Degradation of chlorinated butenes and butadienes by granular iron

• Published in: WIT Transactions on Ecology and the Environment 2008-01, Vol.I, p.295-304
• Main Authors: Saberi, H K, Nikraz, H
• Format: Article
• Language: English
• Subjects: Butadiene; Butenes; Calcium carbonate; Catalytic converters; Chlorination; Chlorine; Contaminants; Dechlorination; Degradation; Groundwater; Groundwater pollution; Groundwater treatment; Half-life; Iron; Kinetics; Mass balance; Mass transport; Permeable reactive barriers; Pollution prevention; Reaction kinetics; Remediation; Rubber
• ISSN: 1746-448X; 1743-3541
• DOI: 10.2495/WP080291

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 beta -elimination pathway. Neither the presence of CaCO3 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 beta -elimination, which was then converted to a mixture of 1-butene, cis-2-butene and trans-2-butene via catalytic hydrogenation.