Bubbles size and mass transfer in a pulsating flow type apparatus with gas-liquid mixture

Hydrodynamics of pulsating flow type apparatus (PFA), namely bubble disintegration, as well as interfacial mass transfer were investigated experimentally analysed theoretically. Influence of several mechanisms on bubble sizes is studied: Kelvin–Helmholtz and Rayleigh–Taylor instabilities, turbulence in the bulk of liquid and near walls of apparatus, dynamic and inertial mechanisms as well as high shear stresses. It was found that the dependence of gas bubble size on energy dissipation rate in PFA, static mixers and stirred tank reactors with Rushton turbine are described by the same exponential equation, and they have comparable parameters. However, each type of the mixers has limitation of energy dissipation rate: ε = 0.5–3 W/kg for baffled agitated tanks; ε = 20–200 W/kg for static mixers, and 30–5000 W/kg for PFA. Due to the intensive mass transfer from/to the bubbles surface as well as high interfacial area induced by several mechanisms of bubbles disintegration, high values of kLa were achieved. Hence, PFA could be recommended as a promising replacement of traditional reactors like stirrers or other kinds of flow type reactors like tubular turbulent apparatus or oscillated baffle reactors (OBRs), Buss loop reactor, Plunging jet absorber, especially for the fast and ultrafast reactions (hydrogenation, chlorination, amination, alkylation, carbonylation, oxidation, ethoxylation, etc.) and other processes (and with recycling for slower reactions). In combination with the tank reactors the PFA could be used as an alternative for the reactors for the processes where long residence time is necessary (e.g. for bioreactions).