Influence of controlled fluid shear on crystal nucleation from solution

This thesis describes work done to investigate the influence of controlled fluid shear on the primary nucleation of glycine from aqueous solution. Crystallisation from solution is vital to many natural and industrial processes. It is widely used for separation and purification in industries such as chemicals, food and pharmaceuticals. Nucleation, which is the first step in the formation of a new crystalline solid phase from solution, is of fundamental importance in determining product crystal quality, however, at present it is poorly understood mechanistically. An improved understanding of nucleation and the effects of relevant industrial process parameters on nucleation pathways and resulting kinetics is therefore necessary to better design and optimise industrial applications of crystallisation. In industrial processes, fluid shear is widely encountered, for example through agitation in a vessel, or transport through pipes. The role of fluid shear on the primary nucleation of small organic compounds from solution has not been well studied to date so in this work, the influence of fluid shear on the primary nucleation of glycine, the smallest amino acid, is studied. Couette and capillary flow setups were used to obtain flow conditions which were well understood and quantifiable. Supersaturated aqueous glycine solutions were exposed to flow in these setups under isothermal conditions and induction times (time between the creation of supersaturation and the formation of a new crystalline phase) were measured. Efforts were taken to ensure that the first crystals formed through primary nucleation and the measured induction times were related to the rates of primary nucleation in the solutions. Dynamic light scattering measurements were also carried out to study the mesoscale clusters which exist in aqueous glycine solutions. The work carried out showed that fluid shear had a profound effect on the primary nucleation of glycine from aqueous solution, with exposure to fluid shear resulting in higher rates of primary nucleation. The onset of nucleation was associated with an increase in average mesoscale cluster size. It is proposed that exposure to fluid shear resulted in the coalescence of mesoscale clusters, with the larger coalesced clusters leading to a more rapid nucleation pathway.This thesis describes work done to investigate the influence of controlled fluid shear on the primary nucleation of glycine from aqueous solution. Crystallisation from solution is vital to many natural and industrial processes. It is widely used for separation and purification in industries such as chemicals, food and pharmaceuticals. Nucleation, which is the first step in the formation of a new crystalline solid phase from solution, is of fundamental importance in determining product crystal quality, however, at present it is poorly understood mechanistically. An improved understanding of nucleation and the effects of relevant industrial process parameters on nucleation pathways and resulting kinetics is therefore necessary to better design and optimise industrial applications of crystallisation. In industrial processes, fluid shear is widely encountered, for example through agitation in a vessel, or transport through pipes. The role of fluid shear on the primary nucleation of small organic compounds from solution has not been well studied to date so in this work, the influence of fluid shear on the primary nucleation of glycine, the smallest amino acid, is studied. Couette and capillary flow setups were used to obtain flow conditions which were well understood and quantifiable. Supersaturated aqueous glycine solutions were exposed to flow in these setups under isothermal conditions and induction times (time between the creation of supersaturation and the formation of a new crystalline phase) were measured. Efforts were taken to ensure that the first crystals formed through primary nucleation and the measured induction times were related to the rates of primary nucleation in the solutions. Dynamic light scattering measurements were also carried out to study the mesoscale clusters which exist in aqueous glycine solutions. The work carried out showed that fluid shear had a profound effect on the primary nucleation of glycine from aqueous solution, with exposure to fluid shear resulting in higher rates of primary nucleation. The onset of nucleation was associated with an increase in average mesoscale cluster size. It is proposed that exposure to fluid shear resulted in the coalescence of mesoscale clusters, with the larger coalesced clusters leading to a more rapid nucleation pathway