MedeAGIBBS
   
Predicting Adsorption and Liquid/Gas Thermodynamic Properties from Monte Carlo Simulations

Scope

MedeA-GIBBS offers state-of-the-art computational capabilities to predict thermodynamic properties such as adsorption isotherms of gas mixtures in nanoporous materials, vapor pressures of pure compounds and mixtures, Joule-Thomson coefficients, and the phase behavior under high pressure and temperature. Combined with comprehensive structural databases such as the Inorganic Crystal Structure Data (ICSD) database and advanced quantum mechanical methods such as VASP and Phonon capabilities, which are an integral part of Materials Design's technology platform MedeA, the GIBBS module expands MedeA's capabilities into the realm of thermophysical properties of fluids and fluid/solid interfaces. These capabilities are of particular importance in the domain of nanomaterials, where complex topologies can lead to novel and unexpected behavior. MedeA-GIBBS allows exploring the thermodynamic and entropic consequences in such systems, thus providing a sound basis for the interpretation of experiments and the design of novel materials.

The GIBBS program is the result of a major ongoing joint research effort by the group of Prof. Alain Fuchs (CNRS and University of Paris, France) and the Institut Français du Pétrole. GIBBS represents a state-of-the-the-art implementation of the Gibbs ensemble Monte Carlo method and related approaches and features a number of innovative and advanced capabilities.

Capabilities

Systems and Statistical Ensembles

  • Thermophysical properties of single phase, multicomponent systems
  • Calculation of equilibria of two-phase liquid-gas, liquid-liquid or multiphase liquid-liquid-gas systems for constant volume or constant pressure
  • Adsorption isotherms in nanoporous structures by representing the steric and electrostatic interactions with the solid phase in the form of a three-dimensional grid

Types of Molecules

  • Rigid molecules with or without charges
  • Flexible linear, branched, and monocyclic molecules without charges, e.g. alkanes and isoalkanes
  • Semi-flexible molecules, e.g. olefins
  • Semi-flexible molecules with charges, e.g. alcohols, mercaptanes, thioethers

Types of Potentials

  • All-atom potentials
  • Anisotropic united atom (AUA) potentials

Types of Interaction Energies

  • Dispersion-repulsion (Lennard-Jones centers) with cut-off and long-distance correction
  • Mixing rules according to Lorentz-Berthelot, Kong, and Waldmann-Hagler for the evaluation of cross-terms
  • Electrostatic energies with cut-off distance
  • Ewald summation
  • Polarization of Lennard-Jones centers

Types of Monte-Carlo Moves

  • Translation of single molecules or all molecules - all statistical ensembles
  • Rotation of single molecules or all molecules - all ensemble
  • Partial re-growth of flexible molecules - all ensembles
  • Rotation of one center around centers of nearest-neighbors for flexible molecules - all ensembles
  • Pivoting
  • Reptation for linear molecules - all ensembles
  • Volume changes for all molecules - single-phase NPT and Gibbs ensemble
  • Transfer between phases, all molecules - Gibbs ensemble

Application example

Separation processes are of critical importance in the chemical and petrochemical industry. In this context, zeolites play a prominent role. Given the wide compositional and structural richness of this class of materials, the selection and optimization of the best materials is a challenging problem. Simulations can help in this process, thus gaining focus and time. As an illustrative example of the use of GIBBS, this application shows the separation of paraxylene from metaxylene by adsorption in NaY, KY, BaX and NaX faujasites (Eluxyl process). The adsorption isotherms are computed using the GIBBS approach. The characteristic behavior of each zeolite is correctly predicted [6], thus demonstrating the viability of the present computational method.

References

  1. A. Boutin, A. H. Fuchs, and P. Ungerer, "New optimization method for intermolecular potentials - Optimization of a new anisotropic united atoms potential for olefins - Prediction of equilibrium properties", J. Chem. Phys 118, 3020 (2003)
  2. E. Bourasseau, P. Ungerer, and A. Boutin, "Prediction of Equilibrium properties of cyclic alkanes by Monte Carlo simulation - new anisotropic united atoms potential - new transfer bias method", J. Phys. Chem. B 106, 5483 (2002)
  3. V. Lachet, S. Buttefey, A. Boutin, and A. H. Fuchs, "Molecular simulation of adsorption equilibria of xylene isomer mixtures in faujasite zeolites. A study of cation exchange effect on adsorption selectivity", Phys. Chem. Chem. Phys. 3, 80-8 (2001)
  4. J. Delhommelle, C. Tschirwitz, P. Ungerer, G. Granucci, P. Millié, D. Pattou, and A. H. Fuchs, "Derivation of an optimized potential model for phase equilibria (OPPE) for sulfides and thiols", Journal of Physical Chemistry B 104, 4745 (2000)
  5. B. Neubauer, B. Tavitian, A. Boutin, and P. Ungerer, "Molecular simulations on volumetric properties of natural gas", Fluid Phase Equilibria 161, 45 (1999).
  6. V. Lachet, A. Boutin, B. Tavitian, and A. H. Fuchs, Langmuir 15, 8678 (1999).
 
 

 

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