| 摘要: | 本實驗以自製奈米級觸媒，包括CeO2、CeO2/HA(氫氧基磷灰石)、TiO2與CeO2/TiO2等四種，在高溫、高壓及供給氧氣環境下催化亞甲基藍之濕式氧化反應，並以染料的脫色率與COD去除率探討反應過程中觸媒對亞甲基藍之催化效能。
研究結果顯示，在未添加觸媒情形下，氧分壓1.5MPa、100ppm亞甲基藍溶液，在CWAO反應下其脫色率及礦化率是隨溫度提升而增加，故亞甲基藍在特定溫度下，具有一定程度的熱分解行為。
本研究使用之觸媒經由SEM、BET鑑定得知，CeO2、TiO2與CeO2/TiO2等三種觸媒粒徑約介於15~21nm，比表面積約介於39~47 m2/g，其中以TiO2觸媒有較小粒徑與較高比表面積，故其反應效能為四者最優，其在亞甲基藍100ppm、溫度180℃、觸媒添加量1g/L、氧分壓1.5MPa條件下，反應四小時後脫色率及礦化率分別為95%、38.5%。溫度從180℃到200℃時，TiO2觸媒催化亞甲基藍之COD去除率隨反應溫度上升而增加；但溫度從200℃到220℃時，COD去除率隨反應溫度上升而下降，故最適反應溫度為200℃。最適觸媒添加量為1.0g/L，少量觸媒添加(0.5~1.5g/L)可以形成較多自由基，添加過量觸媒(1.5~3.0g/L)則抑制自由基的產生。氧分壓以1Mpa之效能為最佳。TiO2觸媒之晶像強度隨煅燒溫度之增加而加強，但以515℃煅燒之觸媒因結構缺陷較多，故其處理亞甲基藍之效能優於300℃與700℃煅燒者。
觸媒再生與耐用性評估方面，新鮮與再生觸媒催化50ppm亞甲基藍之脫色率依次為：再次煅燒>重覆使用>新鮮觸媒>酒精清洗>丙酮清洗，COD礦化率為：新鮮觸媒>再次煅燒>重覆使用>酒精清洗>丙酮清洗，顯示本研究之觸媒再生方式以再次煅燒者為佳。
另外，本實驗挑選效能僅次於TiO2觸媒之CeO2/HA觸媒，研究不同比例CeO2/HA之反應效能，發現以CeO2/HA(1:1/8)之比例為最適觸媒處理亞甲基藍，其效能甚至優於TiO2觸媒，且該觸媒之催化效能隨反應物濃度增加而增加，對2600ppm之亞甲基藍反應四小時脫色率及礦化率分別為99.75%及91.89%，可證明CeO2/HA觸媒對高濃度反應物之適用性。
In this study, we prepared four nano catalysts including CeO2、CeO2/Apatite、TiO2 and CeO2/TiO2 for the catalytic wet air oxidation of methylene blue(MB). Via rate of color removal and COD removal, performance of the catalysts was evaluated to screen for the optimal one and reaction condition of the most active catalyst was also investigated.
The results indicated that the efficacy of WAO without catalyst of 100 ppm methylene blue improved with temperature at O2 partial pressure of 1.5Mpa, which implied heat decomposition occurred in a certain temperature.
The characterization of catalysts of SEM shows the diameter of CeO2、TiO2 and CeO2/TiO2 catalysts are around 15 to 21nm, and the BET analysis are around 39 to 47m2/g. With the smallest diameter and largest surface area, TiO2 catalyst performed the most active among the four. At the condition of 100 ppm methylene blue concentration, 180℃, 1.0 g/L the catalyst loading and 1.5 MPa of O2 pressure, the color removal and COD removal after 4 hrs reaction are 95% and 38.5%, respectively. The rate of COD removal at temperatures of 180~200°C increased as reaction temperature increased, while at temperatures of 200~220°C, the COD removal decreased with increase in reaction temperature, suggesting an optimum temperature for the operation of this catalyst of 200°C. An optimal loading was found at 1.0 g/L, when free radical formation is higher at a lower catalyst loading (0.5~1.5g/L), while at a higher loading (1.5~3.0g/L), free radical destruction dominates. The suitable O2 partial pressure occurred at 1.0Mpa. The intensity of the TiO2 crystals peaks increased calcination temperature increased, while the 515℃ calcinated-temperature catalyst is superior to 300°C and 700℃calcinated-temperature catalyst on CWAO performance with his more structure defects.
As for the assessment of catalyst regeneration and durability, it was found that the order of color removal for 50ppm MB with fresh catalyst and regenerated catalyst was: calcined again > reused > fresh catalyst > alcohol > rinsed with acetone, and also the order of COD removal was: fresh catalyst > calcined again > reused > alcohol > rinsed with acetone, which showed calcined again was the best catalyst regeneration method in the study.
In addition, we selected the second most active catalyst, CeO2/HA, for the CWAO of MB by varying Cerium content. The result indicated that the most active catalyst was CeO2/HA(1:1/8), which performed better activity than TiO2 catalyst. The efficacy of this catalyst increased as the MB concentration increased. At the condition of 2600ppm MB solution, it enabled 99.75% of color removal and 91.89% of COD removal after 4 hrs reaction, which confirmed this catalyst was feasible for high concentration of reactants. |
