## 4 Conclusions  
In this study, petroleum-based pitch was stabilized, which was used to manufacture activated carbon under various chemical activation conditions, and then pelletized. After pelletization, microwave treatment was used to induce surface changes in the pellets and evaluate their adsorption capacity for HCl gas, following the introduction of oxygen functional groups. In the stabilization process, a temperature of 260 \({}^{\circ}\)C demonstrated excellent thermal stability of the pellets and numerous oxygen functional groups, which was determined to be the most suitable temperature. This was followed by the activation process, which demonstrated that the pitch and KOH ratio of 1:4 was the best, with a specific surface area of 3330 m\({}^{2}\)/g, and several micropores (86.5%) were observed; therefore, we chose this ratio for pellet manufacturing. When the pellet was manufactured, its specific surface area decreased from 3330 to 2073 m\({}^{2}\)/g, because the addition of the binder and CMC blocked the pellet pores.  
After microwave treatment, the binder and CMC were confirmed to be melted, and the oxygen element ratio decreased. However, as the processing time increased, more oxygen functional groups were added, confirming that the proportion of oxygen increased. After the microwave treatment, both the specific surface area and pore volume of the pellets increased. The specific surface area treated for 3 min showed a tendency to increase the most at 2236 m\({}^{2}\)/g owing to surface etching. However, at 5 min, the specific surface areas decreased to 2086 m\({}^{2}\)/g, respectively, compared with that at 3 min. This appeared to have caused the pellet surface to collapse due to excessive heat treatment.  
Owing to the adsorption of HCl, the pellet treated with microwaves in 1 M of nitric acid at 600 W for 1 min demonstrated the highest adsorption of 77.99%. For bed utilization, microwave treatment for 5 min demonstrated the highest, accounting for 83.33% of the total. Therefore, the adsorption factor of HCl was attributed to the number of oxygen functional groups, specific surface area, and microporosity.  
Activated carbon plays a critical role in the chemical safety management of hazardous gases like HCl. The activated carbon pellets developed in this study, with their high specific surface area and microporous structure, are highly effective in adsorbing HCl gas, thereby serving as an essential tool for mitigating chemical hazards. This capacity to safely and efficiently manage harmful gases not only reduces the risk of exposure but also enhances overall chemical safety in industrial and laboratory environments.  
**Author Contributions:** Conceptualization, M.S.H., J.G.K. and B.C.B.; methodology, M.S.H. and B.C.B.; validation, M.S.H. and B.C.B.; investigation, M.S.H. and B.C.B.; resources, J.G.K. and B.C.B.; data curation, M.S.H. and B.C.B.; writing--original draft preparation, M.S.H.; writing--review and editing, M.S.H., J.G.K. and B.C.B.; visualization, M.S.H.; supervision, J.G.K. and B.C.B.; project administration, J.G.K. and B.C.B. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data supporting the findings of this study are available from the corresponding author upon reasonable request.  
The authors declare no conflicts of interest.