銅鹽含浸沸石分子篩去除模擬燃煤煙道氣中氣相汞之探討

Removal of Gaseous Mercury from Simulated Coal-Combustion Flue Gases Using Copper-Impregnated Zeolite Molecular Sieve

林志誠(Chih-Cheng Lin)

指導教授 ： 席行正

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00337

摘要

汞一直被視為具有高毒性且能於人體以及動物體內生物累積的高毒性污物，汞物種中又以甲基汞的毒性最高。而燃煤過程所排放的汞往往是最大的人為汞產生源，是近年來備受關注的環境議題。為提升燃煤電廠吸附劑噴入法所用之吸附劑的吸附效能，故許多材料例如活性碳、沸石分子篩都被開發應用作為吸附劑。天然沸石是一種具經濟效益且有高陽離子交換能力的材料，而MCM-48是一種具有中孔立體結構的沸石，可用來作為良好的載體吸附劑。為了增加吸附劑的吸附容量，通常會對吸附劑進行改質。銅鹽於近年也被視為另一可用之含浸試劑，此類金屬鹽類含浸之吸附劑因其具有氧化元素汞能力，能同時提高微量汞吸附量及增加氧化元素汞的效能。故本研究將評估經銅鹽含浸後MCM-48的沸石材料其物理化學性質，並使用此材料來吸附元素汞，以便更了解表面性質與汞的平衡吸附和氧化效能的關係。銅鹽的含浸比例分別為2、4、8、16 wt%，含浸程序為將6 g原始材料MCM-48浸泡於30 mL之CuCl2•2H2O水溶液，然後於60–70°C下以磁石攪拌6 hr，帶水溶液完全蒸發後將樣品至於120°C之烘箱烘乾。汞吸附試驗在模擬煙氣與氮氣兩種環境條件下進行。
整體而言，樣品經含浸過後其比表面積與總孔體積皆有略微的下降，而微孔比表面積與微孔體積則有上升的趨勢。汞吸附實驗結果顯示，於氮氣環境下進行吸附實驗其含浸比例4%與8%的樣品吸附量高，分別為1329與1325 μg g-1，值得一提的是當含浸比例超過10%後吸附效果會有下降的情形；但不論在煙氣環境或氮氣環境下，經銅鹽含浸處理過後，其對於汞之吸附量皆較原樣來的高。從氧化實驗中可發現，在模擬煙道氣條件下，經銅鹽含浸4%與16%的樣品平均氧化百分比皆超過50%。而在動力模式分析方面，在氮氣條件與煙氣條件下皆以零階模擬最符合實驗的結果。

關鍵字

汞 ； 銅鹽含浸 ； 煙道氣 ； MCM-48

並列摘要

Mercury (Hg) emissions from nature and anthropogenic sources have been major focus of environmental works due to their considerable amount and severe health effects. Hg, especially organic Hg, has been recognized to be toxic and can bioaccumulate in human body and animal. Coal-burning power plants are the largest source of Hg pollution. Sorbent injection has been referred to as one of the best available control technologies for removal of low-concentration mercury (e.g., ?g m-3 levels) from coal-fired utility flue gases. Several materials have shown to be excellent sorbents for removing mercury, such as activated carbon, molecular sieve and zeolite. Natural zeolite has recently been found as a cost-effective material due to its low cost and high capability to adsorption and cation exchange those cause high adsorption capacities. MCM-48 is a type of zeolite with mesostructure that could be a good material as Hg sorbent. In order to enhance the adsorption capacity of sorbents for elemental mercury (Hg0), chemical treatments are often employed on various sorbents. A few studies have shown that copper salts can be feasible reagents to improve the control effectiveness of sorbents via both adsorption and enhancing oxidation of Hg0 into Hg2+. This research investigates the effects of CuCl2 impregnation on the physical/chemical properties and Hg0 adsorption of zeolites, with an emphasis on better understanding the resulting surface properties of zeolites samples on mercury adsorption equilibrium and oxidation efficiency.
CuCl2-impregnated zeolites with a targeting Cu content of 2, 4, 8, and 16 wt%, respectively, were prepared by immersing 6 g raw zeolites in a 30 ml CuCl2•2H2O solution. The solution was magnetically stirred at 60–70 °C for about 6 hr, allowing the water completely vaporized. The sample was subsequently air-dried in a 120 °C oven to complete the impregnation process.
Overall, the CuCl2 impregnation caused a decrease in total surface area and pore volume, but led to an increase in micropore surface area and micropore volume compared to those of the raw sample. The Hg adsorption capacity of MCM-4% and MCM-8% are 1329 and 1325 μg g-1, respectively. When the CuCl2 impregnation content was > 10 wt%, the performance of removing Hg0 for CuCl2-impregnated zeolites decreased slightly. The Hg0 adsorption capacity of CuCl2-impregnated zeolites was greater than those of the untreated sample under both N2 and flue gas conditions. The oxidation experimental results showed that the average oxidation percentage of MCM-4% and MCM-16% are > 50% in the flue gas condition. Kinetic analyses showed that the zero-order model can best fit the adsorption results under N2 and flue gas condition.

並列關鍵字

mercury, ； Cu impregnation ； flue gas ； MCM-48

參考文獻

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