Enhanced demulsification of alkaline-surfactant-polymer flooding O/W emulsion by multibranched polyether-polyquaternium based on the size effect of oil droplets

In the alkaline-surfactant-polymer flooding emulsion, oil droplets with various sizes exhibited different interfacial properties , resulting in different stabilization and destabilization behaviors. In view of this, it is expected to achieve outstanding oil-water separation efficiency by screening targeted demulsifier for oil droplets with different size ranges (0–1, 1–5 and 5–10 μm). Based on the size effect of oil droplets, a series of multibranched polyether-polyquaternium demulsifiers that integrated different charge neutralization and interfacial displacement functionalities were designed by regulating the cationicity and EO:PO ratios. As a result, the most effective polyether-polyquaternium variant for each size range of oil droplet was screened out. By employing these three selected polyether-polyquaternium variants in a sequential batch demulsification test, the maximum demulsification efficiency of 95.1% was obtained, which was much higher than that using a single polyether-polyquaternium variant (82.5%, 80.5% and 83.8%). The adsorption behaviors of polyether-polyquaternium variants on the oil/water interface were investigated by the molecular dynamics simulation. Moreover, the interfacial properties and oil droplet size variations during the demulsification process were monitored, so as explore the demulsification mechanism. This demulsification protocol based on the size effect of oil droplets with its excellent oil-water separation performance offered significant technical promise for the emulsified oil wastewater disposal.