W/O Pickering emulsion preparation using a batch rotor-stator mixer - Influence on rheology, drop size distribution and filtration behavior

Hypothesis: Pickering emulsions (PE) are becoming of increasing interest for catalytic multiphase processes. Ultrafiltration of PE is a promising procedure for catalyst recovery to enable continuous processes. Dispersing conditions during production of PE are expected to significantly influence PE characteristics, and control of these properties is essential for robust process design. However, while the impact of PE composition has been studied before, knowledge on dispersing conditions is surprisingly scarce. Experiments: The influence of dispersing time, speed and emulsion volume during the preparation of PE with an UltraTurrax (2 dispersing tools) on the drop size distribution, rheology, stability and filtration was investigated. Findings: In this first systematic study of PE preparation conditions, obtained Sauter mean diameters were correlated with energy density (R-2 = 0.80), energy dissipation rate (R-2 = 0.85) and tip speed (R-2 = 0.86). All emulsions were stable for at least 10 weeks. With increasing tip speed (4-13 m/s), the dynamic viscosity first decreased, passed through a plateau value and then increased again. Filtration of concentrated PE was successful but strong membrane-particle-solvent interactions were revealed. This work contributes to a better understanding of PE properties that are essential for a sound application of PE in continuous multiphase catalysis. (C) 2020 Elsevier Inc. All rights reserved.