Thermal and Mechanochemical Self-Propagating Degradation of Chloro-organic Compounds:  The Case of Hexachlorobenzene over Calcium Hydride

• Published in: Industrial & engineering chemistry research 1999-09, Vol.38 (9), p.3218-3224
• Main Authors: Cao, Giacomo, Doppiu, Stefania, Monagheddu, Marzio, Orrù, Roberto, Sannia, Mariella, Cocco, Giorgio
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Other industrial wastes. Sewage sludge; Pollution; Wastes
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie980790+

We report on the highly exothermic solid-state reaction between hexachlorobenzene and calcium hydride. Once ignited by a thermal spike, the reaction displays a self-sustaining character in the CaH2/C6Cl6 molar ratio of 3:18. The high temperatures reached, i.e., 2550−2900 K, ensure a complete breakdown of the aromatic molecule and of undesired chloro-organic congeners, with only inorganic halide salts being found among the end-products. Combustive-like reactions were also observed when reactant powders were subjected to intensive mechanical treatment by ball milling. The combustive range of mechanically driven processes falls within that found in the true self-sustaining regime even if the activation and the extinction of the reaction were ruled by completely different mechanisms. A neat correlation was worked out relating the temperatures at the combustion front to the total heat evolved in the reaction carried out in the mechanochemical mode. The same end-products were also found. The practical exploitation of a self-sustaining methodology for the disposal of hazardous organochlorine compounds seems feasible.