CO2 desorption catalyzed by carboxyl-functionalized imidazolium ionic liquids: an effective strategy for energy-saving amine-based CO2 capture

Abstract

Reducing the solvent regeneration energy consumption is crucial for the large-scale implementation of amine-based CO₂ capture technology. Herein, this study developed six carboxylic acid-functionalized imidazolium-based ionic liquid (IL) catalysts ([HOOCMIM][PF₆], [HOOCMIM][HSO₄], [HOOCMIM][BF₄], [HOOCMIM]₃PW₁₂O₄₀, [HOOCMIM]₃PMo₁₂O₄₀, and [HOOCMIM]₄SiW₁₂O₄₀), and applied them in catalytically regenerating the 5 M CO₂-loaded monoethanolamine (MEA) solution at 90 °C. All IL catalysts accelerated CO₂ desorption, with [HOOCMIM][PF₆] providing the highest catalytic activity. When the dosage was 2 wt%, [HOOCMIM][PF₆] improved the rate of CO₂ desorption by 200%, and increased the amount of released CO₂ by 221%. It also cut the regeneration energy requirement by 61.1%, demonstrating highly competitive energy efficiency for acid-catalyzed rich-MEA solution regeneration processes. The excellent efficiency of the [HOOCMIM][PF₆] catalyst may be explained by its high acidity and low viscosity. Stability tests over nine CO₂ absorption–desorption cycles indicated no significant deterioration, evidencing its robust stability. The CO₂ desorption mechanism of [HOOCMIM][PF₆] was explored using FT-IR and ¹³C NMR studies. Importantly, [HOOCMIM][PF₆] does not hinder CO₂ absorption in fresh amine solutions, eliminating the need for separating the IL from the amine system. Thus, the [HOOCMIM][PF₆]-amine system can be directly utilized as a new absorbent in existing CO₂ capture apparatus without the need for extra costs of device retrofitting, thereby facilitating broad application. This study presents a viable approach to reducing the energy demand and operational costs of CO₂ capture technology in practical applications.