Molecular Simulation of the Adsorption of Organics From Water

Yazaydin, Ahmet Ozgur

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Molecular Simulation of the Adsorption of Organics From Water

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Molecular simulations have become an important tool within the last few decades to understand physical processes in the microscale and customize processes in the macroscale according to the understanding developed at the molecular level. We present results from molecular simulations we performed to study the adsorption of hazardous organics in nanoporous materials. Adsorption of water in silicalite, a hydrophobic material, and the effect of defects were investigated by Monte Carlo simulations. Silanol nests were found to have a big impact on the hydrophobicity of silicalite. Even the presence of one silanol nest per unit cell caused a significant amount of water adsorption. We also investigated the effect of four different cations, H+, Li+, Na+, and Cs+. Their presence in silicalite increased the amount of water adsorbed. Monte Carlo and molecular dynamics simulations of MTBE adsorption in silicalite, mordenite, and zeolite beta with different Na+ cation loadings were carried out. The results revealed the importance of the pore structure on the adsorption of MTBE. Although these three zeolites have similar pore volumes, zeolite beta, with its pore structure which is mostly accessible to MTBE molecules, is predicted to adsorb significantly more MTBE than silicalite and mordenite. The Na+ cation loading, up to four cations does not have a significant effect on the adsorption capacity of the zeolites studied here, however, for silicalite and zeolite beta increasing the Na+ content increases the amount adsorbed at very low pressures. A new force field was developed by Monte Carlo simulations for 1,4-Dioxane, an important industrial solvent which has emerged as a potentially significant threat to human health. The objective was to develop reliable atom-atom interaction parameters to use in the simulations of the adsorption of 1,4-Dioxane in different adsorbent materials. Predictions of critical point data, liquid and vapour densities, heats of vaporization with our new force field were in good agreement with experimental data and outperformed predictions from simulations with other force field parameters available in literature. To obtain the isotherms of MTBE and 1,4-Dioxane adsorption from water in silicalite Monte Carlo simulations were performed. First we optimized the interaction parameters between the atoms of silicalite and the atoms of MTBE and 1,4-Dioxane. Using these optimized parameters we simulated the adsorption of MTBE and 1,4-Dioxane from water in silicalite. Despite the agreement of simulated and experimental isotherms of pure components, simulated isotherms of MTBE and 1,4-Dioxane adsorption from water in silicalite did not yield satisfactory results. Monte Carlo simulations were performed to investigate the affinity between two hazardous materials, PFOA and 1,1-DCE; and four different zeolites. Binding energies and Henryâ€™s constants were computed. For both PFOA and 1,1-DCE zeolite-beta had the highest affinity. The affinity between activated carbon with polar surface groups and water, and 1,4-Dioxane were investigated to shed light on why activated carbon is ineffective to remove 1,4-Dioxane from water. Results showed that presence of polar surface groups increased the affinity between water and activated carbon, while the affinity between 1,4-Dioxane and activated carbon was not effected by the presence of polar surface groups.

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