title: Dechlorination of lindane, dieldrin, tetrachloroethane, trichloroethene, and PVC in subcritical water.
abstract: Pure water has been used to dechlorinate aliphatic organics without the need for catalysts or other additives. Dehydrohalogenation (loss of HCI with the formation of a double bond) occurred at temperatures as low as 105-200 degrees C for 1,1,2,2-tetrachloroethane, lindane (1,2,3,4,5,6-hexachlorocyclohexane, gamma-isomer), and dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-endo, exo-1,4:5,8-dimethanonaphthalene). Complete loss of the parent compounds was achieved in less than 1 h at 150, 200, and 300 degrees C for 1,1,2,2-tetrachloroethane, lindane, and dieldrin, respectively. The initial dechlorination of lindane had an activation energy of 84 kJ mol(-1) with an Arrhenius pre-exponential factor of 1.5 x 10(6) s(-1). Dehydrohalogenation of lindane formed trichlorobenzenes, followed by subsequent hydrolysis and hydride/chloride exchange to form chlorophenols, lower chlorobenzenes, and phenol as the major final product. Reaction of poly(vinyl chloride) at 300 degrees C for 1 h formed aromatic hydrocarbons ranging from benzene to anthracene and a char residue with a ca. 1:1 carbon-to-hydrogen ratio (mol/mol). The residue contained <1 wt % of chlorine compared to 57 wt % chlorine in the original polymer. All compounds tested yielded chloride ion as the major product (at higher temperatures), indicating that complete dechlorination of some aliphatic organochlorines may be feasible.
authors.affiliation: Energy and Environmental Research Center, University of North Dakota, Grand Forks 58202, USA.
authors.forename: Alena
authors.initials: A
authors.lastname: Kubatova
authors.forename: Arnaud J M
authors.initials: AJ
authors.lastname: Lagadec
authors.forename: Steven B
authors.initials: SB
authors.lastname: Hawthorne
mesh_terms: D002713:Chlorine / Q000737:chemistry*; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D006868:Hydrolysis; D011143:Polyvinyl Chloride / Q000737:chemistry; D013696:Temperature; D018508:Water Purification / Q000379:methods*; D014881:Water Supply
chemical_list: D006843:Hydrocarbons, Chlorinated; D002713:Chlorine; D011143:Polyvinyl Chloride