Experimental and Theoretical Studies of CO2 Absorption Enhancement by Nano-Al2O3 and Carbon Nanotube Particles

The influence of nano-particles on CO₂ absorption was studied experimentally in a stirred thermostatic reactor. Nano-Al₂O₃ and carbon nanotube (CNT) particles which showed different hydrophobic properties were chosen for the investigation. The experimental results were compared with that of micron-size activated carbon (AC) and Al₂O₃ particles. From the results, no enhancement by micron-size Al₂O₃ was found, and with the increase of Al₂O₃ concentration, the enhancement factor decreased. However, nano-Al₂O₃ showed a weak enhancement for the CO₂ absorption. AC and CNT particles all intensified the gas-liquid mass transfer effectively, yet the trend of the enhancement factor with stirring speed for the two particles was different. With increasing stirring speed, the enhancement factor of AC particles was decreased, whereas in CNT suspensions it was increased. The experimental phenomena demonstrated a difference in enhancement mechanism for different size particles. For nano-particles, besides the influence of adsorbability and hydrophobicity, the micro-convection caused by Brownian motion should be also taken into account. Considering the micro-convection effect, a theoretical model was developed to shed light on the absorption enhancement by nano-particles.