Phase Behavior in Natural Gas + Glycol Systems, Part 1: Tri(ethylene glycol) (TEG) and Its Aqueous Solutions

Abstract

Glycols and their aqueous solutions are extensively utilized in the natural gas industry as hydrate inhibitors and desiccant agents. An increasing interest in new applications, such as subsea processing and carbon capture and storage (CCS) gas dehydration, requires evaluations for operations at high pressure. New measurements are presented for methane and a natural gas mixture (methane−ethane−propane− carbon dioxide) in tri(ethylene glycol) (TEG) and TEG aqueous solutions. Solubility measurements were carried out at pressures up to 40 MPa for temperatures T = (273.15 and 353.65) K. Water content data covers temperatures between (278.15 and 313.15) K at p = (6 and 12.5) MPa. In addition, water activities in such solutions are also reported. The experimental data were modeled with three different approaches: the simplified cubic-plus-association (sCPA), a Huron−Vidal Soave−Redlich−Kwong (SRK) equation coupled with the Non-Random Two-Liquid (NRTL) Gibbs energy (g ex ) expression (SRK/HV/NRTL), and the non-density-dependent approach to Peng− Robinson (PR/NDD). The SRK/HV/NRTL model was found wanting for correlating experimental methane solubility data, while the PR/NDD and sCPA were successful in describing the methane/TEG phase behavior but not TEG aqueous solutions. An alternative approach that includes a binary interaction parameter dependent on the liquid phase composition (xk ij ) gave fair to satisfactorily results, particularly in the case of sCPA. For the multicomponent system, sCPA-xk ij has yielded more consistent predictions than PR/NDD-xk ij , especially for total gas solubility. Overall, all the models have failed to give satisfactory results based only on binary parameters.

Vapor–Liquid Equilibrium Measurements and Cubic-Plus-Association Modeling of Triethylene Glycol Systems

“…De Oliveira Cavalcanti Filho et al 4 and Qvistgaard et al 9 have also shown the importance of VLE studies with TEGmulticomponent systems. Their measurements of gas mixture solubility in TEG or TEG aqueous solutions reveal that the addition of heavier alkanes, such as ethane and propane, and other complex molecules, such as CO 2 and water, limits the capabilities of the thermodynamic models when the parametrization is based exclusively on binary parameters.…”

Triethylene Glycol Solubility in High-Pressure Methane: New Experimental Data at 40 to 60 °C

“…This model can effectively describe the solubility of methane in liquid glycol solutions. ,,− However, the use of the same model parameters has been less successful in predicting the vapor pressure of glycol in the corresponding gas phase. Breil and Kontogeorgis successfully fit the vapor pressure data of Jerinic et al, but this set of parameters provides very high deviations for experimental data for pure TEG.…”

P-T-x Measurement and Modeling of Methane + Propane + Methanol or 2,2′-[Ethane-1,2-diylbis(oxy)] Di(ethan-1-ol) and Methane + Propane + Methanol + 2,2′-[Ethane-1,2-diylbis(oxy)] Di(ethan-1-ol) Systems

“…Thermodynamic modeling of the measured data was performed in Aspen Plus V12 using the Cubic Plus Association (CPA) and the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) models and the phi-phi formulation. The CPA model of Kontogeorgis et al has been used successfully to describe the phase equilibrium behavior of mixtures including hydrocarbons, methanol, water, and glycols. − The PC-SAFT model by Gross and Sadowski has also been successfully utilized in predicting and correlating phase behavior data for mixtures including glycols, hydrocarbons, and water. , Hence, these models were deemed appropriate for use in this study.…”