Trichloroethylene, pyrolysis

Mulholland JA, Sarofim AF, Sosothikul P, et al. 1992. Formation of perchloroaromatics during trichloroethylene pyrolysis. Combustion and Flame 89 103-115. 

Most of the ethylene dichloride produced is utilized for the manufacture of vinyl chloride, which may be obtained from it by pyrolysis or the action of caustic soda. Large quantities are also used in anti-knock additives for gasoline. As a solvent It has been displaced by trichloroethylene and tetrachloroelhyJene. U.S. production 1978 4-75 megatonnes. 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

Unreacted EDC recovered from the pyrolysis product stream contains a variety of cracking by-products. A number of these, eg, trichloroethylene, chloroprene, and benzene, are not easily removed by simple distillation and require additional treatment (78). Chloroprene can build up in the light ends... 

Pyrolysis Thermal decomposition of 1,1,1,2-tetrachloroethane produces tetrachloroethylene (by disproportionation), hydrogen chloride, and trichloroethylene via dehydrochlorination (111). The yield of the latter is increased in the presence of ferric chloride (112). Other catalytic materials include FeCl —KCl mixture (113), AlCl (6), the complex of AlCl with nitrobenzene (114), activated alumina (3), Ca(OH)2 (115,116), and NaCl (94). 

Pyrolysis. 1,1,2,2-Tetrachloroethane, like the 1,1,1,2-isomer, is thermally degraded with or without a catalytic agent to give trichloroethylene. 

An aqueous solution containing 300 ng/ iL trichloroethylene and colloidal platinum catalyst was irradiated with UV light. After 12 h, 7.4 ng/pL trichloroethylene and 223.9 ng/pL ethane were detected. A duplicate experiment was performed but 1 g zinc was added to the system. After 5 h, 259.9 ng/pL ethane was formed and trichloroethylene was nondetectable (Wang and Tan, 1988). Major products identified from the pyrolysis of trichloroethylene between 300-800 °C were carbon tetrachloride, tetrachloroethylene, hexachloroethane, hexachlorobutadiene, and hexachlorobenzene (Yasuhara and Morita, 1990). 

Yasuhara, A. and Morita, M. Formation of chlorinated compounds in pyrolysis of trichloroethylene, Chemosphere, 21(4/5) 479-486,1990. 

Figure 7.13 presents a simplified flowsheet, which concentrates the essential features the balanced VCM technology, as conceptually developed in the previous sections, but this time with the three plants and recycles in place chlorination of ethylene (Rl), thermal cracking of EDC (R2) and oxyclorinahon of ethylene (R3). As mentioned in Section 7.3, from plantwide control three impurities are of particular interest (I]) chloroprene (nbp 332.5 K), (12) trichloroethylene (nbp 359.9K), and (13) tetrachloromethane (nbp 349.8). I, and 12 are bad , since the first can polymerize and plug the equipment, while the second favors the coke formation by EDC pyrolysis. On the contrary, I3 has a catalytic effect on the VCM formation, in some patents being introduced deliberately. 

Trichloroethylene and tetrachloroethylene highly diluted in argon were also investigated behind reflected shock waves93. Both halides were believed to dissociate by Cl abstraction and the pyrolysis rates are pressure-dependent. According to the products formed and the Arrhenius parameters, the mechanism was presented in terms of consecutive reactions. 

Derivation (1) By chlorination of hydrocarbons and pyrolysis of the carbon tetrachloride also formed, (2) from acetylene and chlorine via trichloroethylene. 

At high temperatures pyrolysis of trichloroethylene and isobutene gives the same isomer 100 [160] (Reaction scheme 59). 

Yasuhara A, Morita M. Formation of Chlorinated Compounds in Pyrolysis of Trichloroethylene. Chemosphere 1990 21 479-486. 

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