Solid silica gel is industrially made of water glass (sodium silicate) as a raw material, hydrolyzed in an acid medium to form a gel, and then made into silica gel through aging, washing, drying, etc., depending on the water content, translucent or white solid. The products on the market have irregular granular, spherical, and microspherical silica gels, which are usually used as catalysts for vulcanization in fluidized bed operations.
two. When used as a catalyst carrier, the silica gel is usually immersed in a solution containing catalytically active components, so that the solution is absorbed into the pores of the silica gel, and the active components are distributed on the surface of the silica. Gelation through drying, activation, etc. The pore structure of silica gel has an important influence on the properties of the prepared supported catalyst, such as the pore volume and pore size distribution of silica gel. Generally, silica gel with an average pore diameter of less than 15 to 20 is called fine pore silica gel; and an average pore diameter of more than 40 to 50 angstroms is called coarse pore silica gel.
three. The pore structure is not conducive to the diffusion of reactant molecules, but it can reduce the utilization rate of the inner surface of the catalyst, and the product molecules formed in the pores are not easy to escape from the pores, which is possible. Causes a profound side reaction. The pore structure of silica gel is related to the manufacturing method and conditions, such as gelation, aging, pH during washing, temperature, and time. Commercially available silicone daily necessities can be reamed through reaming. The usual method is to heat in an autoclave or add a salt-containing aqueous solution (such as sodium carbonate or sodium acetate), for example, at 320° C., 10 MPa hot-press treatment can change the specific silica gel. Surface and average pore size is 135m2/g and 123? to 26.9m2/g and 508?.
Liquid silicone process introduction
Liquid silica gel is used in industry to dehydrate sodium water into silica sol through ion exchange. It is a translucent milky white liquid with high stability. The solid silica gel becomes a porous solid after drying. For example, in the preparation of (phosphorus-molybdenum-niobium-oxygen)/silica catalyst for preparing acrylonitrile by oxidative oxidation of propylene, a solution containing active components is mixed with silica sol, and microspheres are prepared by spraying catalyst.
