Enhancement of CO2 capture capacity by modifying limestone with propionic acid

Ca-based materials derived from calcined cigarette butts for CO2 capture and thermochemical energy storage

Cigarette butts (CBs) are one of the most common types of litter in the world. Due to the toxic substances they contain, the waste generated poses a harmful risk to the environment, and therefore there is an urgent need for alternative solutions to landfill storage. Thus, this work presents a possible revalorization of this waste material, which implies interesting environmental benefits. CBs were used as sacrificial templates for the preparation of CaO-based materials by impregnation with calcium and magnesium nitrates followed by flaming combustion. These materials presented enhanced porosity for their use in the Calcium Looping process applied either to thermochemical energy storage or CO2 capture applications. The influence of the concentration of Ca and Mg in the impregnating solutions on the multicycle reactivity of the samples was studied. An improved multicycle performance was obtained in terms of conversion for both applications.

Review on the modifications of natural and industrial waste CaO based sorbent of calcium looping with enhanced CO2 capture capacity

The calcium looping cycle (CaL) possesses outstanding CO2 capture capacity for future carbon-capturing technologies that utilise CaO sorbents to capture the CO2 in a looping cycle. However, sorbent degradation and the presence of inert materials stabilise the sorbent, thereby reducing the CO2 capture capacity. Consequently, the CaO sorbent that has degraded must be replenished, increasing the operational cost for industrial use. CaO sorbents have been modified to enhance their CO2 capture capacity and stability. However, various CaO sorbents, including limestone, dolomite, biogenesis calcium waste and industrial waste, exhibit distinct behaviour in response to these modifications. Thus, this work comprehensively reviews the CO2 capture capacity of sorbent improvement based on various CaO sorbents. Furthermore, this study provides an understanding of the effects of CO2 capture capacity based on the properties of the CaO sorbent. The properties of various CaO sorbents, such as surface area, pore volume, particle size and morphology, are influential in exhibiting high CO2 capture capacity. This review provides insights into the future development of CaL technology, particularly for carbon-capturing technologies that focus on the modifications of CaO sorbents and the properties that affect the CO2 capture capacity.

Modified Natural Dolomite and Its Influence on the Production of Glycerol Carbonate: Effects of Structural and Basicity Properties

A systematic study over different treatment conditions, including hydrothermal and acid-thermal, was successfully carried out to determine the most suitable conditions to enhance the textural properties and surface chemical composition of natural dolomite. The reconstruction of dolomite after various treatments enhanced the surface area by 4–5 times and diminished the pore diameter between 70% and 81% compared to the untreated parent dolomite. The Rietveld analysis of the X-ray diffraction (XRD) patterns revealed changes in the crystalline compositions after each treatment. When the treated dolomite was used as a catalyst to produce glycerol carbonate via a transesterification reaction of glycerol and dimethyl carbonate, the crystalline Ca(OH)₂ concentration of the modified dolomite and the apparent glycerol carbonate formation rate (r_gc) are well-correlated. The results suggest that an increase of the crystalline Ca(OH)₂ concentration could be related with surface basicity at the weak and moderate strength sites that may lead to an increase in catalytic activity. The hydrothermal treated dolomite showed a selectivity of glycerol carbonate greater than 99% and r_gc value 3.42 mmol/min·g_cat, which was higher than that achieved on other samples. This study could aid to the proper selection of dolomite treatment for the desired crystalline composition, depending on the applications of this highly available mineral.

Geochemical and mineralogical assessment of sedimentary limestone mine waste and potential for mineral carbonation

