Kinetic study of octanoic acid enhanced crystal growth of boehmite under sub- and supercritical hydrothermal conditions

This paper describes the kinetics of particle growth of boehmite under hydrothermal conditions in the presence of octanoic acid. The size of the boehmite particles formed after hydrothermal treatment between 200 and 400 °C in a batch reactor was measured after various treatment times (several minutes to 1 h). The growth rate was evaluated from the increase in the size of boehmite particles with time. Kinetic analysis was conducted over the initial stage of particle growth (up to 10 min). The effect of diffusion rate on particle growth was evaluated at 400 °C and 30 MPa to reconfirm its insignificance, suggesting that the surface reaction is the controlling step under these conditions. The apparent activation energy obtained from the Arrhenius plot of growth rate coincides well with the values reported in the literature. Addition of octanoic acid to the system significantly enhances particle growth. The effect of octanoic acid concentration on the rate constant was studied in more detail: the concentration dependence implies the formation of an intermediate with the octanoic acid, which controls particle growth.