錳鈰氧化物/氧化鋁觸媒催化醋酸濕式氧化反應之研究

Studies on Wet Catalytic Oxidation of Acetic Acid by Mn-Ce Complex Oxides Supporied on alumina

張卓睿(Labo chang)

指導教授 ： 尋孝國

元智大學/工程學院/化學工程與材料科學學系/碩士(2001年)

摘要

觸媒濕式氧化法主要是利用氧氣或空氣將廢水中的有機物氧化，在這個程序中，有機物會在高溫高壓的環境下被通入的空氣或氧氣氧化成二氧化碳及水，使用高壓是為了保持廢水在液相並且增加氧氣的溶解。一般觸媒的使用多採非均相觸媒，主要是因為反應完後觸媒與廢液的分離較容易。
濕式氧化程序中，許多有機物氧化都會衍生出醋酸，而醋酸是一個穩定且不易氧化的物質，因此使用濕式氧化法並加入觸媒是一個是一個直接且方便可以處理醋酸廢液的方式。
在許多濕式氧化法加入共沈澱法製備之鈰氧化物與其他金屬氧化物混合作為觸媒來處理醋酸的研究中，MnOx/CeO2擁有良好的活性，而本研究利用含浸法來製備MnOx/CeO2/Al2O3觸媒，並在耐高壓鈦合金反應器進行反應。觸媒分析是利用TPR來看還原特性以及XRD觀察其晶態。
實驗解果顯示MnOx/CeO2/Al2O3活性比MnOx/CeO2還好，可能是氧化鋁加入使觸媒擁有較高表面積和較佳分散度，當錳鈰氧化物負載量為16%時，觸媒有最高的單位質量活性。錳鈰雙成份氧化物觸媒也比單一成份反應活性高，顯示兩者混合產生了特殊效應。而XRD可以觀察出Mn2O3/Al2O3和CeO2/Al2O3的晶相但是卻看不出MnOx/CeO2/Al2O3，TPR也發現錳鈰氧化物混合後還原溫度都比混合前降低許多，這都可以印證觸媒活性結果。
由於加入氧化錳和氧化鋯可以使氧化鈰的氧化還原能力變強，我們在錳鈰氧化物中加入氧化鋯以提升觸媒的活性，嘗試了各種比例後，其中以{[CeO2(4)/ZrO2(1)](12.8%)-MnOx(3.2%)}/Al2O3觸媒活性最高。

關鍵字

濕式氧化 ； 醋酸 ； 錳鈰氧化物

並列摘要

Catalytic wet oxidation(CWO) is aimed at reducing the chemical oxygen demand (COD) of wastewater by total oxidation with air or oxygen of dissolved or suspended organic effluents. In this process, oxidation of organic pollutants to carbon dioxide and water by air or oxygen at elevated temperatures. High pressures are also employed not only to keep the water in liquid phase but to increase dissolved oxygen concentration as well. A heterogeneous catalyst is usually used because heterogeneous catalyst is easily separated from the liquid phase either in batch or continuous processes.
In wet oxidation processes many organic compounds gradually degrade to acetic acid, which is quite stable and invariably develop a resistance to further oxidation. Therefore, investigations on the catalytic kinetics of wet oxidation of acetic acid provide a convenient and direct means for catalyst development.
A series of ceria-containing mixed oxides has been prepared by coprecipitation and utilized as catalysts in the oxidation of acetic acid in water. MnOx/CeO2 composite oxides have been proved to have much better activity for wet oxidation of acetic acid. In the present work we explored the catalytic characteristics of MnOx/CeO2/Al2O3 by impregnation. Reaction tests were carried out using a high pressure titanium autoclave. Temperature-programmed reduction(TPR) was employed to study the reduction behavior of catalysts precurses and XRD was employed for the identification of crystalline phases of the catalysts.
Experimental result shows that MnOx/CeO2/Al2O3 has better activity then MnOx/CeO2, that is caused by MnOx/CeO2/Al2O3 has higher surface area and dispersion. When MnOx/CeO2 loading 16% on Al2O3, Catalytic has the best unit activity. MnOx/CeO2/Al2O3 also has better activity then CeO2/Al2O3 and Mn2O3/Al2O3, that was caused by interations between MnOx and CeO2. CeO2 /Al2O3and Mn2O3/Al2O3 were detected by XRD but MnOx/CeO2/Al2O3 was not. TPR also shows MnOx/CeO2/Al2O3 has lower reduction temperature then CeO2 /Al2O3and Mn2O3/Al2O3, all of these phenomenons can explain experimental results.
The incorporation of even relatively small amounts of ZrO2 and MnOx into CeO2 strongly modifies the redox properties of the catalyst thus leading to promotion of the activity. After we try many different compositions to mix ZrO2,, MnOx and CeO2, the best results are obtained with {[CeO2(4)/ZrO2(1)](12.8%)-MnOx(3.2%)}/Al2O3.

並列關鍵字

Wet Oxidation ； Acetic Acid ； Mn-Ce Complex Oxides

參考文獻

1. Foussard, J. N., Debellefontaine，H and Besombes, V.J. “Efficient Elimination of Organic Liquid Wastes: Wet Air Oxidation”J Environ Eng.,115,367-385(1989)

2. Robey, H. L. and Laughlin, R.G.W., “Wet air Oxidation for the Treatment of Aqueous Organic Waste Streams” 23rd Annula Conference of Metallurgists(1984)

4. Zimmermann, F. J. “Wet Air Oxidation of Hazardous Organics in Wastewater.” U.S.Patent 2665249(1950)

8. Laughlin, R. G. ;Gallow, T and Robey, H ”Wet Air Oxidation for Hazardous Waste Control”, J. Hazard. Mater, 8, 1-9(1983)

16.何信儒, 元智大學化學工程研究所碩士論文, “高濃度工業廢水濕式氧化處理之研究”(1994)