| 摘要: | 本研究利用CoAlPO4-5觸媒或CeO2觸媒、擔體鈰觸媒（Supported Ceria），進行觸媒濕式氧化反應（Catalytic wet air oxidation, CWAO）處理不同濃度之偶氮類染料廢水（200~500mg/L）或含酚廢水（400~5000mg/L）中難分解之有機物質，並進行廢水處理效能評估、動力學探討與鑑定觸媒之反應變化。
在染料廢水處理方面，發現添加CoAlPO4-5觸媒處理染料廢水可大幅降低反應之活化能，提升處理的反應速率，有效處理難分解之染整廢水。當CWAO操作在反應溫度為135℃以上，添加2.0g/L觸媒可在反應1小時內使偶氮染料（Red227、Blue21）ADMI值降低98%以上。廢水中COD去除方面，操作溫度145℃，觸媒添加量3.0g/L，氧氣壓力1.5MPa，反應2小時後染料廢水中COD去除效率可達75%以上。使用過之CoAlPO4-5觸媒經XRD分析及重複測試並與新鮮觸媒比較，結果顯示在上述反應條件下，雖然結構略有破壞，催化效率略有降低，但其耐用性仍屬不錯。在動力學的探討方面，對色度的去除可以由下式表示：Rate = k ´ [dye]0.8 ´ W0.5 ´ Pn（145 oC）或Rate = k ´ [dye]0.8 ´ W0 ´ Pn（135 oC），其中k表示常數值，[dye]表示染料濃度，W代表觸媒量，P表示氧氣壓力，n代表不確定值。
在含酚廢水處理方面，以最具氧化活性的A型CeO2觸媒（高熱衝擊下製備）進行CWAO反應，在反應溫度160℃，氧氣壓力1.0MPa，添加2.0g/L的觸媒，處理低濃度含酚廢水（400mg/L）時，對酚的總去除率在2小時內可達到95%；處理高濃度含酚廢水（2500mg/L、5000mg/L）在4小時的反應時間也可達到85%以上去除效率，而在礦化程度上，則有80%以上之TOC去除率；另外，在相同的操作條件下，B型CeO2觸媒（低熱衝擊下製備）與市售CeO2觸媒對酚溶液（400mg/L）經過4小時的反應後，總去除率分別僅有20%和25%。在動力學的探討方面，利用Power Law可求得初速率方程式為：Rate = k × [Ph]1.3~1.4 × W0.5~0.6 × PO20.9~1.1；其中k表示常數值，[Ph]表示酚濃度，W代表觸媒量，P表示氧氣壓力。此結果與假設自由基鏈鎖反應機制所推導之理論初速率方程式頗為一致，以下為氧氣壓力固定下理論之初速率方程式：Rate2 = k22 × [Ph]3 × W1。
在擔體鈰觸媒處理含酚廢水方面，研究結果指出，擔體鈰觸媒確實能在維持高催化活性下，有效降低活性觸媒之製作成本。經由實際反應評估，以鈰金屬含浸量20wt%之觸媒催化活性最佳，而只添加γ-Al2O3擔體之CWAO反應，對酚氧化幾乎不具任何活性；經由BET分析亦證實催化活性高低與表面積大小並無絕對關係。當利用20wt% CeO2/γ-Al2O3觸媒進行CWAO反應，在反應溫度180℃，氧氣壓力1.5MPa，酚濃度1000mg/L時，若添加3.0g/L的觸媒，對酚之去除效率在2小時內可達到100%，TOC去除率亦可達到82%以上。觸媒耐用性評估方面，CeO2/γ-Al2O3觸媒反應後之大量積碳影響再生後之催化活性，可能需要進一步修改再生程序或方法使再生後之活性提高。
The investigation is mainly aimed at utilizing the CoAlPO4-5 catalyst, the CeO2 catalyst, or the supported ceria catalyst to undergo catalytic wet air oxidation (CWAO) of dye solution (100~500mg/L) or prepared phenolic wastewater (400 ~5000mg/L). Wet air oxidation is applicable to the treatment of the majority of organic compounds found in wastewater. In the process, the organic waste was oxidized to carbon dioxide, water and intermediate oxidation products. The results of CWAO could be applied to evaluate efficacy and measure kinetics of wastewater treatment.
CWAO of direct dye solution. Addition of CoAlPO4-5 could effectively improve rate of color removal and the activation energy of color removal could decrease from about 110 kJ/mole to about 75 kJ/mole as the catalyst loading was increased from 0.0 g/L to 3.0 g/L. Via CoAlPO4-5, ADMI of various dye solution（Red227, Blue21）could be largely reduced at 135℃. With no addition of CoAlPO4-5, rate of COD removal was low. Via CoAlPO4-5, the rate of COD removal would increase with catalyst loading, oxygen pressure and reaction temperature. At a reaction temperature of 135℃ and an applied pressure of 1.0 MPa, color and COD removal were as high as 95% and 90%, respectively, after 2 hrs. Kinetic study of color removal is expressed as: Rate = k ´ [dye]0.8 ´ W0.5 ´ Pn (145 oC) or Rate = k ´ [dye]0.8 ´ W0.5 ´ Pn (135 oC) ; where k means rate constant, [dye] means dye concentration, W means catalyst loading, and P means oxygen pressure, and n means uncertain number.
CWAO of phenolic wastewater by various CeO2 and supported ceria. We find that the CeO2 calcined under higher thermal impact (designated as type A CeO2) has higher oxidizing ability and more structure oxygen exchangeable. By using type A CeO2 (2.0g/L), with conditions of phenol concentration at 400mg/L, oxygen pressure at 1.0MPa and the reaction temperature at 160℃, conversion of phenol was 95% after 2 hours. Whilst the conversion after 4hrs was higher than 85% if the phenol concentration was 5000mg/L and implemented under the same conditions. Alternatively, at 160℃ and 400mg/L concentration, TOC conversion of phenol after 4hrs was 80%, and it would increase with reaction temperature. At the same conditions, the type B CeO2 catalyst（calcined under lower thermal impact） and the commercial CeO2 catalyst showed much lower activity, the conversion of phenol after 4hrs reaction time was just 20% and 25%, respectively. Moreover, with no catalyst added, at conditions of 180℃ and 0.5MPa, the conversion of phenol after 4 hours reaction time was just about 20%. Kinetic study of phenol removal is expressed as follows：Rate = k × [Ph]1.3~1.4 × W0.5~0.6 × PO20.9~1.1; where k means rate constant, [Ph] means phenol concentration, W means catalyst loading and P means oxygen pressure. Furthermore, the above rate equation is consistent with the equation derived from reaction mechanism, which is as follows : Rate2 = k22 × [Ph]3 × W1.
For supported ceria, we find that the CeO2/γ-Al2O3 impregnated with 20wt% ceria has higher oxidizing ability, which is nearly the same as that of type A CeO2 for CWAO of phenolic wastewater. Via CeO2/γ-Al2O3, phenol could be effectively removed at 180℃. On the other hand,γ-Al2O3 showed almost no catalytic ability. BET analysis demonstrated the surface area has no evident effect on the oxidizing ability. Using CeO2/γ-Al2O3, at conditions of phenol concentration 1000mg/L, catalyst loading 3.0g/L, oxygen pressure 1.5MPa, and reaction temperature 180℃, the conversion of phenol was 100% after 2 hours. As for TOC conversion of phenol at 1000mg/L, it is 82% at 180℃ and after 4hrs reaction. Oxidizing ability of regenerated catalyst is significantly reduced. This may be due to the deposit of carbonaceous compounds and can be improved via other regeneration methods. |
