Synthesis and evaluation of carbon nanotubes composite adsorbent for CO₂ capture: a comparative study of CO₂ adsorption capacity of single-walled and multi-walled carbon nanotubes

As a preliminary investigation towards obtaining carbon nanotube composite adsorbent for CO₂ capture, in this study CO₂ adsorption performance of three commercial carbon nanotubes (CNTs) one single-walled carbon nanotubes (SWCNTs), and two (2) different multi-walled carbon nanotubes (referred to as A-MWCNTs and B-MWCNTs) were evaluated and compared. The purpose of this study was to compare the different types of CNTs and select the best to serve as the solid anchor in the development of a hydrophobic composite adsorbent material for CO₂ capture. The N₂ physi-sorption of the CNTs was conducted to determine their surface area, pore volume and pore size. In addition, morphology and purity of the CNTs were checked with Transmission Electron Microscopy and Raman Spectroscopy, respectively. The CO₂ adsorption capacity of the CNTs was evaluated using Thermo-gravimetric analysis (TGA) at 1.1 bar, at operating temperature ranged from 25 to 55 °C and at different CO₂ feed flow rates, in order to evaluate the effects of these variables on the CO₂ adsorption capacity. The results of CO₂ adsorption with the TGA show that CO₂ adsorption capacity for both SWCNTs and MWCNTs was the highest at 25 °C. Changing the CO₂ flowrates had no significant effect on the adsorption capacity of MWCNTs, but decreasing the CO₂ flow rate resulted in the enhancement of the CO₂ adsorption capacity of SWCNTs. Overall, it was found that the SWCNTs displayed the highest CO₂ adsorption capacity (29.97 gCO₂/kg adsorbent) when compared to the MWCNTs (12.09 gCO₂/kg adsorbent), indicating a 150% increase in adsorption capacity over MWCNTs.