# The Effects of Methane Storage Capacity Using Upgraded Activated Carbon by KOH
## 3 Results
### Characteristics of CH\({}_{4}\) Storage by Compressed and Adsorbed  
Figure 3a shows the CH\({}_{4}\) storage capacity as a function of pressure under a compressed system. The storage capacity of CH\({}_{4}\) increased with pressure; the storage capacity was 0.176 g-CH\({}_{4}\)/mL at 20 MPa, which was beyond the expectation (0.131 g-CH\({}_{4}\)/mL) because of the compression properties (Z-factor of 0.84 at 298 K) of CH\({}_{4}\)[34].  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Sample** & **S\({}_{\text{BET}}\)** & **V\({}_{\text{Micro}}\)** & **V\({}_{\text{Meso}}\)** & **R\({}_{\text{micro}}\)** & **R\({}_{\text{meso}}\)** & **Methane Storage Capacity** \\  & **(m\({}^{2}\)g\({}^{-1}\))** & **(cm\({}^{3}\)g\({}^{-1}\))** & **(cm\({}^{3}\)g\({}^{-1}\))** & **(\%)** & **(\%)** & **(g-CH\({}_{4}\)/g-AC)** \\ \hline AC-WR & 1152 & 0.50 & 0.59 & 46.1 & 53.9 & 0.17 \\ AC-WA & 3052 & 0.04 & 2.37 & 1.73 & 98.3 & 0.32 \\ AC-CR & 1068 & 0.35 & 0.11 & 75.5 & 24.5 & 0.11 \\ AC-CA & 2258 & 0.48 & 0.43 & 52.5 & 47.5 & 0.25 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Textural properties and methane storage capacity.  
Figure 2: SEM image of altered carbon (AC) such as AC-WR, AC-WA, AC-CR, and AC-CA.  
By using upgraded ACs (AC-WA) in ANG experiments at 3.5 MPa in this study, the CH\({}_{4}\) storage capacity of upgraded samples increased by 59.6% for AC-WR (0.273 g-CH\({}_{4}\)/g-ACs) compared with the low-grade sample (0.171 g-CH\({}_{4}\)/g-ACs). However, its capacity did not show a positive relationship with the packing density (Figure 4b). As mentioned previously, the increase in the number of adsorption sites could lead to the enhanced CH\({}_{4}\) storage capacity in the ANG tank. However, this adsorption process entails an exothermic reaction, so the decreasing patterns of CH\({}_{4}\) storage capacity in Figure 4b could be explained by the increase in packing density. The heat control of adsorption plays an important role in gas storage because it significantly affects adsorption rates. Experimental and modeled results from [PERSON] et al. revealed that the temperature induced by the heat of adsorption at the beginning of the adsorption experiment increased sharply and reached up to 14 K of temperature difference using a coal sample [PERSON] et al. (2018). A few studies on the heat of adsorption according to various pressures, and even on CH\({}_{4}\) stored under compression, were reported in the literature. The temperature difference (\(\Delta\)T) inside the reactor decreased as the pressure decreased, as shown in Figure 4c. At the beginning of adsorption, the rapid increase in \(\Delta\)T influenced the CH\({}_{4}\) adsorption capacity.  
Heat transfer accompanied adsorption. Thus, the temperature of the adsorbent bed had a significant influence on the ANG storage system. We investigated the CH\({}_{4}\) storage as a function of adsorption temperature, as shown in Figure 5. The results showed that the CH\({}_{4}\) capacity in AC-WA increased at low adsorption temperatures. The residual amount of CH\({}_{4}\) after atmospheric pressure (101 kPa) desorption showed that the residual CH\({}_{4}\) increased from 15 to 20% as the temperature decreased. In the vacuum desorption, residual CH\({}_{4}\) increased from 5 to 10% as the temperature decreased. The residues were dependent on both the desorption temperature and pressure.