零價鐵流體化床處理一氧化氮之研究

Reduction of Nitrogen Oxide by Zero-Valent Iron Fluidized Bed

鄭自祐(Chih-Yu Cheng)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境規劃與管理研究所/碩士(2005年)

https://doi.org/10.6841/NTUT.2005.00168

摘要

本研究利用市售微米級零價鐵粉(ZVI)，以流體化床進行還原一氧氧化氮實驗，由實驗結果探討其反應機制及反應動力學。由實驗結果，觀察到ZVI與NO的反應明顯可區分為兩階段反應，根據此一現象以流體化床NO出口濃度對操作時間(t)作圖，以出口NO濃度曲線由平緩段緩慢升高至驟升段之轉折點為反應階段之分割點，將整個反應區分為第一階段反應與第二階段反應進行討論。
就第一階段反應而言，不同反應溫度或不同NO進流濃度之處理效率均可達到95~100%，在反應溫度773K下，NO進流濃度由700ppm上升至1000ppm時，反應速率(-rNO)增加了43%。進流[NO]=700ppm，反應溫度由673K上升至773K時，反應速率增加15%。反應溫度由673K上升至773K，ZVI=1.25g，kobs增加了約17%，反應溫度與kobs關係符合Arrhenius Equation。在不同鐵粉量實驗中，反應溫度773K、[NO]=700ppm條件下，ZVI添加量由0.75g上升至1.25g時，反應速率常數k增加了22%。由實驗結果分析影響第一階段反應速率因子的影響力，依大小順序為[NO]進流濃度>反應溫度>ZVI添加量。
就第二階段反應而言，處理效率隨操作時間增加而逐漸降低，由95%降低至20%時實驗停止(Break through)。由於處理效率的改變，本反應階段是以參與反應之零價鐵逐漸氧化觀點進行討論，以處理效率降至20%之達成時間進行比較，在ZVI=0.75g、[NO]=700ppm下，反應溫度673K時，反應時間為2491秒，773K時反應時間增為3391秒，增加了36%。由於本階段參與反應之零價鐵表面逐漸氧化，因此[Fe]不再視為常數，反應速率式包含反應速率常數k’及鐵失活常數kd，反應溫度由673K上升至773K時，k’增加了約100%，kd則減少了約33%。
由反應後鐵粉的表面ESCA分析，可推測零價鐵與NO的反應機制為:

鐵粉利用率方面，反應溫度由673K上升至773K時，鐵粉利用率由3.1%上升至7.8%，增加了約2.5倍，相同反應溫度(723K)，NO進流濃度由700ppm上升至1000ppm時，鐵粉利用率由5.7%降至4.8%，而鐵粉量的改變，對於鐵粉利用率影響則不明顯。由實驗結果，可計算得反應溫度與鐵粉利用率之對數關係式。至於鐵粉單位處理能力(mgNO/gFe)，反應溫度由623K上升至773K，鐵粉單位處理能力由5.56mgNO/gFe增加至62.37mgNO/gFe，由實驗結果，可計算得反應溫度與單位處理能力之直線關係式。

關鍵字

一氧化氮 ； 零價鐵粉 ； 流體化床 ； 批次式固體連續流 ； 反應動力零 ； 零價鐵粉利用率 ； 零價鐵粉單位處理能力

並列摘要

A novel research was conducted for the chemical reaction between nitric oxide and zero valent iron (ZVI). Because of the ZVI strong reducing abilities, we designed the Zero Valent Iron Fluidized Bed Reactor (ZVIFBR) to execute this study. Three different parameters: temperatures (673K, 723K, 773K), influent concentrations (700, 850, 1000 ppm), and ZVI dosages (0.75g, 1.00g, 1.25g) were tested in the ZVIFBR.
According to the experiment results, we found that effluent concentration curves were related to operating times, and obviously could be divided into two sections. In the first section, the concentration curves are smoothly, but in the second section, the curves are steeper than those in first section.
In the first section, at the same reaction temperature (773K), the influent concentrations by 700 came to 1000 ppm, the reaction rate increases about 43%, and at same influent concentration (700 ppm), the temperature by 673 came to 773K, the reaction rate increases about 15%. The relationship between pseudo rate constant kobs (s-1) and the reaction temperature are matched Arrhenius Equation. When ZVI weight by 0.75g came to 1.25g, the rate constant k (mole-0.4s-1) increases about 22%. The influences of reaction rate parameters are influent concentrations > reaction temperatures > ZVI weights.
In the second section, the efficiency lowered down slowly with the operating time, this is because the ferric oxides gradually covered the surfaces of iron powders. In same influent concentration (700 ppm) and ZVI weight (0.75 g), the temperature through 673 to 773K, the break through time by 2491 sec increased to 3391 sec. The reaction rate equation includes two constants: k’ (rate constant, mole-1s-1) and kd (iron oxide constant,s-1 ), the two constants were related to reaction temperature, but not matched Arrhenius Equation at all, .
XRD (X-Ray Diffraction) and ESCA were conducted to analyze the crystal structure and oxidation state of the reacted powders, several species were determined from the spectrum: Fe0 (ZVI), Fe2O3 and Fe3O4. Apparently, the chemical mechanisms of ZVI and nitric oxide are:
(Equation 1)
The utilization of ZVI also related to reaction temperatures, higher temperature more utilization, the reaction temperature from 673K to 773K, the utilization from 3.1% increased to 7.8%. The Capacity of De-NO per ZVI (mg-NO/g-Fe) is related to reaction temperatures too, the reaction temperature from 673K to 773K, the Capacity of De-NO per ZVI from 5.56 mg-NO/g-Fe increased to 62.37mgNO/gFe.

並列關鍵字

Nitric Oxide ； Zero-Valent Iron(ZVI) ； Fluidized Bed ； Kinetic ； Rate of reaction ； Reaction Order ； Utilization of ZVI(UoZ) ； Capacity of De-NO per ZVI

參考文獻

[1] 黃其聰，醇類燃料對汽油引擎排氣分析研究，碩士，中原大學機械工程學系，桃園，2004。

[2] Marco Piacentini，NOx Formation，http://baiker.ethz.ch/people/PhDstudent/Piacentini/NOx_2。

[12] 楊宗翰，廢液於渦漩式流體化床焚化爐中氧化亞氮排放之研究，碩士，中原大學化學工程學系，桃園，2003。

[16] Mark D. Fokema、Jackie Y. Ying, The Selective Catalytic Reduction of Nitric Oxide With Methan Over Nonzeolitic Catalysis, Catalysis Review, 43(1&2), 1-29, 2001.

[18] G.Z.Gassan-zedeh、S.F.Seyibayova, The heterogeneous catalytic reduction of NO and N2O mixture by carbon monoxide, Applied Catalysis B： Environmental 42, 359-367, 2003.