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Title: Characterisation of turbulent mixing and its influence on antisolvent crystallisation
Author: Brown, Andrew
ISNI:       0000 0004 2744 0049
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2012
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Mixing is a fundamental part of many processes in chemical engineering. In order for molecular processes to proceed there is an implicit requirement for molecular scale mixing. Many processes are so slow that they are effectively independent of mixing as mixing is fast relative to the process. However, for fast processes mixing can be the limiting step and for processes with competitive elements it can control product quality and distribution. Antisolvent crystallisation is one such process which is strongly influenced by mixing. The initial mixing controls the distribution of supersaturation which in turn controls the nucleation rate and hence many key parameters such a particle size distribution. In order to understand antisolvent crystallisation and how the initial mixing influences nucleation it is important to first understand the mixing process itself. In this thesis mixing was measured and quantified by utilising a mixing sensitive competitive reaction scheme with well unders tood and well defined kinetics. The reaction scheme that was chosen was the Bourne IV reaction scheme which has received considerable interest in the scientific literature as a means to quantify and characterise the mixing performance of rapid continuous mixers. The original scheme has some inherent limitations in terms of ranking mixers operating under the conditions commonly encountered in industrial applications; namely the 1:1 flow ratio and the lack of a difference in the physical properties of the streams. This original scheme has been extended in a systematic way to incorporate differences in the flow ratio and physical properties. The results have been analysed in conjunction with a model capable of allowing fair comparison between the flow ratios. Several continuous mixers of various sizes including an impinging jet mixer and a vortex mixer have been characterised over a variety of mixing conditions. The antisolvent precipitation of valine in a confined impinging jet mixer was explored and analysed in conjunction with the mixing characterisation data allowing depth to be added to the analysis of standard crystallisation experiments. It is demonstrated that the initial mixing (over the first second) controls many of the key parameters in antisolvent crystallisation which underlines the importance of designing and scaling the initial mixing process correctly. It is also demonstrated that this is true even when samples are subjected to additional shear over long timescales. The vortex mixer characterised here was utilised in an industrial scale pilot trial and the results contrasted with those obtained using an "off the shelf" cross mixer. This work underlines that controlling the initial mixing step has strong industrial relevance and is one of the single most important parameters in the process design of antisolvent crystallisation processes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available