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.
Highlights
Multiphase systems are common within process engineering and its related disciplines, with the applications including multiphase reaction systems, most separation processes, biotechnology, and wastewater treatment
The literature suggests that the use of photo-optical probes in conjunction with automated image analysis is among the most promising measurement techniques for transient particle size distributions, as it is more precise than laser-based and acoustic methods and is oftentimes used as a reference for the calibration of these.[1,4−10] Image analysis offers the possibility to differentiate particles based on optical characteristics such as the difference in refractive indices or opaqueness
For the application in the model system of aqueous biphasic hydroformylation performed in a stirred tank reactor, some challenges need to be overcome to find an optimal testing setup
Summary
Multiphase systems are common within process engineering and its related disciplines, with the applications including multiphase reaction systems, most separation processes, biotechnology, and wastewater treatment. The unsteady nature of the interfacial area in these systems makes an in situ measurement necessary to avoid distortion of the data by sampling.[3] When multiple dispersed phases are present, including unwanted or trapped gas bubbles in LL systems, the measurement technique must be able to distinguish the present particles to avoid a distortion of the data. The literature suggests that the use of photo-optical probes in conjunction with automated image analysis is among the most promising measurement techniques for transient particle size distributions, as it is more precise than laser-based and acoustic methods and is oftentimes used as a reference for the calibration of these.[1,4−10] Image analysis offers the possibility to differentiate particles based on optical characteristics such as the difference in refractive indices or opaqueness
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