Online process monitoring of a batch distillation by medium field NMR spectroscopy

•Fast and robust method for measuring residue curves in multi component systems.•Particularly interesting for the validation of VLE models that were parametrized with binary data.•Non-invasive online analysis method at unaffected thermodynamic conditions (temperature, pressure, composition of phases).•Appropriate for measuring residue curves, boiling curves and high-boiling azeotropes.•For systems with volatile or unstable components or at pressure below 1 atm. Medium field NMR spectrometers are attractive for online process monitoring. Therefore, in the present work, a single-stage laboratory batch distillation still was coupled online with a medium field NMR spectrometer. This enables quantitative non-invasive measurements without calibration. The technique was used for studying isobaric and isothermal residue curves in two ternary systems: (dimethyl sulfoxide + acetonitrile + ethyl formate) and (ethyl acetate + acetone + diethyl ether) and boiling curves and high-boiling azeotropes in two binary systems: (acetic acid + pyridine) and (methanol + diethylamine). The results of the online NMR spectroscopic analysis were compared to results from offline analysis as well as to results from thermodynamic modeling using NRTL parameters that were parametrized with literature data. The new method for online process monitoring gives reliable results and is well-suited for fast and robust measurements of residue curves.