Synergistic Approach to Exploration of the Microstructure of Novel, Tunable Solvents for Reactions, Separations and Catalyst Recycle

Abstract

Gas-expanded liquids (GXLs) are a new and benign class of pressure-tunable liquid solvents which show tremendous promise as the next sustainable processing medium. In order to realize the potential of GXLs fully, it is necessary to elucidate their cybotactic region and gain an understanding of where properties are different in the bulk and micro-scales and how local structure and order affect both reactions and separations. This work explores the cybotactic region of GXLs and probes the existence and implications of those differences. This study is started by exploring the cybotactic region of ambient liquid mixtures. Thermodynamic models based on intermolecular forces are used to predict the solubility of multi-functional solids in a variety of solvent mixtures. While this part does not lend any insight into GXLs directly, it acts as a stepping stone in both understanding the intermolecular forces that govern the cybotactic region and by opening the gateway to studying solid solubility in GXLs. The rest of the study focuses on the differences between bulk and local properties of GXLs. Different probes of polarity in the cybotactic region are compared and the solute dependence of the local structure is explored. Bulk transport properties are measured with different probes in an effort to see if molecular interactions play a role in governing diffusion processes in GXLs.