Preparation of a selective flocculant for treatment of oily wastewater produced from polymer flooding and its flocculant mechanism

There are residual polymers in the oily wastewater produced from polymer flooding (OWPF); keeping the residual polymer in the water during the flocculation is meaningful and challenging. In this paper, a selective flocculant (denoted as PDC10) which can remove the oil while keeping partially hydrolyzed polyacrylamide (HPAM) in water was prepared by copolymerization of decyl two methyl vinylbenzyl ammonium chloride (C10MVBA) and dimethyl aminopropyl methacryamide (DMAPMA). By using oil removal and HPAM retention as evaluation indexes, the synthesis condition of PDC10 was optimized. The optimum PDC10 exhibited oil removal of 98.0% and HPAM retention of 80.5%. Its HPAM retention is much higher than that of a regular cationic flocculant. Measurements of zeta potential, interfacial tension, interfacial dilational modulus and a dual polarization interferometry (DPI) test were carried out for investigating the flocculation mechanism of PDC10. The mechanism of PDC10 was that it can bridge and flocculate oil droplets by electrostatic interaction and hydrophobic interaction. It also preferred to distribute at the interface, and its interaction with HPAM in bulk water was weak, which confirms its selective flocculation properties.