Dehydration of water-in-crude oil emulsions using polymeric demulsifiers: A model for water removal based on the viscoelastic properties of the oil-water interfacial film

Many petrochemical dehydration units do not operate in steady state. Despite this fact, steady state modelling and simulation of dehydration process is fairly standard today. In this study, the viscoelastic properties was correlated to crude oil dehydration dynamically for the first time. The elastic/storage modulus (G ') and viscous/ loss modulus (G '') of the crude oil-water interfacial films were measured using a shear rheometer. Water removal as a function of time was determined from bottle tests. Experimental variables include the asphaltene content of crude oils, temperature, dosage and type of demulsifiers. Higher G ' values were detected for the crude oil with higher asphaltene contents before the administration of a demulsifier, and the resultant G ' values after demulsifier addition were also found to be higher in the shear rheology measurements for crudes which required higher dosages for water removal in bottle tests. The formation of the elastically dominated solid-like interface, quantified by G ', is likely the main mechanism involved in creating the high stability of the emulsion systems, and a direct proportionality between asphaltene content and film rigidity was observed. Furthermore, the decrement magnitude for G ' with demulsifier addition was found to be influenced by the type of demulsifier administered. On the other hand, the deceleration rate of G ' was higher at higher temperature related to the lower viscosity of crude oils. Very importantly, it was found that the efficiency of the demulsifier on film softening was closely related to the change of G ' especially in the low value range. Therefore, Log G ' rather than G ' was used to correlate the water removal by various demulsifiers, and a dynamic model for the water removal was developed based on the time-related Log G ', contributing to comprehensive understanding of the lively dehydration process in real industrial production.

Automated summary

This study correlates the viscoelastic properties with crude oil dehydration and reveals that the asphaltene content influences film rigidity, and the type of demulsifier and temperature affect the change in elastic modulus. A dynamic model for water removal based on elastic modulus was developed, contributing to a comprehensive understanding of the dehydration process.