental and economic impacts were also analyzed.

The release of carbon dioxide (CO₂) into the earth's atmosphere is a substantial global environmental concern that arises from the processes of industrialization and urbanization. The increase in atmospheric CO₂ concentrations has resulted in the phenomenon of global warming and subsequent alterations in climate patterns. Accelerated CO₂ sequestration in cementitious materials is currently the subject of extensive research as a highly efficacious approach to mitigating the carbon footprint of the concrete industry. The sequestration procedure entails the transformation of gaseous CO₂ into carbonate minerals. The review presented in this paper outlines the most recent carbonation (i.e., CO₂ sequestration) techniques, such as mineral carbonation, accelerated CO₂ curing (ACC), pre-carbonation, and carbonation mixing, that have been recently explored. The potential of mineral carbonation of industrial wastes and the advantages of their incorporation in the concrete matrix is investigated. Carbonation technologies and their effect on the performance of cementitious composites are reported. Information on life cycle assessment are also included to evaluate the environmental impact associated with the production of carbonated materials. Various commercialized CO₂ utilization technologies in construction sector, such as CarbonCure, Solidia, Carbstone, Calera, and Carbon8 are reviewed. Moreover, this review offers a thorough insight into the carbonation technologies, evaluating their advantages, limitations, and the existing gaps in research.

MIL-101(Cr), a class of metal-organic framework, is a potential candidate for CO₂ capture applications because of its high capacity of adsorption and separation capability. However, the intrinsic microporous structure of this nanomaterial poses limitations on its adsorption kinetics. Techniques employed to enhance its adsorption kinetics often adversely impact its adsorption capacity at equilibrium. Herein, as a new approach, we prepared amine-functionalized FAC@MIL-101(Cr) composites with adjustable micro-mesoporous structure and tunable nitrogen content by embedding different ratios of amine-functionalized activated carbon throughout the framework of MIL-101(Cr). This led to a simultaneous improvement in both kinetics and adsorption capacity for CO₂. The best adsorbent, FAC-6@MIL-101(Cr), has excellent textural properties with a high surface area (1763.1 m².g⁻¹), great pore volume (1.29 cm³.g⁻¹), and suitable nitrogen content (4.7 wt%). The adsorption analysis revealed that the modification of MIL-101(Cr) improved its CO₂ adsorption capacity from 3.21 to 5.27 mmol/g under standard conditions of 1 bar and 25 °C. Furthermore, the FAC-6@MIL-101(Cr) adsorbent demonstrated fast CO₂ adsorption kinetics (three times more relative to the pure MIL-101(Cr)), high CO₂/N₂ selectivity, and remarkable cyclic stability. The results confirmed that hybridization enhanced the polarizability of FAC@MIL-101(Cr) samples, causing more robust CO₂-adsorbent surface interactions. Simultaneously, the existence of mesopores in the structure facilitated the transport of CO₂ into the interior pores, resulting in a more efficient contact of CO₂ molecules with all of the amine sites and a faster adsorption rate as well as more efficient regeneration. According to density functional theory (DFT) calculations, hybridization process induces significant changes in composites’ electronic structure, enhancing their capacity to interact with CO₂ molecules more effectively. On the other hand, DFT calculations confirm that N₂ molecule is less activated on the FAC@MIL-101(Cr) as evidenced by calculated small adsorption energy and charge-transfer values.

Formate dehydrogenases catalyze the reversible oxidation of formate to carbon dioxide. These enzymes play an important role in CO₂ reduction and serve as nicotinamide cofactor recycling enzymes. More recently, the CO₂-reducing activity of formate dehydrogenases, especially metal-containing formate dehydrogenases, has been further explored for efficient atmospheric CO₂ capture. In this sense, molecular hydrogen (H₂) as the fuel of the future represents an efficient, cheap and environmentally friendly reducing agent when produced from renewable sources. Hydrogenases are enzymes that catalyze the reversible oxidation of H₂. Herein, the functional interplay between the soluble [NiFe] hydrogenase from Cupriavidus necator and the molybdenum-dependent formate dehydrogenase from Rhodobacter capsulatus was investigated in a coupled biocatalytic system. H₂-driven CO₂ reduction (H₂CO₂R) using methyl viologen as an artificial electron mediator gave a higher product yield of formate than using NAD⁺ as the physiological electron mediator. The enzymes were stable under anaerobic conditions for 18 h, making the coupled reaction suitable for biotechnological purposes.

