Flowing Liquids in NMR: Numerical CFD Simulation and Experimental Confirmation of Magnetization Buildup

Abstract

Process and reaction monitoring by nuclear magnetic resonance (NMR) spectroscopy has attracted considerable attention in the last years not only because of the new generation of low-field NMR spectrometers, but also because of an industrial need of more effectivity and process optimization via real-time monitoring of process and reaction details by diverse analytical tools. Most often, bypass solutions are realized in liquid state monitoring, which leads to questions of residence time distribution, mixing phenomena and accuracy of concentration determination. Exploring chemical engineering knowledge of fluid dynamics and combining it with NMR knowledge of magnetization buildup allow the calculation of magnetization in NMR measurements on flowing substances. This approach reveals the essential parameters to be considered when constructing flow cells and when processing data in NMR process monitoring. 3D computational fluid dynamics combined with Bloch equations allows detailed time and spatially resolved insights into the significant mechanisms of magnetization distribution and opens up new possibilities for experiment design in flow NMR. An experimental confirmation was provided by MRI experiments.