Date

2018

Author

Dönmez, Dila

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Emulsions are fundamental in many applications such as food, petroleum, detergent, pharmaceutical and cosmetic industries. Pickering emulsions are defined as emulsions of any type, either oil-in water, water-in-oil or even multiple, stabilized by solid particles instead of surfactants. Solid particles may prevent the droplets from coalescing by getting adsorbed at the interface, and thus stabilizing the emulsion. Pickering emulsions have more advantages over emulsions stabilized by surfactants in terms of stability, biocompatibility, environmental risks and cost. There are numerous studies about the effect of oil, water and particle properties, but almost no studies about the effect of processing parameters on the formation of Pickering emulsions in a stirred tank. The literature shows that the feed rate of a second phase into the first one has a significant impact on the mixing process, and therefore the product properties. This also applies to formation of Pickering emulsions: the feed rate of the dispersed phase into the continuous phase may be a critical processing parameter that impacts the final droplet size. In this study, the aim was to investigate the effect of feed rate of the oil phase on the final average droplet size when the following hydrodynamic conditions were constant for all configurations: tip speed, power per mass, impeller Reynolds number. Pickering emulsions were produced by using silicone oil as dispersed phase, distilled water as continuous phase, calcite as an emulsifier in a stirred tank where the feed rate of the vi dispersed phase was varied. The experiments were performed with three different impellers: Rushton turbine (RT), up-pumping pitched blade turbine (PBTU), and down-pumping pitched blade turbine (PBTD). All the impellers were tested at two different sizes, T/3 and T/2 where T is the tank diameter. The droplet diameters were measured in Mastersizer® 3000 (Malvern) which is a particle size analyzer. In summary, it was found that the decrease in feed rate causes reduction in the average droplets size due to smaller newly generated droplets and effective particle adsorption. This is only valid if the droplets have not reached the minimum equilibrium size at different hydrodynamic conditions. At lower impeller speeds and feed rates, the effect of feed rate is more pronounced, thereby under these conditions, maximum reduction in the average droplet size is found as 24% with RT-T/3. Besides of the feed rate effect, it was also found that impeller type, impeller size, feeding point and hydrodynamic conditions have an impact on the average droplet size.

Subject Keywords

Emulsions., Mixtures.

URI

http://etd.lib.metu.edu.tr/upload/12622747/index.pdf
https://hdl.handle.net/11511/27678

Collections

Graduate School of Natural and Applied Sciences, Thesis