Predicting branching structure effects on the thermodynamic properties using COSMO-RS
Advancing the chemical engineering fundamentals
Thermodynamics (T2-1P)
Keywords: QUANTUM CHEMISTRY; COSMO-RS; DFT;PHASE EQUILIBRIA
Hyperbranched compounds have many applications including the use as entrainers in separation processes and as drug carriers. Most of these applications rely on their branching and the arrangement of functional groups within the structure. Tailoring a hyperbranched compound to a specific application requires the knowledge of the thermo-physical properties of the molecule. The COSMO-RS model has been proven to be a reliable tool for predicting the interaction behaviour in compounds. It has been shown that the quality of predictions rely on the quality of molecular structures calculated by quantum chemical methods, particularly the consideration of the different conformers of a molecular structure is mostly significant.
Hyperbranched compounds have a large number of conformers, because of their complex molecular structure. Here we present an approach to determine the relevant conformers of such structures and their influence on the phase behaviour. For this reason the compound polyglycerine with 20 hydroxyl-groups has been chosen as a model compound. From NMR spectroscopic data a three dimensional structure is derived. This structure is then pre-optimized using molecular mechanics incorporating the MM3 force field and further optimized by DFT quantum calculations. The optimized molecule serves as the starting structure for a conformer search in the gas phase. The large number of conformers is reduced by energy clustering. To take into account the influence of the surrounding medium, molecular dynamics simulations are performed subsequently on all remaining structures.
The quality of the simulations and the influence of the conformers are tested by the calculation of the phase equilibria of polyglycerine/water and polyglycerine/ethanol and polyglycerine/ethanol/water mixtures.
Presented Monday 17, 13:30 to 15:00, in session Thermodynamics (T2-1P).
