Vapor–Liquid Equilibrium Measurements and Cubic-Plus-Association Modeling of Triethylene Glycol + Water + Methane Systems at 6.0 and 12.5 MPa

Abstract

As a part of a series of studies that aim to expand the experimental database used to assist the design of novel technologies in the field of subsea gas processing, 18 new vapor–liquid equilibrium data points were measured for the system triethylene glycol (1) + water (2) + methane (3) at 6.0 and 12.5 MPa, temperature range between 288 and 323 K, and a glycol content above 95 wt %. The new data include both gas [glycol (y 1) and water (y 2)] and liquid [methane solubility (x 3)] phase composition, with relative experimental uncertainties below 18%. It was observed that one of the experimental data sets available in the literature is not in agreement with the experimental data measured in this work. Furthermore, an important target was to reevaluate the cubic-plus-association (CPA) equation-of-state modeling capability, which has been previously used for triethylene glycol–methane systems. CPA using a 4C association scheme for TEG and one interaction parameter per binary has provided a good description of the newly measured data, with the average absolute relative deviation ranging between 9 and 43%. Binary interaction parameters regressed solely from the corresponding binary data were used for all ternary predictions with CPA.

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

“…Initial experiments were conducted at 40 °C to confirm that the results were consistent with the literature. As shown in Figure 3, our data is most consistent with that of Fisher et al 7 As noted recently by Trancoso et al, 5 the data from Jerinic et al 8 appears high. We were able to record only a single data point at a high pressure (134 bar) due to a loss of cylinder gas pressure.…”

“…These authors concluded that the best approach was to use a new set of parameters with the 4F association scheme. The more recent papers from this research group however 4,5 confirm that the 4C data set proposed by Derawi et al 9 provides the best data fit when their more extensive experimental data set is used.…”

“…The inlet methane pressure was adjusted by a two-stage pressure regulator (PR-1, from BOC Limited) with a maximum outlet pressure of 300 bar. A sliding-stem digital flow controller was used to enable low flow rates (mL/min) at pressures up to 180 bar (CV-1, Fisher Baumann 51,000 Series, Western Process Controls Vic), which Literature data is from Qvistgaard et al, 4 Fisher et al, 7 Jerinic et al, 8 and Trancosco et al 5 Simulations use the CPA equation of state (eq 1) with parameters from Derawi et al 9 and a binary interaction parameter of k ij = 0.136 or 0.1634. was driven by an external power source providing 4−20 mA and 8−30 V. The gas passed in turn through three stainless steel 300 mL cylinders (E-1, E-2, and E-3, Swagelok Australia) each equipped with a central distribution tube, packed with spherical stainless steel beads for effective gas−liquid contact, and filled with liquid TEG. The use of three consecutive cylinders ensured that the gas exiting the last cylinder was at equilibrium.…”

“…Similarly, Arya et al 3 note that "some new experimental data have to be obtained in order to conf irm the existing data sets for the TEG content of a methane vapor phase'". During the preparation of this manuscript, new data was presented by Qvistgaard et al 4 and Trancoso et al 5 which adds to the experimental database. However, much of this data was collected at 25 °C or below, and all experiments contain between 15 and 300 ppm of water vapor.…”

“…Figure 1. Literature data and simulations for the concentration of TEG in ppm in methane as a function of system pressure at 25 °C.Literature data is from Qvistgaard et al,4 Fisher et al,7 Jerinic et al,8 and Trancosco et al5 Simulations use the CPA equation of state (eq 1) with parameters from Derawi et al9 and a binary interaction parameter of k ij = 0.136 or 0.1634.…”