Th.W. de Loos

Phase equilibria and critical phenomena in fluid (n-hexane + water) at high pressures and temperatures

Abstract Phase equilibria in fluid ( n -hexane + water) were measured in the temperature range 610 to 675 K and at pressures from 15 to 140 MPa. The critical curve of the mixture starts at the critical point of pure water ( T c = 646.1 K; p c = 22.1 MPa) and runs via a temperature minimum at T = (627.8 ± 0.2) K and p = (31 ± 2) MPa to higher pressures, suggesting that (gas + gas) equilibria of the second kind occur. The results are discussed in view of phase equilibria of other ( n -alkane + water) mixtures. It is shown that the form of the critical line of (an n -alkane + water) changes systematically with the carbon number of the n -alkane.

Vapour-liquid equilibria and critical phenomena in methanol + n-alkane systems

Abstract Bubble point pressures and vapour-liquid critical points of {(1–x) CH 3 OH + x n-C m H 2m+2 , m = 6,7,8,9,10,12,14 } were measured visually over the temperature range from 425 to 540 K in a high pressure capillary glass tube apparatus by using the synthetic method. It is shown that the form of the vapour-liquid critical curve of binary methanol + n-alkane systems changes systematically with the carbon number of the n-alkane. In systems with m = 6,7,8 absolute azeotropy is found.

High pressure VLE in alkanol + alkane mixtures. Experimental results for n-butane + ethanol, +1-propanol, +1-butanol systems and calculations with three EOS methods

Abstract Bubble point pressures and vapour-liquid critical points of n-butane + ethanol, n-butane + 1-propanol and n-butane + 1-butanol were measured in the temperature range 323–523 K in a high-pressure capillary glass tube apparatus, using the synthetic method. It is shown that the shape of the vapour-liquid critical curve changes systematically with the carbon number of the 1-alkanol. In the system n-butane + ethanol absolute azeotropy is found. Modelling of VLE of alkane+alkanol systems has been performed using the hole quasichemical group-contribution model (HM), the APACT EOS, and the Stryjek-Vera modification of the PR EOS with the Wong and Sandler mixing rules (WS/PRSV). Apart from the mixtures studied experimentally in the present work some more alkanol+alkane systems at high and low pressures are considered to assess the models. The APACT EOS and the HM predict VLE with good accuracy over a wide range of pressures, whereas the predictions by the WS method are slightly worse.

Phase equilibria and critical phenomena in fluid (n-alkane + water) systems at high pressures and temperatures

Abstract In fluid (n-alkane + water) mixtures (gas + gas) equilibria of the second type are found. Phase equilibria in fluid (n-pentane + water) and (n-heptane + water) were measured in the temperature range 600 to 675 K and at pressures from 15 to 170 MPa. The critical curve of these systems starts at the critical point of pure water and runs through a temperature minimum with increasing pressure. Experimental results are compared with previous studies and it is found that the data fit very well within the systematics of other (n-alkane + water) systems.

High pressure solid-fluid and vapour-liquid equilibria in the system (methane + tetracosane)

Abstract Experimental vapour-liquid, solid-fluid, and solid-liquid-vapour equilibrium data of the binary system (methane + tetracosane) in the temperature range 315–450 K and for pressures up to 200 MPa are presented. The experiments were carried out for various mixtures with compositions ranging from almost pure methane to pure tetracosane. It was found that the (solid α-to-solidβ) transition of pure tetracosane has hardly any influence on the shape of the (solid + fluid/fluid) boundary curves and the three-phase equilibrium curve (solid tetracosane + liquid + vapour) of the binary system. The second critical endpoint of the three-phase curve (sC24 + 1 = g), where solid tetracosane is in equilibrium with a critical fluid phase was located at a temperature of T = (322.60 ± 0.25)K, a pressure of p = (104.7 ± 0.4)MPa, and a mole fraction of tetracosane in the critical fluid phase of xC24 = (0.041 ± 0.003).

The influence of nitrogen on the liquid—liquid phase behaviour of the system n-hexane—polyethylene: experimental results and predictions with the mean-field lattice-gas model

Abstract The phase diagram of the system n-hexane+linear high density polyethylene shows a region of limted miscibility in the liquid phase, which is of the lower critical solutions temperature type (LCST behaviour). The influence of nitrogen on the location of this region of limited miscibility is investigated experimentally at pressures up to 7.5 MPa in the temperature range 393–453 K for weight fractions of nitrogen in the liquid phase between 0 and 0.013. Nitrogen induces a shift of the region of limited miscibility to lower temperatures and higher pressures of about 22 K at constant pressure or 2m.Pa at constant temperature per weight percent nitrogen. Model calculations have been performed for the ternary system nitrogen + n-hexane + polyethylene using the mean-field lattice-gas model of Kleintjens and Koningsveld. Parameters used in these calculations were obtained from pure component and binary data only. The results prove that this model is able to predict the observed peculiar behaviour in the ternay system.

