Characterization of potassium doped Li2ZrO3 based CO2 sorbents: Stability properties and CO2 desorption kinetics

In this work, potassium doped and undoped Li2ZrO3-based sorbents for CO2 capture at high temperatures were synthesized through wet impregnation of Li and K salts over a colloidal suspension of zirconia nanoparticles. The synthesized sorbents were characterized by XRD and Raman spectroscopy, and the CO2 sorption/desorption properties of the sorbents were investigated by in-situ Raman spectroscopy and by thermogravimetric analysis at different temperatures and CO2 partial pressures. The stability of the doped sorbent over 30 cycles of CO2 sorption/desorption was investigated by thermogravimetric analysis and by XRD, evaluating the variations of the capture capacity, capture rate and crystallite size over the cycles. The sorbent desorption kinetics was analyzed both in N-2 and in a mixture of CO2/N-2, and is characterized by a relatively fast chemically controlled stage followed by a second slow stage. The second slow stage was assumed to be controlled by diffusion through the lithium zirconate layer and the amount of lithium carbonate converted in the second stage decreases when the regeneration temperature increases. The effect of potassium doping on the CO2 desorption rates in nitrogen flow was analyzed, both in the first and in the second slow stages. The influence of the CO2 concentration on the lithium carbonate conversion rates and on the sorbent capture capacity at the end of the first stage were analyzed for the doped and undoped sorbents. Finally, a zeroth order advancing interface reaction model was identified for the first stage of the CO2 desorption and, by fitting the CO2 desorption thermogravimetric data, the activation energies for both sorbents were calculated.