**10. Influence of different factors on absorption in CNT**

#### **10.1 Nanotube's diameter effect on the process**

The diameter of the nanotubes with sizes of 5, 10, 15, and 30 nm was considered to investigate the effect of the outer diameter of the nanotubes on the process, and the other parameters listed in **Table 5** were selected. As the diameter of the nanotubes increases, the walls of the nanotubes increase, and thus, the active


**Table 2.** *Natural gas and methane properties [1].*
