Arjan Giaya

Liquid and vapor phase adsorption of chlorinated volatile organic compounds on hydrophobic molecular sieves

Abstract This work focused on the potential application of various hydrophobic molecular sieves for the sorption of four model chlorinated volatile organic compounds (CVOCs, i.e., chloroform, trichloroethylene, tetrachloroethylene, and carbon tetrachloride) from dilute liquid water streams. Results obtained thus far have shown that silicalite-1 has a high affinity for these CVOCs, higher in fact than Centaur® activated carbon, used as a benchmark in this study. Loading results for trichloroethylene from both liquid and vapor phase indicated that the liquid phase did not penetrate the pores of silicalite-1, while the solution did penetrate the pores of Centaur® and a dealuminated NaY used for comparison. Finally, three definitions from the literature for the “hydrophobicity” of molecular sieves were considered. An alternative definition for hydrophobicity is introduced here, which is easy to determine and is based on water retention.

Water confined in cylindrical micropores

A model characterizing water-like fluids confined in cylindrical micropores is presented. The equation of state was derived based on perturbation theory assuming that the reference system of hard spheres confined in the cylindrical pores is homogenous. The perturbed state accounts for fluid–fluid, fluid–wall, and hydrogen bonding interactions. Fluid–fluid and fluid–wall interactions are modeled as the pairwise sum of Lennard-Jones potentials. The hydrogen bonding model accounts for the open structure of liquid water, as well as for the fact that the hydrogen bonding capabilities of confined molecules are distorted. This model was used to analyze the dependence of the density of water inside the micropores on the density outside the pores, the pore radius, and the affinity of the pore walls for water molecules. For gas-phase adsorption, the model predicts that the density of water inside the pores depends on the fluid–wall interactions. The state of the adsorbed phase varies from the density of vapor outsi...

Single-component gas phase adsorption and desorption studies using a tapered element oscillating microbalance

Adsorption equilibrium data, usually obtained using volumetric or gravimetric methods, are important for the proper design of adsorption systems. In this work, a tapered element oscillating microbalance (TEOM® series 1500 pulse mass analyzer) was used to characterize the hydrophobicity of some microporous materials, and to obtain adsorption isotherms of some chlorinated volatile organic compounds (CVOCs) on those materials. The sorption capacities of samples of silicalite-1, dealuminated zeolite Y (DAY), and activated carbon for trichloroethylene, chloroform, and water vapor were determined. A “hydrophobicity index” also was determined by monitoring water desorption at elevated temperatures. The adsorption of pure component CVOCs showed that a DAY sample had a higher limiting adsorption capacity than the silicalite-1 sample. The opposite behavior was observed when the CVOC adsorption was in the presence of water. These data supported the conclusion that water interferes with the adsorption of CVOCs in these materials, even though they exhibit significant hydrophobic character.

Response to “Comment on ‘Observations on an equation of state for water confined in narrow slit-pores’ ” [J. Chem. Phys. 117, 8162 (2002)]

In our Response to the Comment on “Observations on an equation of state for water confined in narrow slit-pores,” [J. Chem. Phys. 116, 2565 (2002)] we responded to the points raised by Truskett, Debenedetti, and Torquato. We agree with their point regarding the asymptotic limit of the excess grand potential, i.e., that it should reach a value equal to twice the fluid–wall interfacial tension. However, we also showed, using the mean-field approach, that their model of hydrogen bonding did not produce some aspects of water confined in narrow slit-pores correctly. We believe this was due to limiting the number of favorable hydrogen bonds to only pairwise interactions, while it is known from the literature that up to four favorable hydrogen bonds may be formed. And, while we did not evaluate the temperature dependence of hydrogen bonding, their predicted temperature dependence is inaccurate in some respects.