Synthesis of CaO-based sorbents through incorporation of alumina/aluminate and their CO2 capture performance

Abstract

CaO-based CO2 sorbents derived from various calcium and aluminum precursors were prepared by a wet mixing method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and N2 adsorption–desorption techniques. The as-prepared sorbents consisted of active CaO and inert support materials that could be Al2O3, Ca12Al14O33 or Ca9Al6O18, depending on calcium and aluminum precursors used during the preparation process. A formation mechanism for the inert support materials was proposed. Compared to pure CaO, most of the synthetic CaO-based sorbents showed much higher CO2 capture capability and stability over multiple carbonation/calcination cycles, which was ascribed to the relatively high specific surface area of the sorbents, the bimodal pore-size distribution with a fair number of small pores, and the inert support material that can effectively prevent or delay sintering of CaO particles. Among these synthetic sorbents the CaO–Ca9Al6O18 sorbent with a CaO content of 80wt% (weight fraction) derived from calcium citrate and aluminum nitrate exhibited the best performance for CO2 capture, and can be expected to be applied in the sorption-enhanced steam methane reforming process.