| dc.description.abstract | The need to reduce air pollution in chemical manufacturing processes continues to drive the search for alternative solvents. Ionic Liquids (ILs) have emerged in recent years as a promising solution. In contrast to traditional organic solvents, ILs have negligible volatility, which eliminates air emissions and harmful worker exposure concerns. Various combinations of cations and anions afford distinct properties to an IL, such as melting point, solvation properties, and phase behavior; thus making it possible to molecularly design or engineer ILs for specific tasks across many chemical sectors. Unfortunately, many ILs are synthesized and processed using the very organic solvents which they are purportedly replacing. Despite the exponential growth in this field, very little work focuses on developing alternative synthesis and production methods for ILs. The objective of this dissertation is to investigate novel economically viable and environmentally benign methodologies for ionic liquid production. Three solvent platforms: 1) conventional organic solvents; 2) compressed and supercritical CO2; 3) CO2-Expanded DMSO are considered for the synthesis of IL synthesis. A full understanding of the kinetics and effects of solvent in the synthesis of ILs is of great importance for optimally selecting a benign and economically viable solvent for IL production. Empirical LSER expression, correlating kinetic rate constant with solvent polarity was obtained, which will facilitate rapid data generation needed for engineering production processes of different ILs in varied solvent systems. While some general trends for these Mentshukin-type reactions are widely known, quantitative second (2nd) order rate constants are reported here. The use of CO2 in the synthesis of ILs has many advantages over conventional solvents. CO2 induces IL-solvent mixtures to split into IL-rich and organic solvent-rich phases that can be decanted or extracted for easy separations, simply by controlling pressure, temperature and CO2 loading. This work demonstrates that CO2 is a flexible and tunable solvent for the synthesis of the model IL 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]). Previously, our group has found that among ten organic solvents, DMSO has the highest kinetic rate for the synthesis of [HMIm][Br]). Although DMSO is a relatively environmentally benign solvent, it is beset with a high boiling point (189oC), rendering it both economically and environmentally non-feasible as a solvent option. The synthesis and processing of ILs in gas-expanded DMSO alleviates these issues. Furthermore, gas expanded liquids reduce the amount of organic solvent needed for the reaction. This work, for the first time, leverages the kinetic benefits of DMSO and the thermodynamic advantages of benign CO2 for the production of ILs. Specifically, this study explored another promising solvent media; CO2 expanded liquid DMSO (CXLs).Non-complex separation schemes are proposed from mixture phase behavior. Kamlet-Taft polarity parameters for CO2 expanded DMSO are also reported. Experimental high-pressure phase equilibria data were measured and modeled for CO2 binary, ternary and pseudo-binary systems encountered in the synthesis of [HMIm][Br]. Unique chemical and thermodynamic behaviors are observed in the IL-synthesis mixtures. Using estimated critical properties to correlate the vapor-liquid equilibrium, the Peng-Robinson equations of state, with van der waals 2-parameter mixing rules, were found to sufficiently correlate data. The phase equilibrium data allow better understanding and kinetic characterization of the synthesis of ILs with CO2. Results have important ramifications on the kinetics and process constraints of an actual IL synthesis in high pressure systems. Design considerations for optimizing solvents ratio, kinetic properties and separations are discussed. Here, the systematic risk assessment methodology was extended to ILs systems. Environmental assessments of different IL synthesis routes studied here are performed and presented. Potential issues (unit operations that have the most impact on the environment and profitability) in the life cycle of the processes are identified. Green sustainable methodology was extended to applications of ILs viz cellulose valorization and processing, separations and the fabrication of cellulosic materials. | |
