Extension of the group contribution NRTL-PRA EoS for the modeling of mixtures containing light gases and alcohols with water and salts

Abstract

. Extension of the group contribution NRTL-PRA EoS for the modeling of mixtures containing light gases and alcohols with water and salts. Fluid Phase Equilibria, Elsevier, 2018, 458, pp.194-210. 10 AbstractThe offshore exploitation of petroleum fluids in normal conditions of pressure and temperature of transport and in presence of salt water is concerned with the prevention of gas hydrate formation, generally thanks to continuous injection of inhibitors, or punctual injection of methanol in start-up and shut-down operations. Hence, models of interest should provide both, satisfactory phase equilibrium estimations of hydrocarbon and alcohol mixtures with water and reliable predictions of their behavior in presence of salts.In this work, the NRTL-PRA EoS is extended to the prediction of phase equilibria in mixtures containing strong electrolytes. The proposed model assumes that the a and b parameters of the cubic EoS only depend on the solvent mole fractions (salt-free), while the E EoS g excess Gibbs energy describes all the interactions between solvents and ions with only two contributions: the SMR term, specific of "Short and Middle Range" interactions between solvents and salts, and the LR relation proposed by Pitzer-Debye-Hückel, for the description of "Long Range" electrostatic interactions. The proposed electrolyte version of the NRTL-PRA model was successfully extended to the modeling of phase behavior of mixtures of light gases at high pressures (methane, carbon dioxide, nitrogen and hydrogen sulfide) and alcohols (methanol, ethanol and 1-propanol) with water and salts (mainly, ternary mixtures containing sodium chloride). As far as possible, results were compared with those provided, for the same systems, by other literature models (cubic Eos, SAFT and CPA equations).

An empirical correlation for the relative permittivity of liquids in a wide temperature range: Application to the modeling of electrolyte systems with a GE/EoS approach

“…In [16], Neau et al presented the correlation developed by Neau and Raspo [35] for the representation of the relative permittivity of polar compounds with respect to temperature:…”

“…The values of parameters Ai in Eqs. (2) and 3, together with those given in [16] for Eq. (1), are reported in Table 3; the temperature range of validity of each equation is also indicated, except for Eq.…”

“…The dielectric constant also plays an essential role in the modeling of phase equilibria of electrolyte systems. Indeed, although an abundance of models was proposed in literature for phase equilibria (LIQUAC [5,7], LIFAC [6,7], e-NRTL [8,9], PSRK-LIFAC [10], VTPR-LIFAC [11], e-CPA [12], e-PC SAFT [12], SAFT-VRE [13,14], SAFT-VR Mie [15], NRTL-PRA [16]…), all these models account for ion-ion interactions by means of a long-range term derived from the Debye-Hückel model [17] or the Mean Spherical Approximation (MSA) [18,19]. Both of these long-range interaction models involve the relative permittivity of the solvent.…”

“…Some of them [20,21] are based on theories such as the Onsager [22] and Kirkwood theories [23]. Many empirical correlations were also proposed to represent the dependence on temperature [16,[24][25][26][27][28][29][30] and/or on density [14,15,31,32]. However, except for those developed in [24] for ethanol and in [26] for water, these correlations are limited to temperatures lower than 400K.…”

“…In this paper, the temperature dependent correlation presented in [16] is extended to a wide temperature range by fitting the parameters on a large data base including temperatures up to 823K for water and more than 500K for methanol and ethanol. Considering temperatures above the critical point of water leads to a correlation suitable for chemical engineering processes involving supercritical water such as, for instance, Supercritical Water Oxidation [33], for which salt solubility is of great interest.…”