以電化學氧化法氧化水中異丙醇及其反應路徑之研究

Abstract

異丙醇(Isopropanol，簡稱IPA)為當前用途廣泛之有機溶劑，隨著工業及高科技產業的發展，含異丙醇之廢水問題日趨嚴重，此外，氧化過程中所產生的丙酮，亦會對環境造成負擔。電化學氧化法具有快速、易操作、乾淨等優點，並已成功應用於處理多種有機污染物。本研究將利用電化學氧化法，以與質譜儀相連之自製密閉電化學反應槽，進行異丙醇氧化批次實驗。透過分析產物及中間產物，探討在含氯(氯化鈉)及不含氯(硫酸鈉)系統下，異丙醇氧化情形之差異，並在含氯系統中，改變電化學參數(電解液種類、電流強度、氯離子濃度、初始pH值)，研究含氯物種對異丙醇氧化機制影響。 循環伏安曲線顯示，異丙醇氧化峰電流在不含氯系統中為2mA /cm2，約為含氯系統的兩倍，且經氧化產生之丙酮會在電極表面繼續被氧化，而在含氯系統中，並未出現丙酮氧化峰。在施加0.25 A之不含氯系統中，500 ppm的異丙醇經電解作用後，氧化成丙酮及二氧化碳，去除率達100.0 %。以相同的電化學條件，含氯系統中，異丙醇經氧化後會生成甲酸、乙酸等中間產物，去除率為89.0 %。批次實驗顯示，在含氯系統中，異丙醇去除效率在氯離子濃度20 mM、100 mM及150 mM下，分別為93.5 %、86.8 %及82.9 %，溶液中的丙酮含量隨著溶液中氯離子濃度增加而減少，相對的，有機酸含量增加。異丙醇去除效率在初始電解液pH 5、pH 6.5及pH 9 下分別為87.7 %、82.9 %及85.3 %，pH值越低，有機酸含量越多。 由本研究成果指出，異丙醇於兩大系統有相異的氧化機制，當電解液環境含有氯離子時，異丙醇於溶液體中與活性氯物種反應，且溶液中的活性氯物種會將丙酮氧化成有機酸，使溶液中丙酮含量不再增加。在不含氯系統中，氫氧自由基為主要的活性物種，將異丙醇氧化成丙酮及二氧化碳。本研究可建立以電化學氧化法處理含異丙醇廢水之效率及其氧化產物等資訊。

Isopropanol (IPA) is widely used in different industries. With the development of industrial and high-tech industries, the problem of wastewater containing isopropanol (IPA) has become increasingly serious; moreover, acetone, which is produced during the oxidation process will also cause another environmental problem. The electrochemical oxidation technique has the advantages of efficiency, easy to operate, clean and has been successfully applied to treating a variety of organic pollutants. In this study, an electrochemical oxidation method is used to conduct a batch experiment of isopropanol oxidation with a self-made closed electrochemical reaction tank connected to a mass spectrometer. By analyzing products and intermediate products, the differences of the oxidation of isopropanol under chlorine (sodium chloride) and non-chlorine (sodium sulfate) systems are explored. Electrochemical parameters (electrolyte type. current intensity, chloride ion concentration and initial pH value) are also changed to study the effects of chlorine-containing species to the oxidation mechanism of isopropanol. The cyclic voltammetry curves showed that the oxidation current peak of isopropanol was 2 mA / cm2 in a chlorine-free system, which was about twice the chlorine-containing system, and the acetone produced by oxidation would continue to be oxidized on the electrode surface, in contrast, acetone oxidation peak was unobvious in chloride system. In the chloride-free system with 0.25 A, 500 ppm of isopropanol was oxidized to acetone and carbon dioxide after electrolysis and the removal rate reached to 100.0 %. Under the same electrochemical conditions, isopropanol was oxidized to formic acid and acetic acid in the chloride system, with a removal rate of 89.0 %. Batch experiments showed that in the chloride system, the removal efficiency of isopropanol was 93.5 %, 86.8 % and 82.9 % in 20 mM, 100 mM and 150 mM chloride ion concentration respectively. The increased chloride ion containing would increase the amount of organic acid. The removal efficiency of isopropanol was 87.7 %, 82.9 % and 85.3 % at the initial pH 5, pH 6.5 and pH 9 respectively. The lower the pH, the more organic acid content. According to the results, isopropanol has different oxidation mechanisms in the two major systems. When the electrolyte environment contains chloride ions, active chlorine species react with isopropanol in the solution and further oxidized acetone to an organic acid, therefore, the acetone concentration in the solution was no longer being increasing. In a chloride-free system, the hydroxyl radical is the main active specie, which oxidizes isopropanol to acetone and carbon dioxide. This study can establish information on the treatment of isopropanol-containing wastewater and oxidation products by electrochemical oxidation.