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978-3-8439-1642-4, Reihe Technische Chemie
Molecular Modeling of Adsorptive Interactions between Small Organic Molecules and Zeolites
152 Seiten, Dissertation Technische Universität Dortmund (2014), Softcover, A5
Experimentally, zeolites were shown to adsorb molecules such as alcohols and amino acids from aqueous phase. However, there has not been a satisfactory theoretical explanation on the underlying adsorption mechanisms yet. In this work, density functional theory (DFT) calculations and complementary experiments were performed to increase the knowledge of such adsorption mechanisms and to evaluate the potential of computational chemistry for supporting the experimentally based adsorption process design was shown.
In a first step, the chosen DFT approach was demonstrated to deliver reliable results, which was achieved by comparison with experimental and DFT data from literature for the adsorption of alcohols in the most widely investigated zeolite framework MFI. In addition, it was demonstrated that the gas phase adsorption mechanisms in zeolite BEA and MOR followed the same rule as described in literature for MFI. In a next step, the influence of the pH value on the adsorption of amino acids in MFI-type zeolite was investigated using DFT and microcalorimetric experiments. Different pH values were modeled by varying the amino acids protonation states. The investigated protonation states exhibited two different adsorption motifs in the pores, with the neutral α-C-amino group motifs being significantly less stable than the protonated ones. This result explained the pH-dependent adsorption behavior that has also been observed experimentally. To further explore if the derived model from DFT calculations for MFI was transferable to other zeolites, the adsorption behavior of alanine and glycine in BEA was investigated. Using a microsolvation model, the co-adsorption of water and formation of an intermolecular H bond system between water molecules, amino acid and zeolite was shown.
Overall, the results of this work could be valuable to support the experimental side of adsorption process design in industrial biotechnology by qualitatively predicting binding behavior by means of DFT calculations and simplified model systems.