Kinetic Studies about the Hydrothermal Carbonization of Fructose

Hydrothermal Carbonization is a chemical process for the conversion of biomass into a carbon-rich material called hydrochar. For the construction of a technical production plant an understanding of the chemical reactions during the process is necessary. This research aims to develop a kinetic model for the formation of hydrochar from fructose solutions. Its formation results in a new solid phase from a homogenous solution that must be considered in the kinetic model. The concentration-time curve of the individual substances indicates a causal relationship between the conversion of hydroxymethylfurfural (HMF) and the formation of hydrochar. Consequently, for the development of the kinetic model, polycondensation of HMF has been implemented as the polymerization mechanism to form hydrochar. The reaction order for this reaction was determined in a temperature range between 190-210 °C, and varies between 1 and 2 depending on the reaction time, initial concentration, and temperature. The growth mechanism of hydrochar indicates that those particles grow via coagulation, and therefore, the state of matter of the particles is similar to viscous pitch or tar under the given reaction conditions. The addition of salts causes a shielding of the surface charge and thus reduces repulsive forces during the collision of two hydrochar particles, consequently the coagulation rate increases, yielding larger particles. In summary, key factors determining the reaction rates as well as the growth rate have been worked out in this research, and represent a solid knowledge base for the efficient production of tailored carbonaceous hydrochar particles.