CO_2 absorption by Al_2O_3/NaCl aqueous solution nanofluids

摘要

Recently, many studies have been focused on the reduction of CO_2 emission, which is a main greenhouse gas. However, the temperature of the absorbent during the physical absorption process should be maintained at a low temperature (about -40°C) to increase the CO_2 gas absorption rate according to the Henry's solubility law. Therefore, huge amount of energy is required to keep such a low temperature of the absorbent in the CO_2 removal systems. In this study, Al_2O_3 nanoparticles are combined into NaCl aqueous solution to enhance the CO_2 mass transfer and thermal conductivity of the base fluid (3.5 wt% NaCl aqueous solution). NaCl aqueous solution is similar to the composition of the seawater which regulates the amount of CO_2 at atmosphere. The absorption experiments are carried out in a bubble type absorber system. And the transient hot-wire method is applied for measuring the thermal conductivity of nanofluids. The nanoparticle concentration ranges from 0.005 to 0.1 vol% for the absorption experiment. The thermal properties of nanofluids are measured at a temperature of 20°C. It is found that the CO_2 absorption is enhanced up to 12.5% at 0.01 vol% of Al_2O_3/NaCl aqueous solution nanofluids. And the thermal conductivity of the nanofluids enhances 3.4% at 0.1 vol% of Al_2O_3/NaCl aqueous solution nanofluids. In addition, experiments were carried out to estimate the stable dispersion of the nanofluids. The nanofluids proposed in the present study are expected to be a promising candidate for removing CO_2 gas in a physical absorption process.