The effect of impeller type on silica sol formation in laboratory scale agitated tank

The multiphase polymerization reaction of the silica sol formation produced from silicic acid and potassium hydroxide solutions in laboratory scale agitated tank was studied. The reactor is equipped with four segmental baffle and top entering impeller. The inside diameter of reactor is 9?cm, the baffle width is 0.9?cm, and the impeller position is 3?cm from tank bottom. The diameter of standard six blades Rushton and three blades marine propeller impellers are 5?cm. The silicic acid solution was made from 0.2 volume fraction of water glass (sodium silicate) solution in which the sodium ion was exchanged by hydrogen ion from cation resin. The reactor initially filled with 286?ml silicic acid solution was operated in semi batch mode and the temperature was kept constant in 60 °C. The 3?ml/minute of 1 M potassium hydroxide solution was added into stirred tank and the solution was stirred. The impeller rotational speed was varied from 100 until 700?rpm. This titration was stopped if the solution in stirred tank had reached the pH of 10-The morphology of the silica particles in the silica sol product was analyzed by Scanning Electron Microscope (SEM). The size of silica particles in silica sol was measured based on the SEM image. The silica particle obtained in this research was amorphous particle and the shape was roughly cylinder. The flow field generated by different impeller gave significant effect on particle size and shape. The smallest geometric mean of length and diameter of particle (4.92?μm and 2.42?μm, respectively) was generated in reactor with marine propeller at 600?rpm. The reactor with Rushton impeller produced particle which the geometric mean of length and diameter of particle was 4.85?μm and 2.36?μm, respectively, at 150?rpm.