Optimal computer-aided molecular design of ionic liquid mixtures for post-combustion carbon dioxide capture

Abstract

This work addresses the post-combustion carbon dioxide capture capabilities of optimally designed mixtures of ionic liquids, as well as pure ionic liquids. We postulate that ionic liquid mixtures can display better absorption rates and processing features when compared with pure ionic liquids. The computer-aided molecular design of the ionic liquids mixture was posed as a mixed-integer nonlinear programming problem to determine both the chemical structure and the amount of each ionic liquid in the mixture. Also, multiobjective optimization was performed to determine optimal operating conditions, specifically pressure and ionic liquids mixture feed stream, for an absorption separation process with various optimal mixtures. Results show that the anion [Tf2N] with the chain -(CH)2(CH2)5(CH3)3 was present both in the pure ionic liquid case and in the mixtures of these compounds. Results also indicate that, even though the amount of carbon dioxide absorbed by pure ionic liquid is slightly higher than the absorbed by ionic liquids mixture, there are important operational and environmental advantages of using such type of mixtures since they have milder physical properties than the pure ionic liquid.