Effect of operating conditions on the hydrophobisation of silica-based porous particles in a fluidised-bed reactor: Temperature effect

This study concerns the modification of silica surface wettability by silanisation reaction which consists in the transformation of hydrophilic silanol groups into hydrophobic groups. The chemical modification of silica surface is carried out using n-Octadecyltrichlorosilane (ODTCS). It is a reagent with three chlorines as functional group and with one long alkyl chain containing 18 carbon atoms, responsible for the hydrophobic behavior. The reaction is performed at dry phase by mixing two classes of particles during the fluidisation: target particles to be treated (MP Silica 63–200 Active 6 Å) and ODTCS-carrier particles consisting of coarser porous alumina beads (300–800 μm) containing an adequate amount of reagent. The aim of this work was to study the effect of the temperature (from 30 to 110 °C) at dry condition on the silanisation reaction rate and the silica surface characteristics. The hydrophobisation treatment is characterized by IR/ATR, Washburn method, elementary analyses and RMN. The experimental results show that the reaction rate increases with temperature in dry environment but this effect seems to be more significant at lower temperatures. Also, the quantity of reagents can be estimated by measuring the amount of HCl generated by the reaction using a pH sensor. The RMN spectra showed an increased extent of disordering of the grafted chains at lower operating temperatures.