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针对Pd/Fe体系对含氯有机物催化还原脱氯过程中,零价铁易腐蚀并在颗粒表面形成钝化层,阻碍目标污染物的进一步脱氯去除,本研究利用乙二胺四乙酸(EDTA)与Fe2+和Fe3+的络合作用,消除Pd/Fe颗粒表面的钝化层,使还原脱氯过程得到持续进行.实验考察了EDTA的投加方式和投加量、p H、钯负载率、温度等因素对2,4-二氯苯氧乙酸(2,4-D)还原脱氯的影响.结果表明:1EDTA浓度为25.0 mmol·L-1、投加速率为20 m L·h-1时,苯氧乙酸(PA)生成率在20 min达到了90.7%.而未加EDTA的反应体系,反应210 min后,PA的生成率仅为74.5%;2EDTA可以络合Pd/Fe体系在催化脱氯过程中生成的Fe2+和Fe3+,防止或减缓了Pd/Fe颗粒表面钝化层的形成,提高了反应活性;3适宜的2,4-D催化脱氯条件为:浓度25.0mmol·L-1的EDTA溶液,投加速率20 m L·h-1、初始p H为4.2、钯负载率0.050%、温度30.0℃、搅拌速率200 r·min-1,反应210 min,20.0 mg·L-1的2,4-D几乎可完全转化为PA;42,4-D催化脱氯的中间产物主要是2-氯苯氧乙酸及微量的4-氯苯氧乙酸,最终产物为苯氧乙酸.
In the process of catalytic reduction dechlorination of chlorinated organic compounds by Pd / Fe system, the zero-valent iron tends to corrode and form a passivation layer on the surface of the particles, hindering further dechlorination removal of the target pollutants. In this study, ethylenediaminetetraacetic acid (EDTA ) With Fe2 + and Fe3 + to eliminate the passivation layer on the surface of Pd / Fe particles and make the dechlorination process continue.The experiment investigated the dosage and dosage of EDTA, p H, palladium loading, Temperature and other factors on 2,4-dichlorophenoxyacetic acid (2,4-D) reduction dechlorination results showed that: 1EDTA concentration of 25.0 mmol·L-1, the rate of 20 m L · h-1 , The production rate of PA reached 90.7% at 20 min, while the reaction rate of PA was only 74.5% after 210 min reaction without EDTA. 2EDTA could complex Pd / Fe catalyst The formation of Fe2 + and Fe3 + during dechlorination prevented or slowed the formation of the passivating layer on the surface of Pd / Fe particles and improved the reactivity. 3 The suitable conditions for 2,4-D catalytic dechlorination were 25.0 mmol·L- 1 EDTA solution at a rate of 20 m L · h-1, an initial pH of 4.2, a palladium loading rate of 0.050%, a temperature of 30.0 ℃ and a stirring rate of 200 r · min-1 for 210 min and 20.0 mg · L- 1 of 2,4-D It may be almost complete conversion to PA; Intermediate 42,4-D catalytic dechlorination mainly 2- chlorophenoxy acetic acid and traces of 4- chlorophenoxy acetic acid, phenoxyacetic acid for the final product.