Absorption of CO2 in Nanofluids: Influence of the Material Density of Nanoparticles and a Correlating Principle

Enhancements in mass transfer into conventional media in the presence of nanosized particles have been demonstrated in recent decades and show an effect of the particle size (relative to the penetration depth of the solute) and particle (volumetric) holdup. Limited information exists on the effect of the density of the nanomaterial used and suggests that it could be an important parameter as well. In the present work, we have used nanofluids with a variety of particles of different densities and similar sizes, in the absorption of CO2 in physical absorption (water) and reactive absorption [methyldiethanolamine (MDEA) and monoethanolamine (MEA) solutions], in a capillary tube apparatus. Enhancements are higher in physical absorption than in reactive absorption. A strong dependence of the enhancement on the material density of the nanoparticles is observed, with gold particles giving a 10-fold enhancement in mass transfer coefficients in physical absorption. A semiempirical theory proposed earlier has been revisited, with additional data from this work combined with the earlier body of data, and a general correlative theory to capture the effects of particles has been proposed.