Moodley, Kuveneshan.Naidoo, Paramespri.Nelson, Wayne Michael.Raghunanan, Rahul.2025-11-102025-11-1020242024https://hdl.handle.net/10413/24046Masters Degree. University of KwaZulu-Natal, Durban.Dehydration is a crucial step in the processing of raw natural gas. Water, which is naturally found in natural gas deposits, causes a significant problem during transportation, as it forms clathrate hydrates within the gas pipelines. To inhibit this formation, methanol is added to the extracted gas before piping to dehydration facilities where 2,2′-[ethane-1,2-diylbis(oxy)]di(ethan-1-ol) (triethylene glycol (TEG)) is commonly used to remove water from the natural gas. The presence of the methanol inhibitor in the gas affects the water/gas separation using TEG. This effect is not well understood due to the lack of description of the phase behaviour of the relevant multicomponent mixtures in the literature, which is required to design and optimise the gas dehydration process. This can result in ill-conditioned and inaccurate simulations for natural gas process plants, as predictions from binary VLE data alone have been shown to yield inaccurate descriptions of the separation behaviour. This study aims to further the available knowledge in natural gas processing by conducting highpressure phase equilibrium measurements, particularly, Pressure-liquid composition x, on novel systems of interest to the Gas Processing Association. This was performed for multicomponent mixtures commonly found in gas dehydration plants, with the measured data modelled using suitable thermodynamic models. The device employed for the vapour-liquid equilibrium measurements was a variable volume high-pressure sapphire cell apparatus. Measurements were conducted for the systems of CH4 (1) + CH3OH (2) and CO2 (1) + TEG (2) + water (2) to test the experimental equipment and method. Novel data were measured for the quaternary system of CH4 (1) + CH3OH (2) + TEG (3) + water (4) and the senary system of CH4 (1) + C2H6 (2) + C3H8 (3) + CH3OH (4) + TEG (5) + water (6) at 303.15 K, 313.15 K and 323.15 K. The verification test measurements were found to correlate well with literature data at similar conditions within the experimental expanded uncertainties of 0.06 K for temperature, 0.04 MPa for pressure, and composition uncertainty of 0.03 for the liquid phase composition. The phase behaviour showed a general proportional relationship between the pressure and light hydro-carbon composition except with the quaternary system, indicating higher solubility at higher pressures. The data were modelled using the Cubic Plus Association (CPA) equation of state, the Perturbed Chain Statistical Association Fluid Theory model (PC-SAFT) and the Peng and Robinson equation of state (PR). For the quaternary system, the CPA model performed the best, followed by the PC-SAFT and PR models. The absolute average relative deviation (AARD) and absolute average deviation (AAD) for the simultaneous regression of all three isotherms using the CPA model were 6.56%, 3.47% and 6.02% for the AARD values and 0.405 MPa, 0.325 MPa and 0.341 MPa for the AAD(P) values. For the senary system, the PC-SAFT model performed the best, followed by the CPA and PR models. The AARD and AAD for the simultaneous regression of all three isotherms using the PC-SAFT model were 2.46%, 3.43% and 4.24% for the AARD values and 0.043 MPa, 0.075 MPa and 0.106 MPa for the AAD(P) values. The CPA model exhibited the best performance when considering all measured systems and individual isotherms. The result of this study contributes toward design improvements and optimization of natural gas dehydration plants using TEG and methanol. Its purpose is to fill the gap currently existing in the available phase equilibrium data of fluid mixtures containing the chemicals investigated in this work.enCC0 1.0 Universalhttp://creativecommons.org/publicdomain/zero/1.0/Triethylene glycol.Methanol inhibitor.Gas Processing Association.Thesis