Halogen contaminants

Low reactivity contaminants halogenated hydrocarbons, saturated aliphatics, benzene. 

Ware SA, Weast WL. 1977. Investigation of selected potential environmental contaminants Halogenated benzenes. Washington, DC U.S. Enviromnental Protection Agency, Office of Toxic Substances. EPA 560/2-77-004. 

The technology can potentially treat the following contaminants halogenated volatiles and semivolatiles, nonhalogenated volatiles and semivolatiles (also listed as actual), organic pes-ticides/herbicides, polynuclear aromatic compounds (PNAs), solvents, and benzene-toluene-ethylbenzene-xylene (BTEX). 

For some industrial cooling water applications, where process contamination is often an inherent problem, a high chlorine/low bromine ratio product may be preferable. This type of problem can happen, for example, where repeated hot/cold cycles are part of the process and some valve leakage and interchange of water between circuits may occur. Thus, the (lower cost) chlorine component is employed in satisfying the contaminant halogen demand and the bromine component (perhaps with some degree of Br recycle) subsequently acts as a biocide. 

Water as an impurity accelerates the oxidation rate. Figure 4 compares growth curves for Si02 under dry and steam conditions. Halogens can also be introduced to the oxidation process, thereby reducing sodium ion contamination. This improves dielectric breakdown strength, and reduces interface trap density (15). 

Other Reactions. Primary amyl alcohols can be halogenated to the corresponding chlorides by reaction with hydrogen chloride in hexamethylphosphoramide (87). Neopentyl chloride [753-89-9] is formed without contamination by rearrangement products. A convenient method for preparing / f/-amyl bromide and iodide involves reaction of / f/-amyl alcohol with hydrobromic or hydroiodic acid in the presence of Li or Ca haUde (88). The metal haUdes increase the yields (85 —95%) and product purity. 

Potable Water Treatment. Treatment of drinking water accounts for about 24% of the total activated carbon used in Hquid-phase apphcations (74). Rivers, lakes, and groundwater from weUs, the most common drinking water sources, are often contaminated with bacteria, vimses, natural vegetation decay products, halogenated materials, and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (75). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (76—78) for safety and palatability. 

Groundwater contaminated with chlorinated hydrocarbons is being remediated by a conventional air stripper or a rotary stripper, producing an air stream containing the halogenated hydrocarbon vapors and saturated with water vapor (45), which is then passed through a catalyst bed. 

Another important application area for PSAs in the electronic industry focuses on the manufacturing, transport and assembly of electronic components into larger devices, such as computer disk drives. Due to the sensitivity of these components, contamination with adhesive residue, its outgassing products, or residue transferred from any liners used, needs to be avoided. Cleanliness of the whole tape construction becomes very critical, because residuals like metal ions, surfactants, halogens, silicones, and the like can cause product failures of the electronic component or product. Due to their inherent tackiness, acrylic PSAs are very attractive for this type of application. Other PSAs can be used as well, but particular attention has to be given to the choice of tackifier or other additives needed in the PSA formulation. The choice of release liner also becomes very critical because of the concern about silicone transfer to the adhesive, which may eventually contaminate the electronic part. 

Groundwater Industrial contamination of ground water reserves Reduction of total organic halogens (TOX) and adsorbable organic halogens (AOX) including chloroform, tetrachloroethylene, and trichloroethylene... 

Atmospheres contaminated with acid or halogen gases reduce these values. 

Air contaminants Gases sulphur oxides, halogen compounds Mists aerosols, salt, alkalies Particulates sand, dust, grease... 

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