Degradation of chlorinated butenes and butadienes in granular iron columns

Abstract

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 β-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 β-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.

Keywords:

• Chlorinated butenes
• chlorinated butadienes
• 1,3-butadiene
• reductive elimination
• hydrogenolysis
• catalytic hydrogenation
• granular iron
• kinetics
• mass balance

Acknowledgments

Funding for this research was provided through the NSERC/DuPont/EnviroMetal Industrial Research Chair held by R.W. Gillham. The authors thank Mr. Wayne Noble for technical assistance in the laboratory.

Notes

∗Calculated values for K_H using method outlined in Schwarzenbach et al.^{[ 25 ]} 206–207.

∗∗Solubility data not available from literature, this is the aqueous concentration achieved during laboratory experiments from this study. Actual solubility is expected to be higher.

^a Concentration at final sampling event.

^a Calculated mass balances based on concentrations measured with samples taken from the sampling ports closet to the effluent ends.