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Pickering emulsions (PEs), i.e. particle stabilized emulsions, are used as reaction environments in biphasic catalysis for the hydroformylation of 1-dodecene into tridecanal using the catalyst rhodium (Rh)–sulfoxantphos (SX). The present study connects the knowledge about particle–catalyst interactions and PE structure with the reaction results. It quantifies the efficiency of the catalytic performance of the catalyst localized in the voids between the particles (liquid–liquid interface) and the catalyst adsorbed on the particle surface (liquid–solid interface) using a new numerical approach. First, it is ensured that the overall packing density and geometry at the droplet interface and the size of the water droplets of the resulting w/o PEs are predictable. Second, it is shown that approximately all particles assemble at the droplet surface after emulsion preparation and neither the packing parameter nor the droplet size change with the particle surface charge or size when the total particle cross section is kept constant. Third, studies on the influence of the catalyst on the emulsion structure reveal that irrespective of the particle charge the surface active and negatively charged catalyst Rh–SX reduces the PE droplet size significantly and decreases the particle packing parameter from s = 0.91 (hexagonal packing in 2D) to s = 0.69 (shattered structure). In this latter case, large voids of the free w/o interface form and become covered with the catalyst. With a deep knowledge about the PE structure the reaction efficiencies of the liquid–liquid vs. the solid–liquid interface are quantified. By excluding any other influence factors, it is shown that the activity of the catalyst is the same at the fluid and solid interface and the performance of the reaction is explained by the geometry of the system. After the reaction, the catalyst retention via membrane filtration is shown to be successfully achieved without damaging the emulsions. This enables the continuous recovery of the catalyst, i.e. the most expensive compound in PE-based catalytic reactions, being a crucial criterion for industrial applications.

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 (R2 = 0.80), energy dissipation rate (R2 = 0.85) and tip speed (R2 = 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.

The impact of different silica nanoparticles on rheology, interfacial tension and drop size distributions in liquid‐liquid systems is determined experimentally. The particles vary in wettability and specific surface area. In contrast to commonly used high‐energy devices for Pickering emulsion preparation, low energy input by stirring allows to quantify drop breakage and coalescence in steady state and dynamic conditions. The experiments can provide essential information for drop size model development in nanoparticle‐stabilized emulsions.

Recently, the feasibility of Pickering emulsion membrane filtration has been shown to be a promising procedure for efficient catalyst recovery in continuous liquid/liquid multiphase catalysis. In this work, the impact of temperature on the permeation of the pure solvent 1-dodecene as well as on the filtration of water-in-oil Pickering emulsions stabilized with two different types of silica nanoparticles (differing in particle hydrophobicity) using an organic solvent nanofiltration membrane was experimentally investigated. While a temperature increase led to an increase in flux, the influence of the particle type was negligible. Furthermore, for the first time, a mathematical model to describe Pickering emulsion filtration was successfully developed. The flux of solvent through the membrane could be predicted via the solution-diffusion model including an Arrhenius-type relationship to describe the temperature dependency of the diffusion coefficient. Implementing this into a resistance in series model the Pickering emulsion filtration behavior could be predicted with high accuracy. These results are indispensable for the optimal process design for Pickering emulsion application in catalytic multiphase systems.

In recent years, Pickering emulsions (PE) have become of increasing interest for their application in (bio-) catalytic multiphase processes. To design an economically feasible process, an efficient and effective catalyst recovery is necessary. Ultrafiltration of PE has been shown to be a promising procedure. In this work, the influence of drop size distributions and rheology on the ultrafiltration of water-in-oil and oil-in-water PE stabilized by different nanoparticles as well as organic solvent-nanoparticle suspensions was studied. Particles with higher hydrophobicity led to larger Sauter mean diameters. Depending on the ability of silica particles to form three-dimensional network structures, shear thinning or Newtonian rheological behavior was obtained. When suspensions of particles with gelling properties were filtered, an increase in flux compared to the filtration of the pure organic solvent was observed. Water-in-oil PE showed – regardless of investigated particle type and concentration – a disproportionate increase of flux with pressure. However, adjusting the membrane pre-treatment procedure led to a linear dependency between flux and pressure, which was also observed for oil-in-water PE (without special pre-treatment). This work shows that the ultrafiltration of PE made from various nanoparticles is possible and contributes to a better understanding of PE characteristic properties and their influence on the ultrafiltration behavior.