1.6.3 Inhibition Mechanisms Despite an excellent amount of progress being made in developing kinetic
inhibitors, the detailed mechanism behind inhibition is not well understood.
One analogue of kinetic inhibition, at a conceptual level, is the manner in
which Antarctic fish exist with an abnormally low body temperature (-2°C).
The peculiarity cannot be accounted for via their body glycopeptide content,
since this only provides a thermodynamic inhibition of less than 0.2°C. It was
proposed that the glycopeptides were adsorbed on ice surfaces with a
segment of the glycopeptide molecule extending into the surface of the ice.
The periodic placement of this pendant group fitted across the steps of the ice
crystal and subsequently blocked ice growth.
1.6.4 Anti-Agglomerants The failure of PVP at high degrees of subcooling underlined the need to
explore alternative avenues for hydrate inhibition. Indeed, at ocean bottom
temperatures of around 4 °C, hydrates were observed to form more rapidly in
the PVP solution than from uninhibited seawater. Since these shortcomings
were revealed, there has been much activity in developing new hydrate
inhibitors.
A recently pioneered approach is the ‘anti-agglomerant’ method which involves
the use of a surfactant that prevents hydrate particles from agglomerating into
a larger mass. This may sound similar to the kinetic inhibitors and in many
ways they are. However, for an anti-agglomerant to be effective, a liquid
hydrocarbon phase is required, unlike its kinetic inhibitor counterparts.
Despite this difference, a crucially important aspect lies in the small amount of
inhibitor required. In comparison to the traditional inhibitors (
e.g. methanol),
only a small fraction is required. In fact, a cross-correlation study conducted by
Behar
et al shows that 1 wt.% of an effective anti-agglomerant is equivalent to
25 wt.% methanol.
