Effect of the power series dispersion term on the pressure-volume behaviorof statistical associating fluid theory

It is shown that the statistical associating fluid theory (SAFT) equation o f state with the power series dispersion term can have multiple volume root s at a specified pressure and temperature. Examples considered are based on published correlations for the nonassociating pure components methane and poly(ethylene-propylene) 790 (PEP790). Conditions have been found where two of the five volume roots (one mechanically stable and one unstable) occur at reduced densities greater than theoretical close packing and the equatio n of state has a large negative pressure in the nominal close-packed state. The SAFT fluid can have the least chemical potential at the smallest volum e root, which appears not to have been considered in the correlation of the methane and PEP790 behavior.