Page 252 - Handbook Of Multiphase Flow Assurance

Molecular modeling 251

Study of structural changes in the water hydrogen bonding network incurred by the hy-
drate inhibitors was done. A new method of analyzing the structure of water was used in this
study. The results of simulation are in qualitative agreement with the experimental perfor-
mance of the studied compounds.
Limitations of this study are (1) the docking was performed in vacuo; (2) PVP, PVCap, and
PVCA inhibitors were simulated as single monomers; (3) Scaling of the dielectric interactions
was used in inhibitors effect on water structure study.
A potentially better hydrate inhibitor was suggested based on the computer simulation
results. Molecular dynamics simulation proved not only to replicate the real experimental
data, but to predict the new compounds as well.
This study suggests that the following properties should be present in a good hydrate inhibitor:
1. Presence of a carbonyl group (active site) to introduce structural changes into the water.
2. Presence of a strongly electronegative atom such as nitrogen next to the carbonyl group
in order to enhance the electron cloud of the carbonyl oxygen (electron donating site).
3. Ring structure holding the active and the electron donating sites in order for electron
sharing to be smoothly equilibrated.
4. A polymer chain holding the rings with active and electron donating sites to add a
pattern to the active groups.
The potential new kinetic inhibitors may have the structure similar to cyanuric acid and
its derivatives.
Mechanism of the kinetic hydrate inhibition is most likely in the structural rearrangement of
water molecules. Kinetic inhibitors decrease the number of H bonded polygons driving the struc-
ture of water away from that favoring hydrate and making the formation of hydrate unfavorable.
Several recommendations can be made for the future studies.
Simulation
1. Use oligomers rather than monomers of inhibitor
2. Try solutions of these inhibitors with different concentrations
3. Hydrate the species before docking on the hydrate surface
4. Look at docking on different surfaces of the hydrate crystal lattice
Experimental
1. Pinpoint the xenon-water-neohexane system quintuple point location above 0 °C.
2. Chromatographic analysis is needed for liquid and vapor phases composition in the
xenon-water-neohexane system.

Molecular modeling

Comparison of chemical performance on a solid surface

Computer simulations can be used to gain an understanding of the hydrate inhibition
mechanism. Docking simulation of hydrate inhibitors on surfaces of ice and gas hydrates of
sI and sII reveals the energy with which they adsorb. Inhibitor chemicals included the Winter
Flounder polypeptide biomolecule, PVP, PVCap, and VC-713. Modeling of water and ice was
done using the SPC water model. A study was done of the effect of hydrate inhibitors on the