Oil-in-Water Pickering Emulsions Stabilized by Lignin Nanoparticles with Different Molecular Structures

Emulsification is a crucial process in chemical flooding operations, designed to mobilize residual oil in wells following secondary recovery efforts. As a result, oil displacement efficiency can be enhanced, and volumetric sweep efficiency can be increased by engineering the interactions of the emulsifiers used with the geological formations present in the wells. In this contribution, we report on Pickering emulsification experiments and transient phase maps reflecting phase composition and structure snapshots at a given point in time. These phase maps were obtained using three different oil phases and three lignin nanoparticle (LNP) suspensions as emulsifiers, respectively. The chemical structures of corn lignin, alkali lignin, and Kraft lignin from three different sources were characterized by¹H–¹³C 2D Heteronuclear Single Quantum Coherence (HSQC) NMR and³¹P NMR spectroscopy. Information on the structural differences enabled us to relate variations observed in the emulsification process and transient emulsion morphology to the chemical structure. Hydrodynamic diameters of the LNPs were emulsion characteristics determined by this method. All three types of lignin can effectively form metastable emulsions with the three oil phases. The different emulsification properties of corn lignin compared to the other two lignin types are associated with a higher proportion of carboxylic acid hydroxyl groups present in corn lignin. Our emulsification systems provide new platforms for green and low-cost flooding applications employing lignin nanoparticles.