Development of a multiscale model for the design and scale-up of gas/liquid stirred tank reactors

•A multiscale model is developed as a tool for the design and scale-up of gas/liquid STRs.•It combines a compartmental model, a simplified CFD model and theoretical correlations.•It is shown to predict adequately the mean kLa value of each compartment.•The effects of operating conditions and scale-up on the compartmental values of kLa are analyzed. A multiscale gas/liquid flow model was developed as a tool for the design and scale-up of stirred tank reactors (STRs). The model is based on the compartmentalization of the STR into zones and the use of simplified less computationally intensive gas/liquid flow simulations. It predicts the mean value of the local volumetric mass transfer coefficient (kLa) in each compartment based on the local hydrodynamic parameters therein (i.e., gas hold-up and liquid turbulent energy dissipation rate). The adequacy of the model at each step was carefully assessed using experimental data drawn from the literature. The proposed model was able to predict the overall volumetric mass transfer coefficient in STRs agitated with a Rushton turbine with good adequacy. The effects of operating conditions and scale-up on the distribution of kLa were also studied. The contributions of each compartment to the overall mass transfer inside the STR could be changed considerably by altering the operating conditions and scale-up. It was estimated that by increasing the STR size, the overall volumetric mass transfer coefficient decreased by at least 20% following a conventional scale-up rule. This was explored by combining the concepts of the local residence time distribution (RTD) of the liquid phase and the local kLa values inside the STR. These findings revealed the challenges involved in scaling up multiphase stirred tanks. Lastly, some alternative approaches are suggested for the design and scale-up of multiphase reactors that may mitigate the inherent limitations of conventional rules.