This paper attempts to evaluate the mineralogical and chemical composition of sedimentary limestone mine waste alongside its mineral carbonation potential. The limestone mine wastes were recovered as the waste materials after mining and crushing processes and were analyzed for mineral, major and trace metal elements. The major mineral composition discovered was calcite (CaCO₃) and dolomite [CaMg(CO₃)₂], alongside other minerals such as bustamite [(Ca,Mn)SiO₃] and akermanite (Ca₂MgSi₂O₇). Calcium oxide constituted the greatest composition of major oxide components of between 72 and 82%. The presence of CaO facilitated the transformation of carbon dioxide into carbonate form, suggesting potential mineral carbonation of the mine waste material. Geochemical assessment indicated that mean metal(loid) concentrations were found in the order of Al > Fe > Sr > Pb > Mn > Zn > As > Cd > Cu > Ni > Cr > Co in which Cd, Pb and As exceeded some regulatory guideline values. Ecological risk assessment demonstrated that the mine wastes were majorly influenced by Cd as being classified having moderate risk. Geochemical indices depicted that Cd was moderately accumulated and highly enriched in some of the mine waste deposited areas. In conclusion, the limestone mine waste material has the potential for sequestering CO₂; however, the presence of some trace metals could be another important aspect that needs to be considered. Therefore, it has been shown that limestone mine waste can be regarded as a valuable feedstock for mineral carbonation process. Despite this, the presence of metal(loid) elements should be of another concern to minimize potential ecological implication due to recovery of this waste material.

Effect of Sodium Bromide on CaO-Based Sorbents Derived from Three Kinds of Sources for CO2 Capture

The calcium looping (CaL), which applies carbonation/calcination cyclic reactions of a CaO sorbent, has received extensive attention for postcombustion CO₂ capture. However, as the number of cyclic reactions increased, the capture efficiency of regenerated CaO decreased rapidly. Sodium doping was proposed for modification of a CaO sorbent, but there was little research on whether sodium doping had a good effect on different kinds of sorbents. In this paper, three different kinds of calcium-based sorbents, i.e., CaCO₃, dolomite, and SG-CaO, were modified by NaBr to explore the effect of sodium on CO₂ capture performance. The results showed that the modification effects of sodium on three kinds of precursors were different. For CaCO₃, the modification effect of sodium doping was the best. After 50 cycles, the sorption capacity of CaO/NaBr was over 3.5 times that of an unmodified sorbent; for dolomite, sodium had a moderate effect during initial cycles and then showed obvious improvement in the stability of the sorbent, the sorption capacity of the modified dolomite increased by over 30% after 50 cycles; for the SG-CaO, sodium had a negative effect, the sorption capacity of the modified sorbent decreased by about 30% after 50 cycles. When the atmosphere contained SO₂, the doping of an alkali metal also showed a certain effect.

Mineral carbonation of sedimentary mine waste for carbon sequestration and potential reutilization as cementitious material

This study highlights the importance of mineralogical composition for potential carbon dioxide (CO₂) capture and storage of mine waste materials. In particular, this study attempts to evaluate the role of mineral carbonation of sedimentary mine waste and their potential reutilization as supplementary cementitious material (SCM). Limestone and gold mine wastes were recovered from mine processing sites for their use as SCM in brick-making and for evaluation of potential carbon sequestration. Dominant minerals in the limestone mine waste were calcite and akermanite (calcium silicate) while the gold mine waste was dominated by illite (iron silicate) and chlorite-serpentine (magnesium silicate). Calcium oxide, CaO and silica, SiO₂, were the highest composition in the limestone and gold mine waste, respectively, with maximum CO₂ storage of between 7.17 and 61.37%. Greater potential for CO₂ capture was observed for limestone mine waste as due to higher CaO content alongside magnesium oxide. Mineral carbonation of the limestone mine waste was accelerated at smaller particle size of < 38 μm and at pH 10 as reflected by the greater carbonation efficiency. Reutilization of limestone mine waste as SCM in brick-making exhibited greater compressive strength and lower water absorption compared to the bricks made of gold mine waste. The gold mine waste is characterized as having high pozzolanic behaviour, resulting in lower carbonation potential. Therefore, it has been noticeable that limestone mine waste is a suitable feedstock for mineral carbonation process and could be reutilized as supplementary cementitious material for cement-based product. This would be beneficial in light of environmental conservation of mine waste materials and in support of sustainable use of resources for engineering construction purposes.

