Formation AFPs inhibit

Carlo simulation of ice-crystal growth to study the mechanism of inhibition of AFPs on the surface of the THF hydrate and propane hydrate. They found that most of the octahedron surfaces of the THF hydrate were covered with AFP molecules, which could reduce the growth rate of the THF hydrate only allowing plate growth perpendicular to that surface. It is thus necessary to look for other experimental evidences to clarify the common features of AFPs on the inhibition of the clathrate hydrate formation. 

Table 1 summarizes the results obtained for C02-hydrate film formation in AFP-solution experiments. In each column, the upper value is that obtained in the first run, while the lower number in brackets is the average for all subsequent runs with its variation. For AFP-0.01 mg ml-1 samples, we showed the values in brackets are standard deviation> for 8 times repeating experiments. Table 1 shows that rwas estimated as ranging between 60 and 100 min, which is much longer than the periods observed on the pure water droplet. It is concluded that CO2 hydrate formation was clearly inhibited by the presence of AFP molecules, even though the concentration was as small as 10 ppm. 

The inhibition effects of type-III AFP and trehalose, two cryoprotecting materials produced in animals, on type-I CO2 clathrate-hydrates were examined. For comparison with the results of a previous study in which the lateral growth rates of COi-hydrate film were dependent on temperature, pressure and NaCl concentration, the solution droplet was observed in a high pressure vessel filled with CO2. Type-III AFP was found to increase the induction period and to reduce the lateral growth rate of C02-hydrate films. It worked well at low concentrations, indicating that AFP works as a kinetic inhibitor. It was also indicated that AFP would weaken the memory effect of C02-hydrate formation. Trehalose had similar inhibition effects on both the induction period and the lateral growth rate, but it had little apparent concentration-dependence on them. Since trehalose also causes the equilibrium conditions of the CO2 hydrate to shift to lower temperatures, it works not only as a thermodynamic inhibitor but also as a kinetic inhibitor, especially as an anti-agglomerant. 

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