Issue 3, 2008

Consideration of some sampling problems in the on-line analysis of batch processes by low-field NMR spectrometry

Abstract

A low-field medium-resolution NMR spectrometer, with an operating frequency of 29 MHz for 1H, has been assessed for on-line process analysis. A flow cell that incorporates a pre-magnetisation region has been developed to minimise the decrease in the signal owing to incomplete polarisation effects. The homogeneous esterification reaction of crotonic acid and 2-butanol was monitored using a simple sampling loop; it was possible to monitor the progression of the reaction through changes in CH signal areas of butanol and butyl crotonate. On-line analysis of heterogeneous watertoluene mixtures proved more challenging and a fast sampling loop system was devised for use with a 5 L reactor. The fast sampling loop operated at a flow rate of 8 L min−1 and a secondary sampling loop was used to pass a sub-sample through the NMR analyser at a slower (mL min−1) rate. It was shown that even with super-isokinetic sampling conditions, unrepresentative sampling could occur owing to inadequate mixing in the reactor. However, it was still possible to relate the 1H NMR signal obtained at a flow rate of 60 mL min−1 to the composition of the reactor contents.

Graphical abstract: Consideration of some sampling problems in the on-line analysis of batch processes by low-field NMR spectrometry

Article information

Article type
Paper
Submitted
14 Sep 2007
Accepted
17 Dec 2007
First published
23 Jan 2008

Analyst, 2008,133, 339-347

Consideration of some sampling problems in the on-line analysis of batch processes by low-field NMR spectrometry

A. Nordon, A. Diez-Lazaro, C. W. L. Wong, C. A. McGill, D. Littlejohn, M. Weerasinghe, D. A. Mamman, M. L. Hitchman and J. Wilkie, Analyst, 2008, 133, 339 DOI: 10.1039/B714266H

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