(310b) Reverse Design of Ionic Liquids for CO2 Absorption

Chemical engineering design problems have evolved in recent years from large scale bulk processes to targeted small batch approaches. As a result, product design is reaching beyond the traditional solutions to classic chemical engineering problems such as extraction, purification, removal of sulfur from fuel, CO₂ capture and sequestration, energy storage and biomass pre-treatment. Ionic liquids can provide environmentally benign solutions that can be tailored to specific process requirements. Due to the unique structure of ionic liquids, the cation, anion and length of the alkyl chain can be varied to create a molecule with specific physical properties. It has been estimated that over 10¹⁴ unique molecules exist at room temperature, so experimental trial and error methods will not be effective. More advanced methods must be created determine the ideal combination for a specific set of process requirements.

The purpose of this work is to determine the ideal ionic liquid to capture CO₂, a question which has been the topic of many experimental laboratory studies. However, only a small percentage of the potential ionic liquids have been synthesized and tested for the solubility of CO₂. This innovative approach decouples the solution from time-consuming laboratory study and streamlines the search for the most promising candidates that should be synthesized.

A characterization based group contribution method is combined with density functional theory to determine the ionic liquid that can most effectively absorb CO₂. Infrared spectra data contains descriptor data that can be used to estimate properties of ionic liquids, but does not exist for all ionic liquids. Density functional theory is used to create IR data based on a training set of experimental data. Principal component analysis and partial least square techniques will be employed to reveal important features and patterns in the molecular architecture. A characterization based group contribution method is used to estimate the properties of the new structures. The reverse design of potential ionic liquid molecules will be completed by an exhaustive search of combinations with various cation, anions and lengths of alkyl chains until a candidate molecule is found that provides the highest solubility of CO₂.