Predicting the Phase Equilibria, Critical Phenomena, and Mixing Enthalpies of Binary Aqueous Systems Containing Alkanes, Cycloalkanes, Aromatics, Alkenes, and Gases (N₂, CO₂, H₂S, H₂) with the PPR78 Equation of State

Abstract

The phase behavior of water/hydrocarbon mixtures in a wide range of concentrations, temperatures, and pressures is important in a variety of chemical engineering applications. For this reason, the physical understanding and mathematical modeling of these aqueous–organic mixtures constitute a challenging task, both for scientists and for applied engineers. In this work, mutual solubilities, critical loci, and mixing enthalpies of water + hydrocarbon, water + carbon dioxide, water + nitrogen, water + hydrogen sulfide, and water + hydrogen binary mixtures are predicted using the PPR78 cubic equation of state (EoS). The extremely nonideal behavior of these systems produces unusual and complex thermodynamic behavior. As an example, such mixtures often exhibit type III phase behavior in the classification scheme of Van Konynenburg and Scott and are characterized by a vapor–liquid critical line which first exhibits a temperature minimum and then extends to temperatures above the critical point of pure water. Such a behavior, called gas–gas equilibria of the second kind is a consequence of the large degree of immiscibility of the two components. The selected PPR78 model combines the Peng–Robinson cubic EoS and a group-contribution method aimed at predicting the temperature-dependent binary interaction parameters, k ij (T), involved in the Van der Waals one-fluid mixing rules. Although, it is acknowledged that cubic EoS with a constant k ij are not suitable to predict phase equilibria of such highly nonideal systems, the addition of the H2O group to the PPR78 model makes it possible to conclude that the use of temperature-dependent binary interaction parameters not only results in qualitatively accurate predictions over wide pressure and temperature ranges but also leads to quantitatively reasonable predictions for many of the studied systems.

Impact of non-ideality on mixing of hydrocarbons and water at supercritical or near-critical conditions

“…Because PPR78 has not included the critical locus in their datasets because of technical difficulties [38], UCST results deviate by <20K from the measurements. The phase equilibrium water compositions are shown in Figure 1 with experimental measurements from the literature.…”

Predicting the Phase Equilibria of Carbon Dioxide Containing Mixtures Involved in CCS Processes Using the PPR78 Model

“…The behavior of the CO 2 + H 2 O system has been studied experimentally by different authors (as reported by Qian et al [15]) in the high-temperature/high-pressure region with value of 539 K for the minimum temperature of the critical locus beginning at the water critical point. As shown in Figure 7 f, reliable predictions of the critical coordinates by the PPR78 EoS are obtained until 4000 bar.…”

“…In the current state, the PPR78 model can cover a large spectrum of petroleum fluids, from natural gases to crude oils [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. 20 groups exist and make it possible to accurately predict the phase behavior of mixtures containing alkanes, alkenes, aromatic compounds, cycloalkanes, permanent gases (CO 2 …”

Adiabatic Processes in the Vapor–Liquid Two-Phase Region. 2. Binary Mixtures

“…The binary interaction parameters k ij were either fitted to experimental data or obtained with the PPR78 (predictive Peng−Robinson equation) group contribution method of Jaubert, Qian et al 13,14 The Peng−Robinson equation is known to give reasonably good results for mixtures of nonpolar and weakly polar compounds. While certainly more sophisticated equations of state can be found in the literature, these will not predict qualitatively different thermodynamic properties.…”