Solid-State Reaction of Alkylamines with CO₂ in Ambient Air

This paper explores possible procedures to accelerate CO₂ capture from ambient air by a crystalline alkylamine surfactant (octadecylamine), leading to the corresponding crystalline ammonium-carbamate. Conversion of the amine to the carbamate, in different conditions, is studied by four different techniques: WAXD, FTIR, TGA, and DSC. The WAXD study also gives relevant information on the crystal structures of both amine and derived carbamate. Kinetics of reactions of the crystalline amine are mainly studied by DSC scans, by evaluating melting enthalpies of residual amine. The kinetics of conversion of the amine in ambient CO₂ is strongly accelerated by ball milling with full conversion achieved after only 4 h, while the reaction kinetics of amine powder simply exposed to ambient CO₂ is complete only after nearly 10³ h. A substantial increase in kinetics of the solid-state amine reaction with ambient CO₂ can be also achieved by increasing the temperature up to 50 °C, i. e. at a temperature slightly lower than amine melting. However, the time for full conversion remains much higher than for room-temperature ball-milled amine (roughly 10² h vs 4 h). Hence, suitable ball-milling procedures can lead to complete and relatively fast conversion of the crystalline amine to the crystalline ammonium-carbamate, even with ambient CO₂.