Four diverse microstructured MgO-stabilized CaO sorbents with varying mixing characteristics of Ca and Mg were obtained from untreated, hydrated, precipitated, and milled dolomite. Different morphological characterizations (thermal decomposition, phase composition, morphology, and nitrogen adsorption) were performed, followed by an analysis of 30 carbonation/calcination cycles in a fixed-bed reactor. The mixed metal oxide (CaO−MgO) in the fresh calcined dolomite transformed into separate crystals of CaO and MgO in the cycled sorbent and resulted in a relative decrease in the cyclic CO 2 capture capacity. Favorable structures (decreased crystallinity, increased porosity, and surface area) were generated by water hydration treatment, which was expected to enhance the recyclability, as suggested by some authors. However, this sorbent produced separate Mg and Ca as the major components, leading to a decrease in the CO 2 capture compared to fresh calcined dolomite. Complete segregation between Ca and Mg was observed upon precipitation treatment, which gave rise to the lowest cyclic CO 2 uptake. This segregation was eliminated by the final ball-milling treatment, thereby regaining the original reactivity. These results demonstrate the dominant role of the mixing of Ca and Mg on the cyclic CO 2 capture capacity of dolomite-based sorbents.

No abstract

Abstract-Highly efficient Li 4 SiO 4 -based sorbents for CO 2 capture at high temperature, were developed using waste rice husk ash (RHA). Two different RHAS resulted from different calcination temperature as raw materials for preparing the Li 4 SiO 4 -based sorbents. These raw ashes and their resulting Li 4 SiO 4 -based sorbents were characterized by X-ray diffraction, thermogravimetry (dynamic and isothermically), and nitrogen adsorption. CO 2 sorption stability was investigated in a dual fixed-bed reactor. The characteristic results showed that high calcination temperature could lead to crystalline silica, which may produce the lower crystalline size, higher porosity and larger surface area as compared with the case of low temperature. This favourable structure appeared to be the main reason for increasing in CO 2 capture performance and kinetic behavior as illustrated by the thermogravimetric analyses. This pretreatment Li 4 SiO 4 -based sorbent also maintained a higher capacity during the multiple cycles. It was concluded that the synthesis of Li 4 SiO 4 -based sorbents obtained from biomass ash is a promising approach for CO 2 capture at high temperature.