有機酸催化濕式氧化反應之研究

Studies on Catalytic Wet Oxidation of Organic Acids

黃名儀(Ming -Yi Huang)

指導教授 ： 尋孝國 博士

元智大學/工程學院/化學工程與材料科學學系/碩士(2003年)

摘要

本研究利用semi-batch反應器以低分子量有機酸水溶液為處理對象，旨在探討觸媒濕式(CWAO)氧化反應系統中，各項操作條件對甲酸、草酸、醋酸和丙酸處理效能之影響。其中甲酸和草酸可在大氣壓下反應，對於醋酸和丙酸因其不易被氧化分解成二氧化碳和水，操作須於高溫及高壓(200℃，500psi)的條件下進行。
加入貴金屬觸媒如Ru、Pt及Pd可提升WAO程序對低分子量有機酸溶液之處理效能，在實驗過程中發現，就單成份觸媒中以Ru對醋酸和丙酸反應的的活性最好。由於醋酸和丙酸其抗氧化性較高且不容易分解，我們以接續含浸不同比例的雙成份觸媒(Ru/CeO2/Al2O3)更成功的提高觸媒整體的活性，CeO2和Ru有加乘的作用，大幅提昇觸媒的活性。
結果顯示，反應溫度、壓力與觸媒均為主要影響因素。以Ru/Al2O3觸媒和Ru/CeO2/Al2O3觸媒對醋酸和丙酸的反應而言，當溫度和壓力越高氧化速率越快，但是當壓力高於500psi以上，其對氧化速率之影響並不大。造成此原因可能是因為氧吸附在觸媒活性點上，導致觸媒表面覆蓋率飽和，因而無法再提升氧化速率。
觸媒的分析是TPR來觀察觸媒先驅體的還原情形，並以XRD來鑑定觸媒的晶態和使用CO化學吸附求得Ru的分散度。
就動力學而論以醋酸和丙酸的實驗數據配合Arrhenius equation和Rideal kinetic為基礎。以吸附的觀點來看，由於競爭吸附的關係，因為氧非常容易吸附於活性金屬上，致使有機酸不易吸附於金屬，醋酸和丙酸氧化所得之數據結果是屬一階反應，以Ru/Al2O3觸媒和Ru/CeO2/Al2O3觸媒反應下，醋酸反應活化能(activation energy)分別為20kcal/gmol和20.6kcal/gmol，丙酸分別為17.4kcal/gmol和19.2 kcal/gmol。

關鍵字

濕式氧化 ； 觸媒 ； 甲酸 ； 草酸 ； 醋酸 ； 丙酸 ； 釕 ； 鉑 ； 鈀 ； 二氧化鈰

並列摘要

In the present research, catalytic wet air oxidation of low molecular weight acids, such as formic acid, oxalic acid, acetic acid and propionic acid has been studied by using a semi-batch reactor. Among the acids studied, formic acid and oxalic acid are more liable to be oxidized, and thus the oxidation reactions were carried out under atmospheric pressure. On the other hand, acetic acid and propionic acid are more reluctant to oxidation; consequently elevated temperature and pressure were used in investigation.
Employment of noble metal catalysts such as Ru, Pt and Pd promotes the oxidation efficiency. Among them, Ru catalyst exhibits the best activity. Addition of CeO2 to the noble metal catalysts was implemented by sequential impregnation. It was found that the interaction between Ru and CeO2 greatly enhances the catalyst activity for the wet oxidation of acetic acid and propionic acid.
Experimental results show that temperature, pressure and catalyst are main factors in determining the oxidation efficiency. For the wet oxidation of acetic acid and propionic acid using Ru/Al2O3 and Ru/CeO2/Al2O3 catalysts, the reaction rate increases with the increases of temperature and pressure; however, for the pressure higher than 500 psig, the reaction rate does not increase appreciably with the increase of pressure. This might be attributed to the saturation of oxygen coverage on the catalyst surface.
Characterization of the catalysts was also carried out in the present work. Reduction properties of catalyst precursors were analyzed by temperature programmed reduction. Lattice structure of active components was investigated by X-ray diffraction. In addition, CO chemisorption was used to determine the dispersion of Ru metal clusters.
Arrhenius equation and Rideal kinetic model were applied to account for the observed characteristics of experimental data. It shows that the reaction rate obeys the first-order behavior with respect to the concentration of acetic acid and propionic acid under the pressure higher than 500psig due to the saturation of oxygen adsorption on the catalyst surface. Values of activation energy for the wet oxidation of acetic acid and propionic acid were also obtained, which are 20 kcals/gmol for acetic acid and Ru/Al2O3 catalyst, 20.6 kcals/gmol for acetic acid and Ru/CeO2/Al2O3 catalyst, 17.4 kcals/gmol for propionic acid and Ru/Al2O3 catalyst, and 19.2 kcals/gmol for propionic acid and Ru/CeO2/Al2O3 catalyst.

並列關鍵字

Wet Oxidation ； Catalyst ； Formic acid ； Oxalic acid ； Acetic acid ； Propionic acid ； Ru ； Pt ； Pd ； CeO2

參考文獻

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