Switchable hydrophilicity solvents (SHSs) are an emerging class of solvents for facile and energy-efficient liquid-liquid extraction (LLE) processes with “switching” of physiochemical properties of nitrogenous bases (e.g., amines or amidines). In presence of carbon dioxide (CO2) and water, SHSs undergo protonation caused by formation of carbonic acid (H2CO3), resulting in substantial change in hydrophilicity, polarity, or ionic strength of the SHS. The CO2-triggered tuning of the distribution coefficient of SHS in hydrophobic/hydrophilic media drives the reversible transfer of the SHS in presence of CO2, dramatically reducing the energy needed for LLE processes. This unique characteristic of SHSs have opened a new frontier for energy-efficient chemical separations in various fields ranging from recycling of packaging materials to extraction of algal biomass. Since discovery of SHSs, the fundamental and applied studies of SHSs have typically been conducted using conventional flask-based techniques. However, the relatively low specific interfacial area (e.g., bubble columns offer 50-600 m2/m3) and gas-liquid contact time of conventional reactors for gas-liquid reactions have resulted in long solvent extraction times ranging from 2 h – 10 h, thereby hindering further development of this promising class of solvents. In this work, we utilize an intensified microfluidic reactor for accelerated fundamental studies and screening of SHSs while minimizing the chemical consumption. The developed microfluidic reactor utilizes a highly CO2-permeable membrane (Teflon AF-2400) in a tube-in-tube configuration, providing specific interfacial areas exceeding 4900 m2/m3. Utilizing the developed flow chemistry platform, we systematically studied the effects of both continuous (e.g., CO2 pressure, and reaction time) and discrete (e.g., chemical structure of the SHS) process parameters on the kinetics and extent of the SHS recovery process. The intensified flow reactor integrated with an in-situ process screening probe enables complete SHS recovery in 3~8 min (~100 times faster than a batch reactor), while utilizing only 4~8 μL of SHS mixture (~2500 times less chemical consumption than a batch reactor). The results of this research project provide valuable insights and a robust guideline towards the development of next-generation SHSs for energy-efficient chemical separation.

Accelerated material- and energy-efficient studies of switchable hydrophilicity solvents

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.