Dechlorination thermal methods

Methane, chlorine, and recycled chloromethanes are fed to a tubular reactor at a reactor temperature of 490—530°C to yield all four chlorinated methane derivatives (14). Similarly, chlorination of ethane produces ethyl chloride and higher chlorinated ethanes. The process is employed commercially to produce l,l,l-trichloroethane. l,l,l-Trichloroethane is also produced via chlorination of 1,1-dichloroethane with l,l,2-trichloroethane as a coproduct (15). Hexachlorocyclopentadiene is formed by a complex series of chlorination, cyclization, and dechlorination reactions. First, substitutive chlorination of pentanes is carried out by either photochemical or thermal methods to give a product with 6—7 atoms of chlorine per mole of pentane. The polychloropentane product mixed with excess chlorine is then passed through a porous bed of Fuller s earth or silica at 350—500°C to give hexachlorocyclopentadiene. Cyclopentadiene is another possible feedstock for the production of hexachlorocyclopentadiene. 

Big River Zinc investigated two processes to dechlorinate the oxides. The first process used a water wash accompanied with a pH adjustment to minimize zinc losses. Htis method offered a known technology because Big River Zinc provided assistance to ZTT in Caldwell, Texas, to refine their similar process. Tests showed that washing, followed by neutralization with soda ash, succeeded in reducing the chloride content to less than 1% in the final product. The other process investigated was thermal dechlorination (4). It is known that thermal dechlorination can remove over 90% of the chlorides fiom roaster feeds. A few tests indicated promising results for this technique but the decision was taken to pursue washing as the process of choice. 

The hrst rehable report of the preparation of tetrafluoroethene (TFE) was given in 1933 by Rulf and Bretschneider [643], who decomposed tetrafluoromethane in an electric arc. Other syntheses are based on the dechlorination of yn-chlorodifluoromethane [644], the pyrolysis of chlorodifluoromethane [645], and the decarboxylation of sodium perfluoroproprionate [646]. Since then, a number of synthetic routes have been developed [644-646]. On a laboratory scale, depolymerization of PTFE by heating at about 600 °C is probably the preferred method to obtain a smah amount of pure monomer (97%) [647], along with the highly toxic perfluoroisobutene as well as octafluorocyclobutane as a side product formed by the thermal (2ji -I- 2n) cyclodimerization of TFE [648,649]. The most common commercial approach for the preparation of TFE is the pyrolysis of chlorodifluoromethane [645,650]. The noncatalytic gas-phase reaction is carried out in a flow reactor at atmospheric pressure, yields over 95% TFE at 590 to 900 °C. The synthesis of TFE involves the following steps ... 

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