Hydrodynamic behavior analysis of a rotating disc contactor for aromatics extraction with 4-methyl-butyl-pyridinium-BF4 by CFD

An experimental and numerical simulation analysis of the hydrodynamic behavior for aromatics extraction with 4-methyl-N-butyl-pyridinium tetrafluoroborate is presented. Room temperature ionic liquids (RTILs) have proven to be promising solvents for the extraction of aromatic hydrocarbons, because of their non-volatile nature and their tailoring properties. The RTIL 4-methyl-N-butyl-pyridinium tetrafluoroborate ([4-mebupy]BF4) was therefore tested as a solvent for the extraction of toluene from toluene/n-heptane in a rotating disc contactor (RDC). Hydrodynamic characteristics, like Sauter mean diameter and hold-up, were measured for different total fluxes and stirrer speeds. Unexpected behavior for the hold-up was observed in experiments when the RTIL was applied as solvent. At lower fluxes, the hold-up decreases with increasing rotor speed, when an increase of hold-up was expected. This behavior, however, can very well be explained by the existence of three operating regimes in the used RDC.Computational fluid dynamics simulations of the two-phase flow in the RDC extractor have been performed to investigate the unexpected hold-up behavior. The numerical simulations were done using the commercial CFD software fluent, whereas an Euler–Euler model was applied together with the realizable k– turbulence model for the solution of the liquid–liquid problem. The numerical hold-up results are compared to the experimental profiles. Possible reasons for the hold-up anomalies, namely the path of the RTIL droplets as well as the velocity fields in both liquid phases, are presented and discussed. The work shows, that CFD can predict hydrodynamic characteristics even for extreme examples as in the present RTIL extraction

Simulation of aromatics extraction with an ionic liquid in a pilot-plant Kuhni extractor based on single-drop experiments

Pilot-plant experiments in a Kühni extractor for the extraction of toluene from a heptane+toluene mixture by means of the ionic liquid [3-mebupy][DCA] were performed. Previous work (Meindersma et al., 2010, 2012) has shown that [3-mebupy][DCA] is a promising solvent for the extraction of aromatic substances such as toluene. An alternative approach to performing time and material consuming pilot-plant experiments is modelling with the drop population-balance model ReDrop. Models in the ReDrop program accounting for different phenomena, such as drop sedimentation, drop breakage and coalescence as well as mass transfer, contain liquid-liquid system specific parameters that are fitted to lab-scale experiments with single drops. A single-drop sedimentation experiment with heptane (c)+toluene+[3-mebupy][DCA] (d) was performed and the parameters of the sedimentation model fitted to the experimental data. Models accounting for the hindrance of drop sedimentation due to column internals and models for drop breakage were taken from the literature. On this basis, the Kühni extractor was then simulated with ReDrop. Hydrodynamic parameters such as hold-up and Sauter mean diameter are in good agreement with the experimental data. Also the mass-transfer performance of the [3-mebupy][DCA] in combination with the Kühni extractor was modeled with good accuracy. It was shown that the ReDrop concept is a promising alternative to pilot-plant experiments in terms of need of materials and time to evaluate new ILs for their usability in extraction columns