球狀活性碳對揮發性有機物的吸附與電熱再生

揮發性有機物(Volatile organic compound, VOC)為近年來中央及各地方主管機關在空氣污染管制上的重點物質，而其光化學衍生物也對環境生態以及人體健康有短期和長期的影響，如何限制和控制VOC的排放就成為了空氣污染防制中一個極其重要的課題。球狀活性碳(Beaded activated carbon, BAC)由於其高機械強度、高比表面積及高度流動性等特性，因此成為可被應用於VOC控制之吸附材料，且特別適合被應用於流體化床技術中。而活性碳吸附法除了可以去除低濃度VOC外，也具有回收有價值之蒸氣的潛力。本研究使用商用球狀活性碳，吸附去除甲苯(TOL)及丁酮(MEK)，並搭配電熱再生技術(Electrothermal Swing System, ETS)，在惰性氣體環境中對活性碳通電以加熱球狀活性碳並使吸附質脫附，達到活性碳再利用的目的。由氮氣吸脫附結果顯示材料之BET比表面積介於1135.69－1277.81 m2 g-1，孔體積介於0.473－0.522 cm3 g-1。經過一次吸脫附後球狀活性碳其比表面積與微孔體積有略為減少，而經過循環吸脫附試驗後之球狀活性碳，其微孔表面積與微孔體積有顯著的下降，此下降現象也反映在吸附容量上面。研究以電熱方式對吸附TOL及MEK至飽和之BAC在120、140、160oC三種不同溫度條件下進行再生，吸附TOL之BAC (TOL-BAC)脫附效率介於54.83‒79.68%，而吸附MEK之BAC (MEK-BAC)脫附效率介於84.67‒89.88%之間，兩者均呈現隨著溫度升高，脫附效率也越高。而在循環吸/脫附試驗當中，經過6個循環後，吸附TOL及MEK的BAC吸附容量均有減少，而TOL-BAC相較於MEK-BAC，其影響更為顯著，第二循環之吸附容量已經減少至約原始吸附容量的一半，而MEK-BAC還有著約7成的吸附容量，較低的吸附效率可能源自於活性碳再生過程中孔洞結構的塌陷降低表面積及孔體積。整體而言，本研究探討了電熱系統對於TOL及MEK之脫附效率以及應用於球狀活性碳上之可行性。

關鍵字

球狀活性碳；揮發性有機物；甲苯；丁酮；電熱再生；循環吸/脫附

並列摘要

In recent years, volatile organic compounds (VOCs) have been key substances to concern by central and local authorities due to their toxicity. Their photochemical derivatives also have short-term and long-term effects on environment and human health. Therefore, how to limit and control VOC emissions has become an extremely important topic in air pollution prevention and control. Beaded activated carbon (BAC) has become a useful adsorption material for VOC control due to its high mechanical strength, high specific surface area and high fluidity, and it is particularly suitable for use in fluidized bed adsorption. In addition to removing low-concentration VOCs, activated carbon adsorption also has the potential to recover valuable vapors. In this study, commercial beaded activated carbons were selected and tested. The experiments used toluene (TOL) and methyl ethyl ketone (MEK) as adsorbates in fixed-bed adsorption, and these adsorbateds were regenerated via electrothermal swing system (ETS) with inert gas purging, achieving the purpose of reusing the activated carbon. The results of N2 adsorption showed that the BET specific surface area of received BAC ranged from 1135.69‒1277.81 m2 g-1, and the total pore volume ranged from 0.473‒0.522 cm3 g-1. The specific surface area and micropore volume of the BAC after one adsorption/desorption cycle are slightly reduced, while the micropore surface area and micropore volume of the BAC after the six cyclic adsorption and desorption test decrease significantly. These decreasing trends also reflected on the VOC adsorption capacity. The BACs that saturated with TOL and MEK were regenerated at 120, 140, 160oC by electrothermal heating. The desorption efficiency of TOL-BAC (BAC saturated with TOL) ranged from 54.83‒79.68%, and the desorption efficiency of MEK-BAC ranged from 84.67‒89.88%, both of which showed a trend of desorption efficiency increasing with increasing temperature. In the cyclic adsorption/desorption test, the adsorption capacities of both TOL-BAC and MEK-BAC were decreased after six cycles of electrothermal swing regeneration. Compared with MEK-BAC, TOL-BAC underwent a more significant effect in reducing adsorption capacity, the adsorption capacity of the second cycle has been reduced to about half of the original adsorption capacity. In contrast, MEK-BAC still had about 70% of the original adsorption capacity. In conclusion, this study successfully explores the desorption efficiency of the electrothermal swing system for TOL and MEK and the feasibility of applying this technique to regenerate BACs.

並列關鍵字

beaded activated carbon ； volatile organic compounds ； toluene ； methyl ethyl ketone ； electrothermal swing system ； cyclic adsorption/desorption

參考文獻

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球狀活性碳對揮發性有機物的吸附與電熱再生

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