The volumetric analysis and prediction of liquid-liquid-vapor equilibria in certain carbon dioxide + n-alkane systems

Abstract This article deals with the use of a volumetric technique for obtaining compositional and density data of the L 1 L 2 V equilibria of the systems CO 2 + tetradecane, CO 2 + pentadecane and CO 2 + hexadecane. In these systems a barotropic inversion occurs between the two liquid phases. Primary attention has been given to the influence of experimental inaccuracies on the results. The phase behaviour of the systems CO 2 + tetradecane, CO 2 + pentadecane and CO 2 + hexadecane has been fitted to the Peng-Robinson equation of state and a modified Peng-Robinson equation of state showing no significant difference between these equations of state.

The experimental determination and modelling of VLE for binary subsystems of the quaterhary system N2 + CH4 + C4H10 + C14H30 UP to 1000 bar and 440 K

Abstract As a part of a laboratory study on nitrogen displacement in light-oil reservoirs, in which a mixture of methane, butane and tetradecane is used as a model oil, the phase behaviour of the binary subsystems of the quaternary system nitrogen + methane + butane + tetradecane is investigated in the temperature and pressure range of interest. The phase behaviour of the binary systems nitrogen + methane and methane + butane is known from literature. VLE of the binary systems nitrogen + tetradecane and methane + tetradecane were determined experimentally at 320 – 440 K according to the synthetic method using a high pressure cell with sapphire windows. VLE of the binary system butane + tetradecane were determined experimentally in the same temperature range according to the same method but now using the so-called Cailletet equipment. The experimental data were fitted using several equations of state in combination with a number of mixing rules. It is found that local composition mixing rules of the Huron-Vidal type and density dependent mixing rules as used by Mohammed and Holder and a new density dependent mixing rule, are superior to the conventional mixing rules with one or two binary interaction parameters. With these improved mixing rules a satisfactory description of the experimental data, even at pressures as high as 1200 bar can be realized.

Connectivity of critical lines around the van Laar point in T, X projections

It is shown that the SPHCT equation of state describes qualitatively the same types of binary phase behavior around the van Laar point as the van der Waals and the Redlich–Kwong equation of state. A continuous transition is possible from a binary system with a van Laar point into binary systems that show type II, III, IV and IV* phase behavior. The global phase diagram turns out to be a helpful tool in the exploration of these different types of phase behavior. Special attention is paid to the link between moving across the global phase diagram and the resulting changes in the phase behavior of the corresponding binary mixtures. We will focus on the temperature‐composition behavior of the critical lines in the binary mixtures. This temperature‐composition behavior is very important if one wants to make an experimental verification of the van Laar point or type IV* phase behavior.

A new apparatus to measure the vapour-liquid equilibria of low-volatility compounds with near-critical carbon dioxide. Experimental and modelling results for carbon dioxide+n-butanol, +2-butanol, +2-butyl acetate and +vinyl acetate systems

Abstract A new apparatus has been developed for the experimental determination of vapour-liquid equilibria in systems containing low-volatility compounds and near-critical carbon dioxide. The apparatus combines the advantages of the gas saturation method with those of a circulation method. An air-lift-functioning draft tube is used in the centre of the equilibrium cell to increase contact time between solute and solvent. The apparatus is tested by measuring the vapour-liquid equilibrium (VLE) of the system CO 2 +1-butanol at 313.2 and 333.2 K and at pressures up to 11 MPa. For the systems CO 2 +2-butanol, CO 2 +vinyl acetate and CO 2 +2-butyl acetate, VLE data were measured at pressures up to 10 MPa and at the temperatures of 303.2, 313.2 and 333.2 K. The measured mole fractions of the low-volatility compound in carbon dioxide have an accuracy better than 3%. The solubility isotherms were modelled using the PRSV EOS with Wong-Sandler mixing rules and the LCVM model. It is shown that the solubility of the low-volatility compounds in carbon dioxide can be predicted well with the PRSV-WS EOS (NRTL-G E -model) using the fit parameters obtained from bubble point measurements. The PRSV-WS predicts the solubilities better than the LCVM model (t-mPR EOS with an adapted UNIFAC-G E -model).