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.

Sorption-enhanced gasification of municipal solid waste for hydrogen production: a comparative techno-economic analysis using limestone, dolomite and doped limestone

Sorption-enhanced gasification has been shown as a viable low-carbon alternative to conventional gasification, as it enables simultaneous gasification with in-situ CO2 capture to enhance the production of H2. CaO-based sorbents have been a preferred choice due to their low cost and wide availability. This work assessed the technical and economic viability of sorption-enhanced gasification using natural limestone, doped limestone with seawater and dolomite. The techno-economic performance of the sorption-enhanced gasification using different sorbents was compared with that of conventional gasification. Regarding the thermodynamic performance, dolomite presented the worst performance (46.0% of H2 production efficiency), whereas doped limestone presented the highest H2 production efficiency (50.0%). The use of dolomite also resulted in the highest levelised cost of hydrogen (5.4 €/kg against 5.0 €/kg when limestone is used as sorbent), which translates into a CO2 avoided cost ranging between 114.9 €/tCO2 (natural limestone) and 130.4 €/tCO2 (dolomite). Although doped limestone has shown a CO2 avoided cost of 117.7 €/tCO2, this can be reduced if the production cost of doped limestone is lower than 42.6 €/t. The production costs of new sorbents for CO2 capture and H2 production need to be similar to that of natural limestone to become an attractive alternative to natural limestone.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-02926-y.

CaO recovered from eggshell waste as a potential adsorbent for greenhouse gas CO2

The growing number of industrial carbon emissions have resulted in a significant increase in the greenhouse gas carbon dioxide (CO₂), which, in turn, will have a major impact on climate change. Therefore, the reduction, storage, and reuse of CO₂ is an important concern in modern society. Calcium oxide (CaO) is known to be an excellent adsorbent of CO₂ in a high-temperature environment. However, since deterioration of the adsorbent is likely to occur after repeated cycles of adsorption under high temperature conditions, it would be desirable to mitigate this phenomenon, in order to maintain the stability of CaO. In the present study, common eggshell waste was used as the starting material. The main component of eggshell waste is calcium carbonate (CaCO₃), which was purified to produce CaO. Different surfactants and amino-containing polymers were added to synthesize CaO-based adsorbents with different configurations and pore sizes. The amount of CO₂ adsorbed was determined using a thermogravimetric analyzer (TGA). The results showed that the CO₂ adsorption capacity of the synthetic CaO recovered from purified eggshell waste could reach 0.6 g-CO₂/g-sorbent, indicating a good adsorption capacity. CaO modified with a dopamine-containing polymer was shown to have an adsorption capacity of 0.62 g-CO₂/g-sorbent. Moreover, it showed an excellent adsorption capacity of 0.40 g-CO₂/g-sorbent, even after 10 cycles of CO₂ adsorption. The present study suggests that using eggshell waste to synthesize CaO-based adsorbents for effective CO₂ adsorption can not only reduce environmental waste, but also have the potential to capture greenhouse gas CO₂ emissions, which conforms to the principles of green chemistry.

CO2 Capture at Medium to High Temperature Using Solid Oxide-Based Sorbents: Fundamental Aspects, Mechanistic Insights, and Recent Advances

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO₂ emissions. Solid materials capable of reversibly absorbing CO₂ have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO₂ sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO₂ absorption both at surfaces and within solid materials.

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.

Investigation of Pore-Formers to Modify Extrusion-Spheronized CaO-Based Pellets for CO2 Capture

The application of circulating fluidized bed technology in calcium looping (CaL) requires that CaO-based sorbents should be manufactured in the form of spherical pellets. However, the pelletization of powdered sorbents is always hampered by the problem that the mechanical strength of sorbents is improved at the cost of loss in CO2 sorption performance. To promote both the CO2 sorption and anti-attrition performance, in this work, four kinds of pore-forming materials were screened and utilized to prepare sorbent pellets via the extrusion-spheronization process. In addition, impacts of the additional content of pore-forming material and their particle sizes were also investigated comprehensively. It was found that the addition of 5 wt.% polyethylene possesses the highest CO2 capture capacity (0.155 g-CO2/g-sorbent in the 25th cycle) and mechanical performance of 4.0 N after high-temperature calcination, which were about 14% higher and 25% improved, compared to pure calcium hydrate pellets. The smaller particle size of pore-forming material was observed to lead to a better performance in CO2 sorption, while for mechanical performance, there was an optimal size for the pore-former used.

CaCO3–Polymer Nanocomposite Prepared with Supercritical CO2

A novel process for generation of a CaCO3–polymer nanocomposite with a controlled three-dimensional shape was developed. Specifically, a nanocomposite with a high CaCO3 content was produced by introducing supercritical CO2 into a polymer matrix containing Ca ions. A mixture of poly(vinyl alcohol), Ca acetate, and poly(acrylic acid) was poured into a mold, the mold was placed in an autoclave, and CO2 was introduced to precipitate CaCO3 within the polymer matrix. Laser Raman spectroscopy and transmission electron microscopy showed that this process produced a nanocomposite containing highly dispersed CaCO3 (aragonite) nanoparticles. The flexural strength of the nanocomposite was larger than the flexural strengths of limestone and CaCO3 produced by hydrothermal hot pressing. The use of supercritical CO2 facilitated CO2 dissolution, which resulted in rapid precipitation of CaCO3 in the polymer matrix. The above-described process has potential utility for fixation of CO2.