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.
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada.
Rodney
R
Hughes
Lai
L
Gui
Robert W
RW
Gillham
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