Understanding Shipboard Oil/Water Emulsions Using Macro- and Micro-scale Flows

Cari Dutcher | University of Minnesota, Twin Cities

WP18-1031

Objective

The objective of this work was to enhance the “fundamental knowledge base” of the “generation, stabilization and worsening” of shipboard oil/water emulsions in the presence of complex, yet tunable, hydrodynamic fields with varied chemical conditions. The separation of emulsified oil from bilge waters poses a unique challenge due to the inherent complexity and stability of these oil/water emulsion systems. Comprehensive scientific analysis of shipboard emulsions is needed to facilitate appropriate water treatment necessary for proper disposal. It is hypothesized here that by studying the oil-in-water system on length and time scales relevant to shipboard chemical composition and treatment processes, new insights into dynamics of shipboard emulsions is possible, which will ultimately aid in developing more efficient processing techniques for their separation.

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Technical Approach

This work uses two complementary approaches to study single-droplet (Task 1, Microfluidic flows) and bulk (Task 2, Taylor-Couette [TC] flows) emulsion dynamics at the micro- and macro-scale, respectively. Many of the factors are explored, including “shear/mixing, salinity, interfacial tension, and water/oil/surfactant ratios”. For Task 1, droplet microfluidic platforms are used as a high-throughput method to measure dynamic interfacial tension and quantify coalescence dynamics based on critical parameters such as surfactant type and concentration. This task will yield fundamental knowledge about the effect of additives present in bilgewater on the generation and stability of these complex emulsions. For Task 2, the experimental set-up will include injecting the dispersed phase into the continuous phase during flow using TC flow cell. Changes in droplet size distributions under varied flow types and turbulence intensities will be measured. Ultimately, insight will be gained into the kinetic processes involved in the emulsification process in tunable hydrodynamic fields.

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Interim Results

In Task 1, optimized design of microfluidic devices for dynamic interfacial tension (IFT) measurement and droplet coalescence experiments were successfully reached using surface treatment to yield hydrophilic walls suitable for oil-in-water systems. Dynamic IFT measurement of simulated bilgewater with detergent mix and model surfactants for oil-in-water systems has proven to result in different time-dependent profiles than those obtained in water-in-oil systems, suggesting a curvature dependent surfactant transport mechanism. The characterization of surfactant parameters using different isotherm models reveals the fundamental properties of both model and commercial surfactants in bilgewater system. Finally, the preliminary results of Stokes’ trap experiments have shown successful trap and coalescence of droplets in water-in-oil systems. In Task 2, static emulsion stability tests found the non-monotonic relations for emulsion destabilization times with both oil and surfactant concentration. For oil contents greater than 10% oil, flow-induced destabilization was observed in rheometric shear flows. Similar flow-induced destabilization was observed for lower oil contents, down to 0.1% oil, when exposed to more complex TC flows. The changes in stability were determined through changes in droplet size distributions. Finally, the preliminary results with in situ injection in TC flows enables further advanced studies of the dynamics of emulsion formation and destabilization in flow.

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Benefits

The results from Task 1 provide a new understanding of the effects of water/oil/surfactant ratios on time-dependent properties that impact emulsion formation, stability, and worsening. The results from Task 2 provide a new understanding of hydrodynamic effects on the transient emulsification and destabilization processes. Ultimately, the results of this project can inform the Department of Defense treatment strategies and will “assist the development of methodologies or technologies that can mitigate the formation and undesired consequences of shipboard emulsions”, through improved understanding of the factors that govern emulsions.

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2021

Points of Contact

Principal Investigator

Cari Dutcher

University of Minnesota, Twin Cities

Phone: 612-624-0428

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