Fine bubbles for biocatalytic processes: Microscale phenomena and novel applications
Biotransformations, where one of the reactants is supplied via the gas phase, especially in the case of oxidations, are still a challenge. The aeration of enzymatic reactions using fine bubbles, whose diameters are less than 100 µm, has been investigated by focusing on hydrodynamics and mass transfer effects as well as reaction kinetics of enzymatic systems. However, the fundamental scientific questions regarding the local processes taking place at the gas-liquid interface of a dissolving fine bubble are still to be targeted. This is even more important, if the interaction between a fine bubble and an immobilized enzyme on a surface is addressed, especially, on the background of increasing attention to structured packings as carrier materials for enzymes. The local mass transfer rate and oxygen concentration gradient at the interface is expected to be strongly affected by the Laplace pressure with decreasing bubble diameter. For mass transfer limited enzymatic reactions this mass transfer enhancement and the interaction between the enzymes and the gas-liquid interface are central aspects influencing the effectivity of the reaction. Using Laser Induced Fluorescence (LIF) measurements local mass transfer phenomena can be studied. With the help of these measurements the effect that enzymes are more stable during fine bubble aeration compared to conventional aeration, as demonstrated in the predecessor project, will be analyzed. In this context, investigation of the concentration boundary layer conditions on enzyme denaturation will be carried out for a better understanding of the acting mechanisms.