Determination of clathrate hydrates dissociation conditions in the presence of gas dehydration, sweetening, and other nitrogenated additives using a predictive thermodynamic approach

Abstract

–Despite numerous experimental data on gas hydrate equilibrium conditions in the presence of glycols, alkanolamines, and nitrogenated additives that are frequently utilized in the gas refinery, the apparent lack of a precise predictive thermodynamic model is still perceived. This study presents an unprecedented thermodynamic framework benefitting from the modified van der Waals-Platteeuw (vdW-P) model for the hydrate phase, the Peng-Robinson equation of state (PR EoS) for the vapor/gas phase, and combinations of free-volume Flory Huggins (FVFH) and Pitzer-Debye-Hückel (PDH) equations for the water activity in the aqueous phase, in which the FVFH activity model is utilized for the additives with molecular interactions solely, while the PDH model is employed when the ionic interactions also exist. When the model assessed a databank of 1075 data points, 0.29% (0.80 K) and 9.67% (0.49 MPa) deviations were observed in the temperature and pressure calculations, respectively. In particular, for 877 data points (glycols, urea, acetamide, and formamide), employing FVFH solely resulted in 0.32% (0.88 K) and 10.54% (0.50 MPa) temperature and pressure deviations, respectively, whereas the combination of FVFH + PDH yielded 0.17% (0.48 K) and 5.81% (0.47 MPa) errors in temperature and pressure estimations, respectively in 198 data points of the systems comprised of amines, hydrazine, and piperazine. The maximum deviation of temperature prediction did not exceed 6.80 K (2.39%). The results reveal the effective performance of the proposed calculation approach.