Inorganic carbonate composites as potential high temperature CO2 sorbents with enhanced cycle stability

A calcium magnesium carbonate composite (CMC) material containing highly porous amorphous calcium carbonate (HPACC) and mesoporous magnesium carbonate (MMC) was synthesized. CMCs with varying HPACC : MMC mol ratios and high BET surface area (over 490 m² g⁻¹) were produced. The CMCs retained the morphology shared by HPACC and MMC. All these materials were built up of aggregated nanometer-sized particles. We tested the CO₂ uptake properties of the synthesized materials. The CMCs were calcined at 850 °C to obtain the corresponding calcium magnesium oxide composites (CMOs) that contained CaO : MgO at different mol ratios. CMO with CaO : MgO = 3 : 1 (CMO-3) showed comparable CO₂ uptake at 650 °C (0.586 g g⁻¹) to CaO sorbents obtained from pure HPACC (0.658 g g⁻¹) and the commercial CaCO₃ (0.562 g g⁻¹). Over 23 adsorption–desorption cycles CMOs also showed a lower CO₂ uptake capacity loss (35.7%) than CaO from HPACC (51.3%) and commercial CaCO₃ (79.7%). Al was introduced to CMO by the addition of Al(NO₃)₃ in the synthesis of CMC-3 to give ACMO after calcination. The presence of ∼19 mol% of Al(NO₃)₃ in ACMO-4 significantly enhanced its stability over 23 cycles (capacity loss of 5.2%) when compared with CMO-3 (calcined CMC-3) without adversely affecting the CO₂ uptake. After 100 cycles, ACMO-4 still had a CO₂ uptake of 0.219 g g⁻¹. Scanning electron microscope images clearly showed that the presence of Mg and Al in CMO hindered the sintering of CaCO₃ at high temperatures and therefore, enhanced the cycle stability of the CMO sorbents. We tested the CO₂ uptake properties of CMO and ACMO only under ideal laboratory testing environment, but our results indicated that these materials can be further optimized as good CO₂ sorbents for various applications.

A Ca/Mg/Al oxide composite was synthesised and showed a high CO₂ uptake of 0.537 g g⁻¹ at 650 °C with high uptake even after 100 cycles.

CaO-based sorbent derived from lime mud and bauxite tailings for cyclic CO2 capture

Using aluminum nitrate (AlN) and bauxite tailings (BTs) as different dopants, and lime mud (LM) as calcium source, a series of CaO-based sorbents were prepared for CO₂ capture by dry mixing method; then, the carbonation conversions of multiple carbonation/calcination cycles were detected in a thermogravimetric analyzer (TGA). Effects of different dopants, dopant contents, precalcination conditions, and a long series of cycles on CO₂ absorption properties were scrutinized, and the phase composition and morphologies were tested by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Durability studies show that the sample doped with AlN remains a higher absorption conversion (30.88%) after 30 carbonation/calcination cycles. In the meantime, the sorbent doped with BTs showed a lower conversion, which is probably resulted from the impurities from waste BTs. However, the sample BT has a better cyclic absorption stability. In addition, the incorporation of BTs, as a kind of solid waste, not only decreases the preparation cost but also is good for environment. The occurrence of Ca₁₂Al₁₄O₃₃ phase is considered to provide a stable framework inhibiting inactivation of CaO, and improve the CO₂ adsorption stability. Graphical abstract ᅟ.

Characteristics and performance of CaO-based high temperature CO2 sorbents derived from a sol–gel process with different supports

10 CaO-based sorbents were synthesized by a sol–gel process supported with various materials, and their cyclic behavior was investigated under the same reaction conditions.

Porous spherical CaO-based sorbents via PSS-assisted fast precipitation for CO2 capture

In this paper, we report the development of synthetic CaO-based sorbents via a fast precipitation method with the assistance of sodium poly(styrenesulfonate) (PSS). The effect of PSS on physical properties of the CaO sorbents and their CO2 capture performance were investigated. The presence of PSS dispersed the CaO particles effectively as well as increased their specific surface area and pore volume remarkably. The obtained porous spherical structure facilitated CO2 to diffuse and react with inner CaO effectively, resulting in a significant improvement in initial CO2 carbonation capacity. A proper amount of Mg(2+) precursor solution was doped during a fast precipitation process to gain CaO-based sorbents with a high anti-sintering property, which maintained the porous spherical structure with the high specific surface area. CaO-based sorbents derived from a MgxCa1-xCO3 precursor existed in the form of CaO and MgO. The homogeneous distribution of MgO in the CaO-based sorbents effectively prevented the CaO crystallite from growing and sintering, further resulting in the favorable long-term durability with carbonation capacity of about 52.0% after 30 carbonation/calcination cycles.