I have a problem with a styrene/ethylbenzene distillation column. My system consist on styrene, ethylbenzene, toluene, benzene and alphamethylstyrene, and the work pressure is from 50 mm Hg to 200 mm Hg. I am working with the Chemcad simulator and the program adviced me to use the SRK model, but I read in the help files that for vacuum towers and heavy materials (I don't know if my components are considered heavy, but I think they are not) the ESSO model was better. In addition to this, I have compared the experimental data from DESCHEMA for the system styrene/ethylbenzene to the simulated with the program and the ESSO (Maxwell-Bonnell) data fitted better than the SRK data. The problem is not trivial, because with the SRK model at R/Rmin=1.2 the number of stages is 130 an with ESSO is 73.What model is better for my system? Thanks in advance.