Funded by: DFG (German Research Foundation)
Contact person: Victor Oldhues
Summary of the project:
Mechanochemistry is regarded as green chemistry, as it can significantly reduce solvent use compared to conventional wet chemistry. Furthermore, in mechanochemical reactions, the required energy is supplied mechanically and the reactions are often energy-efficient. Such reactions are often carried out in different types of ball mills, usually used in comminution processes. The mechanical forces break existing chemical bonds or introduce other defects at the molecular level, so that the reactants are mechanically activated and, thus, become reactive. However, the exact mechanistic background of such reactions is still subject of current research and several different theories exist simultaneously.
The aim of this project is to elucidate the driving forces of mechanochemical reactions in ball mills by quantitatively linking mechanical stress conditions with the kinetics of a CaCO₃‑synthesis as a model reaction. In dedicated setups for impact, compressive and shear stress, the first step is to determine which type of stress contributes most significantly to the progress of a mechanochemical reaction. Afterwards, the model reaction will be investigated in a simple milling system by systematically quantifying the influence of several operating parameters on both the stress conditions and the chemical conversion. It will be derived to which extent the characteristic parameters such as stress intensity and frequency affect the reaction kinetics. The aim is to separate between effects related to comminution and those related to the reaction, as well as to clarify the role of temperature. It is expected that the mechanical forces will influence the reaction by promoting particle defects, forming new particle contacts and affecting local temperature development. Where appropriate, mixing and flowability effects may be investigated. The findings obtained will be transferred to various laboratory-scale grinding media mills, including a planetary, a high-energy and a mixer ball mill, for which both experiments and DEM simulations are to be carried out. To evaluate the results, a suitable stress model originating from comminution processes will be applied to the mechanochemical process. It is expected that the total specific energy input and the energy supply in a single stress event are decisive for the reaction kinetics.
Project partners: Ruhr-Universität Bochum