Study on Preparation and Mercury Adsorption Characteristics of Columnar Sulfur-Impregnated Activated Petroleum Coke
Mingqing Zhu, Qituan Yan, Yufeng Duan, Jian Li, Xiang Zhang, Zhongxi Han, Jialin Meng, Shuying Wang, Cong Chen, Hongqi Wei
Abstract
In order to effectively remove mercury from raw natural gas, a preparation method of columnar sulfur-impregnated activated petroleum coke was proposed and mercury adsorption experiments were conducted under simulated natural gas processing operating conditions. The physicochemical properties of the adsorbents were discussed with the aid of characterization methods, including nitrogen adsorption/desorption and scanning electron microscopy (SEM) analysis, ultimate analysis, X-ray photoelectron spectroscopy (XPS) analysis, and thermalgravimetric (TG) analysis. The influence of different preparation procedures, KOH activation, sulfur impregnation, and the modification temperature, space velocity, and inlet Hg0 concentration on mercury adsorption performance were investigated in a fixed bed reactor. The better preparation procedure of the adsorbent of columnar sulfur-impregnated activated petroleum coke was suggested by following the order of KOH activation, columnar shaping, and sulfur impregnation. Proper space velocity and inlet concentrations of Hg0 can effectively improve mercury removal. The results showed that, compared with raw petroleum coke, the mercury removal efficiency of KOH activated petroleum coke increased by 20% and its specific surface area reached more than 1300 m2/g. After both KOH activation and sulfur impregnation, the bulk sulfur content reached more than 10 atom %, surface oxygen functional groups reached more than 24 atom %, and nonoxidized sulfur forms reached more than 8 atom %, which were most beneficial for mercury removal. It was found that the bonding of the short-chain S molecules to carbon matrix was fairly stable. Sulfur impregnation dominated the Hg0 removal and the rich micropores were conducive to more sulfur loading and more active sites for mercury adsorption. The adsorbed mercury species of HgS and HgO were attributed to the surface nonoxidative sulfur forms and oxygen functional groups based on the temperature-programmed-desorption (TPD) and XPS results. Kinetic studies indicated that both external mass transfer and chemisorption played a more important role in mercury adsorption than intraparticle diffusion.