## 1 Introduction  
Although numerous energy sources are being developed to replace the existing fossil fuels, they do not account for most of the energy consumed [1]. This large quantity of petroleum production undeniably produces a significant amount of byproducts [2]. Various crude oil classifications and refining processes are being developed for the eco-friendly and efficient use of these fossil fuels. Interest in high-value-added petroleum byproducts that can be processed or utilized to become more valuable, such as needle coke for graphite and carbon fiber, has recently increased [3]. Among these petroleum-based byproducts, the amount of metal impurities and the sulfur content in petroleum fuel oil (PFO) is significantly low, simplifying the manufacturing of high-quality carbon products; furthermore, relative research and development is actively underway [4]. In particular, this type of PFO, which has a small amount of impurities, high aromatic content, and is cost-effective, is considered a potential source for producing value-added chemicals such as needle coke and high-strength carbon fibers [5]. Owing to their exceptional properties, high-quality carbon products derived from PFO are crucial in various industries. Among these, artificial graphite and carbon fibers are appreciated owing to their high electrical and thermal conductivities, mechanical strength, and thermal and chemical stability [6, 7]. Activated carbon has been recently studied for its applications in gas adsorption, removal, and energy storage using these types of petroleum-based byproducts [8, 9]. When manufacturing activated carbon, the specific surface area and structural properties of activated carbon are significantly affected by the selection of raw materials and process conditions [10]. Typical raw materials used to manufacture activated carbon include lignite, coconut, sawdust, charcoal, peat, chaff, and petroleum coke [11]. Among these materials, petroleum-residue-based pitch has been widely used for the production of activated carbon owing to its low cost, low ash content, high carbon yield, and easily graphitizable properties. Therefore, petroleum-residue-based activated carbon has many advantages over other raw carbonaceous materials [12]. Petroleum pitch-based activated carbon can be manufactured via stabilization and activation processes [13]. It is crucial to use a pitch with numerous activation sites to increase the specific surface area. Therefore, introducing heterogeneous elements, such as oxygen, or inducing defects in the crystal structure is necessary to increase the number of activation sites [14]. In addition, because a pitch below the softening point has a melting property when exposed to heat energy, a non-melting process before the activation process is necessary [15]. The activation process can be divided into physical and chemical processes [16]. Physical activation involves using active gases such as CO\({}_{2}\) or H\({}_{2}\)O to induce reactions, whereas chemical activation involves chemicals such as KOH, NaOH, K\({}_{2}\)CO\({}_{3}\), Na\({}_{2}\)CO\({}_{3}\), and MgCl\({}_{2}\)[17]. Unlike physical activation, chemical activation poses challenges such as device corrosion and environmental pollution owing to the use of chemicals [18]. However, this process yields activated carbon with a well-developed specific surface area and pore structure [19]. Furthermore, the ratio and activation temperature of the chemical agents significantly influence the characteristics and adsorption capacity of activated carbon [20]. Recent advancements in the production of pitch-based carbon materials have highlighted their effectiveness in toxic gas adsorption. Pitch-based carbons, derived from petroleum residues, are particularly noted for their high carbon yield and structural properties, making them ideal for adsorbing hazardous gases like hydrogen chloride (HCl). A critical aspect of utilizing activated carbon for HCl gas adsorption is the chemical safety assessment.