Switchable Water: Microfluidic Investigation of Liquid–Liquid Phase Separation Mediated by Carbon Dioxide

Increase in the ionic strength of water that is mediated by the reaction of carbon dioxide (CO₂) with nitrogenous bases is a promising approach toward phase separation in mixtures of water with organic solvents and potentially water purification. Conventional macroscale studies of this complicated process are challenging, due to its occurrence via several consecutive and concurrent steps, mass transfer limitation, and lack of control over gas–liquid interfaces. We report a new microfluidic strategy for fundamental studies of liquid–liquid phase separation mediated by CO₂ as well as screening of the efficiency of nitrogenous agents. A single set of microfluidic experiments provided qualitative and quantitative information on the kinetics and completeness of water–tetrahydrofuran phase separation, the minimum amount of CO₂ required to complete phase separation, the total CO₂ uptake, and the rate of CO₂ consumption by the liquid mixture. The efficiency of tertiary diamines with different lengths of alkyl chain was examined in a time- and labor-efficient manner and characterized with the proposed efficiency parameter. A wealth of information obtained using the MF methodology can facilitate the development of new additives for switchable solvents in green chemistry applications

Microfluidic Studies of CO₂ Sequestration by Frustrated Lewis Pairs

Frustrated Lewis pairs (FLPs) comprising sterically hindered Lewis acids and bases offer the capability to reversibly capture CO₂ under mild reaction conditions. The determination of equilibrium constants and thermodynamic properties of these reactions should enable assessment of the efficiency of a particular FLP system for CO₂ sequestration and provide insights for design of new, efficient formulations of FLP catalysts for CO₂ capture. We have developed a microfluidic approach to studies of FLP–CO₂ reactions, which provides their thermodynamic characterization that is not accessible otherwise. The approach enables the determination of the equilibrium reaction constants at different temperatures, the enthalpy, the entropy, and the Gibbs energy of these reactions, as well as the enhancement factor. The microfluidic methodology has been validated by applying it to the well-characterized reaction of CO₂ with a secondary amine. The microfluidic approach can be applied for fundamental thermodynamic studies of other gas–liquid reactions