Predicting Vapor–Liquid Equilibria for Sour-Gas Absorption in Aqueous Mixtures of Chemical and Physical Solvents or Ionic Liquids with ePC-SAFT

Abstract

Sour-gas absorption is the main unit operation used in refineries and petrochemical and natural gas processing plants for the effective reduction of climate-wrecking gases, mainly CO 2 and H 2 S. Absorption is typically accomplished in an aqueous solvent mixture. The solvent mixture is vastly dependent on the application range; it might contain chemical solvents (amines), activators, and physical solvents. In this work, the vapor−liquid equilibria for absorption of the sour gases CO 2 and H 2 S was investigated in systems containing the chemical solvent methyl diethanolamine (MDEA) and the physical solvents tetrahydrothiophene-1,1-dioxide (sulfolane) or the ionic liquid 1-butyl-3-methylimidazolium acetate. The solubilities of CO 2 and H 2 S were predicted and validated using experimental literature data in a broad range of temperature (313−373 K), sour-gas loading (up to 2 moles gas per moles of MDEA), and pressure (up to 180 bar) at constant MDEA weight fraction (20.9 wt %) and sulfolane weight fraction (30.5 wt %). The equation-of-state electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) was utilized in this work for the predictions combined with the Born term to physically correctly describe the Gibbs energy of solvation of ions in the aqueous mixture of chemical and physical solvents; this was introduced in a recent work [Bulow, M. et al. Fluid Phase Equilib. 2021, 535, 112967]. Using this approach allowed reducing the total number of binary interaction parameters in these systems of maximum 11 species to a minimum; these parameters were fitted exclusively to data of binary mixtures. The ePC-SAFT predictions of the gas solubility were most accurate at low sour-gas loadings and high temperatures. This work provides a thermodynamic framework for the solvent selection for sour-gas absorption in a broad range of conditions. This enables a realistic decrease in experimental effort for solvent selection in sour-gas absorption.

Vapor Pressure Assessment of Sulfolane-Based Eutectic Solvents: Experimental, PC-SAFT, and Molecular Dynamics

“…The individual-component approach was applied in this work, which requires the availability of pure-component parameters for ILs and sulfolane. The pure-component parameters for sulfolane were taken from Bülow et al Sulfolane was modeled as a non-polar component that is not able to interact via self-association. The pure-component parameters of TBAB and TBPB were fitted in this work using aqueous solution densities (Table S5).…”

Calculation of Multiphase Equilibria Containing Mixed Solvents and Mixed Electrolytes: General Formulation and Case Studies

“…For phase-equilibrium calculation, the composition is translated on a single-ion basis. Considering the components in the order (water, 1-butanol, K + , Cl − , Na + , SO 4 2− ), the ion-based feed composition is z F = (0.310, 0.310, 0.085, 0.085, 0.140, 0.070) in mole fraction. The preprocessing-step procedure will be explained step by step in the following:…”

Solid–Liquid Equilibrium and Binodal Curves for Aqueous Solutions of NH3, NH4HCO3, MDEA, and K2CO3

“…Interaction parameters between CO 2 and MEA, n -methyldiethanolamine (MDEA), , piperazine, or ammonia have been obtained based on different types of phase equilibria (vapor pressure, vapor–liquid, and solid–liquid) and thermal (heat capacity and heat of absorption) data. ePC-SAFT has been used to model the mean ionic activity coefficient, the osmotic coefficient, the liquid–liquid equilibrium (LLE), and the density of alkali metal halides + organic solvent + water mixtures. − The model also provided an accurate prediction of the vapor–liquid equilibrium of sour gas and amine solvents using only parameters obtained from binary data . COSMO-RS-based models have also been successfully used to predict the solid–liquid equilibrium (SLE) and LLE of salt + water/organic solvent systems. − COSMO-based models can perform fully predictive calculations and are excellent tools for solvent screening applications; however, models with adjustable binary parameters (such as the extended UNIQUAC and ePC-SAFT) tend to present smaller deviation from experimental measurements.…”

“…28−30 The model also provided an accurate prediction of the vapor−liquid equilibrium of sour gas and amine solvents using only parameters obtained from binary data. 31 COSMO-RS-based models have also been successfully used to predict the solid−liquid equilibrium (SLE) and LLE of salt + water/ organic solvent systems. 28−30 COSMO-based models can perform fully predictive calculations and are excellent tools for solvent screening applications; however, models with adjustable binary parameters (such as the extended UNI-QUAC and ePC-SAFT) tend to present smaller deviation from experimental measurements.…”