Experimentally measured methane hydrate phase equilibria and ionic liquids inhibition performance in Qatar’s seawater

Abstract

Qatar has the third-largest natural gas reserves in the world and is the second largest Liquefied natural gas (LNG) exporter in the world. These reserves are mainly located in its offshore North Field where the gas is extracted, transported to the onshore units, and is converted to LNG for international export. The formation of natural gas hydrates in the offshore subsea lines can cause unwanted blockages and hinder the smooth supply of gas supply from offshore to onshore units. In the present work, the formation and dissociation of methane gas hydrates have been studied in the ultra pure water system (UPW), artificial seawater (ASW), and Qatar seawater (QSW) at different conditions (4–10 MPa) using standard rocking cell rig. The naturally occurring seawater was collected from Ras Laffan seacoast located in Doha, Qatar. The seawater sample was examined for elemental analysis (SO4, Cl, Na, Ca, Mg, K, and Fe) using inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique and its other properties like density, electrical conductivity, and pH were also measured. The experimental results show that the CH4 pure water HLVE curve is suppressed by about 3 K in Qatar seawater and 2 K in artificial seawater. The hydrate inhibition strength of the Ionic liquids (ILs) salts 3-Ethyl-1-methyl-1H-imidazol-3-ium methane-sulfonate [C7H14N2O3S] and 3-Ethyl-1-methyl-1H-imidazol-3-ium dicyanoazanide [C8H11N5] was evaluated in both the ultra pure water and Qatar seawater systems. Their performance was compared with methanol and other ILs salts reported in the literature. The selected ILs exhibited poor hydrate inhibition effect in the ultra pure water systems, but they show a noticeable thermodynamic and kinetic hydrate inhibition effect in the Qatar seawater system. The computational 3D molecular models of ILs and methanol were generated to cognize the plausible hydrate inhibition mechanism in the presence of these inhibitors.

Can Aluminum Cations Promote Nucleation for THF Hydrate Growth?

“…Therefore, ions in the solution impede nucleation kinetics, as the driving force for hydrate crystallization reduces. Many studies have also reported that salts increase induction time. , For instance, Qureshi et al found that the induction time for ultrapure water was lower than that of seawater. Similarly, Pahlavanzadeh et al reported that the induction time was 5.1, 6.3, 17.2, and 21.3 min at NaCl concentrations of 0, 3.5, 5, and 8 wt %, respectively, for R410a hydrate.…”

Dual Promotional Effect of l-Tryptophan and 1,3-Dioxane on CO2 Hydrate Kinetics in Seawater under Static/Unstatic Conditions for Carbon Capture and Storage Application

“…However, on the basis of the above experiments, the salts in seawater act as hydrate inhibitors. The presence of ions may reduce the availability of free water molecules in the system and may cause electrostatic interactions with the molecules, impeding the formation of gas hydrates and affecting the performance of hydrate promoters . Therefore, more research is needed, including advance computational modeling, nuclear magnetic resonance (NMR), Raman, and other in situ techniques, to understand the acting mechanism of l -tryp and 1,3-dioxane in saline systems.…”

Investigating High-Pressure Liquid CO2 Hydrate Formation, Dissociation Kinetics, and Morphology in Brine and Freshwater Static Systems

“…As sodium chloride [NaCl] is a natural hydrate inhibitor, water-to-hydrate conversion is challenging to a greater extent in such saline systems. − l -Tryptophan, a kinetic promoter that does not affect thermodynamic stability, , was tested to stimulate the formation of CO 2 hydrates . Based on earlier reported investigations with CO 2 hydrates, an optimum dosage of 500 ppm was chosen .…”