Multicomponent vapor-liquid equilibrium measurements and modeling of triethylene glycol, water, and natural gas mixtures at 6.0, 9.0 and 12.5 MPa

Triethylene glycol (TEG) is commonly used for natural gas dehydration, and with subsea processing facilities on the rise, an increasing interest is being shown in complex phase equilibria involving petroleum fluids and polar compounds. In this study, examples of such phase equilibria have been studied. New measurements for multicomponent vapor-liquid equilibrium (VLE) of TEG/Water/Natural Gas systems have been performed at pressures ranging from 6.0 MPa to 12.5 MPa and temperatures in the range 15 °C to 40 °C. Two types of natural gas, a Synthetic Gas (xCH4=0.62) and a Real Gas (xCH4=0.92), were mixed with an aqueous TEG solution, with TEG weight percentages ranging from 95 wt.% to 99 wt.%. Glycol in gas (y1), water in gas (y2), and gas solubility in liquid (xNG) were measured with relative experimental uncertainties below 32%. Since the systems are highly associating, the Cubic-Plus-Association (CPA) equation of state (EoS) was selected to model their phase behavior . Different association schemes (4C, 4F, 5F, 6F and 5C) were tested for TEG, and the classical 4C scheme is shown to perform best. The CPA EoS performed in general terms well, considering the number of components in the systems, the associated complexities, and high measurement uncertainty for such low concentrations (