Process and reaction monitoring by low-field NMR spectroscopy

Molecular Properties of Fatty Acid Mixtures Estimated by Online Time-Domain NMR

“…Measurements of flowing samples require pre-magnetization of the 1 H nucleus in a magnet system for a time of 5T 1 [11]. The dimensions of the NMR probe and magnet system should be appropriate for providing uniform sample excitation and acquisition as well as initial pre-magnetization.…”

“…For example, the NMR relaxation times of fluids were measured under continuous flow with a maximal detectable flow velocity of approximately 30 mm/s by low-field NMR fluid analysis systems [33][34][35]. Reactions can also be monitored using an NMR spectrometer equipped with a flow cell in a bypass with a lower velocity (not exceeding 2 mL/min) than that in the main reactor [11,17,32]. However, the flow velocities in the real industrial processes are typically very high (on the order of m/s).…”

“…However, the flow velocities in the real industrial processes are typically very high (on the order of m/s). In most cases, the process measurements were made during stopped flow [18,35] or in a bypass with a low flow velocity [11,17,32]. Therefore, methods consisting of sample measurements during stopped flow appear to be applicable for real process monitoring, although the sampling of stopped flow can be more time-consuming compared to continuous flow.…”

“…However, traditional high-resolution NMR spectrometers are hardly applied to industrial process control due to their open magnetic field, large size and high price and the required cryogen use. Recently developed low-field benchtop spectrometers with permanent magnets (up to 2 T) are less expensive and more compact and provide sufficient accuracy for chemical analysis, making them competitive with traditional high-resolution spectrometers [11,12]. A compact NMR spectrometer was applied to the determination of several quality parameters of diesel fuel in the paper by Killner et al [13].…”

“…However, TD-NMR has proven usable in industrial applications due to its mobility, low price, robustness, non-destructive analysis, and lack of sample preparation [11,15,16]. Furthermore, online process monitoring by NMR is also an increasingly used technique [11,12,17]. In one study [18], the TD-NMR technique was applied to the online determination of metal ion precipitation in mine water and was subsequently tested in a mine environment.…”