Degradation of chlorinated butenes and butadienes in granular iron columns.
Manufacturing facilities for production of chlorobutyl rubber have the potential to release a mixture of at least 5 chlorinated butenes and butadienes including trans-1,4-dichlorobutene-2 (1,4-DCB-2), 3,4-dichlorobutene-1 (3,4-DCB-1), 2,3,4-trichlorobutene-1 (TCB), 2-chlorobutadiene-1,3 (chloroprene) and 2,3-dichlorobutadiene-1,3 (DCBD) into groundwater environment. To evaluate the potential of using granular iron in the remediation of the above contaminants, a series of column experiments were conducted. Degradation of all 5 compounds followed pseudo-first-order kinetics. The three chlorinated butenes degraded much faster (surface area normalized half-lives, t(1/2)', ranged from 1.6 to 5.2 min m2/mL) than the 2 chlorinated butadienes (t(1/2)' ranged from 102 to 197 min m2/mL). All contaminants fully dechlorinated by granular iron to 1,3-butadiene as a common reaction intermediate that then degraded to a mixture of relatively non-harmful end products consisting of 1-butene, cis-2-butene, trans-2-butene and n-butane. Based on the kinetic data, product distributions, and chlorine mass balances, reaction pathways for these compounds are proposed. For the chlorinated butenes, 3,4-DCB-1 and TCB, undergo reductive beta-elimination reactions resulting in 1,3-butadiene and chloroprene intermediates. Dechlorination of 1,4-DCB-2 to 1,3-butadiene occurs through a reductive elimination similar to reductive beta-elimination. For dechlorination of the two chlorinated butadienes, chloroprene and DCBD, dechlorination occurs through a hydrogenolysis pathway. The common non-chlorinated intermediate, 1,3-butadiene, undergoes catalytic hydrogenation resulting in a mixture of butane isomers and n-butane. The results suggest that granular iron is an effective material for treatment of groundwater contaminated with these compounds.
Hughes
Rodney
R
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada.
Gui
Lai
L
Gillham
Robert W
RW
D002070:Butadienes / Q000737:chemistry*; D002073:Butanes / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002617:Chemical Industry; D006207:Half-Life; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D012408:Rubber; D014881:Water Supply / Q000032:analysis
D002070:Butadienes; D002073:Butanes; D006843:Hydrocarbons, Chlorinated; D002244:Carbon; D012408:Rubber; D007501:Iron