Date

2022-9-9

Author

Özdemir, Meliha Yağmur

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Emulsions are systems consisting of two immiscible liquids. These immiscible liquids are generally oil and water phases. Oil and water phases are called the dispersed and continuous phases, respectively. Emulsions can be classified as single and multiple emulsions. Oil-in-water (o/w) and water-in-oil (w/o) emulsions are the examples of single emulsions, and water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) emulsions are examples of multiple emulsions. Emulsions are an example of immiscible liquid-liquid mixing. Emulsions are thermodynamically unstable and stabilizing agents are required to obtain stable emulsions. Emulsions stabilized by solid particles are known as Pickering emulsions. Pickering emulsions have advantages over surfactant-based emulsions which are stabilized by chemical surfactants. In this thesis, the effect of feeding conditions of the dispersed phase on the drop size of Pickering emulsions produced in an unbaffled stirred tank was investigated. Silicone oil and distilled water were selected as the dispersed and continuous phases, respectively. Hydrophilic zinc-oxide solid particles were selected as the stabilizing agent. Zinc-oxide stabilized oil-in-water (o/w) Pickering emulsions were produced. A standard six-bladed Rushton turbine (RT) with a diameter of one-third of the tank diameter (D=T/3) was used as the impeller. The impeller shaft was positioned at three locations which are at the center, e/T=0 and at two eccentricity ratios, e/T=0.1 and e/T=0.2. Eccentricity (e) is the distance between the impeller shaft and center of the tank, and T is tank diameter. The impeller tip speeds, all corresponding to the turbulent flow regime, were selected as 1.85, 2, 2.32 m/s. To determine the effect of feeding conditions of the dispersed phase on drop size of Pickering emulsions, two feeding conditions were tested: dispersed phase was fed either from the liquid surface within 5 seconds which is referred to as surface feeding, or into the impeller zone over 900 seconds which is referred to as impeller zone feeding. The drop size and drop size distribution analysis was done using dynamic light scattering. In conclusion, the drop sizes and drop size distributions decreased as the impeller tip speed is increased for all positions of the impeller shaft. For both feeding conditions of the dispersed phase (surface feeding and impeller zone feeding), the smallest drop size was obtained at e/T=0.1 and at the highest impeller tip speed, 2.32 m/s. The feeding of the dispersed phase into the impeller zone was found to be more effective for obtaining smaller drop sizes. The impeller discharge stream-wall interactions and the presence of vortex and its connection with impeller blades were found to cause an increase in drop size by affecting the impeller flow pattern. When the feeding condition of the dispersed phase is changed from surface feeding to impeller zone feeding, a significant effect of varying feeding conditions of the dispersed phase on drop size was found at e/T=0.2 and at an impeller tip speed, 2 m/s. It was also found that a reduction in power consumption can be achieved by changing the emulsion production process while obtaining similar drop sizes.

Subject Keywords

Pickering Emulsions, Unbaffled Stirred Tanks, Vortex Formation, Eccentricity Ratio, Feeding Conditions

URI

https://hdl.handle.net/11511/99733

Collections

Graduate School of Natural and Applied Sciences, Thesis