Simultaneous CO2 absorption, mineralisation and carbonate crystallisation promoted by amines in a single process

Amine-Assisted Simultaneous CO2 Absorption and Mineral Carbonation: Effect of Different Categories of Amines

The hybrid technology of CO₂ capture-mineral carbonation (CCMC) using alkaline streams has emerged in recent years. However, thus far, there has been no comprehensive study revealing the mechanisms of the simultaneous CCMC process regarding the choice of amine types and sensitivity of parameters. Combining with the analysis of multistep reaction mechanisms for different amines, we investigated a representative from each category in CCMC using calcium chloride to simulate the alkaline resource after leaching, i.e., primary (ethanolamine, MEA), secondary (diisopropanolamine, DIPA), tertiary (diethylethanolamine, DEAE), and triamine (diethylenetriamine, DETA), respectively. In the adsorption step, increasing the amine concentration beyond 2 mol/L reduced the absorption efficiency of DEAE due to the hydration mechanism, motivating a rational choice of concentration. In CCMC sections, when the amine concentration increased, only DEAE exhibited an increased carbonation efficiency of up to 100%, while DETA showed the lowest conversion. The carbonation of DEAE demonstrated the least sensitivity to temperature. The crystal transformation experiments suggested that over time, the produced vaterite could completely transform to calcite or aragonite, except those from DETA. Thus, with rationally chosen conditions, DEAE was demonstrated ideal for CCMC. These findings obtained in this work provided a theoretical foundation for designing future CCMC processes.

Removal of CO2 from Biogas during Mineral Carbonation with Waste Materials

Biogas represents a source of renewable energy that could provide a replacement for fossil fuels to meet the increasing demand for energy. The upgrading of biogas through the removal of CO₂ to a content of 95-97% of CH₄ is necessary to increase its calorific value. This review focuses on biogas upgrading technologies using wastes or residues that enable the performing of mineral carbonation. In this research, we analyzed a natural biogas or synthetic one with a content of about (40-50%) of carbon dioxide. The chemical absorption is also briefly described in this study, due to its being the first step in innovative absorption and regeneration processes using mineral carbonization. Wastes with high calcium contents, i.e., ashes, steel-making slags, and stabilized wastewater anaerobic sludge, were considered for direct carbonization, taking into account the leaching of particles from carbonated wastes/residues. Moreover, the different types of reactors used for mineral carbonation have been described. The presented technological solutions are easy to use and economical, and some of them also take into account the regeneration of reagents. However, in the context of their direct use in biogas plants, it is necessary to consider the availability of wastes and residues.

Confinement induces stable calcium carbonate formation in silica nanopores

Scalable efforts to remove anthropogenic CO₂via the formation of durable carbonates require us to harness siliceous nanoporous geologic materials for carbon storage. While calcium carbonate formation has been extensively reported in bulk fluids, there is a limited understanding of the influence of nanoconfined fluids on the formation of specific stable and metastable polymorphs of calcium carbonates in siliceous materials that are abundant in subsurface environments. To address this challenge, silica nanochannels with diameters of 3.7 nm are architected and the formation of specific calcium carbonate phases is investigated using X-ray diffraction (XRD), and molecular dynamics (MD) simulations. The formation of stable calcium carbonate (or calcite) is noted in silica nanochannels. The presence of fewer water molecules in the first hydration shell of calcium ions in confinement compared to in bulk fluids contributes to stable calcium carbonate formation. These studies show that nanoporous siliceous environments favor the formation of stable calcium carbonate formation.