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FINAL REPORT - Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments

Description: A magnetically coupled microbalance system has been used to measure adsorption and desorption isotherms and rates of desorption for carbon tetrachloride on dry prepared porous silica particles with narrow pore size distributions in the mesoporous range. Pore size distributions estimated from the carbon tetrachloride isotherms were found to be in close agreement with those determined using standard low temperature nitrogen adsorption. Three different types of particles were studied, with average pore diameters of 2.7 nm, 4.6 nm, and 5.9 nm. Prior to desorption rate studies, evacuated particulate samples were charged with volatile organic vapor at pressures sufficient to fill all mesopores with condensed fluid. Desorption rates into dry flowing helium were determined at 25 °C and atmospheric pressure, using the microbalance system combined with chromatographic analysis of the exit helium stream. Initial rates were found to decrease significantly, as mass adsorbed decreased. This residual mass was desorbing at such a low rate, that it can be considered a migration resistant fraction of the original mass adsorbed. Attempts to remove this residual mass at higher temperatures were partially successful; however, differences between the microbalance and gas chromatograph responses leave open uncertainty about whether the residual mass was pure carbon tetrachloride. To date, attempts at analysis of the residual mass using solvent extraction have not removed completely this uncertainty. For particles prepared using the same template surfactant, but with different average pore sizes, desorption rates were higher for the larger-pore particles, with correspondingly lower residual mass. Particles prepared with another template surfactant did not follow this pattern, exhibiting intermediate desorption rates and slightly lower residual mass, even though these particles had the smallest pores. These particles exhibited desorption isotherm behavior characteristic of larger pores connected by smaller openings. Except for peculiar behavior in the very early part of desorption experiments for one ...
Date: December 11, 2006
Creator: Miller, Dr. Reid C. & Peyton, Dr. Brent M.
Partner: UNT Libraries Government Documents Department