Secondary Amine Functional Disiloxanes as CO₂ Sorbents

Abstract

A series of two different types of secondary amine functional disiloxanes were prepared and screened as CO 2 capture solvents. The first group of materials contained RNHCH 2 CH 2 CH 2 side chains where the R groups were C1–6 alkyls. When R was a primary alkyl group, these materials exhibited CO 2 uptake values slightly in excess of theoretical. As the alkyl groups were changed to more sterically hindered secondary or tertiary alkyls, the uptake was less efficient. Heats of absorption values for these materials were generally in the range 2000–2200 kJ/kg of CO 2, values significantly lower than those obtained for primary amine functional disiloxanes (2500–2700 kJ/kg of CO 2 ). Also explored were a series of secondary amine functional disiloxanes with X-CH 2 CH 2 NH-CH 2 CH 2 CH 2 – substituents. When X was an electron-donating group (RO-, R 2 N-, RO-CH 2 -) the CO 2 uptake was also in excess of theoretical. Interestingly, these compounds were generally found to produce carbamate salts that were flowable, low-viscosity oils. Furthermore, the heat of absorption values determined for these materials were even lower. Most compounds gave values below 2000 kJ/kg of CO 2 . Overall the most promising results were obtained with a methoxyethylaminopropyl derivative, an ethoxyethylaminopropyl-containing material, and a dimethylaminoethylaminopropyl-based compound. These materials showed excellent CO 2 uptake, had low heats of absorption, and produced carbamate salts that were flowable liquids even at room temperature.