Monitoring the kinetics of the ion-exchange resin catalysed esterificationof 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 heterog eneous acid catalyst was monitored by near infrared (NIR) spectroscopy. A s trong acid macroporous poly(styrene-co-divinylbenzene) based ion-exchange r esin was used as catalyst. The liquid phase esterification was carried out in a stirred batch laboratory reactor at 60 degrees C. Samples taken from t he reaction mixture were analysed both by MR spectroscopy and by gas chroma tography (GC). The concentration of the reactants acetic acid and ethanol a s well as the reaction products water and ethyl acetate were predicted from NIR spectra by multivariate PLS calibration model and compared to concentr ations obtained by GC. The results of the PLS predictions showed that the s pectral range from 7600 to 3800 cm(-1) is well suited for concentration mea surements. The concentrations of acetic acid, ethanol, ethyl acetate and wa ter were successfully predicted from the NIR spectra. Reaction monitoring i s simpler and faster by NIR than by GC. NIR spectroscopy enables simultaneo us on-line monitoring of all reaction components with an accuracy better th an that obtained in this work by using GC. (C) 1998 Elsevier Science B.V. A ll rights reserved.