Kinetic Study and CO2 Separation Assessment from a CH4/CO2 Gas Mixture in the Presence of Multiwall Carbon Nanotubes

Abstract

The slow hydrate formation kinetics coupled with limited storage capacity restrict its practical application for gas separation and transportation. This challenge can be addressed by employing nanomaterials as kinetic promoters to enhance the gas hydrate formation process. In this study, the impact of multiwall carbon nanotubes (MWCNT), hydroxylated multiwall carbon nanotubes (OH-MWCNT), and carboxylated multiwall carbon nanotubes (COOH-MWCNT) on the mixture of CH₄ + CO₂ (70:30) hydrate formation kinetics and CO₂ separation is experimentally evaluated. The concentration of nanomaterials is in the range of 0.01–0.05 wt % dispersed in 0.03 wt % SDS solutions or pure water. The results showed that at a pressure of 4.0 MPa and a temperature of 274.15 K, carbon nanotubes slightly enhance the induction time and initial rate of gas consumption. In addition, a successful CO₂ separation with a separation factor within the range of 2.9–3.4 was achieved, and the CO₂ recovery factor was about 65% from the CH₄ + CO₂ (70:30) gas mixture. The separation performance was enhanced by COOH-MWCNT when compared to the other samples. A surfactant-free COOH-MWCNT nanofluid demonstrated higher selectivity to CO₂ when compared to a surfactant aqueous solution at concentrations of 0.03 wt %.