A multi-fluid approach to simulate separation of liquid-liquid systems in a gravity settler

Industrial processes employing homogeneous catalysis face the difficulty of an economic recovery of the catalyst. In order to be able to design an optimal process route, a comprehensive understanding of the separation process is essential. In this work, the gravity-driven separation of a multi-phase system composed of water, 1-dodecene, and a non-ionic surfactant, is investigated. Within the employed ranges of temperature and phase composition, this system exists in a three-phase configuration, consisting of an aqueous, an organic, and a surfactant-rich middle phase. Following the reaction step, a complete separation of the aqueous phase, in which the expensive rhodium catalyst is dissolved, is essential. Extensive experiments have been carried out to determine the drop size distribution (DSD) of the disperse phases using an endoscopic measurement technique. Based on these experimental data, a Computational Fluid Dynamics (CFD) model employing the Euler-Euler multi-fluid framework coupled with the Extended Quadrature Method of Moments (EQMOM) for the solution of the population balance equations (PBEs) for each disperse phase is implemented using OpenFOAM. Within the framework of this CFD-PBE model, a buoyancy-induced coalescence model, which has been previously shown to accurately predict the degree of separation, has been employed. This multi-fluid CFD-PBE model has been used for simulating the separation of the three-phase system in a double-wall glass tank. The time-evolution of observed phase heights is used to fit the model parameters of the coalescence kernel. Subsequently, this numerical model has been used for simulating the gravity-driven separation in a horizontal settler equipped with a coalescer. The predictions of this numerical model are in good agreement with the experimentally observed values.