A Study On Preparation And Modification Of Precipitated Silica In Rotating Packed Bed

Ultra-fine silica powder is one of the most important inorganic powder materials. It’s widely used as an excellent co-reagent in industries such as rubber, plastic, dope, ink and so on. Sulfuric acid precipitation is the primary method to produce ultra-fine silica around the world, there’s big technological gap between domestic and abroad. There are many hydroxyl groups (-OH) on the silica surface, which easily absorb moisture and as a result generally silica is hydrophilic. The hydrophilicity has resulted in many defects of silica, such as it’s difficult to disperse it in the organic medium and band with organic groups. If more effective applications of silica particles are expected, surface modification is needed to weaken the polar property and improve the ability of combining with organic groups.In order to improve the traditional producing process and increase the efficiencies of production and modification, in this paper the preparation and modification of precipitated ultra-fine silica in rotating packed bed is studied. The research of this paper focus on the following:1. Single factor experiments and orthogonal experiments were designed to investigate the influence of experimental conditions on properties of ultra-fine silica powder. The results prove that terminated pH value has the most significant influence on BET specific surface area. Temperature, electrolyte, concentration of sodium silicate and rotational speed are in the next place. Silica powder with BET specific surface area between140-350m2/g can be prepared by changing process conditions. DBP absorption of silica powder is dominated by drying methods, and then the effective order of other factors is temperature, electrolyte, rotational speed, concentration of sodium silicate and terminated pH value. Process conditions have greater effect on BET specific surface area than on DBP absorption.2. Different methods were adopted to dry the wet silica gel to discuss their influences on silica properties. It has been found that both azeotropic distillation process and alcoholic replacement process can decrease the agglomeration and preserve the original structure when water was removed. Compared with normal heating process, azeotropic distillation and alcoholic replacement can enlarge DBP absorption, reduce BET surface area, lessen BJH pore volume and decrease bulk density,etc.3. TMCS,1-octyl alcohol and HMDS were used to modify silica powder. The research results reveal that ultra-fine silica with perfect hydrophobicity can be produced by three surface modification methods. The contact angles between hydrophobic silica powder and water drop are more than130°. After further comparing the characteristics of these three methods, HMDS is recommended as the surface treated reagent of silica. It have the advantages of excellent hydrophobic properties, highly reactivity, little causticity on apparatus and simple subsequent treatment,etc.