Experimental thermodynamic evaluation for a single stage heat transformer prototype build with commercial PHEs

A highly accurate equation of state (EOS) for chain molecules formed from spherical segments interacting through Mie potentials (i.e., a generalized Lennard-Jones form with variable repulsive and attractive exponents) is presented. The quality of the theoretical description of the vapour-liquid equilibria (coexistence densities and vapour pressures) and the second-derivative thermophysical properties (heat capacities, isobaric thermal expansivities, and speed of sound) are critically assessed by comparison with molecular simulation and with experimental data of representative real substances. Our new EOS represents a notable improvement with respect to previous versions of the statistical associating fluid theory for variable range interactions (SAFT-VR) of the generic Mie form. The approach makes rigorous use of the Barker and Henderson high-temperature perturbation expansion up to third order in the free energy of the monomer Mie system. The radial distribution function of the reference monomer fluid, which is a prerequisite for the representation of the properties of the fluid of Mie chains within a Wertheim first-order thermodynamic perturbation theory (TPT1), is calculated from a second-order expansion. The resulting SAFT-VR Mie EOS can now be applied to molecular fluids characterized by a broad range of interactions spanning from soft to very repulsive and short-ranged Mie potentials. A good representation of the corresponding molecular-simulation data is achieved for model monomer and chain fluids. When applied to the particular case of the ubiquitous Lennard-Jones potential, our rigorous description of the thermodynamic properties is of equivalent quality to that obtained with the empirical EOSs for LJ monomer (EOS of Johnson et al.) and LJ chain (soft-SAFT) fluids. A key feature of our reformulated SAFT-VR approach is the greatly enhanced accuracy in the near-critical region for chain molecules. This attribute, combined with the accurate modeling of second-derivative properties, allows for a much improved global representation of the thermodynamic properties and fluid-phase equilibria of pure fluids and their mixtures.

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Accurate statistical associating fluid theory for chain molecules formed from Mie segments

The development of highly accurate and computationally efficient modeling software based on Gibbs energy minimization (GEM) makes it possible to thermodynamically simulate geochemically realistic subsurface fluid-rock interaction processes. This involves consideration of non-ideal multicomponent-multiphase systems that include dilute to concentrated aqueous electrolyte solutions, mineral solid solutions, supercritical fluids, silicate and metal melts, and sorption and ion exchange phases. Predicting the stability and thermodynamic properties of non-ideal solution phases over wide ranges of pressures and temperatures requires that theoretically sound and sufficiently accurate equation of state and activity models are used within the GEM framework. The variety of such models calls for a novel, flexible, and computationally efficient code architecture that supports a wide range of models of non-ideal mixing with different mathematical structures and input data. Here, we introduce the TSolMod C++ class library for equation of state and activity models, implemented within the GEMS3K solver of geochemical equilibria as part of the GEM-Selektor code package (http://gems.web.psi.ch). Essential features of the TSolMod library include a generic and flexible model parameter setup, computationally efficient data exchange with the GEM algorithm, and a straightforward extensibility with any new models of mixing. The current version of TSolMod features a comprehensive selection of fluid, gas, liquid, and solid solution models of interest for geochemical, petrological, material science, and chemical engineering applications.

GEM-SELEKTOR GEOCHEMICAL MODELING PACKAGE: TSolMod LIBRARY AND DATA INTERFACE FOR MULTICOMPONENT PHASE MODELS

High-pressure fluid-phase equilibria: Experimental methods and systems investigated (2000-2004)

Peng-Robinson equation of state: 40 years through cubics

In 2004, we started to develop a group contribution method aimed at estimating the temperature dependent binary interaction parameters (kij(T)) for the widely used Peng–Robinson equation of state (EOS). Because our model relies on the Peng–Robinson EOS as published by Peng and Robinson in 1978 and because the addition of a group contribution method to estimate the kij makes it predictive, this model was called PPR78 (predictive 1978, Peng Robinson EOS). In our previous papers eleven groups were defined: CH3, CH2, CH, C, CH4 (methane), C2H6 (ethane), CHaro, Caro, Cfused aromatic rings, CH2,cyclic and CHcyclic Ccyclic. It was thus possible to estimate the kij for any mixture containing alkanes, aromatics and naphthenes at any temperature. In this study, the PPR78 model is extended to systems containing carbon dioxide. To do so, the group CO2 was added. The results obtained in this study are in many cases accurate.

Predicting the phase equilibria of CO2+hydrocarbon systems with the PPR78 model (PR EOS and kij calculated through a group contribution method)

The PPR78 approach is a group contribution-based thermodynamic model which combines at constant packing fraction the Peng–Robinson equation of state and a Van Laar-type gE model. This article demonstrates that, using classical mixing rules (linear on b and quadratic on a), the PPR78 model may also be seen as a group contribution method for the estimation of the temperature-dependent kij of the widely used PR EoS. Our model is endowed of 15 groups and it is possible to predict the kij for any mixture containing alkanes, aromatics, naphthenes, CO2, N2, H2S, and mercaptans. This study exhibits the capability of this approach to predict the phase behavior of synthetic petroleum fluids containing components of different volatilities. The many comparisons between calculated and experimental data on natural gases, crude oils, and gas condensates allow concluding that the PPR78 approach is a successful model for phase equilibria calculations of this kind of mixtures. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Predicting the Phase Equilibria of Synthetic Petroleum Fluids with the PPR78 Approach

Relationship between the binary interaction parameters (kij) of the Peng–Robinson and those of the Soave–Redlich–Kwong equations of state: Application to the definition of the PR2SRK model

Are safe results obtained when the PC-SAFT equation of state is applied to ordinary pure chemicals?

The study of phase equilibria is one of the most important sources of information about the nature of intermolecular forces in liquids and their mixtures and is of the highest importance for designing and optimizing processes Many of the main features of vapor–liquid and liquid–liquid phase behavior were well characterized experimentally during the early part of the 20th century, and many equations of state were developed to reproduce the many types of phase diagrams observed for binary systems In spite of the quasi-infinite number of possible configurations and rearrangements of fluid–fluid equilibrium phase diagrams, this paper presents a near-exhaustive classification scheme of fluid phase equilibria in binary systems It starts from the one proposed by Van Konynenburg and Scott and brings it up-to-date by detailing the progress carried out on this topic since their classification scheme was first proposed The second part of this paper is devoted to describing the transitions between the various types of systems

Romain Privat

Papers

Predicting the phase equilibria of CO2+hydrocarbon systems with the PPR78 model (PR EOS and kij calculated through a group contribution method)

Predicting the Phase Equilibria of Synthetic Petroleum Fluids with the PPR78 Approach

Relationship between the binary interaction parameters (kij) of the Peng–Robinson and those of the Soave–Redlich–Kwong equations of state: Application to the definition of the PR2SRK model

Are safe results obtained when the PC-SAFT equation of state is applied to ordinary pure chemicals?

Classification of global fluid-phase equilibrium behaviors in binary systems