**10.2 Loading pressure effect on the process**

To evaluate the effect of the applied pressure, pressures of 5, 20, 35, and 50 were applied. The rest of the parameters are listed in **Table 5**. As the applied pressure increases, the amount of gas introduced and the nanotube adsorption capacity increase (**Figure 9**). But increasing pressure has limitations in terms of safety, manufacturing costs, and more. During emptying, the container pressure should be reduced to the ambient pressure. A pressure of 5 Pa was chosen for the ambient pressure. The adsorption capacity tripled when the applied pressure increased from 20 Pa to 35 Pa. This increase in pressure increases the molecular density of the gas in the container space. As the pressure increases, the gas molecules penetrate the inner layers of the adsorbent and the amount of gas absorbed increases [1].

#### **10.3 Surrounding condition effect on the process**

To investigate the effect of temperature (water bath temperature) on the process, environmental conditions (water bath temperature) 298 K, 305 K, 320 K, 335 K, and 350 K were considered. The other parameters are based on **Table 5**.


**Figure 8.** *Adsorption capacity at different porosity [1].*

**Figure 9.** *Adsorption capacity at different pressure [1].*

**Figure 10.** *Adsorption capacity at different temperature [1].*

**Figure 10** shows that the natural gas adsorption capacity of nanotubes that are exposed to temperature decreases. Because the temperature of the container is low at the beginning of the process, the maximum gas absorption capacity is obtained. Therefore, it is better to keep the temperature low and increase the discharge time to get better results during the charging process. For example, the adsorption capacity at 298 K is 0.4945 g/g. By increasing the temperature to 320, by reducing the adsorption capacity by 22%, 0.3826 g/g is obtained. Optimal conditions for this work include the maximum diameter of the carbon nanotubes and the applied pressure and the minimum amount of porosity (**Table 6**).


**Table 6.**

*Comparison of gas adsorption capacity in the presence of different adsorbents [1].*

The absorbed gas in the CNG tank is 11.2 grams, which is 25.9 grams using multiwalled nanotubes. By comparing the results, it can be seen that nanotubes have the highest and best percentage of storage and use to absorb and store natural gas in tanks [1].
