Page 333 - Handbook Of Multiphase Flow Assurance

332 10. Research methods in flow assurance

(5) intramolecular polymer energy averaged over 1000 cycle intervals;
(6) the potential energy of adsorption averaged over 1000 cycle intervals;
(7) running-average energy of the system.
Each polymer adsorption simulation was repeated 4 times with different random number
generator seeds, and the results were averaged.
Visual images of the simulated system were stored every 10,000 cycles. From these images
it was possible to see the conformation of a short polymer chain on hydrate surface and ori-
entations of each side group relative to the surface.
For trimer, pentamer and octamer adsorption three conformations were: (1) laying flat
with the backbone parallel to the surface (train), (2) with some part of the chain adsorbed and
the other part not adsorbed (tail), and (3) with two ends of the chain adsorbed (loop). The
preferred conformation was a train for most polymers (Table 10.21). An example of a polymer
adsorbed on hydrate is presented in Fig. 10.84.

TABLE 10.21 Properties of short polymers' adsorption on {111} face of sII hydrate for each of 4 repeated
simulations.

Conformation Adsorption site
12 4
12 4
12 4
Chemical name Flat Tail Loop In 5 6 cavity Above 5 6 cage(s) Periphery of 5 6
PVCap trimer **** *** ****
PVCap pentamer ** ** *** ***
PVCap octamer *** * ** * ***
PVP trimer **** ** * ***
PVP pentamer *** * ** ****
PVP octamer *** * ** ****
PVA trimer *** * * ***
PVA pentamer *** * ****
PVA octamer ** ** helix *** ****
new-PVP octamer * * ** * * ***
new-PVCap trimer **** ** ****
new-PVCap pentamer *** * ** ****
new-PVCap octamer **** **** ****
8-ring-PVCap-8mer * * ** ** * ****
new-2-PVP-octamer *** * * *** ****
new-2-PVCap-8mer *** * *** ****
new-3-PVP octamer *** * *** ****
Average fraction 0.72 0.18 0.10 0.15 0.25 0.60
One large star indicates a result for one simulation (e.g., PVCap trimer adsorbed flat in all 4 runs).
Small stars indicate that there were two major adsorption sites in one simulation (e.g., part of the PVCap trimer adsorbed in a cavity
and the rest on periphery of a cavity in 3 runs and only on periphery in 1 run).