CO2 Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration

One of the major drawbacks of aqueous alkanolamine based CO2 capture processes is the requirement of significantly higher energy of regeneration. This weakness can be overcome by separating the CO2-captured product to regenerate the corresponding amine, thus avoiding the consumption of redundant energy. Replacing aqueous phase with more stable and practically nonvolatile imidazolium based room-temperature ionic liquid (RTIL) provided a viable approach for carbamate to crystallize out as supernatant solid. In the present study, regeneration capabilities of solid carbamates have been investigated. Diethanolamine (DEA) carbamate as well as 2-amino-2-methyl-1-propanol (AMP) carbamate were obtained in crystalline form by bubbling CO2 in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), was used as aqueous phase substituent. Thermal behavior of the carbamates was observed by differential scanning calorimetry and thermogravimetric analysis, while the possible regeneration mechanism has been proposed through 13C NMR and FTIR analyses. The results showed that decomposition of DEA-carbamate commenced at lower temperature (∼55 °C), compared to that of AMP-carbamate (∼75 °C); thus promising easy regeneration. The separation of carbamate as solid phase can offer two-way advantage by letting less volume to regenerate as well as by narrowing the gap between CO2 capture and amine regeneration temperatures.