Preparation of Modified Kaolin Nanoparticle Demulsifier and Its Demulsification Performance for Crude Oil-in-Water Emulsion

Modified kaolin demulsifiers were synthesized by grafting chitosan quaternary ammonium salt (QC) on kaolin nanoparticles with different particle sizes (KAO1@ATPES-QC and KAO2@ATPES-QC). The morphology, structure, and interfacial activity of kaolin before and after modification were characterized. Contact angle measurement, interfacial tension characterization, and the distribution of nanoparticle materials in the oil–water mixture showed that the nanodemulsifier KAO1@ATPES-QC possessed good interfacial activity and amphiphilicity. ζ-potential measurements showed that grafting QC can significantly increase the ζ-potential of KAO1@ATPES-QC, allowing it to display positive charges over a broad pH range. The demulsification performance of the prepared materials was evaluated by a bottle test. The results show that the modified kaolin with a smaller particle size has better demulsification performance. The prepared KAO1@ATPES-QC possessed excellent demulsification efficiency (DE) in a broad pH range, and the DE reached 99.05% with a dosage of 800 mg/L at 25 °C and pH of 8. Temperature has a very limited impact on demulsification efficiency, indicating that the KAO1@ATPES-QC composite can realize quick and high-efficiency demulsification of the crude oil emulsion at an ambient temperature. The demulsification mechanism showed that good interfacial activity, proper surface charged characteristics, and functional groups are essential for constructing clay mineral demulsifiers with excellent demulsification performance.