ATR-IR Spektroskopie als inline Analytik für kinetische Untersuchungen der zweiphasigen katalysierten Friedel-Crafts Acylierung

• ATR-IR spectroscopy as in-line analytics for kinetic investigations on the biphasic catalyzed Friedel-Crafts acylation

Picard, Marcel; Leitner, Walter (Thesis advisor); Liauw, Marcel (Thesis advisor)

Aachen (2015, 2016)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen, 2015

Abstract

Immobilization of a molecular catalyst in a second phase is a promising approach to facilitate the separation of reaction products from the catalyst. The intrinsic reaction rate is coupled with themass transport through the interfacial area between the phases. A modified Nitsch cell with ATRIR spectroscopy was used in this work for real-time measurements of absolute concentrations without taking samples out of the reactor.To study the kinetics of the biphasic Friedel-Crafts acylation of anisole catalyzed by Indiumtriflateimmobilized in an Ionic Liquid, an extensive calibration was performed to predict concentrationsof all reaction components in both phases with high accuracy (root mean square error of crossvalidation RMSECV < 0.01 mol/L). NMR spectroscopy was used for validation of the results. Forlow concentrations, the error of the IR measurements was higher compared to NMR data, but thisdrawback was compensated by the high data density and the fact that no manual sampling and sample preparation was needed. In experiments without catalyst, a mass transfer coefficient of 10-4 m/s was determined. Monitoring of concentration profiles in both phases in the reactive system provided solid data for kineticstudies. A design of experiments was planned and several experiments were executed to identifyrelevant parameters that influence the total yield of the reaction. A positive impact on the yield was found for high concentration of catalyst as well as with an excess of one of the substrates.The contribution of the reaction temperature could not be fully explained. In reaction runs with high catalyst concentrations an increase of the temperature lead to higher yields whereas inexperiments with low catalyst concentrations, a reaction temperature of more than 60 °C could result in lower amounts or even no product formation.Kinetic modelling based on the experimental data was performed in close collaboration with the process system engineering at RWTH Aachen University, Model candidates with different kineticlaws were fitted to the measured concentration profiles to identify suitable mathematicaldescriptions. The best agreement of theory and experimental results was found for a rate law withexponential product inhibition. The hypothesis is backed by Firas Zayed’s observations incontinuous long term stability tests of this catalyst system. To demonstrate the flexibility of the modified Nitsch cell with inline ATR-IR spectroscopy, a secondreaction was studied. Cyclic ethers like THF can be cleaved under acylating conditions usingIn(OTf)3 as a catalyst in the same biphasic solvent system. A simplified quantification method witha significantly lower amount of calibration samples was developed and tested for this reaction. Concentration profiles in both phases of the substrate were in good agreement with independent offline NMR analysis.