The mean particle size and suspension density of industrial ammonium sulfate and urea crystals were measured by a single ultrasound sensor in a saturated solution at only one frequency. The information on ultrasound velocity and attenuation were combined and related to characteristic properties of the solid phase of suspensions. By model identification, a correlation between the measured signals and mean particle size as well as suspension density were evaluated and verified by additional experiments. The measurements with different particle size fractions and different suspension densities up to 40 wt-% were carried out isothermally. The approach of coupled ultrasound velocity and attenuation provides a simple technique for inline process control on the liquid and solid state of a suspension process like solution crystallization only by a single measurement device.
Stability of carotenoids is a key for successful product form development and of particular interest in synthesis and adjacent crystallization as well as in formulation processes. Ethyl acetate was used as model solvent to demonstrate decomposition of astaxanthin due to the presence of traces of acetic acid and oxygen. Based on solvent pretreatments, i.e., by means of oxygen stripping, the stability could be enhanced significantly. Additionally, the stability was improved with regard to the desired isomeric configuration. Deceleration of the carotenoid isomerization by potassium carbonate was demonstrated in dichloromethane. In the case of corn oil, the degradation was negligible under ambient conditions, while decomposition occurred at higher temperatures. Presence and quantity of peroxides proved to be indicators for oil quality and associated degradation kinetics.
Particle size and suspension density of urea suspensions were investigated by means of ultrasound, optical reflectance as well as focused‐beam reflectance measurement techniques. These techniques provide similar proven nonrealistic results regarding suspension density and crystal size. The resulting data can be explained by the presence of bubbles. The influence of air bubbles on the measurement of different particle size and suspension density monitoring techniques is demonstrated and evaluated. Floating air bubbles as well as crystal‐bubble complexes are strongly affecting the results and have to be considered under real conditions. It can be demonstrated that the negative impacts on the measured data can be decreased. Special precautions have, therefore, to be taken into account for calibrations, their validation, and during crystallization monitoring or controlling to avoid faulty measured suspension densities and particle sizes caused by bubbles.
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