A new equation of state for the thermodynamic properties of natural gases, similar gases, and other mixtures, the GERG-2008 equation of state, is presented in this work. This equation is an expanded version of the GERG-2004 equation. GERG-2008 is explicit in the Helmholtz free energy as a function of density, temperature, and composition. The equation is based on 21 natural gas components: methane, nitrogen, carbon dioxide, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, hydrogen, oxygen, carbon monoxide, water, hydrogen sulfide, helium, and argon. Over the entire composition range, GERG-2008 covers the gas phase, liquid phase, supercritical region, and vapor–liquid equilibrium states for mixtures of these components. The normal range of validity of GERG-2008 includes temperatures from (90 to 450) K and pressures up to 35 MPa where the most accurate experimental data of the thermal and caloric properties are represented to within their accura...

The GERG-2008 Wide-Range Equation of State for Natural Gases and Other Mixtures: An Expansion of GERG-2004

Integral Equation Theories of the Structure, Thermodynamics, and Phase Transitions of Polymer Fluids

Integral equation theory description of phase equilibria in classical fluids

New functional forms have been developed for multiparameter equations of state for non- and weakly polar fluids and for polar fluids. The resulting functional forms, which were established with an optimization algorithm which considers data sets for different fluids simultaneously, are suitable as a basis for equations of state for a broad variety of fluids. The functional forms were designed to fulfil typical demands of advanced technical application with regard to the achieved accuracy. They are numerically very stable and their substance-specific coefficients can easily be fitted to restricted data sets. In this way, a fast extension of the group of fluids for which accurate empirical equations of state are available is now possible. This article deals with the results found for the polar fluids CFC-11 (trichlorofluoromethane), CFC-12 (dichlorodifluoromethane), HCFC-22 (chlorodifluoromethane), HFC-32 (difluoromethane), CFC-113 (1,1,2-trichlorotrifluoroethane), HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane), HFC-125 (pentafluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-143a (1,1,1-trifluoroethane), HFC-152a (1,1-difluoroethane), carbon dioxide, and ammonia. The substance-specific parameters of the new equations of state are given as well as statistical and graphical comparisons with experimental data. General features of the new class of equations of state such as their extrapolation behavior or their numerical stability and results for non- and weakly polar fluids have been discussed in preceding articles.

Equations of state for technical applications. III. Results for polar fluids

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880–2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C1 to C10. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C11 to C192. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C1-C10

An efficient algorithm is given to find the Blum and Ho/ye mean spherical approximation (MSA) solution for mixtures of hard‐core fluids with multi‐Yukawa interactions. The initial estimation of the variables is based on the asymptotic high‐temperature behavior of the fluid. From this initial estimate only a few Newton–Raphson iterations are required to reach the final solution. The algorithm consistently yields the unique thermodynamically stable solution, whenever it exists, i.e., whenever the fluid appears as a single, homogeneous phase. For conditions in which no single phase can appear, the algorithm will declare the absence of solutions or, less often, produce thermodynamically unstable solutions. A simple criterion reveals the instability of those solutions. Furthermore, this Yukawa‐MSA algorithm can be used in a most simple way to estimate the onset of thermodynamic instability and to predict the nature of the resulting phase separation (whether vapor–liquid or liquid–liquid). Specific results are presented for two binary multi‐Yukawa mixtures. For both mixtures, the Yukawa interaction parameters were adjusted to fit, beyond the hard‐core diameters σ, Lennard‐Jones potentials. Therefore the potentials studied, although strictly negative, included a significant repulsion interval. The characteristics of the first mixture were chosen to produce a nearly ideal solution, while those of the second mixture favored strong deviations from ideality. The MSA algorithm was able to reflect correctly their molecular characteristics into the appropriate macroscopic behavior, reproducing not only vapor–liquid equilibrium but also liquid–liquid separations. Finally, the high‐density limit of the fluid phase was determined by requiring the radial distribution function to be non‐negative. A case is made for interpreting that limit as the fluid–glass transition.

Mean spherical approximation algorithm for multicomponent multi‐Yukawa fluid mixtures: Study of vapor–liquid, liquid–liquid, and fluid–glass transitions

The total pressure and vapor and liquid compositions have been measured for N-methyl-2-pyrrolidone + benzene at 330.00 K and 350.00 K, for N-methyl-2-pyrrolidine + toluene at 343.15 K and 373.15 K, for N-methyl-2-pyrrolidone + heptane at 340.00 K and 365.00 K, and for N-methyl-2-pyrrolidone + methylcyclohexane at 340.00 K and 370.00 K. Measurements were made by either a recirculating still or a transpiration method, the method depending on the total pressure of the mixture. The results were correlated using the Redlich−Kister equation, the Wilson equation, and the NRTL equation, with allowance for vapor nonideality.

Vapor−Liquid Equilibria for N-Methyl-2-pyrrolidone + Benzene, +Toluene, +Heptane, and +Methylcyclohexane

Burnett and pycnometric (p,Vm,T) measurements for natural gas mixtures

The standard industrial process for the purification of natural gas is to remove acid gases, mainly hydrogen sulfide and carbon dioxide, by the absorption and reaction of these gases with alkanolamines, but the lack of reliable and accurate vapor-liquid equilibrium (VLE) data impedes the commercial application of more efficient alkanolamine systems. The objective of this research was to develop an FTIR apparatus and an in-situ technique capable of making VLE measurements of acid-gas-aqueous alkanolamine systems and to improve the accuracy of vapor-liquid equilibrium measurements at low hydrogen sulfide and carbon dioxide concentrations. The new FTIR apparatus and technique were tested in VLE measurements of low concentrations of carbon dioxide and hydrogen sulfide in aqueous mixtures of diethanolamine.

FTIR method for VLE measurements of acid‐gas–alkanolamine systems

This paper reports densities of compressed R134a (1,1,1,2-tetrafluoroethane) determined by using a contiuously weighed pycnometer at 20 K intervals between 180 and 380 K at pressures from slightly greater than the vapour pressure to 70 MPa. The results are accurate to within ±0.1%. Saturated liquid densities derived by extrapolation from the experimental values agree with other reported values to within ±0.3%.

K. N. Marsh

Papers

Mean spherical approximation algorithm for multicomponent multi‐Yukawa fluid mixtures: Study of vapor–liquid, liquid–liquid, and fluid–glass transitions

Vapor−Liquid Equilibria for N-Methyl-2-pyrrolidone + Benzene, +Toluene, +Heptane, and +Methylcyclohexane

Burnett and pycnometric (p,Vm,T) measurements for natural gas mixtures

FTIR method for VLE measurements of acid‐gas–alkanolamine systems

Experimental densities for compressed R134a