Transferable Intermolecular Potentials for Nitrates and Phosphates
Advancing the chemical engineering fundamentals
Thermodyanmics: Molecular Simulation & Related Approaches (T2-1d)
Keywords: Nitrates, phosphates, environmental, vapor pressure, octanol-water partitioning.
The Step Potential Equilibria And Discontinuous Molecular Dynamics (SPEADMD) model provides a basis for molecular modeling of thermodynamic and transport properties. It is based on Discontinuous Molecular Dynamics (DMD) and second order Thermodynamic Perturbation Theory (TPT). DMD simulation is applied to the repulsive part of the potential, complete with molecular details like interpenetration of the interaction sites, 110 degree bond angles, branching, and rings.[1,2] The thermodynamic effects of disperse attractions and hydrogen bonding are treated by TPT. This approach accelerates the molecular simulations in general and the parameterization of the transferable potentials in particular. Transferable potentials have been developed and tested for over 250 components comprising 25 families. These families include thiophene, fluorocarbon, alcohol, amine, aromatic, and ring compounds to name just a few examples.[3,4] Methods of predicting the thermodynamic properties are especially valuable when properties are difficult to measure, as for chemicals that are explosive or toxic. This is the case for many nitrates and phosphates.
Nitrates are of special interest in defense and mining applications. New compounds are constantly being sought to enhance stability and reduce toxicity. Being able to leverage a few measurements for a few compounds and predict the properties of isomers and larger molecules is especially valuable. For environmental applications the octanol-water partition coefficient and vapor pressures are of particular interest. We have simulated all the nitrate compounds in the DIPPR database and characterized the interactions for a wide range of molecular structures. Vapor pressures are generally accurate to 15% error.
Phosphates have traditionally played roles as pesticides and nerve poisons. Very few data are available. Nevertheless, we have characterized the phosphate interactions and find accuracy to be near 15% for vapor pressure where data are available. Correlations for octanol-water partition coefficients and preliminary results for correlation of thermochemical properties based on quantum simulation are also presented.
Reference:
1 J. Cui and J. R. Elliott, J. Chem. Phys. 114 (2001) 7283.
2 O. Unlu, N. H. Gray, Z. N. Gerek, and J. R. Elliott, Ind. Eng. Chem. Res. 43 (2004) 1788-1793.
3 N. H. Gray, Z. N. Gerek, and J. R. Elliott, Fluid Phase Eq. Vol 228-229C (2005) 147-153.
4 F. S. Baskaya, N. H. Gray, Z. N. Gerek, and J. R. Elliott, Fluid Phase Eq. 236 (2005) 42-52.
Presented Tuesday 18, 11:20 to 11:40, in session Thermodyanmics: Molecular Simulation & Related Approaches (T2-1d).
