Humic Acids as a New Type of Methane Hydrate Formation Promoter and a Possible Mechanism for the Hydrate Growth Enhancement

Abstract

A comparative investigation of methane hydrate formation from 0.1 wt % solutions of an alkaline extract of humic acids (HA) and sodium dodecyl sulfate (SDS) has been carried out. It was demonstrated that the hydrate grows as a voluminous loose mass squeezed onto the reactor walls in both cases. It turns that about 75% of water transforms into hydrate within 15–20 min. Thus, natural HA can act as kinetic hydrate promoters. At the same time, SDS increases the hydrate nucleation rate compared to pure water under the studied conditions (12.5–13.0 MPa and −5 °C), while HA retards the hydrate nucleation. Visual observation of the hydrate growth in the solutions of HA and SDS allowed us to propose a new mechanism of hydrate growth in the form of a porous loose mass squeezed upward over the reactor walls. The mechanism relates to overgrowing of the hydrate film formed at the gas–solution interface into the solution volume. This results in squeezing some part of the solution onto the reactor walls. Simultaneous contact of the gas, solution, and hydrate facilitates the rapid transformation of the squeezing solution into a loose hydrate mass. Then this mass soaks up the solution due to the capillary forces.