CaAlFe–mixed metal oxides prepared from an aluminum salt–cake and their evaluation as CO2 sorbents at moderate temperature

Abstract

Potentially–CO2 adsorbing solids at moderate temperature have been prepared by calcination at 400 °C and 750 °C of CaAlFe hydrocalumites (a sort of Ca2+–layered double hydroxide), which had been prepared using a salt cake as aluminum source. The characterization of the obtained solids was carried out by powder X–ray diffraction, FT–infrared spectroscopy, thermal analysis, N2 adsorption–desorption isotherms at –196 °C and electron microscopy. After calcination, different crystalline phases were identified as a function of the amount of Fe3+ incorporated. Static sorption equilibrium experiments were performed at 300 °C and pCO2 = 0.3 bar. The CO2 sorption capacity was affected by the presence of different phases in the CaAlFe–mixed oxides (MMOs), being maximum when the amount of Fe3+ was 40 mol % of the trivalent positions. No differences in CO2 sorption capacities were observed between CaAlFe–MMOs–400 and CaAlFe–MMOs–750 (materials calcined respectively at 400 and 750 °C), suggesting that CO2 sorption capacity was not related to SBET. Experiments under dynamic conditions at 400 °C and pCO2 = 0.15 bar showed good behaviors for CaAl–400, CaAl0.60Fe0.40–400 and CaFe–400. In addition, CaAl0.60Fe0.40–400 was evaluated in several CO2 sorption–desorption cycles in the presence of water vapor, finding that the steam presence enhanced the CO2 capture.