Experimental and Modelling of CO2 Absorption in a Bubble Column Using a Water-Based Nanofluid Containing Co-Doped SiO2 Nanoparticles

In this study, we investigated the effect of Co/SiO2 NPs on CO2 absorption in the form of single bubbles rising through a bubble column (20 °C and 1 atm). Co-doped SiO2 nanoparticles were first synthesized through the chemical vapor deposition (CVD) method, then nanofluids with different concentrations of the synthesized NPs (0.001, 0.01, 0.02, 0.05, and 0.1 wt.%) were prepared. Through comprehensive experimental studies, the effects of NPs concentration and
nanofluid volume on the CO2 absorption rate were examined. The stability of nanofluids, as a key factor in nanofluid efficiency, was investigated over a period of 10 days. Based on the experimental data, mass transfer operations were analyzed through dimensionless numbers (Sherwood (Sh), and Schmidt (Sc) numbers) to elaborate the rate of CO2 diffusivity into the Co/SiO2 nanofluid. Results showed that increasing NPs concentration from 0.001 to 0.02 wt.%
caused the CO2 absorption rate to reach a maximum value followed by a downward trend. Increasing nanofluid volume did not affect the gas absorption rate, which is attributed to the fact that the predominant mechanism of CO2 absorption was the Brownian motion of NPs. Results confirmed that the prepared nanofluids had acceptable stability over the test period of 10 days, and the optimum nanofluid (80 mL with 0.02 wt.% of NPs) had the maximum CO2
absorption, 28% more than the base fluid. The magnitude of the CO2 mass transfer coefficient in the nanofluid was found to be 1.953×10-4 (m.s-1), which was 1.89 times higher than the base fluid. Finally, a comprehensive correlation (R2= 0.99) was introduced to predict the CO2 mass transfer coefficient in the Co/SiO2 nanofluid.