【作者】 郑明明；

【导师】 鲍建国；

【作者基本信息】 中国地质大学 ， 环境科学， 2011， 硕士

【摘要】 氯代有机物(Chlorinated organic compounds, COCs)作为典型的难降解有害物,由于其生物累积性和毒性已引起广泛的关注。氯代有机物的毒性与氯代原子数紧密相关。一般地,氯代原子数越多,毒性越高且越难降解。脱氯不仅可以降低氯代有机物的毒性,同时可以增加易处理性。因此,还原脱氯被认为是地下水中氯代有机污染修复的一种有效处理方法,主要包括零价铁和催化加氢。然而,零价铁长期运行后,铁表面发生腐蚀形成氧化膜或氢氧化膜。催化加氢由于其实际实施过程中的困难较少用于地下水的原位修复。针对地下水中氯代有机物污染修复的问题,本文基于氯代有机物先还原继而氧化的思路,提出了一种用于地下水中氯代有机物原位修复的新方法—利用电化学产氢催化加氢还原氯代有机物,继而顺序阳极氧化。本研究首先自制了钯/竹炭催化剂,然后利用外源氢进行液相的催化加氢静态实验,同时考虑pH等与地下水和电化学过程相关因素的影响。其次,在分开的静态电解体系中,利用阴极部分产生的氢气对污染物进行催化加氢,同时考虑电流等因素的影响。在上述基础上,进行动态过柱试验,测试动态体系中利用电化学产氢催化加氢还原,继而阳极氧化阴极还原产物的可行性,实验过程中,污染物水溶液顺序通过阴极、催化剂和阳极。得到的主要结论如下：(1) Pd成功负载在竹炭上,晶体结构是面心立方结构,晶粒平均粒径约为20nm,质量比约10.96%,出现Pd(Ⅱ),但Pd(0)占主导地位。反应后的催化剂Pd有一定程度的团聚,竹炭表面石墨化,晶体仍是面心立方结构,平均粒径约23nm,比反应前稍微增大,竹炭上Pd质量比降低至3.69%,Pd(Ⅱ)含量增多,Pd(0)仍然占主导地位。制备的的钯/竹炭催化剂用于催化加氢还原脱氯具有较好的持久性和稳定性。(2)在直接通氢体系中,在钯/竹炭催化下2,4-二氯酚具有较好的脱氯效果。初始pH值分别为3.5、5.5和11.0时,20min时2,4-氯酚的去除率分别对应为100%、95.6%和21.4%,产物主要是苯酚,出现中间产物2-氯酚或4-氯酚,随着还原反应进行,苯酚还能进一步被还原降解。电解质及腐殖酸浓度大小对反应效率也有影响,低电解质及腐殖酸浓度有利用提高催化加氢效果。当体系硫酸钠的浓度分别为10 mmol/L、70 mmol/L和140 mmol/L时,反应60min 2,4-二氯酚的降解效率对应分别为84%、89%和23%。体系电解质浓度70mmo1/L条件下,当腐殖酸的浓度分别为20mgL和50 mg/L时,2,4-二氯酚的降解效率对应分别为49%和39%。制备的钯/竹炭催化剂用于催化加氢还原脱氯具有一定的持久性和稳定性：在体系pH值为5.5时,催化剂循环利用9次后对污染物2,4-二氯酚的去除效率仍有50%。.(3)在电化学体系的催化加氢脱氯研究中,利用电化学阴极产生的氢气在钯/竹炭催化剂作用下能还原2,4-二氯酚,同时可以看出,所给的电流越大时,污染物的降解效率越高。恒电流50mA,反应60min时,污染物2,4-二氯酚已完全降解去除,而当电流20mA时,2,4-二氯酚的完全降解需要120min,当电流10mA时,120main内2,4-二氯酚的降解效率仅为41%。苯酚是主要的降解产物,同时也出现还原中间体产物2-氯酚。2,4-二氯酚的还原脱氯产物苯酚能在阳极被氧化降解,氧化产物有苯醌、邻苯酚、对苯酚及脂肪酸类等。(4)动态体系中,当进水pH为5.5时,最终出水2,4-二氯酚浓度较进水浓度降低了60%,最终出水中苯酚完全被氧化降解；当进水pH为2时,最终出水2,4-二氯酚及苯酚浓度均未检出,说明2,4-二氯酚完全还原后继而又被彻底氧化降解。低进水pH有利于污染物的去除。在动态体系的还原端,能检测到2,4-二氯酚的还原及苯酚的生成变化情况。动态体系的有效运行不仅验证了利用电化学产氢对地下水中氯代有机物催化加氢还原脱氯的可行性,还证实了电化学一催化加氢联用技术对于处理地下水中有机氯律污染的可行性及高效性。更多还原

