[en] Highlights: • A robust technique for determining melting temperatures in hydrocarbon mixtures by DSC has been established. • Melting temperatures determined via the endset scanning method were found to be consistent with cryoscopic measurements and the stepwise method. • The impact of any sample de-mixing that may have occurred over multiple freeze-melt cycles was negligible. • New SLE data for heptane + hexadecane, hexane + hexadecane and hexane + para-xylene + hexadecane. - Abstract: There is a lack of consistency in the literature about how to determine the melting (liquidus) temperature in a hydrocarbon mixture from thermograms recorded by differential scanning calorimetry (DSC). This paper establishes a robust technique for determining liquidus temperatures by DSC by testing two methods detailed in the literature and assessing the potential for de-mixing to preclude repeatable measurements. Liquidus temperatures determined via the end set scanning method were found to be consistent with literature measurements of the same mixture obtained visually, and with a liquidus temperature measured for a fresh sample using the step method. In contrast, use of the thermogram’s peak temperature produced inconsistent results that often could not be reasonably extrapolated to zero scan rate. The impact of any sample de-mixing that may have occurred over multiple freeze-melt cycles was negligible, as demonstrated by the consistency of the thermograms repeated at the same scan rate, and the consistency of liquidus temperatures obtained with different sample loadings into the DSC. New (solid + liquid) equilibrium results are reported for {heptane + hexadecane (C₁₆)} and (hexane + hexadecane) binaries as well as a (hexane + para-xylene + hexadecane) ternary over a temperature range from (260.80 to 279.17) K at atmospheric pressure. Comparisons of the binary measurements against both literature data and the calculations with a property package implemented in commercial software showed deviations of less than 1 K for mixtures with C₁₆ solute mole fractions around 0.3, and −3 K for the mixture with a C₁₆ solute mole fraction around 0.1, due to the increasing sensitivity of the liquidus temperature on composition as the solute fraction decreases. The ternary mixture, with a C₁₆ solute mole fraction of around 0.1, showed a deviation of −5 K, suggesting the property package does not adequately capture the interactions associated with the presence of an aromatic component.

[en] Highlights: • VLE data for (CH_4 (1) + C_6H_6 (2)) and (CH_4 (1) + C_6H_5CH_3 (3)) were measured. • LLE was observed at T = 198.15 K, a T higher than expected, for (CH_4 + C_6H_5CH_3)_. • Inconsistences in the literature data were identified and assessed. • More data at x_1 > 0.3 for both systems are needed to investigate discrepancies. - Abstract: New isothermal pTxy data are reported for (methane + benzene) and (methane + methylbenzene (toluene)) at pressures up to 13 MPa over the temperature range (188 to 313) K using a custom-built (vapor + liquid) equilibrium (VLE) apparatus. The aim of this work was to investigate literature data inconsistencies and to extend the measurements to lower temperatures. For (methane (1) + benzene (2)), measurements were made along six isotherms from (233 to 348) K at pressures to 9.6 MPa. At temperatures below 279 K there was evidence of a solid phase, and thus only vapor phase samples were analyzed at these temperatures. For the (methane (1) + methylbenzene (3)) system, measurements were made along seven isotherms from T = (188 to 313) K at pressures up to 13 MPa. Along the 198 K isotherm, a significant change in the data’s p,x slope was observed indicating (liquid + liquid) equilibria at higher pressures. The data were compared with literature data and with calculations made using the Peng–Robinson (PR) equation of state (EOS). For both binary systems our data agree with much of the literature data that also deviate from the EOS in a similar manner. However, the data of Elbishlawi and Spencer (1951) for both binary systems, which appear to have received an equal weighting to other data in the EOS development, are inconsistent with the results of our measurements and data from other literature sources

[en] Measurement of oil contamination of produced water is required in the oil and gas industry to the (ppm) level prior to discharge in order to meet typical environmental legislative requirements. Here we present the use of compact, mobile ¹H nuclear magnetic resonance (NMR) spectroscopy, in combination with solid phase extraction (SPE), to meet this metrology need. The NMR hardware employed featured a sufficiently homogeneous magnetic field, such that chemical shift differences could be used to unambiguously differentiate, and hence quantitatively detect, the required oil and solvent NMR signals. A solvent system consisting of 1% v/v chloroform in tetrachloroethylene was deployed, this provided a comparable ¹H NMR signal intensity for the oil and the solvent (chloroform) and hence an internal reference ¹H signal from the chloroform resulting in the measurement being effectively self-calibrating. The measurement process was applied to water contaminated with hexane or crude oil over the range 1–30 ppm. The results were validated against known solubility limits as well as infrared analysis and gas chromatography. (paper)

[en] Highlights: • High quality multi-component natural gas vapor-liquid equilibrium (VLE) presented. • Data measured for mixtures and at conditions relevant to LNG scrub columns. • Predicted VLE of GERG equation of state (EOS) better than Peng-Robinson EOS. • GERG EOS reoptimized for CH₄ + C₄H₁₀ better predicted multi-component VLE. • Reoptimization of GERG EOS for other binaries may further improve VLE predictions. - Abstract: Accurate simulations of scrub columns in liquefied natural gas (LNG) plants are challenging, requiring frequent solution of the non-linear equations governing vapor-liquid equilibrium (VLE), material, and energy balances for multi-component mixtures. Reliable fluid property predictions at high pressures and low temperatures are thus crucial; however, no high-quality multi-component VLE data at conditions relevant to the LNG scrub column are available to test commonly-used equations of state (EOS). Here we report VLE measurements at pressures to 9 MPa and temperatures from (203 to 273) K for mixtures containing CH₄, C₂H₆, C₃H₈, iC₄H₁₀, nC₄H₁₀ and/or N₂. Far from the mixture’s critical point, the GERG-2008 EOS predictions were more accurate than the Peng-Robinson EOS predictions. Above 7 MPa both EOS under-predicted the liquid phase’s methane content and over-predicted its butane content by 10–50 times the experimental uncertainty. Rowland et al.’s recent revision of the GERG model reduced the maximum deviations by (17–35)%. Further optimizations should improve the constituent binary departure functions and hence improve the description of multicomponent VLE data, particularly at conditions relevant to LNG production.