製備廢油砂焦碳活性碳並探討去除模擬燃煤煙道氣中汞之可行性

Preparation of Activated Carbon from Waste Oil Sand Cokes by Microwave-Assisted Activation for Removal of Gaseous Mercury from Simulated Coal-Combustion Flue Gas

吳家維(Chia-Wei Wu)

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(2013年)

https://doi.org/10.6841/NTUT.2013.00165

摘要

汞為毒性污染物質，美國環保署(US EPA)於1990年發布之清潔空氣法案(Clean Air Act, CAA)中，將汞定為有害空氣污染物(Hazard Air Pollutions, HAPs)，而燃煤電廠為空氣中汞污染源之大宗。燃煤電廠汞污染控制技術中，吸附劑噴入法被美國環保署(US EPA)視為最佳可行方法，吸附劑中活性碳最常被使用在去除汞污染技術中，而經由硫含浸過後之活性碳，其對汞之吸附效果會大幅地提升，其缺點為比表面積會有所下降。
廢油砂焦碳為煉製石油後，所產生之廢棄物，因其製程可分為流體化焦碳(Fluid coke)與延遲結焦焦碳(Delayed coke)，而此兩種焦碳具有高碳量及6 wt%硫，可做為此製備活性碳實驗之起始材料，並評估其對汞之吸附效果。
本研究利用不同微波活化時間搭配固定比例之活化劑，均可將廢油砂焦碳開發成，具有一定比表面積之活性碳，而在Hg0吸附實驗結果顯示，在氮氣條件下，油砂焦碳活性碳皆未達飽和吸附量，而原樣F0及D0雖其比表面積不高(12.6及1.5 m2 g-1)，但因其硫含量達6 wt%，使得其汞去除率有90%，而其他活化後之樣品，其去除率皆比原樣低，由此可得知，當微波活化的過程中，原樣中的硫因溫度升高與受熱時間增加，造成樣品中硫損失，進而影響其對汞去除效率，而在氮氣條件下，含硫活性碳對汞之吸附行為較偏向化學吸附。而在煙氣條件下，可由D0之汞去除率下降，及F0與其它微波活化後之樣品對汞之去除率上升，推估在煙氣條件下，含硫活性碳對汞之吸附行為，偏向結合物理及化學吸附，而含硫量之多寡對其去除率影響較大。
而在吸附動力模式分析方面，不管是氮氣條件或煙氣條件，均以零階模擬最符合實驗結果。

關鍵字

油砂 ； 活性碳 ； 汞 ； 煙道氣 ； 硫

並列摘要

Mercury is a toxic pollutant. The U.S. Environmental Protection Agency (USEPA) published the Clean Air Act (Clean Air Act, CAA) in 1990 listing that mercury is a hazardous air pollutants (Hazard Air Pollutions, HAPs). The emission of mercury from coal‒fired power plant is the major source of mercury pollution. Among the options for controlling mercury air pollution from coal-fired power plant, adsorption is deemed to be the best possible method. Activated carbon is the most commonly used adsorbent for the removal of mercury. Activated carbons can be more effective on mercury adsorption after impregnation with sulfur, even though sulfur impregnation may reduce the surface area.
The oil sand coke is the leftover material resulting from the refining of petroleum using oil sand. The oil sand coke includes fluid coke and delayed coke; both cokes have high carbon content and high sulfur content (approximately 6 wt%). Consequently, oil sand coke can be a good precursor for activated carbon production and Hg0 adsorbents.
Activated carbons were successfully prepared under various microwave activation time at a fixed proportion of KOH. The surface area and pore volume were developed within short microwave activation time. An increase in activation time caused the gradual decrease in sulfur, which greatly affects Hg0 absorption. The Hg0 absorption experiments showed that under the Hg0/N2 condition, equilibrium adsorption was not achieved for all the tested samples. Although the raw cokes F0 and D0 have small surface area (12.6 and 1.5 m2 g-1 respectively), both raw cokes had the greatest mercury removal efficiency up to 90% due to their high sulfur content up to 6 wt%. All the resulting activated carbons had smaller Hg0 absorption compared to their coke precursors, indicating the importance of sulfur on Hg0 absorption. Under Hg0/N2 condition, Hg0 appeared to be chemisorbed on activated carbons. Under the flue gas condition, the Hg0 removal of D0 decreased, but the Hg0 removal of F0 and the other samples increased. These results suggest that a combination of physisorpiton and chemisorption may control the Hg0 adsorption when flue gas components involves in.
Kinetic model analysis results showed that under both N2 or flue gas conditions, zero‒order reaction mechanism control the Hg0 adsorption.

並列關鍵字

Oil sand ； flue gas ； activated carbon ； mercury ； sulfur

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