臺灣博碩士論文加值系統

摘要
本研究以矽作為電子供給者對四氯化碳及四氯乙烯進行脫氯反應的探討，以了解用矽作為新穎物質來整治被氯化有機物污染場址的可行性，研究結果顯示四氯化碳及四氯乙烯皆可被矽完全分解，進行連續還原脫氯反應形成含氯較少的同類物，過程中有 85 % 的四氯化碳被轉化成氯仿，63 % 的四氯乙烯被轉化成三氯乙烯，且隨著矽添加量及 pH 的提高，四氯化碳的分解速率亦加快。四氯化碳及四氯乙烯的分解反應符合一階反應動力模式，其速率常數分別為 0.17 L h-1 m-2 及 0.0015 L h-1 m-2。結合矽和鐵的系統對四氯化碳及四氯乙烯的分解速率有顯著加快的效果。推知在矽鐵的系統中，還原脫氯的步驟是四氯化碳主要機制，四氯乙烯主要以 β-消去反應及還原脫氯的機制進行分解。其中還原脫氯反應為在高 pH 值之主要反應機制，而隨著pH的下降，β-消去反應成為控制四氯化烯分解的轉化機制，結果顯示出在分解氯化有機物上，鐵在矽鐵組合的中扮演重要的角色，而矽主要扮演 pH 的調控角色，使 pH 維持在 7.3 ~ 8.1。而添加催化劑及鎳離子可加速四氯乙烯在矽環境中的分解。
本研究所得到的結果可清楚的知道以矽來轉化氯化有機物是可行的，還原脫氯是主要的分解步驟，在結合矽鐵的系統可使產物的分佈趨向無毒的烷類。

Abstract
The dechlorination of carbon tetrachloride (CT) and tetrachloroethylene (PCE) using silicon as an electron donor was investigated. It was to evaluate the feasibility of using silicon as a novel material to remedy sites contaminated by chlorinated hydrocarbons. CT and PCE can be completely degraded via sequential reductive dechlorination to less chlorinated homologs by Si0. The productions of CF and TCE accounted for 85 % of CT and 63 % of PCE dechlorination, respectively. Increasing pH and Si amount also increased the dechlorination efficiency of CT. The degradation of CT and PCE by Si0 followed a pseudo first order kinetics and the rate constants were 0.17 L h-1 m-2 and 0.0015 L h-1 m-2, respectively. The combination of Si and Fe can also enhance the dechlorination rate of CT and PCE. Reductive dechlorination was the main reaction mechanism for CT dechlorination, while b-elimination and reductive dechlorination are the predominant reaction pathways for PCE dechlorination in the Si0/Fe0-H2O system. Reductive dechlorination was dominant at the on-set of the reaction and high pH and b-elimination was the main reaction pathway for PCE dechlorination as pH decreased. Fe0 plays an important role in the reduction of chlorinated hydrocarbons in the Si0/Fe0-H2O system and Si0 would act as pH buffer to maintain the pH in the range of 7.3 — 8.1. This corresponds to a change of 0.8 pH unit as the Fe0 dose increased by 2 orders of magnitude. Addition of catalyst or nickel ion can also enhance the dechlorination of PCE. Results clearly indicated the transformation of chlorinated compounds by silicon is practicable. Reductive dechlorination is the major degradation pathway, while the distribution of products will change to nontoxic alkane when Si0 was applied simultaneously with Fe0.

Content Index
謝誌…………………………………………………………… I
中文摘要…………………………………………………….. II
Abstract……………………………………………………….. III
Content Index………………………………………………….. IV
Table Index……………………………………….………... VII
Figure Index………….……….…………………..……….. VIII
Chapter 1. Introduction and motivation
1-1 Motivation………………………………………….. 1
1-2 Objective……………………………………………… 3
Chapter 2. Background and theory
2-1 Introduction to chlorinated hydrocarbons……. 4
2-1-1 Physicochemical properties of chlorinated hydrocarbons………………… 4
2-1-2 The toxicity of halogenated hydrocarbon.. 4
2.2 Abiotic transformation of chlorinated hydrocarbons..6
2-2-1 Abiotic transformation by zero-valent metals……………………… 6
2-2-2 Abiotic transformation by Si0…………… 12
2-2-3 Abiotic transformation using hydrogen catalyzed by palladium or nickel.....................17
2-3 Environmental factors affecting the dechlorination of chlorinated hydrocarbons………………………………… 18
2-3-1 Oxidation-reduction potential……………………… 18
2-3-2 Effect of physicochemical properties of chlorinated compounds………… 21
2-3-3 Effect of pH on dechlorination by zero-valent metal…………… 23
2-3-4 Effect of surface area on dechlorination..... 24
2-3-5 Effect of metal ions (Ni2+, Cu2+) on dechlorination.......... 26
2-4 Reaction mechanisms…………………… 26
Chapter 3 Research design and methodology
3-1 Experiment Scheme……….…………… 28
3-2 Chemicals………………………………….. 28
3-3 Abiotic transformation experiments…………… 29
3-3-1 Preparation of deoxygenated water……………… 29
3-3-2 Preparation of stock solution………………… 29
3-3-3 Dechlorination experiments………………… 31
3-4 Analytical Methods…………………………. 31
3-4-1 Analysis of chlorinated hydrocarbons………… 31
3-4-2 Analysis of the surface of silcon with ESCA 32
3-4-3 Analysis of the surface of silicon.... 32
3-5 Preparing Calibration curve.......... 35
Chapter 4 Results and discussion
4--1 Dechlorination of carbon tetrachloride by Si 36
4-1-1 Effect of pH……..................... 36
4-1-2 Effect of Si0 amounts on CT dechlorination 42
4-1-3 Dechlorination pathway in Si0-H2O……………… 46
4-1-4 CT dechlorination by Si0/Fe0………………….. 49
4-2 Dechlorination of tetrachloroethylene (PCE)........56
4-2-1 Dechlorination of PCE in the Si0-H2O system 56
4-2-2 PCE dechlorination using Si0/Fe0..... 59
4-2-3 Effect of Fe0 on dechlorination in Si0/Fe0-H2O system…………………................ ... 60
4-3 Reduction of PCE in the presence of catalyst 69
4-3-1 Effect of Pd0 and Ni0…………………......… 69
4-3-2 Effect of metal ........................ 73
Chapter 5 Conclusions............……………..…………..77
References…………………………………………………..……79
Appendix I Technical Data Sheet
Specification of Silicon Powder
Appendix II GC/MS/FID Analysis
Distribution of the products in the degradation of PCE in Fe0/Si0-H2O
Appendix III GC/MS/FID Analysis
Calibration Curve of Chlorinated Compounds

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