Effect of microbubbles on preparation of precipitated silica by carbonization: physical-chemical structure, kinetic parameters and mass transfer characteristics

Silica is widely applied in industrial fields due to its good properties, while preparation of high-quality SiO₂ by carbonization is an important way to utilize CO₂. The experiment was carried out in a microbubble/bubbling experimental device, with its mass transfer kinetics of carbonization analyzed according to the pH-t curves. Under microbubble conditions, with the increasing temperature of 20∼60°C, the specific surface area, oil absorption value and particle size of silica varies at 336.80∼231.29 m²/g, 1.12∼1.81 ml/g and 16.49∼14.60 μm, respectively, which is similar as that with bubble. Aging at 20∼90 °C, they involve in the range of 35.82∼128.76 m²/g, 1.59∼2.44 ml/g and 23.15∼14.46 μm. With total concentration of solution >0.5 M, the concentration increases, the specific surface area and particle size of microbubbles are larger than those of the bubbling silica, and oil absorption value increases at 1.81∼2.44 ml/g. The kinetic analysis shows that it is more consistent with theoretical value, which can be judged as the secondary-reaction process. The microbubbles increase the CO₂ utilization rate and volumetric mass transfer coefficient of carbonization by 2-4 times, while the liquid-phase mass transfer coefficient decreases. It indicates that microbubble mass transfer is achieved by significantly increasing the specific surface area.