Experimental Measurement of Dissociation Condition for Carbon Dioxide Hydrates in the Presence of Methanol/Ethylene Glycol and CaCl₂ Aqueous Solutions

Abstract

In this study, hydrate dissociation conditions of carbon dioxide in the presence of methanol/ethylene glycol + CaCl 2 at the temperature range of 262.2−276.8 K and the pressure range of 1.49−3.36 MPa, not found in the related literature, were measured and reported. The equilibrium data were conducted by isochoric pressure search method. The experimental findings showed that methanol inhibition power was superior to that of ethylene glycol at similar mass concentrations. An available thermodynamic model was used to predict and compare the results with the measured experimental data. In addition, in order to investigate the inhibitory effect of various inhibitors as well as their synergy to one another, the suppressed temperature of hydrate formation in the presence of various inhibitory solutions used in this work and also in the similar studies in the literature was examined. This measurement indicated no effect of pressure on the reduction amount of suppressed temperature for each solution, so that it can be considered to be independent of pressure. Moreover, at low concentrations synergy level of CaCl 2 with methanol or ethylene glycol was negligible, indicating no effect of these two inhibitors on the performance of each other. By increasing the concentration of alcohol and glycol, this rule was interrupted and inhibitors interacted each other and the synergy level increased.

Phase Equilibrium of Methane Hydrates in the Presence of MgBr2, CaBr2, and ZnBr2 Aqueous Solutions

“…The role of inhibitor salts, such as MgBr 2 , CaBr 2 , and ZnBr 2 is to obstruct or delay the hydrate formation. When salts are added to water, it decreases the host water concentration through a phenomenon referred to as “salting-out”, and becomes responsible for not allowing water molecules to come closer, affecting the hydrogen bonding and reducing the activity of the water. , This in turn reduces the guest gas and host water interactions, and ultimately hinders the hydrate formation. As the concentration of the salt in the water increases the inhibition effect also increases. , Therefore, the addition of inhibitors to the system increases the hydrate equilibrium pressure at a given temperature.…”

“…Although gas hydrates show several industrial applications, they are still treated as a nuisance in the oil and gas industry due to their unwanted formation during production, transportation, and processing of natural gas causing operational problems, equipment blockages, and safety concerns. , Because of the continuous formation of hydrate inside the pipelines, the pressure may build between the upstream and downstream sections, and cause the equipment failure and may lead to a pipeline blast . Injection of inhibitor, insulation or heating the facilities to keep the operating conditions outside the hydrate formation zone, and dehydration of the gas flow are some of the ways to avoid hydrate formation.…”

“…Injection of inhibitor, insulation or heating the facilities to keep the operating conditions outside the hydrate formation zone, and dehydration of the gas flow are some of the ways to avoid hydrate formation. The injection of an inhibitor is one of the easiest and the most widely used method among all . Hydrate inhibitors are divided into two major categories, namely kinetic hydrate inhibitors (KHI) and thermodynamic hydrate inhibitors (THI).…”

“…Hydrate inhibitors are divided into two major categories, namely kinetic hydrate inhibitors (KHI) and thermodynamic hydrate inhibitors (THI). Kinetics hydrate inhibitors are further divided into low-dosage hydrate inhibitors (LDHI) and antiagglomerants; whereas, THI are divided into organic inhibitors and electrolytes. − LDHI delays the hydrate formation, whereas the antiagglomerate lets the small hydrate crystal form inside the system but avoids the agglomeration. The THI are typically water-soluble compounds and help in shifting the hydrate equilibrium conditions to high pressures and low temperatures.…”

“…However, the addition of electrolyte to the organic inhibitors reduces the operational cost. The phase equilibrium conditions for methane and carbon dioxide hydrates in the presence of aqueous solutions of methanol and/or ethanol, and/or ethylene glycol along with single electrolytes such as NaCl, KCl, CaCl 2 , and MgCl 2 (i.e., a mixture of organic inhibitor and electrolyte) at different mass fractions have been studied in the literature. ,,− The effect of a single electrolyte such as MgCl 2 in the concentration range of 3–15 wt %, and 3–10 wt %, respectively, on methane and carbon dioxide hydrate formation was studied . High pressure differential scanning calorimetry (DSC) was used to understand the phase behavior of methane hydrate formed in aqueous solutions of NaCl at 12 and 17 wt %, and that of CaCl 2 at 5, 10, 15, 20, 23, and 25 wt % .…”