LATTICE FLUID HYDROGEN-BONDING MODEL WITH A LOCAL SEGMENT DENSITY

A new version of a lattice fluid hydrogen bonding (LFHB) model is pres ented to improve the predictions of the thermodynamic properties of as sociating fluids. The model utilizes the physical contribution to the free energy in the statistical association fluid theory (SAFT). The as sociation term is described by the local density instead of the bulk d ensity, which was used in the original versions of the theory. With th ese two modifications, predictions are improved significantly for hard sphere molecules with association sites and for real molecules. Resul ts are presented for the densities and vapor pressures of pure water a nd 1-alkanols, and for the phase equilibria and association of a mixtu re of benzophenone and water. The predicted degree of hydrogen bonding for pure supercritical water compares quite favorably with molecular dynamics simulation data. Unlike the case for the SAFT model. associat ion depends upon pressure in the new model because of the volume chang e upon hydrogen bond formation.