Isobaric vapor–liquid equilibrium for systems containing sulfur compounds

• Isobaric VLE data for four systems was measured in dilute solution.
• The VLE data in dilute solution were compared with that in the entire concentration.
• The activity coefficients of trace component varied a lot in its low concentration.
• The y–x of the trace component followed the quadratic polynomial equation.
• A concept of multi-scale phase equilibrium was proposed.

Isobaric vapor–liquid equilibrium (VLE) data for the binary systems of thiophenic compounds with three hydrocarbons in gasoline (2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene and n-heptane) were measured in dilute solutions at 101.33 kPa with a modified Rose–Williams still. General Coulomb meter was used to analyze the compositions of the samples from the vapor–liquid equilibrium systems. The VLE data was compared with the calculated value by the Wilson model with the interaction parameters regressed over the entire concentration range. Results found that neither the activity coefficient model nor the Henry's model could describe the VLE behavior of the trace component in the dilute solution accurately. Thus a concept of multi-scale phase equilibrium was proposed.