釩鈦觸媒催化分解氣相戴奧辛之研究

Catalytic decomposition of gaseous dioxins over V2O5/TiO2-based catalysts

楊家正(Chia-Cheng Yang)

指導教授 ： 張木彬

國立中央大學/工學院/環境工程研究所/碩士(2006年)

摘要

在一般燃燒系統中皆可發現戴奧辛之存在，而戴奧辛排放的控制技術以活性碳噴入及觸媒催化分解兩種類型為主流，前者主要是將戴奧辛做相的轉移，使用後之活性碳若未加以妥善處理，恐有二次污染之虞；後者則能將戴奧辛破壞分解成無毒的CO2、H2O及HCl以達到毒性減量的目的。因此本研究嘗試以蜂巢式釩鈦觸媒，在實驗室中模擬真實煙道氣中戴奧辛物種，探討此類觸媒控制戴奧辛之最佳操作參數、控制因子及破壞機制。以萃取MWI+SP飛灰中的戴奧辛作為本研究之進流戴奧辛，後端設備還包括觸媒反應系統以及樣品收集系統。
研究結果顯示，在固定空間流速5000hr-1及戴奧辛入口濃度4.1 ng-TEQ/Nm3之條件下，蜂巢式釩鈦觸媒對戴奧辛的轉化率隨著觸媒床操作溫度的升高而提高，在280℃時轉化率可達77%；而在220℃時，轉化率只有57%。在空間流速10000hr-1時，轉化率在280℃至220℃之間差了10%，而在空間流速為5000hr-1時，轉化率高低之間差了20%，顯示在高空間流速的操作條件下，轉化率受到溫度的影響較小。在固定溫度及戴奧辛濃度，調整空間流速的實驗結果顯示，在空間流速較高的條件下，所得到的戴奧辛轉化率較低，原因是高空間流速造成低反應時間，使得轉化率跟著降低。在戴奧辛17種同源異構物方面，轉化效率隨著氯數的增加而降低，此一現象在空間流速14000hr-1時最為明顯，這可能與戴奧辛的基本物性及在觸媒上的反應時間有關。本研究嘗試加入不同含量之水氣觀察其對戴奧辛轉化率的影響，結果顯示就質量濃度來說，水氣對觸媒轉化戴奧辛不全然是負面的影響，甚至有較佳的水氣含量比例；就毒性當量濃度而言，水氣存在會使戴奧辛毒性當量濃度的轉化率下降。
此外，本研究利用積分型反應器結合Mars-Van Krevelen model 求取蜂巢式釩鈦觸媒應用於OCDD及OCDF的活化能(Ea)和碰撞因子(A)，經由實驗數據計算結果顯示，此類觸媒應用在處理OCDD的活化能為24.8 kJ/mole和碰撞因子為486 1/sec；OCDF的活化能為25.2 kJ/mole和碰撞因子為1978 1/sec。

關鍵字

蜂巢式釩鈦觸媒 ； 實驗室規模 ； 動力模式 ； 戴奧辛

並列摘要

Due to the extremely high toxicity, removal of dioxin from gas streams has been one of the most popular research topics in recent years. The most commonly used removal technologies include adsorption by activated carbon and catalytic decomposition. The latter is better because it can decompose dioxin, rather than phase transfer. The catalytic decomposition of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofruans (PCDFs) was investigated over commercial V2O5-WO3/TiO2-based catalysts at controlled temperature, water vapor content and space velocity in this study.
According to experimental results, at space velocity of 5000 hr-1 and dioxin concentration of 4.1 ng-TEQ/Nm3, the conversion of PCDD/Fs over V-T catalysts increases as operating temperature is increased. The catalytic conversions of PCDD/Fs increased from 57% to 77%, as the temperature is inceased from 220℃ to 280℃. At space velocity of 10000 hr-1, the difference of conversion is only 10% from 220℃ to 280℃. The experimental results indicate that higher space velocity results in lower conversions of PCDD/Fs, and in this situation it has smaller effect with operating temperature. At fixed temperature and PCDD/Fs concentration, catalytic decomposition of dioxins increases with decreasing space velocity due to longer retention time. Of the seventeen 2,3,7,8-substituted PCDD/Fs congeners, the conversion of dioxin increases with decreasing chlorination degree because higher chlornation congeners have higher boiling point and stable structure.
Finally, this study combined integral reaction and Mars-Van Krevelen model to calculate the activation energies of OCDD and OCDF, respectively. The activation energies of OCDD and OCDF are calculated as 24.8 KJ/mole and 25.2 KJ/mole, respectively.

並列關鍵字

activation energy ； kinetic ； PCDD/Fs ； V2O5-WO3/TiO2-based catalysts

參考文獻

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