Solvent Effects on the Photothermal Regeneration of CO2 in Monoethanolamine Nanofluids

A potential approach to reduce energy costs associated with carbon capture is to use external and renewable energy sources. The photothermal release of CO2 from monoethanolamine mediated by nanoparticles is a unique solution to this problem. When combined with light-absorbing nanoparticles, vapor bubbles form inside the capture solution and release the CO2 without heating the bulk solvent. The mechanism by which CO2 is released remained unclear, and understanding this process would improve the efficiency of photothermal CO2 release. Here we report the use of different cosolvents to improve or reduce the photothermal regeneration of CO2 captured by monoethanolamine. We found that properties that reduce the residence time of the gas bubbles (viscosity, boiling point, and convection direction) can enhance the regeneration efficiencies. The reduction of bubble residence times minimizes the reabsorption of CO2 back into the capture solvent where bulk temperatures remain lower than the localized area surrounding the nanoparticle. These properties shed light on the mechanism of release and indicated methods for improving the efficiency of the process. We used this knowledge to develop an improved photothermal CO2 regeneration system in a continuously flowing setup. Using techniques to reduce residence time in the continuously flowing setup, such as alternative cosolvents and smaller fluid volumes, resulted in regeneration efficiency enhancements of over 200%.