Measuring Droplet Sizes Generated by 3D-Printed Stirrers in a Lean Gas–Liquid–Liquid System Using Borescopy

Abstract

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.

Exploring the Hurdles in Thermomorphic Multicomponent Systems in the Rhodium-Catalyzed Multiphase Hydroformylation

“…To understand the phase behavior during the reaction, it was observed under reaction conditions using a reactor setup equipped with a borescope for the observation of the liquid phase as used by Vorholt et al (Figure ). , The borescope allows for an investigation of multiphase reaction mixtures while stirring by observing the droplets of the dispersed phase under reaction conditions. During the first 6 h of the reaction, the conversion and yield increased almost linearly.…”

Effect of Liquid–Liquid Interfacial Area on Biphasic Catalysis Exemplified by Hydroformylation

“…A previous publication of our group established the use of high-pressure borescopy in conjunction with automated image analysis for the study of a LL in lean gas−liquid−liquid systems and proposed an optimized testing setup that is used in this work. 48 With the possibility of measuring a LL on the basis of in situ image acquisition, a new methodology can now be developed to study the effect of the liquid−liquid interfacial area a LL on the progress of the reaction of lean catalytic biphasic reaction systems exemplified by the aqueous biphasic hydroformylation of 1-octene.…”

“…The measurement takes place in a 3 mm gap to prevent larger bubbles from entering the measuring volume that would otherwise obstruct the vision on droplets. A more detailed discussion on this setup can be found in Vorholt et al …”

“…A custom-built 730 mL stirred tank reactor (STR) was used as the reaction vessel, as depicted in Figure 3. More details on the setup are given in Vorholt et al 48 The stirred tank has a height and diameter of 100 mm and comprises a dished bottom to help with emptying. Four stainless steel blades, each with a width of 10 mm, were used as baffles and were held in place by a 3D-printed holder.…”

“…In a previous publication, our group found that the measurement of the LL interfacial area in lean gas−liquid− liquid systems is feasible using commercially available borescopic in situ imaging in conjunction with automated image evaluation. 48 The authors defined an optimized testing setup to prevent dispersed aqueous droplets from adhering on the tip of the photo-optical probe that would otherwise cloud the image acquisition.…”