Optimization-based design and analysis of tailor-made ionic liquids

Solvents comprise two thirds of all industrial emissions. Traditional organic solvents easily reach the atmosphere as they have high vapor pressure and are linked to a host of negative environmental effects including climate change, urban air-quality and human illness. Room temperature ionic liquids (RTIL), on the other hand, have low vapor pressure and are not flammable or explosive, thereby resulting in fewer environmental burdens and health hazards. However, their life cycle environmental impacts as well as freshwater ecotoxicity implications are poorly understood. RTILs are molten salts that exist as liquids at relatively low temperatures and have unique properties. Ionic liquids consist of a large organic cation and charge-delocalized inorganic or organic anion of smaller size and asymmetric shape. The organic cation can undergo unlimited structural variations through modification of the alkyl groups attached to the side chain of the base cation skeleton and most of these structural variations are feasible, from chemical synthesis point of view, due to the easy nature of preparation of their components. Functionally, ionic liquids can be tuned to impart specific desired properties by switching anions/cations or by incorporating functionalities into the cations/anions. It is estimated that theoretically more than a trillion ionic liquid structures can be formed. Due to their tunable nature, these molten salts have the potential to be used as solvents for variety of applications.;This dissertation presents a computer aided IL design (CAILD) methodology with an aim to design optimal task-specific ionic liquid structures for different applications. We utilize group-contribution based ionic liquid property prediction models within a mathematical programming framework to reverse engineer functional ionic liquid structures. The CAILD model is then utilized to design optimal ionic liquids for solar energy storage, as a solvent for aromatic-aliphatic separation, and as an absorbent for carbon capture process. Using the developed CAILD model, we were able to computationally design new ionic liquid structures with physical and solvent properties that are potentially superior to commonly used ILs. The accuracy of the developed model was back tested and verified using available experimental data of common ILs. However, we would like to note that the computational design results from this dissertation needs to be experimentally validated.;This dissertation also developed ecotoxicity characterization factors for few common ILs. The developed characterization factors (CFs), can be used in future studies to perform holistic (cradle-to-grave) life cycle assessments on processes using ILs to understand their environmental and ecological impacts.