Size exclusion chromatography reveals a key parameter of demulsifiers for enhanced water separation from crude oil emulsions

Abstract

Demulsifier is used in gas oil separation plants for the separation of water from crude oil emulsion. One of the important parameters for the enhancement of performance is the optimization of demulsifier formulation with respect to oil composition and produced water chemistry. The consistency in the quality of the formulation is essential to obtain the best separation of water throughout the production period of crude oil. The industry accepted method to optimize formulations is the bottle test method. However, this method remains laborious, time-consuming, imprecise, and requires access to fresh crude oil, which is not convenient from a practical viewpoint. Instead, routine physical and chemical properties are monitored to ensure the consistency of the demulsifier quality. It was, however, observed that there was a significant influence on the performance of a demulsifier from different batches with very close physical and chemical properties. Therefore, we developed a method using size exclusion chromatography to determine the molecular weight distribution of demulsifier base material, in this case, alkoxylated alkylphenol-formaldehyde resin. It was found that all the samples contained two well-separated species with one low molecular weight of about 2700 g/mol and other one with high molecular weight of about 15000 g/mol. The variation in the content of low and high molecular weight species was identified to be a key parameter significantly influencing the separation performance. It is apparent from this study that size exclusion chromatography could provide some additional insights on demulsifier intermediate chain length dispersity which could be correlated to actual separation performance.