Efficient Removal of Enhanced-Oil-Recovery Polymer From Produced Water With Magnetic Nanoparticles and Regeneration/Reuse of Spent Particles

Abstract

Summary Polymer flooding is a proven technology to improve sweep efficiency, while being one of the most economical enhanced-oil-recovery (EOR) processes. Partially hydrolyzed polyacrylamide (HPAM) has been widely used for polymer flooding. As the HPAM usage for EOR increases, the challenge of produced-water management is also raised because residual HPAM in produced water could increase oil content and unwanted viscosity in discharging or reinjecting the water. As the environmental standards and regulations get more stringent, it is difficult for the conventional methods to meet the requirement for discharge. Use of magnetic nanoparticles (MNPs) to remove contaminants from produced water is a promising way to treat produced water in an environmentally friendly way with minimal use of chemicals. The main attraction for MNPs is their quick response to move in a desired direction with application of an external magnetic field. Another attraction of MNPs is versatile and efficient surface modification through suitable polymer coating, depending on the characteristics of target contaminants. In this study, we investigate the feasibility of polymer removal with surface-modified MNPs and regeneration of spent MNPs for multiple reuse. MNPs, in-house synthesized with prescribed surface coating, were superparamagnetic with an average individual particle size of ≈10 nm. The removal efficiency of HPAM from water with the MNPs depended on the type and concentration of brines, concentration of amine-functionalized MNPs, surface coating of MNPs, molecular weight of polymer, and how many times the MNPs were regenerated and reused. Virtually 100% removal of HPAM from water was feasible, depending on the reaction conditions. The regeneration of spent MNPs, with pH adjustment to recover the reactive sites, maintained more than 90% removal efficiency for three-time repetitive usages. The electrostatic attraction between negatively charged HPAM polymer and positively charged MNPs controls the attachment of MNPs to HPAM molecular chains; the subsequent aggregation of the now neutralized MNP-attached HPAM plays a critical role for accelerated and efficient magnetic separation.