Fundamental study of hydrophobic microporous membrane contactors for the recovery of insoluble oil from oil-water mixtures
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Insoluble oil and water mixtures occur in many industries such as food, metallurgical, or biofuel production. In particular, as we strive to meet global energy demands, the associated risks and waste management of the oil and gas industry must be addressed. Technologies capable of separating oil and water efficiently are needed for the treatment of highly variable oil and gas streams such as produced and flowback waters or oil spills. The goal of this doctoral work was to advance the understanding of a membrane contactor process for the recovery of insoluble oil from water. The hydrophobic hollow fiber membrane had been successfully tested in our laboratories for oil recovery from algae slurries. However, a thorough study to understand the fundamental mechanisms of the separation process was necessary for engineering design and process optimization. First, pure oil experiments were performed to define baseline performance attainable with the studied membrane contactors. Then, oil-water separation experiments were conducted to quantify the effect of key operating parameters. Two relevant ranges of oil feed concentration were identified. For high oil feed concentration, increases in transmembrane pressure and influent flow rate were confirmed to increase oil flux, while higher viscosity lowered oil permeation across the fiber walls. However, an important finding was that, for dilute mixtures, decreases in transmembrane pressure and higher viscosity increased oil permeation. The results of this research support the conclusion that oil separation within the particular geometry and design of the membrane contactor is due to both internal coalescence of oil droplets and selective permeation of oil over water. The stability of an oil film on the fibers was critical to enhance effective surface area of the membrane contactor. In addition, the technology showed great promise for long-term high oil removal with no signs of viscous fouling as often observed in hydrophilic membranes. Finally, a model describing the process was developed and can be used as a guideline for membrane sizing and process engineering design.