Adsorption of high-temperature CO by Ca/Na-doped lithium orthosilicate: characterization, kinetics, and recycle.

High-temperature solid adsorbent LiSiO has received broad attention due to its high theoretical adsorption capacity, high regeneration capacity, and wide range of raw materials for preparation. In this paper, a LiSiO adsorbent was prepared by MCM-48 as the silica precursor and modified by doping with metal ions (Ca and Na) for high-temperature capture of low-concentration CO. The results showed that the surface of the Ca-doped (or Na-doped) LiSiO adsorbent developed some particles that are primarily composed by LiCaSiO (or LiNaSiO). Furthermore, the grains of the adsorbents became finer, effectively increasing the specific surface area and enhancing adsorption performance. Under 15 vol% CO, the maximum CO adsorption was 25.63 wt% and 32.86 wt% when the Ca doping amount was 0.06 and the Na doping amount was 0.12, respectively. These values were both higher than the adsorption capacity before the metal ion doping. After 10 adsorption/desorption cycles, the adsorption capacity of Na-doped LiSiO increased by 9.68 wt%, while that of Ca-doped LiSiO decreased by 7.98 wt%. This difference could be attributed to the easy sintering of the Ca-containing adsorbent. Furthermore, a biexponential model was used to fit the CO adsorption curve of the adsorbent in order to study the adsorption kinetics. Compared to the conventional LiSiO, the Ca/Na-doped adsorbent offers several advantages, such as a high CO adsorption capacity and stable cycling ability.