Selective Mechanochemical Dehalogenation of Chlorobenzenes over Calcium Hydride

Abstract

We have shown that in the presence of a reactive substrate, chlorinated organic compounds can be dehalogenated by mechanical treatment, and a specific reaction product can be obtained. We have used a ball milling process at low temperature and atmospheric pressure to produce a dechlorination of up to 100% for both liquid and solid chlorinated compounds. The products of the completed reaction for trials with hexachlorobenzene and chlorobenzene were both principally restricted to benzene and chloride salts. The use of CaH2 as a source of active hydrogen produces a much more specific reaction in significantly less time in comparison with CaO and MgO substrates reacted under hydrogen atmosphere. The process was found to depend on the injected mechanical energy and the collision frequency. In the case of hexachlorobenzene, an explosive-type reaction was observed to occur at specific milling times as a function of the kinetic energy employed.

The Mechanochemical Self-Propagating Reaction between Hexachlorobenzene and Calcium Hydride

“…In the case of chlorobenzene, the products of the completed reaction were restricted to benzene and chloride salts. Neither the breakdown of the organic species into unwanted by-products nor the formation of toxic cogeners was observed (2).…”

“…Calcium and magnesium powders and their oxides were used as reactive substrates (1). The specific use of calcium hydride as a reducing agent allowed the dehalogenation process to be accomplished along a neater and quite straightforward path (2). In the case of chlorobenzene, the products of the completed reaction were restricted to benzene and chloride salts.…”

Mechanochemical degradation of hexachlorobenzene using Mg/Al2O3 as additive

“…Yasumitsu et al [30] used calcium oxide as additive to destruct 1,2,3-Trichlorobenzene (TCB) by ball milling, and found that the final products contained some minor methane and ethane except carbon after 360 min milling. Loiselle et al [21] also detect methane and ethane in the end products during the process of mechanochemical treatment of chlorobenzenes. The alkane formed during milling process indicated that in the process of degradation of POPs a ring-open reaction was conducted.…”

“…Loiselle et al [21] utilized CaH 2 as a source of active hydrogen and chlorinated organic compounds can be dehalogenated by mechanochemical treatment, producing a much more specific reaction in less time compared with CaO and MgO substrates. Although CaH 2 is efficient in the destruction of HCB, more consideration should be paid on its high reactivity and lability in practical implementation [22].…”

Mechanochemical Degradation of Aromatic Sulfonic Acids

“…The former one can be regarded as the reference technique for the degradation of pollutants in liquid solutions, having a high efficiency and relatively high processing rates 8,9 . The latter one has been identified as a viable technique for the destructive treatment of pollutants dispersed in solid matrices [10][11][12][13][14][15][16] .…”