Efficient CO2 Sequestration by a Solid-Gas Reaction Enabled by Mechanochemistry: The Case of L-Lysine

This study describes an efficient and solvent-free method for the regioselective production of L-lysine ammonium epsilon-carbamate by ball-milling L-lysine under a CO2 atmosphere. The regioselective formation of L-lysine ammonium epsilon-carbamate via this mechanochemical approach was confirmed by a complete analytical study, including H-1 -> C-13 and H-1 -> N-15 cross polarization magic-angle spinning NMR measurements as well as liquid NMR analyses, powder X-ray diffraction measurements, thermal analyses, and elemental analyses. The time of milling, rotational speed, milling material, and liquid assistants were screened, while the reversibility of the process was assessed. The milling approach was compared with the synthesis in aqueous solutions and in the solid state without agitation. In addition to being regioselective, the synthesis by solvent-free mechanochemistry was found to be much faster than the other approaches while also producing less waste.