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The improvement of CO 2 absorption by Al 2 O 3 nanofluids with deionized water as the base fluid was studied experimentally. The reactor used was a stirred thermostatic reactor, operated batchwise. Pure CO 2 was employed in all the experiments. The content of Al 2 O 3 in nanofluids ranged from 0 to 0.2 % (wt). Sodium dodecyl benzene sulfonate (SDBS) was employed to improve the stability of the nanofluids, and the combined effect of nanoparticles and surfactants on the absorption enhancement was studied. The parameters such as the concentration of Al 2 O 3 nanoparticles and surfactants, the stirring speed, and the ultrasonic time were varied. The results show that the nanoparticle mass fraction and the ultrasonic time have an optimum value for the CO 2 absorption enhancement. The combination of surfactants and nanoparticles improves the enhancement performance of Al 2 O 3 nanofluids more effectively than that without surfactants. With the increase of the stirring speed, the effective absorption ratio in stable nanofluids declines, while in poorly dispersed Al 2 O 3 suspensions, it is increased first and then reduced. The mechanism of the Al 2 O 3 nanofluid enhancing CO 2 absorption is discussed accordingly. The absorption enhancement by the Al 2 O 3 nanofluid is mainly attributable to convective motion induced by the Brownian motion.

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The hydrophobicity of zeolite was achieved by a method of hydrothermal synthesis combined with acid treatment for the enhancement of CO2 absorption. The influence of zeolite before and after modification on the absorption of CO2 in three kinds of solvents (water, cyclohexane and soy bean oil) was investigated and many different effects were observed. In aqueous solution, modified zeolite showed a very remarkable enhancement with a maximum enhancement factor of 2.2 for a ratio of SiO2 and Al2O3 equal to 86. However, no measurable enhancement effect was found in cyclohexane solution by adding modified zeolite, although unmodified zeolite showed a weak increase in the absorption rate. In soybean oil, almost no change in CO2 absorption was obtained for both unmodified and modified zeolites. These results indicate that the particles with an enhancement effect for CO2 absorption rate need to have two properties, hydrophobicity and a high adsorption capacity for the solute. For predicting the enhancement factor of CO2 absorption by solid particles, a three-dimensional heterogeneous microcosmic mass transfer model was developed, in which the influence of several parameters and the interaction between particles were mainly considered. The results predicted by the present model show good conformity to experimental data, indicating that the model is rational and applicable for the enhancement process of CO2 absorption by modified zeolite particles

The improvement of CO 2 absorption by CNT nanofluids with deionized water as the base fluid was studied experimentally. The reactor used was a stirred thermostatic reactor, operated batchwise. Pure CO 2 was employed in all the experiments. The content of CNTs in the nanofluids ranged from 0 to 0.2% (wt). The acidification treatment of CNTs was employed to improve the stability of the nanofluids. The parameters, such as the concentration of CNT nanoparticles in the nanofluids, the stirring speed, the ultrasonic time for CNT nanofluid preparation, the nitration time and the amount of nitric acid for CNT acidification were varied. The results show that, with the increase of CNT concentration, the enhancement factor first increased and then leveled off after a certain value of the CNT concentration. With increasing stirring speed, the enhancement factor in stable functional CNT nanofluids declines monotonously, while in poorly dispersed raw CNT suspensions, it first increased and then reduced. The ultrasonic and nitration times and the amount of nitric acid have optimum values for the CO 2 absorption enhancement. The mechanism of the CNT nanofluid enhancement of CO 2 absorption is discussed accordingly. The absorption enhancement by the CNT nanofluid should be mainly attributable to convective motion induced by the Brownian motion and the shuttle effect.

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