A NEW GENERALIZED ALPHA-FUNCTION FOR A CUBIC EQUATION OF STATE .2. REDLICH-KWONG EQUATION

The approach described in the previous paper (Twu, C.H., Goon, J.E. an d Cunningham, J.R., 1994a. A new generalized alpha function for a cubi c equation of state. Part 1. Peng-Robinson equation. Fluid Phase Equil ibria, 105: 49-59) is applied to the Redlich-Kwong cubic equation of s tate (RK CEOS) to develop a new generalized alpha function for this eq uation. The new generalized alpha function for the RK CEOS reproduces the vapor pressure for hydrocarbons from the triple point to the criti cal point with almost identical accuracy to the generalized alpha func tion used for the Peng-Robinson CEOS in the previous paper. This indic ates that the approach developed should be a general one, applicable t o any cubic equation of state. The alpha function has been generalized in terms of the reduced temperature and acentric factor, so it can be used for any hydrocarbons and petroleum fractions, with no additional characterization to the standard methods required (Twu, 1984). The ne w alpha function is more appropriate for the RK CEOS than Soave's alph a function, which has been widely used in phase behavior calculations in the petroleum production and refinery industries over the last twen ty years.