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.