【Abstract】 Chlorinated organic compounds (COCs) have aroused intensive concern due to their high refractory nature, bio-accumulation and toxicity. The toxicity of COCs is strongly related to the extent of chlorination. Generally, more chlorination is associated with higher toxicity and difficult oxidative degradation. The release of chlorine leads to the decrease in toxicity and the increase in oxidative degradability. Therefore, reductive dechlorination is considered as an effective method for the remediation of COCs contaminated groundwater. Zero-valent iron (ZVI) and catalytic hydrodechlorination are the two main processes for COCs dechlorination in groundwater. However, the continuous corrosion of iron during decades of field running makes the surface of iron covered with iron hydrates and oxides, which results in the decrease in long-term performance. As to catalytic hydrodechlorination, the practical application of this process is inconvenient because the in situ supply of H2 in the subsurface is difficult and dangerous. In present study, a novel electrolytic system, which is based on sequential catalytic hydrodechlorination and anodic oxidation, was developed to reach in-situ remediation of COCs contaminated groundwater. The Pd/C catalyst was firstly synthesized, and then the catalytic hydrodechlorination using external H2 was carried out, which was used to investigate the influence of the factors which are involved in groundwater remediation by electrochemical process, on the hydrodechlorination of COCs. Secondly, in a divided electrolytic system, the catalytic hydrodechlorination of COCs in cathode compartment by H2 generated at cathode was conducted to verify the feasibility of hydrodechlorination by the H2 generated at cathode and test the influence of current intensity. Finally, a dynamic column system, in which groundwater flew through cathode, Pd/BC catalyst and anode in turn, was employed to evaluate the feasibility of in-situ sequential catalytic hydrodechlorination of 2,4-DCP by the H2 generated at cathode and direct anodic oxidation of Phenol produced. Main conclusions are summarized as follows:(1) Pd was successfully loaded on the bamboo charcoal. The Pd content was measured as 10.11%(w/w), and the Pd particles of FCC structure were evenly scattered on BC surface and the particle size was about 20 nm. The dominant component of the Pd3d binding energy is confirmed as Pd(0). After long-term reaction, the Pd particles on BC was gathered, and the size was slightly increased from 20 nm to 23 nm. The weight fraction of Pd3d decreased from 10.96% to only 3.69%.(2) The catalytic hydrodechlorination using external H2 showed that within 20 min the hydrodechlorination of 2,4-DCP was 100%,95.6%, and 21.4% at the pH of 3.5,5.5 and 11 respectively. Phenol was the main products and it could be further reduced to nontoxic cyclohexanone. During the reaction progress, intermediate products of 2-chlorophenol or 4-chlorophenol emerged. The concentration Na2SO4 and humic acid also had affect on catalytic hydrodechlorination of 2,4-DCP, which lower concentration corresponded to high hydrodechlorination efficiency.The catalytic hydrodechlorination of 2,4-DCP under the Na2SO4 concentration of 10,70 and 140 mmol/L reached 84%,89% and 23% at 60 min, respectively. At the Na2SO4 concentration of 70mmol/L, the hydrodechlorination efficiency of 2,4-DCP were 49% and 39% corresponding to the humic acid concentration of 20 and 50 mg/L in the reaction aquid, respectively. The synthesized Pd/BC catalyst was efficient for 2,4-DCP hydrodechlorination and the performance can be sustained for a long time.(3) In a divided electrolytic system,2,4-DCP could be reduced by the H2 generated at cathode in the attendence of Pd/C, and higher current resulted in faster reduction. For 60 min treatment, reduction at 50 mA led to 100% removal of 2,4-DCP, while at 20 mA the time of complete dechlorination would extended to 120 min at which the hydrodechlorination efficiency of 2,4-DCP was only 41% when 10 mA. Likewise, Phenol was the main dechlorination product, and 2-CP rather than 4-CP was identified as the minor monochlorophenol intermediate. 2,4-DCP reductive dechlorination products of Phenol could be oxidized at the anode degradation, and oxidation products were benzoquinone, catechol, hydroquinone and other fatty acids.(4) In the dynamic flow-through electrolytic system, The final effluent of 2,4-DCP was decreased by 60% than influent concentration at pH of 5.5, and the degradation of Phenol was completely. When the influent pH of 2, the final effluent concentration of 2,4-DCP and Phenol were below the detection limit, which showed that 2,4-DCP was first complete hydrodechlorination and then subsequent thorough oxidation. Low pH is conducive to the removal of pollutants. In the reducing end of dynamic system, the reduction of 2,4-DCP and Phenol formation changes could detect. Dynamic system is not only verify the effective operation of electrochemical generation of H2 for catalytic hydrodechlorination of chlorinated organic compounds in groundwater, but also confirmed that the techniques combined with electrochemical and hydrodechlorination was feasibility and efficiency for the treatment of chlorinated organic compounds in groundwater.更多还原