Solid-state reaction of alkylamines with CO2 in ambient air.

Abstract

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 4h, 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 102h vs 4h). 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.