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The application of compact NMR instruments to hot flowing samples or exothermically reacting mixtures is limited by the temperature sensitivity of permanent magnets. Typically, such temperature effects directly influence the achievable magnetic field homogeneity and hence measurement quality. The internal-temperature control loop of the magnet and instruments is not designed for such temperature compensation. Passive insulation is restricted by the small dimensions within the magnet borehole. Here, we present a design approach for active heat shielding with the aim of variable temperature control of NMR samples for benchtop NMR instruments using a compressed airstream which is variable in flow and temperature. Based on the system identification and surface temperature measurements through thermography, a model predictive control was set up to minimise any disturbance effect on the permanent magnet from the probe or sample temperature. This methodology will facilitate the application of variable-temperature shielding and, therefore, extend the application of compact NMR instruments to flowing sample temperatures that differ from the magnet temperature.
Intensified continuous processes are in focus of current research. Compared to traditional batch processes, intensified continuous production allows the synthesis of new and difficult producible compounds with better product uniformity and reduced consumption of raw materials and energy. Flexible (modular) chemical plants can produce various products using the same equipment with short down-times between campaigns, and quick introduction of new products to the market. Consequently, the demand for powerful Process Analytical Technologies, which can monitor key variables like component concentrations in real-time, is increasing. Low-Field NMR spectroscopy presents itself as such an upcoming smart sensor1,2 (as addressed, e.g., in the CONSENS project3,4).
Continuous measurement approaches can usually be differed in On- or In-line which both have advantages and drawbacks. On the one hand On-line measurements are easy to integrate even in existing setups through bypass systems, on the other hand issues like the representativity of the sampling must be considered. In the case of Inline analysis, where the whole fluid stream is analyzed, this issue can be avoided. Nevertheless, homogeneity of the mixture must be assured using NMR spectroscopy.
This talk shall give a brief summary of current Online and Inline Low-Field NMR approaches. Furthermore, current research results using a tailor-made flow cell for inline analysis are shown pointing out the working range as well as limitations of these method in combination with NMR spectroscopy.