Liquid–Liquid Heterogeneous Mixing Characteristics in a Submerged Rotating Packed Bed

The involvement of liquid–liquid heterogeneous intensification in chemical processes is indispensable due to the presence of phase interfaces that impose limitations on mixing efficiency. Herein, a submerged rotating packed bed (SRPB) was developed to intensify liquid–liquid heterogeneous mixing under a dramatic centrifugal environment. The packing was submerged in continuous liquid to potentially match the heat-sensitive reaction systems. The liquid–liquid heterogeneous dispersion phenomena were photographed using a microscope, and the heterogeneous mixing efficiency was investigated using a sodium hydroxide and aspirin system as the chemical probe. As rotational speed was increased from 300 to 1500 r/min, the Sauter mean diameter of the aqueous phase was remarkably reduced from 110.65 to 19.57 μm, proving that SRPB could effectively disperse the liquid–liquid heterogeneous reaction system. Benefiting from the rotating packing, the segregation index (X_S) and micromixing time (t_m) respectively decreased in the range of 0.33–0.11 and 3.98–1.36 ms, indicating that the mixing efficiency was significantly enhanced under the centrifugal field of SRPB. The increase in the total volume flow rate reduced X_S and t_m, which could stem from the enlarged heterogeneous interfaces by forming multiple composite droplets at large volume flow rates. Compared with conventional RPB, the X_S of SRPB (0.09–0.35) was slightly lower than that of RPB (0.1–0.4), and the t_m of SRPB (1.36–3.98) was remarkably lower than that of RPB (1–10), proving the superiority of SPRB in promoting heterogeneous mixing.