Page 317 - Handbook Of Multiphase Flow Assurance

316 10. Research methods in flow assurance

TABLE 10.14 Energies of adsorption of a PVP monomer on different surfaces.—cont’d
Surface E min, kcal/mol Preferred site of adsorption
3 and 12 Å −15.91 12 Å slice above large cage
4 and 13 Å −15.72 13 Å slice above large cage
5 and 14 Å −14.90 5 Å slice below large cage
6 and 15 Å −13.61 6 Å slice below small cage
7 and 16 Å −15.81 7 Å slice below small cage
8 and 17 Å −12.34 17 Å slice above large cage
sII (1,1,1) sliced at
0 and 5 Å −15.99 0 Å slice below large cage
1 and 6 Å −12.13 1 Å slice below small cage
2 and 7 Å −14.47 7 Å slice above large cage
3 and 8 Å −11.90 8 Å slice above large cage
4 and 9 Å −15.76 4 Å slice below large cage
10 and 15 Å −12.17 15 Å slice above small cage
11 and 16 Å −12.48 11 Å slice below small cage
12 and 17 Å −11.76 12 Å slice below small cage
13 and 18 Å −16.92 13 Å slice below large cage
14 and 19 Å −12.83 14 Å slice below large cage
20 and 25 Å −15.53 20 Å slice below small cage
21 and 26 Å −13.46 21 Å slice below small cage
22 and 27 Å −13.02 22 Å slice below small cage
23 and 28 Å −14.49 28 Å slice above large cage
24 and 29 Å −13.55 24 Å slice below large cage

(2) It was noticed that the monomers tend to adsorb in such an orientation that the ring
group of a monomer would be inside a partial hydrate cage at the surface, while
the backbone part of a monomer would be outside of the cage. Oxygen atoms of the
monomers were usually hydrogen bonded to hydrogens of water molecules on the
hydrate surfaces.
12 2
12 4
(3) The large hydrate cavities (5 6 for sI and 5 6 for sII) are preferred for adsorption since
the monomers adsorbed more frequently near the large than the small cavities.
(4) On the average for all surfaces PVCap adsorbed 10% stronger than PVP on sII {111} faces
which are usually encountered in industry.
For the further simulations one hydrate surface was selected. This was a sII {111} surface
sliced at depths of 8 and 13 Å. The reason for selecting this surface was the presence of open