In this study, synthetic CaCO₃ materials were utilized as precursors for CaO-based CO₂ sorbents. The investigation examined how various operating parameters—such as synthesis temperature (ST), stirring rate (SR), and surfactant percentage (SP)—impact the properties of the adsorbents. Samples were firstly characterized by X-ray diffraction and Scanning Electron Microscopy (SEM), which revealed that the prevalence of calcite or aragonite crystal phases in the synthetic CaCO₃ precursors can be tuned by adequately choosing the dose of surfactant (Triton-X100®), so that it can be used as a crystal habit and growth modifier. The calcination process applied to the CaCO₃ precursors leads to the formation of partially sinterized cubic crystals of CaO, accompanied by minor quantities (< 5 %) of additional compounds like Ca(OH)₂ or CaSO₄. Specific surface area (S_BET) and porosity were determined by measuring the N₂ adsorption isotherms. A CaCO₃ sample with an unprecedented value of S_BET as large as 116 m²/g was prepared operating under optimal conditions. S_BET and pore volumes were successfully correlated with the CO₂ uptake capacity of the samples. S_BET is more influential for experiments carried out under diluted CO₂ atmosphere. When pure CO₂ is used, the influence of meso- and micropore volumes (V_me and V_mi) is clearly predominant, which suggests that in this latter case diffusion through the porous texture of the samples plays a more remarkable role. A double-way approach through Response Surface Methodology (RSM) and the use of Artificial Neural Networks (ANNs) has been used to analyze the CO₂ uptake capacity of the samples. Within the operational interval, excellent results were obtained for pure and diluted CO₂ flow, and RSM and ANNs have demonstrated to be a very efficient tool to correlate the behavior of the CaO-based materials as CO₂ sorbents with the surface area and pore volumes of the samples. Valuable information on (i) the importance of the different factors under study; (ii) their influence on the surface and porosity of the CaO-derived sorbents; and (iii) the subsequent CO₂ capture performance of the sorbents has been obtained. The results suggest that four parameters have a statistically significant influence on CO₂ uptake. These parameters are SR, the square of SR, its interaction with SP, and the square of SP. Additionally, the study assessed the stability of the CaO-based sorbents over 11 consecutive calcination-carbonation cycles. By adequately choosing the synthesis strategy and conditions, an almost negligible shrinkage effect can be achieved, resulting in a more sustained uptake capacity throughout the cycles.

In this manuscript, we describe the synthesis of low molar mass polycarbonate diols by acid cleavage of labile acetal linkages included in high molar mass poly(ether-co-carbonate-co-acetal) terpolymers. These copolymers were prepared by terpolymerization of propylene oxide (PO) with o-phthalaldehyde (OPA) and carbon dioxide (CO₂), using triethyl borane (TEB) as activator and an onium salt as initiator. The advantage of this strategy of synthesis of poly(propylene carbonate) diols (PPC-diols) lies in the minute amounts of TEB and initiator required. Moreover, OPA could be isolated through post-hydrolysis of the terpolymers and recycled for subsequent use. We also demonstrated that this strategy works for the synthesis of low molar mass poly(ethylene carbonate) diols (PEC-diols). The structural integrity of the terpolymers before and after acid treatment, the characterization of low molar mass PPC-diols, and recycling process of OPA were carried out by ¹H NMR spectroscopy, gel permeation chromatography, and matrix-assisted laser desorption ionization time of flight (MALDI-TOF) MS.

