CO2 HYDRATE FORMATION IN AQUEOUS SOLUTIONS: PHASE FIELD THEORY OF NUCLEATION AND GROWTH 

B. Kvamme¹*, L. Granasy²*, T. Pusztai², G. Tegze², T. Kuznetsova^1
1 Department of Physics, University of Bergen, Allégaten 55, N-5007 Bergen, Norway
² Research Institute for Solid State Physics and Optics, H-1525 Budapest, POB 49, Hungary
 * [email protected] and [email protected]

A phase field theory developed recently [1, 2] is applied to describe the formation of CO₂ hydrate in aqueous solutions. Starting from realistic estimates for the thermodynamic and interfacial properties, we show that under typical conditions of CO₂ formation, the size of the critical fluctuations (nuclei) is comparable to the interface thickness, implying that the classical droplet model, which relies on a sharp interface, is rather inaccurate. The phase field theory predicts considerably smaller nucleation barrier than the classical approach and converges, as expected, to the classical prediction with decreasing interface thickness. We determine the dimensionless growth rate of small CO₂ hydrate clusters in aqueous solution. Finally, we explore the possibility to model solidification in porous matter and liquid channel using the phase field theory. We also discuss the extension of the approach to heterogeneous nucleation and growth on the CO₂/water interface and conversion of methane hydrate to CO₂ hydrate.

1. Kvamme, B., Graue, A., Aspenes, E., Kuznetsova, T., Gránásy, L., Tóth, G., Pusztai, T., Tegze G., Towards understanding the kinetics of hydrate formation: Phase field theory of hydrate nucleation and magnetic resonance imaging, Physical Chemistry Chemical Physics, 2003, in press.

2. Granasy, L., Pusztai, T., Tegze, G., Kuznetsova, T., Kvamme, B., Phase field theory of hydrate nucleation: Formation of CO2 hydrate in aqueous solution, in “Recent Advances in the Study of Gas Hydrates”, 2004, Kluwer Academic/Plenum Publishers, in press.