The nonrandom lattice equation of state with hydrogen bonding (NLF-HB EOS) was examined for the correlation of vapor-liquid equilibria (VLE) for binary amine and hydrocarbon mixture at various temperatures. For these mixtures, the consideration of hydrogen bondings in the lattice equation of state clearly improves the prediction for VLE. The amines were divided into four groups due to the different strength of the hydrogen bonding. For all groups, different hydrogen bonding parameters were obtained and evaluated. The effects of varying hydrogen bonding energies for NLF-HB EOS are discussed. For systems containing lower amines, the NLF-HB EOS showed excellent agreement with the experimental data. For the correlation of systems containing tertiary amine molecules, binary interaction parameter had to be involved instead of hydrogen bonding parameters.
A group contribution version of the nonrandom lattice fluid equation of state (NLF-GC EOS) has been used to predict the vapor-liquid phase equilibria (VLE) of esters and their mixtures. The investigated esters were divided into groups according to the contribution scheme. Two different types of parameters were regressed from experimental datasets. Size parameters were fitted to pure component properties, and the group-group energy interaction parameters were simultaneously fitted to several binary mixture data sets. For systems containing propylene oxide, missing binary VLE data was predicted by using the COSMO-RS method. Parameters obtained by using the COSMO-RS method were later used to successfully predict experimentally measured binary propylene oxide+esters systems. The overall good prediction capability of the NLF-GC EOS could be proven for the investigated systems.
This paper proposes a simple empirical correction to improve the near-critical volumetric behavior of a classical equation of state (EOS) which overpredicts the critical point. The focus is on the alternative representation of long-range density fluctuation, an effect neglected in classical EOS, in terms of molecular clustering. To formulate the molecular clustering of interest, the Veytsman statistics is extended and fluctuation parameter is explicitly obtained as a solution to the quadratic equation. The proposed contribution was combined with a quasi-chemical nonrandom lattice fluid (QLF), which overpredicts the critical point. The combined model was found to require three clustering parameters besides three classical parameters and tested against vapor-liquid equilibrium data consisting of 43 nonpolar and polar components. The calculation results showed that the combined model satisfactorily represents the flattened part of the critical isotherm curve for methane as well as the top of the coexistence curve for the tested components.
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