CO<sub>2</sub> Capture
in Alkanolamine-RTIL Blends
via Carbamate Crystallization: Route to Efficient Regeneration
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Abstract
One of the major drawbacks of aqueous alkanolamine based
CO<sub>2</sub> capture processes is the requirement of significantly
higher
energy of regeneration. This weakness can be overcome by separating
the CO<sub>2</sub>-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 CO<sub>2</sub> in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([hmim][Tf<sub>2</sub>N]), 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 <sup>13</sup>C 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 CO<sub>2</sub> capture and
amine regeneration temperatures