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

Nordon, Alison; Diez-Lazaro, Alvaro; Wong, Chris W. L.; McGill, Colin A.; Littlejohn, David; Weerasinghe, Manori; Mamman, Danladi A.; Hitchman, Michael L.; Wilkie, Jacqueline

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 water–toluene 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.

Citation

Nordon, A., Diez-Lazaro, A., Wong, C. W. L., McGill, C. A., Littlejohn, D., Weerasinghe, M., Mamman, D. A., Hitchman, M. L., & Wilkie, J. (2008). Consideration of some sampling problems in the on-line analysis of batch processes by low-field NMR spectrometry. Analyst, 133(3), 339-347. https://doi.org/10.1039/b714266h

• Journal Article Type: Article
• Acceptance Date: Dec 17, 2007
• Online Publication Date: Jan 23, 2008
• Publication Date: 2008
• Deposit Date: Jul 9, 2021
• Journal: The Analyst
• Print ISSN: 0003-2654
• Electronic ISSN: 1364-5528
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 133
• Issue: 3
• Pages: 339-347
• DOI: https://doi.org/10.1039/b714266h
• Public URL: http://researchrepository.napier.ac.uk/Output/2782116