The kinetics of the methylation of triethylamine (NEt3) with dimethyl carbonate (DMC) in methanol have been investigated by means of in situ ATR-IR-spectroscopy. The data show an autocatalytic influence of the ionic product on reaction kinetics. A bend in the reaction rate progress indicates a sudden change from solvated ions to a microstructured biphasic system, which is reflected in the dependence of the reaction rate constant on the product concentration and the Hildebrand parameter.

Biphasic reactions were investigated in a specially designed high pressure set-up that allows simultaneous fibre-optic ATR IR and ATR UV-Vis measurements in both phases. The scope of quantitative spectroscopic measurements is tested on the absorption of CO2 in hexanol and a biphasic switchable solvent synthesis. For both systems, all substances including dissolved and gaseous CO2 can be quantified and a constant total mass balance over all phases can be achieved for every component in the reaction system. This confirms that the quantification methods are applicable and the reactor can be applied to gain further insight into the microkinetics and transport phenomena of multiphase reactions.

A miniaturized modularized tubular reactor setup designed for flexible small-scale experimentation under continuous flow conditions was investigated for its residence time behavior. Studies focused on the question of whether the coil shape of the tubular reactor segments beneficially affects the dispersion behavior of the system by inducing secondary flows in the dispersed plug flow pattern. In the studies, fiber-coupled sensors for the attenuated total reflectance technique were applied to measure concentration profiles of tracer substances by Fourier transform mid-infrared spectroscopy. Sensor flow cells with specifically structured flow geometries were designed in order to reduce the impact on the flow characteristics, and in this context they have proven to be superior to nonstructured flow cells. Quantitative evaluation of the measured spectra yielded good-quality time profiles of the tracer concentration that were subjected to a mathematical approximation with the well-established dispersion model by Taylor and Aris. In accordance with model predictions from literature, the axial dispersion coefficient is drastically reduced in coiled capillaries as compared to the coefficient in the Taylor−Aris case for straight tubes. Depending on the influence of the tube curvature and the flow properties, expressed by the product of the square Dean number and the Schmidt number, the reduction of the axial dispersion coefficient can be by up to a factor of 4. For chemical processes with critical requirements regarding selectivity, this can be of great advantage since the detrimental impact of axial back-mixing is effectively reduced.

The kinetics of the methylation of triethylamine (NEt3) with dimethyl carbonate (DMC) in methanol have been investigated by means of in situ ATR-IR-spectroscopy. The data show an autocatalytic influence of the ionic product on reaction kinetics. A bend in the reaction rate progress indicates a sudden change from solvated ions to a microstructured biphasic system, which is reflected in the dependence of the reaction rate constant on the product concentration and the Hildebrand parameter.