Silica-Supported Sterically Hindered Amines for CO₂ Capture

Abstract

Most\nstudies exploring the capture of CO₂ on solid-supported\namines have focused on unhindered amines or alkylimine polymers. It\nhas been observed in extensive solution studies that another class\nof amines, namely sterically hindered amines, can exhibit enhanced\nCO₂ capacity when compared to their unhindered counterparts.\nIn contrast to solution studies, there has been limited research conducted\non sterically hindered amines on solid supports. In this work, one\nhindered primary amine and two hindered secondary amines are grafted\nonto mesoporous silica at similar amine coverages, and their adsorption\nperformances are investigated through fixed bed breakthrough experiments\nand thermogravimetric analysis. Furthermore, chemisorbed CO₂ species formed on the sorbents under dry and humid conditions are\nelucidated using in situ Fourier-transform infrared spectroscopy.\nAmmonium bicarbonate formation and enhancement of CO₂ adsorption\ncapacity is observed for all supported hindered amines under humid\nconditions. Our experiments in this study also suggest that chemisorbed\nCO₂ species formed on supported hindered amines are weakly\nbound, which may lead to reduced energy costs associated with regeneration\nif such materials were deployed in a practical separation process.\nHowever, overall CO₂ uptake capacities of the solid supported\nhindered amines are modest compared to their solution counterparts.\nThe oxidative and thermal stabilities of the supported hindered amine\nsorbents are also assessed to give insight into their operational\nlifetimes.