<p>One of the most important challenges in the petroleum industry in recent years is the demulsification and desalination of the water in crude oil emulsions. In this study, a novel eco-friendly demulsifier was synthesized by using a suitable combination of ethyl cellulose (EC) and Sodium Dodecylbenzene Sulfonate (SDBS) surfactant for simoultaneous demulsification and desalination of water in crude oil emulsion. Central Composite Design (CCD) method has been used for the statistical modeling and optimization of the effective variables on demulsification. The effect of the demulsifier concentration on demulsification and desalination was examined. Interfacial tension measurements between water and crude oil and micrographs of emulsions have been used to study the demulsification mechanism. The results of the screening parameters represented that the most effective parameters on demulsification efficiency (DE) were temperature, settling time, and demulsifier concentration. The results showed 93% DE using (EC) modified by SDBS (ECS) (demulsifier) dosage and temperature of 125&#xa0;ppm and 55&#xa0;°C, respectively. In addition, using ECS under the same condition, resulted in 90% desalting percentage. Moreover, the comparison between DE of EC and that of ECS indicate that inunder the same conditions, DE of ECS is 80% higher than that of EC due to the change in the hydrophobicity of EC. Based on the results, this demulsifier can be used as an effective demulsifier in the simultaneous application of desalination and demulsification in the petroleum industry.</p> Graphical abstract <p></p>