Thermodynamic and Physical Properties of Glycol Related Systems: Experiments and Modeling

As subsea processing facilities continue to expand, increasing attention is being directed toward the complex phase behavior of systems containing petroleum fluids and polar chemicals such as water, methanol, and glycols. Among these production chemicals, triethylene glycol (TEG) has emerged as the most widely used fluid for natural gas dehydration (NGD) due to its superior cost benefit compared to alternative options. Achieving stringent product specifications during the dehydration process is essential to ensure asset integrity during downstream transport, as the water presence in natural gas is associated with severe operational challenges, including corrosion and gas hydrate formation. On the other hand, while TEG is vital for effective dehydration, its presence in downstream processes and refined products is undesirable due to potential negative impacts. Consequently, there is a pressing need to balance the use of TEG within acceptable process safety margins and its environmental consequences. A fundamental aspect of this balance is understanding the partitioning behavior of TEG between the gas, crude oil, and water phases. Different methods and software can be used to obtain more or less accurate predictions of the interaction between these chemicals. Most of them depend on thermodynamic models, which rely on the precision and accuracy of experimental data. In this context, this Ph.D. project addressed these challenges by expanding the experimental database used for novel technologies development in subsea gas processing. The research focuses on measuring the physical and thermodynamic properties of systems containing glycols, with an emphasis on TEG. Advanced experimental methodologies were employed, including the use of a vibrating density meter to obtain PρT data over a broad range of temperatures and pressures. Equilibrium measurements were conducted using a high-pressure equilibrium cell (Sanchez Technology, France). The unique analytical component developed by Equinor’s technical team is the most outstanding part of this work. This system integrates automated thermal desorption with the gas chromatography/mass spectrometry (Agilent 5975C) techniques to achieve exceptionally low detection limits, in the order of ppb, for TEG content in the gas phase. The experimental measurements were complemented by thermodynamic modeling using the Cubic-Plus-Association (CPA) Equation of State. The CPA model, employing the original 4C parameter set and one interaction parameter per binary, demonstrated qualitatively good performance across all evaluated cases, with AARD ranging from 2.6 to 54.1%. Experimental and modeling trends support optimizing the natural gas dehydration process under subsea conditions.