Robust thermodynamic property prediction is vital to the design of chemical process technologies. SPEAD (Step Potential Equilibria and Dynamics) is a rapid method of vapor-liquid equilibrium property calculations using discontinuous molecular dynamics (DMD) simulations in conjunction with thermodynamic perturbation theory (TPT). Though the potential predicts vapor pressures of several compounds reasonably well, the liquid densities seem to be systematically overpredicted. Equilibrium densities provide a vital test for the accuracy and transferability of a potential, since thermodynamic properties are sensitive to small changes in densities. A new four step potential model called StePPE (Step Potentials for Phase Equilibria) is developed, based on the theory of SPEAD, which reproduces the liquid densities significantly better. The improvement in vapor pressure predictions for the compounds in this study is moderate, but the accuracy is improved for a wider range of reduced temperatures, and is better especially at lower reduced temperatures in comparison to SPEAD. Furthermore, the transferability of parameters is observed to be better than SPEAD for a broader chain length within a homologous series and from one homologous series to another, evidenced by a reduction in the number of adjustable parameters for most of the compounds studied. A guideline for obtaining the first guess of the diameters of the functional groups is developed based on the van der Waal's volumes of the sites. The optimized site diameters are observed to be close to 97% of the first guess. To provide vapor pressure data for compounds for which data is limited or unavailable in literature, new ebulliometers are designed, which can accurately measure the boiling temperatures of pure compounds using a small amount of sample. Activating the heated surface with powdered glass and the use of Cottrell type tube were observed to be effective in removing superheat. Condensate hold-up in these ebulliometers is estimated in order to use these ebulliometers for the measurement of bubble points of binary mixtures, without measuring any of the equilibrium compositions.
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