title: 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.
authors.affiliation: Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020, USA.
authors.forename: Hefa
authors.initials: H
authors.lastname: Cheng
authors.forename: Martin
authors.initials: M
authors.lastname: Reinhard
mesh_terms: D000327:Adsorption; D004787:Environmental Pollution / Q000517:prevention & control*; D006207:Half-Life; D008956:Models, Chemical; D015394:Molecular Structure; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*; D017641:Zeolites / Q000737:chemistry*
chemical_list: D014874:Water Pollutants, Chemical; D017641:Zeolites; C489646:2,2-dichloropropane; D011407:Propane