Reactivity of lithium silicates prepared from bio-silica for the capture of carbon dioxide

BETINA MARÍA FAROLDI; LUIS ALFONSO SALAZAR HOYOS; LAURA MARÍA CORNAGLIA

Santa Fe

Conferencia; VI San Luis Conference; 2018

Universidad Nacional del Litoral

The number of anthropogenic greenhouse gasses is increasing, in especial the carbon dioxide coming from industrial processes, these emissions cause worldwide problems due to it is one of the main contributors to global warming1. Controlling the capture in power plants is considered to be the most direct and effective option for solving greenhouse gas issues for countries that continue to exploit their reserves of fossil fuels while still achieving emission targets. However, the current carbon capture technologies utilizing aqueous amines suffer from large energy penalties mainly due to cooling stages, an alternative of these materials, orthosilicate (Li4SiO4)-based adsorbents are studying for the intermediate-temperature and high-temperature sorbents process2. A thermodynamic study reveals that lithium silicate can reach higher values of CO2 sorption at elevated temperatures, adequate absorption/desorption kinetics for CO2, good cyclability for the absorption/desorption process and appropriate mechanical properties3. In this work, Lithium silicates were synthesized, using rice hush ashes as the precursor of silica, for being used in CO2 capture. A treatment step with water was carried out previous of the rice husk burning. Silica with a high surface area of 249 m2g-1, a yield of 17% and a purity of 92% was obtained. Subsequently, silica was impregnated with LiNO3 employing different Li/Si molar ratios and two different and simple methods, successive incipient wetness impregnation (S) and wet impregnation (H), it is found that the incorporation method and the lithium amount influence of silicate phases obtained, and this, in turn, influences the CO2 capture capacity of the materials. Preliminarily, the results suggest that a higher proportion of orthosilicate favours the capturing ability when the metasilicate (Li2SiO3) phase is present.Raman in situ experience was carried out for Li/Si = 3S and Li/Si =4.1H samples, following the reaction evolution, Li4SiO4(s) + CO2(g) → Li2SiO3(s) + Li2CO3(s), both samples show clearly the signals corresponding to the metasilicate, orthosilicate, and lithium carbonate phases. As the carbonation at 773 K progress, the lithium carbonate and metasilicate signal grow and the orthosilicate signal decrease, confirming the occurrence of the carbonation reaction. Later, the regeneration process takes place and the orthosilicate signal growing again confirming the reversibility of lithium carbonate formation reaction. On the second carbonation stage at 863 K, later of 16 minutes, the signal of orthosilicate phase is disappeared completely, and the solid lithium carbonate signal is large and well defined. That is in accordance with the TGA measurements because the reaction velocity at 863 K is faster than 773 K when the maximum capture capacity was reached for both samples. The stability test of the samples was carried out. In this case, the cycle was repeated 9 times and it is confirmed a good cyclability and stability after several capture/desorption cycles.