Synergistic Hydrate Inhibition of Monoethylene Glycol with Poly(vinylcaprolactam) in Thermodynamically Underinhibited System

Abstract

This study investigates the hydrate inhibition performance of monoethylene glycol (MEG) with poly(vinylcaprolactam) (PVCap) for retarding the hydrate onset as well as preventing the agglomeration of hydrate particles. A high-pressure autoclave was used to determine the hydrate onset time, subcooling temperature, hydrate fraction in the liquid phase, and torque changes during hydrate formation in pure water, 0.2 wt % PVCap solution, and 20 and 30 wt % MEG solutions. In comparison to water with no inhibitors, the addition of PVCap delays the hydrate onset time but cannot reduce the hydrate fraction, leading to a sharp increase in torque. The 20 and 30 wt % MEG solutions also delay the hydrate onset time slightly and reduce the hydrate fraction to 0.15. The addition of 0.2 wt % PVCap to the 20 wt % MEG solution, however, delays the hydrate onset time substantially, and the hydrate fraction was less than 0.19. The torque changes were negligible during the hydrate formation, suggesting the homogeneous dispersion of hydrate particles in the liquid phase. The well-dispersed hydrate particles do not agglomerate or deposit under stirring. Moreover, when 0.2 wt % PVCap was added to the 30 wt % MEG solution, no hydrate formation was observed for at least 24 h. These results suggest that mixing of MEG with a small amount of PVCap in underinhibited conditions will induce the synergistic inhibition of hydrate by delaying the hydrate onset time as well as preventing the agglomeration and deposition of hydrate particles. Decreasing the hydrate fraction in the liquid phase might be the reason for negligible torque changes during the hydrate formation in the 0.2 wt % PVCap and 20 wt % MEG solution. Simple structure II was confirmed by in situ Raman spectroscopy for the synergistic inhibition system, while coexisting structures I and II are observed in 0.2 wt % PVCap solution.

Instrumental Methods for Cage Occupancy Estimation of Gas Hydrate

“…Raman spectroscopy is a very good instrument method for hydrate qualitative study (including composition [26], structure type identification [57,76]) and quantitative study [19,[80][81][82] (including cage occupancy and hydration number). This information will be applied to the hydrate kinetics process study (including formation [46,51,60,65,[83][84][85], dissociation [33,36,64,86], gas replacement [50,60,87,88], and inhibitors [47,89]), structure changes [8,11,31,34,35,41,45,49,90], hydrate distribution [26,38,43], and structural characterization [91][92][93].…”

Synergism of thermodynamic hydrate inhibitors on the performance of poly (vinyl pyrrolidone) in deepwater drilling fluid

“…Daraboina et al (Daraboina et al, 2013) reported that PEO and NaCl could enhance the nucleation inhibition strength of Luvicap. Kim et al (Kim et al, 2014) reported that mixing of monoethylene glycol with PVCap in underinhibited conditions would induce the synergistic hydrate inhibition by delaying the hydrate onset time as well as preventing the agglomeration and deposition of hydrate particles. As the earliest KHI polymer, PVP is the representative product of the first generation KHIs, which has provided theoretic and practical basis for design and development of the subsequent generation of KHIs.…”

Density and Electrical Conductivity for Aqueous Mixtures of Monoethylene Glycol and Sodium Chloride: Experimental Data and Data-Driven Modeling for Composition Determination

“…The formation of gas hydrates is a serious problem in hydrocarbon exploitation, transportation, and processing, for example, plug the flow lines and choke valves. Hence, it is of great importance to prevent gas hydrate formation to avoid these operational problems. , Monoethylene glycol (MEG) is a solvent capable of blending with free water, changing the thermodynamic conditions and avoiding the undesirable formation of gas hydrates. − MEG presents advantages in relation to other inhibitors (for example, methanol): relative low viscosity that gives better outflow, easy recovery based on its low volatility in relation to water, low solubility in liquid hydrocarbons, and low toxicity. − …”