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Title: Dynamic acid/base equilibrium in single component switchable ionic liquids and consequences on viscosity

The deployment of transformational non-aqueous CO2-capture solvent systems is encumbered by high viscosity even at intermediate uptakes. Using single-molecule CO2 binding organic liquids as a prototypical example, we identify the key molecular features controlling bulk liquid viscosity and CO2 uptake kinetics. Fast uptake kinetics arise from close proximity of the alcohol and amine sites that are involved in CO2 binding. This process results in the concerted formation of a Zwitterion containing both an alkylcarbonate and a protonated amine. The hydrogen bonding between the two functional groups ultimately determines the solution viscosity. Based on molecular simulation, this work reveals options to significantly reduce viscosity with molecular modifications that shift the proton transfer equilibrium towards a neutral acid/amine species as opposed to the ubiquitously accepted Zwitterionic state. Lastly, the molecular design concepts proposed here, for the alkyl-carbonate systems, are readily extensible to other CO2 capture technologies, such as the carbamate- or imidazole-based solvent chemistries.
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  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1948-7185; AA6510000
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry Letters
Additional Journal Information:
Journal Volume: 7; Journal Issue: 9; Journal ID: ISSN 1948-7185
American Chemical Society
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE Office of Fossil Energy (FE)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; CO2 capture solvent systems; ab Initio molecular dynamics; classical molecular dynamics; switchable ionic liquids; viscosity