Volume expansion behavior of water–hydrocarbon mixtures at high temperatures and pressures as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with toluene and ethylbenzene have been measured at temperatures and pressures in the 473–623 K and 100–350 bar ranges, respectively. Concentrations of water and hydrocarbons in the hydrocarbon-rich phase have been estimated from the integrated band intensities, and using these results, densities of the hydrocarbon-rich phase have been obtained as a function of temperature and pressure. In order to characterize the density of the hydrocarbon-rich phase, the experimental densities have been compared with the average densities before mixing, which were calculated from the literature densities of pure water and pure hydrocarbon with the experimental concentrations. All the experimental densities of the mixtures are lower than the average densities before mixing at the same condition. Relative volume change for mixing has been estimated and an anomalously large increase in volume has been found in the vicinity of the critical region of the water–hydrocarbon mixtures. This volumetric behavior is very similar to that previously found for water–benzene mixtures, and may be characteristic of the critical behavior of fluid mixtures of water and hydrocarbons.