# Regeneration Performance of Activated Carbon for Desulfurization
## 1 Introduction  
SO\({}_{2}\) is the major air contaminant released in industrial activities. This gas is mainly generated from the combustion of fossil fuels (coal, oil, and gas), which is for power generation and the smelting of mineral ores, like copper, aluminum, zinc, lead, and iron [1]. SO\({}_{2}\) produced by industry can cause acid rain, which contributes to air pollution, soil acidification, water pollution, and destruction of building structures [2]. These environmental problems affect human health, social security, and ecological harmony [3]. Thus, several efficient technologies have been employed for the removal of SO\({}_{2}\) in industrial production by most countries [4].  
Porous solid sorbents, such as activated carbon (AC), zeolites, alumina, and zirconia, attract much attention owing to their characteristics of cheap, low energy consumption, and easy regeneration [5, 6]. In the area of air pollution control, porous solids have been widely adopted for desulfurization, because of their ultra-low sulfur contents and having high selectivity for sulfur compounds [7]. Specifically, AC is one of the main SO\({}_{2}\) adsorbents, which have abundant oxygen- containing groups, highly porous structure, and good thermal stability [8, 9, 10]. The characteristics of abundant oxygen-containing groups and the highly porous structure of AC can enhance the performance for SO\({}_{2}\) physisorption and provide more active sites for SO\({}_{2}\) removal [11, 12].  
AC adsorbs SO\({}_{2}\) until it reaches its saturation limit. On most occasions, the saturated AC fails to be reused, and is landfilled or incinerated [13]. The regeneration of saturated AC has become a desired feature from academic, industrial, and economic perspectives, as it complies with both the regulations of the discharge of solid pollutants and is good for constructing a sustainable society with a clean and tidy environment [13, 14]. The methods of regenerating saturated materials mainly include thermal treatment, oxidation, microwave irradiation, and electrochemical methods [15]. Thermal treatment is the best compromised method in the regeneration of spent adsorbents in the consideration of the cost, the adsorption efficiency, and the number of regeneration cycles. The method is simple and versatile,and it can obtain better environmental and industrial benefits [14]. A versatile reaction mechanism is shown in Equations (1)-(3) in the process of SO\({}_{2}\) adsorption and desorption by AC:  
\[\mathrm{SO_{2}+O_{2}+H_{2}O\rightarrow}\mathrm{H_{2}SO_{4}} \tag{1}\]  
\[\mathrm{AC+2H_{2}SO_{4}\rightarrow}\mathrm{CO_{2}+2 SO_{2}+2H_{2}O} \tag{2}\]  
\[\mathrm{AC+H_{2}SO_{4}\rightarrow}\mathrm{CO+SO_{2}+H_{2}O} \tag{3}\]  
[PERSON] et al. [16] reported an increase in the SO\({}_{2}\) removal efficiency of AC fibers after 1173 K thermal treatment. [PERSON] et al. [17] showed that the bimetallic nanoparticles which are loaded on the modified AC, can simultaneous remove SO\({}_{2}\). [PERSON] et al. [18] revealed that activated carbon obtained from corncob waste showed an effective performance of removal of toluene from flue gas. [PERSON] et al. [19] demonstrated that the thermal regeneration of activated coke may cause carbon consumption, which is mostly influenced by the regeneration temperature. However, the performance of AC in the process of multiple recycle regeneration, has been rarely reported.  
Thus, this study investigated the influence of various experimental conditions on SO\({}_{2}\) adsorption, and focused both on the investigation of the influence of thermal regeneration on the characteristics of AC, and the adsorption efficiency and mechanism of AC after thermal regeneration [1,2].