Sites where chlorobutyl rubber is produced have the potential to release a mixture of chlorinated butenes and butadienes, which are known to be toxic and persistent, into the groundwater environment. The potential contaminants include trans-1,4-dichlorobutene-2 (1,4-DCB-2), 3,4-dichlorobutene-1 (3,4-DCB-1), 2,3,4-trichlorobutene-1 (2,3,4-TCB-1), 2-chlorobutadiene-1,3 (chloroprene) and 2,3-dichlorobutadiene-1,3 (DCBD). Granular iron has been shown to reductively dechlorinate a number of compounds and has been used in permeable reactive barriers (PRBs) for in-situ groundwater remediation. To evaluate the possibility of using granular iron for the remediation of the above contaminants, a series of batch experiments were conducted. Results show that dechlorination reactions for chlorinated butenes closely followed pseudo-first-order kinetics with normalized half-lives ranging from 5.1 to 7.5 h. Chlorinated butadienes degraded much slower in batch tests with normalized half-lives ranging from 38.8 to 128 h. Chlorine mass balance calculations showed that 1,4-DCB-2, 3,4-DCB-1 and chloroprene were fully dechlorinated by granular iron. 2,3,4-TCB-1 was transformed to chloroprene as an intermediate via a reductive β-elimination pathway. Neither the presence of CaCO 3 nor temperature affected degradation rates suggesting that mass transport to iron surfaces was limiting degradation in batch tests. A column experiment was conducted on 3,4-DCB-1 and a normalized half-life of 1.6 min was found. Faster degradation in the column was thought to be due to enhanced mixing effects. 3,4-DCB-1 was converted to 1,3-butadiene via reductive β-elimination, which was then converted to a mixture of 1-butene, cis-2-butene and trans-2-butene via catalytic hydrogenation.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.