Effects of Salinity on DispersantOil Particle Size

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Effects of Salinity on Dispersant/Oil Particle
Size

• By Clair Hollingsworth
• Research Experience for Undergraduates Program
• Texas AM University
• Summer 2005

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Oil Spill Response

• Mechanical means may be not be practical
• Extreme Ocean Conditions High Winds, Choppy
  Waves, etc.
• Environmentally sensitive areas
• Dispersant use may be an option

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What Do Dispersants Do

• Stabilize oil droplets in the water column
• Reduce oil-water interfacial tension
• Less mixing energy required
• Droplets incorporated into water column
• Lowered economic and ecological impact on the
  shoreline

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What are Dispersants

• Contain Surfactants
• Hydrophilic head
• Hydrophobic Tail
• Solvent
• Reduce viscosity
• Facilitate dispersal

Surfactant molecule
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Salinity Conditions

• Ocean seawater (30-33)
• Costal Environments have a range of salinities
• Bays and Estuaries may be much lower (range 10
  - 25)

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Problem Statement

• How effective is dispersant use in coastal
  environments?
• Lower salinity
• Low mixing energy
• Application effectiveness

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Research Objective

• Investigate dispersant effectiveness in differing
  salinities
• Lab scale study
• Salinity 10, 20, 30
• Mixing held constant (low level energy)
• Premixed and Non-premixed treatments
• Multiple replications

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Methods

• Continuation of M. Sterling doctoral research
• Experimental Design
• Reactor Set-up
• Saltwater Preparation
• Dispersant/Oil
• Premixed/Non-Premixed
• Sterling did premixed only
• REU non-premixed as well
• LISST 100-X instrument
• Measure oil droplet size

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Methods

• Reactor Set-up
• Rectangular Plexiglas Reactor
• Filled with 32L artificial saltwater
• Mixer w/ impeller
• LISST instrument

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Saltwater Preparation

• Carboy System
• Instant Ocean and DI water
• Hydrometer to check salinity

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Dispersant/Oil

• Corexit 9500 dispersant
• Low toxicity
• (manufactured Exxon/Nalco)
• Arabian Medium Crude Oil
• Artificially weathered

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Premixed/Non-Premixed

• Dispersant oil ratio
• 110
• Premixed scenario
• Injected mixture w/ syringe into water
• Non-Premixed scenario
• oil added to water surface
• Use ring to contain slick
• Sprayed dispersant onto slick
• Remove ring

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The LISST-100X Instrument

• Laser In-Situ Scattering Transmissometry
• Laser diffraction to obtain particle size
  distribution
• Angle Scattering Distribution
• 32 logarithmically scaled ring detectors
• Particle Size ranges 1.2 to 250 microns

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RESULTS

• 14 four-hour experimental runs
• Lots of data
• Due to presentation time contraints
• Present data for 2 runs
• premixed scenario
• non-premixed scenario
• Then discussion points

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Discussion PointsFor All Salinities
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Salinity 10 Comparisons
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Salinity 10 Discussion

• Premixed (3 runs)
• 2 runs similar
• Visually Chocolate milk like
• 3rd run
• lower initial oil volume
• Visually Oil floating on surface
• Non-premixed (3 runs)
• Fairly consistent
• Premixed more effective than Non-premixed

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Salinity 20 Comparison
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Salinity 20 Discussion

• Premixed (2 runs)
• Runs comparable
• Non-Premixed (2 runs)
• Runs comparable
• Premixed runs more effective than Non-Premixed
  runs

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Salinity 30 Comparison
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Salinity 30 Discussion

• Premixed (2 runs)
• Different initial oil volumes
• Non-Premixed (2 runs)
• Different initial oil volumes
• Premixed more effective than Non-Premixed
• Non-Premixed more effective at 30 than other
  salinities(10, 20 )

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C/Co Comparisons
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C/Co Discussion

• Resurfacing rates larger at higher salinities
• Particle Surface Charges
• Compression of charge layers surrounding particle
• Van der Waals force (prominent)
• Droplet Coalescence
• Resurfacing of newly formed larger droplets

Negatively Charged Particle

Negatively Charged Particle













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Conclusions

• At all salinities Premixed treatment outperformed
  Non-Premixed treatment
• For Premixed treatment
• at higher salinities the resurfacing rate was
  greater
• Non-Premixed treatment
• was more effective at higher salinities

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Application in Real World

• WHAT IF?
• 1-Day-Old oil spill in Galveston Bay
• Low salinity (17)
• Relatively calm water
• Arabian Crude Oil
• Should dispersant use be recommended?

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Recommendations

• Continue investigations of salinity effects
• More replication needed
• Some results appear not very reproducible
• Dispersant application method
• Investigate new data analysis for Non-Premixed
  runs
• C/Co graphs were not as meaningful

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Recommendations

• Do weights so lifting the LISST is easier

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Acknowledgements

• Mentors
• Cheryl Page
• Shahidul Islam
• Tope Ojo
• Dr. Bonner
• Dr. Honeycutt
• The National Science Foundation for funding the
  internship