Process Applications of NMR
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Abstract
This thesis describes applications of NMR techniques to flowing liquid streams to
obtain quantitative information about the contents of the streams. The quantitative
accuracy of NMR spectroscopy for composition measurement of liquid mixtures is
measured as ±0.34 mol% and ±1 mol% for static and flowing mixtures respectively.
The effects of flow on NMR spectroscopy are analysed using the residence time
distributions of the streams in the magnet and the detection coil. Algorithms are
developed for automated analysis of the NMR spectra of the mixtures, in which
automatic phase and baseline correction are performed together. A peak-assignment
algorithm is written that identifies components in a mixture based on the patterns
observed in the pure-component spectra. Automated composition analysis of mixture
spectra is performed using these algorithms in less than 4 minutes with an accuracy of
±0.66 mol%. A mathematical model is derived for the NMR spectrum of a mixture
that considers the spectrum a weighted sum of pure-component spectra shifted in
frequency. The experimental lineshape observed in an inhomogeneous magnetic field
is poorly fitted by a Lorentzian lineshape, so a new model lineshape is developed
based on the distribution of resonance frequencies across the sample. Volume
selective NMR spectroscopy using the STEAM and PROJSAT pulse sequences is
optimised to give quantitative results from well-defined volumes with minimal signal
contamination. The STEAM pulse sequence is modified to include flow-compensated
slice selection gradients. The accuracy of the compositions measured from volume
selective spectra is measured as ±1 mol% and ±2 mol% for static and flowing
mixtures respectively. Pulsed field gradient NMR sequences using double echoes for
flow compensation are tested on flowing water, then used to determine the droplet
size distributions of flowing emulsions. Flow images are acquired of a vertical liquid
jets showing the narrowing and acceleration of the jet and the entrainment of the
surrounding water.