Competitive desorption of carbon tetrachloride + water from mesoporous silica particles

Matthew Bywater Mower

Equilibrium and desorption rate studies have been conducted for carbon tetrachloride + water on prepared mesoporous silica particles with mean pore sizes of 27 Å and 47 Å. Partial carbon tetrachloride isotherms were obtained for the purpose of determining the equilibrium amount of carbon tetrachloride required to completely fill the pores. The total volume of carbon tetrachloride adsorbed by the 27 Å particles agreed with previous work done on these particles. A novel measurement technique was developed to measure the very high carbon tetrachloride desorption rates (> 0.1 g/g sample/h) encountered at the start of a sweep experiment, by use of gas chromatography. By performing a carbon tetrachloride sweep using 27 Å particles, current measurement techniques were found to yield data in close agreement with prior work. Empty holder sweeps were done to determine release rates of carbon tetrachloride from the gas phase of the microbalance cell under standard operating conditions. The amount of carbon tetrachloride from integration of these rate curves agreed with ideal gas law calculations based on the estimated cell volume. The empty holder sweep results were used to correct desorption rates of carbon tetrachloride for sweep experiments with particles present. Water and carbon tetrachloride + water mixtures were loaded onto both types of particles, and amounts of each component determined for both the gas phase and the adsorbed phase. It was found that a much smaller volume of pure water was adsorbed by both particles than for pure carbon tetrachloride. However, the volumes of mixtures loaded were higher than pure water for the 47 Å particles and were both lower and higher than pure water for the 27 Å particles. Sweeps were performed on both particles loaded with pure water and carbon tetrachloride + water mixtures, to determine total and individual component desorption rates. It appeared that pore size had a small effect on the overall desorption rates, with slightly higher rates for the larger pore particles. However, the more water initially loaded on the particles, the larger the total amount of mass remaining on the particles at the end of a sweep. It appeared that the residual mass for the mixture sweeps was mostly water. In spite of the improved accuracy with which the early parts of the sweeps were defined, it was not possible to quantify the amounts of each component in the residual masses by integration of the individual rate curves. An analytical technique still needs to be developed to measure the amount of carbon tetrachloride remaining on the particles at the end of a sweep experiment.

Competitive desorption of carbon tetrachloride + water from mesoporous silica particles

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