Formation of Ice, Tetrahydrofuran Hydrate, and Methane/Propane Mixed Gas Hydrates in Strong Monovalent Salt Solutions

Abstract

Electrolytes can thermodynamically inhibit clathrate hydrate formation by lowering the activity of water in the surrounding liquid phase, causing the hydrates to form at lower temperatures and higher pressures compared to their formation in pure water. However, it has been reported that some thermodynamic hydrate inhibitors (THIs), when doped at low concentrations, could enhance the rate of gas hydrate formation. We here report a systematic study of model natural gas (a mixture of 90% methane and 10% propane) hydrate formation in strong monovalent salt solutions in a broad range of concentrations, using a high pressure automated lag time apparatus (HP-ALTA). HP-ALTA can apply a large number (>100) of cooling ramps to a sample and construct probability distributions of gas hydrate formation for each sample. The probabilistic interpretation of data enables us to mitigate the stochastic variation inherent in the nucleation probability distributions and facilitates meaningful comparison among different samples. The electrolytes used in this work are lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), sodium chloride (NaCl), sodium bromide (NaBr), sodium iodide (NaI), potassium chloride (KCl), potassium bromide (KBr), and potassium iodide (KI). We found that (1) some salts may act as kinetic hydrate promoters at low concentrations; (2) the width of the probability distributions (stochasticity) of natural gas hydrate formation in these salt solutions was significantly narrower than that in pure water. To gain further insight, we extended the study of the solutions of the same nine salts to the formation of ice and model tetrahydrofuran (THF) hydrate for comparison.

Effect of Brine Salinity on the Stability of Hydrate-in-Oil Dispersions and Water-in-Oil Emulsions

“…While salt is well known for its THI properties, highly saline systems will also lower the driving force for nucleation and growth of the hydrate phase, because they reduce the equilibrium solubility of hydrocarbon components in the aqueous phase. 25 Understanding and incorporating salt-induced changes to gas solubility into kinetic growth models is an important area for future work. In the present study, however, hydrates were intentionally formed under high (50 K) subcooling conditions, so that the effect of brine concentration on growth kinetics was negligible.…”

Potential applications of distributed optical fiber sensor in hydrate‐induced sedimentary deformation research

“…Ice is an ideal analog for methane hydrate for two reasons: (a) it is stable at ambient pressure conditions, and (b) the ice formation and melting processes in a porous medium are similar to those of methane hydrate. 40,41 The experimental setup is shown in Figure 4. A water bath (GDH-2015, Ningbo Scientz Biotechnology Co., Ltd, China, measuring error ±0.02 K), which was filled with a solution of 50% ethylene glycol by volume, was used to keep the reaction vessel and the methane injection pump at the required temperatures.…”

Thermodynamic study on gas hydrates: experimental determination of equilibrium data by high-pressure microcalorimetry and modeling up to 100 MPa.

“…The non-inhibited systems present smaller fractions of hydrate at 5 mol% than using both ILs and methanol. As previously mentioned, the acceleration of hydrate formation by employing usual thermodynamic inhibitors and ionic liquids has been reported in the literature (AMTAWONG et al, 2016;BOBEV;TAIT, 2004;CHA et al, 2013;KE et al, 2013;LEE et al, 2016;MCLAURIN et al, 2014;SOWA et al, 2014;SOWA et al, 2015;). Therefore, the inhibitors investigated in this work seem to contribute to hydrate formation and growth at low concentrations.…”

“…In fact, the same compound may act as both hydrate kinetic promoter and thermodynamic inhibitor at low concentrations, as discussed in previous works involving the following inhibitors: methanol for carbon dioxide and methane hydrates (BOBEV; TAIT, 2004;KE et al, 2013); monoethylene glycol for natural gas hydrate (CHA et al, 2013); salt solutions for methane-propane and tetrahydrofuran hydrates (SOWA et al, 2014;SOWA et al, 2015) (BLESIC et al, 2007;DUPONT, 2004). The presence of surfactants reduces the surface tension, thus favoring the gas solubilization and providing better conditions for hydrate nucleation and growth (CHEN et al, 2008;DI PROFIO et al, 2005;SHEN et al, 2016).…”