For the first time the formation and decay of the thermally very sensitive bis(μ-oxo)dicopper species was monitored at ambient temperature in a continuous flow setup and the rate constant of the decay was measured.
The description and prediction of the highly transient processes on the molecular scale in gas-liquid Taylor flows in microchannels are a great challenge. Due to a lack of in situ measurement techniques with satisfactory spatial and temporal resolution, existing models and numerical simulations of reactive two-phase flows are poorly developed. The Raman spectroscopic and holographic system presented herein overcomes shortcomings regarding the high temporal resolution and concomitant difficulties with the high energy densities that must be coupled into microstructured devices to give good limits of detection. It gives insight into the concentration profiles in the liquid phase within the microchannel to study the interaction between hydrodynamics, mass transport, and reaction kinetics.
The reaction of Cu(I) bisguanidine complexes with nitric oxide and the formation of intermediate species were monitored via UV-vis spectroscopy at low temperature, with the occurrence of characteristic absorption bands. The origin of the emerging species and their character were substantiated by electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) studies showing a delocalized {CuNO} 11 radical species. Furthermore, this system was transferred to the SuperFocus mixer setup, which allows rapid mixing and the determination of decay constants at ambient temperatures of the thermally sensitive species. However, these experiments demonstrated the limits of these systems, such as the NO saturation in organic solvents and a preferably precise temperature control within the SuperFocus mixer, which should be addressed in the future.
Abstract. For a reaction between a gaseous phase and a liquid phase, the interaction between the hydrodynamic conditions, mass transport and reaction kinetics plays a crucial role with respect to the conversion and selectivity of the process. Within this work, a sensor system was developed to simultaneously characterise the bubble dynamics and the localised concentration measurement around the bubbles. The sensor system is a combination of a digital Mach-Zehnder holography subsystem to measure bubble dynamics and a confocal Raman-spectroscopy subsystem to measure localised concentration. The combined system was used to investigate the chemical absorption of CO 2 bubbles in caustic soda in microchannels. The proposed set-up is explained and characterised in detail and the experimental results are presented, illustrating the capability of the sensor system to simultaneously measure the localised concentration of the carbonate ion with a good limit of detection and the 3-D position of the bubble with respect to the spot where the concentration was measured.
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