Phase equilibria, kinetics and morphology of methane hydrate inhibited by antifreeze proteins: application of a novel 3-in-1 method

The action of three distinct recombinant antifreeze proteins (AFPs) as methane hydrate inhibitors was examined using a recently-developed reactor. Compared with traditional approaches, this reactor uses minimal reactant volumes and short experimentation times to assess phase equilibria, kinetics and morphology of a hydrate system in a single experiment (3-in-1). Two of the recombinant AFPs are considered highly active with respect to the inhibition of ice: 'Maxi', a fish AFP, and a beetle AFP (TmAFP). The third protein from a grass, is classified as a low activity AFP (LpAFP). 'Maxi', an AFP that has not been tested previously as a hydrate inhibitor, slowed hydrate growth rates up to an order of magnitude compared to pure water. TmAFP and LpAFP also exhibited kinetic inhibition, but were less effective than 'Maxi'. In the presence of AFPs, hydrate films were thinner and showed a single growth mechanism compared to multiple crystal growth mechanisms observed in control experiments. The addition of TmAFP generated large irregular hydrate halos that propagated outside the original water boundary. Halo propagation was somewhat less prominent with LpAFP, and was not observed with 'Maxi'. Although, none of the AFP's showed thermodynamic inhibition properties, 'Maxi' appeared to form clusters of hydrate which remained metastable in the liquid-vapour region.