Study of the sorption properties of alkali zirconate-based sorbents at high temperature in the presence of water and low CO2 concentration

Abstract

Li2ZrO3, K-doped Li2ZrO3, and mixed Li2ZrO3-Na2ZrO3 based sorbents were synthesized through wet impregnation of alkaline solutions in a suspension of zirconia nanoparticles. Structural Raman and surface XPS characterizations were performed and the zirconate reactivity was analyzed through operando Raman experiments. t-Li2ZrO3, m-Na2ZrO3, m-ZrO2, m-Li2CO3 and m-Na2CO3 phases were detected by Raman spectroscopy and XRD. Sorption tests were performed at 500 °C with low and high CO2 concentrations (15% and 50%, respectively) and 0%, 10%, 20% and 30% H2O. All samples presented good sorption properties under dry conditions and 50% CO2. The addition of growing amounts of water played a positive effect on the capture properties, mainly in experiments with 15% CO2. For the KLiZr and NaLiZr samples, the addition of 10% H2O produced a more marked increase on the capture capacity, mainly observed at lower capture times. Accordingly, an enhancement of Li2ZrO3 and Na2ZrO3 reactivity was observed in the presence of water through operando Raman measurements. Water is believed to increase the ionic mobility and, consequently, the reactivity of alkali zirconates. The multi peak CO2 TPD profiles obtained during the regeneration of the Na-Li and K-doped samples were associated with their structural and compositional properties. KLiZr presented excellent stability over 10 sorption/regeneration cycles with capture under humidified conditions (15% CO2-10% H2O), while the capture capacity of NaLiZr decreased. The loss of capture efficiency in NaLiZr could be related to structural rearranges that affected the reaction kinetics.