AN APPROACH FOR THE EXTENSION OF A 3-PARAMETER CUBIC EQUATION OF STATE TO HEAVY HYDROCARBONS

A generalized temperature and acentric factor dependent function of th e attractive term, called the alpha function, of the Twu-Coon-Cunningh am (TCC) cubic equation of state (CEOS) (1992) has been developed. The approach developed in this work makes the alpha function become a lin ear function of the acentric factor at a constant reduced temperature, not a fourth order or a sixth order function as suggested by Soave an d other researchers. The advantage of a linear function in the acentri c factor is obvious in the extrapolation of the alpha function to heav y hydrocarbons and petroleum fractions. The new generalized alpha func tion, when used with the TCC CEOS, allows the accurate reproduction of the vapor pressure data from the triple point to the critical point f or hydrocarbons. The new CEOS provides much more reliable and accurate vapor pressure prediction than the SRK (Soave, 1972) or Peng and Robi nson (PR) (1976) equations for both light and heavy hydrocarbons.