A green and scalable synthesis of highly stable Ca-based sorbents for CO2 capture

Abstract

High-temperature sorption of CO₂via calcium looping is a promising technology for the implementation of carbon capture and storage (CCS). However, the rapid deactivation of CaO sorbents due to sintering is currently the major drawback of this technology. We, for the first time, report an economical and environmentally benign strategy to reduce sintering by adding fly ash, a waste stream of coal-fired plants, into Ca-based sorbents through a simple dry process. The as-synthesized sorbents were tested using a TGA and showed an extremely high stability under the most severe multi-cycle conditions (calcined at 920 °C in pure CO₂). Upon 100 cycles, its CO₂ capture capacity was 0.20 g(CO₂) g(sorbent)⁻¹, and the average deactivation rate was only 0.18% per cycle. The most possible stabilization mechanism was discussed on the basis of a range of characterizations including N₂ physisorption, SEM, TEM (coupled with EDX mapping) and XRD; it was concluded that stable and refractory gehlenite (Ca₂Al₂SiO₇) particles were formed and evenly dispersed around CaO crystal grains during calcination at 950 °C, leading to sintering resistance. This strategy achieved superior enhancement in the cyclic stability of Ca-based sorbents as well as the reuse of industrial solid waste, and is thus a green technology for scaled-up CO₂ capture.