Solvent Extraction Design for Highly Viscous Systems

The change from fossil-based feedstock to bio-based raw materials will lead to changes in the molecular structure of reagents used in the chemical industry. Bio-based raw materials are richer in oxygen, leading to intermediates and products rich in oxygen as well. This will lead to lower vapor pressure and higher viscosity of the systems. Thus liquid-based separations like solvent extraction will increase in importance. Also separation-process design needs to be adapted to properly account for higher viscosities. With drop-based simulation, extraction-column performance can be predicted to better than 10% accuracy, being time and resources saving compared to pilot-plant experiments. In previous work, appropriate models describing all drop phenomena like sedimentation and mass transfer were combined in a simulation tool, called ReDrop (REpresentative DROPs). The models implemented in ReDrop have been largely validated for low-viscous systems. In order to extend the capabilities of ReDrop and describe the entire viscosity range, models have to be tested for a variety of different material system with single-drop lab-scale experiments. In this work mass transfer has been evaluated with single-drop experiments for two systems with different viscosity. The first one is the standard EFCE system composed by water + acetone + butyl acetate. Results were compared with the mass-transfer evaluation for the aqueous two-phase system with higher viscosity composed by water and PEG + albumine + water and phosphate. The results show that the transport of a component between two immiscible phases is strongly influenced by the viscosity of both phases as well as the molecular size of the transferred component. The single-drop results are the basis for validation and extending the applicability of existing models to higher viscosity, which are then introduced into ReDrop.