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    Zein for hydrocarbon remediation: Emulsifier, trapping agent, or both?

    Year: 2020

    Journal: Colloid Surf. A-Physicochem. Eng. Asp., Volume 589, FEB 20

    Authors: Marshall, Tatianna; Gravelle, Andrew; Marangoni, Alejandro G.; Elsayed, Abdallah; Pensini, Erica

    Organizations: Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada (NSERC)CGIAR [RGPIN-2018-04636]

    Keywords: Zein; Remediation; Hydrocarbons; Emulsions; Gels

    Pump and treat of hydrocarbons from the subsurface is largely ineffective because capillary forces impede hydrocarbon mobility. This study uses zein (corn protein) dissolved in water at pH = 13 at low concentrations (4 and 8 g of zein/L) as a natural surfactant to emulsify hydrocarbons, facilitating their recovery from the subsurface (biosurfactant flushing). The effectiveness of zein in emulsifying a model hydrocarbon (toluene) was verified with bottle tests, optical microscopy and confocal microscopy. Interfacial tension measurements conducted with an optical tensiometer and the pendant drop method demonstrated that zein adsorbed onto hydrocarbon-water interfaces. Langmuir-Blodgett interfacial zein films deposited onto glass slides were smooth, as demonstrated using a scanning electron microscope (SEM). Langmuir trough experiments indicate that interfacial zein films either rapidly re-adsorbed or did not desorb from oil-water interfaces upon compression, followed by rapid expansion and recompression. Uncontrolled hydrocarbon migration through the aquifer is a risk associated with surfactant flushing. Therefore, this study also uses zein at high concentrations (33 g of zein/L) to form barriers around the areas where hydrocarbons are emulsified, preventing their migration. Barriers were formed by gelling zein dissolved at pH = 13 with either glacial acetic acid or salts (CaCl2 , KCl, and NaCl). Zein gelation was confirmed with compression tests, tensile tests, and shear rheology. Zein gels formed with CaCl2 and glacial acetic acid had the highest shear viscoelastic moduli and tensile strength. The effectiveness of zein gels in impeding contaminant migration was demonstrated in flow experiments conducted using sand columns. This study is a proof of concept that zein can be simultaneously injected in the polluted zones to emulsify hydrocarbons to enhance their recovery, and around the polluted areas to ensure that they are safely contained.
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