請用此 Handle URI 來引用此文件: http://hdl.handle.net/11455/5553
標題: 多壁奈米碳管應用於苯廢氣處理之特性研究
A Study on the Adsorption Properties of Benzene Vapor onto Multi-walled Carbon Nanotubes
作者: 李孟珊
Lee, Meng Shan
關鍵字: Multi-walled carbon nanotubes
多壁奈米碳管
adsorption
benzene
adsorption model
吸附

吸附模式
出版社: 環境工程學系所
摘要: 本研究係利用多壁奈米碳管(外徑小於10nm)為吸附材料,應用於苯廢氣之處理,同時進行其吸附特性之探討與管柱吸附模式之開發。吸附材料係藉由化學活化預處理技術及物理高溫處理以提高奈米碳管的純度及其吸附效能,研究中並將原始與經改質程序後的奈米碳管進行吸附特性的比較。影響吸附效能之影響因子如吸附質物化特性、吸附劑表面特性、操作溫度、環境濕度及氣流進流濃度等皆於本研究中進一步探討。 經過氫氧化鈉活化預處理與高溫熱處理後之多壁奈米碳管,因去除金屬觸媒及非奈米碳管之雜質碳等,使得多壁奈米碳管之物化特性穩定並且吸附苯蒸氣之效能亦被提昇。於奈米碳管表面特性與吸附效能之研究中,顯示微孔表面積與微孔孔洞體積與吸附效能呈現正相關,進一步證實苯分子吸附反應之主要位置。於苯蒸氣之進流濃度為50至800ppmv範圍中,環境溫度及濕度分別為25℃及0%時,發現其等溫吸附曲線呈現第一類型(type I)吸附曲線,由此可說明奈米碳管吸附苯蒸氣之行為為單層吸附且奈米碳管為微孔型吸附劑。同時,使用BET、Langmuir及Freundlich等等溫吸附模式模擬之結果,發現BET吸附模式較適用於描述多壁奈米碳管吸附苯蒸氣之行為,而經純化改質後之多壁奈米碳管其最大吸附容量為65.24 mg/g,大於未經改質之多壁奈米碳管(59.50mg/g)。在環境因子對吸附行為之影響研究中,苯蒸氣於多壁奈米碳管之吸附量隨著溫度之增加而呈現線性遞減,然而,當氣流中之相對濕度增加時,與吸附量呈現多項式關係遞減之現象。苯蒸氣於奈米碳管之等容量吸附熱皆為負值且大約為苯蒸發熱之1至4倍,其結果顯示奈米碳管吸附苯蒸氣之反應為物理性放熱反應。 於奈米碳管管柱吸附模式之研究中,使用基礎熱力學理論結合輸送現象所發展之吸附模式,由模擬值與實驗值驗證之結果發現,於不同操作溫度及進流濃度下,實驗值與模擬值皆可吻合,如此說明此模式可被廣泛應用於不同條件下操作效能之評估。
Vapor adsorption is an important process for environmental protections. The unique microporous structure of carbon nanotubes (CNTs) is speculated to have remarkable adsorption properties. Therefore, commercially available multi- walled carbon nanotubes (MWCNTs, external diameter <10 nm) were employed as adsorbents for benzene vapor adsorption from air stream in an inlet concentration range of 50-800 ppmv, and the environmental conditions were controlled at 25℃ and 0% relative humidity. This study is part of an attempt to understand vapor adsorption by systematically studying the influence of adsorbent, adsorbate, temperature, and relative humidity on the adsorption equilibrium. A purification process, activating (concentrated sodium hydroxide) and then heating treatments, was used to improve the properties of MWCNTs such as purity, structure, and nature of the surface. These improvements made MWCNTs become more stable and suitable for adsorption of benzene vapor. The isotherm on both raw and purified MWCNTs were generalized as typical type I adsorption isotherm, which describes monolayer adsorption mechanisms exhibited by microporous adsorbents. The adsorption equilibrium data were found to be best correlated with the BET isotherm model. The maximum adsorption amount of benzene adsorbed at equilibrium calculated by BET isotherm were found to be 65.24 mg/g for purified MWCNTs, and it was greater than that of raw MWCNTs(59.50 mg/g). In the temperature range of 5 to 45 oC, the adsorption capacity linearly decreased with a rise in temperature. Negative values of isosteric heats of adsorption for both MWCNTs were presented as 1-4 times to the heats of vaporization, which is typical exothermic physical adsorption of organic vapors on porous carbons. Meanwhile, a polynomial decrease in the adsorption capacity was observed between 0 to 91% relative humidity. A numerical model using basic dynamic reaction theory for simulating the kinetics of adsorption in column operations was also conducted. Results showed that the model could well predict the adsorption isotherms and removal performances as well under various conditions.
URI: http://hdl.handle.net/11455/5553
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