Insights into the Adsorption of Carbon Dioxide in the Presence of Water Vapor Utilizing a Low Molecular Weight Polyethylenimine-Impregnated CARiACT Silica Sorbent

Thermogravimetric analysis was employed to investigate the CO2 and H2O adsorption rates and water vapor equilibrium on anhydrous and prehydrate linear polyethylenimine (LPEI) sorbent impregnated within a commercially functional CARiACT G10 (HPV) silica support. Water vapor experiments utilizing specific humidities of 2%, 8%, and 16% in contact with an anhydrous PEI sorbent resulted in proportional quantities of water vapor uptake. Subsequently, both anhydrous and prehydrated PEI-impregnated sorbents were made available to identical humidified gaseous streams containing a CO2 concentration of 10% at 60 °C. CO2 capacity increased dramatically in the presence of different levels of humidity. Various kinetic models were systematically employed to interpret the experimental data including single- and multiple-step models. The rate data was best represented by a reaction mechanism pathway involving the interplay of CO2 with PEI-impregnated sorbents exhibiting a quick adsorption phase followed by a slow approach to equilibrium. Moreover, a phenomenological rate model was developed to describe the dynamic H2O and CO2 uptakes at specific humidity levels studied. The kinetic study showed good agreement with experimental data. Furthermore, the effects observed during the adsorption and hydration are shown to be complementary to known chemical and physical transformations within the polyethylenimine's macromolecule.