POROUS CARBON SUB-MICROCAPSULES APPLIED TO CARBON DIOXIDE CAPTURE VIA ENCAPSULATED IONIC LIQUIDS (ENILS)

摘要

Ionic liquids (ILs) are being investigated for their use as alternative solvents for many different fields, [1] mainly due their unique properties (high chemical and thermal stability, high solvent capacity, very low vapour pressure, etc.), which can be conveniently modulated by the adequate selection of the cation and anion that conform the IL. Their application in gas separation processes is receiving increasing attention, in particular as solvents for CO2 capture. [2] Among the wide number of ILs tested for that purpose, some of them have shown enhanced capacity associated to the chemical absorption of CO2 by the IL absorbent. Among them, imidazolium-based ILs with acetate anion, instead of common inorganic anions as PF6~- or BF4~-, allow increasing one order of magnitude the amount of absorbed CO2 at 1 bar and ambient temperature, as it was firstly reported by Shiflett et al. [3] The 1-butyl-3-methylimidazolium acetate ([bmim][acetate]) IL can be considered a CO2 chemical absorbent of reference in this group of ILs. In the proposed IL, carbon dioxide reacts with the imidazolium ring of the cation to form a carboxylate, being the reaction displaced to the product side. This favourable reaction thermodynamics displacement is responsible of his great absorption capacity at low carbon dioxide partial pressures (< 1 bar) and ambient temperature. The kinetic aspects are also crucial regarding of ILs in absorption. The available evidences so far indicate strong unfavourable mass transport properties of [bmim] [acetate] absorbent, mainly due to the high viscosity of this IL and its reaction product.