Green Chemistry in ball mills: Mechanical stress shaping reaction kinetics
- Mechanochemical methods enable sustainable and efficient chemical reactions. Mechanical stressing activates the reactants and triggers chemical transformations without the need for solvents. Previous investigations in simple setups using a model reaction (1) have shown that both the stress type and stress intensity have a significant influence on the reaction kinetics.
Na2CO3 + CaCl2 → CaCO3 + 2 NaCl (1)
These findings are now being transferred to grinding media mills, in which impact, compressive and shear stress occurs together. For the investigations, media mills with different movement patterns were selected (high-energy, planetary and mixer ball mill), whose grinding media introduce the mechanical energy into the reactants at different normal and tangential speeds. With the help of DEM simulations, the impact and shear influences can be analysed separately by quantification of the effective stress energies. Experiments in the respective mills allow a correlation of the stress conditions from the simulations with theMechanochemical methods enable sustainable and efficient chemical reactions. Mechanical stressing activates the reactants and triggers chemical transformations without the need for solvents. Previous investigations in simple setups using a model reaction (1) have shown that both the stress type and stress intensity have a significant influence on the reaction kinetics.
Na2CO3 + CaCl2 → CaCO3 + 2 NaCl (1)
These findings are now being transferred to grinding media mills, in which impact, compressive and shear stress occurs together. For the investigations, media mills with different movement patterns were selected (high-energy, planetary and mixer ball mill), whose grinding media introduce the mechanical energy into the reactants at different normal and tangential speeds. With the help of DEM simulations, the impact and shear influences can be analysed separately by quantification of the effective stress energies. Experiments in the respective mills allow a correlation of the stress conditions from the simulations with the experimentally determined reaction kinetics, whereby the stress type, number and intensity were in focus. It can be shown that the dominant stress mechanism varies as function of the mill and that a certain minimum stress intensity is beneficial for an efficient chemical conversion. During processing, significant caking of the powder on the grinding chamber and media was observed, which changes the amount of captured powder and the elasticity of the impacts. Both variables influence the stress intensity and, thus, potentially the reaction kinetics. By combining numerical and experimental data, new insights into the stress conditions of grinding media mills and their influence on the reaction kinetics of a mechanochemical model reaction were gained. PARTEC 2025 261…

