Further Discussion of Nanocomposite Pour Point Depressants on the Influence of Paraffin Wax Crystallization: A Novel Small Angle X-ray Diffraction Study

Paraffin wax acts as a nuisance for the flow assurance of deep-water crude pipelines where temperature varies sharply. The nanocomposite pour point depressant (NPPD), an additive in modifying the crystallization of paraffin wax, is proved to be effective in the battle against wax deposition and has attracted increased attention. In our previous work (Fuel, 2018, 257-268), the effect of the NPPD on wax crystal lattice parameters is investigated with X-ray diffraction. It is found that the NPPD which mainly performs as nucleation templates modifies the lattice parameters of wax crystals, resulting in the significant improvement of waxy oil fluidity. In this research, the influence of the NPPD on the crystallization process of paraffin wax crystals is further discussed from a novel insight inspired by small angle X-ray diffraction (SAXS). The mesoscopic structural variation of crystal grains with/without NPPD modification is focused particularly. A differential scanning calorimeter and a rheometer are further applied to demonstrate the regulation of PPDs on the crystallization process and volume network strength of paraffin wax crystals. In addition, a comparison of the relative modification effect is made between the ethylene vinyl acetate polymer (EVA) and NPPD. It is revealed that due to the modification effect of the EVA and NPPD in crystal grain morphology, the first long period, radius of gyration, thickness of the interfacial layer, and fractal dimension all decrease contributing to a weakened strength of the volume network and also a decreased yield stress. With a discussion on interaction mechanisms, we demonstrate that the cocrystallization of the EVA and heterogeneous nucleation of the NPPD should be, respectively, responsible for the difference in the microstructure and associated mesoscopic properties of paraffin wax crystals. This work provides a further understanding for the crystallization process of paraffin wax modified by PPDs.