Adsorption of low concentration CO ₂ by modified carbon nanotubes under ambient temperature

Solid amine adsorbents for low concentration CO ₂ removal were developed using carbon nanotubes (CNTs) impregnated with tetraethylenepentamine (TEPA) and triethylenetetramine (TETA). The adsorbents were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FITR), N ₂ adsorption/desorption, elemental analysis and thermogravimetric analysis (TGA). After impregnation, the shapes, fundamental channels and pore structures of the adsorbents were unchanged. However, the surface area and pore volume decreased. The adsorption behavior toward low concentration CO ₂ was investigated in a fixed-bed column. The results indicated that the adsorption capacity was enhanced substantially by modification. The CO ₂ adsorption capacity of CNTs-TEPA was higher than that of CNTs-TETA with the same amount of amine loading. The adsorption capacity increased steadily from 126.7 to 139.3 mg·g ^-1 for CNTs-TEPA and from 101.2 to 110.4 mg·g ^-1 for CNTs-TETA as the temperature increased from 20 to 30 °C. The adsorption capacity of the raw CNTs experienced a modest increase, but began to decrease gradually with further temperature increases. Suyadal and Yasyerli deactivation models were applied to investigate the experimental breakthrough curves of raw and modified CNTs. It was concluded that the Yasyerli deactivation model is more appropriate to analyze the breakthrough curves of CO ₂ adsorption on solid amine adsorbents.