Local Mass Transfer Phenomena and Chemical Selectivity of Gas‐Liquid Reactions in Capillaries

Abstract

Dedicated to Professor Rüdiger Lange on the occasion of his 65th birthday Gas-liquid reactions in microreactors play an important role in scientific research and industry. Enhancing heat and mass transfer allows overcoming mass transfer limitations in gas-liquid reactions. Mass transfer can be further increased by employing helically coiled capillaries, which induce Dean vortices and improve radial mixing. A colorimetric technique is proposed for gas-liquid reactions in straight and helically coiled capillaries in order to visualize local mass transfer phenomena and concentration distributions. This method is based on the consecutive oxidation of leuco-indigo carmine and enables noninvasive investigation of mass transfer and chemical selectivity in microchannels with high temporal and spatial resolution.

Kinetic Study of Leuco‐Indigo Carmine Oxidation and Investigation of Taylor and Dean Flow Superposition in a Coiled Flow Inverter

“…Starting at time step t 1 at cross section A in the rear very close to the bubble generation step, the concentration distribution of the three indigo carmine species is expected to be very similar to the symmetric concentration distribution in a straight tube, which is mainly influenced by Taylor flow . This includes central oxygen transport, product generation at the rear cap encased by the yellow reactant, and further blue product near the wall area due to returning liquid from the front interface.…”

“…By introducing glucose in alkaline solution this reaction can be reversed. This method is based on image processing and has been calibrated and validated by means of UV‐Vis spectroscopy and is described in more detail in Krieger et al .…”

“…with t as time for rate of concentration change, as concentration of dissolved oxygen, C LIC as concentration of leuco‐indigo carmine, C Int as concentration of the intermediate product, C KIC as concentration of keto‐indigo carmine, ν as stoichiometric coefficient that is equal to 1 , , and k 1 and k 2 as reaction rate coefficients.…”

“…By introducing glucose in alkaline solution this reaction can be reversed. This method is based on image processing and has been calibrated and vali-dated by means of UV-Vis spectroscopy and is described in more detail in Krieger et al [28]. It is known from the work of Yang et al [32] that a similar redox dye, namely dihydroresorufin, contributes a negligible amount to the enhancement of mass transfer (E = 1.03) for the investigated conditions, but a study for the oxidation of leucoindigo carmine has not been done so far.…”

Smart Equipment – A Perspective Paper

“…Wavelength regions that are usually used for quantitative analysis of substances are ultraviolet and visible (UV‐vis), near‐infrared (NIR), and infrared. Instead of using a commercial photometer, absorption measurements in the visible light region on laboratory scale can also be carried out by using very simple equipment, such as a light source behind the sample and a DSLR camera . The resulting photos are processed, e.g., in Matlab®, by analyzing the color intensity in each pixel.…”