Modelagem e simulação cfd da hidrodinâmica e transferência de massa em um biorreator coluna de bolhas para a produção da levedura Saccharomyces cerevisiae em batelada alimentada

Abstract

Ethanol is the world’s main biofuel and is predominantly produced via the fermentative conversion of biomass. In Brazil, ethanol production relies mainly on sugarcane and requires, among other inputs, high yeast concentrations. However, this process is constrained by the Crabtree effect, i.e., the conversion of sugars into ethanol even under aerobic conditions. Therefore, continuous oxygen transfer and sugar concentration control are required. In this context, pneumatic reactors, particularly bubble column reactors, are suitable due to their high oxygen transfer efficiency. To quantify oxygen transfer, a bubble column reactor was simulated using computational fluid dynamics (CFD) with Ansys® tools. Reactor hydrodynamics were analyzed by assessing the inclusion of the turbulent dispersion force in a model already accounting for interphase drag. Gas holdup and interphase slip velocity were compared for three different computational meshes. After mesh selection, two scenarios were investigated: case 1, considering only drag force; and case 2, considering both drag and turbulent dispersion forces. The inclusion of turbulent dispersion improved agreement between simulated and experimental gas holdup and volumetric oxygen transfer coefficient, both qualitatively and quantitatively, whereas case 1 progressively deviated from experimental data. Slip velocity profiles were similar for both cases at all air flow rates, and maximum values were nearly identical regardless of flow rate. In case 1, air-phase velocity was concentrated in the column core, while the liquid phase exhibited higher velocities near the wall. In case 2, this behavior resulted from a proportional reduction in the maximum velocities of both phases. Yeast cultivation modeling for Saccharomyces cerevisiae was carried out assuming a fed-batch operation with exponential feeding and constant kLa, based on CFD results. The simulations showed that the use of pure oxygen increased cell concentration and productivity. The effect of operating pressure was also evaluated, indicating that at 2 atm the minimum desired cell concentration was achieved for specific growth rates of 0.1 and 0.2 h⁻¹.