title: 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 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.
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, UK G1 1XL. alison.nordon@strath.ac.uk
authors.forename: Alison
authors.initials: A
authors.lastname: Nordon
authors.forename: Alvaro
authors.initials: A
authors.lastname: Diez-Lazaro
authors.forename: Chris W L
authors.initials: CW
authors.lastname: Wong
authors.forename: Colin A
authors.initials: CA
authors.lastname: McGill
authors.forename: David
authors.initials: D
authors.lastname: Littlejohn
authors.forename: Manori
authors.initials: M
authors.lastname: Weerasinghe
authors.forename: Danladi A
authors.initials: DA
authors.lastname: Mamman
authors.forename: Michael L
authors.initials: ML
authors.lastname: Hitchman
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Wilkie