Page 321 - Handbook Of Multiphase Flow Assurance

320 10. Research methods in flow assurance

its backbone pointing into cavity rather than only its side group. Such a conformation is im-
probable in a real polymer system from steric considerations.
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The results of our simulations performed using Cerius have shown that monomers of
both inhibitors and non-inhibitors exhibit favorable but different energies of adsorption on
hydrate surface (no polymer evidence presented yet). Non-inhibitors poly(vinylalcohol),
poly(acrylamide) and poly(N-succinimide) adsorbed with a 9–48% weaker interaction than
PVP or PVCap.
Simulating the motion of a water molecule around a fixed monomer of PVP was done
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using the Cerius to determine whether the carbonyl group of inhibitors or a nitrogen atom
interact with water. Monte Carlo simulation of a single water molecule near the PVP mono-
mer has indicated that even without explicitly calculated hydrogen bonding water is most
likely to be near the carbonyl oxygen of PVP. Fig. 10.75 shows the locations of the water mol-
ecule center of mass during the simulation. The more dense region near the double-bonded
carbonyl oxygen indicates that water preferred to associate with this part of a PVP monomer.
The less dense regions near the hydrocarbon parts of the monomer represent a hydrophobic
solvation shell around the monomer.

Using the hand-written software for studying interaction of water and monomers
Some force fields (CHARMm, DREIDING) use a hydrogen bond potential to describe
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interactions between atoms involved in hydrogen bonds. The used module of the Cerius
program didn't have explicit hydrogen-bonding between the hydrate surface and an inhibitor

FIG. 10.75 Association of water molecule with the carbonyl group of a PVP monomer.