A Model to Stabilize CO2 Uptake Capacity during Carbonation-Calcination Cycles and its Case of CaO-MgO

Advanced High-Temperature CO2 Sorbents with Improved Long-Term Cycling Stability

Developing novel sorbents with maximum carbonation efficiency and good cycling stability for CO₂ capture is a promising route to sequester anthropogenic CO₂. In this work, we have employed a green synthesis method to synthesize CaO-based sorbents suitably stabilized by MgO and supported by in situ generated carbon under inert atmosphere. The varied amounts (10-30 wt %) of MgO were used to stabilize the CaO. The supported mixed metal oxide (MMO) sorbents were screened for high-temperature CO₂ capture under CO₂ rich (86% CO₂) and lean (14% CO₂) gas streams at 650 °C and atmospheric pressure. The MMO sorbents captured 53-63 wt % of CO₂ per gram of sorbent under 86 and 14% CO₂, accounting for about 98% carbonation efficiency, which outperforms the CO₂ capture capacity of limestone derived CaO (L-CaO) sorbents (22.8 wt %). All of the synthetic MMO sorbents showed greater capture capacity and cyclic stability when compared to benchmark L-CaO. Because of the high carbonation efficiency and cycling stability of g-Ca_0.69Mg_0.3O sorbent, it was tested for 100 carbonation/regeneration cycles of 5 min each under CO₂ lean conditions. The g-Ca_0.69Mg_0.3O sorbent showed exceptional CO₂ capture capacity and cycling stability and retained about 65% of its initial capture capacity after 100 cycles.

Constructing Hierarchical Porous Carbons With Interconnected Micro-mesopores for Enhanced CO2 Adsorption

A high cost-performance carbon dioxide sorbent based on hierarchical porous carbons (HPCs) was easily prepared by carbonization of raw sugar using commercially available nano-CaCO3 as a double-acting template. The effects of the initial composition and carbonization temperature on the micro-mesoporous structure and adsorption performance were examined. Also, the importance of post-activation behavior in the development of micropores and synthesis route for the formation of the interconnected micro-mesoporous structure were investigated. The results revealed excellent carbon dioxide uptake reaching up 2.84 mmol/g (25oC, 1 bar), with micropore surface area of 786 m2/g, micropore volume of 0.320 cm3/g and mesopore volume of 0.233 cm3/g. We found that high carbon dioxide uptake was ascribed to the developed micropores and interconnected micro-mesoporous structure. As an expectation, the optimized HPCs offers a promising new support for the high selective capture of carbon dioxide in the future.

Acquiring an effective CaO-based CO2 sorbent and achieving selective methanation of CO2

CO₂ capture, utilization, and storage are promising strategies to solving the problems of superfluous CO₂ or energy shortage. Here, mechanochemical reduction of CO₂ by a MgH₂/CaH₂ mixture was first performed, by which we achieve selective methanation of CO₂ and acquire an effective CaO-based CO₂ sorbent, simultaneously. The selectivity of methanation is near 100% and the yield of CH₄ reaches 30%. Four MgO and carbon-doped CaO-based CO₂ sorbents (MgO/CaO/C, MgO/2CaO/C, MgO/4CaO/C, and MgO/8CaO/C) were formed as solid products in these reactions. Among them, the MgO/4CaO/C sorbent shows high initial adsorption amount of 59.3 wt% and low average activity loss of 1.6% after 30 cycles. This work provides a novel, well-scalable, and sustainable approach to prepare an efficient inert additive-including CaO-based CO₂ sorbent and selectively convert CO₂ to CH₄ at the same time.

We achieve selective methanation of CO₂ and acquire an effective CaO-based CO₂ sorbent by reduction of CO₂ with a MgH₂/CaH₂ mixture.

Nano-TiO2 promoted CaO-based high-temperature CO2 sorbent: influence of crystal level properties on the CO2 sorption efficiency

This work investigates the multi-cycle CO₂ sorption and the kinetics of the carbonation reaction of nano-TiO₂ promoted CaO synthesized from commercially available micron sized CaCO₃.

Structure Property-CO2 Capture Performance Relations of Amine-Functionalized Porous Silica Composite Adsorbents

In order to investigate the influence of support structure properties on CO₂ capture performances of solid amine adsorbents, a novel three-dimensional disordered porous silica (3dd) with hierarchical pore networks was developed and then compared to other three materials as adsorbent support, namely, hierarchical porous silica (HPS), MCM-41, and SBA-15. They were all functionalized with tetraethylenepentaamine (TEPA) to prepare CO₂ adsorbents. The adsorbents' ability to capture CO₂ was examined on a fixed-bed reactor. When these supports had 60 wt% TEPA loading, the amounts of CO₂ captured followed the order 3dd > HPS > SBA-15 > MCM-41 at 75 °C; the adsorption capacities were 5.09, 4.9, 4.58, and 2.49 mmol/g, respectively. The results indicate that a larger pore volume can promote the dispersion of amine species to expose more active sites for CO₂ capture. The larger pore size can decrease the CO₂ diffusion resistance. High surface area is not an important factor in determining capture performance. In addition, compared with conventional single-size mesopores, the hierarchical pore networks can disperse the TEPA species in different levels of the channel to limit undesired loss/aggregation of impregnated TEPA species. Thus, the 3dd support exhibits the best stability and highest regeneration conversion compared to the other three supports. This work demonstrates that the rational design of adsorbent support systems can effectively relieve the trade-off between amine loading and diffusion resistance. One method to surmount this trade-off is to utilize an adsorbent platform with hierarchical pore networks. Thus, this work may provide a feasible strategy for the design of CO₂ solid amine adsorbents with high capture amount and amine utilization efficiency.