First Investigation of the Kinetic Hydrate Inhibition of a Series of Poly(β-peptoid)s on Structure II Gas Hydrate, Including the Comparison of Block and Random Copolymers

Reyes, Fernando T.; Kelland, Malcolm A.; Kumar, Nishant; Li, Jia

doi:10.1021/ef502539u

Cited by 37 publications

(49 citation statements)

References 25 publications

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“…This percentage decreases somewhat toward lower average onset temperatures. 24,25 The T a value indicates the slow hydrate growth region prior to the rapid hydrate formation, where the KHI can no longer stop or prevent the hydrate from growing. The difference between T o and T a indicates the ability of KHI to hinder the rapid crystal growth after the first detectable hydrate formation has first begun.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Kinetic Hydrate Inhibition with N-Alkyl-N-vinylformamide Polymers: Comparison of Polymers to n-Propyl and Isopropyl Groups

et al. 2015

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Gas hydrates in the upstream oil and gas industry often cause problems during production, such as plugged pipelines causing down time and loss of revenue. Kinetic hydrate inhibitors (KHIs) have successfully been used in the field for about 2 decades. KHIs work to delay hydrate nucleation and/or crystal growth in the hydrate-stable operating region. KHIs, such as polymers containing N-vinyl amide units, for example, methacrylamide-based KHI polymers with isopropyl groups, have been commercialized and are now used in field operations. However, there are no reports of polymers with n-propyl groups that have been commercialized as a KHI. Using a structure-II-forming natural gas, we have now investigated the KHI performance of homopolymers with n-propyl and isopropyl groups based on the N-vinylformamide (NVF) monomer. A range of copolymers with NVF with higher cloud points were also synthesized and tested because the cloud points of these homopolymers were found to be lower than preferred for most field operations. The polymer series containing nPr-NVF monomer was found to perform better as KHIs than the iPr-NVF series as KHIs at 2500 ppm concentration in deionized water at all copolymer ratios with a similar molecular weight. Two of the best polymers from each of the nPr-NVF and iPr-NVF series were tested at varying concentrations from 1500 to 5000 ppm. A similar trend was found as with the tests of the complete series, in which the nPr-NVF polymer performed better than the iPr-NVF polymer. Poly(N-(n-propyl)-N-vinylformamide) homopolymer gave a similar KHI performance as a commercial sample of polyvinylcaprolactam (PVCap). ■ INTRODUCTIONNatural gas hydrates tend to form at elevated pressures and low temperatures, which are typical conditions in cold-climate upstream oil and gas fields and subsea multiphase pipelines. 1,2 Under these thermodynamic conditions, water molecules form cage-like structures and trap small gas molecules within these hydrate structures. Typical gas molecules are small hydrocarbons, such as methane, ethane, and propane, as well as carbon dioxide and hydrogen sulfide. 2−4 Low-dosage hydrate inhibitors (LDHIs), such as kinetic hydrate inhibitors (KHIs), are used in the oil and gas industry as a method for preventing the formation of gas hydrates; logistically, they can be more efficient and/or less expensive than other hydrate management methods. 2,5−8 KHIs delay the hydrate nucleation, which is the first stage of hydrate formation. 9 When the temperature and pressure conditions reach the hydrate-stable region, hydrate nuclei (clusters of water and gas) come together, grow, and disperse to reach the critical size for hydrate crystal growth. 2,10 Mechanisms for how the inhibition works on a molecular level are not fully understood, but some theories have been proposed. 11,12 It is generally believed that the KHI causes perturbation of the water and/or water/gas (hydrocarbon) interaction; therefore, the hydrate clusters will not reach the critical size, thus delaying the hydrate formation. 13,14 ...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Kinetic Hydrate Inhibition with N-Alkyl-N-vinylformamide Polymers: Comparison of Polymers to n-Propyl and Isopropyl Groups

