Quantum Model Supported Online Monitoring of Heterogeneous Catalyzed Hydrogenation Reactions

Reliable information on the kinetics of heterogeneously catalyzed multiphase reactions is important for the design and safe operation of industrial reactors. The challenge for these studies is to perform them under conditions similar to those found in industrial reactors. In particular, perturbations of the reactions by sampling must be avoided. We will present a laboratory reactor setup that perfectly meets these requirements. It uses inline benchtop NMR spectroscopy for quantitative analysis of the reaction mixture. The applicability of the reactor and the analytical method was demonstrated by studying the hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE). This synthesis is known both for its importance in the production of vitamins and for the occurrence of undesirable secondary and side-products. Online monitoring was performed up to pressures of 1 MPa. To enable quantitative analysis of overlapping and small peaks that occur in benchtop NMR spectra, we applied a mathematical analysis method. This method uses a quantum mechanical model of the species expected in the reaction mixture. It is fitted to the measured spectra to obtain the unknown relative composition of the different species. By applying prior knowledge from spectral databases and high-field NMR spectra to the model, we were able to identify various side-products and suggest new reaction pathways. Our approach demonstrates the great potential of benchtop NMR measurements to provide deep insight into industrially relevant syntheses under realistic conditions.