Energy & Fuels, Vol.34, No.2, 1482-1491, 2020
Influence of Wax on Cyclopentane Clathrate Hydrate Cohesive Forces and Interfacial Properties
As pipeline transportation in the oil and gas industry is moving to offshore conditions, the prevalent high-pressure and low-temperature conditions in the subsea flow lines may lead to hydrate formation and wax precipitation occurring simultaneously. The presence of wax may alter the interfacial properties and particle interactions, resulting in the change in hydrate cohesion behavior. In this study, cyclopentane hydrate cohesive forces are measured with different wax contents using a micromechanical force (MMF) apparatus. A custom wax sample with the composition from C17 to C39 was mixed with cyclopentane and used as the bulk phase. It was found that the cohesive force decreased with increasing wax content from 0 to 5 wt % then increased with further wax contents from 5 to 8.75 wt %. Dilution MMF measurements demonstrated that two competitive mechanisms, the oleophilic effect and reduced hydrate conversion rate were synergistically responsible for the observed changes in the cohesive force. In an MMF measurement with 10 wt % wax and 6 h annealing period, the wax was found to deposit on the hydrate surface and effectively reduced the cohesive force, indicating that wax crystals have a potentially inhibiting effect on hydrate cohesion. Furthermore, the bulk phase/water interfacial tension decreased with increasing wax contents. Finally, a possible mechanism is presented to illustrate the effect of wax on the hydrate cohesive force, considering the oleophilic effect, hydrate conversion, and wax deposition. This work provides insight into the influencing mechanisms of wax on hydrate cohesion, which can be useful for flow assurance applications where both hydrates and waxes are present.