Studies of phase transitions in fluids, oils and fats by DSC and ultrasound spectroscopy

The use of acoustic techniques as Process Analytical Technology (PAT) tools is
relatively low compared to their electromagnetic counterparts, with buffer rod
techniques having especially scarce use. Some work has been completed using
acoustic techniques to monitor crystallisation and mostly consists of pulse echo
techniques. Use of acoustic techniques as PAT is mostly limited to single
frequency transducers and using the most basic acoustic parameters to gain
information on the process. This thesis aims to fill this gap in knowledge through
the use of both a buffer rod and broadband transducers for the
acoustic/ultrasound monitoring of crystallisation processes.
Current PAT, many of which are based on electromagnetic waves, have a range
of limitations including an inability to accurately measure opaque solutions. Low powered acoustic techniques are relatively underutilised for studying phase
transitions despite providing unique information – speed of sound and adiabatic
compressibility of the system studied. Low power (<10 W m-2
) pulsed acoustic
techniques, such as ultrasound reflectance and velocimetry, have the benefit of
being non-material altering, affordable, non-invasive and can study opaque
systems without any dilution. Here we present a novel in-situ ultrasound
technique, whose application is corroborated with optical turbidity in the
measurement of the metastable zone width of glycine in water with good
agreement.
Differential scanning calorimetry (DSC) has been used extensively in a range of
industries since the 1960s. However, traditional DSC is limited by small sample
size and lack of stirring; additionally, it is traditionally an offline type of
measurement. In particular, in the case of crystallisation, quiescent conditions
present a substantial issue as nucleation times can be extremely long. Most
industrial processes are on a large scale and have some degree of shear
involved; therefore, the relevance of traditional DSC to industrial scale processes
may be questionable. Here, the first attempt to overcome the limitations of
traditional calorimetry is presented, using a novel measurement concept that
applies an in-situ, non-material altering acoustic buffer rod method to measure
thermal properties of aqueous solutions.
This thesis aims to determine whether low-powered acoustic buffer rod
techniques can be used as an effective, multipurpose PAT tool for crystallisation
processes.