*Article* **Screening and Demulsification Mechanism of Fluorinated Demulsifier Based on Molecular Dynamics Simulation**

**Xiaoheng Geng 1,2,\*, Changjun Li <sup>1</sup> , Lin Zhang <sup>3</sup> , Haiying Guo <sup>2</sup> , Changqing Shan <sup>2</sup> , Xinlei Jia 2,3, Lixin Wei <sup>3</sup> , Yinghui Cai <sup>4</sup> and Lixia Han <sup>4</sup>**


**Abstract:** In order to solve the problem of demulsification difficulties in Liaohe Oilfield, 24 kinds of demulsifiers were screened by using the interface generation energy (IFE) module in the molecular dynamics simulation software Materials Studio to determine the ability of demulsifier molecules to reduce the total energy of the oil–water interface after entering the oil–water interface. Neural network analysis (NNA) and genetic function approximation (GFA) were used as technical means to predict the demulsification effect of the Liaohe crude oil demulsifier. The simulation results show that the SDJ9927 demulsifier with ethylene oxide (EO) and propylene oxide (PO) values of 21 (EO) and 44 (PO) reduced the total energy and interfacial tension of the oil–water interface to the greatest extent, and the interfacial formation energy reached −640.48 Kcal/mol. NNA predicted that the water removal amount of the SDJ9927 demulsifier was 7.21 mL, with an overall error of less than 1.83. GFA predicted that the water removal amount of the SDJ9927 demulsifier was 7.41mL, with an overall error of less than 0.9. The predicted results are consistent with the experimental screening results. SDJ9927 had the highest water removal rate and the best demulsification effect. NNA and GFA had high correlation coefficients, and their R<sup>2</sup> s were 0.802 and 0.861, respectively. The higher R<sup>2</sup> was, the more accurate the prediction accuracy was. Finally, the demulsification mechanism of the interfacial film breaking due to the collision of fluorinated polyether demulsifiers was studied. It was found that the carbon–fluorine chain had high surface activity and high stability, which could protect the carbon–carbon bond in the demulsifier molecules to ensure that there was no re-emulsion due to the stirring external force.

**Keywords:** demulsifier; fluorinated; demulsification mechanism; molecular dynamics simulation; neural network analysis; genetic function approximation