et al. 2015

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“…The mechanism of KHIs has still not been fully understood. Most KHIs are water-soluble polymers. ,,− It is known that monomers of KHIs exhibit little inhibition effect and that the performance of KHIs increases sharply with increasing polymer size and then decreases gradually under a constant wt % of the inhibitor. ,,, Figure shows the size dependence of the supercooling ability of PVCap for methane hydrate taken from an experimental study of Sloan et al In their experiment, methane hydrate formed at Δ T = 6 K in the absence of PVCap when the temperature decreased at a constant rate of 2.5 K h –1 at 206 bar (formation of methane hydrate was detected by a rapid decrease in pressure). The effect of monomers was found to be negligible in concentrations as high as 5 wt %.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study of Kinetic Hydrate Inhibitors: The Optimal Inhibitor Size and Effect of Guest Species

2018

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We propose a model for slowing down of clathrate hydrate formation caused by kinetic hydrate inhibitors (KHIs) on the basis of the Gibbs–Thomson effect. The residence time of inhibitor molecules bound to the hydrate surface and the intrinsic growth rate of the clathrate hydrate without KHIs are key ingredients of the model. The binding free energies of the monomer, dimer, tetramer, and octamer of a KHI, polyvinylcaprolactam (PVCap), are calculated using molecular dynamics simulations to estimate the residence times, which are far beyond the feasible simulation time. Our model accounts for the kinetic inhibition mechanism while reproducing experimental data of the size dependence of PVCap very well. We demonstrate that this model explains why blends of high and low-molecular-weight polymers show better performance than the KHI with a unimodal molecular weight distribution and why quaternary ammonium cations are good KHIs for tetrahydrofuran hydrate although they cannot inhibit formation of natural gas hydrates.

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“…As one of the typical LDHIs, kinetic hydrate inhibitors (KHIs), with the advantages of low dosage and high efficiency [5,6], have attracted the attention of many researchers. KHIs can inhibit hydrate formation by effectively delaying the hydrate nucleation or inhibiting hydrate growth [7][8][9][10][11][12][13]. Polyvinylpyrrolidone (PVP) is one representative KHI found by Long et al [14].…”

Section: Introductionmentioning

confidence: 99%

Inhibition Effect of Kinetic Hydrate Inhibitors on the Growth of Methane Hydrate in Gas–Liquid Phase Separation State

Cheng

Wang

et al. 2019

Energies

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The effect of kinetic hydrate inhibitors (KHIs) on the growth of methane hydrate in the gas–liquid phase separation state is studied at the molecular level. The simulation results show that the kinetic inhibitors, named PVP and PVP-A, show good inhibitory effects on the growth of methane hydrate under the gas–liquid phase separation state, and the initial position of the kinetic hydrate inhibitors has a major effect on the growth of methane hydrates. In addition, inhibitors at different locations exhibit different inhibition performances. When the inhibitor molecules are located at the gas–liquid phase interface, increasing the contact area between the groups of the inhibitor molecules and methane is beneficial to enhance the inhibitory performance of the inhibitors. When inhibitor molecules are located at the solid–liquid phase interface, the inhibitor molecules adsorbed on the surface of the hydrate nucleus and decreased the direct contact of hydrate nucleus with the surrounding water and methane molecules, which would delay the growth of hydrate nucleus. Moreover, the increase of hydrate surface curvature and the Gibbs–Thomson effect caused by inhibitors can also reduce the growth rate of methane hydrate.

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First Investigation of the Kinetic Hydrate Inhibition of a Series of Poly(β-peptoid)s on Structure II Gas Hydrate, Including the Comparison of Block and Random Copolymers

Cited by 37 publications

References 25 publications

Kinetic Hydrate Inhibition with N-Alkyl-N-vinylformamide Polymers: Comparison of Polymers to n-Propyl and Isopropyl Groups

Kinetic Hydrate Inhibition with N-Alkyl-N-vinylformamide Polymers: Comparison of Polymers to n-Propyl and Isopropyl Groups

Molecular Dynamics Study of Kinetic Hydrate Inhibitors: The Optimal Inhibitor Size and Effect of Guest Species

Inhibition Effect of Kinetic Hydrate Inhibitors on the Growth of Methane Hydrate in Gas–Liquid Phase Separation State

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