Record:   Prev Next
Author Cheng, Hefa
Title Sorption and hydrolysis of chlorinated aliphatic hydrocarbons in hydrophobic micropores
book jacket
Descript 134 p
Note Source: Dissertation Abstracts International, Volume: 67-09, Section: B, page: 5317
Adviser: Martin Reinhard
Thesis (Ph.D.)--Stanford University, 2006
This study examined the sorption and hydrolysis of chlorinated aliphatic hydrocarbons, trichloroethylene (TCE) and 2,2-dichloropropane (2,2-DCP), in synthetic and natural microporous solids. The objective was to elucidate the mechanism of micropore sorption and its impact on transformation of hydrophobic organic contaminants. First an experimental method was developed to quantify the hydrophobic micropore volumes of geosorbents based on the mass desorbed in the slow-desorbing fraction. For sediment from an alluvial aquifer, the total and hydrophobic micropore volumes were estimated to be 4.65 muL/g and 0.027 muL/g (0.58% of total), respectively. Sorption of water and the dehydration behavior of three dealuminated Y zeolites ranging from moderately hydrophilic to hydrophobic showed that hydrophilic centers (surface cations and hydrogen bonding sites) present in zeolite micropores determine their water affinity. At a partial pressure of 0.136, TCE filled only 0.034% of the micropore volume in wet CBV-300 (surface cation density: 2.07 site/nm 2), but 16.9% and 18.6% in wet CBV-720 and CBV-780 (surface cation densities: 0.42 and 0.16 site/nm2), respectively. It was concluded that sorption in hydrophobic micropores is a displacement process driven by the enthalpy gain of loosely bound water transferred from the micropores to bulk water and the entropy gained by removing dissolved TCE from water
Hydrolytic transformation experiments show that only 81.5%, 6.3%, and 5.0% of 2,2-DCP molecules in micropores of CBV-300, CBV-720, and CBV-780 underwent dehydrohalogenation after incubation at 50°C for 10 h, respectively, less than the >99.99% expected in aqueous solutions. Results also indicate that 2,2-DCP molecules sorbed near the pore openings transformed faster than those sorbed deeper in the hydrophobic micropores. Inhibition effect was also observed for 2,2-DCP dehydrohalogenation in geosorbent micropores. Inhibition of hydrolytic transformation was attributed to the lack of solvation by water and the lower water activity in hydrophobic micropores. Results also suggest that 2-chloropropene produced from 2,2-DCP dehydrohalogenation further inhibited transformation of the remaining 2,2-DCP by blocking its contact with water in hydrophobic micropore spaces. These results suggest that sorption in hydrophobic micropores of geosorbents is a possible mechanism for the observed preservation of hydrolyzable organic contaminants in the subsurface
School code: 0212
Host Item Dissertation Abstracts International 67-09B
Subject Environmental Sciences
Engineering, Environmental
Alt Author Stanford University
Record:   Prev Next