Estudo da adsorção seletiva de CO2 em sólidos micro e mesoporosos utilizando simulação de Monte Carlo

Abstract

Many endeavors have been undertaken in the attempt to develop new adsorbent materials employed in the removal of CO2 in exhaust gas streams. Concurrently, computational techniques have progressively contributed to this subject matter. Therefore, this study aims to investigate, through molecular simulation, the selective adsorption of CO2 in operational conditions similar to a post-combustion capture scenario. Thus, we developed molecular models of the adsorbents NaX, MCM-41, Cu-BTC, IRMOF-1 and UiO-66, besides hybrid solids created through impregnation with primary, secondary and tertiary amines in faujasite and mesoporous silica. The force fields used were able to predict accurately single and multicomponent adsorbent behavior of different gases, namely: CO2, N2, O2, NO2 and H2O. To that end, the grand canonical ensemble was used coupled with the Monte Carlo method (GCMC) to calculate isotherms of 0-100 °C in a broad pressure range. The results with NaX and its hybrids pointed to a preferential adsorption of CO2 when compared to N2. Evaluating CO2 selectivity in relation to N2 (SCO2/N2), it was observed that, in low temperatures, the hybrids produced similar values to unmodified NaX. In high temperature, a higher sensitivity was observed for that parameter, with the hybrid NaX-DEA as the best adsorbent. In the study with a humid stream, it was observed that the presence of water vapor, even in small amounts (1%v/v), is enough to saturate the adsorbents and promote a drastic decline in CO2 adsorption, possibly due to the strong competition between the CO2 and H2O molecules for the solid’s site III. The model developed for MCM-41 was able to replicate the experimental tendency of the adsorption of CO2, N2 and the CO2/N2 system. Furthermore, it was possible to identify the preferential location of the CO2 and N2 molecules in the silica. The SCO2/N2 was investigated evaluating the influence of temperature, pressure, stream composition, pore size and impregnation of amine groups. The results showed that a higher SCO2/N2 is achieved at low temperature and pressure, pore size between 12-17.5 Å, and with DEA immobilized with, approximately, 21% in mass. In the study with the MOFs, results showed that Cu-BTC was able to adsorb more CO2 than IRMOF-1 and UiO-66 in the investigated temperature range. It was estimated that at 100 °C the CO2 adsorption capacity in Cu-BTC was 2.8 times higher than in IRMOF-1 and 1.5 times higher than in UiO-66. On the other hand, evaluating the CO2/N2, CO2/O2 and CO2/NO2 selectivity, it was observed that zirconium MOF had better performance than the others, especially in high temperatures. The study of multicomponent adsorption with MOFs also revealed the strong competition between the CO2 e NO2 molecules, confirmed by energy histograms and adsorption instantaneous.