The processing of crude oil often requires the extraction of a large amount of water. Frequently, crude oil is mixed with water to form water-in-crude oil emulsions as the result of factors such as high shear at the production wellhead and surface-active substances that are naturally present in crude oil. These emulsions are undesirable and require demulsification to remove the dispersed water and associated inorganic salts in order to meet production and transportation specifications. Additionally, the demulsification of these crude oil emulsions mitigates corrosion and catalyst poisoning and invariably maximizes the overall profitability of crude oil production. Recently, there has been growing research interest in developing workable solutions to the difficulties associated with transporting and refining crude oil emulsions and the restrictions on produced water discharge. Therefore, this paper reviews the recent research efforts on state-of-the-art demulsification techniques. First, an overview of crude oil emulsion types, formation, and stability is presented. Then, the parameters and mechanisms of emulsification formation and different demulsification techniques are extensively examined. It is worth noting that the efficiency of each of these techniques is dependent on the operating parameters and their interplay. Moreover, a more effective demulsification process could be attained by leveraging synergistic effects by combining one or more of these techniques. Finally, this literature review then culminates with propositions for future research. Therefore, the findings of this study can help for a better understanding of the formation and mechanisms of the various demulsification methods of crude oil to work on the development of green demulsifiers by different sources.

The crude oil mix with water through processing and under significant shear at the wellhead and with the assistance of surface-active substance which is present naturally in the crude oil leading to the formation of water-oil emulsions. These emulsions are undesirable and cause problem like pipeline corrosion, pump malfunctions, poisoning of downstream refinery catalysts, and other problems. Emulsions are needed to demulsify and separate the water. There are various parameters related in crude oil demulsification that can both reduce or rise the stability of the emulsion by altering each. Therefore, this study presents an overview of research efforts on the state-of-the-art demulsification techniques through the last years and the parameters affecting the demulsification process. Firstly, an overview of the crude oil emulsion, kinds, formation, and stability. After that, a short discussion of the different demulsification techniques process. Finally, the study of the parameters affecting the demulsification process, including salinity, temperature, pH, water content, and emulsifier/demulsifier dose. The review of literature culminated in the proposition for future research.

Crude oil as a complex fluid often consists of colloidal particles. These colloidal particles are made up of asphaltenes and resins diffused in a blend of aliphatic and aromatic solvents. At various stages of crude oil production, there is usually an occurrence a water-in-oil emulsion. The stability of the emulsion formed is dependent on the occurrence of the interfacial barrier which prevents the coalescence of the dispersed water droplets. Several operational difficulties are often encountered during crude oil processing as a result of the presence of water. These difficulties range from corrosion in equipment and pipelines as well as an increase in the production cost. Hence, to mitigate these economic and operational challenges, it is crucial to ensure that the water is separated from the crude oil prior to transporting or refining the oil. Demulsification using surfactant is one of the effective techniques used for the separation of crude oil from water. This paper presents a short review of the various application of surfactants for demulsification, their structure, classification as well as their properties. In addition, the mechanism and techniques for demulsification of crude oil were also presented.