在超臨界二氧化碳中降解多氯聯苯與多環芳香烴

Degradation of Polychlorinated Biphenyls and Polycyclic Aromatic Hydrocarbons in Supercritical Carbon Dioxide

陳韻潔(Yun-Chieh Chen)

指導教授 ： 葉華光

中原大學/理學院/化學研究所/博士(2012年)

https://doi.org/10.6840/cycu201201067

摘要

持久性有機污染物的污染問題漸漸受到重視，由於其在環境中不易被分解，對於我們的生存環境會造成持久性的破壞。因此，許多科學家致力於研究持久性污染物的除污技術，希望可以解決這個日益嚴重而且非常棘手的問題。有鑑於此，本研究選擇同屬於持久性有機污染物的多氯聯苯與多環芳香烴作為研究對象。
本研究利用近年來發展迅速之超臨界流體技術，降解多氯聯苯與多環芳香烴。在零價鐵粉與超臨界二氧化碳100atm下降解多氯聯苯的實驗中，多氯聯苯在反應溫度300℃時，反應4小時，可完全降解Aroclor 1254，生成毒性較低的聯苯，且生成之產物種類單純，方便後續應用之開發。
本研究亦成功的將在日常生活中常見又便宜的鋼絲絨，透過鹽酸蝕刻的鋼絲絨表面的簡單加工之後，由SEM結果中，其表面產生許多奈米級孔洞，在超臨界二氧化碳下降解多氯聯苯，可以完全反應生成毒性較低的聯苯，沒有殘留任何多氯聯苯。所需的價格較零價鐵粉便宜，以零價鐵粉1/5的價格就可以買到。
本研究成功的開發以初濕含浸法製備的1%Pd/SBA-15觸媒，在超臨界二氧化碳加氫氣時，控制適當的反應條件，可得到單一產物bicyclohexyl。當SBA-15中導入雙金屬(Pd與Pt)觸媒時，不論Pd與Pt比例為何，其所具有之多氯聯苯降解能力，皆優於1%Pd/SBA-15觸媒，只需要較低的反應溫度與較短的反應時間，就可以得到較好的結果(單一產物bicyclohexyl)。由實驗的結果可以發現，反應溫度50℃時，4%Pd+1%Pt/SBA-15觸媒，反應120分鐘後，可得到的單一產物bicyclohexyl。1%Pd+4%Pt/SBA-15觸媒，只須短短的30分鐘，便可以達到非常好的脫氯還原效果，得到單一產物bicyclohexyl。
在多環芳香烴降解實驗中，1%Pd+4%Pt/SBA-15觸媒，在二氧化碳與氫氣中進行降解反應，不論是多氯聯苯或是多溴聯苯，亦或是長碳鏈的烯類，皆可成功進行加氫反應。因此，本研究所開發的1%Pd+4%Pt/SBA-15的觸媒，可以廣泛的應用到得到許多環境污染物上。

關鍵字

鉑 ； 鈀 ； SBA-15 ； 鐵粉 ； 鋼絲絨 ； 超臨界二氧化碳 ； 多氯聯苯 ； 多環芳香烴

並列摘要

Persistent organic pollutants (POPs) are defined as organic compounds that pollute and persist in the environment. Polychlorinated biphenyl (PCB) is a family of 209 congeners that well fits the classification of POPs. PCBs have high thermal stability, high chemical inertness, resistance to acid, alkali, and corrosive chemicals, and are difficult to biodegrade. Owing to their low polarity and fat solubility, they are very difficult to metabolize in animals, thus continue to accumulate in food chain in nature and ultimately affect human health.
In this research, PCBs are reductively dechlorinated by zero-valent iron (Fe0) in supercritical carbon dioxide (sc CO2) at 100 atm and 300 ℃. The results show that hydrodechlorination of Aroclor 1254 after four hours of reaction is complete, with the sole product being biphenyl. These highly successful results demonstrate that zero-valent iron coupled with scCO2 may be an attractive method for the complete conversion of PCBs to the much less toxic biphenyl.
Inexpensive household steel wool was also used as a reducing agent for the reductive dechlorination of PCBs in sc CO2. Untreated steel wool does not produce significant results. Steel wool treated with 6 N HCl, however, showed complete reduction of the PCBs (Aroclor 1254) used. Scanning electron microscopy (SEM) reveals formation of nanoscale pits (nanopits) on the surface of steel wool after etching with HCl. These nanopits are responsible for the high efficiency of the hydrodechlorination process.
In a separate but similar theme, PCBs are completely reduced to bicyclohexyl in scCO2 by the use of hydrogen gas and a novel, lab-synthesized catalyst that contains palladium and/or platinum nanoparticles impregnated onto Santa Barbara Amorphous 15 (Pd/SBA－15). This catalyst was synthesized by mixing 1 to 4 % palladium (w/w) and/or 1 to 4 % platinum (w/w) with the mesoporous SBA－15 by the Incipient Wetness Impregnation (IWI) method. With addition of 5 atm hydrogen gas into the supercritical carbon dioxide at 100 atm and 160 ℃ with a 1% Pd/BSA-15 catalyst, all PCBs studied were completely converted to bicyclohexyl. Hydrodechlorination of PCBs with a Pt＋Pd/ SBA15 catalyst with addition of 5 atm hydrogen gas into the supercritical carbon dioxide at 100 atm and 50 ℃ was also successful, with all PCBs studied completely converted to bicyclohexyl. A 1%Pd+4%Pt/SBA-15 catalyst can also be successfully applied to hydrogenation of polycyclic aromatic hydrocarbons.

並列關鍵字

zero-valent iron ； palladium nanoparticles ； Platinum nanoparticles ； SBA-15 ； PCBs ； bicyclohexyl ； sc CO2 ； hydrodechlorination

參考文獻

吳榮宗，工業觸媒概論，國興出版社，1989。

顏聖鴻，在超臨界二氧化碳中以零價鐵還原多氯聯苯，中原大學化學系碩士論文，2006。

廖俊旺;黃振聲，農藥之毒性危害，行政院農業委員會農業藥物毒物試驗所技術專刊第 130號，1-12。

http://www.bhp.doh.gov.tw/ (行政院衛生署國民健康局)

李龍平，具氰基官能基之中孔洞材料 SBA-1 的合成與鑑定，國立中央大學環境工程研究所碩士論文，2007。