Sustainable Nanofluids Constructed from Size-Controlled Lignin Nanoparticles: Application Prospects in Enhanced Oil Recovery.

Lignin, a widely available, cost-effective, and structurally stable natural polymer, has recently attracted significant attention due to its diverse potential applications. A promising approach is to prepare lignin nanoparticles (LNPs) as a substitute for conventional nanoparticles to fulfill a variety of functions. In this study, LNPs with controlled size, regular morphology, and excellent dispersibility were synthesized by using industrial alkali lignin. The antisolvent method was employed, utilizing an aqueous solution of the anionic surfactant sodium apolyolefin sulfonate (AOS) as the antisolvent. Subsequently, the prepared LNPs were used to formulate nanofluids in combination with AOS and nonionic surfactant coconut diethanolamide (CDEA). The incorporation of LNPs has significantly enhanced the interfacial activity of the resulting nanofluids, thereby improving their emulsion stabilization, spreading on quartz surfaces, and oil droplet removal capabilities, which establish a strong foundation for the AOS/CDEA/LNPs nanofluid to achieve high performance in enhanced oil recovery (EOR), which was validated through microscopic visual physical model experiments. The quartz crystal microbalance with the dissipation monitoring (QCM-D) technique was employed to investigate the adsorption of surfactants onto quartz surfaces. It was found that the incorporation of LNPs significantly reduces the adsorption loss of surfactants, presenting a potential solution to overcome the challenges associated with surfactant adsorption in chemically enhanced oil recovery (EOR) processes, such as high cost and unreliable efficiency. This study reveals the good performance of LNPs/surfactant nanofluids and provides a potential approach to the advancement of green, sustainable, and intelligent EOR technologies.