Fabricación de materiales basados en silicatos de litio (Li4SiO4 y Li2SiO3) para captura de CO2

Abstract

Nowadays there is an intense research focused to the development of new technologies for carbon dioxide (CO2) emissions control. The study of both solid sorbents and ceramic membranes are good examples of the above mentioned. The present work shows a systematic study on the fabrication and CO2 absorption properties of a series of lithium silicates including Li4SiO4, Li2SiO3 and the solid solutions with general formula Li4+x(Si1-xAlx)O4 and Li4-x(Si1-xVx)O4. In order to obtain structural and microstructural characteristics that promote the performance of solid sorbents on the CO2 capture process, the different materials were prepared by several synthesis methods including the conventional solid state reaction, as well as hydrothermal crystallization and high energy milling. In addition, the effect of water vapor presence during the absorption reaction was studied. The structural and microstructural characterizations of different materials were carried out by X-ray diffraction, Nuclear Magnetic Resonance, Scanning Electron Microscopy, Transmission Electron Microscopy, Infrared Spectroscopy (FTIR) and N2 Sorption measurements. Besides, CO2 sorption properties of the different materials were determined by thermogravimetric analysis. Diffraction analyses revealed the successful crystallization of pure Li2SiO3 single phase by hydrothermal technique, even without further heat-treatments. Electron microscopy analyses revealed that Li2SiO3 powders were composed of uniform micrometric particles with a hollow sphere morphology and nanostructured walls which enhance the chemical reactivity of absorbent. CO2 absorption evaluation revealed that both textural properties and water vapor presence promotes the capability of Li4SiO4 and Li2SiO3 to absorb CO2. In fact it was founded that as higher is the reactivity of the absorbent with water, as higher is its reactivity with CO2 in presence of water. The above was attributed to the formation of intermediate species like MeOH which are more prone to react with CO2 than the adsorbent itself, giving as a result a general increase of the kinetic of capture. Finally, diffraction analyses revealed the successful formation of solid solutions Li4+x(Si1-xAlx)O4 and Li4-x(Si1-xVx)O4 by both solid state reaction and high energy milling, in the last case even without further heat-treatments. Thermal analyses into a CO2 flux showed that Li4+x(Si1-xAlx)O4 solid solutions present a much better CO2 absorption than that observed for Li4-x(Si1-xVx)O4 solid solutions as well as for pure Li4SiO4. Isothermal analyses were performed to the samples in order to obtain additional kinetic information; base on the above a physical model to describe the behavior of absorbent particles during CO2 capture process is proposed.