In
this work, the absorption process of carbon dioxide is performed
in a custom designed high pressure experimental setup in which the
gas and nanofluid are in direct contact at static state in a closed
vessel. The initial condition of the tests are set at 20, 30, and
40 bar and 308 K. Nanoparticles of SiO2, Al2O3, Fe3O4, and carbon nanotubes
(CNTs) are dispersed in pure water to form nanofluids at concentrations
of 0.02, 0.05, and 0.1 wt %. Also, CNT nanoparticle has been dispersed
in methyldiethanolamine and diethanolamine aqueous solutions at the
concentration of 0.02 wt %. The absorption performances of different
nanofluids are compared with the base solutions and with other nanofluids
at different conditions. The results show that SiO2 and
Al2O3 are more effective at higher nanoparticle
concentrations (0.1 wt %), and they can enhance the absorption capacity
up to 21% and 18%, respectively. Fe3O4 and CNT
are more effective at lower nanoparticle concentration (0.02 wt %),
and they can increase it up to 24% and 34%, respectively. CNT nanoparticle
is more effective for methyldiethanolamine solution compared to diethanolamine
solution with an increase in the absorption capacity up to 23%. It
seems that gas adsorption on the nanoparticles surface leads to higher
absorption capacity of nanofluids at equilibrium condition.
In this work, suspensions of Fe 3 O 4 , CNT, SiO 2 , and Al 2 O 3 nanoparticles in distilled water are produced and tested as new absorbents in a gas−liquid hollow fiber membrane contactor to investigate the effect of nanoparticles on the rate of mass transfer during CO 2 absorption. For this purpose, a pilot-scaled hollow fiber membrane contactor was constructed. A gas mixture was passed through the shell-side, and the nanofluid flowed cocurrently through the lumen side of the fibers. The effects of different operating conditions including gas flow rate, liquid flow rate, inlet CO 2 concentration, and nanoparticle concentration on the CO 2 absorption have been studied. The results showed that among the operating parameters, liquid flow rate and nanoparticle concentration had the greatest effects on the CO 2 absorption. Moreover, UV−vis spectroscopy and DLS method were employed to explore the dispersion stability and hydrodynamic diameter of nanoparticles in the base fluid. The results revealed that nanofluid stability and hydrodynamic diameter of nanoparticles in the base fluid are the key factors in nanoparticle selection for CO 2 absorption in membrane contactor. The obtained results showed that the highest absorption rate enhancements for nanofluids are 43.8% at 0.15 wt % Fe 3 O 4 , 38.0% at 0.1 wt % CNT, 25.9% at 0.05 wt % SiO 2 , and 3.0% at 0.05 wt % Al 2 O 3 , as compared to the absorption rate by base fluid.
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