A new solventless process to hydrophobize silica powders in fluidized beds

A new hydrophiztaion technique was developed in a fluidized bed reactor to modify the surface of silica‐based powders with n ‐octadecyltrichlorosilane (ODTCS). The reaction was performed at dry phase by mixing two classes of particles during the fluidization: “target‐particles” to be treated (a fine microporous silica powder) and “ODTCS‐carrier” particles consisting of coarser porous alumina beads containing an adequate amount of reagent. The results showed that ODTCS was successfully anchored on silica surface and achieved high surface coverage (1.4 groups/nm 2 ) in only few minutes with an interesting hydrophobic behavior. The energy consumption is reduced if the reaction is carried out at low temperatures, but using humidified air (7% RH). These conditions promote, however, a vertical polymerization of the reagent on solids surface.