Thermodynamics of supercritical steam + carbon dioxide mixtures

This study compares one relatively simple analytical and two unequally sophisticated molecularly inspired associative contributions to the Helmholtz free energy of SAFT-VR-Mie equation of state in predicting the thermodynamic properties of pure water and the global phase behavior of water−hydrocarbon (alkanes, alkenes, and aromatics) systems in the entire thermodynamic phase-space. The classical van der Waals one-fluid mixing rules with zero values of the binary adjustable parameters are implemented. Although this entirely predictive implementation is particularly challenging, the considered approaches can be characterized by a satisfactorily good accuracy. However, despite the expectations, the most sophisticated molecular-inspired association kernel does not exhibit an overall advantage not only comparing with its less complicated version, but also with the substantially simpler analytical approach. Consequently, the current results indicate that the advanced molecular background does not necessarily guarantee an improvement of the overall robustness and reliability in estimating actual thermodynamic data.

Section: Resultsmentioning

confidence: 99%

Some Observations Regarding the Association Kernel of SAFT-VR-Mie. Is the Molecularly Inspired Contribution Always Necessary?

Garrido

Cea-Klapp

Polishuk

2018

“…Evidence for a specific interaction between water and carbon dioxide is found by Worwald et al; the data was obtained by measurements of the excess enthalpy of steam + carbon dioxide in condition of 363 to 698 K and pressures up to 6 MPa. Our interaction energy is found to be rather small if compared to the experimental value of Δ H = −14 ± 2 kJ mol –1 (which is equivalent to 1683 K) but still acceptable.…”

Section: Mixture Vle and Lle Behaviormentioning

confidence: 94%

“…Many authors describe water + CO 2 mixtures using only a dispersive k ij correction ,,− often resulting in large k ij values, sometimes temperature dependent. Yet, carbon dioxide is known to form strong interactions with water, , which can be described by the so-called “solvation”, induced- or cross-association effect . This approach was preferred by Button and Gubbins, who consider four sites on the CO 2 molecule, and more recently by Ji et al, who use three sites with a temperature dependent cross-association energy.…”

Section: Mixture Vle and Lle Behaviormentioning

confidence: 99%

Modeling Liquid–Liquid and Liquid–Vapor Equilibria of Binary Systems Containing Water with an Alkane, an Aromatic Hydrocarbon, an Alcohol or a Gas (Methane, Ethane, CO₂ or H₂S), Using Group Contribution Polar Perturbed-Chain Statistical Associating Fluid Theory

NguyenHuynh

Hemptinne

Lugo

et al. 2011

The present paper proposes to use the group contribution (GC) polar perturbed-chain-statistical associating fluid theory (GC-PPC-SAFT) equation of state (EoS), that has already been used with success on various organic mixtures, and extend it to model simultaneously the liquidÀliquid equilibrium (LLE) and vaporÀliquid equilibrium (VLE) of hydrocarbons þ water systems, in wide ranges of pressure and temperature. Mixtures of water with aliphatics, aromatics, alcohols, carbon dioxide, and hydrogen sulfide have been investigated. Pure water is assumed associative (according to the 4C association scheme) and dipolar; the aromatic compounds are quadrupolar. Alcohols are autoassociative with a 3B association scheme. A cross-association between water and alcohols or H 2 S is taken into account. Cross association between water and other polar molecules (CO 2 or aromatic molecules) was also taken into account explicitly. Only one set of cross association parameters ε cross /k and k cross values were used for all the water þ aromatic mixtures considered here. ε cross /k was adjusted on experimental data, whereas k cross is set to the value found for pure water. For each system, the same binary interaction parameter k ij was used for simultaneous modeling LLE and VLE. This parameter was correlated to pseudo-ionization energy parameters for pure compounds through London's dispersion force theory, and reused from previous works [

“…However, following the approach of our previous work, cross-association with water is considered. This choice is motivated by the large k ij values needed by the authors who used SAFT approaches with nonassociating CO 2 and water. − On the other hand, carbon dioxide is known to form strong interactions with water , and has been modeled with cross-association by other authors . For this, two negative sites are placed on the CO 2 molecules.…”

Section: Modelmentioning

confidence: 99%

Modeling of Strong Electrolytes with ePPC-SAFT up to High Temperatures

Rozmus

Hemptinne

Galindo

et al. 2013

An extension of the PPC-SAFT equation of state to treat strong electrolyte aqueous solutions is presented. It is capable of describing the behavior of such systems up to 473 K with a good precision and without requiring temperature-dependent model parameters. Long-range Coulombic interactions are taken into account using the mean spherical approximation (MSA) for a primitive model of the electrolyte solution, and the effect of solvation is described using short-range ion–water interactions mediated through association sites. Pairing between anions and cations is also treated through site–site interactions. A Born term is added to describe the change of dielectric constant resulting from solvation. A single ion-specific, temperature-independent model parameters are used, for 20 alkali-halide aqueous solutions. The Pauling ionic diameters are used for all terms (hard sphere, MSA, and Born). The dispersion energy of the ions is considered negligible. In the resulting ePPC-SAFT model, only the water–ion association energy is considered as an adjustable parameter. The results show coherent energy density behavior with respect to ionic size. The approach allows the calculation of the mean ionic activity coefficient, density, or vapor pressure of the aqueous solutions over a wide range of temperatures and molalities (298–573 K and 0–6 m). Moreover, salting out of carbon dioxide and methane in saline water can also be predicted accurately. A discussion of the changes in ion hydration at different salinity is also presented taking advantage of the model proposed that explicitly includes ion–water site–site interactions.