Article pubs.acs.org/EF
Secondary Amine Functional Disiloxanes as CO2 Sorbents Michael J. O’Brien,* Rachel L. Farnum, Robert J. Perry, and Sarah E. Genovese Department of Chemisty and Chemical Engineering, GE Global Research, Chemisty and Chemical Engineering, 1 Research Circle, Niskayuna, New York 12309, United States ABSTRACT: A series of two different types of secondary amine functional disiloxanes were prepared and screened as CO2 capture solvents. The first group of materials contained RNHCH2CH2CH2 side chains where the R groups were C1−6 alkyls. When R was a primary alkyl group, these materials exhibited CO2 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 CO2, values significantly lower than those obtained for primary amine functional disiloxanes (2500−2700 kJ/kg of CO2). Also explored were a series of secondary amine functional disiloxanes with X-CH2CH2NH-CH2CH2CH2− substituents. When X was an electron-donating group (RO-, R2N-, RO-CH2-) the CO2 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 CO2. Overall the most promising results were obtained with a methoxyethylaminopropyl derivative, an ethoxyethylaminopropyl-containing material, and a dimethylaminoethylaminopropylbased compound. These materials showed excellent CO2 uptake, had low heats of absorption, and produced carbamate salts that were flowable liquids even at room temperature.
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primary amine functionality.5,6 During the course of our earlier work, we did explore a limited number of siloxanes containing secondary amine functionality.2 However, most of these materials contained primary amines as well, as in the case of bis(aminoethylaminopropyl)tetramethyldisiloxane. The CO2 uptake values that were measured for these materials did not match expectations based on their amine concentrations. Most of the issues encountered in these cases resulted from poor mass transfer due to the formation of very viscous or semisolid carbamate salt/amine blends. Given the limited number of derivatives explored and the potential for a substantial reduction in absorption energy, a closer look at secondary amine functional disiloxanes was undertaken.
INTRODUCTION Over the last several years we have been exploring the use of amine functional siloxanes as CO2 sorbents.1−3 Our goal has been to develop materials usable in processes that would satisfy the U.S. Department of Energy’s (DOE) target for the capture and sequestration of 90% of the CO2 in flue gas generated from coal-fired power plants, with a cost of capture
