In Situ and in Operando Characterization of Mixing Dynamics in Liquid-Phase Reactions by 129 Xe NMR Spectroscopy.

129 Xe NMR spectroscopy is applied under in situ and in operando conditions to study the mixing process in a multicomponent liquid mixture with partially miscible components. The process of mixing of an oil-methanol mixture was triggered by an industrially relevant catalytic transesterification reaction to form fatty acid methyl esters and glycerol. Up to date, kinetic limitations in liquid-phase reactions originating from the poor miscibility of the reacting species have been addressed solely under ex situ conditions, typically by chromatography. In the approach presented here, xenon gas, solvated in the reacting species, acts as a sensor, providing information on the progress of mixing and on the composition during the course of the catalytic reaction. We believe that this study offers a new tool to the set of established techniques for addressing mixing and/or separation processes in liquids, including but not limited to the ones resulting from catalytic reactions.