Abstract

It is well known that the hydrodechlorination (HDC) of chlorinated aromatic contaminants in aqueous effluents enables a significant increase in biodegradability. HDC consumes a low quantity of reactants producing corresponding non-chlorinated and much more biodegradable organic compounds. Two commonly used precious metals free Al alloys (Raney Al-Ni and Devarda’s Al-Cu-Zn) were compared in reductive action in an alkaline aqueous solution. Raney Al-Ni alloy was examined as a universal and extremely effective HDC agent in a diluted aqueous NaOH solution. The robustness of Raney Al-Ni activity is illustrated in the case of HDC of polychlorinated aromatic compounds mixture in actual waste water. In contrast, Devarda’s Al-Cu-Zn alloy was approved as much less active for HDC of the tested chlorinated aromatic compounds, but with a surprisingly high selectivity on cleavage of C-Cl bonds in the meta and sometimes the ortho position in chlorinated aniline and sometimes chlorinated phenol structures. The reaction of both tested alloys with chlorinated aromatic compounds in the aqueous NaOH solution is accompanied by dissolution of aluminum. Dissolved Al in the alkaline HDC reaction mixture is very useful for subsequent treatment of HDC products by coagulation and flocculation of Al(OH)3 caused by simple neutralization of the alkaline aqueous phase after the HDC reaction.

Highlights

  • Chlorinated aromatic compounds (Ar-Cls) are used on a large scale as industrial solvents or intermediates in the synthesis of specialty organic chemicals, in other words, dyestuffs, pesticides and drugs

  • A set of 12 different Chlorinated anilines (Cl-ANs) was used in the HDC experiments for a comparison of reductive efficiency of Raney Al-Ni and Devarda’s Al-Cu-Zn alloy in aqueous NaOH

  • Commercially available Cu- and Ni-based Al alloys produced in multiton amounts for application in the chemical industry were tested and compared for a new application in the area of HDC-based detoxification of common chlorinated aromatic aqueous contaminants

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Summary

Introduction

Chlorinated aromatic compounds (Ar-Cls) are used on a large scale as industrial solvents or intermediates in the synthesis of specialty organic chemicals, in other words, dyestuffs, pesticides and drugs. We attempt to compare the HDC activity of two commercially available and well-defined Al alloys, Raney Al-Ni alloy and Devarda’s Al-Cu-Zn alloy at room temperature and ambient pressure in an alkaline aqueous solution for HDC of Ar-Cls. Exclusively room temperature and ambient pressure was used due to the minimization of capital costs and the environmental impact of this method in assumed industrial application for treatment of water contaminated with Ar-Cls. In this study, the long reaction time (around 16 h) was used usually in describing HDC experiments to achieve completion of the HDC reaction (at least more than 10 half-lives of HDC reaction) [21,26]. Changes in the structures of both mentioned alloys are presented during a HDC reaction in the diluted aqueous NaOH solution

Dechlorination of Chlorinated Anilines
Dechlorination
Dechlorination of Chlorinated Benzenes Using Devarda’s Al-Cu-Zn Alloy
The polychlorinated
Dechlorination of Chlorinated Benzenes Using the Raney Al-Ni Alloy
Observed
Dechlorination of Chlorinated Phenolic Compounds
Possible
The composition ofreaction reaction mixture at the end ofof ofof
Possible Pathway of Devarda’s Al-Cu-Zn Alloy HDC Action
Methods
Chemical Analysis
HDC of Chlorinated Anilines and Phenols Using Studied Al Alloys
HDC of Chlorinated Benzenes Using Studied Al Alloys or Al Foil
HDC of Chlorinated Benzenes Using in Situ Generated Cu or Ni
HDC Kinetic Experiments Using Raney Al-Ni Alloy
HDC of Real Wastewater Sample
Conclusions
Full Text
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