Reverse Design of Ionic Liquids for the Absorption of CO2

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. 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. 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 further laboratory study and streamlines the search for the ideal candidate. A characterization based group contribution method is combined with density functional theory to determine ionic liquids 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 are employed to reveal important features and patterns in the molecular architecture. A characterization based group contribution method is used to estimate properties. The reverse design of potential ionic liquid molecules is 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.