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

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.