Dependence of the Kinetic Hydrate Inhibition Effect of Poly(N-vinylpyrrolidone) upon the Molecular Weight Is Influenced by Water Mobility in Millisecond Dynamics

Abstract

Explosive formation of a natural gas clathrate hydrate in production lines has been a technical bottleneck in ocean field natural gas drilling and gas transport. To mitigate this problem, polymer inhibitors can be used as a low-dosage kinetic inhibitor during operation. Key factors affecting the physicochemical performance of a benchmark inhibitor, poly(N-vinylpyrrolidone) (PVP),are not yet completely known. It is found here that the ability of PVP to delay the rapid crystal growth of the clathrate hydrate is correlated to the surrounding water dynamics. PVP can produce immobilized non-freezable water molecules with fast transverse relaxation on a sub-millisecond to millisecond time scale as revealed by nuclear magnetic resonance relaxometry. The unique water dynamics are also determined as a form of non-freezable bound water measured by differential scanning calorimetry. Changes in the molecular weight of PVP lead to changes in the entire inhibition time before the rapid growth of the hydrate crystals, and an optimal size of the PVP chain is found for the best inhibition. The hydrate crystallization rate constants are lowered by 1−2 orders of magnitude when the PVP chains have near the optimal size, further providing an explanation of the chain length dependence of the inhibition time.

Unraveling Amphiphilic Poly(N-vinylcaprolactam)/Water Interface by Nuclear Magnetic Resonance Relaxometry: Control of Clathrate Hydrate Formation Kinetics

“…In Table 2, the trend in n and k values is almost similar to that for PVP. 41 The decreasing k values on going from PVCap M n polymer was lowered gradually, the heat of the endothermic transition was gradually decreased and could be extrapolated to zero at a certain mass ratio. The amount of the endothermic transition heat versus the R values are shown for different PVCap samples in Figure 6.…”

Adsorption‐Inhibition of Clathrate Hydrates by Self‐Assembled Nanostructures

“…[69] In contrast, PVP binds to hydrates but not to ice, probably via filling cavities (i. e. open cages) with its pyrrolidone ring [17,29] rather than by the clathrate water mechanism. It is also possible that PVP binds to hydrates via ordered waters, [14,15] but the layer of waters formed on the polymer is not a good match for ice surfaces.…”

“…[12,13] Li et al measured the water mobility in Polyvinylpyrrolidone (PVP), a known hydrate inhibitor, suggest that PVP exhibits ordered water molecules that might facilitate binding to the surface of the crystal. [14,15] However, the mechanism by which KHIs inhibit hydrate growth is not fully understood.…”

A chromatographic approach for studying the adsorption of polar small molecules on tetrabutylammonium bromide semiclathrate hydrate

“…1): I) adsorption via hydrophobic hydration of the hydrophobic part of LDHI on the CH surafce; [8][9][10][11][12] II) adsorption via hydrogen bonds (H-bonds) between the polar groups of LDHIs and water molecules comprising CH crystals, in some cases concomitantly with deformation or destruction of the CH cages; [13][14][15] III) partial dissolution of the hydrophilic part of LDHIs into a quasi-liquid layer (QLL) on the CH surface; 16 and IV) a combinational mechanism of I and II, i.e., H-bonding adsorption of the polar groups accompanied with hydrophobic interaction of the hydrophobic parts. 17 One of the reasons for such various mechanisms proposed is probably that these mechanisms were proposed based on various experiments conducted under different conditions. In practice, previous reports imply that the adsorption mechanism depends on the properties of the 4 hydrate/liquid interface (in particular, whether the interface is hydrate/aqueous or hydrate/hydrocarbon) 18,19 and the structure of the LDHIs (size and hydrophilicity/hydrophobicity of the functional groups).…”