Monitoring the kinetics of the ion-exchange resin catalysed esterification of acetic acid with ethanol using near infrared spectroscopy with partial least squares (PLS) model

The esterification of acetic acid with ethanol in the presence of a heterogeneous acid catalyst was monitored by near infrared (NIR) spectroscopy. A strong acid macroporous poly(styrene-co-divinylbenzene) based ion-exchange resin was used as catalyst. The liquid phase esterification was carried out in a stirred batch laboratory reactor at 60°C. Samples taken from the reaction mixture were analysed both by NIR spectroscopy and by gas chromatography (GC). The concentration of the reactants acetic acid and ethanol as well as the reaction products water and ethyl acetate were predicted from NIR spectra by multivariate PLS calibration model and compared to concentrations obtained by GC. The results of the PLS predictions showed that the spectral range from 7600 to 3800 cm−1 is well suited for concentration measurements. The concentrations of acetic acid, ethanol, ethyl acetate and water were successfully predicted from the NIR spectra. Reaction monitoring is simpler and faster by NIR than by GC. NIR spectroscopy enables simultaneous on-line monitoring of all reaction components with an accuracy better than that obtained in this work by using GC.