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

Water-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.

Polymer Hydrogel Supported Ni/Pd Alloys for Hydrogen Gas Production from Hydrolysis of Dimethylamine Borane with a Long Recyclable Lifetime.

Hydrogen gas production can be produced from dimethylamine borane by the catalytic effect of metal nanoparticles. Past research efforts were heavily focused on dehydrogenation in organic solvents. In this study, hydrolysis of the borane in aqueous solutions was investigated, which bears two significant advantages: that two-thirds of the hydrogen generated originate from water and that the hydrogen storage materials are non-flammable. Polymer hydrogels serve as good carriers for metal particles as catalysts in aqueous solutions. Kinetic analysis of hydrogen production was performed for Ni/Pd bimetallic nanoclusters dispersed in a polymer hydrogel with a 3-D network structure. The reaction catalyzed by the bimetallic nanoclusters has an activation energy of only 34.95 kJ/mol, considerably lower than that by Ni or other metal catalysts reported. A significant synergistic effect was observed in the Ni/Pd bimetallic catalysts (Ni-Pd = 20/1) with a higher activity than Pd or Ni alone. This proves the alloy nature of the nanoparticles in the borane hydrolysis and the activation of water and borane by both metals to break the O-H and B-H bonds. The hydrogel with the Ni/Pd metal can be recycled with a much longer lifetime than all the previously prepared catalysts. The aqueous borane solutions with a polymer hydrogel can become a more sustainable hydrogen supplier for long-term use.