Sorption and Inhibited Dehydrohalogenation of 2,2-Dichloropropane in Micropores of Dealuminated Y Zeolites

Abstract

Contaminant transformation rates in the subsurface can be slowed by sorption onto geosorbents. We evaluated the effect of micropore sorption on contaminant transformation in a model system consisting of dealuminated Y zeolites and 2,2-dichloropropane (2,2-DCP). 2,2-DCP dehydrochlorinates in water to 2-chloropropene (2-CP) at a rate of 2.93 x 10(-4) min(-1) at 24 degrees C. The Y zeolites used range from hydrophilic (CBV-300) to hydrophobic (CBV-720 and CBV-780). Wet zeolite samples were loaded with 2,2-DCP at 24 degrees C and reacted at 50 degrees C for 10 h. Results show that the hydrophobic zeolites (CBV-720 and CBV-780) sorbed nearly 900 times more 2,2-DCP than the hydrophilic CBV-300 under wet conditions. 2,2-DCP transformed less when sorbed in micropores of CBV-720 (6.3%) and CBV-780 (5.0%) than in micropores of CBV-300 (81.5%), and significantly less than in water (> 99.85%). Inhibition in hydrophobic micropores is interpreted as lack of water solvating the transition state of 2,2-DCP dehydrohalogenation and the H+ and Cl- formed. Near the micropore openings, the transformation was relatively fast, consistent with greater abundance of water associated with the hydrophilic edge sites. These results indicate that in the subsurface the half-lives of reactive organic contaminants may be longer than predicted from bulk water data.