Review of liquid nano-absorbents for enhanced CO2 capture.

Abstract

Liquid nano-absorbents have become a topic of interest as a result of their enhanced mass-transfer performance for CO2 capture. They are believed to have revolutionized the conventional CO2 chemisorption process by largely improving CO2 capture kinetics and reducing the energy requirement for solvent regeneration. Two classes of nanomaterial-based CO2 capture absorbents, amine-based nanoparticle suspensions (nanofluids) and nanoparticle organic hybrid materials (NOHMs), have been developed, with significant progress achieved in recent decades. This review addresses two key questions for these two state-of-the-art nanomaterials: how are the physical and chemical properties of the prepared liquid nano-absorbents transformed relative to those of the base fluids? And how does the transformation of the properties affect the CO2 capture behavior? While the current synthesis procedure for liquid nano-absorbents is quite straightforward, more advanced synthesis methods for long-term nanoparticle stability have been suggested for the future. Nanofluids have been shown to increase the CO2 uptake by over 20% and the CO2 capture rate by 2-93% compared with the values observed with neat amine solvents. Nanoparticles with catalytic effects on CO2 capture can significantly increase the CO2 desorption rate by as high as 4000%. NOHMs exhibit the interesting feature of enhanced mass transfer in CO2 capture because of the unique pathway network that is created in them for CO2 to reach specific functional groups. NOHMs promise an effect of combined CO2 capture and conversion, and can be used especially as electrolytes for CO2 electro-reduction. However, there are still some challenges for the application of these materials in real life, such as poor stability and high viscosity. Therefore, efficient CO2 capture processes using these solvents need to be urgently developed and studied in the future.