Hydrothermal Carbonization of Fructose: Growth Mechanism and Kinetic Model

Hydrothermal carbonization experiments were performed with fructose solutions as feedstock. A kinetic model is proposed that models hydrochar formation based on molar concentrations. On the basis of SEM pictures, the mean particles size of the hydrochar was determined, and it could be demonstrated that the growth of the particles is not directly related to the formation rate of hydrochar or the decreasing rate of the intermediates concentration in the aqueous solution. Four additives (salts) have been tested, and the results point out that the ionic strength is an important factor to control the particle size. Together, these observations lead to the conclusion that coalescence is an important driver for the growth of the particles and that a LaMer-like nucleation followed by diffusion-controlled growth is unlikely to be the formation and growth mechanism of hydrochar.