Antifreezes Act as Catalysts for Methane Hydrate Formation from Ice

Abstract

Contrary to the thermodynamic inhibiting effect of methanol on methane hydrate formation from aqueous phases, hydrate forms quickly at high yield by exposing frozen water-methanol mixtures with methanol concentrations ranging from 0.6-10 wt% to methane gas at pressures from 125 bars at 253 K. Formation rates are some two orders of magnitude greater than those obtained for samples without methanol and conversion of ice is essentially complete. Ammonia has a similar catalytic effect when used in concentrations of 0.3-2.7 wt%. The structure I methane hydrate formed in this manner was characterized by powder X-ray diffraction and Raman spectroscopy. Steps in the possible mechanism of action of methanol were studied with molecular dynamics simulations of the Ih (0001) basal plane exposed to methanol and methane gas. Simulations show that methanol from a surface aqueous layer slowly migrates into the ice lattice. Methane gas is preferentially adsorbed into the aqueous methanol surface layer. Possible consequences of the catalytic methane hydrate formation on hydrate plug formation in gas pipelines, on large scale energy-efficient gas hydrate formation, and in planetary science are discussed.

Some current challenges in clathrate hydrate science: Nucleation, decomposition and the memory effect

“…Experimentally, hydrate formation from ice is a two-stage process with a relatively fast conversion of the ice surface [42][43][44]34] and a much slower process for bulk ice. Catalysts that interrupt surface hydrogen bonding can speed up this process by orders of magnitude [45].…”

Molecular Dynamics Simulations of Hydrogen Bonding in Clathrate Hydrates with Ammonia and Methanol Guest Molecules

“…This was experimentally observed in our recent work. 27 Adding methane to empty small cages of the sI hydrates increases the lattice constant. However, the clathrate hydrates with methane in the small cages have smaller lattice constants than analogous clathrate hydrates with NH 3 or CH 3 OH in the small cages.…”

In situ Raman and 13C NMR spectroscopic analysis of gas hydrates formed in confined water: application to natural gas capture

“…A mono-ethylene glycol (MEG) aqueous solution system has been also investigated as a comparison with the silica system, because it is reported that MEG may promote the hydrate formation kinetics. 25,26 In attempting to understand the formation process of hydrate phase, we formed mixed hydrate from a gas mixture (methane, ethane, and propane) and measured the amount of consumed gas during the formation process. In situ Raman spectroscopy was used to monitor the inclusion process of gas molecules in hydrate cages.…”