Effect of Oxygen Addition on the Thermokinetic Properties of CO₂ Chemisorption on Li₂ZrO₃

Abstract

Lithium zirconate doped with potassium (K-Li 2 ZrO 3 ) was synthesized by solid-state reaction and then its CO 2 chemisorption capacity was evaluated using different CO 2 -O 2 gas mixtures. These experiments were performed in order to evaluate the effect produced by the O 2 on the kinetic parameters and on the CO 2 absorption reaction mechanism. Although the CO 2 capture dynamic experiments did not show significant variations as a function of the O 2 content, isothermal experiments and their fitting to the Eyring's model did. Different enthalpy activation (∆H q ) values were estimated for the CO 2 chemisorption process, as CO 2 capture is produced by two processes: Initially, the CO 2 chemisorption occurs directly over the K-Li 2 ZrO 3 surface. Then, once a Li 2 CO 3 -ZrO 2 external shell is produced, CO 2 chemisorption is kinetically controlled by diffusion processes, which must imply the lithium and oxygen diffusion. The ∆H q values, of the CO 2 direct chemisorption, increased as a function of the O 2 content. It was explained in terms of a CO 2 -O 2 competition to occupy the Li 2 ZrO 3 surface. On the other hand, the ∆H q values, of the CO 2 chemisorption kinetically controlled by diffusion processes, decreased as a function of the O 2 content. This result confirmed the oxygen diffusion dependency of the CO 2 chemisorption on lithium zirconate.

Thermokinetic and conductivity analyzes of the high CO2 chemisorption on Li5AlO4 and alkaline carbonate impregnated Li5AlO4 samples: Effects produced by the use of CO2 partial pressures and oxygen addition

“…In general, these results evidence that k 1 values (direct CO 2 chemisorption in Li 5 AlO 4 particle surfaces) are one order of magnitude higher than k 2 values (CO 2 chemisorption kinetically controlled by diffusion processes). This is a typical behavior observed for the CO 2 capture process in alkaline ceramics at high temperatures [8,11,25,26] . Thus, k 2 value indicates that the diffusion processes are the limiting process.…”

“…Nevertheless, isotherms where oxygen was present were faster than those obtained in the oxygen absence, and the amounts of CO 2 captured did not vary in more than 2 wt%. In order to further analyze these isotherms, with and without O 2 , all of them were fitted to the double exponential model, as in previous works related to Li 5 AlO 4 and other lithium ceramics [8,11,25,26] . The double exponential model is:…”

“…Consequently, these oxygen atoms must diffuse as well. So, the presence of this gas in the whole reactive atmosphere would modify the reaction kinetics [26] .…”

High temperature capture of CO2 on lithium-based sorbents from rice husk ash

“…where y represents the weight change of CO 2 absorbent, t is the time, k 1 and k 2 are the rate constants for the CO 2 chemisorption produced directly over the Li 4 SiO 4 particles and CO 2 chemisorption kinetically controlled by lithium diffusion [37,38], respectively. In addition, the pre-exponential factors A and B indicate the intervals at which each process controls the whole CO 2 capture process, and the C constant indicates the y-intercept.…”

High-temperature and low concentration CO2 sorption on Li4SiO4 based sorbents: Study of the used silica and doping method effects

“…9 were fitted to a double exponential model (Essaki et al, 2005;Venegas et al, 2007;Mejía-Trejo et al, 2008;Olivares-Marín et al, 2010;Rodríguez-Mosqueda and Pfeiffer, 2010;Martínez-dlCruz and Pfeiffer, 2010):…”