CO_2 Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration

摘要

One of the major drawbacks of aqueous alkanolamine based CO_2 capture processes is the requirement of significantly higher energy of regeneration. This weakness can be overcome by separating the CO_2-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-l-propanol (AMP) carbamate were obtained in crystalline form by bubbling CO_2 in alkanolamine- RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium bis- (trifluoromethyisulfonyl)imide ([hmim][Tf_2N]), 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 ~(13)C NMR and FTIR analyses. The results showed that decomposition of DEA-carbamate commenced at lower temperature (～55 ℃), compared to that of AMP-carbamate (～75 ℃); 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 CO_2 capture and amine regeneration temperatures.