Enhancing CO2 chemisorption on lithium cuprate (Li2CuO2) at moderate temperatures and different pressures by alkaline nitrate addition†
Lithium, sodium and potassium nitrate-containing Li2CuO2 samples were prepared to analyze the CO2 capture process at moderate temperatures, using different pressure conditions. Initially, in a CO2 saturated atmosphere, all these samples showed high CO2 capture efficiencies between 150 and 350 °C, in comparison to the pristine Li2CuO2 (T ≥ 500 °C). These results evidenced that Li-, Na- and K-nitrate addition on Li2CuO2 importantly enhances the whole CO2 capture. These results were corroborated kinetically. Moreover, the effects and reaction mechanism of alkaline nitrate addition were determined by X-ray diffraction, infrared spectroscopy and differential scanning calorimetric analyses. Nitrate anions melt and work as donor/acceptor oxygen anion intermediates during the Li2CuO2 carbonation process. Moreover, the carbonation may be completed (Li2CO3 and CuO production) through Li3Cu2O4 formation. When the CO2 capture process was evaluated using low partial pressures, the results presented similar efficiencies to those obtained using a saturated CO2 condition, showing differences only during the decarbonation process (T > 700 °C), as the CO2 chemisorption–desorption equilibrium was shifted. Finally, pristine Li2CuO2 and alkaline nitrate-containing Li2CuO2 samples were evaluated at high pressures. The pristine Li2CuO2 sample did not show any CO2 capture improvement, while alkaline nitrate-containing Li2CuO2 samples did improve. This was attributed to the alkaline nitrate melting process and the pressure equilibrium conditions.