Thermodynamics of semicontinuous n-alcohol/ultra-low sulfur diesel blends

Two methods for calculating activity coefficients of ultra-low sulfur diesel (ULSD) and its blends with pure alcohols (C1–C5), namely, UNIFAC-continuous and UNIFAC-Dortmund-continuous, are presented. ULSD was modeled as a continuous blend of paraffins, naphthenes, and aromatics. The molar distribution in each family was expressed as a function of carbon number using the gamma distribution function. The parameters of the distribution function can be easily fitted from experimental distillation data of ULSD and extrapolated to n-alcohol/ULSD blends. The activity coefficients obtained were used to model the ASTM D86 distillation curves. UNIFAC-Dortmund-continuous exhibited the best fitting to the experimental results. Based on that, three new correlations for calculating the boiling point, vapor pressure and structural groups of complex ULSD are proposed here.