Mineralization halogenated compounds

A project at the University of Arizona (FEDRIP 1996) will study microbial dehalogenation of several compounds, including chloroform. A major part of the study will focus on the facultative anaerobic bacteria Shewanella putrefaciens sp., which is known to catalyze the transformation of carbon tetrachloride to chloroform and other as yet unidentified products. The organic substrates will also contain metals. It is hoped that the end-products from the biochemical treatment can be subjected to a photolytic finishing process that will completely mineralize any remaining halogenated compounds. 

Halogenated compounds Fluochloro hydrocarbons with 5 to 50 C atoms chlorinated hydrocarbons Vegetable oils waxes, mineral oils plus their sulfated derivatives (including those of animal oils and fats) Lubrication-oil and grease distillation vegetable-protein glues... 

Thus, for example, "mineralization" of any hydrocarbon to C02 and HzO involves oxidation (see Chapter 12), and dechlorination of any halogenated compound to hydrocarbon products involves reduction. 

Nevertheless, the incorporation of relatively low amounts of nanoparticles in polymers by several processing methods is unable to meet fire performance standards in comparison with usual FRs, such as hydrated minerals, halogen, phosphorus, or nitrogen compounds, for which the loading is generally higher, up to 65 wt % for some metallic hydroxides. 

ACETIC ACID, DIMETHYLAMIDE (127-19-5) C4H9NO Combustible liquid [explosion limits in air (vol %) 1.8 to 13,8 flashpoint 158°F/70°C oc autoignition temp 914°F/490°C Fire Rating 2]. Violent reaction with strong oxidizers, halogenated compounds carbon tetrachloride hexa-chlorocyclohexane. Reacts violently in the presence of iron. Incompatible with mineral acids, strong acids, ammonia, isocyanates, phenols, cresols. Attacks many plastics, rubber, and coatings. When heated to decomposition, emits carbon oxides,... 

ACETDIMETHYLAMIDE (127-19-5) Combustible liquid (flash point 158°F/70°C). Violent reaction with strong oxidizers, halogenated compounds. Incompatible with mineral acids, strong acids, ammonia, isocyanates, phenols, cresols. Attacks plastics, rubber, and coatings. 

The reaction requires a dehydrating catalyst, which, for reactions in the liquid phase, is an acid substance this is usually a concentrated mineral acid, but may also be an organic sulfonic acid, acid salt, or halogen compound such as boron trifluoride, zinc chloride, or aluminum chloride. For etherification in the gaseous phase the alcohol vapor is passed over a solid catalyst such as A1203, Ti02, or dehydrated alum.656... 

Reductive dehalogenation is a mechanism for the anaerobic biotransformation of chlorinated hydrocarbons such as hexachlorobenzene (HCB). In reductive dehalogenation, the halogenated compound serves as the electron acceptor rather than the donor that requires a separate carbon source. In a microbially catalyzed reaction, a halide ion is replaced by a hydrogen ion (Figure 13.7). The removal of halide ions results in compounds that are generally easier to degrade, and, in some instances, are completely mineralized. 

TEAs can be both natural and man-made. Natural TEAs include oxygen, nitrate, sulfate, ferric iron compounds, and manganese minerals such as pyrolusite (Mn02), carbohydrates, and carbon dioxide. In the biodegradation process, halogenated compounds can also be considered to be TEAs. 

Thus the microbial activity is chiefly responsible for the mineralization of halogenated compounds, which enter into a variety of natural habitats. The toxic, mutagenic, and carcinogenic effects of various chlorinated compoxmds make studies of these compounds at various levels, extremely important. As excellent recent reviews on the microbial degradation of halogenated aromatics are available [5-8], a brief description of tiie degradation of some important chloroaromatics, with available enzymological studies, will be presented. 

The mineralization products recorded by the coulometer are shown as chloride. Tbe content of "extractable organic halogen compounds (EOX)" is calculated in pg/1 EOX and quoted as a chloride concentration. 

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