Morphology Study on the Effect of Thermodynamic Inhibitors during Methane Hydrate Formation in the Presence of NaCl

Abstract

In this study, we investigate the morphology of methane hydrate formation and growth in the presence of wellknown thermodynamic inhibitors, monoethylene glycol (MEG) and methanol (MeOH) in a quiescent system. Morphology changes observed during the growth of methane hydrate while employing 5 wt % MEG and MeOH solutions in the presence and absence of NaCl are presented. When 5 wt % of MEG or MeOH was present in an aqueous solution individually, hydrate grew predominantly within the bulk solution featuring a "ridge"-shaped formation above the interface. In the presence of 3.5 wt % NaCl, an enhanced inhibition was observed for methane hydrates formed from 5 wt % MEG solution with limited hydrate growth in the bulk solution and above the gas-liquid interface. In contrast, 5 wt % MeOH solution in the presence of 3.5 wt % NaCl resulted in an increased hydrate growth in bulk (compared to the system without NaCl) and on the reactor wall above the gas−liquid interface, implying a weak promotion rather than the inhibition. Further, the effect of subcooling (ΔT) on the morphology of methane hydrates in the presence of MeOH/NaCl and MEG/NaCl was examined.

Assessment of commercial hydrate inhibitors using the 3‐in‐1 method

“…The surface roughness of the hydrates varies considerably among the inhibitors used, as well as the degree of translucency. Several authors have reported the increase in surface roughness with the addition of KHIs, as well as with THIs . Classical KHIs such as polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCap), and other lactam ring‐containing polymers form rough hydrate films with ridges or wrinkles on methane, tetrahydrofuran (THF), and gas mixtures …”

“…This dependence of the crystal habit on subcooling, namely the density of grains, ridges, and dendrites, has been reported for several KHIs and THIs, although the particular morphologies are different in each case . Since crystal habit changes to yield morphologies with the lowest energies, these differences can be seen as the system's response to the presence of KHI.…”

Estimation of the methanol loss in the gas hydrate prevention unit using the artificial neural networks: Investigating the effect of training algorithm on the model accuracy

“…The thermodynamic inhibitors prevent hydrate formation by shifting pressure and temperature to values at which hydrants are unstable. There are several traditional THIs, namely, alcohols (e.g., methanol), electrolytes (e.g., NaCl), and ethylene glycols 18,19 …”

“…There are several traditional THIs, namely, alcohols (e.g., methanol), electrolytes (e.g., NaCl), and ethylene glycols. 18,19 As high concentrations of the thermodynamic inhibitor agents (10-50 wt%) must be utilized, the gas hydrate prevention unit may be costly. Methanol injection costs more than $500 million annually to avoid hydrate formation.…”

Investigation of Hydrate Inhibition System for Shallow Water Gas Field: Experimental Evaluation of KHI and Simulation of MEG Regeneration Process

“…formation process through the ring-structure connected in chains, during which water molecules convert to the hydrate crystal structure, while simultaneously decelerating the growth of hydrates by adhering to growth points after hydrates are formed (Kim et al, 2018b).…”