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.
Vapor−liquid equilibrium measurements using the PTx method have been made on three binary
mixtures: difluoromethane/hydrogen chloride, cis-1,3-dichloropropene/trans-1,3-dichloropropene, and
pyrrole/water. Each binary mixture was studied at two temperatures. Equilibrium vapor and liquid-phase compositions were derived from the PTx data using the Soave−Redlich−Kwong equation of state
to represent the vapor phase and the NRTL activity coefficient model to represent the liquid phase. The
pyrrole/water system exhibited a region of immiscibility at the lower temperature at which it was studied.
Karl Fischer titration was used to determine the compositions of the equilibrium liquid phases.
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