Reduction of 1,2‐dibromoethane in the presence of zero‐valent iron

Abstract

Abstract-The degradation reaction of 1,2-dibromoethane (ethylene dibromide or EDB) in water was studied in the presence of zero-valent iron (acid-cleaned, cast iron) in well-mixed batch aqueous systems. The observed products were ethylene and bromide ions. Carbon and bromine mass recoveries of Ͼ95% were obtained. Bromoethane and vinyl bromide were not observed. The reduction rates of bromoethane and vinyl bromide with iron indicate that they should have been observed if they were significant reaction intermediates for EDB. The results indicate that reductive ␤-elimination may be the dominant reaction pathway. Reaction kinetics are rapid and pseudo-first order. The activation energy was determined to be 50 kJ/mol, indicating that the reaction rate may not be aqueous phase diffusion controlled but rather controlled by the chemical reaction rate on the iron surface. Metallic iron may be a suitable treatment approach for EDB-contaminated groundwater in above-ground, as well as in situ applications, due to rapid kinetics and nontoxic products.

Mass Transfer Effects on Kinetics of Dibromoethane Reduction by Zero-Valent Iron in Packed-Bed Reactors

“…The only organic product detected was ethylene and the carbon mass balance was near 100%. This is in agreement with Rajagopal and Burris (1999) who studied the reduction of EDB by Fisher 40-mesh cast iron. They determined that ethylene was the major product of EDB reduction and that no bromoethane or vinyl bromide was formed.…”

“…In similar experiments (5g Fisher 40 mesh iron and 100 mLDI) the half life of EDB was found by Rajagopal and Burris (1999) to be 1.3 h, and the approximate half lives of 1,1,1-trichloroethane, TCE and PCE were 1.6, 24, and 120 h, respectively (Johnson et al 1996;Campbell et al 1997). The faster reaction kinetics of EDB reduction by ZVI would allow for shorter residence times, possibly expanding the engineered treatment options available for EDB contaminated groundwaters.…”

“…Relative response factors were determined for EDB (dimensionless Henry's constant at 20°C was 0.035) and ethylene (H=8.9) (Sanders 1999), by adding known masses to 160 ml vials containing the same liquid/ vapor ratio as the reaction vials. Standards were equilibrated at the same temperature as the reaction vials (Rajagopal and Burris 1999).…”

“…k y at 20°C was found to be independent of initial EDB concentration (0.011-0.12 mM) and independent of mixing rate at rotation speeds greater than 8 rpm (data not shown). The portion of EDB in the headspace was less than l()9£ (Rajagopal and Burris 1999), thus the vapor-liquid partitioning was not expected to significantly affect the reaction kinetics. An Arrhenius plot [Eq.…”

“…More recently, Rajagopal and Burris (1999) found that when EDB in water was exposed to Fe° the only observed products were ethylene and bromide BrH 2 CCII 2 Br+Fc°^H 2 CCH 2 + 2Br+Fe 2 (1)…”