(487g) Scale-up Rules for the Generation of Solid-Stabilized Emulsions

Effects of scale-up on the generation of solid stabilized emulsions (SSEs) were investigated experimentally. Considering unbaffled systems of 0.25, 5, and 35 Liters with geometrical similarities, emulsions were prepared using off-centred pitched blade and Rushton turbines. Standard scale-up criteria allowing for the calculation of impeller speed at a larger scale based on N_large = N_small(D_large/D_small)^a and commonly used for surfactant-stabilized emulsions (energy dissipation, Weber number, Reynolds number, impeller tip speed and circulation time) were applied for concentrated and diluted formulations of SSEs. Silicone oil (50 cSt) was used as the dispersed phase in water and solid glass microspheres (d₃₂ ~ 3µm) as stabilizers. Emulsions were characterized by means of droplet size measurements using Mastersizer 3000 from Malvern. Sauter mean diameter (d₃₂), dv₁₀ and dv₉₀ were used to compare the resulting emulsions. A well-established decolorization technique was used to evaluate mixing times. The results from the experiments showed that none of the standard scale-up criteria is suitable for scaling-up Pickering emulsions processes. Weber number, Reynolds number and tip speed as scale-up criteria lead to larger diameters with increasing scale while the opposite tendency is observed with circulation time and energy dissipation. Results tend to indicate that constant drop size distribution can be obtained using an intermediate between the energy dissipation rate and the tip speed suggesting that the suitable scale-up exponent a of N_large = N_small(D_large/D_small)^a would be between 2/3 (energy dissipation rate) and 1 (impeller tip speed). The presentation will present the results and their interpretation.