電化學氧化技術應用於水中MTBE之去除

The Cleanup of MTBE in Water by the Application of Electrochemical Oxidation

林宗志(Zong-Chih Lin)

指導教授 ： 吳庭年

崑山科技大學/工程學院/環境工程研究所/碩士(2005年)

摘要

本論文主要以電化學電解氧化技術去除在水中之MTBE。分別使用白金電極、鎳電極、氧化銥/鈦電極以及二氧化鈦/鈦電極，探討不同操作參數下對電解MTBE之影響，以及副產物生成情形。
使用白金電極實驗組，以電壓2.40 V(vs. Ag/AgCl)，電解質1.00 M Na2SO4為最佳電解條件，電解180 min 後MTBE可達到68 %的去除率；在實驗中發現，MTBE的去除效率隨著電壓、電解質的濃度以及pH值的提升皆有增進的作用，但電壓過高會造成電解水反應，反而會使MTBE去除效果下降；添加1.00 mM Ag+ 可提升MTBE去除率，若添加過量Ag+可能AgO之生成，使電流效率降低，阻礙MTBE的去除。藉由GC/MS鑑定MTBE可降解為丙酮及CO2，並由CO2生成得知MTBE有礦化現象，丙酮累積量會隨著電解電壓、電解質濃度及pH值提升而有增加的現象，且添加較高濃度的媒子亦會造成丙酮的累積量增加。
使用鎳電極實驗組，以循環伏安法分析得知，在電位0.35 V與0.30 V( vs. Ag/AgCl)有氧化還原峰出現，最佳電解條件為電解電壓0.35 V( vs. Ag/AgCl)電解質1.00 M KOH之條件下，電解180 min後MTBE可達到73 %之去除率。鎳電極在強鹼條件下，較容易自發性生成NiO(OH)/Ni(OH)2做為氧化MTBE之氧化還原媒子，而使用較高濃度KOH電解質在電解電壓0.35 V( vs. Ag/AgCl)之情況下，會藉由NiO(OH)/Ni(OH)2氧化還原媒子之間接反應，使MTBE氧化降解較為顯著。MTBE降解可生成丙酮以CO2，其降解途徑與白金電極實驗相同，MTBE經過降解後轉換成丙酮的比率較多。
使用氧化銥/鈦電極實驗組，以使用電解質為1.00 M H2SO4，電解電壓3.00 V(vs. Ag/AgCl)為最佳條件，在電解180 min後MTBE去除率可達到92 %。MTBE降解可經由電極表面的直接氧化，及S2O82－/SO42－氧化還原媒子的間接氧化兩種方式同時進行；添加Ag+可提升MTBE的去除效果。而使用Fe2+做為氧化還原媒子對MTBE去除效果較Ag+佳。MTBE降解可生成TBA、丙酮及CO2，循MTBE降解至TBA，再依序降解為丙酮，最後礦化為CO2的降解途徑進行。
使用二氧化鈦/鈦電極實驗組，曝露在可見光環境中，即有光催化效果，使用電解質1.00 M Na2SO4，施加電壓0.50 V(vs. Ag/AgCl)為最佳條件，MTBE的去除率可達72 %，因電子跟電洞量數會隨著施加的電位達到飽和，施予過高電壓會促成電解水反應，反而使MTBE去除效果下降；在照射紫外光的環境下，施予電位－0.25 V (vs. Ag/AgCl)即可形成光催化反應，以電位－0.50 V (vs. Ag/AgCl)，電解質1.00 M Na2SO4為最佳條件，電解180 min後MTBE的去除率為68 %。若施加正電位時並不會產生光電流反應，對MTBE降解並無助益。MTBE降解可生成丙酮及CO2，其降解途徑與白金電極及鎳電極實驗相同。