The imperative to mitigate industrial CO₂ emissions amidst global climate change has led to the development of innovative strategies that align economic growth with environmental sustainability. This study introduces a comprehensive CO₂ allocation and utilisation framework, designed to reduce the environmental impact on the production of Liquefied Natural Gas (LNG). Demploying a multi-objective Linear Programming (LP) approach, the study introduces a system that dynamically allocates CO₂ from a major source to several sinks, each with unique characteristics and requirements. Focusing on the State of Qatar, a major player in the global LNG market, advanced simulation tools, such as Aspen HYSYS and QASR Simulator are utilised to define the parameters of these sinks, ensuring precise and efficient CO₂ allocation. An integral component of the model is the incorporation of a carbon tax, considered for both the source and the sinks. The results demonstrate that the profit maximisation objective generated a $23.6 billion annual profit, although with high emissions of 23.37 Mt/year. In contrast, the emission minimisation objective curbed emissions to 19.01 Mt/year at a profit of $1.4 billion. The multi-objective approach garnered $18.6 billion annually with emissions at 22.37 Mt/year. The CO₂/LNG metric was used to gauge LNG's environmental footprint. Objective 1 yielded a ratio of 0.3033, while objective 2 achieved the best score at 0.2463. The multi-objective approach balanced both, with a ratio of 0.2905. These findings illuminate the feasibility of optimising industrial practices for producing low-carbon LNG through deliberate CO₂ allocation and within a circular economy framework.

This investigation delineates the enhancement of fly ash (FA) properties through mechanical treatments for sustainable construction applications and reducing carbon dioxide (CO₂) emissions. FA, a byproduct of coal combustion in power generation, inherently exhibits limited pozzolanic activity. This research evaluates the impact of particle size reduction via dry and wet milling treatments on FA's pozzolanic behavior. The study's comparative analysis involves three FA variants: untreated raw material, dry-milled, and wet-milled FA. Extensive characterization encompassed chemical composition, physical properties, and microstructural features. Results demonstrate a marked improvement in pozzolanic activity in milled FAs, with wet milling yielding superior outcomes in particle size reduction (98% diminution compared to raw FA) and pozzolanic reactivity. The comparative assessment underscores wet milling's efficacy over dry milling and untreated FA in enhancing FA's performance as a sustainable construction material. In light of these findings, the study advocates for continued exploration of FA treatments, aiming to optimize their utility in eco-friendly construction practices.

The CO₂ in thermal power plant and factory exhaust gases and the air must be addressed because all have low-concentration CO₂. However, applying low-concentration CO₂ to developed reactions that use high-purity CO₂, energy- and cost-intensive pretreatments, such as CO₂ purification, concentration, and compression, are required. Thus, a technology that directly converts low-concentration CO₂ into useful chemicals without these pretreatment processes is attractive for energy saving and cost reduction. Such technology has been achieved in the fields of methane and methanol synthesis via the hydrogen reduction of CO₂. Recently, the concept of directly using low-concentration CO₂ has been applied to the synthesis of high value-added chemicals without hydrogen reduction. The synthesis of useful chemicals from CO₂ without hydrogen reduction is a technology that will be put into practical use without waiting for the widespread use of green hydrogen. Thus, this review introduces the technology for the direct synthesis of useful chemicals, such as dialkyl carbonates (DRCs), carbamic acid esters (CAEs), and urea derivatives from low-concentration CO₂ contained in exhaust gas or air, without hydrogen reduction. DRCs, CAEs, and urea derivatives are synthesized via the non-hydrogen reduction route of CO₂. They are expected to contribute to long-term, large-volume CO₂ fixation because they are raw materials of functional polymers, which have long-material-life and large market potential. Details on how to synthesize these compounds directly from low-concentration CO₂ are presented, focusing on the efforts to devise CO₂ capture processes, reactants, and catalysts.