Insights on the Depressing Effect of Polymer-Nano Composites on the Pour Point of Waxy Crude Oil

A nanoparticle depressant (NPPD) was synthesis by grafting octadecyl methacrylate maleic anhydride on nano-silica. This nano composite depressant was evaluated on the pour point and viscosity of Shengli crude oil to reveal its functional mechanism by comparing with poly (octadecyl methacrylate-maleic anhydride) (MPPD). The results showed that at 400 ppm, MPPD effectively lowered the pour point of the crude oil by 6 ℃, while NPPD reduced it by 14 ℃, and the corresponding decrease in viscosity stood at 16% versus 41.2% (30 ℃). By polarizing microscope and particle size analysis, it was shown that, when MPPD was added, the wax crystal was petal-like and its size ranged from 10 to 17 μm. While NPPD was used, the wax crystal tended to be spherical and more compact, and its size was mainly distributed in the range of 5–12 μm. The above differences can be ascribed to different microscopic mechanism: for MPPD, its polymer chain bonds on the surface of wax crystals by adsorption between octadecyl side chain and wax crystals, then hindering their further growth, and finally they flocculate into pedal-like shape by the polar moiety attraction. For NPPD, the octadecyl chains attached on the particle surface act as nucleus or adsorption dot for wax crystals which leads to the formation of wax crystals that possess a higher degree of regularity and compactness, and accordingly with smaller size, thus resulting into its lower viscosity and lower pour point.