EFFECT OF WATER VAPOR OVER CO2 CAPTURE PROPERTIES OF Li4SiO4 AFTER EXPOSURE AT LOW TEMPERATURE

M. L. GRASSO; P. ARNEODO LAROCHETTE; F. C. GENNARI

Congreso; XXIX INTERNATIONAL MATERIALS RESEARCH CONGRESS; 2021

MRS

Lithium orthosilicate (Li4SiO4) shows attractive properties for CO2 capture due to its high capacity (theoretical value of 36.7 wt% of CO2) and selectivity to CO2 absorption from gas mixtures. Li4SiO4 reacts with CO2 in the range of 450ºC-700ºC forming Li2CO3 and Li2SiO3 as products. In addition, this compound has a great stability after multiple carbonatation/decarbonation cycles. A relevant property regarding to Li4SiO4 application is its physicochemical stability during handling and storage in air. In this work, we systematically studied the properties of Li4SiO4 samples after prolonged storage in presence of moisture. Li4SiO4 samples were prepared by solid-state reaction at 800ºC for 5 hours. Thereafter, the samples were milled in air for 1 hour to improve the specific surface area. To analyze the effect of Relative Humidity (RH) on the Li4SiO4 physicochemical stability, a specific apparatus was designed, which consists in a water reservoir mounted on a heating plate. RH and temperature were recorded with a DHT11 sensor coupled with an Arduino UNO. For each experiment, a different as-milled sample was exposed to RH of 92% at 32°C for different times (1, 5 and 10 h). After RH exposure, the samples were tested by non-isothermal CO2 absorption measurements (until 700ºC) using thermogravimetric technique. In addition, cycles of carbonation (pure CO2 flow) and decarbonation (He flow) were performed at 725°C after exposure to RH for 1h. TG, XRD and FTIR results suggest that Li4SiO4 powders in the presence of water vapor at ambient temperature were activated forming Li2O and Li2SiO3, favoring the Li2O hydroxylation. Then, the surface of Li4SiO4 covered by LiOH and LiOH.H2O, reacted with the CO2 present in the air to produce Li2CO3. This fact was observed in the first carbonation cycle, which showed a smaller CO2 capture capacity with respect to the unexposed Li4SiO4. Similar results were found after prolonged exposure of samples to atmospheric conditions. On the other hand, the experimental CO2 capture properties of Li4SiO4 could be recovered after heating at 700°C under an inert atmosphere. Concerning cycling, the samples maintained their absorption capacity after 30 consecutive cycles without a significant decrease (< 5 %).