Monitoring of Copper(II) Sulfate Pentahydrate Crystallization Using Ultrasound

Abstract

Ultrasound is beginning to be used to characterize many types of industrial two-phase dispersions, both suspensions and emulsions. It also has great potential as a process-monitoring tool alongside the well-established techniques of conductivity, pH, optical turbidity, tomography, and so forth. This paper describes a small volume test cell that has been developed to ultrasonically monitor the batch crystallization of a hydrated salt from saturated solution. The interaction of low-power, low-frequency (2− 7 MHz) ultrasound with a two-phase dispersion is discussed, and a series of experiments are outlined that have been carried out on a crystallizing 24% w/w (anhydrous) solution of copper(II) sulfate. The nucleation and growth of the crystals have been successfully monitored ultrasonically. Crystal size distributions of the final crystallized product have been obtained using light scattering and are used to model the effects that crystallization has on the ultrasonic data. It is shown that the Allegra and Hawley model of ultrasonic propagation in a two-phase dispersion, in a form modified to account for time dependent changes in the continuous phase, gives reasonable correlation with experimental data.

Model-Based Optimization of Particle Size Distribution in Batch-Cooling Crystallization of Paracetamol

“…[9][10][11] More recent studies suggest the adoption of ultrasound attenuation, where rather spacious in-line probes have been developed, but a calibration is still required. [12][13][14] On the contrary, the focused beam reflectance measurement (FBRM) is carried out using a cylindrical probe that is easily applicable in crystallization vessels ranging from laboratory to production scale. [15][16][17][18] The FBRM provides on-line data of particle size and concentration in the form of a chord length distribution (CLD).…”

“…In contrast, the on-line monitoring of the solid phase in general and of the PSD in particular remains challenging. Laser diffraction has been used in most previous studies, but in this case sampling and dilution of the suspension are necessary. − More recent studies suggest the adoption of ultrasound attenuation, where rather spacious in-line probes have been developed, but a calibration is still required. − On the contrary, the focused beam reflectance measurement (FBRM) is carried out using a cylindrical probe that is easily applicable in crystallization vessels ranging from laboratory to production scale. − The FBRM provides on-line data of particle size and concentration in the form of a chord length distribution (CLD). Although useful in general, CLD data cannot be converted directly into a PSD, i.e., they cannot be directly integrated into population balance modeling approaches.…”

Perspective on the Use of Ultrasonic Monitoring for In Situ Diagnostics of Zeolite and MOF Crystallization

“…Comparison with SEM especially revealed that US spectroscopy reflects reality the best. The importance of the crystallization mechanism can be emphasized with regard to a study by Wilkinson et al 91 who investigated the crystallization of copper sulfate pentahydrate in a similar way as Tebbutt et al 92,93 Their results showed that the crystal size was strongly influenced by the cooling rate; however, at a size of roughly 300 μm the crystals break resulting in a similar PSD independent of the cooling rate. As mentioned before, Kippax et al emphasize the importance of accurate data for the physical properties of the particles and the liquid for the characterization of organic crystals by US attenuation spectroscopy as well.…”

Ultrasonic Characterization of Lactose Crystallization in Gelatin Gels

“…There have been several attempts to use ultrasonic techniques to follow crystallization processes. For example, the change in crystal size distribution during crystallization of copper (II) sulfate pentahydrate from bulk (Tebbutt and others 1999) and seeded (Marshall and others 2002) solutions were calculated from ultrasonic spectra using scattering theories. However, the results showed some deviation from light scattering measurements.…”