| Energy shortage and environmental pollution have been the most critical problems that hinder the development of modern human societies. Until the middle of this century, the condition of using coal as main energy source in China will not change. SO2, NOx, particulate matter, mercury and other toxic pollutants emitted from the combustion of coal threaten the human health seriously. Mercury, duo to some environment safety problems such as high toxicity and biological accumulation has brought the attention of the whole humanity. The mercury emission in China is largest in the world,for this reason, an environmental protection law(Emission standards of air pollutants for thermal power plant) had been enacted in the year of 2012, which confirms the standards for mercury emissions from coal-fired power plants. However, the control technologies of mercury emissions are not yet used widely in China, especially the removal of Hg0. Thus, it is necessary to enhance the research of mercury emission control technologies, which should be a practical prospect of high efficiency and economy.Except the existing flue gas purification equipment, the commercial technology of flue gas demercuration was adsorption by active carbon. However, some drawbacks such as the short contact time, the low adsorption efficiency, the large consumption of activated carbon and high cost limit its application. Researches showed that modified treatment of AC to improve the mercury adsorption efficiency was an economic and efficient method. In this study, a new modified method, impregnated with succinic acid on AC, was proposed to improve the mercury capture efficiency. Preparation condition SA/ACs and a series influences of reaction conditions on the mercury capture efficiency were investigated. The physical structure and chemical properties of the SA/ACs were also characterized. In addition, the adsorption and oxidation of Hg0 over SA/AC and the regeneration process of SA/ACs were explored. Finally, mechanisms of Hg-captured and Hg-desorption over SA/AC samples were proposed. The results demonstrates that the SA/ACs exhibit high mercury removal efficiency and stability. This method is an efficient technology with the advantages of operation simplicity, environmental friendly, no "three wastes" pollution, low-cost, renewable for materials, and low requirements for equipment.The contents and results of this research are listed as follows:(1) Mercury-capture activities of different activated carbons after modified by succinic acid were investigated in the laboratory simulated flue gas. Compared with the fresh AC, Mercury capture efficiency on modified ACs was greatly increased. The influence of space velocity(5000-50000 h-1), loading capacity(0.5-10%), experimental temperature(30-170 ℃), oxygen concentration on the mercury capture efficiency were investigated. Results indicted that in the absence of oxygen, the activity of SA/AC rapidly reduced. In the presence of oxygen, reaction temperature of 110 ℃,5% SA/AC showed the highest mercury-capture efficiency,and the mercury adsorption was up to 890 μg·g-1.(2) The samples were characterized by Elemental analysis(EA), Fourier transform infrared(FTIR), Specific surface and pore structure analysis, X-ray photoelectron spectroscopy(XPS), Temperature programmed desorption(TPD), Transient response and other methods. The physical and chemical characteristics of SA/AC and the mercury capture mechanism were also explored. It was found that both the bonding oxygen-containing groups and the dissociative SA are on the surface of SA/AC. In the presence of oxygen-containing functional groups, Hg0 can react with O2 to generate Hg O, which can further react with succinic acid to generate mercury succinate and then migrated away from the active sites. The previously occupied activity sites were recovered, thereby greatly increasing the mercury capture ability.(3) The desorption behavior of mercury in the process of thermal regeneration of SA/AC-Hg was investigated. Results indicated that only Hg0 existed in the exhaust gas and more than 92% of mercury released from SA/AC-Hg. From the mercury desorption concentration curves, it can be observed that mercury can desorbed at low temperature within a narrow temperature range below 190 ℃. And the concentration of mercury in exhaust gas is almost zero when the temperature exceeded 400 ℃. It because the reduction of SA in the desorption process and the desorption temperature was decreased with the rise of SA loading. The performance of SA/AC after thermal regeneration was equal to the fresh AC, and the activity can be recovered after by treatment with SA again.(4) AC was modified by series of carboxylic acids which have the similar structure with SA. Compared with the fresh AC, mercury capture efficiency of modified ACs were greatly increased. Additionally, except glutaric acid, the mercury capture efficiency of the rest carboxylic acid/AC had positive correlation with the melting point of carboxylic acid, and the higher the melting point, the higher the mercury capture efficiency.(5) The feasibility of technical and economic were discussed when the carboxylic acid modified activated carbon were used for mercury removal in the industrial flue gas. |
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