Multiple activation mechanisms of CaO-based sorbents promoted by pre-sintering-hydration

Abstract

Highly reactive CaO sorbents based on natural limestone with enhanced stability and re-usability were obtained via a pre-sintering-hydration method. It was found that several active mechanisms including generation of oxygen vacancies, promotion of ion replacement and improvement in pore structure were involved during the process of pre-sintering-hydration. The limestone-based sorbents obtained at a pre-sintering temperature of 1100 °C showed the highest CO2 capture capacity of 0.71 g-CO2 g−1 in the first cycle with a specific surface area of 28.65 m2 g−1. Electron spin-resonance analysis and high-resolution transmission electron microscopy demonstrated the existence of stress-induced oxygen vacancies and the promoting effect of hydration on ion replacement. The CO2 capture capacity of sample Ca-1100Mg-1:7 can still maintain at 0.47 g-CO2 g−1 at the 30th cycle, which was 2.8 times that of Ca-lime. After every 30 cycles, the recovered CO2 capture capacity of sample Ca-1100Mg-1:7 can achieve about 96.9 % of its initial valve. The improved stability and re-usability of the prepared sorbents can be attributed to the combined action of multiple active mechanisms introduced by pre-sintering-hydration treatment.