Kinetics of CO2 capture by novel amine-functionalized magnesium oxide adsorbents

Abstract

The continuous release of high carbon dioxide (CO2) emissions to the atmosphere is associated with a number of serious negative consequences. Although there are some published studies on CO2 capture at elevated temperatures using magnesium oxide (MgO) and its molten salts, there is a lack of studies on developing amine-functionalized MgO adsorbents and their use for CO2 adsorption at mild conditions. Thus, we present in this study a novel and facile method for the functionalization of magnesium oxide (MgO) with 3-aminopropyl-triethoxysilane (APTES), polytheylenimine (PEI), and diethylenetriamine (DETA). After the characterization of the aminated MgO adsorbents using different techniques, they were utilized to capture CO2 at different temperatures. The results revealed that the functionalization of MgO with APTES and DETA provides a significant enhancement in CO2 adsorption over the entire temperature range (30−100 °C) studied herein. Additionally, although the functionalization of MgO with PEI reduced the CO2 uptake at 30 °C, this adsorbent outperformed all other adsorbents at elevated temperatures. The endothermic adsorption of CO2 on PEI-MgO, unlike the exothermic adsorption on the other adsorbents, makes it the best choice (among those investigated in this study) for CO2 capture at elevated temperatures (up to, at least, 100 ⁰C). The obtained results were modeled using different adsorption kinetic models. The modelling studies revealed that despite the reduction in the CO2 uptake capacity by MgO, APTES-MgO, and DETA-MgO with increasing the adsorption temperature, its adsorption rate becomes faster. The rate of CO2 adsorption on PEI-MgO also increases with temperature. In addition to the abovementioned results, a multiple regeneration cycles (at mild conditions) of the most two effective adsorbents (i.e., APTES-MgO and DETA-MgO) have been also demonstrated in this work. These two adsorbents (particularly APTES-MgO) are promising materials for CO2 adsorption at ambient conditions with potential commercial applications upon further research and development.