Pulverisation of emulsions with supercritical CO2

With the use of a carbon dioxide-assisted high pressure spraying process, it is possible to manufacture solid emulsions with or without the employment of surfactants. Depending on the process parameters, such as spray pressure, temperature, and gas-to-liquid ratio, various powder morphologies and sizes in the range of micrometers can be obtained. The aim of the project is to investigate and compare the fundamental differences in the spray formation mechanisms of this process to the conventional ones. To this end, firstly various high pressure thermo- and fluid dynamic data have been investigated to define the process and identify different effects coming from the liquid's properties. Two model emulsions, water, and tristearin (water in oil) and rapeseed oil and polyethylene glycol (oil in water) have been chosen. Using a pseudo shadowgraphy technique spraying experiments with pure and gas-saturated liquids as well as the emulsions have been carried out with a flat fan orifice. The images of the sprays illustrate that the carbon dioxide generally leads to an earlier sheet breakup by gas nucleation. An increase in saturation pressure led to atomisation directly after the nozzle for rapeseed oil and tristearin. A decrease in breakup length of the liquid sheet was also observed for the water in oil emulsion. Solid emulsion particles were also produced in the range of 10 mm with various concentrations of the dispersed phase. It was shown that these can be produced without the use of an emulsifier. Moreover through the employment of an optical chamber, the encapsulation efficiency of the process was linked to the quality of the emulsion, that is size of dispersed droplets.