title: Dynamic Acid/Base Equilibrium in Single Component Switchable Ionic Liquids and Consequences on Viscosity.
abstract: The deployment of transformational nonaqueous CO2-capture solvent systems is encumbered by high viscosities even at intermediate uptakes. Using single-molecule CO2 binding organic liquids as a prototypical example, we present key molecular features that control bulk viscosity. Fast CO2-uptake kinetics arise from close proximity of the alcohol and amine sites involved in CO2 binding in a concerted fashion, resulting in a Zwitterion containing both an alkyl-carbonate and a protonated amine. The population of internal hydrogen bonds between the two functional groups determines the solution viscosity. Unlike the ion pair interactions in ionic liquids, these observations are novel and specific to a hydrogen-bonding network that can be controlled by chemically tuning single molecule CO2 capture solvents. We present a molecular design strategy to reduce viscosity by shifting the proton transfer equilibrium toward a neutral acid/amine species, as opposed to the ubiquitously accepted zwitterionic state. The molecular design concepts proposed here are readily extensible to other CO2 capture technologies.
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: David C
authors.initials: DC
authors.lastname: Cantu
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Juntaek
authors.initials: J
authors.lastname: Lee
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Mal-Soon
authors.initials: MS
authors.lastname: Lee
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Heldebrant
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Phillip K
authors.initials: PK
authors.lastname: Koech
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Freeman
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Roger
authors.initials: R
authors.lastname: Rousseau
authors.affiliation: Physical Sciences Division, ‡Energy Processes and Materials Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Vassiliki-Alexandra
authors.initials: VA
authors.lastname: Glezakou