Biphasic catalysis enables the effective recycling of homogeneous catalysts by their immobilization in an additional liquid phase immiscible with the products. The introduced liquid− liquid interfacial area implies mass transfer limitations that play an important role in understanding these catalytic systems, with many rate enhancement strategies revolving around optimizing said area. In this contribution, the relationship between liquid−liquid interfacial area and catalytic activity is elucidated by applying a methodology that utilizes an image-based in situ measurement of the transient droplet size distribution. When the industrially highly relevant aqueous biphasic hydroformylation of the long-chain olefin 1-octene is taken as the model reaction, it is found that the product nonanal and the addition of the ligand increases the interfacial area by a factor of up to 5. The rate of conversion is found to depend on the stirring speed. By variation of the catalyst concentration, it is shown that an accumulation of the catalyst species at the interface is unlikely. Using a mathematical model, it is highlighted that the effect of the aqueous−organic interfacial area on the catalytic activity is not linear as was previously assumed in the literature. Instead, a change in the interfacial composition is proposed that causes a shift in the dependence of catalytic activity on said area. Thus, the dynamic physical properties of a lean gas−liquid−liquid system were linked to the catalytic performance of the system.

Photo-optical probes with automated image analysis are among the most promising measurement techniques for gas−liquid− liquid systems, but the literature on the application in lean water-in-oil dispersions is scarce. Taking water-in-1-octene as a model system, adhering droplets that severely cloud the images are successfully prevented using a polymeric disc made of polycarbonate or fluorinated ethylene propylene. Sharp bright-field imaging is enabled using a neither fully diffuse nor specular reflection pane. Various 3D-printed stirrers are characterized by their energy input, including gas-inducing modifications. Gas induction impairs the energy input of the stirrer and the imaging of droplets. Nevertheless, the measurement technique reliably provides droplet size distributions that exclude gas bubbles. Axial stirrers are preferable if one position at high stirring speeds is measured, as the homogeneity of droplet sizes along the reactor height is promoted. Radial stirrers are preferable if the stirring speed is varied, as the same trend of the droplets sizes is measurable along the reactor height. For radial stirring, the most beneficial position of the probe is close or slightly above the stirrer. The use of borescopy is thus found to be feasible if adhering droplets can be prevented and vision on droplets is not obstructed by too many bubbles.

deactivation, the segregation of the reaction network was considered and experimentally implemented. In a two-stage reactor cascade, first, the aforementioned Ni/(Al)MCM-41 is applied to generate a hydrocarbon mixture of ethene and butene, and second, a commercially well-known W/SiO 2 catalyst is used for the cross-metathesis towards propene. In a developed miniplant setup, a beneficial reactor operation is obtained. The overall process selectivity is significantly enhanced to 80 %, providing a proof-ofconcept.