Thermal dechlorination

Lidov A process for chlorinating cyclopentadiene to octachloropentadiene, which is then thermally dechlorinated to hexachlorocyclopentadiene (HCCP), used as an intermediate in the manufacture of insecticides and flame retardants. The initial chlorination is catalyzed by phosphoms pentachloride or arsenious oxide. Invented by R. E. Lidov in The Netherlands and commercialized by the Shell Chemical Company. 

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. 

Without additional reagents Thermal dechlorination of perchloro compounds... 

Certain CFCs are used as raw materials to manufacture key fluorinated olefins to support polymer apphcations. Thermolysis of HCFC-22 affords tetrafluoroethylene and hexafluoropropylene [116-15 ] under separate processing conditions. Dechlorination of CFC-113 forms chlorotrifluoroethylene [79-38-9]. Vinyhdene fluoride [75-38-7] is produced by the thermal cracking of HCFC-142b. 

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. 

Bowmer and Tonelli [161] have also studied the thermal characteristics of the whole range of ethylene-vinyl chloride copolymers prepared by partial reductive dechlorination of PVC using tri-n-butyltin-hydride. Naqvi [162] has substantiated further his explanations for the thermal stability characteristics of ethylene-vinyl chloride copolymers reported by Braun et al. [159] using the results of Bowmer and Tonelli [161] as a basis. 

Newton R, Aranovich L (1996) Simple granulite melting in concentrated NaCl-KCl solutions at deep crustal conditions. Geol Soc Am Annu Meet Abstracts with Programs 158 Numata M, Nakamura N, Koshikawa H, Terashima Y (2002) Chlorine isotope fractionation during reductive dechlorination of chlorinated ethenes by anaerobic bacteria. Env Sci Tech 36(20) 4389-4394 Numata M, Nakamura N, Gamo T (2001) Precise measurement of chlorine stable isotopic ratios by thermal ionization mass spectrometry. Geochem J 35(2) 89-100 Owen HR, Schaeffer OA (1995) The isotope abundances of chlorine from various sources. J Am Chem Soc 77 898-899... 

The relative ratio of regioisomers of PCDD/F and other chlorinated compounds formed in incinerators is called the incineration pattern. The pattern can be derived from statistical analysis of a large number of measurements of the same plants, and can be used for elucidation of thermal formation mechanisms in plants. In principle regioisomers can be formed either by stereospecific chlorination or dechlorination processes. The pattern has also been used as a part for explaining of the formation mechanism of PCDD/F and other chlorinated compounds formed in incinerations (see Figure 8.4). 

Hutchinson GE (1957) The thermal properties of lakes. A treatise of limnology. 1 426-540 Hwang I, Batchelor B (2000) Reductive dechlorination of tetrachloroethylene by Fe(II) in cement slurries. Environ Sci Technol 34 5017-5022... 

From a chemical point of view TCDD is considered to be a stable compound, but due to its extreme toxicity, its chemistry has not been fully evaluated. However, it undergoes substitution reactions like chlorination to octa-CDD (11 as well as photochemical dechlorination (12 ). Thermally, TCDD is quite stable, and rapid decomposition occurs only at temperatures above 750°C... 

POLVINYLIDENE FLUORIDE. This product is made by the free-radical chain polymerization of vinylidene fluoride (H2C=CF2). This odorless gas which has a boiling point of —82°C is produced by the thermal dehydrochlorination of 1,1,1-chlorodifluoroethane or by the dechlorination of 1,2-dichloro-l.l-difluoro-ethane. As shown by the following equations, 1,1,1-chlorodifluoroethane may be obtained by the bydroflnorination and... 

The catalytic hydro dechlorination of chlorobenzene has also been studied on Pd/Nb205 catalysts. Also in this case, the catalysts prepared under microwave irradiation are more resistant towards deactivation than the corresponding catalysts prepared under thermal conditions75. 

Friis AK, Edwards EA, Albrechtsen H-J, Udell KS, Duhamel M, Bjerg PL (2007) Dechlorination After Thermal Treatment of a TCE-Contaminated Aquifer Laboratory Experiments. Chemosphere 67 816... 

Based on the operating temperature of the desorbent, thermal desorption processes can be categorized into two types. The first is high-temperature thermal desorption (HTTD), in which waste is heated to temperatures from 320 to 560°C (600 to 1000°F). This process is frequently used in combination with incineration, solidification/stabilization, or dechlorination of SVOCs, PAHs, PCBs, and pesticides. The second type is low-temperature thermal desorption (LTTD), in which waste is heated to temperatures from 90 to 320°C (200 to 600°F). Nonhalogenated VOCs, SVOCs, and fuels can be effectively treated by LTTD. 

Dioxins 0.00001- 0.05 0.5 90-99.9 Dechlorination, soil washing, thermal destruction... 

Su C, Puls RW. Temperature effect on reductive dechlorination of trichlorethene by zero-valent metals. In Wickramanayake GB, Hinchee RE, eds. Physical, Chemical, and Thermal Technologies Proceedings of the First International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, 18-21 May 1998. Columbus, OH Battelle Press, 1998 1(5) 317-322. 

Unsubstituted 2,7-naphthyridine (50) is probably best made by oxidation of 2,7-naphthyridine-4-carbaldehyde to 2,7-naphthyridine-4-carboxylic acid (49) (KMn04, AcMe, 20°C 88%) and subsequent thermal decarboxylation (Cu powder, gentle heat 78%) 630 earlier syntheses involved direct hydrogenolysis of 1,3,6,8-tetrachloro-2,7 naphthyridine (51 R = Cl) (Pd/C, H2, MeOH, AcOK 71 %)1374 cf 22 or indirect dechlorination of l-chloro-2,7-haphthyridine (51, R = H) by hydrazi-nolysis and subsequent oxidation (ILNNIL-ILO, EtOH, 100°C then CuS04, fUO 76% overall) 1279 also homologs.188... 

Successful chlorination at a 3° carbon was reported for the acetate esters of cedryl and patchoulyl alcohols [2], Several ethers were photochemically monochlorinated at the a-position, for example THF afforded its 2-chloroderivative (51%) because of their lability, the products were isolated as esters [3], Ketones underwent Dechlorination by (dichloroiodo)benzene not only photochemically but also thermally in warm acetic acid in high yield. Under these conditions 2-butanone gave a mixture of 3-chloro- and 3,3-dichlorobutanone (80 20), whereas under photochemical conditions, in benzene, the selectivity was considerably improved (98 2). Diketones, both j8- and 5-, were similarly monochlorinated [4,5]. 

A full-scale pyrolysis-catalytic process in which the catalytic cracking zone is directly connected to the pyrolysis zone was developed in Japan (Fuji Process) [19]. In this process, after separation of PVC and impurities by wet techniques, waste plastics are thermally pretreated at 300°C for dechlorination and then introduced into the pyrolysis reactor and thermally cracked at 400°C. Subsequently, degradation products are fed directly to the fixed-bed reactor using a ZSM-5 catalyst. 

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