Effect of EO and PO positions in nonionic surfactants on surfactant properties and demulsification performance

Demulsifiers provide an important means of breaking water-in-oil emulsions that occur in industrial processes. The properties and the performance of 20 blocked copolymers from four surfactant families were investigated and three pairs isomeric compounds were compared. The results show that different positions of the ethylene oxide (EO) and propylene oxide (PO) in block copolymers lead to different hydrophile–lipophile balances (HLB) of surfactant. The sequential block copolymer is more hydrophilic than the reverse-sequential one with similar chemical composition. The greater the molecular weight, the greater the difference between the hydrophile–lipophile balances of the two surfactant types. Generally, the demulsification performance of sequential copolymers is better than that of reverse-sequential copolymers. Position isomerism of the surfactant affects demulsification performance by changing the hydrophile–lipophile balance, interfacial properties, and steric characteristics at the interface.