關鍵字

鎳電極 ； 白金電極 ； 電解氧化 ； 二氧化鈦/鈦電極 ； 甲基第三丁基醚(MTBE) ； 氧化銥/鈦電極

並列摘要

This study is focused on the removal of MTBE from groundwater by the mechanism of electro-oxidation with platinum, nickel, IrO2/Ti and TiO2/Ti electrodes. The influences of MTBE removal as well as by-product production were examined during the experiments of each electrode.
As using the platinum electrode, the optimum operation was found to be 2.40 V (vs Ag/AgCl) as working voltage and 1.00 M Na2SO4 as electrolyte. The removal of MTBE can be reaching as high as 68 % through 180 mins of electro-oxidation. The efficiency of MTBE removal can be improved as increasing working voltage, electrolyte concentration or pH in the electrolytic cell. However, the occurrence of over-voltage may waste energy on the electrolysis of water to cut down the removal of MTBE. The efficiency of MTBE removal can also be enhanced by the addition of 1.00 M Ag+ as mediator, however the excess Ag+ may form AgO on the electrode to reduce the current efficiency and to hamper the removal of MTBE as well. The analysis of GC/MS indicated that MTBE could be degraded to acetone and CO2. The production of CO2 revealed that MTBE could be successfully mineralized by electro-oxidation. The accumulation of acetone was favorable as increasing working voltage, electrolyte concentration, solute pH and the addition of mediator.
As using the nickel electrode, a pair of redox peaks was observed within 0.30 V and 0.35 V on the cyclic voltammetry. The optimum operation was found to be 0.35 V (vs Ag/AgCl) as working voltage and 1.00 M KOH as electrolyte, and the best efficiency of MTBE removal is 73 % through 180 mins of electro-oxidation. Under a strong basic condition, the nickel electrode can be oxidized to form NiO(OH)/Ni(OH)2 as mediator, spontaneously. Because of the mediator reaction of NiO(OH)/Ni(OH)2, the removal of MTBE is remarkable with 0.35 V of working voltage under a strong basic condition. MTBE can be degraded to acetone and CO2, and acetone is the major yield of MTBE conversion.
As using the IrO2/Ti electrode, the optimum operation was found to be 3.00 V (vs Ag/AgCl) as working voltage and 1.00 M H2SO4 as electrolyte. The removal of MTBE can be reaching as high as 92 % through 180 mins of electro-oxidation. MTBE can be degraded through the direct oxidation on the electrode surface or through the indirect oxidation of the formed mediator S2O82－/SO42－. The addition of Ag+ as well as Fe2+ can improve the removal of MTBE, and Fe2+ can achieve a better performance on the mediator effect. The degradation pathway of MTBE is following to form TBA, acetone and CO2 in a row.
As using the TiO2/Ti electrode, the photocatalytic reaction can be conducted in the environment of the visible light. The optimum operation was found to be 0.50 V (vs Ag/AgCl) as working voltage and 1.00 M Na2SO4 as electrolyte, and the best efficiency of MTBE removal is 72 % through 180 mins of electro-oxidation. Because the quantity of electrons and electric holes can reach a saturated state, over-voltage may cause the electrolysis of water to reduce the removal of MTBE. Under the irradiation of UV light, the supply of －0.25 V (vs Ag/AgCl) can initiate the photocatalytic reaction. The optimum operation was found to be －0.5V (vs Ag/ AgCl) as working voltage and 1.00 M Na2SO4 as electrolyte, and the best efficiency of MTBE removal is 68 % through 180 mins of electro-oxidation. Under the supply of positive voltage, it is not helpful for MTBE degradation because the photocatalytic reaction cannot be triggered. Similar to the platinum electrode and the nickel electrode, MTBE can be degraded to acetone and CO2 as using the TiO2/Ti electrode.

並列關鍵字

Methyl Tertiary Butyl Ester(MTBE) ； IrO2/Ti electrode ； Nickel electrode ； Electrochemical Oxidation ； Platinum electrode ； TiO2/Ti electrode

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