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Unraveling Amphiphilic Poly(N‑vinylcaprolactam)/Water Interface by Nuclear Magnetic Resonance Relaxometry: Control of Clathrate Hydrate Formation Kinetics
journal contribution
posted on 2022-04-05, 20:36 authored by Dong Wang, Dongfang Li, Malcolm A. Kelland, Haokun Cai, Jie Wang, Ying Xu, Ping Lu, Jian DongWater-soluble amphiphilic polymers
are vital chemicals in the oil
and gas industry to retard crystal growth of hydrocarbon hydrate via surface adsorption and suppress nucleation of a pristine
hydrate nucleus, thereby preventing formation of hydrate blockages
in flow lines during oil and natural gas production. Apart from a
few theoretical modeling studies, an experimental method to study
the polymer/water interface in the crystal growth is critically needed.
Here, water motions in the hydration shells of an exemplary kinetic
inhibitor, poly(N-vinylcaprolactam), during hydrate
formation from the tetrahydrofuran/water system are revealed via nuclear
magnetic resonance relaxometry. Unequivocal experiments show that
the pivotal interfacial water in the tightly bound state gradually
freezes at rates depending on the polymer molecular weight (MW). This
is supported by nonfreezable water analysis, which is correlated to
the inhibition time. The polymers tune the kinetics of the hydration
process via interaction with and perturbation of
the water molecules. The free water component in the polymer solution
crystallizes at a very slow rate when in partially restricted mobility,
whereas the bound water component increases in the reaction, with
the polymer/water interface serving as the reaction sites. The appropriate
MW (including average MW and polydispersity values) of the inhibitive
polymers can give rise to maximal retardation of the hydrate crystal
growth. This work will help control other multiphase crystallization
kinetic processes through the design of inhibitors or promoters functioning
in the interface.
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unequivocal experiments showtheoretical modeling studiespartially restricted mobilityexemplary kinetic inhibitor>- vinylcaprolactam ),thereby preventing formationpivotal interfacial waternonfreezable water analysisnatural gas productionfree water componentpristine hydrate nucleussoluble amphiphilic polymerspolymer solution crystallizespolymer molecular weightincluding average mwretard crystal growthhydrate crystal growthwater interface servingcrystal growthhydrate formationwater systemwater motionswater moleculeswater interfacegas industryhydrocarbon hydratehydrate blockagespolymers tunemw ).inhibitive polymersappropriate mwvital chemicalsvia surface adsorptionsuppress nucleationslow raterates dependingpromoters functioningpolydispersity valuespoly (<n maximal retardationinhibition timehydration shellshydration processgive riseflow linesexperimental methodcritically needed