| Understanding the phase behavior of asymmetric hydrocarbon mixtures (i.e., those containing hydrocarbons with large size differences) is important for many industrial applications. Consider, as an example, Fischer-Tropsch synthesis with a slurry bubble column reactor. Asymmetric mixture phase behavior is of interest for modeling reactor phase equilibria, the separation of the catalyst from the wax, and fractionation of the wax product. The objective of this study was to improve our understanding of asymmetric hydrocarbon mixtures by fundamental experimental measurements and by evaluation and improvement of existing equations of state.; Vapor-liquid equilibrium (VLE) compositions were measured for binary mixtures of hexane with hexadecane, 1-hexadecene, 1-hexadecanol, tetracosane, squalane, and hexatriacontane at temperatures from 473 to 623 K and pressures from approximately 6 bar up to the mixture critical points. For all systems measured, Type I phase behavior was observed, and critical locus curves extended to higher pressures with increasing system asymmetry. Comparison of the three hexane + C16 backbone systems indicates that the presence of a double bond has little effect on phase behavior, but the effect of the hydroxyl group is significant.; The modeling of asymmetric hydrocarbon mixtures was examined using two equations of state, Peng-Robinson and SAFT. Peng-Robinson was found to fit the three hexane + C16 backbone systems, but its ability to model mixtures of hexane with the longer-chain alkanes decreased as the molecular weight of the alkane chain increased. By fitting pure component parameters to vapor pressures and liquid densities instead of critical properties, an improved fit of Peng-Robinson to binary mixtures of hexane with long-chain alkanes was obtained.; The SAFT equation was found to be capable of predicting liquid-phase compositions for all of the alkane mixtures measured, as the optimized binary interaction parameters were essentially constant for all systems and temperatures. However, SAFT consistently underpredicted vapor-phase solute solubilities. |
