Effect of Vinyl-Acetate Moiety Molar Fraction on the Performance of Poly(Octadecyl Acrylate-Vinyl Acetate) Pour Point Depressants: Experiments and Mesoscopic Dynamics Simulation

Polar moieties of the conventional polymeric pour point depressants (PPDs) greatly influence the PPDs' performance on waxy crude oil. However, the influencing mechanism of the polar moieties on the PPD's performance is not clear. In this paper, four poly(octadecyl acrylate-vinyl acetate) (POA-VA) PPDs with different VA molar fractions were first synthesized; then, the performance of the four PPDs on Dingbian waxy crude oil was investigated by experiments and mesoscopic dynamic simulation. The experimental results show that the crystallization ability of the PPDs deteriorates with increasing VA molar fraction, while the performance of the PPDs first increases and then decreases with the increase of VA molar fraction. At a moderate VA fraction 25 mol %, the PPD-3 shows the best performance in decreasing the WAT, pour point, and viscosity of the crude oil. The simulation results correlate well with the experimental data and confirm that (a) the addition of the PPDs inhibits the transformation of wax molecules from the initial amorphous state into the crystalline state and thus decreases the WAT of the crude oil; (b) the VA molar fraction controls the stretching state of the PPDs molecules in wax crystals and the polar attraction among the wax crystals contaminated by the PPDs; (c) the addition of the PPDs favors the formation of a more compact wax crystals' structure. At moderate VA molar fraction, the PPD-3 not only has good crystallization ability and stretching state, but also strengthens the polar attraction force among wax crystals, all of which trigger the formation of the largest and the most compact wax crystal flocs and thus impart the best performance to PPD-3.