Page 232 - Handbook Of Multiphase Flow Assurance

Hydrate stability and crystal growth 231

TABLE 10.1 Geometry of hydrate structures.
Hydrate crystal structure I II H
3 6 3
12 2
12 4
12 8
Cavity type 5 12 5 6 5 12 5 6 5 12 4 5 6 5 6
Number of cavities per unit cell 2 6 16 8 3 2 1
Average cavity radius, nm 0.391 0.433 0.3902 0.4683 0.391 0.406 0.571
Effective free diameter, nm a 0.51–0.52 0.57 0.48–0.50 0.69 – – –
Number of water molecules per 46 136 34
unit cell
Space group Pm3n Fd3m P6/mmm
Crystal system cubic cubic Hexagonal
Lattice parameter, nm 1.2 1.71 a = 1.22; c = 1.02
a From Istomin et al. (1988), assuming the van der Waals radius of water being equal 0.14 nm.

FIG. 10.8 Stereoscopic view of sI. Obtained with Hyperchem® software.

FIG. 10.9 Stereoscopic view of sII. Obtained with Hyperchem® software.