Elucidation of the Role of Gas Bubbles in the Fractional Precipitation of Paclitaxel

In this study, the effect of gas flow rate and air stone pore size on the gas bubble-assisted fractional precipitation efficiency of paclitaxel was investigated. As the gas flow rate increased and the air stone pore size decreased, more numerous and smaller bubbles were generated and the bubble surface area increased. Additionally, at gas flow rates of 0.5 to 1.5 L/min, the precipitation yield and rate constant increased to be 2.2 to 2.4 and 3.2 to 4.3 times (air stone pore size 10 µm), 1.8 to 2.2 and 1.6 to 3.2 times (air stone pore size 30 µm), and 1.7 to 2.1 and 1.5 to 2.8 times (air stone pore size 43 µm) higher than those obtained in the conventional precipitation. Also, as the gas flow rate increased and the bubble size decreased, the changes in activation energy decreased. The results seem to confirm that the bubble surface acts as a heterogeneous nucleation site, lowering the free energy barrier for nucleation and thus improving the precipitation efficiency.