Water–Hydrocarbon Phase Equilibria with SAFT-VR Mie Equation of State

Abstract

The study of water -hydrocarbon phase equilibria is very important both for scientific as well as industrial purposes. This work is a thorough investigation of the predictive capability of SAFT-VR Mie equation of state (EoS) for aqueous hydrocarbon phase equilibria, including n-alkanes, alkenes, cycloalkanes, branched alkanes and aromatic hydrocarbons. For alkenes and alkyl benzenes, induced association (solvation) with water is considered. The model is able to capture the correct phase equilibrium topology for mixtures of n-alkanes and alkyl-benzenes with water as Type III according to Van Konynenburg and Scott, but is not able to predict the barometric shift for alkanes longer than n-hexacosane, due to the overshoot of the critical temperature of water.Quantitative results for the solubility of water in light hydrocarbons such as methane, ethane and ethylene, as well as the mutual solubility of hydrocarbons and water above the solubility minimum are possible. The latter is not predicted with SAFT-VR Mie EoS, similar to other EoS in the literature. Accurate predictions are also reported for the pressure of the three-phase equilibrium and the critical lines for the binary mixtures. The Henry's law constant is often used for the prediction of low-pressure vapor-liquid equilibrium, due to the low mutual solubility of hydrocarbons and water. EoS calculations are in reasonable agreement with experimental data for the Henry's constant, especially at higher temperatures. Qualitatively, SAFT-VR Mie captures the maximum of the Henry's constant with temperature, as well as the shift with carbon number at temperatures near critical to water. SAFT-VR Mie is shown to be overall capable for straightforward prediction of phase equilibria of aqueous hydrocarbon mixtures.

Mixed Solvent Electrolyte Solutions: A Review and Calculations with the eSAFT-VR Mie Equation of State

“…The physical term of the SAFT-VR Mie EoS − has been extended to electrolyte solutions by adding a DH and a Born term. The model has been described in detailed in our previous publications, − , and especially in our latest work, and will not be repeated here. This version of the eSAFT-VR Mie EoS was parameterized on MIAC of aqueous electrolyte solutions and successfully extended to nonaqueous single solvent electrolyte solutions, without any new adjustable parameters, by using a salt-dependent expression for the relative static permittivity .…”

A Review of Electrolyte Equations of State with Emphasis on Those Based on Cubic and Cubic-Plus-Association (CPA) Models

“…Overall the developments with eSAFT-VR Mie have been quite interesting and there are some very promising results. The eSAFT-VR Mie project has been continued also by the Texas A&M and DTU groups, as shown in a number of publications [72][73][74], where now the full DH equation is used for ion-ion interactions as well as a Born term which is salt composition-independent, thus not affecting the phase equilibria. Selam et al [72] applied the eSAFT-VR Mie with two fitted parameters for each ion (ion-size and dispersion interaction with water) obtained from mean ionic activity coefficients and densities with good results at room temperature but T-dependent interaction energies are needed at higher temperatures.…”

“…Activity coefficients and densities for mixed salts are well-represented in most cases. Novak et al [73,74] have illustrated the success of the approach for water-alkane VLE and LLE (even in absence of interaction parameters) and also applied successfully eSAFT-VR Mie to a very wide range of salting-out curves for many gases and salts. Very good results are obtained with newly estimated T-dependent ion-water parameters (shown for 9 ions) and ion-gas parameters fitted to gas solubility data (efforts to predict this parameter are shown but are not very successful).…”

“…While these arguments appear, at a first glance, convincing, we cannot be sure that they are entirely correct, at least we cannot be convinced they represent the only way to develop engineering electrolyte models. Many e-EoS have been proposed where the Born term and/or composition dependency of the relative permittivity have been ignored and still successful results are obtained [61][62][63][70][71][72][73][74], as the physical terms carry the effect otherwise assumed by the Born term (when the relative permittivity depends on salt concentration). For example, in our recent study [23] with eSAFT-VR Mie, we show that when all electrolyte terms are added (Born+ion-ion), their sum is comparable in magnitude to the "physical" term (as the Born term is positive and the ion-ion term is negative for the ion activity coefficients/chemical potentials).…”

The Effect of Binary Interaction Parameters and Induced Association on the Performance of the PC-SAFT Equation of State: Validation against a Benchmark Database of High-Quality Binary-System Data

“…While a lot of research activity is put on the improvement of existing EoS − and the development of new and more sophisticated ones, − the adoption rate of new models from the industry is rather low. Currently implemented models are replaced only if the advantages of newly proposed ones are very obvious. − The major factor for this slow industrialization of thermodynamic models seems to be the absence of extensive validation against accurate experimental data that cover a wide range of conditions and properties …”