Hydrate formation and wax deposition pose great flow assurance challenges to subsea oil pipes, especially when the two phenomena co-occur. Wax crystals can have a significant impact on hydrate nucleation and growth kinetics, but this phenomenon has not been studied in great detail. Here, the effect of wax crystals on hydrate nucleation was investigated using both molecular dynamics simulation methods and experiments conducted using a custom-designed high-pressure autoclave equipped with an on-line viscometer. Both the simulation and the experimental results demonstrated that the presence of wax crystals inhibits hydrate nucleation. The simulations showed that water droplets tend to approach and adsorb on wax crystals prior to nucleation, thus inhibiting the formation of hydrate cages. The experiments demonstrated that water cut and stirring rate play a significant role in determining the hydrate nucleation rate. In addition, adding more wax increased the viscosity of the emulsion, which limits mass transfer of gas to the oil−water interface.

Chromium-doped α-Fe 2 O 3 samples are successfully synthesized by using a ball-milling-assisted rheological phase method combined with heat treatment. The electronic properties of undoped α-Fe 2 O 3 and 4.0 at % Cr-doped α-Fe 2 O 3 are investigated by first-principles calculations. The calculation results show that Cr doping can reduce the band gap and impurity levels that appear in the band gap. The structure and morphology of the samples are evaluated by X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. The Cr-doped α-Fe 2 O 3 electrode delivers a higher reversible capacity and outstanding rate capability as the anode of a lithium-ion battery compared with the undoped α-Fe 2 O 3 electrode. The initial discharge/ charge capacities of the 4.0 at % Cr-doped α-Fe 2 O 3 electrode can reach 1624/1065.9 mAh g À 1 , respectively, and exhibit an excellent reversible capacity of 971.3 mAh g À 1 after 150 cycles at a current density of 0.1 A g À 1 . Even after 200 cycles, the capacity can remain as high as 758.1 mAh g À 1 at a current density of 0.5 A g À 1 , far beyond than that of the undoped α-Fe 2 O 3 electrode (376.5 mAh g À 1 ).

The formation of hydrate increases the uncertainty of the flow system in subsea multiphase transportation pipelines. Waxes and asphaltenes have been found to influence hydrate formation, but the detailed mechanism of their interaction remains unclear. A labscale high-pressure stirring reactor was used to analyze the influence of asphaltenes on CO 2 hydrate evolution behavior in waxy water-inoil (W/O) emulsions. Results demonstrated that waxes inhibited CO 2 hydrate nucleation. The addition of asphaltenes promoted the inhibition effect of waxes, and the enhancement effect was nonmonotonic with the asphaltene contents increased. Based on microscopic observation and wax precipitation characteristics, this behavior could be interpreted as the competitive effect of increased adsorption of wax crystals on the surface of the droplets and reduced amount of wax precipitation. Moreover, asphaltenes were found to facilitate the decomposition process of CO 2 hydrates in waxy systems by decreasing the wax precipitation amount and stabilizing the emulsion. This work can provide potential engineering guidance for flow assurance applications.