A SQUARE-WELL BASED EQUATION OF STATE TAKING INTO ACCOUNT THE CONNECTIVITY IN CHAIN MOLECULES

An equation of state for chain molecules is developed. It uses a hard- chain reference term based on the theory of Wertheim. Attractive inter actions are described using a square-well potential with temperature-d ependent well width. The proposed model accounts for the connectivity of the chain segments also in the attraction term using the analytical expression for the radial distribution function at contact for chain fluids derived by Chiew. For the description of a pure component three parameters are required: segment number, segment diameter and the squ are-well potential depth describing the segment-segment interactions. These parameters were estimated for numerous substances, Vapor pressur es and Liquid densities of volatile fluids as well as polymer densitie s can be reproduced with high accuracy. A comparison with the original SAFT model and the modified GFD theory shows that the proposed equati on of state can fit the pure-component behavior better than the other two models. (C) 1998 Elsevier Science B.V. All rights reserved.