Study on demulsifier crude oil interactions at oil-water interface for crude oil dehydration

Abstract

Stabilization mechanisms of water-in-oil emulsions have been well studied. The process of dehydration with demulsifiers in these previous works have focused primarily on macro scale bottle tests or on microscale investigations of asphaltene film. A connection between the two scales, however, is necessary to better understand the mechanisms of dehydration using demulsifiers. In our present work, results from bottle tests of undiluted crude oil were compared with the coalescence process of water droplets in solvent diluted crude oil and with visualization experiments of the interfacial film rigidity through observing the crumpling of water droplets in diluted crude oil. To gain further insight into the molecular interactions between the native surface active materials and three different polymeric demulsifiers at the solvent-water interface, Langmuir interfacial isotherms were measured using diluted crude oil-water systems with and without the addition of demulsifiers. The highest water removal percentage was obtained though the addition of a random biopolymer demulsifier, butyl acrylate/2-(dimethylamino) ethyl acrylate (P1), that also rendered the shortest coalescence time of the three polymers tested, indicating the importance of coalescence behavior in dehydration. In addition, the smallest crumpling ratio which corresponds to lowest rigidity was detected for the P1 treated interface. For the first time, we observed that the diluted crude oil-water interfacial film collapsed easily upon compression with the administration of the very efficient demulsifier P1. It was found that the collapse pressure can be used as a measure of the rigidity of very soft interfacial films that may not be measurable directly by compression energy. Based on the close relation between the dehydration process and the interaction between demulsifiers and natural active surfactants, it can be deduced that, efficient demulsifiers essentially disrupt the continuity of the asphaltenic interfacial films and reduce the strength of anchoring of these natural surfactants at the interface, allowing for the collapse of segments and resulting in efficient dehydration.