Chemical Engineering and Catalysis

Biography

Biography: Mojtaba Mirdrikvand

Abstract

The in-situ analysis of catalytically gas phase reactions offers not only an accurate characterization of the reactions but also the possibility to validate numerical simulations. The latter allows optimizing operational performance and reducing industrial costs as well as predicting possible risks at scaled up reactors. Accurate measurement of temperature profiles along radial and axial direction of the reactor requires non-invasive approaches to obtain a realistic assessment of the operating systems, without interfering with the process. Among in-situ approaches, Nuclear Magnetic Resonance (NMR) offers a huge flexibility to perform various direct and indirect spatio-temporal measurements for heterogeneous systems. In this work, two NMR techniques were implemented to obtain a quantitative temperature analysis for a broad temperature range. Magnetic Resonance Spectroscopic Imaging (MRSI) and Diffusion Weighted Magnetic Resonance Imaging (DW-MRI) were applied on a 7T MRI system to assess temperature profiles in the reactor environment and the catalyst bed at high temperatures. The first approach, MRSI, uses capillaries (OD: 0.3-0.6 mm) filled with ethylene glycol as thermometers for temperature measurements in the range of 20-150 °C by evaluating the chemical shift difference between the CH3 and the OH signal. However, the MRSI approach depends on a sufficient spatial homogeneity of the magnetic field, which limits the applicability in some cases. Therefore, the second method, DW-MRI, was implemented as a fast and robust toolkit for measurements in a broader temperature range (T<350 °C), being more robust against magnetic field inhomogeneities than MRSI. The optimized 3D DW-MRI method acquires images with high spatial resolution (~ 0.5⨯0.5⨯1.5 mm3) using four different diffusion sensitizing gradients corresponding to different diffusion weightings (b-values). Fitting the measured signal intensities S(b) in each voxel according to S=S0*exp(-bD) allows to determine the temperature dependent diffusion coefficient D, and thus the temperature. Initial experiments used glycerol as probing liquid. To enable measurements of temperature up to 350 °C, high-boiling ionized liquids are currently investigated.