J. de Swaan Arons

Exergy analysis with a flowsheeting simulator—I. Theory; calculating exergies of material streams

Abstract This paper presents a method for calculating the absolute exergy of multicomponent liquid, vapour or two-phase flows. The method is different from those described by most authors in that it enables a clear division of the total exergy of a material stream into three terms such that the exergy change of mixing is calculated separately from the chemical and the physical exergy. The method has been implemented in a set of external subroutines which have been integrated with a flowsheeting simulator, in order to calculate exergies of material streams along with the traditional energy- and mass-balance calculations. Except for an external database containing values of standard chemical exergies, the exergy calculations require no additional input data. Exergies are calculated as an extensive stream property and are therefore accessible to various procedures supported by the flowsheeting simulator, e.g. optimization. Furthermore, this also enables the determination of exergy losses by simple accounting. A complete exergy analysis, of course, must also incorporate the interpretation of these exergy losses and a suggestion or indication of ways to reduce them. These will be discussed in part 2 of this article with the case of synthesis gas production from natural gas, showing the exergy method as a useful diagnostic tool for analyzing chemical processes.

Volume expansion in relation to the gas–antisolvent process

Abstract The underlying work is part of an extensive study to develop appropriate thermodynamic criteria for an optimum gas–antisolvent (GAS) process. It turned out that the ‘classical’ definition of volume expansion is inappropriate to define these criteria. An alternative definition of this property has been introduced in this work. This study was carried out for a number of binary and ternary systems of which the experimental data were taken from literature. The Peng–Robinson equation of state was used to describe the fluid phases, whereas for the solid phase an independent relationship was applied. It will be shown that the definition for liquid-phase volume expansion as proposed in this work is useful for the selection of the optimum pressure for the GAS process.

Illustrations towards quantifying the sustainability of technology

This paper attempts to quantify the sustainability of technological processes. It is based on thermodynamics with energy carriers and materials (products, waste, etc.) expressed in the same calculable quantity–exergy (Joule). The results have three considerations. One factor reflects to that extent renewable resources are used. In addition, the technological efficiency has to be accounted for as it affects sustainability. Finally, the results take into account the generation of waste products and the exergy required for converting the waste into products which are harmless or assimilable in the ecosphere. The proposed measure of sustainability has been illustrated for two types of products. In the first illustration, ethanol production was studied. Two routes were investigated, one starting from fossil oil and the other from agricultural products. Additionally, a route based on the synthesis from carbon dioxide and hydrogen was examined, in which hydrogen was generated by splitting water with electricity from photovoltaic solar energy conversion. The second product studied was electricity, generated from the combustion of natural gas or from photovoltaic solar energy conversion. The merit of the obtained results are that they treat technological sustainability not only in qualitative but also in quantitative terms. The insights obtained can help to account for sustainability in the development of new concepts of chemical technology.

Influence of water-insoluble organic components on the gas hydrate equilibrium conditions of methane

Abstract In this study, certain organic additives to systems of water+methane are investigated for their effect on the hydrate equilibrium pressure. The additives studied are cyclic organic components, i.e., tetrahydropyran (THP), cyclobutanone (CB), both forming structure II (sII), and methylcyclohexane (MCH), forming structure H (sH) and fluoroalkanes, i.e., fluoroform (CHF 3 ) and tetrafluoromethane (CF 4 ), both forming sI or sII depending on the concentration. Hydrate equilibrium data for single hydrates of the fluoroalkanes were determined, of which the ones of CHF 3 were compared to previous data from literature. The hydrate equilibrium pressures were experimentally determined using the Cailletet apparatus in a range of pressures from 2 to 14 MPa and temperatures up to approximately 303 K. A reduction of the methane hydrate equilibrium pressure was observed with all additives except for CF 4 . The experimental data were modelled to retrieve the Kihara fit parameters for the various additives as present in the van der Waals–Platteeuw model. By using these parameters to correlate the hydrate equilibrium pressures, deviations within approximately 3% from the experimental hydrate equilibrium line were obtained. The modelling results showed that reduction of hydrate equilibrium pressures is accompanied by a significant reduction of storage capacity for methane, which is not recommendable for practical applications.

Application of the Peng-Robinson equation of state to calculate interfacial tensions and profiles at vapour-liquid interfaces

In this work gradient theory of inhomogeneous fluids is used to describe planar interfaces. With the Helmholtz energy of the homogeneous fluid and the influence parameter of the inhomogeneous fluid, the interfacial profiles and tensions of interfaces can be predicted by gradient theory. The interfacial tension calculations, based on the Peng-Robinson equation of state and related models for the influence parameter, are presented. Laboratory as well as field studies have established that carbon dioxide is an efficient oil-displacing agent in enhanced oil recovery. Therefore special attention was given to the interfacial tension behaviour of some binary and ternary model systems, containing carbon dioxide, butane and decane. In general the predictions from the method presented in this contribution are superior in comparison with the parachor estimations.

Experimental determination and modeling of structure II hydrates in mixtures of methane+water+1,4-dioxane

Abstract Hydrate phase equilibrium conditions were measured with a Cailletet apparatus in the pressure range 2

Phase equilibria in binary mixtures of propane and hexacontane

Peters, C.J., de Roo, J.L. and de Swaan Arons, J., 1993. Phase equilibria in binary mixtures of propane and hexacontane. Fluid Phase Equilibria, 85: 301-312. This paper reports on the phase behaviour of binary mixtures of propane with hexacontane (n-C60H122). The measurements cover a temperature range from about 310 K up to 430 K. Pressures up to 15 MPa were applied. In the binary propane + hexacontane, a three-phase equilibrium liquid + liquid + vapour (l1l2g) occurs in the near-critical region of propane. However, in this system the lower critical end point (LCEP) was hidden by solidification of hexacontane. The pressure-temperature coordinates of the upper critical end point were determined at 369.95 K and 4.275 MPa. Because the three-phase equilibrium l1l2g is interrupted by the three-phase equilibrium, solid hexacontane + liquid + vapour (SBlg), a Q-point solid hexacontane + liquid + liquid + vapour (SBl1l2g) is present in this binary. Its pressure and temperature coordinates were located at 352.0 K and 3.05 MPa.

Phase equilibria in binary mixtures of propane and tripalmitin

Abstract The possibility of using near-critical propane as an extraction solvent for triglycerides is the subject of investigation. This contribution reports on the phase behaviour of the binary mixture of propane and tripalmitin. The analysis of the experimental data with respect to the phase behaviour indicates various extraction routes. There is evidence that liquid propane just below its critical point will be far more effective in terms of solvent capacity than its supercritical equivalent.

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.

Liquid–liquid immiscibility loops predicted with the simplified‐perturbed‐hard‐chain theory

In this study, it will be shown that in binary mixtures, type VI phase behavior, according to the classification of van Konynenburg and Scott [Philos. Trans. R. Soc. London, Ser. A 298, 495 (1980)], can be obtained from a simple, semitheoretical equation of state. The applied equation of state was derived from the simplified‐perturbed‐hard‐chain theory (SPHCT). In literature, there are no known examples of type VI phase behavior being obtained from a simple equation of state. In addition, the systematic changes in phase behavior from type I via type V towards type VI will be discussed in this contribution. Surprisingly, a new type of phase behavior was found that was foreseen by Schneider [Ber. Bunsenges. Phys. Chem. 70, 497 (1966)]. It is proposed to call this new phase behavior type VIII.