| Activated carbon injection (ACI) is one of the most commercial promising mercury removal technologies. However, due to its high operating cost, it is difficult to achieve large-scale industrial applications. Therefore, developing efficient and inexpensive alternative sorbents has become a hot topic. High sulfur petroleum coke, which is abundant and inexpensive, is an industrial byproduct of delayed coking unit. The high sulfur petroleum coke is good raw material to produce activated carbon because of its high carbon content, high sulfur content and low ash content. Due to the sulfur content in high sulfur petroleum coke is close to that of commercial sulfUr impregnated activated carbon, so it was proposed that the high sulfur petroleum coke was used to produce sulfur-rich mercury removal sorbent, which has the advantage of high efficiency and low cost.Firstly, the release characteristics of gas-phase products in the process of high sulfur petroleum coke pyrolysis and activation was analyzed by TG-FTIR. The results show that, the pyrolysis process of high sulfur petroleum coke experiences dehydration and the decomposition of long chain aliphatic hydrocarbon and fused ring aromatic hydrocarbon stages. In the pyrolysis process, the gas-phase products include CO2, CH4, SO2, water vapor, aromatic compounds, aliphatic compounds and so on. The gas-phase products at different temperature have significant differences because of the decomposition of various substances. In the initial stage of high sulfur petroleum coke activation process, the main gas-phase product is water vapor, and in the following stage, the main gas-phase product is CO2 and CO. In the initial stage of activation process, the weight loss rate increases first and then decreases, with the weight loss peaks distributed at 120?,184? and 370?, respectively. In the intermediate satge, the weight loss rate is low, but as the temperature reaches 600?, the weight loss rate increases fast because of the occurance of acute activation reaction.Secondly, several mercury sorbents such as pyrolyzed high sulfur petroleum coke, activated high sulfur petroleum coke and sulfur impregnated activated high sulfur petroleum coke were prepared from raw high sulfur petroleum coke in a tube furnace apparatus. The methods of N2 adsorption/desorption, ultimate analysis, XPS and TG-MS were applied to analyze the surface area, pore structure and sulfur species of sorbents qualitatively and quantitatively. The results show that, the pore structure parameters of the activated high sulfur petroleum coke are influenced by many factors such as alkali coke ratio, activation temperature and so on. The high sulfur petroleum coke activated at 750? has the optimal pore structure with the alkali coke ratio of 1:1. The sulfur content in the petroleum coke is reduced after the KOH activation. The surface area of the sulfur impregnated activated high petroleum coke increases with the impregnation temperature. However, the sulfur molecules escape out quickly at high temperature because of the sulfur transformation from the long chain sulfur species to the short chain species, which leads to the decrease of sulfur content with the impregnation temperature. The distribution of sulfur in high sulfur petroleum coke is not uniform and the mutual transformation of sulfur species occurs with the pyrolysis temperature. At low temperature, the sulfur transformates from sulfide to thiophene and at high temperature the thiophene decomposes. Activator KOH can efficiently convert organic sulfur of thiophene, sulfoxide and sulfone into K2S, which will be further oxidized into sulfate. Therefore, the sulfur on the surface of activated high sulfur petroleum coke mainly exists in the sulfate specie. The sulfur exists on the surface of sulfur impregnated activated high sulfur petroleum coke is mainly in the from of elemental sulfur and sulfate. The kinds of elemental sulfur include short chain sulfur S2, S6 and long chain sulfur S7, S8. With the increase of impregnation temperature, elemental sulfur tends to exist in the form of short chain, the content of elemental sulfur gradually decreases, and the content of sulfate gradually increases.Finally, experimental study of Hg0 adsorption by petroleum coke sorbents was carried out in a fixed bed apparatus. The results show that, the sulfur exists on the surface of the raw high sulfur petroleum coke, which has a high graphitization extent, is mainly in the form of thiophene, leads to the poor mercury removal capacity. The formation of the pore structure by the volatilization of the volatiles during pyrolysis process leads to the improvement of the removal capacity. Although the sulfur exists on the surface of the activated high sulfur petroleum coke is mainly in the form of sulfate, which is weak in the reaction with mercury, the mercury removal capacity is greatly improved because of the developed pore structure. The high sulfur petroleum coke activated at the temperature of 750 ? has the optimal removal capacity. The adsorption of Hg0 by the activated high sulfur petroleum coke is mainly in the form of physical adsorption, which is caused by Van der Waals forces. With the rise of adsorption temperature, Van der Vaals forces become weak, results in a decline of mercury removal capacity. After elemental sulfur impregnation, the sulfur impregnated activated high sulfur petroleum coke shows an efficient mercury removal capacity, which is mainly influenced by the factors of surface area, surface sulfur content and the distribution of sulfur species jointly. Elemental sulfur, sulfide and thiophene may be positive for the adsorption of Hg0, while the promotion of adsorption by sulfoxide and sulfate is not strong. In addition, with the rise of adsorption temperature, the mercury removal capacity declines greatly for that the chemical adsorption of Hg0 by Sulfur is an exothermic process. |
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