Effect of metal and glycol on mechanochemical dechlorination of polychlorinated biphenyls (PCBs)

doi:10.1016/j.chemosphere.2008.04.051

Chemosphere

Volume 73, Issue 1, August 2008, Pages 138-141

https://doi.org/10.1016/j.chemosphere.2008.04.051 Get rights and content

Abstract

This paper assesses the potential of mechanochemical method with fine metal powder, glycol and alkali for polychlorinated biphenyls (PCBs) removal from waste insulating oil. The effects of relevant parameters, such as kinds of chemicals, rate and time of milling were examined. After each run, the total PCBs content in waste insulating oil was measured. Polyethylene glycol 200, long chain-glycol was more effective than triethylene glycol and ethylene glycol, short chain-glycol as hydrogen donor in mechanochemical dechlorination of PCBs. A maximum of 99.9% PCBs removal (below 2 ppm) and 94% total chlorine removal were achieved with the mechanochemical process for 2 h.

Introduction

Polychlorinated biphenyls (PCBs) are very stable industrial chemicals. They are produced by chlorination (2 < n_cl < 10) of biphenyl (C₁₂H₁₀); the two-ring structure allows the formation of 209 congeners (Hutzinger et al., 1974). The PCB mixtures of congeners are ubiquitous and persistent pollutants in the global ecosystem (Lang, 1992). Their well known physical and chemical stability, along with their excellent dielectric properties, has led to a widespread industrial application as insulating materials for the electric industry, in capacitors and transformers. Destruction of these toxic chemicals has centered on incineration, plasma incineration, and other chemical methods such as wet oxidation and sodium-based reduction. Each of these methods has limitations. For example, incineration as well as chemical methods can generate HCl or Cl₂ or small traces of PCDD/PCDF. Other chemical methods can require inert atmospheres and sensitive reagents. Thus, it is desirable to develop ways to rapidly dehalogenate organic molecules prior to their safe incineration. Recently, much attention has been paid to the mechanochemical treatment of toxic substances, due to its easy operation and practicability regarding the vast amounts of contaminated samples at low concentrations and the toxic chemical itself (Cocco et al., 1999). It is known that grinding plays a significant role in causing mechanochemical effects on solid particles as well as being a simple operation to reduce particle size (Birke et al., 2004). One of the unique phenomena of this effect is the ability to dissociate the material by rupturing the bonds (Birke et al., 2004). Mechanochemical dechlorinations of persistent organic pollutants (POPs) by milling with metals, alkali, and certain hydrogen donors like alcohols, ethers and so forth are discussed (Birke et al., 2004).

In this work, we examined the effect of metals and glycols on mechanochemical dechlorination of PCBs.

Section snippets

Experimental work

Aluminum, magnesium, iron and zinc powder of 99% purity and of range from 100 to 200 mesh were purchased from Junsei and Kanto and used without any pretreatment. Potassium hydroxide (KOH), ethylene glycol (EG), triethylene glycol (TEG) and polyethylene glycol 200 (PEG 200) were manufactured by Junsei and Yakuri. Attrition mill apparatus was composed of 1 l tank, impeller, 3 mm-zirconia ball, motor, and rpm controller.

Present investigation was carried out in batch mode. Predetermined quantities of

Effect of metals on the reaction

The general reaction of hydrogenation/dechlorination of PCBs occurring during the mechanochemical treatment is given in Eq. (1) (Aresta et al., 2003). $C_{12} H_{x} {Cl}_{y} + M \overset{E}{\to} C_{12} H_{x} + MCl$ where

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C₁₂H_xCl_y: polychlorobiphenyl with 0 < x < 8 and 2 < y < 10;
•
M: zero-valent metal;
•
E: energy transferred by milling;
•
C₁₂H_x: hydrocarbon; and
•
MCl: chloride salts.

The milling energy had a fundamental role in the PCBs’ dechlorination process (Aresta et al., 2003). The transferred energy caused the nucleophilic substitution of Cl⁻ with H⁻

References (6)

M. Aresta et al.
Solid state dehalogenation of PCBs in contaminated soil using NaBH₄
Waste Manage.
(2003)
S. Sabata et al.
Limits to the use of KOH/PEG method for destruction of PCB liquids of Czechoslovak production
Chemosphere
(1993)
V. Birke et al.
Mechanochemical reductive dehalogenation of hazardous polyhalogenated contaminants
J. Mater. Sci.
(2004)

There are more references available in the full text version of this article.

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Short CommunicationEffect of metal and glycol on mechanochemical dechlorination of polychlorinated biphenyls (PCBs)

Abstract

Introduction

Section snippets

Experimental work

Effect of metals on the reaction

Waste Manage.

Chemosphere

Mechanochemical reductive dehalogenation of hazardous polyhalogenated contaminants

J. Mater. Sci.

Short Communication
Effect of metal and glycol on mechanochemical dechlorination of polychlorinated biphenyls (PCBs)