Effect of host fluid and hydrophilicity of multi-walled carbon nanotubes on stability and CO2 absorption of amine-based and water-based nanofluids

Nanofluids have a wide range of engineering applications, especially in the CO2 absorption processes. In this study, concentrated acid-treated multi-walled carbon nanotubes (aMWCNTs) and amine functionalized multiwalled carbon nanotubes (nMWCNTs) were prepared and subjected to FTIR and FESEM analyses. Subsequently, the CO2 absorption in N-methyldiethanolamine (MDEA) and MDEA-based nanofluids, containing raw and chemically treated MWCNTs, were measured in a fixed temperature stirred reactor. The effect of hydrophilicity/ hydrophobicity of nanotubes on the CO2 absorption enhancement was examined and the optimum concentration of nanotubes in nanofluids was determined. Moreover, the effect of the base fluid on the performance of nanotubes was also investigated. For this purpose, MDEA, which is a tertiary amine and monoethanolamine (MEA) as the primary amine, were selected as the base solvents and the effect of nanotubes on increasing CO2 absorption in these solutions was examined. Subsequently, the effect of nanotubes on increasing CO2 absorption of the amine mixtures was designed and implemented. Finally, the stability of nanofluids was studied. The results show that all MWCNTs, nMWCNTs and aMWCNTs enhanced alpha(10min) (the mole of CO2 absorbed after ten minutes). However, the enhancement by hydrophobic nanotubes was seen much higher. The effect of nanotubes on alpha(10min) during the process of CO2 absorption by MDEA solution was much higher than that of MEA solution.