Adsorção de CO2 em peneiras moleculares mesoporosas a base de óxido de alumínio

Abstract

Due to the demand to reduce excessive concentrations of carbon dioxide in the environment, several technologies have been studied and developed for this purpose. Currently, the use of molecular sieves has been used and optimized, due to the efficiency of CO2 capture and the easy recovery of the material, avoiding losses. The mesoporous molecular sieves stand out, because their structure allows the access of the molecules to the interior of the pores with ease, since they have high surface area and volume of pores, and are thermally stable. This work aimed to use molecular sieves, based on aluminum oxides, for CO2 adsorption. The synthesis treatment temperature (60, 90, 120, 150 and 180 °C) was evaluated and the use of two different directing agents: caprylic acid and stearic acid. This difference in the driving agent caused a change in the textural properties of the material. The materials were characterized by nitrogen adsorption at -196 °C, thermogravimetric analysis (TGA/DTA), scanning electron microscopy (SEM), CO2 desorption at the programmed temperature (TPD-CO2). The prepared adsorbents were subjected to the evaluation of the carbon dioxide (CO2) adsorption capacity using the thermogravimetric method. All samples obtained results close to the surface area (305 ± 13 m2/g), with a trend of proportional increase in the pore diameter as the synthesis treatment temperature increased. Thermogravimetric analyzes showed that the organic compound left and that the higher the temperature of the heat treatment in the synthesis, the higher the temperature of removal of the surfactant indicated/observed by the thermogravimetric curves. The scanning micrographs show that there is a greater agglomeration of the particles when the synthesis temperature increases. Samples synthesized with caprylic acid had the number of basic sites per gram of adsorbent reduced, while those synthesized with stearic acid increased, as the treatment temperature increased. The results obtained in the CO2 adsorption tests showed that the higher the heat treatment temperature in the synthesis, the greater the adsorption capacity, reaching 24.6 and 26.79 mgCO2/gads for samples synthesized with caprylic acid and stearic acid both treated at 180 °C, respectively, whose value corresponds to an increase of 237 and 414%, respectively, in relation to the same samples treated at 60 °C.