title: Monitoring of an esterification reaction by on-line direct liquid sampling mass spectrometry and in-line mid infrared spectrometry with an attenuated total reflectance probe.
abstract: A specially designed thermal vaporiser was used with a process mass spectrometer designed for gas analysis to monitor the esterification of butan-1-ol and acetic anhydride. The reaction was conducted at two scales: in a 150 mL flask and a 1L jacketed batch reactor, with liquid delivery flow rates to the vaporiser of 0.1 and 1.0 mLmin(-1), respectively. Mass spectrometry measurements were made at selected ion masses, and classical least squares multivariate linear regression was used to produce concentration profiles for the reactants, products and catalyst. The extent of reaction was obtained from the butyl acetate profile and found to be 83% and 76% at 40°C and 20°C, respectively, at the 1L scale. Reactions in the 1L reactor were also monitored by in-line mid-infrared (MIR) spectrometry; off-line gas chromatography (GC) was used as a reference technique when building partial least squares (PLS) multivariate calibration models for prediction of butyl acetate concentrations from the MIR spectra. In validation experiments, good agreement was achieved between the concentration of butyl acetate obtained from in-line MIR spectra and off-line GC. In the initial few minutes of the reaction the profiles for butyl acetate derived from on-line direct liquid sampling mass spectrometry (DLSMS) differed from those of in-line MIR spectrometry owing to the 2 min transfer time between the reactor and mass spectrometer. As the reaction proceeded, however, the difference between the concentration profiles became less noticeable. DLSMS had advantages over in-line MIR spectrometry as it was easier to generate concentration profiles for all the components in the reaction. Also, it was possible to detect the presence of a simulated impurity of ethanol (at levels of 2.6 and 9.1% mol/mol) in butan-1-ol, and the resulting production of ethyl acetate, by DLSMS, but not by in-line MIR spectrometry.
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Owen
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.
authors.forename: Edith A J
authors.initials: EA
authors.lastname: McAulay
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK. Electronic address: alison.nordon@strath.ac.uk.
authors.forename: Alison
authors.initials: A
authors.lastname: Nordon
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK. Electronic address: d.littlejohn@strath.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Littlejohn
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Lynch
authors.affiliation: Hull Research & Technology Centre, BP Chemicals, Hull, HU12 8DS, UK.
authors.forename: J Steven
authors.initials: JS
authors.lastname: Lancaster
authors.affiliation: Thermo Fisher Scientific, Winsford, Cheshire, CW7 3GA, UK.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Wright
keywords: In-line mid infrared spectrometry; On-line direct liquid sampling mass spectrometry; Process analysis; Quantitative reaction monitoring; Thermal vaporiser; Trace analysis