Gibbs Free Energy Minimization for Prediction of Solubility of Acid Gases in Water

Abstract

The disposal of acid gas (CO 2 /H 2 S mixtures) is a critical aspect in the production of hydrocarbons from sour gas fields. The increasing emphasis on CO 2 sequestration has also renewed interest in the disposal of flue gas mixtures (primarily containing CO 2 and H 2 S). A common strategy for safe disposal, in either case, is to inject the acid gas in aquifers close to production plants. These strategies rely on solubility calculations at different pressures and temperatures, governed by the field operating conditions. We present a comprehensive approach using Gibbs free energy minimization to calculate acid gas solubility in water at high temperatures (298−393 K) and pressures (0.1−80 MPa). The advantage of this approach is the flexibility to use different thermodynamic models for different phases. The proposed model uses the Peng−Robinson (PR) Equation of State (EOS) description for gas components while the liquid components are described using the ideal assumption for the temperature range 298−323 K and the Nonrandom Two-Liquid (NRTL) activity coefficient model at temperatures greater than 323 K. The model predictions compare well with experimental data for binary (CO 2 −H 2 O and H 2 S−H 2 O) and ternary mixtures (CO 2 − H 2 S−H 2 O). The model can also be easily extended to predict the solubility of any gas in water as well as brine containing ions to incorporate geochemical reactions.

Organic acid concentration thresholds for ageing of carbonate minerals: Implications for CO2 trapping/storage

“…The NaCl was dissolved in deionized water (Ultrapure from David Gray; electrical conductivity = 0.02 mS/cm), which was equilibrated with calcite by rigorously mixing with calcite off-cuts while continuously monitoring the pH value. [36,37] Subsequently the NaCl brine was equilibrated with CO2 at experimental conditions in a high pressure mixing reactor. [38] Acetone (99.9 mol%; from Rowe Scientific) was used as surface cleaning agent, drops of hydrochloric acid (ACS reagent, concentration 37 vol%, Sigma Aldrich) were used to control the pH of the brine (see ageing procedure below for more details) and stearic acid (≥ 98.5 mol%; from Sigma Aldrich) was selected as a model for organic acid molecules present in the subsurface.…”

Solubility of Syngas Components in Water, Acetic Acid, and Alcohol Using New Standard Fugacity Methodology

“…Many of these studies apply CPA for all phases, but some still use − approach even at relative high pressure conditions, e.g. García et al (2006) 16 , Spycher and Pruess (2010) 17 , Hou et al (2013) 18 , Mao et al (2013) 19 and Venkatraman et al (2014) 20 .…”

“…Many of these studies apply CPA for all phases, but some still use γ−φ approach even at relative high pressure conditions, e.g. Garci ́a et al, 16 Spycher and Pruess, 17 Hou et al, 18 Mao et al, 19 and Venkatraman et al 20 In this work, we focus on the thermodynamic of 15 systems which may be of relevance for process simulation studies in connection with the biological synthesis of solvents, chemicals, or the production of biofuels from syngas. A thermodynamic model is presented which describes the solubility of CO, H 2 , CO 2 , CH 4 , and N 2 , i.e., the main component of biomass derived syngas, in combination with the three polar hydrogen bonding solvents: water, ethanol, and acetic acid.…”

“…Peng-Robinson EoS35 with the classical mixing rules was used to model the vapor phase nonideality in order to obtain the necessary fugacity contributions, � ( , , ), � ( , , ) and( )|, required in Eq (19). and Eq (20)…”

Modelling the impact of geochemical reactions on hydrocarbon phase behavior during CO2 gas injection for enhanced oil recovery

“…Compositional simulations are routinely used in the oil and gas industry to predict oil recovery. The entire reservoir is described as a sum of gridblocks in 15 these macroscopic simulations. Phase behavior computations are performed to obtain equilibrium compositions at every time step at different pressures but for a constant temperature in each gridblock.…”