Study on Preparation and Mercury Adsorption Characteristics of Columnar Sulfur-Impregnated Activated Petroleum Coke

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 Hg 0 concentration on mercury adsorption performance were investigated in a fixed bed reactor. The better preparation procedure of the adsorbent of columnar sulfurimpregnated activated petroleum coke was suggested by following the order of KOH activation, columnar shaping, and sulfur impregnation. Proper space velocity and inlet concentrations of Hg 0 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 m 2 /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 Hg 0 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.

The Effects of Physical-Chemical Evolution of High-Sulfur Petroleum Coke on Hg0 Removal from Coal-Fired Flue Gas and Exploration of Its Micro-Scale Mechanism

“…For combined pyrolysis and KOH activation, Zhu et al [ 31 ] proposed a two-step preparation method of columnar sulfur-impregnation in which KOH activation under 750 °C for 1 h played an effective step to promote the development of pores. When the weight ratio of KOH solution to raw petroleum coke came to 3:1, the specific area and the total pore volume dramatically increased to 1713.8 m 2 /g and 0.8615 cm 3 /g, respectively.…”

“…While the method of KOH activation to improve rich micropore structure was conducted for biomass [ 29 ] and petroleum coke [ 31 ], the sulfur in HSPC would be cleared up, which could not be the full utilization of sulfur in HSPC for mercury removal. Shan et al [ 53 ] further gave out the transformation of sulfur species during KOH activation of HSPC samples collected from Zibo in China and America to ensure the results are reliable.…”

“…Zhu et al [ 31 ] almost cleaned up the conventional sulfur in petroleum coke by KOH activation and further conducted element sulfur impregnation with a S/samples weight ratio of 1:2 under 400, 500, and 600 °C. It was found that the higher impregnation temperature would lead to better Hg 0 removal efficiency of 60%, which could be explained that shorter chains of elemental sulfur were generated with increasing impregnation temperature.…”

“…Zhu et al [ 31 ] pointed out that the surface oxygen functional groups reached more than 24 at. % by KOH activation and SO 2 impregnation, which was significantly more than that of Xiao et al [ 38 ].…”

“…Wu et al [ 30 ] obtained a specific surface area of at most 3000 m 2 /g, which came up with commercial activated carbon. The fresh high-sulfur petroleum coke, which contained 6.2% total sulfur, was activated using KOH by Zhu et al [ 31 ]. Although the specific surface area reached 1713.8 m 2 /g, the sulfur for element mercury oxidation almost lost and was not fully utilized.…”