Effects of diethanolamine and ethylene glycol + diethanolamine aqueous solutions on methane hydrate stability conditions: Experimental measurements and thermodynamic modeling

Abstract

In this work, a total of 83 dissociation conditions data of methane hydrate in the attendance of diethanolamine (DEA) and diethanolamine + ethylene glycol (EG) aqueous solutions were first experimentally measured: 45 data for DEA and 38 data for DEA + EG aqueous solutions. The data were measured using a stainless steel (SS–316) cell by employing an isochoric pressure-search method. The methane hydrate stability conditions in various aqueous systems containing 0.09, 0.15, 0.25 mass fractions of DEA, (0.05 mass fraction of DEA + 0.05 mass fraction of EG), (0.05 mass fraction of DEA + 0.10 mass fraction of EG), and (0.15 mass fraction of DEA + 0.10 mass fraction of EG) were measured in the pressure range of 3.23–8.38 MPa and the temperature range of 274.1–283.0 K. It was observed that DEA causes thermodynamic inhibition of methane hydrate formation, and using 0.25 mass fraction of DEA in an aqueous solution shifts the methane hydrate stability temperatures to about 4.2 K. Also, it was concluded that although DEA has weaker strength compared to EG, it can be used as a gas sweetening agent and thermodynamic hydrate inhibitor. For modeling purpose, the van der Waals–Platteeuw (vdWP) model was employed for the hydrate phase, the Peng-Robinson equation of state (PR EoS) was utilized to compute the methane fugacity in the gas phase, and the NRTL activity coefficient model was applied to calculate the nonideality of the aqueous phase. The AAEs (K) obtained from this thermodynamic model for DEA and DEA + EG aqueous solutions are 0.2 and 0.4, respectively.