| In the process of fossil fuels burning, waste incineration and metal smelting, a number of elemental mercury from the flue gas is discharged to atmosphere. More and more people pay attention to the mercury hazards on human and ecological. In this paper, took advantage of molecular sieves with unique pore structure and adsorption property. Molecular simulation and laboratory experiment study was carried out to removal elemental mercury by ZSM-5 molecular sieves.Materials Studio software was applied in conjunction with several other conditions to selecte mercury removal molecular sieve from 145 kinds of different zeolite framework structure, as the result, ZSM-5 molecular sieve was the best. To improve the adsorbed property of elemental mercury of ZSM-5 molecular sieve,filter out K2 Fe O4 and Cu Cl2 as the active substance. Modified ZSM-5 molecular sieve, combined into composite adsorbent K2 Fe O4-ZSM-5 molecular sieve and Cu Cl2-ZSM-5 molecular sieve. In the experimental studies, ZSM-5 was modified through solid-state ion exchange by K2 Fe O4, and dipping by Cu Cl2. The ZSM-5 molecular sieve removal mercury performance was explored by using controlled variable method. Specific findings were as follows:(1) Sing cell molecular sieves of 145 kinds of different skeletal structure were studied to adsorption elemental mercury by Materials Studio software. Then, obtained the number of mercury molecules were adsorbed when equilibrium was reached under the same conditions. Under the conditions of skeletal structure constituted only by Si and O atoms, the ranking of adsorption property strength are MFI >VNI >PAI. Combined with the efficient screening criteria to get the best choose was ZSM-5 molecular sieve.(2) With the Monte Carlo method(GCMC), Simulation pure ZSM-5 molecular sieve adsorbed of mercury and active substance loaded on it. Silica to alumina ratio, temperature and other factors affecting adsorption property were observed. Simulation results showed that, the higher aluminum content of ZSM-5 molecular sieve, the more mercury adsorbed. At low-temperature and atmosphere, mercury adsorbed on the ZSM-5 molecular sieve was linearly increased, and the adsorption isotherm can be well described by the Henry adsorption principle. Moreover, removal efficient of mercury was decreased when the temperature increased. According to Clausius-Clapeyron equation, isosteric heat of adsorption of potassium ferrate load on ZSM-5 molecular sieve was about 381-383kcal/mol, as for Copper chloride was approximately 13-14kcal/mol. Through the isosteric heat of adsorption of potassium ferrate to illustrate that load was securely. However, as for Copper chloride was weak. By load distribution location map can be observed that potassium ferrate only distributed on ZSM-5 molecular sieve surface. But Copper chloride went to the internal pore. The energy distribution curve displayed two active substances in ZSM-5 molecular sieve to be multiple adsorption sites.(3) The experiments of ZSM-5 molecular sieve adsorbed elemental mercury in the laboratory show that its Si/Al ratio had big influence on adsorption mercury. In the context of Si/Al ratio less than 50, with the ratio increased, the mercury removal efficiency increase. While ratio greater than 50, the efficiency stabilized at around 55%. As for composite adsorbent, K2 Fe O4 and ZSM-5 molecular sieve mixing with the best quality ratio of 10:1.6. The optimum adsorbed temperature for composite adsorbent was 80℃. The best solubility by mass for impregnated of Cu Cl2 and ZSM-5 molecular sieves was 5%, and the optimum adsorbed temperature for composite adsorbent was 30℃. After modified, the adsorption efficiency of ZSM-5 molecular sieve was greatly improved, which the highest mercury removal efficiency of K2 Fe O4-ZSM-5 was 85%. The highest mercury removal efficiency of Cu Cl2-ZSM-5 was up to 80%. |
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