Measurement of the Speed of Sound in Near-Critical and Supercritical <i>n</i>‑Heptane at Temperatures from (513.40 to 650.90) K and Pressures from (2.5 to 10.0) MPa

The speed of sound in <i>n</i>-heptane was measured by the Brillouin light scattering (BLS) method. The examined region is <i>T</i> = (513.40 to 650.90) K along seven isobaric lines at <i>p</i> = (2.5, 3.0, 4.0, 5.0, 6.0, 8.0, and 10.0) MPa, which was near the critical point of <i>n</i>-heptane. The relative expanded uncertainty (<i>k</i> = 2) of BLS experimental system is estimated to be <0.013 for the speed of sound measurement. The variation tendencies of the speed of sound with increasing temperature and pressure were illustrated. Moreover, the calculated results from the multiparameter equation of state (EOS) proposed by Span and Wagner were employed to assess the experimental data in this paper. The absolute average of the deviations (AAD) between the experimental data and the calculated results is 1.22% in the whole investigated <i>p</i>–<i>T</i> region

Mesoscopic Diffusion of Poly(ethylene oxide) in Pure and Mixed Solvents

We present results from an experimental dynamic light-scattering study of poly­(ethylene oxide) (PEO) in both a pure solvent (water) and a mixed solvent (tert-butanol + water). The concentration dependence of the diffusive relaxation of the PEO molecules is found to be typical of polymers in a good solvent. However, the mesoscopic diffusive behavior of PEO in the mixed solvent is very different, indicating an initial collapse and subsequent reswelling of PEO caused by co-nonsolvency. Furthermore, in the solutions of PEO with very large molecular weights, we found additional hydrodynamic modes indicating the presence of PEO clusters and aggregates similar to those found by some other investigators

Measurements of the Speed of Sound in Liquid and Supercritical <i>n</i>‑Octane and Isooctane

The speed of sound in <i>n</i>-octane and isooctane (2,2,4-trimethylpentane) was measured by the Brillouin light scattering (BLS) method. The examined regions for <i>n</i>-octane are <i>T</i> = (297–580) K along five isobaric lines at <i>p</i> = 0.1, 4.0, 7.0, 10.0, and 12.0 MPa for liquid and <i>T</i> = (573–673) K along ten isobaric lines with <i>p</i> = (3.0–10.0) MPa for supercritical fluid. The examined regions for isooctane are <i>T</i> = (294–525) K along five isobaric lines at <i>p</i> = 0.1, 3.0, 6.0, 10.0, and 12.0 MPa for liquid and <i>T</i> = (543–630) K along six isobaric lines with <i>p</i> = (3.0–10.0) MPa for supercritical fluid. The relative expanded uncertainty of the speed of sound is estimated less than 1.3%. Polynomial representations for the speed of sound in liquid <i>n</i>-octane and isooctane were fitted to the experimental results, respectively. The AADs are 0.27% for <i>n</i>-octane and 0.19% for isooctane. The influence of temperature and pressure on the speed of sound was also analyzed. Moreover, the data were also used to assess the predicted ability of three equations of state for <i>n</i>-octane

High Solubilities of Small Hydrocarbons in Trihexyl Tetradecylphosphonium Bis(2,4,4-trimethylpentyl) Phosphinate

Experimental solubilities are reported for methane, ethane, ethylene, propane, and propylene in trihexyl tetradecylphosphonium bis­(2,4,4-trimethylpentyl) phosphinate [P(14)­666]­[TMPP] from 313 to 353 K up to 6.7 MPa. A literature review on solubilities of small hydrocarbons in ionic liquids shows that solubilities in [P(14)­666]­[TMPP] are appreciably larger than those in other ionic liquids. Contrary to solubilities in ionic liquids studied earlier, solubilities of paraffins (ethane and propane) in [P(14)­666]­[TMPP] are larger than those of the corresponding olefins (ethylene and propylene). Because, at fixed temperature, the vapor pressure of an olefin is larger than that of the corresponding paraffin, the relative volatility of the olefin exceeds that of the corresponding paraffin, contrary to the relative volatility observed in conventional extractive distillation with polar solvents where the volatility of the paraffin exceeds that of the corresponding olefin