Experimental studies of CO2 absorption enhancement in water-based nanofluids of carbon nanotubes

Abstract

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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