Droplet Coalescence and Spontaneous Emulsification in the Presence of Asphaltene Adsorption.

In a refinery, undesired high levels of salt concentration in crude oils are reduced by the contact of water with crude oils, where an emulsion is formed. Later, the separation of the water from the desalted oil is essential for the quality of both wastewater discharge and refined oil. However, complex components of crude oils such as asphaltenes may stabilize these emulsions, causing difficulties in efficient separation. Here, we show the coalescence inhibition caused by asphaltene adsorption for both water-in-oil and oil-in-water emulsions, where the oil phase consists of a simple model of asphaltenes dissolved in toluene. We find that oil-in-water emulsions are less stable than water-in-oil emulsions by using a newly developed instrument where controlled experiments can be performed to measure the coalescence time of a single droplet against an oil/water interface as a function of asphaltene aging (associated with the adsorption process of asphaltene molecules onto the interfaces) and asphaltene concentration. Furthermore, we find that the coalescence time for water droplets exhibits a maximum because of a spontaneous emulsification at the oil/water interface that produces droplets consisting of asphaltene-laden water droplets.