- 學位論文
零價鐵粉蝕刻之探討及其對多氯聯苯還原效果之影響
Study on the Etching of Zero-Valent Iron Powder and Its Influence of Reducing Polychlorinated Biphenyls
摘要
本研究目的為探討鐵粉在不同蝕刻條件下，所呈現不同型態之表面，對還原多氯聯苯之影響。 實驗結果顯示，使用硝酸和硫酸對鐵粉表面型態影響不大，硝酸蝕刻後之鐵粉表面與蝕刻前的類似，並沒有太大的改變，而硫酸蝕刻之鐵粉表面，呈現類似階梯狀型態，其細部狀態，有出現類似絲狀情況，而鹽酸蝕刻效果與硫酸相似，不過鹽酸較硫酸更為顯著，出現孔蝕的情況。鹽酸蝕刻最佳條件為6 N酸洗8分鐘，其表面呈現類似蜂窩形狀，且非常完整，測其表面積為5.1 m2/g，是未處理鐵粉之170倍。 此外，我們使用鐵粉還原多氯聯苯，探討鐵粉比表面積、溫度、時間和氯所佔之位置探討這些效應對還原多氯聯苯之影響。 由實驗數據顯示，比表面積越大，溫度越高，時間越長對還原效率越好，而對於氯所佔位置而言，在鄰位(ortho)較難還原，所以BZ#4極難還原成biphenyl，而BZ#15與BZ#11在250 ℃，還原時間為4小時，便可完全還原成biphenyl，而BZ#4必須將溫度提高至320℃，還原時間加長至15小時，才能將其完全還原，但卻無法完全還原成biphenyl，其還原成biphenyl之比率可高達94 %，至於Aroclor 1260，其在350 ℃，還原時間為18小時，其還原效果與BZ#4相似，其還原成biphenyl比率為96 %，由此可以證明我們所蝕刻之鐵粉擁有良好的還原效果。
並列摘要
The purpose of this research is to study the morphology of the surface of iron powder after subjected to different conditions of acid etching, and to investigate the effect of different surface morphology of the iron surface on reductive dechlorination of polychlorinated biphenyls (PCBs). The specific etching capability of three dilute inorganic acids, namely hydrochloric acid, sulfuric acid, and nitric acid, with concentration range from 1 N to 6 N were studied. Of the three dilute acids investigated, hydrochloric acid showed the most promising etching effect which generally yield a coral-shaped, or irregular honeycomb pattern. Nitric acid produces the least promising results from etching studies with the iron power surface remains similar to the untreated ones. Sulfuric acid produces some surface pitting morphologies that are different from that of hydrochloric acid; the typical pattern is more “ladder” like with only shallow convolutions in general. Based on the experiments, the optimum results were obtained with a treatment of 6 N HCl for 8 minutes, yielding a surface area 170 times that of the untreated iron powder. For reduction of PCBs, effects of surface area, temperature, and reaction time were investigated. Our data show that greater surface area, higher temperature, and longer reaction time all result in better reduction efficiency. Our results also revealed that reduction efficiencies for meta and para positional isomers of PCBs were significantly higher than that of the ortho’s. For example, BZ#4 (2,2’-dichlorobiphenyl) is extremely difficult to reduce to biphenyl. At 250 ℃ and 4 hours of reduction time, BZ#15 (4,4'-dichlorobiphenyl) and BZ#11(3,3'-dichlorobiphenyl) can be reduced to biphenyl completely, whereas BZ#4 can only be totally reduced at 320 ℃ for 15 hours of reaction time. For Aroclor 1260 (a commercial PCB mixture), a treatment at 350 ℃ and for 18 hours results in complete dechlorination with 96% of the PCB mixture recovered as biphenyl.