Study of the Kinetic Hydrate Inhibitor Performance of a Series of Poly(<i>N</i>-alkyl-<i>N</i>-vinylacetamide)s

Ajiro, Hiroharu; Takemoto, Yukie; Akashi, Mitsuru; Chua, Pei Cheng; Kelland, Malcolm A.

doi:10.1021/ef101107r

Cited by 97 publications

(72 citation statements)

References 25 publications

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“…Previous tests in our laboratories gave percentage variations of similar magnitude. 15 Stochasticity of hydrate formation in a small cell leads to these scatterings. In addition, there is one result in some of the test series that lies outside the distribution, which could be neglected.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Kinetic Hydrate Inhibition of Poly(N-isopropylacrylamide)s with Different Tacticities

et al. 2012

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Poly(N-isopropylacrylamide)s (PNIPAMs) and poly(N-isopropylmethacrylamide)s have been investigated recently as kinetic hydrate inhibitors (KHIs). Now, poly(N-isopropylmethacrylamide) is commercialized. These are usually made by standard radical polymerization methods, which do not allow for control over the polymer tacticity. For this study, PNIPAMs were synthesized using new polymerization methods, giving a fairly high degree of tacticity control. We report here results on the performance of different tacticities of PNIPAMs with similar molecular weights in KHI tests with natural gas in stirred autoclaves and on tetrahydrofuran (THF) structure II hydrate crystal growth. From the results, we can conclude that the polymer tacticity does affect the KHI performance of PNIPAMs. PNIPAM with a higher syndiotactic percentage performed better than PNIPAM with a lower syndiotactic percentage. Both polymers demonstrated some kind of crystal surface adsorption by affecting the morphology of the THF hydrate crystals. ■ INTRODUCTIONNatural gas hydrates are crystalline solids, in which gas molecules (guest molecules) are trapped inside hydrogenbonded water cavities. Typical guest molecules include carbon dioxide and small hydrocarbons, such as methane, ethane, and propane. In the mid-1930s, it was discovered that thermodynamic conditions (elevated pressure and low temperature) favoring hydrate formation occur in pipelines and that natural gas hydrates were blocking gas transmission lines. 1 Natural gas hydrate plugging is one of the costly and challenging problems for the oil and gas industry, especially for deepwater fields. The prevention of gas hydrate formation can be accomplished in a few methods. Among them is the chemical treatment, which includes the usage of kinetic hydrate inhibitors (KHIs). They are generally water-soluble polymers. The mechanism is to delay the nucleation and crystal growth. The main classes of KHIs that have been in commercial use are polymers based on homo-polymers and co-polymers of vinyl caprolactam (VCap) as well as hyperbranched polyesteramides. 2 A group of KHIs based on the polymer of alkylacrylamide was developed. It was also pointed out that poly(N-monoalkyl(meth)acrylamide)s are also known to perform well as KHIs, especially when isopropyl serves as the alkyl group. 3 Therefore, we are interested in studying the KHI performance of this new KHI class.One of the important properties of polymers are their tacticity, which describes the relative stereochemistry of adjacent chiral centers within a macromolecule. 4 As shown in Figure 1, there are three types of tacticities, namely, isotactic with all pendant groups located on one side of the backbone, syndiotactic with alternating orientated pendant groups, and atactic with randomly orientated pendant groups. In a previous work, the KHI performance of poly(N,N-dialkylacrylamide)s was studied to determine the effect of polymer tacticity of this KHI class. 5 The results show that syndiotactic poly(N,Ndialkylacrylamide)s perform better than other...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Kinetic Hydrate Inhibition of Poly(N-isopropylacrylamide)s with Different Tacticities

et al. 2012

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“…It was hypothesized that polyvinyl pyrrolidone (PVP), a well-known KHI, inhibits hydrate formation by adsorption through hydrogen bonds2627. Accordingly, KHI abilities of a variety of polymers18282930313233343536 on hydrate inhibition and morphological changes1737 of hydrate crystals induced by the adsorption of KHIs have been reported. However, a more recent study demonstrated that PVP has no direct contact with the hydrate surface3839, raising the possibility that adsorption is not the only mechanism of hydrate inhibition.…”

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Hydrophobic amino acids as a new class of kinetic inhibitors for gas hydrate formation

Kwak

Lee

et al. 2013

Sci Rep

211

137

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As the foundation of energy industry moves towards gas, flow assurance technology preventing pipelines from hydrate blockages becomes increasingly significant. However, the principle of hydrate inhibition is still poorly understood. Here, we examined natural hydrophobic amino acids as novel kinetic hydrate inhibitors (KHIs), and investigated hydrate inhibition phenomena by using them as a model system. Amino acids with lower hydrophobicity were found to be better KHIs to delay nucleation and retard growth, working by disrupting the water hydrogen bond network, while those with higher hydrophobicity strengthened the local water structure. It was found that perturbation of the water structure around KHIs plays a critical role in hydrate inhibition. This suggestion of a new class of KHIs will aid development of KHIs with enhanced biodegradability, and the present findings will accelerate the improved control of hydrate formation for natural gas exploitation and the utilization of hydrates as next-generation gas capture media.

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“…One widely‐used technique uses a constant temperature stirred crystallizer, and the changes in pressure, or the amount of gas supplied to maintain a constant pressure, are recorded as the system forms hydrates . These measurements require experimental samples in the range of 20‐500 mL and experimental times in the order of 10‐15 hours per datum . Recently, we developed a novel technique that allows the use of liquid sample sizes of 20 μL and experimental times of less than an hour per datum .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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Phase equilibria, kinetics, and morphology studies of gas hydrates require separate pieces of equipment and experimentation times in the order of days. Recently, we designed a reactor that allows for tight control of the crystallization temperature. Coupled with a novel method, this reactor can screen the crystal morphology, phase equilibria, and apparent kinetics of gas hydrates. Compared to traditional multi‐trial methods, the main advantage of this method is that only a single experiment, completed in the order of hours, is required to assess: (a) the change in hydrate growth velocity with respect to temperature, (b) the HLV equilibrium temperature at the experimental pressure, and (c) the change in crystal morphology with respect to driving force. Using this 3‐in‐1 method, methane hydrate growth and dissociation was studied in the presence of four commercial inhibitors. Phase equilibria, kinetics, and morphology were obtained for all hydrate systems with inhibitors. The standard uncertainty for the HLV equilibrium temperature was 0.05 K and for pressure 0.005 MPa. The apparent rates of growth were measured for all systems (standard uncertainty was 0.008 mm · s−1) and the difference between the inhibited systems and the pure system was very clear. Crystal habits varied considerably among inhibitors and radically with respect to the uninhibited system. Overall, we present an innovative technology to assess the morphology, kinetics, and thermodynamics of hydrate forming systems with a single apparatus. Furthermore, with little time investment, small sample sizes can be used to obtain replicates with minimum temperature and pressure uncertainties.

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Study of the Kinetic Hydrate Inhibitor Performance of a Series of Poly(N-alkyl-N-vinylacetamide)s

Cited by 97 publications

References 25 publications

Kinetic Hydrate Inhibition of Poly(N-isopropylacrylamide)s with Different Tacticities

Kinetic Hydrate Inhibition of Poly(N-isopropylacrylamide)s with Different Tacticities

Hydrophobic amino acids as a new class of kinetic inhibitors for gas hydrate formation

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

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